Bass reflex speaker design – easy explanation
What is a bass reflex subwoofer?
A bass reflex speaker is just like a normal closed box speaker, but in addition, has a an open tunnel, or port, which allows air to circulate freely in and out of the box. This vent helps increase
the efficiency of the woofer, with substantial contribution on the low frequencies. This type of enclosure is very popular and is the pick of the range when stacked against a sealed enclosure. It’s like a sweet spot, if you will, for woofer enclosures. It gives the best balance between efficiency, low end extension and build difficulty. While building a bass reflex enclosure is pretty straight forward, designing it will take a bit more effort and the end result doesn’t tolerate designing errors, like a sealed enclosure does.
Why choose a bass reflex speaker design?
Here are some pros :
- +3 db efficiency compared to the equivalent volume sealed enclosure.
- Lower cutoff frequency. Normally after reaching the resonance frequency of the driver, the response will start to go down hill, but that is when the port starts to put in some work and extends the frequency response.
- Lower distortion at resonance frequency. At this point, the port does most of the work. The speaker barely moves at the resonant frequency of the box. This means less distortion and more power handling.
There are some bad points for a bass reflex speaker as well. After resonance frequency is achieved, the response is degraded with a steep roll-off of 24 db / octave. The vent, if not designed correctly or at high sound levels, can get noisy, as the air escapes the port. Transient response is not as good as sealed equivalent.
How does bass reflex work ?
We know that the whole point of an enclosure is to separate the waves created by the back of the speaker from the ones generated by the front. Because these waves 
are out of phase, when they meet, they will cancel each other out. You can make an analogy with math, positive numbers are in phase and negative numbers are out of phase. And just like in math : – x + x = 0.
But wait a minute! If I use a port, doesn’t that mean that the back waves travel through the port and reach the front waves and achieve cancellation ? That is a very good question, because at first glance, that looks like a valid theory. In reality, something else happens. The port acts like a Helmholtz resonator, and back waves reverse phase and come out the port in phase with the front waves. Because of this, not only it does not cancel the front waves, it reinforces them ( +x +x = 2x ). This is where the +3 db efficiency comes from.
This effect only happens when reaching the resonance frequency of the port. Above this point (higher frequencies), the mass of air inside the port is too great to respond to the speaker movement, and it acts like a perfectly sealed enclosure. Below this point, the port acts just like a hole in a sealed box . The back waves do not reverse phase and come out of the port, only to cancel the front waves. That is why the bass reflex speaker has such a steep roll-off (24 db / octave) below the resonance frequency point.
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Achieving a desired fB (resonant frequency)
To achieve a desired resonant frequency of the box, now you have to take into account the dimensions of the port as well. The air inside the port has its own mass and resonates according to the movement of the air “spring” inside the box (see the closed box article for more information about this “spring”). The internal volume of the box and the internal volume of the port are key to defining the resonance frequency.
- Altering the size of the box :
- Making the box bigger => lowering the resonant frequency
- Making the box smaller => increasing the resonant frequency
- For a given port diameter, altering the length of the port :
- Making the port longer => lowering the resonant frequency
- Making the port shorter => increasing the resonant frequency
Remember, when choosing the dimensions of the port to achieve a certain resonant frequency, there are 2 things that matter : the mass of the air inside the port and the compliance. If the port needs to have 2 L of volume, you don’t just pick any dimensions for radius and length just to hit that target volume. Compliance needs to be taken into account. If the port is wide, it’s more compliant, because air moves with less restriction. This means that the port needs to be made long enough to meet the desired compliance. In a reverse fashion, a small port is less compliant and doesn’t need to be long. So, the radius and length of the port are interconnected and must be matched correctly to reach the desired result. You can see this relation, between length and radius, in the visual graph just below.
Port size
The most common used shapes for a bass reflex port is either cylindrical or rectangular. Rectangular ports are made using pieces of the material you are using to make the box, but most often circular ports are used. These are made by various materials (mainly plastic), but if your local audio store is out of bass reflex ports, you can successfully use PVC pipe for example. For the ongoing discussion about these vents, we are going to focus on the cylindrical one, as it is more popular.
The port dimensions plays a major factor into deciding the resonating frequency (fB) of the box. I’m not going to write the formula for calculating the fB of the box, because you are going to use specialized software for this.
- But I am going to mention that (for a given speaker) the tuned frequency of the box (fB) will depend on 3 factors :
- Length of the port
- Radius of the port
- Volume of the box (VB)
Choosing port dimensions
The dimensions of the port are somewhat at your choosing. For example : if you want to achieve a certain fB using a certain volume of the box, you can alter the length of the port as you choose, but you will have to change the radius of the port accordingly, so that the first 2 values (fB and VB) remain constant. Even though it looks like you have the freedom to choose the dimensions you like, in reality there are certain factors you need to take into account seriously.
The diameter of the port needs to have a minimum value. When the frequency reaches the resonance value (fB), the port radiates almost all of the acoustical power (the speaker moves very little and the port does most of the work) and because of this, the vent needs to have a minimum volume displacement in order to prevent power compression.
Mr. Thiele and Mr. Small have come up with their own formula of deciding which is the recommended minimum diameter for the port. Depending on who you fancy more, you will end up with a different result. But in reality this has little relevance because you are always going to aim for a bigger port. Making the port bigger in diameter means that you have to make the port longer to keep the same resonance frequency, so you can understand that there are some limitations on how big can you go. Vents operate in a nonlinear fashion no matter the dimensions you choose, but going for a larger one, will almost certainly end up with less nonlinear performance. Therefore, bigger diameter means that there is less air turbulence, and it will translate in less port noise at high volumes.
Diameter to length correlation
For a fixed box volume and to maintain the desired fB , here is a real world example of the relationship between diameter and length of the port :
- Port diameter 2″ (5 cm) => Length of 2.3″ (5.8 cm)
- Port diameter 3″ (7.5 cm) => Length of 6.2″ (15.5 cm)
- Port diameter 4″ (10 cm) => Length of 12.3″ (30.8 cm)
- Port diameter 6″ (15 cm) => Length of 30″ (75 cm)
These numbers are just to make a point. A random box was used to generate them. Please don’t use them for your project.
As you can see, going too high with the diameter can yield impressive lengths for the bass reflex port. Longer ports tend to resonate themselves and that does introduce some minor frequency response alterations. You shouldn’t worry too much about this and think about how smaller vents are way worse.
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Recommended minimum size
You have to match your bass reflex speaker size to the size of the port. Here are some recommendations on minimum vent size compared to speaker size :
- 1″ vent => 4″ speaker
- 2″ vent => 4″ or 5″ speaker (6″ max) (Amazon affiliate link)
- 3″ vent => 6″ speaker (8″ max)
- 4″ vent => 8″ or 10″ speaker (12″ max)
- 6″ vent => 12″ or 15″ speaker
As the diameter goes up, the length of the port goes up, so if you are using big woofers and need a longer vent, you can use one of these solutions
- Use a 90° elbow to redirect the vent up or down. This way you don’t have to make the enclosure really deep to accommodate the long vent.
- Use multiple ports. To find the combined diameter of 2 ports use the formula : dt=(d12+d22)1/2. So if you have two 5″ ports, it will equal to one 7.07″ port.
Another way to increase the linearity of the vent is to use a flared port. Having a flare at both ends of the vent reduces distortion and minimizes the noise the air makes when it rushes out the port. At high volume levels, it is said that a flared port reduces noise for about 5 db, which is significant. Some companies, like B&W, have gone even further and made the flare of the port like a golf ball texture. They call it flowport and reduces air turbulence even further.
Additional factors to consider
Subsonic filtering. Below the resonant frequency of the box-port assembly, the vent acts just like a hole in a sealed box. As a result, the compliance of the box is really high and the speaker moves unrestricted. In the absence of the internal air “spring”, the woofer is not damped anymore and can reach impressive excursions, over the quoted Xmax, if push too hard. In conclusion, use a passive or active filter, to reduce the chance of speaker damage.
Damping material. Like with sealed enclosures, damping material can be used to reduce panel resonances and standing waves. Unlike the sealed enclosure, you don’t stuff the box with damping material, because you will obstruct the port. Just place 1-2″ absorbent material on the the walls of the enclosure (on one of each opposite sides or all of the walls).
Conclusion
The bass reflex speaker design, while not difficult to build, will take a bit more time to design. However, we will cover more about designing the bass reflex box in a future article, because we only mentioned the basic principles (check out the bass reflex alignments). This should not discourage you to try something more challenging. Building and designing a sealed enclosure is pretty straight forward and you should definitely start with one of those. Ported boxes are not so tolerant to design and build errors. So, when you are ready to take a step forward, and think that the advantages of a bass reflex subwoofer are something you want, you should definitely give it a try.
References
- Loudspeaker Design Cookbook 7th Edition by Vance Dickason (Audio Amateur Pubns, 2005). (Amazon affiliate link)
- The Audio Expert: Everything You Need to Know About Audio by Ethan Winer (Focal Press, 2012). (Amazon affiliate link)
- Image source : link.
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201 comments
I have never built any speakers before and i am new to the world of audiophillia, but found your info very helpfull and alot easier to understand.
Does the reflex port have to exit via the front of the speaker or can exit via the base?
The port can be placed on any side of the box, but consider your personal application. For example, if you plan to place them against a wall, a rear-firing port is not recommended. The wall will “choke” the port and can introduce unwanted wind noise, since the air cannot escape freely.
Hello
How do i make my sub louder ?
I have this sub pioneer ts-311s4, 2cu ft box with 3in diameter x 6 inch port..is it that i purchased the wrong sub ?
Thanks for replying
Indeed that subwoofer is nothing to brag about. I don’t think you can make an enclosure that will go that much louder, considering you already got a decent sized one. You will have to make a woofer upgrade if you want more volume.
Upgrade the woofer how?
Well, since the enclosure is already big enough, to warrant good efficiency, the only thing left to do is upgrade the woofer. Which means something with more power.
hi i have 2x 6×9 mtx speakers and i need to box them to sit under my bed in my van and will also be used as a shelf . i can make the box any size , i cant find anything to tell me the air volume the speakers require for boxed situation and also should it be ported or not what would be better
6×9 speakers are usually made for rear parcel shelf placement. This means their parameters are tailored for infinite baffle. An infinite baffle is more or less an over-sized sealed box. Just make a box as big as the available space. Optionally, you can fill it up with sound dampening material (wool or fiber glass).
What bass reflex cu ft capacity is needed for a 12″ or 16″ woofer ?
Woofer size doesn’t tell much about volume demands. You need the T/S parameters to draw an educated conclusion.
Read this : https://audiojudgement.com/bass-reflex-alignments-explained/
Maybe it will clear things up.
Hi
Do we need to add ‘sound absorbent material Volume’ to Vb to find exact box Volume?
Or is it a negligible Volume?
Thanks..
Only solid thing count to total volume. You can press the absorbent material down to a thin sheet, so it doesn’t count.
However, in a sealed box, where you fill the box up with dampening material, it actually increases (counter-intuitive eh?) the perceived volume of the box (you can check the sealed box articles for more info).
But if we are talking about bass reflex, where you place like max 1″ of material on the walls, you should not account this for anything.
Nice concise article. Random question – is it plausible to design a port that is outside of the box? I’m toying with the idea of building enclosures as sculptures and outside ports could be cool.
Of course you can. As a plus, you won’t have to add the volume of the port to the overall volume of the box.
Hi,Thanks for the nice detailed article.
I need to build some subwoofer for church, both for indoor and outdoor use. I intend to use Eminence Omega pro, 2×15″(twin) and 2×18″ (twin)
Kindly advice on the best sizes for the boxes and port dimensions.
For dual 18″ go for a 423 liter box with 3 ports of 150 mm diameter and 260 mm long (each).
For dual 15″ go for a 219 liter box with 2 ports of 150 mm diameter and 180 mm long (each).
Great article and I wonder if you could help me. I have a pair of floorstanding speakers that are ported. Unfortunately one of the ports has “gone missing”, the result of lending them someone. I have tried to get a replacement but unfortunately cannot find an exact match.t
The internal port size appears to be 48mm and the nearest replacement I can find is 50mm. How do I work out how much longer the port would need to be to cater for the increased diameter or would such a small difference matter?
Thanks in anticiption.
Don’t sweat too much on that. 48 mm is basically 50 mm. Replace it with one of the same length and you should be fine.
Thanks a lot.
Hi
I want to make box for “Ground Zero 12” Nuclear SPL Subwoofer GZNW 12SPL”
Fs : 38.9
Vb: 150 Liter
Plz help me about port size by flared port
Port length?
Port diameter?
Thank you.
The numbers given by you suggest a box for high output rather than sound quality. Go for a 150 mm (6″) diameter port. The length should be 125 mm. If the port is flared go for around 150 mm total length.
Que fs es bueno en un subwoofer para calidad de sonido amigo gracias
Thanks for a nice easy-to-read article but………
If I understood correctly, rear radiation from the driver reinforces front radiation only at resonance. Doesn’t this make the acoustic output peak at the resonance frequency relative to other frequencies?
It depends on the size of the box and the tuning frequency. For example, you can chose to tune the port below the resonant frequency of the driver (where the speaker has a bad response) and it will blend well. But this isn’t the only case, it’s balance between box size and port tuning frequency. Let’s say you choose a box size and port tuning frequency that results in a linear response. If you keep the port tuning frequency the same. but make the box larger, the response will start to peak (like you said). If you keep the same volume but increase the tuning frequency of the port, the response will start to peak also. Read more about this here : https://audiojudgement.com/bass-reflex-alignments-explained/
Hi, this is very helpful artical.
I have bolton 8″ 8 ohm woofer, could u suggest me to design of box size and airvent size
That is not enough information to design a box. Also, I don’t know your personal preference when it comes to sound, so my recommendation might not be to your taste.
You can read more here :
https://audiojudgement.com/bass-reflex-alignments-explained/
Or you can enroll into my video course and learn everything you need to know to design a bass reflex box :
https://www.udemy.com/acoustics-101-speaker-design-basics-and-enclosure-design/?couponCode=AJDISCOUNT10
Hi could you you tell me if this ported box is right for this subwoofer. This is what the manufacturer say for the subwoofer I will be using. Sealed N/A
Ported 2.50 ft^3
Displacement 0.20 ft^3
Depth 9.67″
Outside Diameter 12.68″
Cut-Out 11.09″
Recommended Tuning 32hz
Recommended Port Area 40 in^
And this is what I plan on making myself.
Sub back port, port back
Net volume 3.29 ft3
Gross volume 4.46 ft3
Tuning 32.30hz
Port area 37.00 in2
Port volume .83 ft3
Port area per foot: 11.24 in2
I need the speaker specs to give you any advice. Giving me the manufacturer box recommendations doesn’t help at all.
Sundown x12 v.2 d4 12″ 1500w rms dual 4-ohm
Judging by the specs of the speaker, the enclosure they recommend is a SPL enclosure, which suits this type of woofer. It will make a lot of noise and move a lot of air. It has a +4 dB peak. The enclosure you want to make has a +5 dB peak. So, your enclosure will be a tad louder.
Thank you for the advice but should I use some sound proofing on the inside of the box or not
There is no need for sound dampening in this kind of box. What I recommend is to use at least 22 mm MDF (or better yet, plywood), with a double baffle.
Hi a friend of mine said I should make to this.
Gross volume 6.38 cf
Net volume 5.24 cf
Running 22 hz
Port area 28. 2 inch
Port area 5.3.2 per c.f.
18mm
36mm baffle
This is bad advice. The modeled frequency response looks awful. Just make it as the manufacturer recommends or the one you planned to make in the first place.
Thank you I will definitely be making the first one I mentioned
Very informative article. I could use some help designing a box for a smaller sub using this driver.
I came up with 30litres and using two 5cm ports of 20cm length.
Am I terribly off?
Monacor sph200tc
Impedance (Z)
2 x 8 ohm
Resonant frequency (fs)
28Hz
Max. frequency range
f3-4,000Hz
Rec. crossover freq. (fmax.)
2,500Hz
Music power
2 x 100WMAX
Power rating (P)
2 x 60WRMS
SPL (1W/1m)
88dB
Suspension compl. (Cms)
1.01mm/N
Moving mass (Mms)
32g
Mech. resistance (Rms)
0.9kg/s
Mech. Q factor (Qms)
6.19
Electr. Q factor (Qes)
0.25
Total Q factor (Qts)
0.24
Equivalent volume (Vas)
65 l
DC resistance (Re)
2 x 6.8 ohm/ 3.4 ohm
Voice coil induct. (Le)
2 x 1.0mH/ 1.0mH
Voice coil diameter
50mm
Voice coil former
Kapton
Voice coil winding height
15.5mm
Air gap height
8mm
Linear excursion (XMAX)
±3.75mm
Eff. cone area (Sd)
210cm2
Volume displacement (Vd)
78.8cm3
Force factor (BxL)
8.9Tm
Reference efficiency (No)
0.6%
Magnet diameter
120mm
Magnet weight
840g
Mounting cutout
Ø 185mm
Mounting depth
102mm
Dimensions
Ø 210mm
Weight
2.6kg
The get a butterworth response out of this speaker you will need a 13 liter box (net volume) and one single port of 50 mm diameter and 180 mm in length. Tuning frequency will be at 46 Hz, so don’t expect really deep lows. In contrast, the box is really small.
Thank you!
Hi Marius, very nice article and good to read.
I have a question:
On a project i would like to build, the suggested BR-area is 400 cm2, length is 192mm. Placed at the bottom of the frontbaffle. Can i divide the BR-area in two, thus making it 2 x 200 cm2 (top and bottom of the enclosure) so 2 ports in the front baffle. Mainly for the looks of the cab?
Specs:
2 x Kappalite 3012LF 8 Ohm (parallel to 4 Ohms)
http://www.eminence.com/pdf/Kappalite_3012LF.pdf
Vbox 145 liter
A=400 cm2 – L=192mm
Thank you, kind regards
Paul
You can do 2 x 200 cm2 area, but the length will be 243 mm for each port (not combined length), to have the same resonant frequency.
Thank you for your answer. I couldnt figure it out 🙂
Paul
.Pl let us know how to determine Vas and free response of a speaker, not known.
You can buy a Dayton Audio Test System (DATS) to easily find all the parameters of the speaker.
Hi Marius,
Do you have any suggestions or guild line that we can follow for rectangular ports?
Also if you make it flared, that would help reducing the distortion like the circular ones, correct?
Great articles btw!
Thanks,
Andy
Going for a rectangular port is the same deal. If you have a circular port with an area of 100 cm2 and a rectangular port with an area of 100 cm2, they will have the same resonant frequency if their lengths are the same. And yes, flaring a rectangular port helps to reduce turbulence and distortion.
Thank you for the answer!
Andy
Hi there,
I’m new to building speaker enclosure, just did a 5.1 “portable” speaker for my studies. I want to build a pair of small bookshelf. Here’s the parts I intend to use : Dayton Audio TCP115-4 4″ woofers, Dayton Audio ND20FA-6 tweeters. I’ve design some 4.3 L box (inside volume). With some online calculator, I found that 1.2″ large and 7″ long bass port would work great with the resonant frequency researched. can I use 2 1.2″ large and 5″ long bass ports instead ?
Thanks a lot,
Adrien
Please notice that’s English is’nt my mother tongue, so if I make mistake, please tell me.
Adding another port will only make things worse. They will have to be 15.6″ long each to have the same resonant frequency of a single 1.2″ at 7″ in length. The solution is to use a smaller diameter port. A 1″ diameter port will demand a 4.75″ in length to reach the same resonant frequency (which I calculated to be at 50 Hz from the numbers you quoted). Problem with smaller diameter ports is that they might introduce wind noise (chuffing). But the woofer is pretty small, and it might be just fine. If you want to be on the safe side, make sure that your port is flared, preferably at both ends.
Hi Marius . You are profi. Great article, thank you.
Tell me please, I have a WHES-AU-P810 full range frequency speaker 8 “diameter; 8 ohm; 50 Hz to 20 khg, with Qts = 0.651; SPL = 94db; Fo = 50.392 Hz; Vas = 107.98 liters. it’s sellers’s info.
But such a large box is not for me. Can I make a good sound on a box of about 40 liters?
Music – the Beatles, Queen of Jazz.
Thank you.
Bare minimum would be 45 liters. But go as large as you can. Something like 120 liters or more would be more appropriate. Regardless of the volume you choose, make sure you stuff the enclosure with sound dampening material.
Hmm… I thought the tube reflex could helps me on the better sound with the small box.
And since we’ve no place to go
Let it snow, let it snow, let it snow…
it means let it be in a small box. No other place…
No. Bass reflex boxes demand larger volumes. I’m talking about sealed boxes.
Understand the sealed box is the closed cabinet with only speaker.
It’s clear that they need a big volume box. Each speaker seller send you a recommendation for the sealed box size. In my case it is 108 litters, calculated just for my speaker head.
I have only 40 liters, and no way to have the bigger one (the 50 is maximum).
So I thought the regulated tube bass reflex in the small sealed box wil help me.
No, it will be worse, trust me. If you are limited in the volume department, the solution is to make a sealed box as big as you can in the available space and stuff it with polyfill.
I trust you, no doubt. Otherwise I would not ask you.
Do you think, will it be better for my specific speaker head, if I use the open box ( no rear wall), or Acoustic Resistance Panel as the perforated rear panel with a tight cloth?
Thank you.
Yes, since the driver has a reasonably high Qts value, it can be used in an open baffle setup. You can try to absorb the back wave, but I doubt it will be very effective. Depending on the size of the baffle you will encounter some back-wave cancellation. Try it and see how it works out, but expect degraded bass response, more or less.
Hi there!
I found your article very helpful and I have a question.
I bought a really small woofer in a box only 1.5 liter with a port 1.6cm diameter and 7.2cm length it sounds unexpectedly good regarding it’s size and I recently changed the driver with a whopping 10.5cm dual cone speaker to get sort of a full range but my port starts suffocating the speaker at high volumes. Can I divide it in two ports or change it with a wider one? And what dimensions should they be? (my box is 11x13x13cm)
Thanks in advance!
Can’t really give advice without driver specs. Making the port larger will increase the resonant frequency of the box (if the length remains the same). That may or may not be a good approach. The first thing I would try is to transform it into a sealed box. Since you upgraded the speaker, the box is most likely misaligned. Going for bigger speaker demands a bigger box, but a sealed box demands less volume than a bass reflex. Seal the port off by filling it up with a piece of cloth. Socks are a good candidate :). See if it sounds better.
Thanks for the advice! My goal is to mainly help the low end in any way I can. I fitted a new wider port yesterday (before reading the post) that had the same volume as the previous one not knowing about compliance, and it was wayy off high (I am still learning about these stuff). So I made the wide port longer outside of the enclosure (2cm diameter x around 14cm long) and it came to the same level as the original port but with a lot lower wind noise. I tried the sock thing you mentioned and ironically it isn’t too far off. I used a spectrogram to see the frequency response and I loose around 3db at ~33hz with the sealed enclosure. Which of course is ridiculous in such a small speaker even talking about these lows. I wonder if by making it sealed I make it less efficient (I plan on making a portable small speaker that has an acceptable low range so Im first trying in these) So I sort of care about efficiency.
I want your opinion on this build, is it worth it making a portable sealed enclosure with this speaker around 2 liters so I can fit the other components too, or making the external port I built, internal with an elbow and making a slightly bigger than 2 litter box. I am trying to keep the size as small as possible.
My speaker is a 4ohm 33-24000hz Pioneer
ts-g1331i that I ordered by mistake.
Any input will be appreciated!
Nick
That fact that it’s a car speaker does not help your cause. Usually, they have a high Qts value, because they are intended for infinite baffle (like the rear parcel shelf in you car). Having said that, these drivers are not suited for small volume sealed enclosures and definitely not suited for bass reflex. Furthermore, placing a longer port inside the box will reduce even more the internal net volume of the enclosure. Since you cannot go for a large sealed box, make one with the space you have available. In addition, fill the box with polyfill. This will increase the perceived volume of the box by 15-20%.
Thank you very much for your help!!
Hi Marius,
I got, I need the subwoofer additionally to my full-range speaker drivers.
What can you recommend me – which driver for bass I have to buy and what woofer-box I need to build? If possible, please with the box dimension.
Thank you.
Hi! Thanks for a great article and awesome of you to answer questions.
I’m currently designing a guitar cabinet in winISD and want a ported cab since I often tune as low as 55hz(wouldn’t need anything below this though).
After messing about with numbers and getting a curve that looks nice for my needs I find that winISD says I can get away with a very short port and still have an ok diameter.
Currently I have it set to a single port 13,5 cm in diameter and only 3,6 cm in lenght which also happens to be the planned thickness of my front baffle.
So three questions:
1: Do these numbers seem reasonable or am I missing something?
2: Can a simple hole in the front baffle work well as a port provided the baffle is thick enough?
3: If I were to use a router to chamfer the sides of the hole, would this count as a flared port and how much would that change things?
If it matters, I’m going with an Eminence Delta12-A and the box is currently calculated to 136 litres.
Would be extremely grateful if you felt you had time to answer any of these questions.
1) Yes they seems reasonable. Large box volume and high tuning frequency. Both factors lead to shorter port length.
2) Yes
3) Yes
Thanks a lot! Pretty much set to get started on the build then 🙂
I’m guessing making the port flared will have minor effects on the tuning but be good for air flow?
Recommended is to flare both ends, because the air resonates inside the port. This means it goes in and out by the same degree.
Hello Marius,
I have read and enjoyed your article as well as your responses to everyone’s comments!
I am looking for some advice/help on building a bass reflex box for 2 11″ focal utopia 27 wx woofers. They are for a vehicle application. I have been unable to find any box specs online.
The specs for the subs are as follows:
27cm (11″) subwoofer
65mm(2.5″) v, coil
Muti magnet 12x60mm(12×2-3/8″)
Sensitivity 2.8v/1m
Frequency response 25hz-1.5khz depending on load.
I am hoping to build a down fire box as well as it is for a old Toyota 4Runner with the back top off.
Please let me know if I need to provide anymore info.
Thanks for your time.
These are SQ subs and are designed for sealed boxes. In this case make a 130 liter box to house both woofers, and you are done.
However, if you insist in making a bass reflex box, make a 100 liter box tuned to 35 Hz. This means 2 ports of 100 mm diameter and 310 mm in length (each).
Sounds good. I think I will go with the sealed enclosure. How much polyfill should I add to the box. Thanks again for your quick response!
Well, you have to fill the box. You can play with the density, see how you like it. There is no right or wrong.
Hello everyone I’m interested in Bass reflex tube QE 1222 – ESX subwoofer I have a box size box 680mm height 310mm width 280mm which should be the thickness and length of the port thanks
Those are internal or external dimensions? If you are measuring the box from the outside, what is the thickness of the panels?
Hello. Your post is very informative and super helpful. But I was wandering”I have a 4 inch and 6 inch woofer. Both of them are rated 30watts. I have seen some Chinese companies making vented systems with these woofers. I want to design one too. But I don’t have any manufacturer data. And they are pretty cheap. Need some help ??
You can buy a Dayton Audio test system and measure the speaker. Or if you are really hardcore you can do it with a multimeter and a signal generator.
Hello, I state that I’m using the online translator. Congratulations for what you do and for the help you give to those in need. I allow myself to ask you for advice because I can not understand well what I need. I own two Hertz 100.3 coaxial speakers that I would like to use for testing. I would like to put them in a single box (like boombox). The specifications are these:
D mm 85
Xmax 1,5 mm
Re Ω 3.3
Fs Hz 115
MH @ 1 kHz –
MH @ 10 kHz –
Vas l 1.7
Mms g 5.0
Cms mm / N 0.38
BL T · m 3.5
Qts – 0.79
Qes – 0.96
Qms – 4.33
Spl dB 92
I would have calculated (certainly bad) an internal volume of about 26 liters and a cone of 5 cm x ????. I know it’s a non-professional project, but in my small way, I’d like to do a good job. Thanks if you want to help me.
Best regards
Those speakers are made for car applications, so they work best in infinite baffle solutions. In that case you should place them in sealed enclosures. Make the enclosure as large as your boombox permits. Also, fill the enclosure with sound dampening material. This is the best compromise for your type of speaker.
Thank you very much, Marius
As everyone else has said great write up. That being said I have a 15″ ct sounds exo dual 2 ohm sub. Ive built several slot ported boxes for it and the bass is ridiculous. But I fell as if I’m still not getting all it has. Sub was bought second hand so I dont have any paper work for it and cant get a response from the manufacturer and ive only found one t/s sheet and it was on a eBay sale listing so I’m hoping its true for the sub. Could you help me out with proper dimensions? Thanks
Fs-29.676hz
Qts-0.294
Qes-0.311
Qms-5.434
Vas-38.993
Ported @4.0 ft^3
Normally I wouldn’t advise for such a big enclosure, but since this is a sub for bass-heads there are no rules :). OK, so if you want an enclosure of 4 cubic feet, you might as well go for 45 Hz tuning. So, since this is a 15″ woofer, your slot port would be somewhere around 450 mm (17.7″) in height. Therefore, make it 50 mm (2″) wide and 170 mm long (6.7″).
Hi Marius, what is the ideal distance for the placement for a round port away from the woofer?
Rgds. Aldo Douce from Mauritius Island.
Hello Aldo
Ideally you want to place it close to the speaker to reduce phase irregularities. However, bass wavelengths are very long (several meters) and the positioning doesn’t make much difference in this regard. You see ports on the back panel, bottom panel, no problem.
Can you recommend dimensions of a port for 8″ subwoofer and 11×12×11 inch box ?
Can’t recommend anything without drivers specs. It should be 3″ in diameter but can’t tune the length without driver specs.
Hi Marius. I have a pair of Visatron V20 experience which I really like. However, they do not fit in my new lounge anymore. What would change if I cut the lower most 25cm of the boxes and seal them again, basically reducing the total volume by 20% or so. Thanks, Jochen
It’s nice that Visaton provides all the information about the enclosure and drivers. Knowing that, I can predict what happens. When you say you will decrease the volume by 20%, my guess it’s a bit more than that because the lower part of the enclosure is not equal in volume with the top part (where the mids and tweeters are). Having said that, you will increase the resonant frequency of the box from 36 Hz to 42 Hz. You will lose some low end bass but will increase the output around 45 Hz (by a marginal bit because you decrease the volume as well).
That doesn’t sound as bad as I thought. If increasing the resonant frequency by a few hertz is the only effect and there are no other new resonances appearing at more critical frequencies then I might risk this operation. Thanks a bunch for your reply. 🙂
hello hopfully you can help me i m going to build 2 custom speakers with 2 10″ woofer and one horn tweeter with crossover coming from the klipsch rf 7 II in each speaker
High efficiency with sensitivity on 101 dB with 1 watt / 1 meter
Frekvensgang: 30 Hz – 24 kHz (+/-3dB)
the speaker volume is 111271.936 cm3
i m going to use 2 ports in front.
what dia and length shuld the ports be ? i do not have any more info
Uhm, there is not enough info to give you any solid advice. But, I would go for two ports of 10 cm diameter and 400 mm length.
Hello Marius,
Thank you for your informative website.
I have a couple of (perhaps a bit stupid) questions about rear-ported speakers.
1. You noted that it’s not a good idea for a rear-ported speaker to be up against a wall. Is 6″ clearance sufficient for the port to function as intended?
2. Does sound actually come from the port? So, if the wall the speaker is near is between me and a neighbour, would there be more sound projected their way than with a front-ported speaker?
Thank you for your help.
Brad
1) Minimum clearance should be the diameter of the port.
2) Yes, sound comes out of the port. Technically it would be more sound, but not a perceivable difference, compared to front firing port.
Hi, Marius,
Please can you suggest me the way how to do the bass cabinet for the 8″ speaker.
the passport frequency rate is 60-17000 Hz. Do you think it is possible to get a bass for home acoustic?
If you give me the name of the speaker maybe I can help you with some numbers, but an 8″ speaker is too generic.
it is Chinese speaker, I do not know o trust or not:
Features:
– 1pc 8 Inch Bass Speaker Systems
– Output Power: 400 Watts
– Non-fatiguing Butyl Rubber Surround
– Standard 8 inch Size Fits OEM Locations
– Impedance: 4 Ohm
-RMS: 60W
– Sensitivity: 95 dB
– Frequency Response: 60Hz~17Khz
-Installation Depth: 3 Inch
Round Shaped Design: Poly Injection
A substance called ‘Polyurethane’ and is categorized as a ‘Polymer’. It is a resilient, flexible and durable manufactured material that can take the place of paint, cotton, rubber, metal or wood in thousands of applications across virtually all fields. It can be hard like fiberglass, squishy like upholstery foam, protective like varnish, bouncy like rubber or sticky like glue.
Voice Coil: Aluminum
In the specific case of our cones, this material allows for maximum flexibility that produces great sounding speakers lasting you a long time.
Surround: Rubber
Our speakers are capable of higher or elevated temperature strength and fatigue properties that will increase performance and efficiency of heavy duty play time through lower weight and higher operating temperatures.
That is all, what I know.
Do you think, it can be possible to get a bass from the one?
I need the Fs, Qts and Vas parameters to accurately design an enclosure. By the description it looks like a woofer designed for car applications. This means, most likely, it’s designed for infinite baffle situations. In your case, if you want to use it at home, i would suggest to make a sealed box. Make it as big as you are comfortable / space allows. The bigger the better.
Thank you.
Seemingly you are right, by ” chinese classification” the drivers of 4 ohm are for cars, but of 8 ohm – for a music. the T/S parameters are fully unknown for the chinese seller.
So I will do it as you recommend.
Well, I got some figures from the seller. It is:
8 Inch 400W Car Speakers 4 Ohm Impedance Bass Speaker for any Car Mid-Range KTV Stage Home Louder
Fs: 62hz
Qts:0.38
Vas: 15liters
So what do you think, can it be possible to use it as a home bass additionally to stereo boxes?
Thank you.
Those are really poor specs for a subwoofer But you can try a bass reflex box. An 18 liter box with a 75 mm diameter port and 130 in length. Don’t expect much from this woofer.
Hello Sir, this is the best article about subwoofers.
I want to know that as you written about multiple port, eq. area can be calculated by the formula, but what about length of port.
If i want a 4inch diameter and 24 inch length and i want to split this in two ports. So what should be the area and length of ports?
Combine the areas of the 2 ports and consider it as a single port. Calculate the length. Use that length for each port (individually). Don’t split the length between the ports.
Do you think, a quarter labyrinth could be suitable (to compare with a phase inverter) ?
Like I said, the driver is something very modest. You shouldn’t try to make a fancy enclosure, like a transmission line. Just go for a simple bass reflex and call it a day.
Dear Sir, what may you suggest for the following driver?
12” Powerful Car subwoofer
Size: 12 inch Subwoofer Design in USA.
Unique design
PureAluminium cone ( more soft sound )
Rubber edge subwoofer
Impedance: 4 Ohm
Fs : 41 Hz
Frequency range: 41Hz to 15000Hz
Sensitivity: 96dB/W/m
Big Magnet size: 50 Oz
Voice coil: 50mm KSV for more Power
Max power: 2500watts
Is it good enough for my home music bass?
To design an enclosure you need Fs, Qts and Vas. Besides that, you cannot tell if a speaker is good or not, just by looking at some numbers.
Well, you are right. The seller does not know the figures. All what I have dragged from him are the following:
Size 12 inches,
Fs=38Hz,
RMS=70 W,
Qts=0,45,
Vas=33liters
Do you think, It can be good bass for home music?
I’d be very appreciated if you could recommend me the appropriate cabinet design,
Thank you.
53 liter enclosure. Port of 100mm diameter and 265 mm in length
Oh, the box volume you recommend is 53 (fifty three) liters?
But why the producer indicates 33 liters?
Vas is the equivalent compliance as a volume of the speaker. It’s not the recommended enclosure volume.
Thank you.
Hi Marius,
what do you think about the follows :
speaker 10″
Fs=35 Hz,
Vas=30 L,
Qts=0,42
33-17000 Hz
RMS=60 W.
Do you think, it is good for bass box?
Could you recommend me the box and the port size?
Thank you.
40 liter box, 75 mm diameter and 200 mm in length port
Thank you!
I am trying.
Dear Marius,
Please suggest is it necessary to put some sintepon cloth inside the subwoofer box?
if so, how much it should be there?
Not really that useful for bass reflex. If you have a sealed enclosure, then stuffing it with damping material has its benefits.
Hello Marius, greetings from Estonia! I read your comments here and maybe you can help me, please. I’m building a woofer to home. Unfortunately the box get ready before the driver was selected.. but i have some choiches. But.. The box is 500 x 395 x 285mm ~56L (real liters, inside) and made 20mm weatherproof plywood [driver panel (biggest side on the box) 2 x 20mm thick double panel] sealed box. The question is, should i keep it sealed or make it bass reflex box and what would be the dimensions of port? Drivers i’d like to install it: Audes, 75W104-4
4 Ohm
29 – 2000 Hz
(2,83 V/1 m) 94 dB
Bl 9,31 T∙m
Qms 8,99
Qes 0,31
Qts 0,30
Vas 80,7
Or
Audes, 75W87-4
4Ohm
32 – 2000 Hz
(2,83 V/1 m) 91,5 dB
Bl 9,11
T∙m Qms 8,95
Qes 0,28
Qts 0,27
Vas 35,6 l
Whichever i should select to get possibly nice deeper bass with my little 56L box? I hope you understand me and sorry for my English..
Best wishes, Allar
Well, first of all the numbers you quoted, don’t match with what I found online.
https://audes.ee/products/speaker-drivers/75w104-4/
I’m going to use the numbers on their website. So, I suggest you go with the 10″ model 75W104-4.
Tune it to 40 Hz. Simply add a 100 mm diameter port with a length of 210 mm.
Thank You!
But 40 Hz, is it maximum low what i can get with this box, or i should change driver choiche to get lower? Because 40 Hz sounds like not so low or thers no point?
Best wishes, Allar
With this driver, there is no point in going lower. But 40 Hz is a good tuning frequency. Very rarely music tracks have sounds which go lower than 30 Hz. But they often have 40-50 Hz sounds.
Thank You! I’m trying that 100 x 210mm port 🙂
Hello Marius,
I have already done with that project, it sounds very good and low. But i glued to enclousure a damping acustical foam britty much every wall. If i do a simple freguency test, i hear woofer comes in about 30Hz.. is it now bad?
Absolutely not. Depends on what you are listening, but anyone appreciates a subwoofer that can play low. And most importantly, if you like how it sounds, it sounds good.
fb learned to adjust frequency. But What determines fb frequency? No cabin I made sold on the market doesn’t sound like subwoofers. they make more sound. I noticed their sound came from the port.
Sound sounds like big subwoofer, from small subwoofer. How?
Thank you
Well you are basically trying to defeat physics. Fb is determined by the volume of the enclosure and the size of the port. However, if you driver doesn’t play low enough naturally, tuning the box too low, won’t achieve much. A sub sounds like a sub, because it’s a sub :). Ports absolutely help, but don’t ask the impossible from them.
Regardless of what I said above, the high amount of port sound you mention is achieved when you tune the enclosure higher than “normal”. The diver will have a good response in that area, therefore the port will have a high output also. Furthermore, higher tuning don’t require large volumes, so it’s easier to make a big box compared to tuning frequency. Downside is that it won’t play the lowest notes.
Heloo i use a two Dexon IRB 20/100/01,8 and the Vas will be 60,8liters plus one 10cm wide and 11cm long port (0,8l) total Vas will by someting about 62l.It is this port too big or small.I put him in the middle of cabinet.
Vas is the equivalent compliance expressed in liters. You are confused. You don’t add vas with the volume of port. Please the read the article again carefully.
I now when i have got one 8inch woofer i can use 4inch or 3 inch port but how big port i must use when i’ve got two 8inch woofer please?
Heloo i have got two 8”midbass speaker.Please how big port i must use?
I now when i’ve got one 8”bass i can use 3”or4”port.
If they are sub-woofers, you need a 4″ port. If they are mid-bass drivers, you can get away with a 3″ port.
Hello Mr Tanasescu, speaker builder from Norway here, I really appreciate your knowledge in speaker construction. I’ve done some simple projects already, now Im designing a 4×15″ cabinet for bass guitar. Im planning on using this driver: https://www.eminence.com/pdf/Delta_15LFA.pdf. I will also add a 3″-5″ fullrange driver cutoff under about 2500Hz for treble . The recommend vented volume for one of these drivers is 85.00–167.00 liters. I plan on a 400 liter cabinet. Any recommendations for ports? Regards, Dag from Norway
Actually these speaker need a way bigger enclosure than that. If you plan to use 4 of those drivers in a 400 liter box I would suggest tuning it to 45-50 Hz. This would mean 3 ports of 150 mm in diameter and length of 50-90 mm in length.
Thank you so much!. But, how big a cabinet would you recommend for vented? I’ve also speculated in making it sealed, that would mean a way smaller cabinet. Sensitivity should not be a problem, I will run this on a 500 watt Ampeg amp. Eminence recommends about 40 liter pr driver. Thougths on this?
I don’t know where do you get those recommendations. This is a high Vas and medium-high Qts driver. It requires large enclosures. However, you can use 40 liters per driver and you will get a 3 db peak, which is fine, I guess. Some prefer it this way. Maybe it’s better for your application, I dunno.
Doing it this way, it will go down till 73 Hz compared to the bass reflex which will go down to 53 Hz.
Ok, thanks again. The 40 liter recommendation was from the Eminence website. I guess the conclusion is; go as big as possible.
Have a nice weekend!
Hi Marius,
Could you please advise me please ?
I’m trying to build my first home theatre bass reflex box. I’am reading a lot of about it, also try use win ISD.
Speaker will be 12¨ parameters:
350 W RMS 700 W Music,
Xlin +/- 15 mm Xmax +/- 25 mm ,
RDC: 3,7 Ohm
SD: 492 cm²
Qms 4,25
Qes: 0,53
Qts: 0,47
fs: 30 Hz
VAS: 53 l
Mms: 152 g
Rms: 8,00 kg/s
Cms: 0,16 mm/N
B*L: 13,2 Tm
Sensitivity (2,83V / 1m): 90 dB
fb = 26 Hz
I like to know box volume and diameter and lenght of port(s).
Thank you in advnance.
Anton
Go for a 50 liter box tuned to 35 Hz. This means 100 mm diameter and 310 mm in length
Thanks man, and if i want lower freqencies ? about 25 hz, larger box? (90l)
Yeah, yo can also go for a 90 liter box tuned to 27 Hz. 1 port of 100 mm diameter and 290 mm in length
Heloo.I use 2 Mid-Bass speaker.
Sd = 201.00 cm2, Vas = 30.40 l, cms = 5.35e-04 m/N
mmd = 21.99 g, mms = 23.57 g, Rms = 3.62 Ns/m
fs = 44.8 Hz, Bl = 8.82 N/A, Re = 7.54 Ω, Le = 0.60 mH
Qms = 1.83, Qes = 0.64, Qts = 0.48, η0 = 0,41n %
100W RMS
From 30Hz to 3,5kHz
Please i like to now diameter and lenght of port and box volume.
You can make it a 142 liter box with 1 port of 150 mm diameter and 137 mm in length. Or you can use 3 ports of 100 mm diameter and 256 mm in length each
And if i want max 61l box?Then 10cm and 20cm long ?
If you want to go for 61 liters, I would advise to use 2 ports of 10 cm diameter and 40 cm long each.
And whats happend if i put one 10cm and 12cm long port.But thank you for the help.You are best.
you could use only one with 12 cm in length. But you might get wind noise, since you have 2 large woofers and only 1 port. But it could work, you can try.
And when i have lower than 61l it will be have worst bass?
i´ve got two 8inch mid-bass speaker and on one speaker is VAS 30,4 liters.And two together must have 60.8l box?
Lower volume equates to lower efficiency. The enclosure doesn’t have to be the size of your Vas number (most of the time, this is not the case).
Okay thanks,but how big box in (liters) i musst have ?
You got the dimensions above. You can use 61 liters, I would advise to use 2 ports of 10 cm diameter and 40 cm long each.
thank you.
And if i´ve got 36liter box?
and where will be better bass in 61l box or 36l box??
THANK YOU
No I’m sorry, I was trying to reply to someone else. You cannot make a box that small (36 liter). I mean you can, but it’s best to make it 61 liters at least.
its okay thank you.
Heloo i use one SICA loudspeaker.
Nominal Diameter 210 mm (8″)
Nominal Impedance 8 Ω
Rated Power AES(1) 200 W
Continuous Program Power(2) 400 W
Sensitivity @ 1W/1m (3) 88.8 dB
Voice Coil Diameter 50 mm (2″)
Voice Coil Winding Depth 18 mm
Magnetic Gap Depth 5 mm
Flux Density 0.89 T
Magnet Weight 930 g
Net Weight 2.7 kg
Thiele & Small Parameters (4)
Re 6.1 Ω Fs 38.0 Hz
Qms 5.25 Qes 0.53
Qts 0.48 Mms 32.7 g
Cms 536 µm/N Bxl 9.45 Tm
Vas 34.8 l Sd 213.8 cm2
X max(5) +/-6.5 mm X var(6) +/-9.0 mm
η0 0.35 % Le (1kHz) 0.59 mH
Please how smallest box(in liters) i can use for this spesaker?
The smallest box you can use is a 20 liter sealed box. 15 liters minimum
And wented box?
35 liters tuned to 40 Hz. 75 mm diameter port with 182 mm in length
And wented box?
sorry i post it 2 times thank you.
You´ve got some school or from where you now all this things?
Hello.I´ve got question.When i do box for speaker (for example Vas 30)l 30l box and i use damping material(2cm think), i must do a bigger box ?is that because damping material do smaller box or what can you help me?
Normally adding damping material to a box will increase the perceived volume of the box, so you would need to make the box smaller to compensate. But the effect is like 10% for a fully stuffed box. Adding 2 cm will be negligible. So you might as well consider that you don’t have any dampening material at all.
the damping material increase the volume? than i must do smaller box(for exeample 30x30x30cm(1,8cm think wood+ 2cm damping material) and when i´ve got this size how small i mus have got the box?
Maybe you don´t understand m question but when i use damping materials how many cm i must do smaller box please?
You are worrying about things that don’t matter. If you add 2 cm of damping material it doesn’t do anything. Just consider that you don’t have any dampening material (even though you do).
ok thank you,
because i do one box with 1.8cm think wood and 2cm damping material and i calculate volume like the damping material will be 2 cm wood but thank you.
No, you calculate the volume like there is only 1.8 cm of wood.
Heloo.I want to use one STX W.18.200.8
Vas is 32l.
But recommended box is 15l@40hz bass reflex.
How big box (liters) and port i must use?
I suggest using a 20 liter box tuned to 45 Hz. This means a 50 mm port with 110 mm in length
Thanks.
hello , i just changed the woofer in a 2.1 set from a 4 inch to a 6.5 inch ( just what i had laying around , and as expected the sound is way off , so i need to modify the reflex pipe accordingly , it had a 2×3 inch (w l ) what can you recommend to put in there now , as much i understand from your article it should be a 3 inch width pipe , the box is 10.5 x 9.5 x 6.5 inch ( h d w ) nice and tiny hahaha
thanks
Maarten
Thailand
First of all, you should try to using the same box with no modifications. It will probably sound good. The resonant frequency of the box is given by the box itself. The fact that you are swapping the driver, doesn’t change the resonant frequency of the box. A bigger driver demands a larger port to minimize port noises and port compression, but 2 x 3 inches doesn’t seem small at all. My advice is to leave the box as is and see how it sounds.
ok box sound pretty fine but it sounds less stressed when i take the tube out so i would like to change the tube for i bigger diameter you think it would do with a 3×3 pipe ?
didn’t do much modifications on the box itself except a whollotta silicone to fill gaps and a small compartment to close the volume bass tone pods assembly that was as leaky as a mosquito net
greets from Thailand by the way
Yeah you can try a larger port, but try to make it a bit longer if space permits.
Hi ! Recently I upgraded some cheap chinese ( Dibeisi brand, and burned ) speakers i had laying around. They are two way, 15” ported design , trapezoid shaped, with internal volume of 67 Lt and two front facing ports measuring ( 7cm in diameter and 10 cm in length each ).
For the LF drive I used the Eminence Delta 15A since it was readily available in my country.
Firstly, am i correct to assume ( based on some online box calculators ) that the volume is not enough ? And what would be an ideal volume / port dimensions for these speakers ?
Secondly, is there anything i can do to the ports or other, in order to improve the current boxes ?
Also, since i will be using them for parties or other loud events 🙂 , they will be playing close to their max rms rating of 450W most of the time.
Thanks for your time and help,
Panagiotis.
Well, really there is not much improvement to be gained if you fiddle with the ports. You really need more volume for that kind of speaker. My advice is to accept this compromise or make another (larger) box.
Thank’s for the reply. Something final i was thinking about. Will any attempt to seal the speakers better ( painting the inside , using silicon adhesive on the joints and equipping the handles and the connection terminals with rubber gaskets ) make any noticeable improvement ? Cause when i crank up the volume i can fill tiny gusts of air escaping mainly from the handles …
Yes you should seal any leakage that you might find. There are ones which aren’t that obvious. To check for any small leakages you can put your chin/lips close to the most suspicious spots while the speaker is playing. You will immediately feel any small gusts of air if there are any.
Hi:
I have a port baffle diameter of 2 inches. The last update ( when speaker was in production ) was 3” in diameter and about 4.5 inches length. (Spendor BC1)
How do you glue the tube to the inside 2 inch port hole?
Can it be installed from the BACK of the speaker cabinet opening and the tiny outer LIP glued to the baffle hole?? What type of glue? ( I would insert 3/8 inch open cell foam inside the tube length)
Thanks
Howard
I like to use regular silicone (caulk). When I use regular adhesive it might not create a perfect seal between the panel and the port. This will created unwanted noise. If the silicone oozes out, you can clean the excess after it dries out.
Very very informative article indeed.
I’m trying to design a box for 1-8 inch sub .14.4×15×15. 3/4 inch MDF. 1 4″ port,24″ long. Speaker displacement is .069. All measurements are outside dimensions
Hi. I wanted to put a port for a cylindrical speaker, I wanted to ask you for a good place to do this. The woifer is 6″,and the box is 104cm.The cylinder material is made of compressed paperexactly like wood.
Well, you can place the speaker on the top of the cylinder and the port on the bottom of the cylinder. Can’t see another feasible way.
Hi
My question is regarding rectangular port….
Modeling 18″ subwoofer box with rectangular port @ base. Box size is 25″H*25″W*27″D. According to win-isd, port is 3.75″H, 23.5″W & 22″ long.Cross sectional area of port is 88sq.inches. Actually the port is too wide, so i am going to add two supports in port at equal distance up to full length i.e.22 “(this is like dividing port in 3 equal sections)
1. Should i consider these are three seperate ports of equal vol…if yes, then total cross sectional area of three ports is 82.6sq inches is much lesser than required (88sq inches). Can i increase cross section area of each port to match 88sq. inches?
2. Is there any modifications in port supports (dividers)so i can use it as a single port of 88sq inches?
Thank you.
Yes, these will be considered 3 separate ports. If their added area is the same then the length will be the same. In reality the length is a smudge longer, but don’t stress about that.
To be honest, enter in WinISD that you have 3 rectangular ports, and enter the new dimensions. And see how long the ports need to be. Since the added area will be somewhat lower, then the port will need to be longer to maintain the same resonant frequency.
Thank you sir
Hi,Thanks for the nice detailed article.
I need to build a cabinet for a speaker of Sica 12 CX3P
Qts 033, Fs 49 Hz & Vas 72.8 liter. Its a full range speaker
Kindly advice on the best sizes for the boxes and port dimensions.
I would suggest a 33.71 liter box tuned at 59 Hz. Use a 150 mm diameter port of 343 mm in length. If you can’t find one use 100 mm diameter port of 128 mm length. Remember that the 33.71 liter volume is the net volume, so you have to add the volume displaced by the speaker and by the port.
Thank you sir for a prompt reply and valuable suggestions.
Hello Marius.
I have two questions regarding ports on commercially available speakers.
I see many ready made speakers with 18 or 20 inch woofer in a cabinet sized like a small fridge, and they use a couple of triangular vents in the corner between the driver and the corner of the cabinet. Not a port but a simple hole, a cut out in the baffle. How do they get away with that? Is it any kind of proper port?
The other side of the question is about a small pair of Sony bookshelf ported speakers (5.5 inch driver, 1.5″ diameter by 7″ length, approx port ). I can plug the ports sealed with cork, cardboard, etc. and do not notice any change in sound quality, listening level similar to a loud conversation.
I do not have yet acquired the skills for precise measurement, but using an app called Spectroid didn’t reveal any change either. Why could that be? My guess is that a mass producer would not waste material and process time if that wouldn’t make a difference so why would they put there a port that seems to do nothing?
(B.t.w. The app may not be accurate for professional work, but has proven good enough for me to find error and correct speaker cabinets I made myself, so I trust it.)
Hello
If you increase the volume of the box, the length of the port needs to be smaller and smaller to achieve the same resonant frequency. If the box in large enough, the length can coincide with the baffle width, yes.
Maybe the port is tuned too low, where it doesn’t get “excited” much by the speaker (as the speaker is small enough to not reach very low frequencies). As a result, if you cover it or leave it open, it’s the same thing. This is a possible scenario.
You need to do nearfield measurements to check the differences. It’s actually not a straightforward measurement.
ok box sound pretty fine but it sounds less stressed when i take the tube out so i would like to change the tube for i bigger diameter you think it would do with a 3×3 pipe ?
didn’t do much modifications on the box itself except a whollotta silicone to fill gaps and a small compartment to close the volume bass tone pods assembly that was as leaky as a mosquito net
greets from Thailand by the way
Jeg har en PSP Subwoofer 10″, hvordan finner jeg ut hvor beste plassering for den er ???
Jeg har prøvd “krype” metoden:
Sette subben i sofaen (i riktig høyde !), og sette på noe med trøkk i…og krype rundt i stuen….der hvor det er best/mest lyd….er plassen….👍 Stemmer dette ???
Det rare er at den spiller best på den plassen !!!
Og en annen ting:
Bryterene 0 og 180 grader (skjønner det!) og CROSSOVER BYPASS: “ACTIVE OR BYPASS…?
Alt annet er korrekt oppkoblet (+ og -), (A/V : ONKYO 868 THX, 7.1.2, men det kommer mest bass med stillingen i 180 grader ????!!🤪🤪🤪🤪 og crossover i off-…🤪🤪
mvh
Jarle Strømsem, 7033 Trondheim, NORWAY, +47 90589003, (Siv.Ing. Data & Elektronic)
Hi Marius,
I’m in the process of constructing a 3-way floorstanding speakers with two 6,5″ woofers each, crossed at 400Hz. I’m aiming to tune the box at 43Hz which using WinISD gives me about 20,5cm lenght of the port with 10cm width and 45L inner box volume. When taking away 18mm thickness of mdf panel which this port will be mounted in it gives me roughly 19cm of the port lenght inside the enclosure. Port is made of 2mm thick PVC pipe.
Therefore my question is, do you think at that lenght (and width) the port inside the enclosure might have some unwanted vibations at higher levels? Is the port too long to be just on it’s own without any additional support i.e. some sort of bracing for the port itself to stop any potential vibrations? I’m guessing it wouldn’t hurt it but is it necessary as it would obviously take additional work and take away the enclosure’s inner volume? Taking to account Xmax of the speakers I will be feeding it a maximum of 60W per channel.
Thanks
19 cm long port is not that long. Just leave at as it is, it’s fine.
Cool. Good to hear!
Thanks for the reply Marius.
Cheers
Pete
Dear Marius, I am asking for your advice on the following questions:
1.) I have a pair of VISATON TIW 200 XS speakers, do you recommend a bass reflex or closed box design (Qts = 0.5). Different box size calculation formulas gave different volume and port values, what would be the correct volume value for a bass reflex or a closed box.
2.) I have a pair of MR130 speakers, Should I build a 3-way speaker with the above-mentioned subwoofer or use it for a W200 subwoofer, which is a little lower quality. The size of the box is also a question here, or can you provide the formula you think is correct?
Thank you, Sandor
Hello! First of all Qts is 0.46 (Qes is 0.5)
1) For 2 woofers I would suggest a 163 liter box tuned at 27 Hz (2 x 4″ ports at 32 cm in length)
2) You can use the TIW 200 as they have a low power rating for a subwoofer.
hi, what needs to be taken into account when calculating the bass reflex so that there is a lot of wind?
Hi,
I have ATC PA 100 375 BLC drivers with Qts = 0.22, Fs = 44 Hz, Vas = 134 litres, Qms = 1.20
I’ve found a secondhand a pair of commercial cabinets that previously held otherwise unknown 15″ Peavy drivers with dimensions H W D is 60 x 46 x 40 cm.
Thus their volume from this before even taking anything else into account is only 110 litres.
There is a working teeeter and a fron facing rectangular flanged port about 15 cm long and 2.5 cm high internal hole, and spreading to about 23 cm long and 5 cm high at the outer edge of the flange
Would I be compromising the sound and/or risking damaging the ATCs if I put one in each cabinet? That is, is the internal volume likely too small for these? What cabinet volume in litres, Vb, would be optimal?
Thanks.
Don’t really understand the port dimensions from your description. Anyway, this looks like a PA driver that wasn’t meant to play low frequencies. Judging by the specs, even though it ha a high Vas, the Qts is so low that the volume requirements are low as well. Something like 20-30 liters tuned pretty high 70-80 Hz. The fact that you have a 110 liter box, you can go ahead and mount that driver on that box and see how it sounds. You can’t damaged the speaker if the box is too small or too big. Only if you abuse it with too much power or too much distortion. Since you have such a big box, you can try and tune it lower 55-60 Hz.
Thanks for the quick reply Marius. What physical aspects of the cabinets are best altered to garry out the tuning you mention?
Hello everyone this sub woffer box design is fascinating as i read up,
Would the distance of air travel would have an effect to enhance bass at all Marius Tanasescu?