Sealed enclosure explained in detail and calculator
Sealed enclosure / Closed box / Acoustic suspension / Air suspension
These are the many names for the sealed enclosure. The explanation of the latter names is simple. Because the box is air tight, the air inside the cabinet acts like a spring. When the speaker moves, it pushes against the “spring” and then it is pushed by the “spring”, similar to a suspension, hence the term acoustic suspension Logically, if the volume of the box is smaller, the “air spring” is stiffer. Inversely, if the volume gets bigger, the “air springs” effectiveness diminishes.
Increasing the volume too much, will lead to denying the effect of the spring, and the enclosure is an infinite baffle. Actually, the term infinite baffle is exactly what it sounds like, a baffle that extends indefinitely. This will lead to no resonances, no diffraction and other benefits. But in the real world, we can convene that the infinite baffle is just an oversized sealed box.
Couple of relevant T/S parameters
Cms – The compliance of the suspension (the spider and the surround, to be exact). If the suspension is stiff, the driver is not compliant. So, the easy it is to move the speaker, the more compliant it is. Cms is measured in m/N.
Vas – The air inside the cabinet has its own compliance. If the box is small, the air is less compliant and if the box is larger, the air is more compliant. Vas describes the volume of the air inside the cabinet (measured in liters), where the compliance of the speaker matches the compliance of the air inside the box.
- This is an oversimplification:
- If (volume of the enclosure) < (Vas) then it’s an acoustic suspension enclosure.
- If (volume of the enclosure) >= (Vas) then it starts to become an infinite baffle.
- Example : If Vas = 30L and I make a box of 29L or lower, the air inside the box starts to act like a suspension and I just made an acoustic suspension. I just like to keep it simple like that. Because if you want to get really technical, the term acoustic suspension is valid only when the compliance of the driver is 3 times (or more) larger than the compliance of the box.
Why choose a sealed enclosure ?
There are many reasons why you would want to choose a sealed enclosure. Here are a few :
The roll-off is very smooth
Roll-off is about 12 db / octave. This is compared to other enclosures, like bass-reflex, which has a steep roll-off of about 24 db / octave. You can see from this graph, the frequency response of the driver. Blue is for sealed and red is for bass-reflex. Let’s consider, for argument’s sake, that they both play linear till 60 Hz, and then they start to roll-off. While the bass-reflex will play louder than the sealed counterpart, when it has reached the resonance frequency, it starts to roll-off quickly, while sealed will keep playing even the lowest notes (at an increasingly lower output, of course). You can see from the graph, that sealed plays louder at 30 Hz than bass reflex, because of this smooth roll-off. Please understand that this graph exists just to make a point, in real life things aren’t so perfect.
It has a great transient response
This means that the speaker is very “lively”. It can play with little effort short term sudden sound waves, like drums, for example. For a good transient response, the speaker needs to start and stop exactly when it needs to. The internal air “spring” that acts like a suspension, helps with achieving these good transients. Also, the fact that it has a gentle roll-off slope of 12 db / octave, helps as well.
The difficulty of construction is very easy.
You just have to make sure that the box doesn’t leak air, and you are pretty much set. The only thing you need to calculate beforehand is the internal volume of the box. Now, there is no particular best volume for each speaker. You just have to understand what you are using it for, what are your tastes in sound, and then you can calculate the volume of the box. Meddling with the volume affects another T/S parameter (called Q).
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We will talk about Q in a second and how does it affect the frequency response. Besides the fact that it is easy to build, if you get the volume wrong after you made the box, it’s not that big of a deal. Let’s say you wanted a 25 L sealed enclosure, and after it’s done, because of some building errors, it has 28 L. It will still sound good even with the 3 L extra. For a band-pass enclosure these kinds of errors are disastrous for the end result. You can even buy prefab boxes, since the only variable is the volume.
The major negative point for the sealed enclosure is the low efficiency. To make a comparison with bass-reflex : you would need a 200 W amplifier to drive a certain woofer in a sealed box, at the same output, you would only need 100 W, to drive the same woofer in a bass reflex box. Sealed will sound tight and deep, but not loud (unless you are pumping some serious watts). If you want loud, there are certainly better options out there.
Stuffing / Filling of the box
It is common practice to stuff the box with absorbent material. Many materials can be used : polyurethane, fiberglass filling, bonded cellulose acetate fiber, long fiber wool etc . The stuffing has various advantages :
Absorbing standing waves
The whole point is to separate the waves generated by the front of the speaker from the ones generated by the back. It is obvious that absorbing some of the back waves will do some good.
Diminishes panel resonances
Placing absorbent material on the walls of the enclosure, ensures low resonances. The thickness of the damping material is important, if you need to absorb sound waves of certain frequencies. The back panel is the one who needs this damping the most, because back waves reflect of the back panel, come back towards the speaker and come out through the speaker.
Increases the internal volume of the box
This is a bit harder to understand, but the technical term is isothermal propagation. Pressure and temperature are correlated (for example if pressure goes up, temperature goes up). In our case, we talk about sound pressure. Now, when we add damping material into the mix, it creates this isothermal environment to some degree. This material, although not a good temperature conductor, it conducts temperature better than air. In this case the pressure drops, which means the velocity of sound drops, which means the compliance of the box rises, which is the exact same thing as making the box bigger. Adding stuffing to your box will translate into 15 % – 25 % volume increase. We are talking about the effects, that happen when increasing the volume, because obviously the physical box size will remain the same.
Increases efficiency
If the damping of the box is done right, you are looking at up to 15% efficiency increase. Here is how a bag of poly fill (Amazon affiliate link) looks like.
Q
When people talk about Q, they are trying to describe the damping of the driver, or the whole driver/box configuration. In reality, Q is a composite term, it takes into factor all the mechanical, electrical and pneumatic properties of the speaker/cabinet and describes how it affects resonance. So it actually describes damping in a reverse way. It is referred to as quality factor, but generally accepted that it describes damping.
- More to the point :
- When Q goes down => damping goes up.
- When Q goes up => damping does down.
What is this damping?
The cone tends to vibrate a lot at resonance and damping keeps this in check. Lets split damping into smaller parts :
- Qms : Mechanical Q. It describes the damping made by the suspension of the driver : the surround and the spider of the speaker.
- Qes : Electrical Q. It describes the damping made by the coil – magnet assembly. When the coil moves through the magnetic field it generated a current which opposes this motion (hence the electrical damping).
- Qts : Total Q. This is the number you will need when establishing the desired volume of the box: The formula is : 1/Qts = 1/Qms + 1/Qes.
- Qtc : This describes the total Q when you take into consideration the damping of the box as well.
- When Volume of the box goes up => Qtc goes down.
- When Volume of the box goes down => Qtc goes up.
Box-speaker damping (Qtc)
When you adjust the volume of the box, you are basically trying to hit certain values of Qtc, because these values translate into characteristics that have the following description :
- Qtc = 0.5 : Perfect transients, but low efficiency (over damped).
- Qtc = 0.707 : This is the number most people try to reach for, as it gives good transients and flat response with minimum cutoff.
- 0.7 < Qtc < 1.2 : Better efficiency, somewhat degraded transients, steeper roll off.
- Qtc > 1.2 : High efficiency, bad transients, bad frequency response (under damped).
How to design loudspeakers - video courses
Regarding the value of Qtc, you can strive to get the 0.7 value, and you can’t go wrong. You can go a little up, like 0.8 – 0.9, to get a little more fun sound, which will translate into a few db more on the bass notes (at the expense of transient response). Going towards to Qtc of 1.2 is pushing it, and should do that only if space is an important factor and you need a small box. You should avoid going beyond 1.2, because you will end up with a “one note woofer”. This means it will play a very narrow frequency range, loud (see the graph), and it will overpower the rest of frequency spectrum.
To calculate Qtc, the volume of the box (Vc) according to desired Qtc, and resonant frequency of the box (fc) use these formulas :
- Qtc = Qts * (Vas / Vc + 1)1/2
- Vc = Vas / [(Qtc / Qts)2 -1]
- fc = fs * (Vas / Vc +1)1/2
- f3 = { { (1/Qtc2 -2) + [(1/Qtc2 -2)2 + 4]1/2 } /2 }1/2 * fc
Recommended speakers for sealed enclosure
If you want to build a sealed enclosure, picking the right woofer will be very easy. You are looking at low free air resonance (Fs), high cone mass and long voice coils. Don’t get too caught up by the actual values, because most of them will work fine in a sealed enclosure. If you really want to get more technical, you can calculate the Efficiency Bandwidth Product (EBP)
- EBP = Fs / Qes
- If EBP around 50 or less, then the woofer is suited for sealed.
- If EBP > 100 then the woofer is suited for bass reflex.
- If EBP is between 50 and 100, then it is good for either closed or bass reflex.
The length of the voice coil is something to consider also, because in a sealed enclosure, the woofer will have a longer excursion than the equivalent bass reflex.
- What are you looking for these Xmax values (please don’t stress too much on this) :
- For small woofers (6″ – 8″) Xmax should be 2-4 mm.
- For larger woofers (10″ – 12″) Xmax should be 5-8 mm.
Conclusion
When you are building the enclosure, you should really focus on making the box air tight. You can ensure this by applying silicone sealant to all of the joints. If you do this, make sure you don’t place the speaker just yet, because the fumes from the fresh silicone will “attack” the speaker. Make sure you let it rest for at least 12 hours before placing in your speaker.
After figuring out which Qtc you want to hit for, you can find out the volume of the box. Take into consideration that after you calculated the net volume of the box, you should add the volume dislocated by the back of the driver (magnet assembly) , crossovers, bracing etc, so you get the gross volume of the box. Also, if you add stuffing, this will effectively increase the volume of the box, so keep that in mind also. If you are building your first speaker box, then the sealed enclosure is probably the safer bet.
References
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- Loudspeaker Design Cookbook 7th Edition by Vance Dickason (Audio Amateur Pubns, 2005). (Amazon affiliate link)
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- Newnes Audio and Hi-Fi Engineer’s Pocket Book by Vivian Capelm (Elsevier, 2016). (Amazon affiliate link)
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- The Audio Expert: Everything You Need to Know About Audio by Ethan Winer (Focal Press, 2012). (Amazon affiliate link)
- Image source : link.
68 comments
Hello, thank you for your article, very insightful.
However, it is not clear to me how Vas and Vc are different, as according to this article both seem to denote the box volume?
Can you pls. elaborate a bit?
A speaker has a certain compliance or Cms. This is given by the suspension of the driver. Cms is measured in meters/newton. Vas expresses the same compliance of the speaker in terms of volume. Imagine a syringe without the needle. Close up the nozzle with your finger. If you try to push the plunger, you will encounter resistance from the air trapped inside the tube. This amount of air has a certain compliance. If the syringe is bigger (higher volume of air), the air is easier to compress, therefore, higher compliance. So having a high Vas number means that the speaker is more compliant.
Both Cms and Vas denote compliance, but Vas is measured in liters (or other units of volume, like cubic feet). Vc is the volume of the closed box, which is in direct correlation with Vas. As you can see from the formula : Vc = Vas / [(Qtc / Qts)^2 -1]
Some sweeping statements, omitting some detail:
Vas is a volume of air that provides the same degree of damping (or compliance) of the speaker driver itself. Vc is the designed box volume.
The Vas is related to the speaker driver’s diaphram (pistonic) area and the compliance of the foam (or rubber) surround. These result in a ‘springiness’ of these components.
The Vas is the volume of air that is as ‘springy’ as the speaker driver’s inherent ‘springiness’.
Vc is the box volume. This can be ‘engineered’ to exhibit the audible characteristics desired by the box designer.
A small box (low Vc) will sound taught and have only modest bass extension. A large box (high Vc) will sound less controlled but exhibit more bass extension.
The relationship between the two is based on the designer’s selection of sealed vs. ported box design, relative dimensions of the H x W x D triple and the desired Qtc (system damping factor). Selecting a particular value of Qtc influences the box volume (Vc).
Applying formulae to Vas, Qtc and box type allow the designer to arrive at a box volume, Vc, that will exhibit the designer’s desired characteristics. The observed results are, however, always a compromise between audible characteristics, box volume (ie. the amount of space taken up in a room) and the bass extension.
Very interresting article thank you! Sealed it is!
I am left with one question, which I have asked on the community diyaudio forum:
“How will the frequency response line differ when enlarging or reducing the box size?”
http://www.diyaudio.com/forums/subwoofers/317008-somewhat-larger-sealed-woofer-box-frequency-response.html
As an expert I invite you to have a look and paste your comment too! Thanks 🙂
Well, the answer is actually inside the article. If you take a closer look at the Qtc comparison chart all shall be revealed :). As you increase the volume of the box, Qtc will go down (0.7 , 0.5 etc). By doing this, you make the “frequency response line” very smooth. It reaches the very low-end of the spectrum. Very good transient response, but not very impressive on the output department. As you lower the volume of the box, you will start to get a peak in the response (as you are increasing the Qtc). Anything with a Qtc above 0.7 will have a peak in the frequency response. The transient response starts to degrade, and the frequency response doesn’t extend as low. However, you get a boost in output. If you keep decreasing the volume, the peak gets so large, that it basically plays only that frequency (“one note subwoofer” as they call it). You will see subwoofer manufacturers which opt for a 0.8 – 0.9 Qtc, because it results in a slight peak in the response, and people appreciate the extra output (and they are more commercially successful). Audiophiles aim for 0.7 because it offer the maximally flat response.
Awesome thank you very much Marius! Now I see it much clearer! I can now read/understand your diagram indeed! Have I calculated correctly, that for my dayton audio 18″ (for my home made 3 way active system, for the lowest flat “audio phile” base in a sealed and stuffed box) I need a volume of 100 liters to reach Qtc of 0.7 at Fs 60Hz? Of course I would love to get a lower Fs of 30Hz but how? Using a pro equaliser? Thanks!
http://www.daytonaudio.com/index.php/loudspeaker-components/loudspeaker-drivers-by-series/pro-sound-series/pa460-8-18-pro-woofer.html
Your calculations are correct. If you want to go lower, you will have to opt for a bass reflex design. A volume of 186 liters and tuned to 34 Hz will result in an f3 point of 39 Hz (f3 is 3 dB below linear response). To tune it to 34 Hz use a 150 mm diameter pipe with a length of 140 mm. Good luck!
If you find this confusing make sure you check my articles about bass reflex design :
https://audiojudgement.com/bass-reflex-speaker-design/
https://audiojudgement.com/bass-reflex-alignments-explained/
Thanks for taking the time to write the article and share your knowledge. I’m a bit confused over the following statements from the article, which seem conflicting:
1: If the volume of the box is smaller, the “air spring” is stiffer.
2: When Volume of the box goes down => Qtc goes up.
3: When Q goes up => damping goes down.
I would think that when the suspension gets stiffer, then damping goes up, not down? What am I missing?
Many thanks, Trond
All of the analogies regarding Q are confusing. Maybe forget about the air spring. Q is a measure of how much of the input energy is retained and how much is dissipated as heat. If more energy is retained than lost, Q will be greater than 1. As the box gets larger, Q gets lower, damping does up. Damping goes up as more energy is lost (either in the suspension or on the electrical side via back-EMF). That’s what damping means in this case, it damps some of that input energy, so the driver doesn’t ring or vibrate uncontrollably at certain frequencies.
Very useful articles and helped me in my project
Excellent article, thank you! I’m curious, how do these calculations change in a sealed speaker cabinet with multiple drivers? For instance a 2×12 or 4×12 guitar cabinet compared to a 1×12. Thank you!
When working with more than 1 speaker, all of the variables remain the same except for Vas. If you have 2 speakers, multiply Vas by 2. If you have 4 speakers, multiply Vas by 4.
As an amateur, I will humbly add that when calculating internal volume, you have to consider the volume of the driver itself, and possibly subtract this from the calculated internal volume. Big drivers have a considerable volume, and if you start adding several drivers this certainly becomes a factor in the calculations.
Yes, of course. When calculating a box volume, that is the net volume. You have to add anything that takes up space : speaker, port, crossover, braces etc
Hi Marius ,
This Debu From New Delhi India .
Your article is fabulous and explains a lot to a first time DIY enthusiast ,
I have a query , when you deal with speakers less then 50 mm cone size how do you then calculate the Vc , as in small units like Amazon Echo Dot etc.
I am designing a small table top Bluetooth Enabled speaker using PUI AS 04004 PR-P driver .
the enclosure for the speaker is on the base side down firing with vents/slots all around .
Dia 82mm x rear height of speaker enclosure is 35 mm. can you give some guidance on this.
Regards
Debu
debu.dasgupta@gmail.com
Hello Debu
First of all, it doesn’t matter the size of the speaker. The T/S parameters dictate the enclosure design. Secondly, you are asking about the volume of a closed box and you are describing a bass reflex. To be honest, when dealing with portable speakers (small boxes), the low amount of air inside the box demand a very long port, and there is not enough room. I don’t know the actual size of yours, and it might work. However, you will find that for most portable speakers, passive radiators are popular choice (instead of bass reflex ports). They do not add more size to the enclosure (like a port does for bass reflex) and they do not blow annoying air.
Hi Marius,
I intend to build two sealed baffles for professional application using a 21inches woofer.
The internal dimension is 22inWx28inHx22D.
I intend to use the followin….
CROWN.JH.216 woofer
https://web.facebook.com/crownspeakersph/photos/a.1411116199141599/1415197402066812/?type=3&theater
CROWN.CA.1250 amplifier
https://web.facebook.com/crownspeakersph/photos/a.1411116199141599/1417639345155951/?type=3&theater
Please advise on this.
Thank very much.
Can’t find the thiele small parameters of these speakers. Can you provide them?
Thanks for this wonderful article. Trying to calculate box size for SB Accoustics SB13PFCR25 5 inch woofer and result is 5.5 inch box in each side. However, the box type suggested is bass reflex. Now, if i make sealed, still the calculation and f3 holds true or the f3 now is for bass reflex box? The f3 calculation comes as 66Hz- i doubt a 5″ woofer in 5.5″ each side box will produce such low note. Thanks in advance.
Oops, sorry for hyjacking. Wrongly posted as reply. I wanted to post as comment.
Bass reflex has a tuning frequency. It has nothing to do with that calculator. For bass reflex, you need a 4.3 liter box with a port of 1″ diameter and 3″ long. The f3 will be at 71 Hz
Appreciated your fast response. But, if i make a sealed box? As per the calculation you mentioned, the sealed volume is approx 2.78L with f3 66hz.
Or, the formula just does not hold true for drivers not recommended for sealed box? Thanks again.
You must be doing some calculation errors. For Qtc of 0.707 (maximally flat response) the box volume needs to be 2.71 liters. In that case f3 is at 107 Hz.
I don’t even know how to thank you !!!!
Excellent article for Diy beginners like me. Thanks a lot !!!
I like 10¨ guitar speaker that has the following parameters: fs 82.4 Hz; Vas 26 liters; Qts 0.58; Qes 0.5 etc.
Obviously, according to your reasoning expressed in this article, it is not suited for sealed enclosure (guitar speaker) since EBP is around 168. But, I would like to make a sealed enclosure since I really do not care much about bass performance since cut-off below 100 Hz in guitar cabinets are actually desirable. I like good, very good transients, but would not like the cabinet to be too big. Your calculations with chosen favorite Qtc of 0.7 give me a nice, rather small enclosure of 53 liters. Would that work fine? Also, if I go little higher with speaker cabinet volume, say around 60 liters, would that improve transients substantially that it merits increasing the size-weight of the cabinet (I do not like to carry around heavy speaker boxes, that is why I chose a Neodyimium 10¨ guitar speaker in the first place, Jensen Jet Series Tornado 10¨!). Also, if Width of cabinet is given, at 0.43 meters inner width, do other two dimensions have to follow certain rule for proper acoustic behaviour of this speaker cabinet (I used to read something about standing waves and such… )? ANY ASSISTANCE IS VERY APPRECIATED. Sincerely, Sven B.S.E.E. … more importantly, a guitarist… In other words, HOW WOULD YOU MAKE A GUITAR SPEAKER CABINET WITH THESE PARAMETERS AVAILABLE?
It seems that you got it all figured out. Just make a 53 liter box. You will be fine
Thanks!
Oh, sorry to bother you… I take it that the volume of a 10¨ guitar speaker is not taken into an account (about 1.5 to 2 liters, usually), that is, is 53 liters ONLY air or shall the dimensions of the cabinet include 53 plus 2 liters? Second, is there any filling inside the cabinet? I take it that there is no filling (?). Third, does one need to make an opening for the speaker in the center of the front panel (where two diagonals intersect in a rectangle) or should it be slightly off-center? I know that one or two liters in these matters really do not matter too much anyway (speaker volume), but just curious to know… as for the filling, it is important to know whether there is some acoustic foam inside and how does it get calculated if such filling is needed (do we calculate only volume of pure air or what?). Your article is so excellent that it is a pity not to include these informations, just for the sake of having a full picture and be able to use it in DIY projects… Thanks. Sven
Here you can find some info about damping material. https://audiojudgement.com/how-to-build-a-sealed-subwoofer-box/
Adding polyfill will increase the perceived volume so it will compensate with the volume displaced by the speaker. And yes, in a sealed enclosure +/- 5% volume is not gonna be a noticeable difference.
Thank you…. much appreciated!
This is my third question, but it is needed… hope you see that… there is an issue, a controversy of sorts, but a big one indeed, with speaker data given by manufacturer (Jensen Company) of my speaker of choice (Jensen Jet Series Tornado 10¨ Neodymium guitar speaker), as compared to the formula in your article of getting the speaker Total Q (Qts) from Qms and Qes. Namely, when I use manufacturer’s numbers for Qms and Qes given on their Web page (see the link below), in the simple formula that you have in your article (1/Qts = 1/Qms + 1/Qes) to get Qts, I get result Qts of 0.495. But manufacturer states that Qts of this speaker is 0.58! Now, which Qts should I use? Manufacturer’s Qts makes it work, the other one does not make it work, seems to me (I get Volume of the cabinet of 26 liters, which is not too likely?). Where is the catch? Is the manufacturer’s data faulty? Since I wish to use your article as my DEFINITE GUIDE to actually build me a cabinet, it is plainly obvious that I MUST use the correct number for Qts in order to make this build a success… Kindly assist. Thanks!
https://www.jensentone.com/jet-series/10-tornado-classic-100
Well yeah, there is an error in the manufacturer spec sheet. Problem is you don’t know which one is incorrect. For example, Qts might be correct and Qes incorrect, or some other combination.
I know this will be a silly question but, How would you get close to a suitable box design for a driver that did not have required T/S parameters listed? Could you get close by magnet weight for the size of the driver, suspension material ( foam or accordian) etc.
Hi there,
Thank you for the excellent articles and work 🙂 I enjoy reading through them very much!
I’d like to ask you for some advise please, I’ve got a pair of small bookshelf DIY Sealed Box 2-way speakers which a friend of mine made out of MDF – it’s a 5 inch Focal car woofer + a SEAS silk tweeter! They sound pretty good however I’m pairing them with an active Subwoofer since the rolloff starts at around 200hz with -3 db @ 93 hz. This is a pretty small box of 4 litres – like Focal recommended for a Qtc = 0.7. Crossover point is around 3k-3.5k hz
The real question here is how much stuffing should I have inside and in which shape or form shall I apply it? I’ve got pieces of white polyglass or fiberglass but I’m not sure how much of it and how to apply it inside the box?
So I will need optimal advice on the following:
1. What’s the recommended ratio of filling relative to the box volume? like 50% of the volume, less or more?
2. Do I need to dampen (line) the box walls internally with some other material that I can stick onto the internal walls (like the standard grey acoustic insulating foam)? Or is this not needed as it’s only required if it were a ported box? Will it muffle the mid-range if I do?
3. Do I need to fluff the white polyglass with my hands rather than it being condensed when I put it in, so it takes up more volume and being more loose?
4. Any other considerations?
Please be aware this is a very solid construction out of thick MDF boards. I’m aiming for optimal frequency response and especially mid-range and upper-bass richness and clarity here (ideally to be able to hear all the woofer), I wouldn’t want too much stuffing to start having diminishing returns on my sound output and quality! Aiming for gold here 🙂
I appreciate your efforts, thank you in advance.
You will probably have minimal improvements with sound dampening material. Don’t stress too much on the details, just add 50% stuffing and you are good to go. The Qtc will go down a bit, but that’s fine.
Hello,
Excellent article and website ! I have a question about the stuffing please.
I have buy soundeasy software and i don’t found the factor for the materials stuffing quantities … Like the Qa parameters in bassbox 6 or WinISD …
Have you a idea ?
Musically Romain
Well, as a theory the total box losses are equal to : Qt= Qb + Qp + Qa
Total losses = Box losses + port losses + absorption losses
We convene that in a bass reflex box, port losses are negligible and since dampening material is not popular in bass reflex boxes, Qa is minimal as well. Therefore Qt = Qb (Total losses = box losses equal to whatever leakage the box has).
You won’t find Qa in soundeasy but you will find the Qb parameter, which might as well stand for all 3. So if you want to modify Qa, you might as well fiddle with Qb instead.
Hi, this article was very helpful thanks. I have one problem, I want a sealed box. But my EBP is 115.06. What will this affect on a sealed box?
What is the Qtc of the speaker?
Hello! I’m confused about one thing after reading the article. You mention that adding stuffing essentially increases the volume of the box as well as the efficiency, but the article also says that a larger box (smaller Qtc) produces a smoother response but lower output. How can stuffing “increase” the volume (Qtc) but also efficiency? Thanks!
Don’t confuse efficiency with raw output. A larger box will be more efficient. Why? Because the air inside the box won’t oppose the speaker movement as much. But if the box is small you will need more power to move the speaker, as you have to fight the (now harder to move) air inside the box. Efficiency means that with less amplifier power you reach the same output level.
Above you mention that a Qtc>1.2 has high efficiency, but a smaller enclosure versus a larger one will have a higher Qtc. Your explanation that a larger box would be more efficient makes sense to me. Is there something I’m missing? Thanks again!!
I thought I would run away with a simple analogy :). Anyway, things are not that straightforward. The end result is a mix of a lot of parameters, that contribute in different ways. For example, if you fill a box with dampening material, you gain efficiency because of the reason I mentioned in the previous comment. You are altering the acoustic compliance of the enclosure. However, adding dampening material also decreases efficiency, because you are changing the total moving mass of the system. This is because you are restricting air flow behind the speaker. However, the overall effect is to increase the efficiency because the first characteristic is more pronounced, and there are ways to mitigate the second effect.
In a similar fashion, adding dampening material will increase efficiency by increasing the acoustic compliance of the enclosure, but also decrease the efficiency because Qtc will go down. Also, dampening materials absorb unwanted back-waves as well. And like I said, the whole thing is a mix of a lot of factors. But bottom line is that if you place dampening material in the right place inside the enclosure, and the correct amount and density, you will get a boost in efficiency.
I like your site, thanks! May I add another aspect to the above discussion? As you have indicated in the “What is damping” section here with the graphs of various system Qtc, the system (driver +box) with too high of a Q will have a more pronounced upper bass, and sound louder; but as you have indicated the lower 2 octaves will be unnaturally overshadowed or drowned-out by the overly resonant (higher Q) upper bass. It will also not be as precise at reproducing transients and subtleties with it’s loud upper bass. Basically you more end up hearing the box, not the recorded instruments.
Resonances in a system are more tolerable to my ears when used to augment the lowest octave. This is the case with bass reflex (ported), passive radiator, transmission line and band pass. Still, well designed sealed systems (Q of about .7) sound cleaner to me, This is most important when reproducing recognizable acoustic instruments like piano, string bass and tympani, but is also true for drums and electric bass. But with a smaller system or driver it is nice to have some bass, even if helped by a resonant cabinet, albeit one that emphasizes the lower 2 octaves (20-80hz). Please feel free to comment.
Thank you for all this information. I have one question…I am installing 2 Wolfram 18″ subs in my Caddy where the back seat once was. They are 4000 watt rms, 4″ voice coil, fs 30 hz, Qts 0.48, BL 21, Xmas 33mm (one way) with a W4500.1 (4500watt Rms mono block amplifier) to each Subwoofer. Will this work in a sealed enclosure for a loud sq build?
You have 4 kW of power and you are asking if it will be loud? Yes it will, regardless of the type of enclosure.
If a speaker is suggested to be used in ported box by t/s parameters Fs/Qes being 133, still the calculation for sealed volume and f3 freq holds true? Can I use the speaker in sealed box and get the calculated output? I am talking about SB13PFCR25 driver having fs= 44Hz, Qes= 0.33, Vas= 13.4L. Thanks.
you can use this for sealed if you want.
Much appreciated. One more thing- considering 12″ sealed box is my criteria, which should i prefer for more bass? Bigger speaker resulting inadequate sealed volume but lower Fs or smaller speaker in perfect volume but higher Fs? Thanks.
it depends on your amplifier. If power is no problem, I would go for smaller box and larger woofer.
Excellent. Thanks for your kind help. Got lots of conceptions clear now. Once again, thank you so much.
Excellent professional work Mario, very precise and informative. I have a simple question. How much stuffing represents the percentage 50% . I am constructing a 54 L closed box in which I shall fix a Peerless sub 830668. So how do I calculate 50% stuffing? Is it calculated in volume that is half of 54L?
It depends on the density. Imagine that you use that poly fill stuff, which is very light. If you fill the box 100% and then you press it with your hands with moderate force, and now it’s just 50% of its original volume, then the box is 50% filled.
Thank you for the clarification. I take this opportunity to congratulate you for your latest excellent video on diy floor standing speaker project.Thank you also for sharing your knowledge.B rgds
Thanks mate! Appreciate it
Thank you so much for this great read.
I have a big doubt,
1) If I decrease the Vbox from a sealed box. Then the stiffness increases and the transient response improves.
2) According to the equation Vas/Vbox = (Qtc/Qts)ˆ2 – 1, if I decrease Vbox, then Qtc increases (for a fixed driver). And if Qtc increases, the transient response deteriorates.
1) and 2) say different things. I want to understand
Let me give you a practical example. A speaker has a certain Qts (let’s say 0.35). If I put this speaker in an infinitely large box, the resulting Qtc will be the same as the Qts of the speaker (0.35). As I start to make the box smaller Qtc will start to go up (0.37 … 0.40 … 0.45 etc).
At some point Qtc will be 0.5. That is the perfect transients point. As I go to Qtc=0.7, that is the maximally flat response in terms of frequency response and the transient response is also good. As I continue to make the box smaller, Qtc will go up indefinitely and the transient response worsens as the box gets smaller and smaller.
Thank you so much!!!
Very good explanation of things but in reality a ported box will play bass deeper and sound more explosive, but maybe slightly less detailed, if you have botg subwoofers tuned high as shown here 60hz, then obviously the sealed will sound better, but if you tune the ported box to 30-32hz with a larger box, it’s game over for sealed subwoofer… it’s mostly good for space saving, including passive radiator speakers, , very little space needed to create bass
Great article, thanks! You seem to be focusing on subwoofers, but if someone (like me) wanted a 10″ or 12″ mid-bass in sealed enclosure, from 100 to 1000 Hz range, does your EBP calculation and other tips still apply? When not using all the xmax and power handling of the driver, but just looking for best possible sound quality, would you give any other advice?
Hi,
Thank you for the helpful article.
I am not able to correlate below 2 statements:
1) Qtc > 1.2 : High efficiency, bad transients, bad frequency response (under damped).
2) Going towards to Qtc of 1.2 is pushing it, and should do that only if space is an important factor and you need a small box.
When I am going towards Qtc 1.2, I am actually making the box larger right? While 2) says I should do that if I want smaller box.
Shall appreciate if you can help me understand.
Hello! As you make the box smaller, Qtc goes up.
I don’t understand why a speaker is consider overdamped when it is in a larger box (Qtc < 0.707). Wouldn't a smaller box, with more acoustic suspension, cause more damping?
I always wondered that myself. It should be the other way around in my opinion.
Hi,
Still a great article!
On the above chart it looks as if a bass reflex will produce say 3 dB more output in the *higher* frequencies than a sealed box. You also write: “While the bass-reflex will play louder than the sealed counterpart (…)”.
A BR will sure be louder in the lower frequencies, but would why would that also be way above the resonance freq?
Thank you.
Yup, that doesn’t seem right. Article that I wrote a long time ago. It’s just the low frequencies like you mentioned.