Types of enclosures – speaker boxes – easy explanation
Among the many existing types of enclosures, which one is the best for you ?
There are many types of enclosures out there. But first, let’s start off by clearing up some things. When we talk about enclosures / boxes, it is common sense that we are going to use it for bass drivers. Tweeters usually come capsulated and do not need enclosures. Midrange drivers need their own chamber, mainly to separate it from the bass driver (so the pressure from the bass doesn’t interfere with the midrange’s cone), but volume is not to be neglected, as it does affect the sound signature. The role of a speaker box is the separate the waves produced by the front of the speaker, from the waves produced by the back of the speaker. If they meet, they will cancel each other, since they are out of phase, and will lead to poor bass response. This happens especially to the lower frequencies (bass).
Now, since we got that cleared out of the way, let’s ask a question : How much does the enclosure affect the sound quality ? The answer is : a lot ! I’m not exaggerating by any means, if I say that an exotically priced speaker, with poorly designed enclosure, will sound worse than an average speaker in a great box.
Which enclosure is best suited for you ? That’s for you to decide !
Types of enclosures / boxes, starting from simple to complex:
Sealed / Closed enclosure
A sealed enclosure is exactly what it sounds like. A box, of whatever shape you wish, that is air tight. When the speaker moves, the air does not escape the box, it only alters the pressure inside it. This is the easiest enclosure to design and build. You only need to calculate the internal volume of the box, which is done with little effort. Stuffing the box with sound damping material will help absorb stationary waves produced by the back of the speaker and yield better results.
Pros
- If space is an issue, sealed enclosures are the smallest.
- Easy to design.
- Easy to build.
- Design errors don’t have big impact on overall sound.
- High power handling.
- Great transient response (plays with little effort short duration sudden sound waves, like drums).
- Smooth roll-off of 12 db / octave.
Cons
- Low efficiency.
More about sealed boxes here.
Infinite baffle or Free-air
The theory of infinite baffle is that you place a woofer onto a board or baffle, and the baffle extends in all directions so much, that even the longest sound waves don’t reach the edge of the baffle. This way, the waves created by the back of the speaker never meet the waves created by the front of the speaker, no resonances, no diffraction. With a good speaker, this sounds like the recipe for a great audio system. The concept is hugely impractical and cannot be perfectly implemented in real life.
Real world infinite baffle enclosures are merely a particular case of sealed box. If you make a sealed box large enough, the air inside the box will not alter the compliance of the driver and there you have it : infinite baffle. However this does not eliminate the diffraction and resonance issues, like a true infinite baffle. You can go crazy with your imagination and picture a home infinite baffle enclosure, where you have a wall of woofers and the “sealed enclosure” is the room next to the wall. This is a highly engineered setup, with lots of practical drawbacks, but with the potential to sound very good.
Pros
- Doesn’t need much power.
- Usually less distortion compared to other enclosures.
- In an ideal infinite baffle setup (which is actually a finite baffle, but sufficiently large), there are no resonances and no diffraction issues.
Cons
- Hard to separate back waves from front waves in a basic, real life setup (like a car).
- The woofer can reach maximum excursion easily, so you need to be aware not to damage it.
How to design loudspeakers - video courses
Bass reflex / Ported / Vented
This is the cookie cutter enclosure, the meat and potatoes when it comes to speaker boxes. Why ? Because it offers a great balance between sound quality, output/efficiency, design and build difficulty. There is a lot to talk about bass reflex enclosures, but I am going to keep it as simple as possible. This type of enclosure has a port(Amazon affiliate link), which is usually cylinder shaped (or rectangle).
The port has a predefined length and diameter (these dimensions are important as they set a certain resonant frequency). Now to sum it up really quick : some frequencies that come out the back of the speaker, reverse their phase and come out the port. This way, they add with the waves from the front of the speaker (because they have the same phase) and increase the output sound.
This is a very rudimentary explanation and it’s not all fine and dandy. For example, waves below the tuned frequency of the port, don’t reverse their phase and when they come out the port, they cancel the waves in front of the speaker. So below the tuned frequency of the port, the vent acts like a hole in a sealed enclosure. Considering all types of enclosures out there, this is by far the most popular.
Pros
- Higher efficiency than sealed. On paper it’s 3 db.
- Speaker can reach lower frequencies, outside its frequency response.
- Reduced distortion (speaker doesn’t need to move as far near resonance frequency).
Cons
- Not as good transient response as sealed.
- More difficult to design and build compared to sealed.
- Bass reflex port can become noisy at high volumes.
- Larger than sealed.
- Steep roll-off of 24 db/ octave.
While port usage is very popular, a passive radiator (a speaker without the magnet and coil) is the alternative. When the active speaker moves, the passive radiator moves in a push-pull fashion. It yields the same results, pretty much, with some differences of course. The passive radiator doesn’t make extra noise, but has limited extension.
More about bass reflex boxes here.
Bandpass
There are a few types of enclosures when it comes to bandpass (4th / 6th / 8th order bandpass). The speaker is out of sight, inside the cabinet and the sound comes out only through the port(s). For the 4th order bandpass, one side of the speaker is placed in a sealed enclosure, while the other side is placed in a ported enclosure. In this type of enclosure the woofer plays louder than bass-reflex, but has a narrow frequency response. You can make the woofer play a broader spectrum, but that is at the expense of efficiency. 6th order bandpass has both chambers ported, while 8th order bandpass has an additional ported chamber.
Pros
- High efficiency. Theoretical +5 db compared to sealed. Even higher efficiency for 6th and 8th order.
- Low woofer excursion.
- Good choice for high SPL applications.
Cons
- Enclosure can get impractically big.
- Extremely difficult to design, with no room for error (especially for 6th and 8th order).
- If tuned for efficiency, sound quality is very poor.
- If pushed to the limit, you don’t hear the woofer “struggling” (as it is inside the cabinet) and might kill it unknowingly.
More about 4th order bandpass boxes here.
Transmission line
Unlike sealed or bass reflex boxes where the inside of the box is left as is (except for damping material and / or bracing), the transmission line design creates a labyrinth on the back side of the speaker. The idea is, that the back waves generated by the speaker, travel through this labyrinth, which has a fixed length, which is directly correlated to the wavelength of the resonance frequency of the speaker in free air. This way, when these waves come out, they are in phase with the waves generated by the front of the speaker. The hard part is to fill this labyrinth with damping material of different thicknesses and densities. You have to stuff it in various patterns, until all of the upper frequencies are absorbed. Among all types of enclosures out there, this is one of the most difficult to design, because it is very unpredictable.
Pros
- Great low frequency response.
- Can reach subsonic frequencies.
- Not so sensitive to positioning.
Cons
- Because of the extra elements inside the cabinet, it is more complex to produce.
- Hard to calculate the design.
- The boxes can reach impressive dimensions.
- The woofer moves, more or less, freely and can reach maximum excursion easily (careful not to blow it up).
More about transmission line boxes here.
How to design loudspeakers - video courses
Folded horn
Horns are excellent devices to improve the efficiency of the driver. Although we are discussing types of enclosures, the horn is actually a coupler for the speaker and not an actual enclosure in itself. By following the shape of the horn (from narrow to broad), the sound waves make a smoother transition from the driver to the air. Horns are used for tweeters and midrange drivers because when you go down in frequency, the horn has to be bigger. Few centimeters might be enough for a tweeter, but for woofers, we are talking about meters.
Folded horn enclosures are a good choice for woofers, since they make use of space in an efficient manner. You don’t need to stick a massive “trumpet” in front of the woofer, you just have to make the path of the sound waves narrow near the driver (the throat) and broader near the exit (the mouth). In the case of folded horn, the speaker sits inside the cabinet and the waves are following a snail shell shape (more or less) path. Same technique as the “trumpet” horn, but more space efficient.
Pros
- Up to +10 db more efficient than sealed .
- Excellent for outdoor, very large rooms.
Cons
- Big enclosure.
- Poor off-axis response (the speaker needs to fire directly at you for best frequency response).
- Not so good for the very deep notes.
More about folded horns here.
Conclusion
Of course, there are a lot of enclosure types out there, but my interest was only for the most popular ones, and just the general facts. By focusing on the main points, you can make up your mind easily and choose one that suit your needs. For the inexperienced enthusiast, the decision lies between sealed and bass reflex. If you want a small box or maybe you want to start with something very easy to build, then sealed is for you. If you want more output and like more bass, you should go for bass reflex. The other types of enclosures should be studied in detail, as they are more difficult to design and build.
References
- Loudspeaker Design Cookbook 7th Edition by Vance Dickason (Audio Amateur Pubns, 2005). (Amazon affiliate link)
- How to Build Speaker Enclosures by Alexis Badmaieff and Don Davis (Howard W. Sams & Co, 1966). (Amazon affiliate link)
- Newnes Audio and Hi-Fi Engineer’s Pocket Book by Vivian Capelm (Elsevier, 2016). (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.
29 comments
I own the remains of a custom built-in stereo system that was made in the early ’60’s. The cabinet face was blond wood and held a Voice of Music amp & tuner, a Webcor turntable inside a pull-out drawer and two speaker enclosures on the sides that held 12″ Quam co-axial woofer w/3″ midrange and a tweeter horn (2′ x 7″) at the top of a 7″ x 9″ opening above the woofer. Believed there was a horn behind the 7″ x 5″ opening beneath the tweeter. I only got to inspect it for a few minutes 25 years ago before the new homeowner told her carpenter remove it for me in one piece. Unfortunately he only saved the components and tore up everything else. He got fired and I got the remains which wound up being stored until now. I’m planning on making a small console for the components and separate speaker enclosures. The co-axials still sound decent but have paper surrounds so little bass bottom. I’d like to replicate their original horn or whatever Quam used back then. I contacted Quam but got no reply so wondered if you had any idea?
If you want my honest opinion, I would channel my efforts into some other project. 50-60 year old drivers most likely suffered severe alteration of the original parameters. This is due to suspension aging. Furthermore, back then, drivers were designed with efficiency as top priority, since powerful amps weren’t an option. This meant very big enclosures and horn design were a must. My advice is to invest in some newer drivers. The cabinet construction cost and effort is the same, or lower. But there is a higher chance that you will be satisfied with the end-result.
hey guys can anyone help me,I want to build a speaker enclosure for my 6.5 inch speaker(speaker details https://www.sonicelectronix.com/item_9831_Kenwood-KFC-M1628A.html) I want to know what type of enclosure is best and the enclosure measurements.I would really like to build a sealed enclosure i don’t know if the speaker is compatitable for sealed enclosure. Please send me the best enclosure type for this speaker and the measurements. THANKS^_^
I can’t find the parameters for your speaker, but judging by the type, it should work well in a 10 liter sealed box.
You didn’t indicate. What your goal is. Hi-fi, PA, Mudicsl instrument speaker?
Hello Marius,
Congratulations for the good articles!
I have pair of audio pro soniq 202. They are sealed and sound OK, but bass is practically non existing.
If I move the drivers to larger ported enclosure, bass could improve. How can I calculate the dimensions and the port parameters, if I don’t know the drivers specs?
Thanks
If you don’t know the parameters, you’re basically in the blind. Your speakers are quite small and even if you knew the parameters a ported enclosure won’t help that much. They were designed to work with a subwoofer. So your best bet is to get a subwoofer to cover the low frequency range.
Hello Marius! I always read your newsletter with enthusiasm. Thank you for your work! I bought a measuring microphone and a preamplifier. Now I can use the help of your explanations to measure the frequency response of drivers. I also learned to measure the parameters of Thiel-Small. Now I’m studying the construction of crossovers. There are a lot of useful information on your page. I understand that all steps of measurements and calculations are very necessary. But it would be great if you wrote a step-by-step instruction on how to make a loudspeaker from scratch. I’m talking about the sequence of actions! Do you understand what I’m saying? Step by step!
Thanks!
Oleg
Dear Sir, mine is 8 inch, 100 watt speaker for woofer and 4″ five satellite speaker, which are fixed in five small speaker box,
I need heavy bass dj sound in my home. kindly suggest me the size of main woofer box and should i go for bandbass, if yes then which one 4th, 6th or 8th.
If you are talking about a 5.1 computer audio system, you should probably let it be. You are not gonna gain much if you change the enclosure. If you haven’t made an enclosure before, you should probably stay away from bandpass designs, as they are more complicated.
Twice I have romoved the amp from factory speaker box and connected them into a 12″ low wattage sub and box. So he can do that then create a box for that sub?
Dear sir, I’m trying to design a transmission line box to fit behind the seat of a Nissan truck. Sounds crazy but that’s just me. Been doing pro audio for 25+ years now and want to be different. If I’m using 2 8in cerwin vega 82 2 subs, how do I get the line width and height for 2 cones?
The rules of making a transmission line are simple. In reality, you might encounter some difficulties. Basically you need to make the line about the same size as the speaker. So if you have 2, the enclosure needs to be twice as large, and the line following the same trend. I don’t know how big your truck is, but the enclosure size will be an issue.
Also if the box is tapered at the top, how will I calculate the line with a taper. OK I have 6 inch bottom, 2in top, 45 in wide, both drivers in the lower section then start the line to the side and end at the top section of the box. So the mouth will also be tapered
You can taper the line, yes. Actually there are some benefits to this. From what I have seen, the taper is like in horn enclosures but in reverse. So, instead of going from small throat to large mouth, you go from large throat to small mouth. So, the reverse expansion rate can be hyperbolic, exponential, conical etc
Hi Marius, what do you think i would try in my f150 98? speakers? i have a soundstream t5-15, a sony XS-L121P5, and a pair of Zebra 10″ bigmouth 250w, as a amplifiers 1 phantom 5000D and a crossfire 1600.2, crossover planet audio and pioneer usb mp3
I would use the soundstream t5 with the 5000D.
Very useful article. Thanks for sharing.
Great article for someone new to this field like me. Clearly explained without getting bogged down in the details. Thank you 👍
I love this but lost on which to pick for my sound needs. Ive been pushing to achieving the best sounds for years now but not grown at all. Am still like at entry level. This article has opened me up. Am into church sounds to be more specific in the seventh day adventist church live sounds. Its mostly vocals or acapella but bass singers whats deep bass and been hard to get. Its why was checking on net and came across your article. Please help me in that area. We have camp meetings coming and are mostly outdoor.
Best regards
Marshal Tembo
Temchi Sound Systems &Electronics, Lusaka zambia
Central Africa.
Cell: +260976788117/+260955789118
Well, it’s very hard to achieve deep bass outdoors. You should probably use folded horn subwoofers which use pro audio drivers. Those are more likely to suit your outdoor needs.
Hello Sir,
Thanks for this well written article. I have a pair of 3 inch full range drivers of 15W. If I want to get the most out of them, what type of enclosure should I build? I want to improve the low frequency response to get more bass. I am new to speaker design. But I have the parameter for the driver:
Qms = 5.66, Qes = 1.41, Qts = 1.129, Fo = 124Hz
Judging by the specs, I’m guessing transmission line would be best. You can find articles about transmission line. Including on this site. If you are wondering about the length of the line, it’s should be quarter wavelength of 124 Hz. Which is 2.76 m / 4 = 0.69 m. Quite long, but maybe you can fold it in such a way that it makes sense.
Thanks for the valuable reply. As explained in the article, transmission line speaker is the most difficult to implement, right? Does some slight errors in design, like change in length of line affect the sound very much?
For an easier design/implementation, to achieve more bass, can I go with the ported enclosure?
You can go for ported, if you want. However, the speaker has a very high qts and it’s not really suited for ported. Rather for infinite baffle or very large sealed boxes. Or, as I said, transmission line.
Good Day Sir, I have an 8inch sub, and I want to know which will give me more output and low end, I don’t want to build a ported box again, I want something new with good low end and more output. I’m thinking about double bass reflex, folded horn, tapped horn and transmission line, don’t know which one will be the best.
Thanks
Well horns are pretty much out of the question for subs. In my opinion, normal bass reflex is the way to go if you want more output, and it’s not difficult to make.
I have a set of Weconic floor standing tower type speaker boxes ( 40″ tall x 8″ wide and 12″ deep ) they have 2 x 7″ mid range speakers and a 4″ tweeter in the front and an additional 7″ speaker on one side of the tower. my question is which way do I face the towers ? with the side speakers, towards each other or away from each other.
Also on the rear of the tower speakers are four terminals ( two red and two black ) one set above the other, which pair do I use ?
Check if there are markings of left and right speaker and position them accordingly. If not, it shouldn’t matter that much how they are oriented (with the side speaker to the interior or exterior). In the end, you can check both positions, have a listen, and choose whichever you prefer.
The 2 pairs of binding post are for bi-amplification. I’m guessing you don’t have the equipment to bi-amp them. In that case, make sure the binding posts are connected between them with a metal plate (it should be already in place). If the metal plate is in place, you can connect the amp to whatever pair of binding posts.