# Enclosure design theory (especially bandpass)



## siucsaluki11

Well, im wondering if any of you have any links to some good reads on enclosure design theory. I used to have some good ones on horns and transmission lines and a bit on ported, but my comp crashed and i lost it all before i got around to reading it all. Well, ive had my new car since august, and im finally done paying off enough of my debts to start saving. Im going to need to be building a new box, and i think im going to play with the subs i have and experiment with them. I am most interested in bandpass design theory. If you have any links to some good info on design theory, please share.


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## m3gunner

Google is your friend:

Car Audio Help Guide

Shavano Online - Sub Woofer; 4th Order Bandpass Calculator

If you're looking for a book, I recommend the Loudspeaker Design Cookbook by Vance Dickason. Very indepth analysis of all loudspeaker designs including pros and cons along with a bunch of info on xovers and such...


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## betteraudio

I second the LSDC by Dickason suggestion, and here's a brief primer on at least 4th order bandpass design, which I can give off the top of my head...

Larger the sealed chamber, the lower the center frequency of the passband.
Larger the ported side, the narrower the band, and higher the boost at the tuning frequency.


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## JayBee

You know i never really thought about it much, but that does make sense.


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## betteraudio

JayBee said:


> You know i never really thought about it much, but that does make sense.


Well, I worked R&D and Tech Support for Savard way back in the day, and I designed a LOT of bandpass boxes (several hundred), so I got a pretty good feel for them. Done right, they can be remarkably effective enclosures. Done wrong, however, they can also cause catastrophic driver failure. I've actually seen large chunks blown out of the cone when a sub with an unreinforced paper cone was put in a bandpass with a very small sealed chamber. Also, while it's fine to have a common ported chamber, I highly recommend divided sealed chambers.


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## TRumble

In my 16 years experience, I would not recommend more than cone surface area, based on a standard port equation. But that goes hand in hand with port length, you can't have the perfect answer. As well as where the port is in reference to the sub. A standard port calculation will be close to 180 degress out of phase with sub, = cancellation. If you have room calculate port size until it reaches a quarter to half wave of the port tuning frequency. then you would want the port as close as possible to the speaker without compromising baffle integrity. I spend about 100 hours average for every spl box I build, like Tesla I build about 200 boxes, all in my head, and test them, sleep on it, dream about them, then build. I bleed, sweat and sometimes drop tears on my projects, You need true dedication for spl, not just wood and screws. Building a box is like raising a child to me. Crazy, maybe. ADD, OCD high school dropout definitely. My first competition, two Bi-Mart subs, Jensen xs1010's, $15 a piece, A $99 Thump !000 Watt max (Total ****, melted the solder leads and added 12 gauge wire from point to point, adding a fan to help), in a stock, 3 cylinder 1.3L Geo metro, burning out my headlight switch from power consumption. A 6th order dual chamber tuned bandpass enclosure. $80 pioneer deck. Some dynamat. Broke ass kid on minimum wage. 138.7 Db. Rattled eye balls, blew out my bic lighter flame. 

Next design, a quasi double-1/2 wave triple reflex eighth order bandpass for one Diamond TDX12D4, 544WRMS Alpine MRD-M500, in theory designed to hit 160DB at 3 feet from box, not taking in cabin gain or full wavelength generation/development at mic placement at dash. If you want to win, you must LIVE FOR BASS, or go the hell home. "If you follow your bliss, you will find doors where there were only walls, doors that would be there for no-one else.":laugh:


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## TRumble

Oh yeah, was and still is my bible, Advanced Speaker Systems by Ray Alden, back when RadioCrap still sold books and not hover on your balls to sell you a cell phone or $60 USB cable.


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## Oliver

TRumble said:


> Next design, a quasi double-1/2 wave triple reflex eighth order bandpass for one Diamond TDX12D4, 544WRMS Alpine MRD-M500, in theory designed to hit 160DB at 3 feet from box, not taking in cabin gain


YouTube - Breaks Windshield - Adassa Audio SPL Subs

156.6 > 3 adassa audio 18s on 3 sundown 3ks ^^^


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## Andy Slater

I will just tell you a little about personal experience with bandpass.

I have been a long die hard bandpass box builder. I have built well over 1000 bandpass boxes in the last 20 years and I have done every thing you can imagine in bandpass. I have used box calculators , software (witch is great in helping you get it right) and mostly trial and error using customer cars as Ginnie pigs. Here is a few things I found to be true in bandpass boxes.

Starting with dual reflex.
The sound I like to hear is a low rumblie really tight and accurate bass response that hits the kick-drum really hard with all the upper harmonics and the lows that are fast and rigid sounding. I do not like "boomy" bandpass boxes that sound extremely loud at 40-50hz only.
So getting to the point, I found a few ratios that are important in a good dual reflex. One is the chamber's. It is commonly known to do 2/3's to 1/3 box volume and kinda get the two chambers to have a octavely coupled to each other as far as the box resonances. Well the idea is good but in real practice it does not do anything like that. You can build a variety of sizes and have acceptable tuning and make it sound good and loud. NOW there are a few things that I found GOLDEN in making a dual reflex sound really super good.
1st. The front chamber needs to breathe easily. Smaller than 1/2 of total vas but bigger than 1/5th vas . The rear chamber needs to be tuned perfectly.
2nd DON'T do any "tuning" (below 100hz) on the front chamber. What I mean by that is in a car there is no way to tune a front chamber to a usable frequency below the frequency that you will electronically cross over anyways while keeping the port length short enough to allow the box to breathe in a way to make it sound good. (again im not saying tuned sounds bad im just saying shorter port sounds better with a electronic crossover on it..PORT; like less than 3 inches long )

The rear chamber has to be tuned below 30hz, anywhere between 15 and 30 hz is where the back chamber has to be tuned. The lower the longer the port. The bigger the mouth the better the box will sound, so it is a balancing act you really need to do successfully with some software.
Make the rear chamber as big as possible witch allows you to make the port's mouth bigger with a shorter length. If the rear chamber gets too big there will be allot of ripple and power handling will go to poo and it will not compress properly. and if you use software the levels will be out. Pay attention to port mach velocity. Keep it low. Keep everything in the green.

THE PORTS;
If using vents, I have always had better sounding boxes using a long skinny wood vent. square shaped vents perform less. I prefer a long thin one. Again make it as long as possible down one side of the box and make the vent get larger in the X direction as port length gets just as long that will fit into the box. 

Round ports: ( all for single sub boxes)for 1-12'' I use 6 to 8 inch ports. 6 inch on rear and 8 inch on front. OR one 6 inch on front and one 6 inch on rear.
For 10" sub I always use two 5 inch ports. There are hard to find but they are out there and 5 inch is perfect for 10" sub

For 8" sub 5 or 6 inch on front and 4 or 5 inch on rear.

For 15inch sub 6, 8 or 10 inch port on rear and 6 , 8 or 10 inch on front.

I have never gotten multi-port bandpass boxes to sound as good as single port or vent.. When tuning the rear chamber ( i use software) start at a low frequency with a average box size or a targeted box size that fits your car application best. Start the port at a reasonable size. For example lets say your doing a single 12 inch sub. you have 1.1ft3 front and 3.0ft3 on rear, you are using a 6 inch round port. Now lets say you "tuned" the front at 160hz and the rear you start at 15hz. lets say at 15hz the port length is 35inches. So Now you start tuning the rear chamber up 1hz at a time. Looking at port length it should not get much shorter until you hit the frequency where the port jump like 10 inches shorter just by tuning it up 1hz. That is the area where the tuning is going to start to make sense. Stay in there if possible and it will do very well in most cases. Remember to keep the lengths in the green and lower than 30hz. The reason is a dual reflex unloads at like sometimes 100db per octave and the phase shifts from loaded compliance to port echo and wind very quickly.

The front port will be loading in the back of your car and the port size will need to be short and tuned super high. way above 100hz. the pass band of the box will not be flat, you dont want flat on a good sounding dual reflex. You want to have to cut with active XO and use A EQ if possible. Most amps have a 12-18db boost on them at like 40-45hz USE IT! the bottom end of the dual reflex on the graph will show way less output at to the +17db spike at 110hz. Ignore the graph. The bass eq will boost the lows. The lows of the box will have less output on the graph but will handle allot more power in that range, the bass eq will make sound good. Your active XO will cut the spike at 100-200hz to a nice drop around 50-100 hz depending on your xo. The super short port will allow you to hear the box ring inside the front chamber witch gives you the rumble you hear. Actually the rumble comes from the low tuned back and the big front port/ the box ring and you actually hear some of the boxes chambers through the cone of the speaker. The speakers material will contribute to how the box sounds. I like crushed treated paper pulp with foam surround. But Byutle and poly sounds good too. It is a preference thing there so chefs choice.

Single Reflex. Short Big single port tuned ABOVE 80hz and small sealed chamber (s). Kinda hard to not make a good sounding single reflex box as long as the port is short. And short means shorter than the width If 6 inch port HAS to be shorter than 6 inches long. I have never done a single reflex with a single 6 inch port longer than 4 inches. I like to use 6,8 &10, inch ports on single reflex boxes. Again small sealed chambers./ BIG ported chamber with a short port.


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## Andy Slater

TRumble said:


> then you would want the port as close as possible to the speaker without compromising baffle integrity.


Very TRUE

to elaboriate. The ports opening inside the box. One end of the port can be on the oppisate side of the box. Just the opening where the air travels up you want near the speaker, Preferably the speaker firing directly into the port so the port is not butted up to a wal but butted up to the basket


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## sundownz

Is this band-pass for SPL (as the section posted in would imply) or for musical accuracy ?

I tend to use 1:5 ratio in a 4th order for SPL or sometimes even bigger on the front side... have designed two band-pass enclosures this way, both for 12x 12" woofers... one is doing 157s the other has blown out the windshield twice before getting the max score... but metered 159.7 with tape on the glass.

Both are right around 1:5 ratio tuned to mid 40s to peak at high 40s to 50 Hz for SPL.

We also did a series tuned 6th order recently for three 18s in a wall -- it's in the 156s at 40 Hz and has a much wider bandwidth as we tuned to 30 and 60 Hz respectively. Still in the 150 range around 30 Hz.

I'll keep a log when I do my 4th order... looking at 1:15 or so ratio as an experiment to see how high I can push the peak.

This type of band-pass are a bit different from one designed for musical accuracy.


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## Andy Slater

sundownz said:


> Is this band-pass for SPL (as the section posted in would imply) or for musical accuracy ?
> 
> I tend to use 1:5 ratio in a 4th order for SPL or sometimes even bigger on the front side... have designed two band-pass enclosures this way, both for 12x 12" woofers... one is doing 157s the other has blown out the windshield twice before getting the max score... but metered 159.7 with tape on the glass.
> 
> Both are right around 1:5 ratio tuned to mid 40s to peak at high 40s to 50 Hz for SPL.
> 
> We also did a series tuned 6th order recently for three 18s in a wall -- it's in the 156s at 40 Hz and has a much wider bandwidth as we tuned to 30 and 60 Hz respectively. Still in the 150 range around 30 Hz.
> 
> I'll keep a log when I do my 4th order... looking at 1:15 or so ratio as an experiment to see how high I can push the peak.
> 
> This type of band-pass are a bit different from one designed for musical accuracy.


Yeah, you have a good point. I Wouldn't have thought of that because I guess I am just used to all bandpass boxes as considered high gain. But specifically used for spl, I never have done anything trying to make a box for just spl. Usually my customers listen to music so I always have gone the SQ route in my ambitious Journey of selling bandpass boxes to customers just so I could experiment of there car. 

Those ratios look about right for what your saying.


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## sundownz

Indeed -- I think your suggestions sound on-par for a more musical 4th order as well. So now we have covered both types between the two of us


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## Oliver

Pass the Band


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## siucsaluki11

This will be for a musical setup. Just want to play with a 4th order. It looks like its back to the drawing board for now.


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## TRumble

Check your group delays. Your going to need an amp with Time correction if you don't want that and/or phase shifting much more than a sealed. But, 4th order will work better than a standard ported box in terms of phase and group delay.


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## siucsaluki11

Im not sure what im looking for in my group delays. And how is Time correction going to change that? Isnt delay related to the box, so it will be the same no matter what you do to the signal, so how will time allignment/correction fix that. To be honest i dont quite know what GD is yet, doing some research to see how it pretains to what im trying to do.

But heres a new design i worked up.

Sealed chambers come out to 1.15 ft^3 total (about .57 cubes each)
Ported is 4.5 cubes before port and subs, about 4.2-4.3 after. 
8" port at 4" long (thanks for that tip andy)


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## TRumble

Group delay is how long the bass takes to reproduce after your mids and highs play the sound, so a tome or kick drum will sound muddy with a group delay, because the small speakers will play a third of a second before the subs do.


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## siucsaluki11

didnt realize how small it resizes the pics. Ill upload to photobucket and re-post them up a little later when i get back to my computer. Ive been looking for a HU that is reasonably priced that has built in tuning capabilities because i was wanting to run an active front stage. I am doing an SQL build, not SPL, not SQ, somewhere in the middle. I have to buy speakers, a new HU, and wire. I dont have as much as i was hoping to spend but ill see what i can do for something with TA.

Heres the pics


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## siucsaluki11

Bump for the pics i added, and to say happy easter everyone. BTW, volumes were calculated off the final deisgn, not from what BBP6 said it is for the parameters i entered into it.


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