Help with designing a box

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Well...actually a tube.

I want to build a pair of line arrays using 16/18 4" full-range drivers per side split into two stacked cabinets with 8/9 drivers each. For the cabinets I am using VERY well damped sono tubes. The baffle is an 8" wide 34” L x 3/4" maple board bolted through the tube to a piece of Baltic birch plywood of the same dimensions so that together squeeze the tube to create an 8" wide flat front. I'm thinking of capping the top and bottoms of the tubes with 1” – 1 ½”corian.

This is my first DIY speaker project so a little guidance to the right path would be very welcome.
I ran the T&S parameters. Through an on-line cabinet calculator and got the following.

Butterworth B4

Vas = 0.11 ft^3
fs = 120 Hz
Qts = 0.63
D = 4 in

Dimensions
Vb = 0.25 ft^3
= L x W x H
f3 = 77.1 Hz
fb = 77.1 Hz
Dv = 1 in
Lv = 0.68 in

Do these numbers scale?
In other words can I just divide the total volume of the tube by the total number of drivers?
If so I get the number .25ft^3 for each driver and the cabinet is the right size.
Can I scale up the port to a single port per cabinet? Where should I place the port?
Does the f3 and fb = 77.1 Hz mean I can expect the finish product to be close to this as a low-end cutoff point?
Am I hopelessly lost?
 
Here's the picture to go with the dimentions.
Thanks
Tom
 

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Hi Tom,

I have no experience with line-source speakers, but as to the multiple driver questions, you are right in that IN GENERAL, you divide the box volume by the number of speakers to get the volume that each speaker "sees" There may be adjustments for the many speakers you plan to use but I am not aware of any.

As for the port, you tune the port to the box, not to the speaker. So, once you get the port tuning frequency for each speaker in its own piece of the box volume you calculated before, then consult your chart or program to find the port dimensions for that frequency in the entire box volume. Port location is as much preference as anything, but dont let the interior end terminate too close to a driver or interior wall.

Cheers, Dan
 
Hi Dan,
Thanks for the reply. As for tuning the port to the box. If I understand you right...I take the 77.1 Hz that I get from the program and plug it in again using the total volume of the cabinet (4 ft)?
What about effective cone diameter? is it 4" or 4x8=32"? using 32 i get a 6" Diameter and a 2.99" Length. Am I on the right track?
Tom
The new Dimensions from the program.

--------------------------------------------------------------------------------
Vb = 9.13 ft^3

= L x W x H
f3 = 77.1 Hz
fb = 77.1 Hz
Dv = 6 in
Lv = -2.99 in
 

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diyAudio Moderator Emeritus
Joined 2001
Two things:

A) Is your cabinet 4 cubic feet? If so, WinISD calculates that to tune that volume to 77 Hz requires a square port that is 6" X 10". The depth is .85"-a simple hole in a 3/4" or 1" wall will do fine. I thought making it square would fit better.

B) That Qts of .63-is that for the unenclosed speaker? If your speaker has an unenclosed Qts of .63, then a ported box is not a great idea. Generally, ported boxes are not recommended over .55 Qts, and even that is a stretch. The higher your Qts in a ported box, the more distortion you get in the lowest octave. A Qts of .45 or below is recommended. You can still do the ported box if you insist, however.

You might want to consider putting the speakers in a closed box. If you have .11 cubic foot for each speaker, then the Q of your speaker is raised to .89-very desirable. Your F3 is also raised to 143 Hz. Were you planning to run these fullrange, or were you planning on a subwoofer?

C) Like the previous poster, I am no expert on arrays. However, other posters here have said that research shows that arrays have uneven response due to interference patterns unless steps are taken. Again, I cannot vouch either way, not having build an array.
 
Hello kelticwizard,

kelticwizard said:
Two things:

A) Is your cabinet 4 cubic feet? If so, WinISD calculates that to tune that volume to 77 Hz requires a square port that is 6" X 10". The depth is .85"-a simple hole in a 3/4" or 1" wall will do fine. I thought making it square would fit better.



B) That Qts of .63-is that for the unenclosed speaker? If your speaker has an unenclosed Qts of .63, then a ported box is not a great idea. Generally, ported boxes are not recommended over .55 Qts, and even that is a stretch. The higher your Qts in a ported box, the more distortion you get in the lowest octave. A Qts of .45 or below is recommended. You can still do the ported box if you insist, however.



You might want to consider putting the speakers in a closed box. If you have .11 square inch for each speaker, then the Q of your speaker is raised to .89-very desirable. Your F3 is also raised to 143 Hz. Were you planning to run these fullrange, or were you planning on a subwoofer?


C) Like the previous poster, I am no expert on arrays. However, other posters here have said that research shows that arrays have uneven response due to interference patterns unless steps are taken. Again, I cannot vouch either way, not having build an array.
A)Sorry the cabinets are 3 cubic feet. I am not trying to hit a target low-end frequency I am really trying to get the best sound I can from the project. How can I get the WinISD program?

B)I have to plead ignorance on how the measurements were taken.
I was planing on a sub so a closed box is just fine with me.
I have 201 sq. inches for each cabinet, that’s 25.12 inches for each of the eight drivers in each of the four cabinets.

C) I have done a lot of research on arrays on the web and I understand about the spacing of the drivers to avoid comb filtering. There is very limited information out there on how to build an array.
I am very thankful for all the help on this great board.
Tom
 
I would also like each driver to see an independant box. some how I find this helps. why dont ask me? my knowlege is emperical.

so youwill need 7 partitions fo 8 drivers. the partitions can be 6-12mm MDF. I prefer 12mm or more (I am using 35mm MDF for braces in my present project) as it is easier to screw/nail.
 
Thanks for all the help so far from everyone.
It looks like a sealed 3 cu ft tube is the only way to go.

For now I am not going to separate the drivers into individual compartments in the cabinets. The next pair might get this treatment just to compare the difference. The final incarnation of this design I vision having a Plasma super tweeter module mounted between the top and bottom cabinets and separate isobaric 12" subs. But thats a ways away.
This forum is just amazing! Thanks Agian!
 
you can say that with 2 drivers in series each looks like an inductor to the other but the inductor value of teh drivers are a bit small and hence can be ignored. all the same with 2 drives in parallel each looks like an inductor to the other too only this "inductor is in parallel not series.

if you are not going to partition the cabinets atleast dont veneeer or finish it so you can add partitions later.
 
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