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Old 7th July 2003, 02:41 AM   #1
behnkem is offline behnkem  United States
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Default Building home theater sub - questions!

I am building a modest home theater sub - I had an 8" car subwoofer already and since I don't have a HT sub or the $$ to buy the one I would like I thought I'd see what I could do with this.

I have the box almost built - about 1.2 cub. feet not including bracing, etc. I used 3/4" MDF, sealed with caulk, etc. I have a couple of questions:

1) ports? I plan to use 2 ports - 2" diameter, and according to the only multiple port formula I could find, about 4.5" long each. Does that seem right? According to the formula, that should tune it to about 32hz with the speaker specs and box size.

2) batting? I plan to put batting in the box to help its accoustics, and the woofer is a downward firing woofer. Do I need to build something inside the box to keep the batting up off the speaker? I was thinking of a kind of "net" built out of 3/16" dowel rods to to keep it up right above the speaker - is that a good/bad idea?

3) amp? I am looking for a 100 watt +/- amp. I was looking at the ApexJr amp at: http://www.apexjr.com/ApexJunior.htm and wondered if anyone had any experiance with this or similair, or had any recomendations? I could possibly build my own given a kit, but am not sure I'm ready to try that unless its a drastic price decrease.

Also, I was thinking of just building a "side" cabinent onto the back of the sub box to hold the amp, rather than cutting into the cabinent itself and sitting the amp down in. Any pros/cons to this? I would make sure that the fins were ventilated, but want the option of using the box somewhere else if (when?) I get a larger HT sub.

thanks for any and all help! This is my first HT speaker project (i'v done a few car sub boxes). I'm hoping it all comes out well. I'v been taking pics of the work, and will post a site when done.

Mike
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Old 7th July 2003, 04:53 PM   #2
OMNIFEX is offline OMNIFEX  Jamaica
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Hello Mike

You will find you will get more input, if you post the TS
Parameters of the driver you are planning to use.

There are A LOT of designers on board that are
willing to help you once you post the numbers.

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Old 7th July 2003, 06:07 PM   #3
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Quote:
Originally posted by OMNIFEX
There are A LOT of designers on board that are
willing to help you once you post the numbers.
And even help you get the real numbers by measurement if you don't have them
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Old 7th July 2003, 10:38 PM   #4
behnkem is offline behnkem  United States
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Default TS Parameters

Heres the parameters I have from the tech sheet. I don't think I have the equipment to measure it yet, but let me know what I would need (or point me to the proper thread), if you could - I would like to do this with my whole system.

Vas 0.75
Qts 0.55
Fs 36.80
Displacement (CuIn) 38.00
SPL 84.50
Mounting Depth 3 13/16
Qms 10.18
Qes 0.58
Pmax 100.00
Xmax (mm) 7.50

I have a 1.2 cu ft. box half built at the moment (top is not attached yet) - no port holes drilled yet - probably soon though.

The tech sheet recommended a .5 to 1.2 cub. ft enclosure with or without a port. I could definately use some help figuring out the port length/size - I have 2" PVC pipe to use if that will work. If it wouldn't hurt, I would like to use 2 ports (for looks and to reduce the total length of the port).

Thanks!
Mike
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Old 7th July 2003, 10:39 PM   #5
behnkem is offline behnkem  United States
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Quote:
Originally posted by pinkmouse


And even help you get the real numbers by measurement if you don't have them
I would like to know how to do this to make sure the numbers I have are correct.

Thanks!

Mike
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Old 7th July 2003, 10:47 PM   #6
Vikash is offline Vikash  United Kingdom
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For the box/port size numbers, use a free design package such as WinISD. Enter the T/S parameters and it will give you a box and port size to start with.

To measure the T/S parameters (if you don't want to accept the ones that you've already got) takes a little more work. Download Speaker Workshop. You may want to build a Jig to do all the tests. It's takes some time but it's well worth it and you can use it in future projects. Do a search on these packages. There's a lot of help out there for you
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Old 7th July 2003, 11:51 PM   #7
behnkem is offline behnkem  United States
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ok - I've been playing around with WinISD (where was this program when I started this project!?!)

According to the program, if I put in a port tuning of 40htz and a 1.2 cb ft box - if I use 2 ports of 2" diameter they need to be 0.182 inches long - does that seem right? Everything I was getting was in the range of 4-5 inches for 2 ports, trying to do it by hand.

I'm using the specs THEY have in their database for the calculations, which could be part of the difference. Are they generally accurate? I'm not 100% on the specs I have as I have an older model and thats the best Kicker could give me (Its a Comp 8" Kicker sub, 4ohm)

Thanks for the help!
Mike

The other program recommended looks great also!
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Old 8th July 2003, 12:26 AM   #8
behnkem is offline behnkem  United States
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can you extend the port outside of the box? With a couple configurations (can't think of the exact numbers right now) the port needed to be longer than the box is wide.

thanks!
Mike
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Old 8th July 2003, 01:31 AM   #9
OMNIFEX is offline OMNIFEX  Jamaica
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Hey behnkem

Just wanted to confirm if your graph resembles this
Attached Images
File Type: jpg graph.jpg (69.5 KB, 504 views)
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Old 8th July 2003, 01:36 AM   #10
OMNIFEX is offline OMNIFEX  Jamaica
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I don't use WinSID. Never could understand their
venting method. Maybe someone else that uses
that software can give you some input.

Yes. You can extend the port outside the enclosure.
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