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Old 22nd August 2010, 06:39 PM   #1
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Default Could use some advice/info on my 1st build...

This is going to be my 1st ported build and would like someone to give my design the once over before I start construction.

My sub is a late model 12" Adire Audio Brahma which will be powered by a 500w OAudio Bash plate amp.

My design so far is as follows:
Box Volume 4ft3 (Before sub/amp displacement, bracing and acoustic dampening)
Port 3" x 12" (flared)
Tuning Freq. 19hz

Sub specs are as follows:
Fs 19 Hz
Qms 11.6
Qes 0.41
Qts 0.39
Vas 92.3
Re 2x1.4 Ohm
Le 2x0.5 mH
Sd 436 cm2
BL 12.8 N/A
Xmax 28.5mm one way linear
Pmax4 600W RMS
SPL 83.8 dB @ 1W, 1m


Thanks in advance.
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Old 22nd August 2010, 07:59 PM   #2
GM is offline GM  United States
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A ~maximally flat alignment tuned this low tends to sound very 'one note' if not out in the middle of the room if there's any output to speak of below 25-35 Hz depending on the room's acoustics and where it is in the room; plus, if much power is required below this BW, the vent system must either be much larger and/or both the box and vent need to be heavily stuffed as required to keep it from audibly chuffing which in turn will roll off its bottom octave, which at least helps WRT blending with the room.

BTW, what do you mean by 'late'? The specs I have for the Brahma 12 are quite a bit different to yours, so is it a Mk II or some-such, or just accurately measured?

GM
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Old 22nd August 2010, 10:28 PM   #3
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Thanks GM...

Here's a link:
Adire Audio Brahma Subwoofer

A little more info... My goal is a sub with a relatively flat response that can play the low notes for movies.
My house is an old victorian so no dedicated theater/media room. The living room this is going in is 15'x14' with 9' ceilings.
This is going to be for 70% movies/30% music.

I plugged the parameters in WinISD online and came up with an acoustic power rating of .9 which produced a vent mach of .04. Maybe I messed something up somewhere, which is why I am seeking advice prior to committing to a design.

What box volume, tuning frequency, and port size do you recommend?
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Old 23rd August 2010, 04:03 AM   #4
GM is offline GM  United States
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You're welcome!

Interesting, didn't know AV was out of business.

Well, considering how low some movies go these days you theoretically need tuning down to near DC, so EQ'd sealed seems the only practical solution in a relatively compact bulk, but even with all that Xmax it won't play all that loud higher up where it counts unless there's considerable room gain which I assume yours doesn't have. Then again, even at 500 W its dynamic headroom is fairly low for HT.

Anyway, browsing the amp manual it appears you can tailor the alignment a good bit, so pick a Qt between 0.5 - 0.7 (critically damped - maximally flat) that appeals to you and try its different EQ settings.

FWIW, assuming the space is available, I'd do a TQWT since it has more gain down low and the driver's specs dictate such a large/long vent to go low. This one is ~91 L (~3.214 ft^3) + driver + internal dividers/bracing. Note that the sim is in 1pi space, i.e. up against a wall/floor joint:

GM
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Old 23rd August 2010, 02:14 PM   #5
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Thanks again...

Are there any programs out there that will help me design a TQWT? Mind you, this is my first ported build. I'm nervous about screwing the port size up and having this thing sound terrible.

Size isn't an issue as I am recently divorced . I can put it along a wall/behind a couch.

I appreciate your input... I haven't been able to get any help anywhere. I'm so confused, that I almost decided to just go sealed, but knew I wouldn't be as happy in the end.

If the TQWT is going to be too difficult for me to build, what would your next suggestion be? (Sorry, I'm totally lost)
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Old 23rd August 2010, 10:20 PM   #6
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Do you think a pair of Passive Radiators will pair nicely with the Brahma?
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Old 24th August 2010, 03:51 AM   #7
GM is offline GM  United States
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You're welcome! Not that it was of any use, I just 'ran the numbers' to get the design, but I see it's not large enough at the driver location for it to physically fit unless it's mounted magnet side out. This is a problem with ultra low Fs, Vas drivers and I forgot to check it before posting it. It can be larger though and damped to suit.

The program I used to display my suggestion is one and there's the more complex AkAbak, though probably the most popular and best documented is MJK's MathCad software: Quarter Wavelength Loudspeaker Design

Well, if a pair of PRs can be tuned low enough, it's a viable option. I use to have a dual 15" driver/dual 18" PRs that was tuned to 14 Hz, but they were custom prosound units that aren't available anymore AFAIK and I don't keep up with what's available, so do a search to find if there's anyone offering 15" or 18" adjustable weight PRs that can be tuned to at least 14Hz in ~4 ft^3 and preferably 11-12 Hz. Note that they will probably be expensive.

GM
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Old 24th August 2010, 03:51 AM   #8
zobsky is offline zobsky  India
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Quote:
Originally Posted by JohnnyPraze View Post
Thanks again...

Are there any programs out there that will help me design a TQWT? Mind you, this is my first ported build. I'm nervous about screwing the port size up and having this thing sound terrible.

Size isn't an issue as I am recently divorced . I can put it along a wall/behind a couch.

I appreciate your input... I haven't been able to get any help anywhere. I'm so confused, that I almost decided to just go sealed, but knew I wouldn't be as happy in the end.

If the TQWT is going to be too difficult for me to build, what would your next suggestion be? (Sorry, I'm totally lost)

If you're worried about building difficulty, my suggestion is to use lowes 4 ft (or 8 ft) x 1 ft x 1/2" precut particle boards. Takes a lot of the hassle out of building horns / TLs . ALso, use PL brand polyurethane expanding glue when sealing up the cabinet, so you don't have any leaks.

You can see what I mean at Tapped-TQWT Stuffing - To Stuff or To Line ?
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Last edited by zobsky; 24th August 2010 at 03:54 AM.
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Old 24th August 2010, 01:56 PM   #9
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Thanks guys... I'll keep searching.

I'll be sure to let you know what I come up with and post pics once it's done.
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