Subwoofer design question... Rarely asked?

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undertow

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Subwoofer design question... Rarely asked?
« on: 2 Sep 2014, 06:15 pm »
Hello,

This circle states it is a designer circle so I guess this question is best posted here?

After looking into a bunch of other subwoofer designs, and overall pro's & con's such as Vented vs. Sealed etc... I have a question I can't find much info on.

What is the best material and / or method of tuning the sub cabinet?

I realize that with most plate amp subs or even more exotic types using outboard processors you can do a lot to "Tune" the sub to your room, and main speakers of course electrically.

My question is on the Acoustic tuning side of this -

From my understanding nearly all conventional damping materials like resonance damping pads on the side walls, foam, dacron, wool etc... Actually more or less have no effect on tuning much below 200 hz anyway?

I currently have a Sealed sub system which uses dual 12" woofers and a 1000 watt amp that is sealed in a separate chamber as well. So in fact electronics getting tangled up in something is not an issue, and neither is heat with this design.

What material or combination of materials if any should the enclosure be treated with to make sure it is tuned to get the most efficient output, power handling + woofer control, and of course smooth response?

Or being it is a sealed sub is it best to just leave the bare wood walls internally?

Thanks

Russell Dawkins

Re: Subwoofer design question... Rarely asked?
« Reply #1 on: 2 Sep 2014, 11:53 pm »
Your use of the term "tune" in this context makes me nervous. I think the ideal sub/room combination favors no frequency at all and could properly be thought of as un-tuned. Indeed, the best sounding sub arrays seem to involve semi-random placement of the largest number of subs feasible, at least up to 6–4 being effective, and these being placed so the distances from each sub to the nearest reflecting surfaces are all different from each other.

In a similar vein, the best sounding sub box I have heard was notable for its lack of resonance as much as any other characteristic. It consisted of two drivers back-to-back and opposing.

I have not heard the Bag End sub  http://www.bagend.com/  , but the reports suggest a similar characteristic, although achieved in a completely different manner - by running the driver/box entirely below its resonant frequency and compensating with a contour network with a sharp cut-off at something like 8 Hz.

Duke

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Re: Subwoofer design question... Rarely asked?
« Reply #2 on: 3 Sep 2014, 02:12 am »
Hi Undertow,

What I look for in a subwoofer's "native" frequency response is a gentle roll-off that is the approximate inverse of room gain.   So in a sealed box sub, I generally aim for a very low Qtc. like .50 or less.   In general, stuffing material is a step in the right direction, but it all starts with woofer choice and box size... stuffing material isn't going to make that much of a difference, though it can help a little. 

Hope this helps.

Best of luck with your project.

G Georgopoulos

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Re: Subwoofer design question... Rarely asked?
« Reply #3 on: 3 Sep 2014, 02:26 am »
How do you determine room gain?... :green:

Duke

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Re: Subwoofer design question... Rarely asked?
« Reply #4 on: 3 Sep 2014, 03:06 am »
How do you determine room gain?... :green:

I've come across several researchers who use the figure of 3 dB per octave for low-end room gain.  While I'm sure that's not precise, varying from room to room as well as with proximity to room boundaries, and the initial roll-on frequency depends on several factors including room size, that's the approximation I use.

I have customers who claim to have measured +/- 3 dB in-room down to 20 Hz or so with my Swarm multi-sub system (without using the EQ that's built into the subwoofer amp).  The Swarm modules are tuned to gently roll off at about 3 dB per octave across the 80-20 Hz region, so I guess that's a bit of anecdotal evidence that the 3 dB per octave figure is in the ballpark. 

jtwrace

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Re: Subwoofer design question... Rarely asked?
« Reply #5 on: 3 Sep 2014, 11:11 am »
I have customers who claim to have measured +/- 3 dB in-room down to 20 Hz or so with my Swarm multi-sub system (without using the EQ that's built into the subwoofer amp). 
Yes, this is easily attainable with a Swarm system as long as the customer puts the effort into tuning it.   :thumb:

undertow

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Re: Subwoofer design question... Rarely asked?
« Reply #6 on: 3 Sep 2014, 01:25 pm »
Hi,

Thanks for the Responses...

Actually this is a name made sub so its not a project...

Russell Dawkins you will be happy to know it is in fact a back to back "Opposed" sealed design, but not a bag end  :thumb:

I was just more curious about what in general really has effect on a sealed sub as reading in the past I noticed mostly acoustic materials in the box were done for Mid's and don't have much effect on lower frequencies.

This was more out of Curiousity to what makes for a good sub internally for an acoustic environment.

Duke says basically just stuff it. I assume more or less just to dampen or control the excessive backwave / cone movement not necessarily "tune" to a certain frequency response.

Thanks