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Phil Olson 22nd May 2010 08:51 PM

Sub mounting location
In the past, I've built down firing sonosubs but I am now going to build one that will be viewable in the room so I'm doing a box.

If I built a down firing box with only the front open would that cause problems?

The driver is a 10" and the front opening would be 3 1/2 x 11 3/8. Would that act like a tuned chamber?

If the recommendation is to front mount it instead, is the optimum location down towards the floor to pick up a boundary? It would be easier to center mount the driver to facilitate stuffing both up and down through the driver hole, but a real pain to stuff all the way from the bottom to the top, (the down firing would have the same problem unfortunately).

Finally, how much bracing would be required for a box ~13x13x50? I was planning on two braces at 16 and 33 up from the bottom, but if I could get away with less, so much the better. The material will be 3/4" MDF.


Rademakers 23rd May 2010 12:47 AM

I think it would act as a tuned chamber. However if the dimensions are small enough the resonance will be way out of the intended frequency band width. Such an enclosure (and it's effects) is easily simulated with HR.

If it's used for bass/ sub, a front mounted woofer will have not much concern as to how it's best mounted for boundary loading, as the frequencies involved are of such (large) size that boundary loading will take place mostly anyhow. However personally I would put it no higher than half the cabinet high'ed.

I would prefer to use more bracing then that. The smallest bass cabinet I build up to date was 11 1/4" cubed. It was loaded with an 6,5" (TB) driver and build from quality 3/4" MDF (un-braced). With a few 100 Watts going into it (peak), it was still vibrating quite a lot.

Best regards Johan

Phil Olson 23rd May 2010 04:59 PM

Thanks for the feedback. It is indeed a subwoofer and I have a separate LFE I've already built so this one will only handle from 80 Hz down.

I'm confused about your vibration comment though. Any single driver sub will vibrate due to the inertia of the cone, (any action will cause an equal and opposite reaction and all that). If you mean resonance then I get it.

My LFE is a CSS DX15 in the recommended box which is heavily braced and it will definitely shake even though it is easily over 100 pounds. Last week I made the mistake of setting some stuff on it then forgetting. Halfway through a movie, I heard things crashing behind the screen and when I looked, the stuff was all on the floor. :eek: Luckily nothing was damaged.

I guess I will try a front mount somewhat below center but high enough that I can get my hand to the top so I can stuff it properly. The driver I'm using is a CSS DX10 so it should perform well. I still have to figure the cabinet resonance though. Is it a concern for such a narrow bandwidth? By adding the two braces, I've raised the resonant frequency by 3x so shouldn't that do the trick?

vadi 23rd May 2010 06:57 PM

I read that standing waves can be an issue if the cabinet is big enough too. That can be helped with non-parallel internal walls I think.

chris661 23rd May 2010 07:12 PM

The wavelengths of LF are huge (about 3.4m for 100Hz), so I think he'll be safe there.

Phil Olson 23rd May 2010 10:27 PM

Chris, you are correct sir!

I guess my only issue is cabinet resonance. As I have it now planned, the 13x13 dimensions wouldn't be a problem, I should think. By adding the two braces along the long dimension, the 50 inch high wills are divided into three 16 inch sections. I should think this would also be more than sufficient to keep the resonances in check but I can't know for sure.

Is there some cheap and easy software that will allow some simulation of box resonance depending on material? I have a Solidworks model of the box so it would be great if a tool existed that wouild allow some kind of standard data input.

Rademakers 23rd May 2010 10:51 PM

I'm not talking about resonance persť. I'm talking about vibration (of the enclosure walls) at any frequency whereas resonance is frequency specific. Correct me if I'm wrong here but if resonance would be the only issue then a infinite thin enclosure would do the trick easily.

If you're going to use the thin material you suggest it's going to be easy to make it vibrate at any frequency, at low level output, the more so at resonance. Adding bracing will stiffen the material up, raising resonance frequencies out of the pass band but also work against vibration in general. Vibration, as it's releasing energy at a later moment, colours the sound and converts energy, dissipating heat.

If the CSS DX10 is the animal I have in mind I would suggest doubling the material thickness (increasing stiffness 8-fold IIRC and adding mass), as well as add more bracing.

Best regards Johan

vadi 24th May 2010 04:22 AM

Maybe try a sandwich construction with ceramic tiles and bitumen to increase mass. :)

Phil Olson 24th May 2010 06:59 PM

I think you are right. If the driver is pumping a lot of air outward, it is also pumping it inward, causing the material to flex, which is indeed not resonance.

Since the recommended enclosure for the X15 is 3/4" MDF I think I am safe there. After studying the bracing for the X15 I think I'm in good shape doing what I am planning.

If the X10 is anything like the X15 in performance it should handily do the trick.

chris661 24th May 2010 08:35 PM

Sounds like you know what you're doing.

I wish you the best of luck, and demand that you post pictures :D


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