Down firing sub question

[PoorboyMike]

How much does carpet affect the performance of a down firing sub? I'm putting the finishing touches on one right now and was planning on putting a ply or mdf base on the bottom, but if it's not a huge difference, I think that legs would look better.

My guess is the carpet and pad might absorb too much sound but I've seen commercial subs without a base. What do you guys think?

[Wildcard26]

Came across a thread on this over at diyaudio.com and the point that was brought up was that sub woofers use more low frequencies that are more felt. The highest frequency that a sub puts out is not directional anyways so it isn't as discernible as frequencies in the higher octaves which can be greatly degraded in a situation involving carpet and even tiles. I don't think it's that big of a deal as I am running a down firing sub that I built and haven't noticed any loss otherwise. I think the idea of a base is also optional as I see it used in Sonosubs and I believe it's HSU uses a base for a line of their subs. Just my 2 cents.

[PoorboyMike]

Thanks for the reply Wildcard.

Have you tried putting your sub on a sheet of plywood to see if there is much of a difference?

[Wildcard26]

No but I had it on bare concrete for testing and I can't say there was any audible difference. I have a piece of MDF so I guess I will give it a try to it just for academics sake to see if there is a difference due to the type and density of the surface. The carpet is also resting on concrete as well.

[PoorboyMike]

I went ahead and drilled out some holes to connect the base to the sub. I tried to do a dry fit last night but I'll need some help trying to line up the 8 dowels. Nobody was home and I was starting to get :M so I just gave up.

Here is the progress so far, in the upside down position.

[Wildcard26]

Looks good. Why not just try it with the piece of MDF just to see and let me know what you think. I am sure you can figure out something else to get it on if you have to.

[jkrutke]

Hello,

Nice looking sub. Great work on that.

I've done some tests with downfiring subwoofers. Generally, it's best to fire right into the carpet. All of the sub's working bandwidth will come through just fine, but some of the sub's air and mechanical noise will be absorbed, along with a lot of upper harmonics. This will help to make the sub less locatable, and is the best thing a downfiring sub has going for it.

Of course the negative is cone sag. Most downfiring (or upfiring) subs have a limited lifespan. You're probably familiar with the equations that tell you if a sub will sag too much under it's own weight, but that doesn't account for a reduction in elasticity due to suspension fatigue. The harder you use the sub, the sooner it will sag to a point of substantially reduced Xmax in the down direction. Is it a worthy trade off? Probably, considering the fact that a front firing woofer's life is limited by the ability to be kicked by a stray foot during a party or a stray football played indoors. (I have experience with those. :B )

[PoorboyMike]

Thanks for the reply John. I'll just make oak "feet" for it and call it good.

And I know what you mean when it comes to the life span of a front firing sub. Full auto air soft guns and sharp pencils tend to shorten it considerably. :M

[Wildcard26]

I agree with all said except the part about the frequency part. The sub is already crossed to reproduce from the highest omni directional frequency (usually about 150 Hz). Like in Smaller so called subs (HTIB) it's not like you can locate the sub but the lower the frequency response the harder it makes it to locate. I guess it can't hurt to negate frequencies that reside in the 100-150 Hz octave which in that case would back up your point but at the end of it I find it a subjective topic. Just enjoy your build man.

[MarcE]

hm, interesting. A couple of questions, would the sagging suspension apply less to underhung voice coils with smallish x_maxs? Also, if the crossover frequency was higher, say in the case of a three-way in the 200 Hz range, would the downfiring woofer help balance out (i.e. lower) natural room attenuation of low frequencies?

[Wildcard26]

In a case of a three way I think down firing would wreak havoc on the sound dispersion. Anything 200 Hz and up being directed at some surface is asking for trouble if your design design is a 3 way. I think Downfiring is also reserved fro sub configuration. As for underhung drivers I can't say that I have reviewed this in it's entirety to respond. I also came across this topic on a thread at diyaudio as well. Check it out.