Down firing Sub-Woofer

[indoubt]

Sloped baffles are for phase and time alignment of two (or more) units. With subwoofers you can do the time alignment in the sub amp and often also in a HT amp. Most sub amps can adjust the phase with a pot from 0 to 180 degrees. If you need your sub to go relatively high frontfiring can be a better option as some lower mid will be audible. If you can stay low (say below 70-80Hz) then there is no reason not to go downfiring. As you mention a thor sub I assume that you keep the crossover low.

[Paradise_Ice]

Would you really want to do that in a ideal world? i would rather not have the need for any crossovers as we all agree they mar the sound even if there an important part of the design for many reasons, I dont know if your remember but Naim had a 15 in driver with an isolated mid and treble units on top, each one was staggered back from each other.

[johninCR]

Originally posted by Paradise_Ice
Would you really want to do that in a ideal world? i would rather not have the need for any crossovers as we all agree they mar the sound even if there an important part of the design for many reasons, I dont know if your remember but Naim had a 15 in driver with an isolated mid and treble units on top, each one was staggered back from each other.

Subs must have some kind of crossover, since none can play into the upper frequencies. I'm a minimalist by necessity and want as little in the signal path as possible, but for a sub an xover is mandatory to send it only the lower frequencies.

The staggering you refer to is for time alignment purposes.

The bottom line is that some sub drivers function reasonably well in a down firing alignment. Adire Audio has some calculations to help determine whether a specific driver is suited for downfiring, however, downfiring affects any driver in a negative way. It reduces useable Xmax and affects the impulse response both of which are a simple matter of physics and the effect of gravity. Downfire if you have to and it might be OK for HT, but for music I'd say no don't.

[ppfred]

Hi again,
I'm back, and thank-you everyone for the enlightened discussion. The consensus seems to be: Do it if you must, and I must.

Originally posted by DanWiggins
You'll have sag issues if facing up or down:
http://www.adireaudio.com/Files/Tech...rientation.pdf
I'd say either look at downfiring or frontfiring; if crossing over fairly low (below ~125 Hz), downfiring is perfectly acceptable, provided your driver can work in that orientation.
Dan Wiggins
Adire Audio

Thanks Dan for the info. I calculated the sag factor for the Peerless 12" XLS subs and with an Xmax of 12.5mm, it comes out to 6%. (Their 10" XLS sub comes in at 5.5%.)
I'll be Xing over at approx. 80Hz.
Not that I want to seem to be shunning your advice, I will be setting up the subs as down-firing - 6% is not that far off, and the subs are already bought. An important consideration has to be room size, placement and esthetics, and in my case down-firing is the best compromise.
I will be making a removable base/stand so if it turns out badly I'll be able to revert to front-firing, which brings me to my next question:

Originally posted by BillFitzmaurice
Downfiring will inject some acoustic LP filtering into the equation, ...

You should figure out the clearance via an RTA after completeing the box, as the distance to the floor will affect the boundary loading and is something you'll want to be able to fine tune.

Thanks Bill for your information.
What should the driver/floor clearance be? Is their and optimum figure? Or more importantly, what is an "RTA" and where do I get it?

By the way, the boxes are completed. I just have to cover them with plastic laminate - black mat, then I'll be making an active Xover which appeared in Speaker Builder.

Thanks all again,
fred p.

[BillFitzmaurice]

RTA is a Real Time Analyzer; you can download a program for one from the Allen Heath site; alternately just use a test tone CD and sound level meter to check response of the speaker and make the legs what ever length they need to be for best results, usually about four to six inches.