Down-firing Subs

Crazy Steve

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Nov 18, 2019
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Well, my second attempted repair to my ULD 15 didn't work, so I'm in the market for a new sub...

The ULD 15 is a down-firing sub but they've seemed to have gone out of style. I like that style, they're considerably less 'obvious'. From what I can find, audible differences are slight (depending of course on set-up and who you talk to), it appears to me that the change to front-firing was more of a 'wow factor' esthetic rather than a marked improvement in sound. But the current limited crop of down-firing subs isn't what I'm looking for.

So I'm looking at 'conventional' box subs with an eye to converting one to down-firing. Biggest hassle will be relocating the now-typical-built-in-amp, but that's not insurmountable as I intend to re-veneer the cabinet anyway (I'm not fond of black). I'd like to remove the amp completely from the 'box' and install it in my custom cabinet that contains the other components, anybody see an issue with that? As long as I use adequate size wire to prevent voltage drop, I don't see a problem. Opinions?

The other issue is how tall should the cabinet legs be? Is there at optimum length or maximum? The legs on the ULD are only 3", I'd like to go taller. I would think that would help with 'de-coupling' the sub from the floor. Again, any opinions?

I've been looking at Rythmik subs as I like their feedback control, with the F18 or F25 being the likely choice. The F25 features two 15" speakers, would that be an issue in a down-firing configuration? Again, opinions?

If I had a basement, I'd look very hard at a infinite baffle set-up, but I don't....
 
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Folsom

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Oct 25, 2015
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Not all subs like to hang. You may find DIYaudio website more helpful on this subject.

Down firing doesn’t make much difference from other orientations because all the frequencies are fairly omnidirectional that are subwoofer frequencies.
 

Ron Resnick

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Jan 24, 2015
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. . .
So I'm looking at 'conventional' box subs with an eye to converting one to down-firing. Biggest hassle will be relocating the now-typical-built-in-amp, but that's not insurmountable as I intend to re-veneer the cabinet anyway (I'm not fond of black). I'd like to remove the amp completely from the 'box' and install it in my custom cabinet that contains the other components, anybody see an issue with that? As long as I use adequate size wire to prevent voltage drop, I don't see a problem. Opinions?

. . .

Respectfully, this sounds like a lot of brain damage for not an obviously good reason. This is an exaggeration of course but why buy a car with a mid-engine configuration, and spend time and money relocating the engine to the front hood compartment, when you could just buy a front-engine car in the first place? (I appreciate that there are very few down-firing subwoofers currently available.)

But the fact that there are very few down-firing subwoofers available today suggests that designers have decided it is an inferior configuration. I liked my REL Stentor III, but REL dropped down-firing subs, and that tells me a lot.

Just buy one or two Seaton subwoofers or Funk subwoofers.

Of course if you just want a DIY project, then have at it! :D
 

Al M.

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Sep 10, 2013
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But the fact that there are very few down-firing subwoofers available today suggests that designers have decided it is an inferior configuration. I liked my REL Stentor III, but REL dropped down-firing subs, and that tells me a lot.

The problem seems to be that downfiring subs strongly interact with the floor surface beneath them. That's probably fine with concrete floors, with or without rigid wood cover, but can be bad with suspended wood floors like mine.

I had a downfiring REL Storm III sub, but it sat on an ASC SubTrap, an excellent platform, which isolated it from the floor. The audible benefits of the SubTrap were pronounced. Now I have dual frontfiring JL Audio F112v2 subs, also on ASC SubTraps. The new subs are superior.
 

dbeau

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Apr 20, 2018
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I am interested in REL25 subs but notice they are not recommended (or maybe ignored) by those here whose opinions I respect.
Why??
 

Robh3606

Well-Known Member
Aug 24, 2010
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So I'm looking at 'conventional' box subs with an eye to converting one to down-firing.

There is a good chance it won't work. The driver has to have a stiff enough suspension, designed for that type of mounting, otherwise it will sag from gravity and displace the VC.

Rob :)
 
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Duke LeJeune

[Industry Expert]/Member Sponsor
Jul 22, 2013
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I agree with the cautions that Folsom and Robh3606 posted. You need to calculate the woofer sag, Google will help you find the forumla. It may be inconsequential but best to spend a few minutes finding out. You'll probably have to make some educated guesses about the woofer's parameters. Or at least ask the manufacturer about re-orienting the sub to be down-firing.

One small difference down-firing makes is this: The air mass that is sandwiched between the bottom of the enclosure and the floor is partially "coupled" to the woofer cone, increasing its effective moving mass by a few grams without actually adding weight. This lowers the resonant frequency a little and can extend the low end a little bit deeper.
 

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