New sub idea. Tell me what you think please...

[chops]

So I still have two Dayton 15DVC sub drivers. I'm pretty limited on space, so I want to keep the enclosure somewhat small, but still be able to get some decent performance from 50Hz and below, with extension down a little below 20Hz, or at least very solid 20Hz output. The sub will be used for both music and movies, music being the most important.

This is what I'm thinking... And yes, I realise that you loose about -3dB of output doing this type of design.

I want to do a "front-to-back" isobarik sub with a total internal volume of about 4 cu.ft. sealed. That would be somewhat equal to 8 cu.ft for one driver. I figure that should get me pretty good output down to FS (19-20Hz), maybe a little lower.

Please remember, I'm not building this for movies, but mainly for music, am not concerned with total SPL output (my room is only 13x17 w/ 8' ceiling) but will be powering it with a 600W amp bridged to 8 ohms mono.

Whatcha think?

Thanks in advance!

[GhettoSQ]

I'm in a very similar situation with a pair of 8's, so I'm thinking of going vented. But identical cutoff and usage. Unfortunately mine is a double room. I'm not much help but at least 2 of us have the same idea!

[djk]

The difference in output is 6dB, not 3dB.

With two 295-190 drivers isobaric in 4 cu ft net the Qtc=0.848 and is 3dB down at 25.78hz (Du-MAx data in BassBox v6.0).

With the same two drivers in the same 4 cu ft net box in a push-pull configuration like M&K uses you will have less distortion because of less cone motion. Qtc=1.259, F3=34.71hz, with a Linkwitz transform this would be my choice over isobaric any day.

[GhettoSQ]

do you get the same halving of required box volume doing push-pull instead of true isobarik?

[chops]

Originally posted by djk
The difference in output is 6dB, not 3dB.

With the same two drivers in the same 4 cu ft net box in a push-pull configuration like M&K uses you will have less distortion because of less cone motion. Qtc=1.259, F3=34.71hz, with a Linkwitz transform this would be my choice over isobaric any day.

Ok, -6dB. I knew it was something like that. Thanks, I stand corrected.

As for the enclosure, I am not totally limited to 4 cu.ft. I can expand it out to about 6-6.5 cu.ft. net, if that would help lower the F3 some. (sorry, I didn't mean FS in my initial post)

Also, I have no clue, nor do I have the means to build a Linkwitz transform. I wouldn't even know where to begin. I think they have to be built specifically for the drivers and application, right? I would probably have to find someone to possibly build it for me.

Oh, and for the actual design, what would be the optimal driver positions? Would they have to be like the M&K style (1 below, 1 up front), or could they be opposing eachother like Sunfire and Earthquake SuperNova subs?

I only ask because I DO have a limit on the total height of 26" so it can fit under my projection screen.

Thanks again!

[chops]

Originally posted by djk
The difference in output is 6dB, not 3dB.

With two 295-190 drivers isobaric in 4 cu ft net the Qtc=0.848 and is 3dB down at 25.78hz (Du-MAx data in BassBox v6.0).

With the same two drivers in the same 4 cu ft net box in a push-pull configuration like M&K uses you will have less distortion because of less cone motion. Qtc=1.259, F3=34.71hz, with a Linkwitz transform this would be my choice over isobaric any day.

According to WinISD Pro, running two 295-190 drivers isobarically (it doesn't have an option for push-pull), horizontally opposed (like the Carver Sunfire subs), in a 6.3 cu.ft. sealed enclosure (after displacement), I should have a Qtc of 0.630 and an F3 of 34.5Hz.

Being that WinISD Pro sees this as an isobaric design, I'm guess these #'s are way off.

But going from what you said about the push-pull design, and that I now have 2.3 cu.ft. more to go with, I'm certain my F3 will be somewhat lower than 34.71hz as you mentioned.

I'm getting ready to go buy the 0.75" MDF now and have it cut for me as I don't have the proper tools right now for the job. The enclosure is going to be a 24" cube. Both baffles on either side will be 22.5" square, as will be the center brace.

So once I get it all home, all I have to do is cut out 4 holes on the piece for the brace and cut out the two 15" holes for the drivers, then glue and screw it together.

[chops]

Whatever... Nevermind. I'm already done.

[djk]

BassBox says F3=30hz, Qtc=1.0 for 6.3 cu ft.

Try the drivers one on each side, one driver with its magnet out and its wiring reversed. If the back of the woofer is too noisey (some 'wheeze'), then you can flip it back in and re-wire.

With room gain and the lower Qtc you can probably get away without the Linkwitz transform.

[GhettoSQ]

Originally posted by chops
Whatever... Nevermind. I'm already done.

How's it sound? how did you cut holes for the drivers? (I have no tools either)

[chops]

Originally posted by djk
BassBox says F3=30hz, Qtc=1.0 for 6.3 cu ft.

Try the drivers one on each side, one driver with its magnet out and its wiring reversed. If the back of the woofer is too noisey (some 'wheeze'), then you can flip it back in and re-wire.

With room gain and the lower Qtc you can probably get away without the Linkwitz transform.

Thanks djk! At least now I somewhat know the specs to my sub thanks to you.

As for driver mounting, I have them on either side of the enclosure, both facing out, all .75" MDF construction, center braced and plenty of screws and silicone! There is very very little vibration coming through the cabinet.

After listening to a couple of well known recordings (pipe organ), in my room I am easily getting solid bass down to 16Hz without a problem. And these subs are even reaching lower to where you just feel it. No joke!

In the movie "AEon Flux", towards the beginning where she gets captured and she's stuck in that cell with the vent in the ceiling, there's a really low and quiet rumble that sounds/feels much lower than 16Hz. You can actually hear/feel the individual beats. I wonder what freq that actually is.

Needless to say, I am very impressed with this sub. Dare I say it betters my old SVS PB12-ISD/2 tuned to 16Hz!

Again, thanks for the help djk.