One push-pull or 2 sonotube TLs?

[GhettoSQ]

I've got a pair of Seas CA21RE 8" woofers and have been playing with Sonotubes...I have them mound push-pull in a 48"x10" tube running passive right now. If I mount them separately will I get enough SPL to keep them passive? Or should I keep this arrangement and get a plate amp? Right now they are sharing my NAD 3020 with Boston A60s.

thanks!

[owdi]

If you are looking for more output I would try a push push configuration with the drivers facing out on each end of the sonotube. You could stand the sonotube up to reduce the amplitude of room modes.

Dan

[GhettoSQ]

Neato! How does that config boost output? I assume if they were wired in phase I would lose the push-pull harmonic cancellation?

[ScottG]

Originally posted by owdi
If you are looking for more output I would try a push push configuration with the drivers facing out on each end of the sonotube. You could stand the sonotube up to reduce the amplitude of room modes.

Dan

..push-push in that configuration would be a dipole. It would reduce output (spl).

..push-pull in that configuration would increase output above the T-line's output and reduce output starting a bit below the T-line's output.

[ScottG]

Originally posted by GhettoSQ
I've got a pair of Seas CA21RE 8" woofers and have been playing with Sonotubes...I have them mound push-pull in a 48"x10" tube running passive right now. If I mount them separately will I get enough SPL to keep them passive? Or should I keep this arrangement and get a plate amp? Right now they are sharing my NAD 3020 with Boston A60s.

thanks!

short answer:

mount each in their own tube with correct lengths for the driver's fs (..and dampen the tubes with fiber fill);

if stereo then connect each to their own plate amps, if mono connect the drivers in parallel to a single plate amp;

plate amps are cheap. In particular note this thread:

Buyout Plate Amp

[GhettoSQ]

I'd be interested in the long answer too, since I always want to know why something is I had seen a few project sites with push-pull setups they raved about, but Mr. Pass and our own GM recommended dual tubes.

The trick is, it will be a few months before even a $50 plate amp is in my Spouse Acceptance Factor parameters. So I was hoping the dual tubes might be a lot better passive than one push-pull...or at least wondering. I suppose the best approach is to wait, get an amp, and try different tube configs; sounds like it will be impossible to compare passive setups.

For the record, she calls it "El-poop-o."

[ScottG]

Originally posted by GhettoSQ
I'd be interested in the long answer too, since I always want to know why something is I had seen a few project sites with push-pull setups they raved about, but Mr. Pass and our own GM recommended dual tubes.

The trick is, it will be a few months before even a $50 plate amp is in my Spouse Acceptance Factor parameters. So I was hoping the dual tubes might be a lot better passive than one push-pull...or at least wondering. I suppose the best approach is to wait, get an amp, and try different tube configs; sounds like it will be impossible to compare passive setups.

For the record, she calls it "El-poop-o."

Well for that then we would need to exactly how the drivers are utilized.

IF its like Pass's first "legend of el pipe-o" then the 2nd order distortion cancelation via push-pull operation is at best minimal. (..the reasons are complex - basically the pipe operates in a not to disimilar fashion to a a push-pull configuration, utilizing both methods at the same time substantially counteracts the effectiveness of the push-pull operation.)

Furthermore the pipe with 2 drivers will not exhibit as strong an spl in the pipe's range of operation when compared two pipes (which effectivly double spl, almost +3db, at these lower freq.s).

And sure, you can use two pipes with drivers connected together in parallel and hooked up to your current amp - essentially the same as you currently have. With this you should be able to increase the spl of lower freq. response by almost +3db as mentioned above. There are of course several reasons to buy a plate amp, but if you can't "swing" the purchase right now thats OK - it will still be worthwhile going the two pipe route.

[GhettoSQ]

Originally posted by ScottG


Well for that then we would need to exactly how the drivers are utilized.

IF its like Pass's first "legend of el pipe-o" then the 2nd order distortion cancelation via push-pull operation is at best minimal. (..the reasons are complex - basically the pipe operates in a not to disimilar fashion to a a push-pull configuration, utilizing both methods at the same time substantially counteracts the effectiveness of the push-pull operation.)

Wow, interesting. Seems like I saw a lot of tube projects with push-pull drivers, though? like this: http://www.teresaudio.com/haven/subs/subs.html

what do you mean by how they are utilized? right now they are mounted clamshell, out of phase, with the in-phase woofer downfiring. Sag is about 4.8%.

I thought the whole point was to guide the back wave, but Pass has his second version firing up. Sure would be easier for mounting since that way you don't need a box on the bottom. at the end he says:
"If you have an 8 foot ceiling, you can make two out of a 12 foot piece of 8 inch diameter, and find yourself decent 8 inch woofers resonant at about 40 Hz."
These drivers' relevant specs are:
Qts: .48
Vas: 81.3l or 2.871cu.ft.
Fs: 31Hz

Quarter-wavelength at Fs is 9 feet or so, I suppose I could fold an 8 inside a 10 (tubes). But it seems like with room gain a lot of folks prefer to tune for a bit above that. I estimate about 50-60Hz with a 48" tube stuffed...

[ScottG]

Originally posted by GhettoSQ


Wow, interesting. Seems like I saw a lot of tube projects with push-pull drivers, though? like this: http://www.teresaudio.com/haven/subs/subs.html

what do you mean by how they are utilized? right now they are mounted clamshell, out of phase, with the in-phase woofer downfiring. Sag is about 4.8%.

I thought the whole point was to guide the back wave, but Pass has his second version firing up. Sure would be easier for mounting since that way you don't need a box on the bottom. at the end he says:
"If you have an 8 foot ceiling, you can make two out of a 12 foot piece of 8 inch diameter, and find yourself decent 8 inch woofers resonant at about 40 Hz."
These drivers' relevant specs are:
Qts: .48
Vas: 81.3l or 2.871cu.ft.
Fs: 31Hz

Quarter-wavelength at Fs is 9 feet or so, I suppose I could fold an 8 inside a 10 (tubes). But it seems like with room gain a lot of folks prefer to tune for a bit above that. I estimate about 50-60Hz with a 48" tube stuffed...

"How they are utilized".. by that I mean do both drivers:
1. exit in-phase to the room?..and,
2. exit reverse-phase to the pipe?

Pass's second version is better with respect to distortion and T-line operation. (i.e. place the driver on the end like Pass has in the second version.) Note that you can further dampen the driver's resonance and its fs with a HIGHLY stuffed pipe. (i.e. less distortion and a more extended response.) The downside is that you will loose some efficiency and should utilize a slightly longer pipe. Furthermore the sub becomes less suitable for extended operation at higher freq.s.

Do NOT shorten the length of the pipe.. consider horizontal placement in-room instead (i.e. "running" along the bottom edge of the room). Conversly, consider a folded or spiral line.

[GhettoSQ]

Originally posted by ScottG
[B]


"How they are utilized".. by that I mean do both drivers:
1. exit in-phase to the room?..and,
2. exit reverse-phase to the pipe?

Not exactly sure. One is mounted in the pipe, down-firing, in phase with the mains. The other is mounted in front of it (under), reverse-phase.

It sounds like as long as I'm going to be passive for a bit it's worth a try. Should I do 2 8" tbes or 2 10" tubes?

I could buy a third tube of either size, cut it in half, attach the halves to the originals (good place for some kind of stuffing-stopper) and have 2 72" tubes. with 8" tubes this gives me a Vb of 2.094cu.ft, still a little under Vas.