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In Reply to: RE: Push-pull woofer alignment questions posted by 3LockBox on June 25, 2007 at 15:42:48
Greets!
Vas is summed, see the layout comparisons in the link. Since the layout averages out any driver stroke non-linearity, even order, though one can argue that since we find even order distortion euphonic and odd not, that we're 'cutting off our nose to spite our face'.
GM
Loud is Beautiful if it's Clean!
Follow Ups:
"though one can argue that since we find even order distortion euphonic and odd not, that we're 'cutting off our nose to spite our face'."
Having built many push-pull designs, I find they sound so much better without the distortion, thank you.
I agree, any audible reduction in distortion is moving in the right direction even though I didn't hear any difference with the only PP sub I built, but not everyone feels as we do.
Loud is Beautiful if it's Clean!
My application is not for a sub, though it would be for two woofers rolled off fairly low. Actually, I'm experimenting with my three-ways in which I have reconfigured two 6.5" woofers for PP operation. It does sound cleaner to me, though some of the boom is gone (which one guy's boomy is another person's phat). I imagine the benefit to this alignment might be more evident in a larger (louder) woofer.
Vance Dickason is one of those who say Vas is halved and odd order harmonics are cancelled.
Hmm, PP shouldn't affect any tendency to 'boom', but whatever sounds best is all that matters.
I don't have any of his books, but in '99 it was posted on the basslist that at least the Dutch translated version said odd order, though no mention was made of Vas being halved referenced to a single driver like in a Isobaric or its PP variant.
Yeah, I used under-hung HE drivers, but I can see where high Xmax over-hung drivers could benefit from PP. The kids around here like the PP 'look' in their rolling boom-boxes, but for sure they don't care about any potential distortion reduction as it would be about as obvious as noticing the beach had lost a grain of sand........
Loud is Beautiful if it's Clean!
there are a few push pulls
here are some pics
http://www.audiomagazine.ru/img/stat/bass1_3.jpg
an mtx subwoofer is like the first one on the left
or here
http://www.mkprofessional.com/images/speakers/subs/5310/mps5310_250x345.jpg
as far as I know, isobarik is more like the one 2nd from the right with the drivers fronts attached together.
http://pros.orange.fr/audiomobile.online/images/Caisson_push-pull_double_events.gif
In this opperation you can run with half the area required than 1 subwoofer, but you have 2 drivers in parallel and you lose output. this clamshell pushpull is 3db softer than 1 driver. If you put 2 drivers in a box more like picture a, you'd pick up about 6db (2 x 8ohm = 4ohm). You then have a net difference of -3db compared to +6db. (db is HUGE in the bass region).
Now on the multiple sub picture, if you took the picture 3rd from the left
and had the opening so both subs fire outwards........
That's good sound.
Like this link only not open baffle.
http://www.linkwitzlab.com/images/graphics/d_woof1.gif
norman
Thanks for the links.
Actually, I've seen the Linkwitz site before. His Orion speakers look incredible. Most all of his designs are dipole. His approach makes sense, but requires some serious power and tricky EQing. I actually have in mind to 'ape' his Orions, by making a bass section with either two 8" or 10" woofers (mounted in PP), in a cab w/ PR, rolled off around 300-400hz, with a wideband driver mounted above in OB, and perhaps a super tweeter, depending on what wideband driver I use. Sure, I could make things easier using a biamp approach and lots of power, but I have this obcession with super efficiency and low powered amps.
I've never heard them but........
I don't like the idea of using massive eq to make up for a small open baffle.
more eq = more movement = higher harmonic distortion.
yes he uses low distortion drivers so that helps.
But to me the low distortion would work better if it did not have more eq, to me it'd cancel out the benefit of low distortion drivers.
And we all seem to love the narrow open baffle speakers because the rear wall reflestion is so intoxicating. You'd lose that if the baffles were large.
The current trend is small speakers and to me these fit the bill and sound very good from what I've read.
Norman
I've been tossing around crossing 300hz to a full rnage driver (actively).
currently with one project. I'm using a Ratshack 1354 (5.25" fullrange driver) that had a whizzer-ectomy, and has the hole in dome tweak. Since I'm running it wideband, I didn't want the dual cone interaction, and the hole in the dome reduces upper-midrange distortion. This little wideband is flanked by a supertweeter, and capped with a 40uf polycap. I'm using two 6.5" woofers for the low-end. I get very good bass but these won't go that low, or at least, they don't do sub-bass very well. But I'm convinced that this configuration will translate well in a larger size, with larger woofers, and a dipole wideband. We'll see.
I have seen and heard them. There is no way around needing EQ and large baffles for dipole bass. If the wideband mid-range can run down near 100 hertz I hear nothing bad in having the woofer in a box.
My mid range will only go down around 250 hertz and even that isn't too bad with a bass reflex box on the bottom. But now woofer quality becomes more important. I am running a pair of 12" per side at the moment.
Russ
10" drivers - supposed to hit like sledgehammer
> 10 years ago with passive radiator "vent" by advanced K builder Wayne N PIC
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