Building push-pull subwoofers

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I'm interested in doing this as well, with 4 high excursion 15's in 2 separate sealed enclosures. I've decided not to do isobaric loading, as I don't want to lose all the maximum output and efficiency. I've heard that a push-pull arrangement can reduce certain types of distortion etc, but I've never tried it before. And no, it doesn't have to be an isobaric enclosure to be push-pull (take M&K, EAW, and many others, for example).
Isn't there push-push as well?
 
Yeah, I was interested in push-pull isobaric loading when I was wanting to use these drivers previously mentioned in massive vented enclosures. But, I soon came to the conclusion that it just wasn't an option, mainly due to space constraints. On top of that, I've changed plans (again!) and a sealed alignment with LT or EQ would be better for use strictly under 40Hz or so, I think. So, now a push-pull sealed enclosure seems more logical.

Thinking about it.. one driver moves in, while the other moves out. Theoretically, odd order harmonics from the drivers and their motors should be cancelled out, or at least a large portion of it. Am I looking at this correctly? Sounds right to me, anyway.

My main question is.. are there ANY disadvantages to push-pull versus the conventional methods? If not, why don't we see it more often in commercial designs? I've seen many, but it seems that most designs using 2 or more subwoofers don't utilize it, which doesn't make sense to me. The only thing that comes to mind is that a tad bit more complicated enclosure design might come into play if hiding the back of the driver is desired...but I would think that would be very easy to do the majority of the time.
 
So, with 4 Ascendant Avalanche 15's (XBL^2 motors, 27mm xmax, etc), you don't think the difference would be very noticable? I'm very curious to know what it'd sound like this way. Because if I did them push-pull, 2 per sealed enclosure, I'd build it to where the bottom driver is mounted backwards...with the bottom section of the enclosure several inches shallower than the top part, but with the MDF extending from the bottom portion to meet flush with the top part, and kind of hide the back of the bottom driver some how...know what I mean? I'd probably try to make it where at first glance, it only looks like a single 15 in a larger sealed enclosure. But if it's not worth it, I won't bother building it like that. What do you think?

Also, one thing I've never been absolutely clear on..
In a push-pull, the two drivers have to be in the same enclosure, right?
Because if I ended up not doing push-pull, I'd put them in 4 separate enclosures.
 
yes non linearity is not a big issue, richie is rite if u have a decent enclosure and driver u dont need any non linearity complensation
iso-barik, reduces the enclosure volume but is less efficient

iso barik and push pull both coupling removes odd harmonics
bridge mode push pull amplifer, that will also cansel out the even harmonics

BTW , i refered to this link
http://www.eaw.com/technology/nonproprietary/pushpull.html

diffrence-
isobarik is less efficient, but pushpull is more efficient
isbarik reduces the enclosure volume, but pushpulldoes not reduce any volume
similarity-
is both reduce distortion due to non-linearity

in isobarik, example u stick 2 subs front to front. push pull is like in a single enclosure u fix 2 subs 1 facing inwards other 1 facing outwards(they share common enclosure twice the enclosure size for 1 sub)
 
Klook said:
But I can't find in web detailed explanation about how to design the cabinet according to the driver parameters.

What do you mean? It'd be the same as designing a subwoofer of any other enclosure type.. If you're doing a sealed push-pull with two identical drivers, it's the same as a sealed enclosure for one of those drivers x2. Same thing goes for vented, or bandpass, or whatever. Perhaps I don't understand what information you're trying to obtain? If you're just wanting to figure out how to design subwoofer enclosures around different types of drivers, in regards to theile-small parameters, that's another whole subject. Otherwise, those rules don't change for designing a push-pull cabinet.
 
BHTX,
Ok, understood. So the box dimensions I already know how to design, but...
For example: I have a given sub driver and I have simulated it using WinISD (for example) for a single driver sealed cabinet. Ok now I have the dimensions of the box.
How can I simulate the results of the subwoofer in the push-pull configuration? What's gonna be the frequency response and SPL?
WinISD doesn't consider push-pull config, only isobaric.
How can I figure out, in theory, the results of adding a new driver to the box, in push-pull configuration?

regards
Klook
 
"Decent drivers don't have such bad non-linearity problems to make the benefits that big.

But the main reason is cosmetic."

Spoken by someone that has not listened to a push-pull system.

The difference is plainly audible.

Just make sure the woofer that is mounted backwards is quiet. Some of the woofers have vents that are too small and they 'wheeze', tinsel lead slap can be a problem too.
 
djk said:
Spoken by someone that has not listened to a push-pull system.

The difference is plainly audible.

That's good to hear. :)

djk said:
Just make sure the woofer that is mounted backwards is quiet. Some of the woofers have vents that are too small and they 'wheeze', tinsel lead slap can be a problem too.

Yeah, this is what I'm most concerned about. And as these would only be used strictly below 40Hz or less, I suspect it'll even worsen the effect somewhat. The Ascendant AVA15's were great drivers, especially for the price when compared to some others around that time, but they're definitely not the most quiet. Bieng pretty beastie and stuff, they have a vented pole piece. And the tensil leads aren't woven into the spider. They have the padding on the bottom of the cone for the leads to slap against, which of course helps, but it's still plainly audible when the driver isn't in a box and running free-air. Also, from what I remember when I ran my first one free-air after getting it over a year ago, distortion definitely didn't seem that low either. At anywhere around 50Hz with a few watts, it sounded like it was about to break out into a square wave or something. Strangely, these subs were supposedly the best for the money at the time, and heaps of people all over the internet were crazy about them. Even more strangely, while knowing all of this, I now own 4 of them, and spent a pretty hefty amount.

Hrmm...I guess I'll just have to try some things out and see. :xeye:
 
I just took the newest one I got a few months ago and hooked it up for to a ButtKicker amp, and connected it to the PC. Downloaded some test tones to check it out closely again, as it was quite a while back the last time I did this.

This particular Avalanche 15 out of the 4 I have was actually brand new, and supposedly hasn't had a signal applied to it yet. So, it's definitely not broken in the least bit..

So far, after just a few minutes of briefly toying around with various sine waves, I honestly don't see this driver's 'noise' being much a problem, as far as being a potential candidate for push-pull configuration. Actually, there's really NO whistling whatsoever. So, that's great to know. The most audible noise was simply the tensil leads patting against the foam cushion thingies that are glued to the rear of the cone, but it's not all that bad usually, and certainly wasn't very audible when I had one of my other ones in a small sealed enclosure previously.

As I experienced a long while back with my first Avalanche 15, this one also started producing a bit of audible distortion when approaching 40-50 Hz and up. However, I also noticed that much of this distortion is due to the ButtKicker amplifier. Strangely, I'd noticed in the past how the RCA input on this amplifier doesn't seem to like much voltage, and quickly gets very distorted. After turning the volume on the PC down even more thru the Windows Volume Control, it sounded a bit better. But, it's clearly audible that these particular subwoofers do their best at the very lowest of low octaves, which shouldn't be a problem for the potential application at hand. So, I think it should actually work out quite nicely.

Only problem I'm still faced with is... building the enclosures!
No woodworking tools, no experience with woodworking!

Oh well, I'll figure something out soon enough..
 
Been breakin' 'er in for I guess over 2 hours now..

The tensil slap against the spider might very well end up being a nuisance.

Sounds absolutely disgusting in free-air on music at higher volumes. :(

Now I remember why I was almost debating selling the first one I got. :xeye:

But I had planned on using it in a conventional sealed config at the time, and hadn't even thought about push-pull back then.
 
PUSH PULL WOOFERS

LINKS:

http://blog.stereophile.com/ces2007/010907bgsub/

http://www.bgcorp.com/news.read.php?article_id=64

Laure Fincham described Bandpass Subwoofers in the AES Journal some time ago. Here is a Push-Pull Version, with TWO Drivers opeating on one slot.

In this configuration, he has a stack of four. He further suggests
stacking four stacks to get a Line Source Sub-Woofer !

the bgcorp line is to a press release for CES 2007, but the product has not materialized on their website ...

I haven't seen any web material, except for Fourth Order Bandpass Subwoofers with ONE Driver ...
 
Re: hello

Amit_112dB said:
I am not sure what u mean by push pull sub, heard of push pull amp thou,
i think what u might be looking for is called ISO BARIK loading of 2 woofers, face to face, try searchin ISO BARIK loaded
or see this
http://en.wikipedia.org/wiki/Isobaric_speakers
let us know if ur looking for this

best of luck with your search,bbye

Hehe, the wiki page states "the pressure between the two drives is essentially constant if the drivers are matched". This is wrong. If the pressure had been constant, the inner volume could be made very small and it would have no effect on the motion of the outer cone.

For ultra low frequencies, where the effect of acoustic load of the box is largest, the sound pressure in the cavity between the drivers is somewhere around half the pressure in the inner cavity.

Towards higher frequencies, when the motion is mass controlled, the two cones will move nearly identical, and here the pressure between the cones is nearly constant.

However, for frequencies where the volumes matter, and the box design is important, the pressure between the drivers is far from constant.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.