Thoughts about push-pull subs?

[ktaillon]

M&K use a push-pull setup for their sub and now JM-Lab uses a push-pull for the bass drivers in their Diva tower. Both of these are vented, I though push-pull was to be used in a sealed enclosure.

I did play around with a pair of 8" drivers in a isobaric enclosure - not very happy with it.

Has any of you tried the push-pull?

[JonMarsh]

It's a way to reduce even order harmonic distortion - a cheaper way than improving motor linearity. BUT, it doesn't reduce odd order distortion, and will have only a limited effect on IM products.

If one uses it with high quality drivers to tweak the best performance out of them when they're pushed near their Xmax, (and if the drivers have no tendency towards oilcanning), then apart from the assembly and configuration issues, it's a pretty reasonable idea. See Sigfried Linkwitz's Orion for an example of push-pull done right.

In box type speakers, I think it's a little more problematical. And ugly. And remember, the concept won't make a silk purse from a sow's ear- if the driver's aren't good in a conventional configuration, they're not likely to be anything special in push-pull.

YMMV, all the usual legal disclaimers apply, including my disavowing any particular claim to knowledge of subwoofer design and development. (built first one in '75, a date many on this board weren't yet alive....)

Why don't you try building a sub design in both push-pull and conventional configurations with good drivers, and see what you measure and hear? :T And let us know the results.

[Jack Gilvey]

I did play around with a pair of 8" drivers in a isobaric enclosure - not very happy with it.

The "push-pull" that M&K uses, the type that Jon describes, is not isobaric.

[Carl V]

as has already been stated Isobaric & push pull aren't always the same.
M&K has for years used a push pull arrangement. Whether it's truly
advantagous or marketing spin is debatable. A number of years ago
I and a few friends built a M&K 200 & 350 clones so to speak. Shivas & Tempests were used. Hypex Plate Amps (500watts) Enclousures were
well made BB & well braced. They were large as the 200 & 350 models
were....actually larger as the Big SVS box subs became. They were
very good subs. Another guy did dual Stryke 12" metal cone M&K clones.
He used bash Amps with a LT circuit. We used a BASISS box...then
a BFD. Isobaric is of some use as well. I've built a few ISO Shiva & Tempest
tubes back in the day, both sealed & Ported...tubes allow room for adequate
port length. I believe Thomas has an Iso-Rava style sub in his Bedroom.
I imagine it's nice sounding....despite the 'simnple driver desgin' & straight
box alignment. Applying the laws of physics is of some benefit.

The question not answered was, would single driver
subs have been just as good. Would Bipolar (push-push a'la Mirage)
have been just as effective. Going to a few Omni-Theaters & IMAX
theaters I see that they too employ large numbers of Push Pull bass
drivers. Pro-sound reinforcement has used this. I know we are into
apples & oranges baliwicks/needs.

Technically, the use of two well engineered drivers operating well within
their linear range has it's advatages....and subsequently nice headroom.
Question is nowadays with the vastly improved motor desgins, affordable
watts & great Bass management boxes (DSP or otherwise) is it needed?
From a mfg'r standpoint I'd say probably not (not many other companies
have gone down that path) 2 drivers to account for...2 holes to cut...
bracing needs to account for two drivers & routed panels...weight goes up..
...QC issues. BUT, DIY is another matter.

[JonMarsh]

as has already been stated Isobaric & push pull aren't always the same.
M&K has for years used a push pull arrangement. Whether it's truly
advantagous or marketing spin is debatable. A number of years ago
I and a few friends built a M&K 200 & 350 clones so to speak. Shivas & Tempests were used. Hypex Plate Amps (500watts) Enclousures were
well made BB & well braced. They were large as the 200 & 350 models
were....actually larger as the Big SVS box subs became. They were
very good subs. Another guy did dual Stryke 12" metal cone M&K clones.
He used bash Amps with a LT circuit. We used a BASISS box...then
a BFD. Isobaric is of some use as well. I've built a few ISO Shiva & Tempest
tubes back in the day, both sealed & Ported...tubes allow room for adequate
port length. I believe Thomas has an Iso-Rava style sub in his Bedroom.
I imagine it's nice sounding....despite the 'simnple driver desgin' & straight
box alignment. Applying the laws of physics is of some benefit.

The question not answered was, would single driver
subs have been just as good. Would Bipolar (push-push a'la Mirage)
have been just as effective. Going to a few Omni-Theaters & IMAX
theaters I see that they too employ large numbers of Push Pull bass
drivers. Pro-sound reinforcement has used this. I know we are into
apples & oranges baliwicks/needs.

Technically, the use of two well engineered drivers operating well within
their linear range has it's advatages....and subsequently nice headroom.
Question is nowadays with the vastly improved motor desgins, affordable
watts & great Bass management boxes (DSP or otherwise) is it needed?
From a mfg'r standpoint I'd say probably not (not many other companies
have gone down that path) 2 drivers to account for...2 holes to cut...
bracing needs to account for two drivers & routed panels...weight goes up..
...QC issues. BUT, DIY is another matter.

Good comments and background info. Personally, I see more value in a good push-push configuration that balances the cone reaction forces on the enclosure, one reason I usually buy sub drivers in pairs....

In a dipole, given the LF roll off and natural "amplification" of the harmonics, push-pull may make more sense- but again, only once you've got the best parts otherwise available, and if you see that 2nd order products are dominating. Otherwise, don't think it's worth the effort.

~Jon

[chasw98]

See Sigfried Linkwitz's Orion for an example of push-pull done right.

Jon:
Not to hijack or get off topic, but what do you think of the Orion system? Thanks for your insight.

Chuck