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[Al Limberg]

Hmmm, It has been nearly 5 years (hard to believe!) but I would be nearly willing to bet that the distortion measurements were made with a single LAB since we only had individual samples of the two Community cabs and pairs of the BassMaxx offerings.  Perhaps John Halliburton or Paul Bell or David would be able to confirm or correct my supposition.  I'll definitely call and harass Too Tall tomorrow.
I guess maybe I'm still a little slow on understanding why we are making such a big deal out of distortion figures outside of the design parameter of the speakers in question.  I suspect I'd have a hard time calling Jerry McNutt my friend if I ran my LABs with an HPF at or below 20hz.  Methinks he might shuffle my emails  off to the junk bin and place my phone calls on permanent hold.

Al

[Antone Atmarama Bajor]

      And what harmonic is being tracked,  I would think its probably 3rd Harmonic.

     Did you do any 3rd Harmonic Sweeps Wayne???

     The Second Harmonic is quite simply the Octave, so it will always be Consonant,  and less noticeable.  3rd on the other hand is more of a problem and can cause dissonance.  Push pull does not help here.  So the push pull may give superior results at reducing
2nd order HD but not Odd, I'm not sure if it does anything for the other Even Harmonics.

Antone-

[Wayne Parham]

Al Limberg wrote on Mon, 05 November 2007 20:52

Hmmm, It has been nearly 5 years (hard to believe!) but I would be nearly willing to bet that the distortion measurements were made with a single LAB since we only had individual samples of the two Community cabs and pairs of the BassMaxx offerings.  Perhaps John Halliburton or Paul Bell or David would be able to confirm or correct my supposition.  I'll definitely call and harass Too Tall tomorrow.

Might be interesting to find out.  I just quoted what I saw on the Michigan Subwoofer website.  Even if we are talking about only one box though, we can still see pretty clearly that the LABhorn has the same distortion at 25 watts that the 12Pi has at 1600 watts.

Al Limberg wrote on Mon, 05 November 2007 20:52

I guess maybe I'm still a little slow on understanding why we are making such a big deal out of distortion figures outside of the design parameter of the speakers in question.

The reason is Tom jumped in on this thread (and many others) to say push-pull drive used in the 12Pi basshorn sub doesn't work.  I don't see how he can look at the data and come to that conclusion.  The evidence is overwhelming that it does.

Tom claims that the LABhorn measures lower in distortion.  He later admitted that he had never measured one, so I don't know why he ever said anything in the first place.  There was no hard evidence to make any assertion as forcefully as he has done.  The only data I've seen of LABhorn distortion was made with only 25 watts input power.  That's not pushing it very hard, really.  We need to see what the LABhorn does at 100 watts, 200 watts 400 watts and 800 watts.  These higher power levels are where the rubber hits the road.

Even with just the 25 watt chart, we can clearly see a difference in the LABhorn and the 12Pi basshorn subwoofer.  Where the distortion rises below 35Hz in the LABhorn, it rises much more slowly in the 12Pi.  The same distortion you're getting from LABhorns at 25 watts, you don't see in the 12Pi until it reaches 1600 watts.  That's pretty significant, don't you agree?

The push-pull arrangement is most effective at very low frequencies.  It is designed to be of most benefit near cutoff, where the horn is starting to lose its ability to load the cone.  It does that beautifully, as the data clearly shows.

After looking at this data, I can find absolutely no reason to make a basshorn with two woofers without configuring them in a push-pull arrangement.  In any installation where more than one woofer is used, I would suggest that they be done in push-pull pairs.

Antone Atmarama Bajor wrote on Mon, 05 November 2007 22:25

And what harmonic is being tracked,  I would think its probably 3rd Harmonic.

At the Prosound Shooutout, the way we measured distortion was to track the fundamental and bandstop it, bandpassing the two octaves above it.  That way we got the 2nd and 3rd harmonics.  The window is rather wide though, so it can "see" a lot of noise too.  That's why we call it a THD+N measurement, because I think most harmonics from loudspeakers are 2nd and 3rd and because noise is included in the data.

Antone Atmarama Bajor wrote on Mon, 05 November 2007 22:25

The Second Harmonic is quite simply the Octave, so it will always be Consonant,  and less noticeable.  3rd on the other hand is more of a problem and can cause dissonance.  Push pull does not help here.  So the push pull may give superior results at reducing 2nd order HD but not Odd, I'm not sure if it does anything for the other Even Harmonics.

The thing is, the second harmonic falls within the passband of the horn.  Since horn output is strong to about 180Hz, second harmonics of fundamentals up to 90Hz are acted upon by it.  Basically, the whole usable range of the sub is vulnerable to second harmonic distortion generated by the woofers.  As much as possible, the drive units should be made free of second harmonics.

The third harmonic is higher in frequency, so the low pass function of the front chamber and horn folds serves to attenuate it.  Since horn output starts to fall above 180Hz, third harmonics of fundamentals above 60Hz are attenuated by the low pass acoustic filters formed by the folds and front chamber.

To me, this makes a very good pairing of technologies.  I think push-pull drive is ideally suited for basshorns.  Some have said basshorns don't need it, or that it is better suited for direct radiators.  I think push-pull drive is perfectly suited to folded basshorns.  Push-pull works best at low frequencies, where summing is good and the cancellation of harmonics is best.  Basshorns are acoustically small, so they start to lose their ability to load the woofer at the lowest frequencies.  They can use the extra help down low.  This makes the two technologies ideally suited for one another.  Basshorns and push-pull drive work very well together.

I wouldn't do it any other way.  Can't see why anyone else would either.  Can anyone give me one good reason not to use push-pull drive in a folded basshorn?

[Mike {AB} Butler]

Wayne Parham wrote on Tue, 06 November 2007 15:16

Even with just the 25 watt chart, we can clearly see a difference in the LABhorn and the 12Pi basshorn subwoofer.  Where the distortion rises below 35Hz in the LABhorn, it rises much more slowly in the 12Pi.  The same distortion you're getting from LABhorns at 25 watts, you don't see in the 12Pi until it reaches 1600 watts.  That's pretty significant, don't you agree?

Not really, as the horn probably sports better distortion figures than the LAB 12 driver that get used in it..  

Wayne Parham wrote on Tue, 06 November 2007 15:16

I wouldn't do it any other way.  Can't see why anyone else would either.  Can anyone give me one good reason not to use push-pull drive in a folded basshorn?

I am thinking at this moment, the line from the Shakespeare play Hamlet, where the Queen says "methinks the lady doth protest too much.." I think you are pushing this waayy too hard. Why not spend your time building and perfecting these - if they are as good as you say they are; the marketplace will be your judge. Getting into a debate with Mr. Danley isn't doing much to get you the renown for your hard earned efforts thus far. Maybe it would be time to consider channeling this discussion into an action plan.. to build and prove your theories on some other platform, such as smaller boxes, which are desperately needed for many of us that don't have the space that a LAB sub or 12 pi take up.
Really. See if you could come up with a push-pull design that would be a fraction the weight, size, and still have the incredible power handling.. and go to at least 40 hz with solid, high level SPL. THAT would get everyone to sit up and notice, IMO..
Respectfully,

[Wayne Parham]

Mike {AB} Butler wrote on Tue, 06 November 2007 15:41

See if you could come up with a push-pull design that would be a fraction the weight, size, and still have the incredible power handling.. and go to at least 40 hz with solid, high level SPL.

We're working on a smaller version.  I think it will have some trade-offs, but we're working on ways to minimize that.  The current model is fine for people with large trucks that have ramps, but a smaller version would be nice for people that don't.

[Grant Rider]

I don't see debate here. What I see is an attempt at obfuscation, more Topsy the Elephant.

[Pascal Pincosy]

Honestly most of us are completely over the debate. We've been hearing it over and over for years now. Wayne says the push-pull reduces distortion. Tom says it's second harmonic distortion that doesn't sound bad. Wayne says the cooling plug is the best thing since sliced bread. Tom says it's only good for certain situations. No-one ever comes up with a new viewpoint or new facts. The same arguments go round and round. Everyone except for Wayne gets really annoyed. And then the whole argument starts over again a couple months later...  

[Mac Kerr]

Yeah, but what about that kick drum mic?  

Mac

[Grant Rider]

"Edison carried out a campaign to discourage the use of alternating current, including spreading information on fatal AC accidents, killing animals, and lobbying against the use of AC in state legislatures. Edison directed his technicians, primarily Arthur Kennelly and Harold P. Brown, to preside over several AC driven executions of animals, primarily stray cats and dogs, but also unwanted cattle and horses. Acting on these directives, there were demonstration to the press that alternating current was more dangerous than his system of direct current. Edison's series of animal executions peaked with the electrocution of Topsy the Elephant."

[Tom Danley]

Hi Grant

I have saw the video of Topsy once and I suppose reading this thread may feel a little like that, hopefully without all the smoke..
On the other hand, perhaps you were suggesting that all this is an effort to put out the flame of “push pull”?
You reference it twice anyway.

Here is the thing, you can’t make outrageous claims with out overwhelming evidence and be taken seriously scientifically.
To find how much difference really makes you need to compare results “with and without” where being “push pull” was the ONLY thing that was different.

Keep in mind too that the driver is not what most people would have thought to use in a horn at the time either but that drivers parameters with the right front and rear volumes and horn produces very low distortion anyway.
Comparing to other horn systems using other drivers isn’t telling you anything about push pull.

Unlike Topsy’s days, back at the frontiers of  high speed elephant BBQ, the idea of push pull is neither new or untried.  
Some people have used it, conceptually it sounds like a good idea so it is good marketing..
Loudspeaker drivers are simply not so chronically flawed that push pull performs some miracle over conventional mounting  and Wayne’s reported level of improvement (reducing all harmonic distortion components, not just the second) does not reflect the magnitude of what others have found or the math that describes the situation..

You can probably understand why I am skeptical and suggesting that he actually compare an identical horn with and with out push pull mounting as a way of determining just how big the effect is.  What he has is a really good horn driver for that frequency range and horn parameters that makes very low distortion anyway.
Best,
Tom