Discussion: push pull design and minimal distortion does it matter ?

I was always under the impression that the lower you go the harder it is to hear distortion. Apparently a new range of subs is out which states otherwise. My thoughts are if you hear distortion at those frequencies you would hear "more" further up. Any thoughts on this?
 
Low end distortion will cause harmonic distortion further up the range. The degree depends on the driver, but push any driver hard enough and you will eventually begin to notice. Push pull helps reduce this, but does not completely remove it. The benefits though are only really going to be of benefit if you thrash your sub, and thats something I have tested myself. Unless I thrashed my PP design, the PP mechanic seemed to make no difference to audible sound quality. Perhaps if your going to use smaller more average drivers in a fairly compact cabinet, push pull is worth the difficulty in its implementation, otherwise I would say its not something you really need to be worrying about, unless your pushing your dual driver sub to the limit anyway.
 
masking is strong at frequencies above the masking tone - especially for low harmonics

so for not too unreasonable distortion level/profiles sub nonlinearity may not be intrusive

basically all of the in band product of a sub fits in the lowest critical band - our auditory system pretty much lumps it all together

voice coil heating "themal compression" however is a possible "in band" problem

other audible problems can be "non harmonic" noises like flow turbulence, rattles at much higher frequencies
 
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Nothing negates the PP design, if you want to take advantage of the benefits of it. Every driver distorts to varying degrees at varying levels, and the PP mechanic will help reduce the harmonic distortion present in any driver. The question really is, will you be pushing your sub hard enough for it to matter. Its like adding something to you car that will improve its handling over 150 mph, if you never hit those speeds, then is there really any benefit. For me personally, I used larger drivers, and employing push pull becomes quite a headache to put together when your trying to keep already larger cabinet sizes down, so I opt not to go PP. I did experiment with it to be sure though.

Shorting rings in a driver help to keep it cooler, so they are something desirable in a driver design, though it adds to cost and is something you generally see in more expensive models.
 
I was always under the impression that the lower you go the harder it is to hear distortion. Apparently a new range of subs is out which states otherwise. My thoughts are if you hear distortion at those frequencies you would hear "more" further up. Any thoughts on this?
Our hearing is less sensitive to low frequencies, low frequency distortion primarily consists of harmonics of the fundamental frequencies, where our ears are more sensitive.
For instance, the second harmonic of 30Hz is 60 Hz, 60Hz at 75 dB would sound as loud as 30 Hz at 90 dB. A harmonic only 15 dB down from the fundamental is about 18% distortion, when a sub is driven below Fb distortion can rise to 100% quite rapidly.

Push pull reduces even order harmonics, leaving odd order harmonics.
Even order harmonics are musical sounding, octaves of the fundamental.
Odd order harmonics often sound bad, as they change the nature of the music.

Reduction of even order harmonics while leaving odd order harmonics may subjectively sound worse, as I found out in this test:

http://www.diyaudio.com/forums/subwoofers/191833-push-pull-vs-normal-distortion-compared.html

Art Welter
 
The 3rd harmonic argument is specious.

The biggest drawbacks of my PPSL designs are:

1) Not all drivers are quiet enough from their back side to use (in which case all they need do is flip the reversed driver).

2) When an amplifier clips the speaker suddenly starts putting out obvious amounts of odd-harmonic distortion. Up to this point it is not obvious.

3) Some people like the thick, distorted sound (in which case all they need do is flip the reversed driver)

If you don't like the 'sound' of a servo sub (Infinity, Velodyne, etc.), you probably won't like a PPSL design.
 
The 3rd harmonic argument is specious.
Dennis,

Even order harmonics are octaves, always musically harmonious to the fundamental as recorded.

Odd order harmonics result in various musical chords, which may not be musically harmonious to the fundamentals as recorded.

Push-pull loading does not reduce odd order harmonics.

Slot loading (not mentioned in the OP which I responded to) does create a band pass, which reduces both even and odd order distortion.

If you think my statements are specious or fallacious, please explain why.

Art
 
Hi Y'all,

Even though it does not directly address the original question, it may be interesting to note that if you combine push-pull with the ACE BAss feedback concept (e.g.: Patent #4118600) you would get more than just 2nd order cancellation, and maybe that would be the way to go if you are really concerned about subwoofer distortion.

Regards,
 
Taking aside the 2nd harmonic cancellation of the sub box/driver design what if you power said sub design that has a amplifier power source that is maybe designed deliberately to re-inforce said 2nd order harmonics? Does this give you the perfect sub?
A "perfect" sub or sub amplifier would have no distortion.

An amplifier or speaker designed to increase harmonic content may be OK when used for a musical instrument. The Ampeg SVT, a 300 watt tube amp typically using 8 x 10" speakers sounds great for bass guitar, but I would not want to listen to it for low frequency reproduction.

There are effects such as MaxxBass that increase the even order harmonic content of low bass, giving a sonic illusion of the missing fundamental.
As they say at the midway, close but no cigar, after hearing real clean bass down in the 20-30 Hz range sonic illusions don't make the grade.

Art
 
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Better sounding than non push pull given the same design.
We are not comparing sealed, ported, tranny lines, that's a different can of worms.

In a single subwoofer, the upper harmonics are easier to hear as the loudness increases, simple harmonic distortion. Say you have 110db @ 80hz. A sealed non-push pull may be 90db or more at 160hz (it should be zero) while the push pull may be 20-40db lower. I'll have to dig to find the testing graphs.

The drivers' distortion is reduced.
Bass sounds more like organ bass instead of chunky distorted in your face bass.
I'd been told the cheaper the driver, the more the improvement.

But things like vent noise, a push pull cannot fix that.

Norman
 
Has anyone use this type of design in conjunction with Stahl's Ace Bass theory? I would imagine it would be pretty low on the distortion front?.


Hi hoppaz,

Nearly 40 years ago I designed and made quite a few ACE-bass based Subs using push -pull drivers, but today I think it's a moth-point:
There are many good drivers with sufficiently low distortion characteristics that when used at excursion levels with a margin lower than x-max performs blameless.

b :)
 

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