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Old 11th November 2012, 10:04 PM   #1
hoppaz is offline hoppaz  United Kingdom
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Default 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?
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Old 11th November 2012, 10:11 PM   #2
Moonfly is offline Moonfly  Spain
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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.
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Old 11th November 2012, 10:14 PM   #3
hoppaz is offline hoppaz  United Kingdom
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Thanks so shortening rings are not something that negates the push pull design
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Old 11th November 2012, 10:25 PM   #4
jcx is online now jcx  United States
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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

Last edited by jcx; 11th November 2012 at 10:31 PM.
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Old 11th November 2012, 10:26 PM   #5
Moonfly is offline Moonfly  Spain
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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.
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Old 12th November 2012, 06:11 PM   #6
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Quote:
Originally Posted by hoppaz View Post
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:

Push Pull vs Normal Distortion Compared

Art Welter
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Old 12th November 2012, 06:47 PM   #7
djk is offline djk
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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.
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Old 12th November 2012, 07:22 PM   #8
hoppaz is offline hoppaz  United Kingdom
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Thanks for the response guys
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Old 12th November 2012, 07:27 PM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by hoppaz View Post
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.
Hi, the statement is wrong and is some form of marketing BS, rgds, sreten.
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Old 12th November 2012, 07:30 PM   #10
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Quote:
Originally Posted by djk View Post
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
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