Perlisten D215s: Is This the Most Accurate Subwoofer on the Planet?

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cutedaddy

Audioholic Intern
What is not really clear from the explanation of the push pull alignment, is why one of the drivers should be facing 'inward' (cone facing into the cabinet). The air pressure utilised to moderate cone motion, where both drivers basically are connected by their shared air 'spring' (i suppose the sealed volume of this 'spring' needs to be twice what's recommended per single driver) does not explain the necessity of turning the driver (and its phase) around. Why would the working principle not apply if the drivers are in phase, both cones facing outward? Anyone?
 
ryanosaur

ryanosaur

Audioholic Overlord
What is not really clear from the explanation of the push pull alignment, is why one of the drivers should be facing 'inward' (cone facing into the cabinet). The air pressure utilised to moderate cone motion, where both drivers basically are connected by their shared air 'spring' (i suppose the sealed volume of this 'spring' needs to be twice what's recommended per single driver) does not explain the necessity of turning the driver (and its phase) around. Why would the working principle not apply if the drivers are in phase, both cones facing outward? Anyone?
I'm gonna take a stab at this in hopes I can be corrected and learn something from my mistake. :)

If I understand what is happening correctly with this design, one woofer is excusing outwards away from the motor while the second is excursing outwards towards the motor, and it would be in that action which the distortions of the drivers are minimized.

Anybody? Am I getting this? :)
 
C

cutedaddy

Audioholic Intern
Wait, Jeffca may have answered the question i just posted, although i'm not sure why facing both cones outward and connecting drivers in phase wouldn't also improve non-linearities. Supposedly, reading the assumptions of the technology, the non linearities are similar from one sample of the driver to the next (continuity in production is a must at this level) so wouldn't they cancel out, aligned back to back?

On another note, using one Hypex NCore amp per driver, the damping factor of those (around 13.000 !!!!!) would be a much cheaper way to keep the cone from performing any motion that is not in the signal. These amps just cancel out any non-linearity electronically: by inverting the signal (generated by the unsolicited cone movement) at the amp output. Total control of cone movement at around $ 1.000,= per 1.200W amp + 2.000W SMPS.

And these amps behave completely linear up to full power! So anyone will be hard pressed to want for more than 1.2K per driver (peaking 2K@20Hz). Just sayin..
 
C

cutedaddy

Audioholic Intern
I'm gonna take a stab at this in hopes I can be corrected and learn something from my mistake. :)

If I understand what is happening correctly with this design, one woofer is excusing outwards away from the motor while the second is excursing outwards towards the motor, and it would be in that action which the distortions of the drivers are minimized.

Anybody? Am I getting this? :)
That can't be right, the drivers would cancel out each other's SPL, the sub would hardly make any sound. Like the article says: the drivers are out of phase. Since they are also placed front to back, they are IN PHASE moving with respect to the cabinet.
 
ryanosaur

ryanosaur

Audioholic Overlord
That can't be right, the drivers would cancel out each other's SPL, the sub would hardly make any sound. Like the article says: the drivers are out of phase. Since they are also placed front to back, they are IN PHASE moving with respect to the cabinet.
Again, I could be completely wrong in my understanding, but Shady described the process a little in the review. Yes, there is still some confusion, and I'm not afraid to say I'm in that camp. ;)
But the driver orientation doesn't matter as long as both cones are traveling outwards (in relation to the cabinet) at the same time.
If the bottom cone was traveling inwards while the front cone was traveling outwards, then you would have cancelations.
 
NINaudio

NINaudio

Audioholic Samurai
My understanding is that the drivers do not have the same non-linearity issues in both movement directions. (this is something that is generally true of all drivers) By aligning them this way they are allowing those distortions to be minimized by having one move in it's favorable direction while the other moves in it's less favorable direction. Between that and the changing air volume in the enclosure this helps to minimize the distortions.
 
NINaudio

NINaudio

Audioholic Samurai
To quote the article:

"the non-linear motion that only occurs in one way of travel is mitigated by the other driver since motion is restricted by the increase in air pressure by the inward motion of each cone. In other words, the cones are coupled together by the constant level of air pressure inside the sealed cavity, so the motion of one of the cones in one direction is always modulated by the other cone’s opposite direction of travel. If the cone has uneven excursion with respect to inward and outward oscillation (as all drivers do to some extent), that is balanced out by the interior air pressure change created by the opposite motion by the other driver. This reduces even-order harmonic distortions which are created by nonlinear motion in just one direction of the cone’s travel. "
 
ski2xblack

ski2xblack

Audioholic Samurai
Why would the working principle not apply if the drivers are in phase, both cones facing outward? Anyone?
I have an old M&K pp sub that's still kicking. It's slumming it doing garage duty these days.

I think the low distortion is probably due to doubling of total driver surface as much as anything else. Two drivers move less than a single driver would to play the same freq at the same spl. Reduced cone motion equals lower distortion.

Conceptually, I have a tough time understanding why driver induced distortion would cancel, as opposed to sum, regardless of how the drivers are mounted. Are the distortion components of one driver's output completely and exactly out of phase with that of the other driver? I just don't know if such distortion components are that symmetrical on the out strroke vs the instroke of the drivers, which would need to be the case.

I suspect a sealed sub with both motor structures inside the box would perform similarly as one in/one out would. That's just a guess.
 
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shadyJ

Speaker of the House
Staff member
I have an old M&K pp sub that's still kicking. It's slumming it doing garage duty these days.

I think the low distortion is probably due to doubling of total driver surface as much as anything else. Two twelves move less than a single twelve would to play the same freq at the same spl. Reduced cone motion equals lower distortion.

Conceptually, I have a tough time understanding why driver induced distortion would cancel, as opposed to sum, regardless of how the drivers are mounted. Are the distortion components of one driver's output completely and exactly out of phase with that of the other driver? I just don't know if such distortion components are that symmetrical on the out strroke vs the instroke of the drivers, which would need to be the case.

I suspect a sealed sub with both motor structures inside the box would perform similarly as one in/one out would. That's just a guess.
The push-pull design really works to reduce distortion. Watne Parham did a comparison and found that push-pull resulted in a major reduction in even-order distortions. Furthermore, just look at the even-order distortion quantities in the D215s. As was said in the article, Perlisten found a 10 to 12dB reduction in even order distortions by using a push-pull design. You don't have to understand the principle, but you can't argue with the results.
 
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cutedaddy

Audioholic Intern
Lots of thoughts, but Shady J finally answers the question by reference to the Watne Parham explanation. THAT is why turning one of the drivers around makes sense. And for those in confusion: NO, the air pressure inside the chamber the drivers share is NOT constant, but, as could be expected, just functions as two sealed subs on one chamber. The air spring is used by both drivers at the same time and thus rises on inward travel and lowers on outward travel, aka basic acoustic suspension. Push-Pull is really about the orientation of the driver (and works only with paired identical drivers from an already very consistent production line). My questions answered, tx for alll the comments..
 
highfigh

highfigh

Seriously, I have no life.
View attachment 49654
First off, given the frequencies being covered, comb-filtering is not a issue since the room reflections and nodes do more to degrade the bass response than having subs spaced out in the room. When the frequencies get below 100Hz, you'd need a huge room for comb filtering to even begin to become a consideration. You might want to research that.

I have a modest, finished basement and 4 Rythmik 12" servo subs in it where I use them as speaker stands for the front L/R speakers. There's enough space to easily add 4 more subs in the rear. 4 subs, though, are enough to cause the concrete floor to vibrate while still playing very cleanly.

As to the weight issue, each of these Rythmik subs weighs in around 55 lbs. All together, they weigh just a hair more than the Perlisten sub. When I need to move them, I don't mind that.

They can easily make it to 20 Hz and, aggregately, do it as cleanly as the Perlisten sub.

As to cost, they, in total, are around $2,200. Adding 4 more would still come in less than half the cost of the reviewed sub and blow that thing away in a room or a lab. Also, the servo system really does it's bit to decrease distortion.

In the end, low bass reproduction comes down to the total radiating area of the drivers. More drivers means more radiating area (two 12" drivers = one 18"). It also means less distortion since the drivers need to work much less hard to reproduce the low frequencies.

Also, there is no woofer on the planet that can take much more than 800 Watts at a sustained level. Most consumer woofers top out around 400. Having 3.5kW driving 2 woofers is a gigantic waste of money. It's BS. It is, though, a great marketing ploy to get the ignorant to spend $9K on a sub (it costs more so it must be better!).

Again, not saying that the Perlisten isn't a great performing sub, but, it's too big, too heavy and too expensive for my tastes.

This is from a bass player and audio engineer.
Some good points, but even in relatively small rooms, the phase problems can easily be in the 60Hz-80Hz area, which is where mine were, due to the limitations on placement of my speakers.
 
C

cutedaddy

Audioholic Intern
I'm gonna take a stab at this in hopes I can be corrected and learn something from my mistake. :)

If I understand what is happening correctly with this design, one woofer is excusing outwards away from the motor while the second is excursing outwards towards the motor, and it would be in that action which the distortions of the drivers are minimized.

Anybody? Am I getting this? :)
So actually, in hindsight, that IS right. I just didn't read that correctly. Yes, one is moving outward away from the motor while the other is also moving outward, towards the motor. So moving in phase (with respect to the cabinet, the signal, the soundwave they produce) and out of phase with respect to the direction in which they're facing.

As Watne Parham explains, the assymmetry of the cone movement (different non-linearities on the inward excursion than on the outward excursion) are more or less evened out by making one's backward travel coincide with the other's forward travel and vice versa, with respect to the motor assembly.

So excuse me for interpreting your accurate comment incorrectly.
 
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cutedaddy

Audioholic Intern
The question that remains object of study in my mind is:

Why, how, and how much, would the 'RMS' of non linearities resulting from one forward and one backward movement (w/respect to motor assembly) of two cones, by two drivers simultaneously (and all this twice), be an improvement over the 'RMS' of non linearities of one backward and one forward movement of one cone of one single driver (and all that times two)?

Which is what you get when you just put two drivers facing outward, in phase, but sharing the sealed cabinet. So they still moderate each other through their common air spring, just not in push pull.

Do we know a researcher that did AB measurements for both alignments? In an otherwise identical cabinet? Or in two cabinets, where the one with push-pull has a smaller air chamber, as is mentioned in this thread somewhere? (Why would that be, btw?!). Did Perlisten publish anything on that? Any white papers anywhere?
 
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shadyJ

Speaker of the House
Staff member
The question that remains object of study in my mind is:

Why, how, and how much, would the 'RMS' of non linearities resulting from one forward and one backward movement (w/respect to motor assembly) of two cones, by two drivers simultaneously (and all this twice), be an improvement over the 'RMS' of non linearities of one backward and one forward movement of one cone of one single driver (and all that times two)?

Which is what you get when you just put two drivers facing outward, in phase, but sharing the sealed cabinet. So they still moderate each other through their common air spring, just not in push pull.

Do we know a researcher that did AB measurements for both alignments? In an otherwise identical cabinet? Or in two cabinets, where the one with push-pull has a smaller air chamber, as is mentioned in this thread somewhere? (Why would that be, btw?!). Did Perlisten publish anything on that? Any white papers anywhere?
Wayne Parham is the only one that published an actual comparison in this area. One thing Perlisten could do to compare is publish distortion measurements for their single 15" driver sub. If distortion is disproportionately low at -6dB max output versus the D215s, that should be good evidence of the push-pull advantage.
 
ski2xblack

ski2xblack

Audioholic Samurai
Can't argue against the cold, hard data (thanks for the links, guys!). It apparently works. I have enjoyed what it does in my old M&K sub for years.
 
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chuckychuck7

Audiophyte
FYI: The push-pull configuration was patented by Ken Kreisel in 1996 and used extensively in Miller & Kreisel (M&K) sub-woofers.

That is incorrect.

The patent's abstract says:

"A modification and addition to the prior art type of multiple driver push-pull loudspeaker system for subwoofer, bass, or lower midrange frequencies, which prior system is able to reduce the even-order push-pull out-of-phase driver-produced 2nd, 4th, etc. distortion harmonics by the order of 15 to 25 dB in the radiated sound waves."

"The present invention reduces the important remaining in-phase distortion harmonics using outputs of sensors mounted on the voice coils of each driver to generate electrical signals which are processed and used to substantially lower the remaining in-phase distortion with feedback through a single signal amplifier chain."

Source: https://portal.unifiedpatents.com/patents/patent/US-5537479-A

Therefore, the patent is for 'push pull configuration' and 'servo', not just 'push pull configuration', which was not invented by Kreisel/M&K.
 
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vpnogueira

Audiophyte
@james Larson, thanks for the review of the Perlisten D215s!
Since you have also heard the REL 25, could you compare these two subs? Which one do you prefer? I am considering purchasing either a pair of Perlisten D215s or a pair of REL 32 (similar to REL 25) for stereo music listening (I have a large room). Since I will not be able to compare them in my system prior to purchase, your feedback would be highly appreciated. Thanks.
 
ryanosaur

ryanosaur

Audioholic Overlord
@james Larson, thanks for the review of the Perlisten D215s!
Since you have also heard the REL 25, could you compare these two subs? Which one do you prefer? I am considering purchasing either a pair of Perlisten D215s or a pair of REL 32 (similar to REL 25) for stereo music listening (I have a large room). Since I will not be able to compare them in my system prior to purchase, your feedback would be highly appreciated. Thanks.
James is @shadyJ .
;)
 

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