speakers, pmc

ATL™ is the proprietary use by PMC of a folded transmission line. Many other speaker brands have used transmission line loading of a speaker, but PMC lay claims of utilising it in a unique way for their speakers.

In general it's meant to produce the effect of having a bigger box, diffracting rear resonances, adding structural stiffness, lowering impedance ridges at crossover, keeping port output in phase to driver output and all other sorts of goodies.

thanks

Indeed, the transmission line has an effect similar to adding a third bass driver .. but doing this mechanically rather than electrically.. the length of the transmission line determines the bass frequency response.

Is it considered preferable to, say, the Isobarik principle?

Hi Loki. I don't know.. Huge might have a view on this...

Loki posted:

Is it considered preferable to, say, the Isobarik principle?

C'mon. If you ask PMC they will say yes. If you ask Linn they will say no and if you ask ProAc or Quad they will say something else.

It's a means to an end and the skill in engineering the implementation of these technologies means everything. I'm not sure how you would even devise a median standard for comparison. Best to have a listen to speakers in your price range that are known to satisfy any positioning restrictions you have and start with that irrespective of what technologies they use.

I've heard rear ported designs that work close to walls and sealed designs that need 3 feet of air behind them and vice versa. Make no assumptions.

FWIW I've used about every design under the sun and all I will say is transmission lines are easy to screw up. Isobariks are allegedly hard to design welk but Briks and Keltiks were outstanding with well controlled linear bass. I use Twenty5.23 now and love them. They are not very forgiving of room placement compared to older Twenty.23 though.

IMO FZ has it right on the money there.

wiwa posted:

I want by PMC twenty.5.23 speakers

but what is the meaning of "Effective ATL™ Length: 3m"

 

mvg

william

It means that the sound output from the TL port output will be delayed by 8.77ms + 180°.

(Sound travels 342m/s [@STP] hence 8.77ms delay; and the sound is sourced from the rear of the bass/mid cone hence starts 180° out of phase).

Huge posted:

wiwa posted:

I want by PMC twenty.5.23 speakers

but what is the meaning of "Effective ATL™ Length: 3m"

 

mvg

william

It means that the sound output from the TL port output will be delayed by 8.77ms + 180°.

(Sound travels 342m/s [@STP] hence 8.77ms delay; and the sound is sourced from the rear of the bass/mid cone hence starts 180° out of phase).

Yup. I beleive PMC accomodate for the the delay in the crossover in the Fact and pro audio range. As do most manufacturures to some degree since the stop point of most tweeters will be several cm forward of the stop point of LF drivers. In the Twenty/Twenty5 series, the 5 degree slant attempts to acheive this mechanically. It aligns the stop points of the HF and LF units leading to a simpler crossover. I am not sure if the slant completely compensates for the transmission line delay - I suppose if you are good with the math you could figure it out. However, sluggish is the last word anyone would use to describe PMC.

Though that might be the first word I'd use to describe some other transmission lines I've heard.

You can't compensate for TL delay in the crossover.

The TL port output of a TL of 3m effective length will always be 8.77ms + 180° after the forward output of the bass driver, no matter what changes you make electrically.

The slant compensates for the difference in the effective center of pressure of the bass/mid and HF drivers.  Nothing to do with the TL.

that does make sense.

 To my ears, TL designs  have produced the best sounding deep bass of anything I've heard (admittedly I haven't heard full bass loaded horns covering the bottom couple of octaves). So whilst there inevitably is a phase delay in TL designs with a bass output from the end of the line as Huge notes, to me it is a small price to pay for the good bass.

But there is a literal cost due to the complexity of the cabinet, both in terms of design R&D and construction cost.

wiwa posted:

I want by PMC twenty.5.23 speakers

but what is the meaning of "Effective ATL™ Length: 3m"

 

mvg

william

To understand if you need to read up transmission line loudspeaker theory, but in simple terms the line is 'tuned' to a particular frequency, related to the characteristics of the speaker drive unit, to minimise internal reflections back to the cone and in most designs also to augment output in the bottom octave or so utilising the sound from the rear of the driver. The 'tuning' is based on 1/4 wavelength, so taking the speed of sound to be about 340 m/s, 3m is about 28Hz, making it likely that the speaker will achieve output down to st least that frequency (though that alone doesn't tell you if the response will be flat down to there).

The PMC bass is good, and in my room the mid performance was fairly good too, however after extended listening to me the performance of the tweeter lets the twenty5 series down.. it's just not as refined or detailed as say the Neat, ATC, Kudos or Russel K tweeters.. once you appreciate and rely on clean extended hf, going back to something less capable or slightly less refined is difficult even if there are strengths elsewhere. It might be Electronics bandwidth related.. I found PMC sounding most obviously not right  on a Statement system, and less so, but still noticeably so  on my 252DR/250

Simon

Are you talking about the performance of the tweeter of the Twenty5 series or the Twenty series?

Sorry, I have been listening to the Twenty5 speakers. But I understand the tweeters are the same with the earlier series?

They are slightly different. I prefer the Twenty series tweeter.

According to PMC there are "refinements to its established Sonolex fabric dome tweeter to improve dispersion for a wider soundstage".

I think the dispersion is from the metal refraction grill over the front of the tweeter dome - can't see that would affect the performance of the tweeter per se - but what do I know.

I think that is indeed the result of the new refraction grill. But i have the impression that imaging with the Twenty series is better than with the Twenty5 series. I don't know if this is the result of the refraction grill or the (modified?) crossover.

It seems that indeed only the grill of the tweeter has been modified according to this info: "High frequency response from the already class-leading twenty series Sonolex™ fabric dome tweeter has been further refined through fine-tuning of the geometry and perforations of its mirror finished stainless steel grille, which improves dispersion for a wider soundstage."

This results in a wider soundstage but according to my experience imaging is worse than with the Twenty series.

Erwin posted:

I think that is indeed the result of the new refraction grill. But i have the impression that imaging with the Twenty series is better than with the Twenty5 series. I don't know if this is the result of the refraction grill or the (modified?) crossover.

I think this may be true. Having moved from Twenty.23 to Twenty5.23 to find how very different they are. Still waiting for replacements from the insurance company (they are on the way) but the current 25.23s are fairly well run in now.

Not sure if the effect is the mesh on the tweeter but more likely to be the new very sharp roll off on the crossover, but the 20.23 may just have edge in terms of smoothness. Of course the 25s have a much much larger soundstage, the 20s might be a little more precise and more forgiving.

I know what Simon means though. Some tradeoffs are hard to go back to. While I find the 20.23s better in terms of ease of placement, forgiving top end and so forth, I couldn't give up the amazing mid range on the 25.23s.

Simon-in-Suffolk posted:

 however after extended listening to me the performance of the tweeter lets the twenty5 series down.. it's just not as refined or detailed as say the Neat, ATC, Kudos or Russel K tweeters.. once you appreciate and rely on clean extended hf, going back to something less capable or slightly less refined is difficult

Simon

My feelings exactly, although I would also add the Proac and Dynaudio tweeter to the list, PMC, to me, have always had a strange offsetting sound that I just couldn't put my finger on.

They also seem that the price to sound quality was disproportionate.

badlands posted:

Simon-in-Suffolk posted:

 however after extended listening to me the performance of the tweeter lets the twenty5 series down.. it's just not as refined or detailed as say the Neat, ATC, Kudos or Russel K tweeters.. once you appreciate and rely on clean extended hf, going back to something less capable or slightly less refined is difficult

Simon

My feelings exactly, although I would also add the Proac and Dynaudio tweeter to the list, PMC, to me, have always had a strange offsetting sound that I just couldn't put my finger on.

They also seem that the price to sound quality was disproportionate.

It raises an interesting perspective. When choosing the original 20.23s I noted that they were good in all areas but other speakers beat them on performance for specific aspects. I absolutely did hear things that had clearer high frequencies, better low end, superior soundstaging, but not all in one package. Everything that excelled over the PMC in one area seemed to have some deficiency somewhere else. Ultimately what I found compelling about the original 20.23s wasn't the strengths but the distinct lack of any deficiencies making them a compelling all round package. I found that find a speaker that excelled over the 23s in any specific area AND was at least as good in the others required a quantum shift in budget (like 2-3 times more).

Not saying that is the correct approach. Certainly, I have friends who specifically place high frequency response as far more important and would suffer all manner of problems elsewhere as long as they attain the best performance in a specific area. That just isn't for me. This is about the selection process though rather than justifying the PMCs. Each persons's idea of correctness and what constitutes a defficiency differ.

FWIW, I still haven't quite found the right position for the 25.23s after many weeks. Though I am holding off really trying until the new pair arrives and I can get the resonant cartons from the damaged pair out of the room. One thing the 20.23s really have over the new 25.23s is that they were really undemanding and easy to keep happy. With greater capability comes more fussiness.