PMC Twenty.21 Bookshelf Speaker Review

[pozz]

These speakers, the Twenty.2* range, are new not something from "back then".
This performance is nothing even vaguely similar to what the BBC was producing or using.
I did not know PMC had supplied the BBC, or which department if they had, but I am 100% sure they never used anything like these.
Rogers produced several designs to BBC specs for years. They were nothing like this in design or performance.
@Pluto maybe knows where PMC may have been used in the BBC.
All BBC designs were ported except the LS3/5 and have been for over 50 years, nowt new there.

From Toole's book:

Both of the above are commercial models, while the below is pro:

They support your case although I wish we had measurements of those old PMC speakers or the bigger TL designs to compare.

 

[Xyrium]

I can't tell you how much I'm looking forward to this. ATC have had a high rep for nearly as long as the BBC "heritage" brands.

I owned both the SCM7 and SCM11 at one point in my quest. I was trying to integrate them with a pair of sealed 12" subs, and could never make it happen. Alone, the SCM7's were anemic, as expected. Unfortunately, the 11's weren't that much better. They were both very dry designs, though they never sounded harsh to my ears. Perhaps they were indeed flat, and their sealed design might assist with that, but they dropped off like a bomb at 200Hz, and my subs didn't play nicely that high. YMMV

I'm also surprised at the review of the SCM40's posted earlier. I was under the impression that anyone could time align speakers now. It's sad to see that ATC isn't doing it.

They sure market the crap out of their in-house drivers though...

 

[AudioSceptic]

These speakers, the Twenty.2* range, are new not something from "back then".
This performance is nothing even vaguely similar to what the BBC was producing or using.
I did not know PMC had supplied the BBC, or which department if they had, but I am 100% sure they never used anything like these.
Rogers produced several designs to BBC specs for years. They were nothing like this in design or performance.
@Pluto maybe knows where PMC may have been used in the BBC.
All BBC designs were ported except the LS3/5 and have been for over 50 years, nowt new there.

And, BBC designs from 50 years ago probably sound better and have a flatter response than this PMC.

 

[AudioSceptic]

I must say that this is no surprise to me. I listened to a pair a few years ago and the first failure of the speakers was to have no relationship between the bass and rest of the music, they sounded like the the mids upwards were from a transistor radio and the bass from a car audio system parked outside the shop.

It was recently mentioned to me that PMC speakers have crossovers with s***loads of components to try to correct for their shortcomings, dunno if this is the case or whether it has a bearing on the measurements.

If I see transmission line port on speakers now my ears have a Pavlovian response and fold over.

Thanks for that great description. I heard some PMCs briefly in the mid-90s (I think) and found the sound really odd, but I couldn't really say why. You've got it I think!

I don't think PMC actually know how a TL is supposed to work. Hear some IMFs or TDLs before you dismiss the concept forever.

 

[Vindermere]

PMC is not in the same league that ATC. If you compare the measurements of the ATC SCM7v3 with the twenty 5. 21 (entry level of both brands), you see the first one benefits from a serious engineering :
https://www.stereophile.com/images/214ASCM7fig4.jpg

https://www.stereophile.com/content/atv-scm7-v3-loudspeaker-measurements

 

[Soniclife]

Again, as always, I just don't understand why the professional market is in on this whole atmosphere of not knowing what they're buying.

Remember that in the pro world they use extensive room treatment and EQ, if done correctly frequency response isn't anything like as important. But given the output from so many is so low there is little evidence they know what they are doing.

 

[Pluto]

@Pluto maybe knows where PMC may have been used in the BBC.

The only significant use of PMC monitors within the BBC is/was, to my knowledge, within music studios specializing in the “pop”* genre where illegally high sound levels were sought; typically their “BB” product. I know of no other general use of PMC speakers with the Corporation although different models will be found here and there for, presumably, specialized purposes.

The general view within the “trade” is that their truly pro. speakers are excellent but the domestic line is mediocre, a fact that is sadly true of many professional audio manufacturers who have ventured into audiopile territory with a product line that lacks the design and execution excellence of the professional range but relies upon the name in order to sell the product.

Pete Thomas was (mainly) a maintenance engineer at BBC Maida Vale where, back in the day, most of the in-house music for radio was done. The original BB speaker was designed for MV4, the main purpose-built rock’n’roll studio within the facility.

*How else does one generically describe music this isn't “classical”? How does one generically describe “classical” music correctly?

 

[AudioSceptic]

I first heard PMCs at the BBC Maida Vale studios, (BB5 I think they were, with XBD bass extenders) where they had been installed to replace the KEF KM1s. I subsequently heard the larger PMCs at other studios, and always thought them very nice indeed.

On the other hand, I've not been a fan of their consumer models, always found them a bit 'boom&tizz'.

The larger PMCs use 'proper' Transmission Line loading, by which I mean they have to have long line, and therefore are big. Small TLs just don't work, Those of us of a certain age may remember IMF loudspeakers, which also used TL bass loading. The smallest which had a 'proper' TL was the TLS50, the smaller ALS40 had what IMF called an 'active' line by putting a driven cone where the vent would be (not totally successfully) as the box was too small for a full TL.

A proper TL absorbs ALL the rear radiation so doesn't need a vent, but needs to be infinitely long, so all practical TLs are a compromise, the larger the box the less the compromise. B&W's Nautilus used a spiral TL, which was long enough and tapered enough not to need a vent, but that was very large and very expensive.

S.

It's a relief to hear that the pro models are nothing like the consumer ones, and thanks for the description of how a TL is supposed to work. I think even the biggest IMFs and TDLs still needed a port, but very little came out of it because so much had already been absorbed by the TL (you still needed the port to avoid reflections back up the line).

 

[raindance]

Now we know what "Detailed" "transparent" "airy" "revealing" all mean in subjective reviews.

Hahahaha!!! I love it, Amir.

 

[Colonel7]

Y'know, my Klipsch R-41MP may be really lame, but,
View attachment 71282
They're not 2 grand lame B)
View attachment 71283

And I doubt the .21s go on sale for $99 a pair for Costco members

 

[AudioSceptic]

One Harbeth has been tested: https://www.audiosciencereview.com/forum/index.php?threads/harbeth-monitor-30-speaker-review.11108/

Somehow I missed that one. I confess I've never heard a Harbeth but get the feeling that the LS3/5a-sized ones are probably the best.

 

[AudioSceptic]

Isn't the Nautilus bass "snail" closed and continuously reducing its cross section for absorption?

Also Vivid Audio calls their constructions "Exponentially Tapered Tube enhanced bass reflex", in the end often mixed bass enclosure design form are used like also the tapered quarter-wave pipe.

Yes, the Nautilus's TL is long enough for that to work. Any shorter and it would need an opening/vent to avoid reflection back up the line.

 

[tonapo]

I would be interested to see if the following speaker iterations actually changed anything or not, the Twenty5 21, and the recent Twenty5 21i. Or perhaps going up the range, the bigger standmount Twenty5 22 before coming to the 23, which is the floormount. Thought provoking as ever!

 

[Kal Rubinson]

I feel a apology on behalf of my nation is in order ..,

No need. Compared to the PMC, my much less expensive Monitor Audio ".....Silver 8s provided more energy in the lower frequencies, achieving what seemed to me a more natural balance. " Confirmed by the measurements, of course.

 

[Kal Rubinson]

Not that the Pro-series is likely to be much better (JA measured the IB-1S here) but why would any pro worthy of his badge mix with a domestic-series toy-sized speakers anyway?

Yes, they had many similar characteristics.

 

[AudioSceptic]

I owned both the SCM7 and SCM11 at one point in my quest. I was trying to integrate them with a pair of sealed 12" subs, and could never make it happen. Alone, the SCM7's were anemic, as expected. Unfortunately, the 11's weren't that much better. They were both very dry designs, though they never sounded harsh to my ears. Perhaps they were indeed flat, and their sealed design might assist with that, but they dropped off like a bomb at 200Hz, and my subs didn't play nicely that high. YMMV

I'm also surprised at the review of the SCM40's posted earlier. I was under the impression that anyone could time align speakers now. It's sad to see that ATC isn't doing it.

They sure market the crap out of their in-house drivers though...

Interesting that the small ones can't really be used on their own. As for the in-house drivers, I would market the crap out of them too, when so many speaker makers are just stuffing boxes with drivers made by someone else.;-)

 

[Ron Texas]

How does this company stay in business?

 

[sergeauckland]

Isn't the Nautilus bass "snail" closed and continuously reducing its cross section for absorption?

Also Vivid Audio calls their constructions "Exponentially Tapered Tube enhanced bass reflex", in the end often mixed bass enclosure design form are used like also the tapered quarter-wave pipe.

Yes, the B&W Nautilus was closed at the end, being long enough and tapered so that any possible reflection back up the line was so weak by the time it got to the top that it had insufficient energy to colour the sound. Shorter and less tapered lines still have sufficient energy that if unvented, that energy would go back up the line and colour what's coming out of the driver and delayed in time. For short lines, like 1/4wave, that energy coming out of the vent can help hold up the bass, but then it isn't a true Transmission Line.

The main difference between a bass reflex and a Transmission Line is that the BR is tuned such that at the resonant frequency it has a phase inversion that adds to the main driver output, and whilst a TL is untuned, and shouldn't add at all but in practice does, so the length of the line is arranged so that it does. The bigger the loudspeaker, the longer the line can be so the less any vent actually does.

S.

 

[Kal Rubinson]

Real transmission line speakers have been around for 50+ years. The first I heard were IMFs.
The problem isn't that they don't work but that they are much more expensive to make. The B&W Nautilus has one and the top Vivid models all do.
I guess PMC have a "transmission line" in this model is that they have rather hung their hat on the transmission line is better peg whereas only their big pro monitors probably have a proper one.

Hmm. One thing that characterized the IMF (and the Radford/Bailey) was that there was a relatively large volume space directly behind the driver and before the entry to the line. Also, the entry to the line was at least as large in area as that of the driver. The line tapered smoothly from there. IMHO, none of PMCs cabinets are big enough to do that.

Nice to see you mention IMF there. Did you also ever hear any models by TDL, who carried on the IMF tradition for a while?

Yes and I built a few.

In comparison, it looks like PMC don't even understand how a transmission line is supposed to work.

See above.

 

[Deleted member 65]

I first heard PMCs at the BBC Maida Vale studios, (BB5 I think they were, with XBD bass extenders) where they had been installed to replace the KEF KM1s. I subsequently heard the larger PMCs at other studios, and always thought them very nice indeed.

On the other hand, I've not been a fan of their consumer models, always found them a bit 'boom&tizz'.

The larger PMCs use 'proper' Transmission Line loading, by which I mean they have to have long line, and therefore are big. Small TLs just don't work, Those of us of a certain age may remember IMF loudspeakers, which also used TL bass loading. The smallest which had a 'proper' TL was the TLS50, the smaller ALS40 had what IMF called an 'active' line by putting a driven cone where the vent would be (not totally successfully) as the box was too small for a full TL.

A proper TL absorbs ALL the rear radiation so doesn't need a vent, but needs to be infinitely long, so all practical TLs are a compromise, the larger the box the less the compromise. B&W's Nautilus used a spiral TL, which was long enough and tapered enough not to need a vent, but that was very large and very expensive.

S.

Had these in the 70’s driven by GAS Thaedra & Ampzilla, great combo.