PMC Twenty.21 Bookshelf Speaker Review

[tuga]

C'mon man! I'm genuinely curious...clue me in because I'm missing something. lol

I had always wondered why the spectrum had that tilt from bass to treble and it was fun to learn it followed the spectrum of white pink noise.
I posted those two examples to illustrate infinitesymphony's.

If I'm not mistaken the classical music example shows some roll-off above 2kHz because instruments are mic'ed more distantly.

 

[infinitesymphony]

I had always wondered why the spectrum had that tilt from bass to treble and it was fun to learn it followed the spectrum of white noise.
I posted those two examples to illustrate infinitesymphony's.

If I'm not mistaken the classical music example shows some roll-off above 2kHz because instruments are mic'ed more distantly.

*Pink noise has the slope (-3 dB/octave), white noise has a flat power spectrum (link: colors of noise).

Low frequencies lose less energy over distance, which means acoustic sounds in a large enough room will have a natural high-frequency rolloff. The frequency spectrum of an orchestra playing in a hall is the perfect example of a flat recording chain producing a slope similar to the pink noise curve due to energy dissipation.

 

[Pharos]

To assert that a loudspeaker should have an HF roll-off in a replay room because that room absorbs HF, is a non sequitur.
If a flat response is required, and the replay room is absorbent, a boost is required to correct that.

I think we need a standard for control rooms which is similar to a nominally average home listening room, and of course, very accurate monitors in that control room, only then can we attempt to replicate what the sound engineers have created - if our equipment is good enough that is.

A few years ago I came across an article which asserted that a flat mono speaker would, if used in stereo, result in an increase in overall HF energy.

There was also a few months ago on diyaudio, a discussion on the BBC dip, which veered into the point being discussed here.
One contributor, Soundbloke, referred to AES papers, out of my reach, asserting that a speaker should have a downward slope, and he referred to partials.

 

[TimVG]

I think we need a standard for control rooms which is similar to a nominally average home listening room, and of course, very accurate monitors in that control room, only then can we attempt to replicate what the sound engineers have created - if our equipment is good enough that is.

The EBU standard is a good starting point

https://tech.ebu.ch/docs/tech/tech3276.pdf

 

[itsikhefez]

Just putting this here:

 

[amirm]

To assert that a loudspeaker should have an HF roll-off in a replay room because that room absorbs HF, is a non sequitur.

No one is saying there should be such a speaker.

The tilt shows up when *you* measure a speaker in a room. Side reflections tend to have less high frequency energy because the highs are more directional. And, there is high frequency absorption in the room. Combine these two an you measure a titled down response. Not because someone designed a speaker with on-axis that tilts down.

 

[Pharos]

That was what I had always thought, but have been criticised for, and on the diyaudio forum was 'set upon' by a group of well qualified people in a concerted effort to annihilate this view, especially one called "Soundbloke".

But some speakers do seem to have a deliberately tilted down response.

 

[Spocko]

Looks like when paying above $3,000, Genelec and JBL are one of the few premium "PRO" speakers that excels in all measures while sounding great. Looking forward to Focal's active Trio series to come in for measurements.

 

[thewas]

Looking forward to Focal's active Trio series to come in for measurements.

Some detailed measurements of the (admittedly not disapointing) Focal Trio11 Be:
https://www.soundandrecording.de/equipment/focal-trio11-be-−-midfield-monitor-im-test/

 

[tuga]

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.

The Rogers LS5/9 measured in 1986 by Hi-Fi News:

 

[Listen first]

You make an interesting point. All things being equal a flat response from a hifi loudspeaker is ideal. However all things are rarely equal. For example the whole idea of having a flat loudspeaker is so that all the frequency bands are reproduced at the same amplitude. So that the loudspeaker isnt adding any tonality. This works fine as long as the content was mixed in the same conditions. Flat studio monitoring system, mix level and playback level the same and the studio engineer has shaped their mix to allow for human hearing sensitivity vs frequency changes. Studio monitors that were often preferred by mix engineers who mix classical music usually had a bass tilt IE more energy at lower frequencies. This was preferred as it gave a closer representation to what they heard when they listened to an orchestra acoustically in a concert hall. IE boundary proximity LF coupling, and increase in reverberation time at low frequencies. So to choose the ideal frequency response for a home listening loudspeaker we need to consider the content, how it was mixed, mix level vs playback level, the acoustics of the listening environment as well as the frequency response of the loudspeaker system. Lots of variables which make it difficult to say that a flat frequency response is correct for every situation. I have done quite a few listening tests where we tune a loudspeaker to have a bass rise and then create a variant which is flat. With level matched listening comparison the majority prefer the one that inst flat for music playback, but prefer the flat response for speech. I can only conclude that they prefer the bass rise as the musical content was mixed on a speaker system that had a similar bass rise and the flat tuning is too lean. Lots of musical genres depend on significant levels of bass and when that is taken away the sound falls apart. So yes you do have to judge a loudspeakers system performance on what you hear at the listening position rather than what you see on an analyser, although a good measurement system is a great tool for getting the response to where it needs to be for the particular application.

That would make no sense to me, because you hear everything with the those dips. So if you hear a real non-recorded sound you hear it with those dips, and to create that with a loudspeaker you would need a perfectly flat response to reproduce it exactly the same. It wont ever be exactly the same, because the transducer is different....but it most definitely wont even be the same if the response is not flat. Maybe my train of thought is wrong though...

a

 

[Deleted member 16502]

Well. Maybe records should then come with their individual set of matching speakers where the faults in the frequency response the master engineer heard are correctly reproduced

 

[Southall-1998]

Not the same PMC though -

S.

 

[MattHooper]

It seems to me that Steve G. has swallowed the "it's made by a company that does pro monitors, so it must be a neutral, truthful speaker" line.
And so when he talks about the speakers showing how horrible many tracks sound, he's presuming it's telling him the "truth" about those tracks, rather than it being the result of a wonky frequency response that exacerbates highs and "detail."

 

[amirm]

Not the same PMC though -

S.

He is such a schmuck. Holds the soundtrack of movie Sneakers with Robert Redford and says it wasn't a good movie! Them are fight words!!! Sneakers is a great, great, entertaining and smart movie. Much more watchable than anything Steve produces.

 

[Pepperjack]

Well. Maybe records should then come with their individual set of matching speakers where the faults in the frequency response the master engineer heard are correctly reproduced

Now your going to far. All we need is an embedded file of the frequency response at the original mixing point and a graph of the ear capability of the mixer , an upload of our personal ears frequency response reception capabilities and an upload of the graph at your listening position and then let the system match it up, no? Easy peasy.

 

[Kal Rubinson]

It seems to me that Steve G. has swallowed the "it's made by a company that does pro monitors, so it must be a neutral, truthful speaker" line.

I don't think that neutrality is one of his standards anyway.

 

[MattHooper]

I don't think that neutrality is one of his standards anyway.

Definitely not. Which is maybe why he would misidentify it ;-)

 

[tuga]

So yes you do have to judge a loudspeakers system performance on what you hear at the listening position rather than what you see on an analyser, although a good measurement system is a great tool for getting the response to where it needs to be for the particular application.

What is the chance of a speaker which doesn't produce a flat anechoic frequency response on-axis ever doing it in-room at the listening spot?

 

[tuga]

German Stereo has tested one of the really large ones (MB2 XBD SE):

https://www.stereo.de/hifi-test/produkt/pmc-mb2-xbd-se-1514

Low-frequency extension (-3dBSPL): 22 Hz
Harmonic Distortion: 63 HZ - 0,3% ; 3 kHZ - 0,03% ; 10k Hz - 0,03 %