PMC... are they that good?

[insider9]

Could anyone explain to me what the PMC sound is all about, please. I hear so much good about them. I was considering getting a pair of PMC GB1 for my Naim system. Heard it's a good combo and would benefit from more power to get the full benefit of my speakers as Naim is only 50Wpc.

But after looking at measurements I have serious doubts. I then looked at another random pair from same source SoundStage! and they share some similarities.

Sources are here if you want to look at all the measurements GB1 and Twenty.24

Do all of the reasonably priced models have a gaping hole in bass? I thought they were famous for their bass...

PMC GB1

PMC twenty.24

As a comparioson non smoothed and in room measurements (as opposed to anechoic chamber and non specified smoothing above) of my Jamo speakers (run by a modest Sony STR-DB930 and a Yamaha WXC-50 as a source)

Website won't allow me to paste the picture from Flickr, which is available to view - here

 

[QuestForThe13thNote]

Could anyone explain to me what the PMC sound is all about, please. I hear so much good about them. I was considering getting a pair of PMC GB1 for my Naim system. Heard it's a good combo and would benefit from more power to get the full benefit of my speakers as Naim is only 50Wpc.

But after looking at measurements I have serious doubts. I then looked at another random pair from same source SoundStage! and they share some similarities.

Sources are here if you want to look at all the measurements GB1 and Twenty.24

Do all of the reasonably priced models have a gaping hole in bass? I thought they were famous for their bass...

PMC GB1

PMC twenty.24

As a comparioson non smoothed and in room measurements (as opposed to anechoic chamber and non specified smoothing above) of my Jamo speakers (run by a modest Sony STR-DB930 and a Yamaha WXC-50 as a source)

Website won't allow me to paste the picture from Flickr, which is available to view - here

PMC are all about mixing the bass with treble and mid range and achieving a really good balance. Ie meshing the bass with the other elements and coming out well. Also low levels of distortion with the transmission line used in all their speakers. These are the virtues the mags go on about the most and i think it's true too. Im on my second pair. First twenty 23 , now twenty5 23

Also you get good levels of detail, and they are also known for their dynamics I'd say. The twenty5 series are rated in this regard by the reviews.

If you are going for the speaker you mention, id instead try and listen to a twenty 23 or 24. I'd say this as I've heard many people comment, who have owned older pmc's and then the twenties, that the twenty series is better Some dealers sell them in the graphite finish (but I think you'd have to look hard as almost all have the latest 25 series speaker as demo sets, unsurprising due to price hike between 20 to 25) . Pmc stopped making the wooden veneers of the twenty series when the twenty5 series came out. No doubt due to production constraints and to concentrate on a new model.

when pmc introduced the twenty5 series you got better midrange and lower beefier bass, but also better dynamics. These are the obvious plus points over the 20 series.

but I tried many brands of speakers at the same price when I bought my 20 speakers from pro ac, kef, spendor, atc, rega, and totem, and the pmc's were easily the best balanced speakers

Since I've taken the time to give feedback (and will happily give more) can you explain to me exactly how those graphs are measured, how the plots are joined up, and whether it's possible to predict sound from a plot. I must admit I have limited knowledge of what these are meant to show as I just listen. But how come the spikes etc, do you think. But I must say I'm very dubious at how it's ever possible to predict sound quality from such a graph, but I don't doubt it can help show some things or not e.g. Where bass trails off etc. But If it's about the depth of bass but not about balance, I'm pretty sure that graph won't tell you anything. I stand corrected if I'm wrong though.

 

[Pedro]

You were asking for it, Insider...

 

[lindsayt]

Looking at the Sterophile measurements for the PMC DB1i shows a similar suck-out at 200 hz:

Looking at their chart of the individual drivers plus transmission line shows:

On the face of it, the most obvious explanation is that at the 1 metre measuring distance the transmission line is out of phase with the mid-bass unit at 200hz. And at 120 hz it's more in phase.

As for how this translates into how they sound, the best way to explain is to get the PMC's in a comparative demo with other speakers insider9. Please feel free to arrange one and I'll be happy to bring some "other" speakers.

 

[QuestForThe13thNote]

I've often wondered why they quote those graphs in a mag. I suspect in most respects to gauging sound quality and what a speaker will sound like, as useful as an ashtray on a motorbike or as welcome as a fart in a space suit.

 

[insider9]

PMC are all about mixing the bass with treble and mid range and achieving a really good balance. Ie meshing the bass with the other elements and coming out well. Also low levels of distortion with the transmission line used in all their speakers. These are the virtues the mags go on about the most and i think it's true too. Im on my second pair. First twenty 23 , now twenty5 23

Looking at distortion graphs at SoundStage! for GB1 again I'm not convinced. In fact rather shocked by that one. Close to 4% THD at 1kHz. That's nasty! 9% at 100Hz, dear me...

Then again twenty.24

3% THD at around 8kHz...

Have a look compared to my Jamos in room distortion. Be mindful that it was done on the end of an amp which costs circa £50 second hand. So with better electronics it could be even better.

My THD hardly ever goes above 1% from 33Hz all the way up! They're around 2% THD when they start to roll off at 27Hz.

Measurements can be found - here

If you are going for the speaker you mention, id instead try and listen to a twenty 23 or 24. I'd say this as I've heard many people comment, who have owned older pmc's and then the twenties, that the twenty series is better Some dealers sell them in the graphite finish (but I think you'd have to look hard as almost all have the latest 25 series speaker as demo sets, unsurprising due to price hike between 20 to 25) .

If you can find any twenty series under £500 I would be interested.

Since I've taken the time to give feedback (and will happily give more) can you explain to me exactly how those graphs are measured, how the plots are joined up, and whether it's possible to predict sound from a plot. I must admit I have limited knowledge of what these are meant to show as I just listen. But how come the spikes etc, do you think. But I must say I'm very dubious at how it's ever possible to predict sound quality from such a graph, but I don't doubt it can help show some things or not e.g. Where bass trails off etc.

Well, I don't intend to write a book about it It is a big subject but I'll do my best. Graphs are as described Y axis is SPL (volume if you like) X axis frequency. The plots are not joined up. SoundStage! measurements show 3 measurements (Top curve: on-axis response, Middle curve: 15 degrees off-axis response, Bottom curve: 30 degrees off-axis response).

Spikes are very normal and most measuements you see posted on the internet have smoothing applied to them. See the same measurements of my speakers below

No smoothing (posted in #1) - here

1/24 octave smoothing - here

1/6 octave smoothing - here

I don't know what level of smoothing was used for SoundStage! measurements.

Regardless the measurements are taken with a calibrated measurements microphone. Measuring a frequency sweep. My measurements should show massive deficiencies vs theirs as I don't own a anechoic chamber. That's what bother me. On paper my speakers measure better. Would they sound better also I don't know but would rather not spend £500 for a speaker that is less than what I have.

As to if it's possible to predict the sound? It's not only possible to tell certain things about the sound from measurments (depending what you're looking at). You can definitely tell the balance of the speakers (warm, neutral, bright) you can definitely tell issues you might have with a speakers. That especially with GB1 are a plenty.

Looking at the both PMC graphs there's about 10dB difference between 100Hz and 150/180Hz. That's twice as loud. From 150Hz to 100Hz with GB1.

But If it's about the depth of bass but not about balance, I'm pretty sure that graph won't tell you anything. I stand corrected if I'm wrong though.

Very wrong indeed on this one. Unfortunately

 

[insider9]

Looking at the Sterophile measurements for the PMC DB1i shows a similar suck-out at 200 hz:

Looking at their chart of the individual drivers plus transmission line shows:

On the face of it, the most obvious explanation is that at the 1 metre measuring distance the transmission line is out of phase with the mid-bass unit at 200hz. And at 120 hz it's more in phase.

SoundStage! measurements are taken at 2 m. But I take your point it could be phase, which would make sense.

As for how this translates into how they sound, the best way to explain is to get the PMC's in a comparative demo with other speakers insider9. Please feel free to arrange one and I'll be happy to bring some "other" speakers.

That would be great

Please feel free to suggest an alternative to PMC to be driven by Naim Nait 5i-2. I am quite fond of the amp.

 

[insider9]

I've often wondered why they quote those graphs in a mag. I suspect in most respects to gauging sound quality and what a speaker will sound like, as useful as an ashtray on a motorbike or as welcome as a fart in a space suit.

How did you get to that conclusion? You said earlier...

I must admit I have limited knowledge of what these are meant to show

 

[insider9]

You were asking for it, Insider...

I don't know what you mean... *pardon*

 

[lindsayt]

Speakers are a highly personal choice. More so than any other hi-fi component.

The sort of speakers that I like are probably the sort of speakers you'd hate. Looks, age, size.

However it's sometimes useful to do comparative auditions against speakers that you'd have no intention of buying to highlight the relative sonic strengths and weaknesses of speakers that you would consider buying.

 

[insider9]

Speakers are a highly personal choice. More so than any other hi-fi component.

The sort of speakers that I like are probably the sort of speakers you'd hate. Looks, age, size.

However it's sometimes useful to do comparative auditions against speakers that you'd have no intention of buying to highlight the relative sonic strengths and weaknesses of speakers that you would consider buying.

Not so sure I'm using 1989 "ugly" Jamo's I'd love to hear your EVs

 

[lindsayt]

Please PM me via one of the other UK based hi-fi forums and we'll see what can be arranged, insider9.

 

[insider9]

Please PM me via one of the other UK based hi-fi forums and we'll see what can be arranged, insider9.

Edit:
Will do, thank you!

 

[ellisdj]

Could it poor on axis response to give a better power repsonse? I dont know how you measure power response but thats a big thing Harman push.

i.e. its all good having a smooth and flat on axis but the power repsonse can be all over the place from the same speaker

 

[ellisdj]

LindsayT Insider is going to want to measure your big bad boys to check THD etc. Be very interesting see how well they measure

 

[QuestForThe13thNote]

PMC are all about mixing the bass with treble and mid range and achieving a really good balance. Ie meshing the bass with the other elements and coming out well. Also low levels of distortion with the transmission line used in all their speakers. These are the virtues the mags go on about the most and i think it's true too. Im on my second pair. First twenty 23 , now twenty5 23

Looking at distortion graphs at SoundStage! for GB1 again I'm not convinced. In fact rather shocked by that one. Close to 4% THD at 1kHz. That's nasty! 9% at 100Hz, dear me...

Then again twenty.24

3% THD at around 8kHz...

Have a look compared to my Jamos in room distortion. Be mindful that it was done on the end of an amp which costs circa £50 second hand. So with better electronics it could be even better.

My THD hardly ever goes above 1% from 33Hz all the way up! They're around 2% THD when they start to roll off at 27Hz.

Measurements can be found - here

If you are going for the speaker you mention, id instead try and listen to a twenty 23 or 24. I'd say this as I've heard many people comment, who have owned older pmc's and then the twenties, that the twenty series is better Some dealers sell them in the graphite finish (but I think you'd have to look hard as almost all have the latest 25 series speaker as demo sets, unsurprising due to price hike between 20 to 25) .

If you can find any twenty series under £500 I would be interested.

Since I've taken the time to give feedback (and will happily give more) can you explain to me exactly how those graphs are measured, how the plots are joined up, and whether it's possible to predict sound from a plot. I must admit I have limited knowledge of what these are meant to show as I just listen. But how come the spikes etc, do you think. But I must say I'm very dubious at how it's ever possible to predict sound quality from such a graph, but I don't doubt it can help show some things or not e.g. Where bass trails off etc.

Well, I don't intend to write a book about it It is a big subject but I'll do my best. Graphs are as described Y axis is SPL (volume if you like) X axis frequency. The plots are not joined up. SoundStage! measurements show 3 measurements (Top curve: on-axis response, Middle curve: 15 degrees off-axis response, Bottom curve: 30 degrees off-axis response).

Spikes are very normal and most measuements you see posted on the internet have smoothing applied to them. See the same measurements of my speakers below

No smoothing (posted in #1) - here

1/24 octave smoothing - here

1/6 octave smoothing - here

I don't know what level of smoothing was used for SoundStage! measurements.

Regardless the measurements are taken with a calibrated measurements microphone. Measuring a frequency sweep. My measurements should show massive deficiencies vs theirs as I don't own a anechoic chamber. That's what bother me. On paper my speakers measure better. Would they sound better also I don't know but would rather not spend £500 for a speaker that is less than what I have.

As to if it's possible to predict the sound? It's not only possible to tell certain things about the sound from measurments (depending what you're looking at). You can definitely tell the balance of the speakers (warm, neutral, bright) you can definitely tell issues you might have with a speakers. That especially with GB1 are a plenty.

Looking at the both PMC graphs there's about 10dB difference between 100Hz and 150/180Hz. That's twice as loud. From 150Hz to 100Hz with GB1.

But If it's about the depth of bass but not about balance, I'm pretty sure that graph won't tell you anything. I stand corrected if I'm wrong though.

Very wrong indeed on this one. Unfortunately

What you are telling me is distortion at various frequencies. Right? Where is that in the graph ?But even if there are measurements less favourable than a cheaper speaker, the measurements might be low comparatively to other speakers higher distortion.

Another thing is that if you measure the bass at the woofer, wouldn't it be low on a pmc, since the microphone isn't at the lower transmission line port, where the lowest frequencies emanate. How would the microphones sync in with one another to reflect correct results. Can I ask where you got the pmc graphs from?

I bet the number of variables to determine sound from a graph or graphs is so huge, that it cannot easily be done. So I think your attempts around seemingly attempting to predict sound quality from a graph, are far from ideal, even if attempting this in a small way. If we could convince ourselves a kef ls50 sounds better by a graph to a kef blade, then it could save us a lot of money. Although I know with the right room size and amps which one I'd prefer and ignoring a graph(s) in the process. The adage of listening is so important then.

 

[insider9]

LindsayT Insider is going to want to measure your big bad boys to check THD etc.  Be very interesting see how well they measure 

Not quite. I'm not a complete nutter

However I find it very useful to look at measurements. Not saying everything can be said about a system via measurement but it helps.

Biggest shock I've had when I got my speakers completely flat (neutral) and I hated the sound.

 

[ellisdj]

Flat is no good, need rising bass.

Rising treble for when you get older and the ears are not so good.....

 

[QuestForThe13thNote]

No unfortunately this is the sort of stuff for my money that puts everyday non technical people off owning great hi fi.

We measured the pmc at the woofer but not the transmission line (which is what I think Lindsay was alluding too by talking about off axis), then someone says it has no bass, then someone corrects them like Lindsayt, and then it goes on and on. A total headf--k. I mean we are just bods on a hi fi forum, not technical specialists. Most of us anyway. So whose to know if there are other explanations for other aspects mentioned by insider.

I suspect as Lindsayt may be as an engineer? much of these explanations get ripped apart by people who know their stuff very probably the people at pmc. That's why we pay all that money on hearing it better, or at least pmc customers, because I can listen to it, it beats most if not all the competition, and I can rely on pmc, and just do the bloody bit I want to do. Listen to music at very good quality for frigg sake. And then if someone reckons they can get a speaker to sound the same for £50 then bloody well good luck to them (in a million years), but I'll just listen to my hi fi.

 

[ellisdj]

Sorry quest there is nothing wrong with knowing the frequency response of a speaker.

In fact if you dont know what your frequency response is at your listening position how can you even be sure what your listening to is High Fidelity in the first place? Regardless of what boxes you own its extremely important.

 

[insider9]

What you are telling me is distortion at various frequencies. Right? Where is that in the graph ?But even if there are measurements less favourable than a cheaper speaker, the measurements might be low comparatively to other speakers higher distortion.

THD percentage has to be calculated based on that graph. 4% at 1kHz could be audible. I never want a hifi speaker to produce distortion in midrange that's above 1%. In fact the lower the 1% the better across the range with exception to bass. I could not care how much the speaker cost.

Another thing is that if you measure the bass at the woofer, wouldn't it be low on a pmc, since the microphone isn't at the lower transmission line port, where the lowest frequencies emanate. How would the microphones sync in with one another to reflect correct results. Can I ask where you got the pmc graphs from?

Source material was linked. SoundStage! magazine see OP. Lindsayt was refering to Stereophile. Not sure why you say lowest frequencies. The dips are in upper bass region.

But argument that you have to a position the mic lower is strange... do you normally listen with your ears level with transmission line port? Bass isn't directional as mids or upper frequencies. The mic needs to be at the usual listening position.

No unfortunately this is the sort of stuff for my money that puts everyday non technical people off owning great hi fi.

We measured the pmc at the woofer but not the transmission line (which is what I think Lindsay was alluding too by talking about off axis)

Not at all. He was referring to phase which can be a huge factor. Stereophile did their measurements at 1m, SoundStage! at 2m. Both show an upper bass dip. Genreally associated with lean bass. I would agree it could be phase related but differences in measuring distance indicate it is not as straight forward. Anyway, I listen at circa 2m and want the speakers to perform at their best in that distance.

I bet the number of variables to determine sound from a graph or graphs is so huge, that it cannot easily be done. So I think your attempts around seemingly attempting to predict sound quality from a graph, are far from ideal, even if attempting this in a small way. If we could convince ourselves a kef ls50 sounds better by a graph to a kef blade, then it could save us a lot of money. Although I know with the right room size and amps which one I'd prefer and ignoring a graph(s) in the process. The adage of listening is so important then.

Firstly, I said certain things can be said about sound. Secondly, nothing to do with convincing myself, yourself or anyone else. That's the beauty of measurements.

But I think you're missing the point of this thread. I've always heard from others about PMC speakers having a good tuneful bass. The last thing I expected was to see a measurement showing dips in upper bass. After close inspection I've noticed other things that concerned me like the distortion. The only PMC speakers I've heard were Twenty.26 and they sounded fab on the end of a Linn system. Would I care after listening to them if someone have said that they measure "wrong"? Not at all.

So going back to GB1 measurments.

Do they matter in the grand scheme of things? Not necessarily. / Would I buy a speaker like this without listening to it? Depends on the price. / Does it mean it sounds poorly? No

 

[QuestForThe13thNote]

Sorry quest there is nothing wrong with knowing the frequency response of a speaker.

In fact if you dont know what your frequency response is at your listening position how can you even be sure what your listening to is High Fidelity in the first place? Regardless of what boxes you own its extremely important.

because the consideration isn't hi fidelity but bloody good fidelity. I don't need to know that from a graph.

 

[lindsayt]

I suspect as Lindsayt may be as an engineer?

By education and early career I'm a mechanical and production engineer.

And yes I do largely agree with you Quest in that measurements only tell a highly restricted part of the story and that the best way to "measure" a speaker is to listen to it in a comparative demo and "measure" it with our ears and brain.

Insider9 is raising some interesting points in this thread. It's quite possible that his old Jamos do measure better than a number of PMC's in certain respects and that this might be reflected in them sounding better overall.

And as for measuring my EV's if I take them round to Insider9's, yes he's quite welcome to do anything he likes with them (as long they don't get damaged). I'd be mildly interested to see how they measured.

Getting better sounding speakers than PMC twenty5 23's for £50 would probably take a lucky right place right time once in a lifetime find. I suspect that doing it for £500 is quite possible.

 

[QuestForThe13thNote]

What you are telling me is distortion at various frequencies. Right? Where is that in the graph ?But even if there are measurements less favourable than a cheaper speaker, the measurements might be low comparatively to other speakers higher distortion.

THD percentage has to be calculated based on that graph. 4% at 1kHz could be audible. I never want a hifi speaker to produce distortion in midrange that's above 1%. In fact the lower the 1% the better across the range with exception to bass. I could not care how much the speaker cost.

Another thing is that if you measure the bass at the woofer, wouldn't it be low on a pmc, since the microphone isn't at the lower transmission line port, where the lowest frequencies emanate. How would the microphones sync in with one another to reflect correct results. Can I ask where you got the pmc graphs from?

Source material was linked. SoundStage! magazine see OP. Lindsayt was refering to Stereophile. Not sure why you say lowest frequencies. The dips are in upper bass region.

But argument that you have to a position the mic lower is strange... do you normally listen with your ears level with transmission line port? Bass isn't directional as mids or upper frequencies. The mic needs to be at the usual listening position.

No unfortunately this is the sort of stuff for my money that puts everyday non technical people off owning great hi fi.

We measured the pmc at the woofer but not the transmission line (which is what I think Lindsay was alluding too by talking about off axis)

Not at all. He was referring to phase which can be a huge factor. Stereophile did their measurements at 1m, SoundStage! at 2m. Both show an upper bass dip. Genreally associated with lean bass. I would agree it could be phase related but differences in measuring distance indicate it is not as straight forward. Anyway, I listen at circa 2m and want the speakers to perform at their best in that distance.

I bet the number of variables to determine sound from a graph or graphs is so huge, that it cannot easily be done. So I think your attempts around seemingly attempting to predict sound quality from a graph, are far from ideal, even if attempting this in a small way. If we could convince ourselves a kef ls50 sounds better by a graph to a kef blade, then it could save us a lot of money. Although I know with the right room size and amps which one I'd prefer and ignoring a graph(s) in the process. The adage of listening is so important then.

Firstly, I said certain things can be said about sound. Secondly, nothing to do with convincing myself, yourself or anyone else. That's the beauty of measurements.

But I think you're missing the point of this thread. I've always heard from others about PMC speakers having a good tuneful bass. The last thing I expected was to see a measurement showing dips in upper bass. After close inspection I've noticed other things that concerned me like the distortion. The only PMC speakers I've heard were Twenty.26 and they sounded fab on the end of a Linn system. Would I care after listening to them if someone have said that they measure "wrong"? Not at all.

So going back to GB1 measurments.

Do they matter in the grand scheme of things? Not necessarily. / Would I buy a speaker like this without listening to it? Depends on the price. / Does it mean it sounds poorly? No

That's fine but its all very academic to me but I am only mildly interested in what someone measures, since I've no idea what they are measuring to the extent of relating it to sound and what they are using microphone wise. If you've got a mic on a speaker in the sound deadening chamber you mentioned you'd not be measuring the transmission line bass, but in a normal room, that bass would be reflected, so how do we relate a graph measured at woofer/tweeter height no doubt in such a chamber, using say the 25-23, against real world bass. You can't obviously just use the graph as you say, to tell you how much bass the speaker produces. Same with the speakers you have been looking at which are all tl design.

You could say it could be audible on thd, but technically if you can't say if it is or not, not worth being a factor to use for comparison purposes. Also ask yourself the question how relative is it, as I mentioned. But again I've no idea how this is even measured or how correct it is. but i agree with you it's about listening.

I agree with your conclusions because what has been accepted between us I think, is that technical measurements mean nothing against how it actually sounds. So I then wonder why graphs keep getting banded around.

 

[insider9]

I suspect as Lindsayt may be as an engineer?

By education and early career I'm a mechanical and production engineer.

 

And yes I do largely agree with you Quest in that measurements only tell a highly restricted part of the story and that the best way to "measure" a speaker is to listen to it in a comparative demo and "measure" it with our ears and brain.

 

Insider9 is raising some interesting points in this thread. It's quite possible that his old Jamos do measure better than a number of PMC's in certain respects and that this might be reflected in them sounding better overall.

And as for measuring my EV's if I take them round to Insider9's, yes he's quite welcome to do anything he likes with them (as long they don't get damaged). I'd be mildly interested to see how they measured.

 

Getting better sounding speakers than PMC twenty5 23's for £50 would probably take a lucky right place right time once in a lifetime find. I suspect that doing it for £500 is quite possible.

Yes, I admit bass is one of Jamos strengths. Not only low but clean and tuneful. It's a pair of 8" woofers in an isobaric arrangement. But for best bass they do need a beefy amp. Roksan Kandy KA-1 Mk III did really well controlling them.

If you'd like to visit that would be lovely. It would be great to have feedback from someone more experienced. Should you bring your speakers measurements wouldn't take long either I sent you a PM via Wigwam.