KEF LS50 vs. Revel Performa M105

[aarons915]

Generally IMD measurements are done on a single driver. Doing IMD on a multi-way speaker, and setting one tone well in the passband of one driver and the other tone well into the passband of a different driver should give you no IMD at all. In the case of a standard two-way tweeter over woofer, a tone of 100Hz and a tone of 4kHz would put the first tone in the woofer range and the second in the tweeter range, so there should be practically no IMD (assuming infinite slope crossovers). But a tone of 100Hz and a tone of 400Hz *would* show some IMD because both tones are played by the same driver. Likewise 4kHz and 10kHz.

I think you're chasing ghosts trying to capture this complex problem with a simple measurement.

I agree, I never thought there was an issue myself, especially when used at typical listening levels with a subwoofer, as I believe all smallish monitors should be used. I was mostly getting some kind of data to show it's not a problem because for some reason there is this myth of IMD distortion whenever coaxials come up.

And I understand how IMD distortion works and you're right in a typical 2 way but we're talking about a coaxial driver, where the midwoofer cone acts as a waveguide to the tweeter so driver excursion could affect the tweeter response., That's also why I assumed, maybe falsely, that the crossover frequency wouldn't be a bad place to play the 2nd tone. Maybe if I'm in the mood to measure soon I'll try 100Hz along with 200, 400 as well just out of curiousity but again I don't think even the LS50 have a problem, my driver doesn't move when I'm cranking them pretty loud.

 

[aarons915]

I haven't seen any posts or statements from Toole/Revel saying or implying that the KEF LS50s are bright/edgy. I have seen some statements saying they didn't do all that well in blind testing despite having good spinorama measurements, and that was attributed to what people are calling IMD..

I'm not sure if you're on AVS as well but I was talking to a few people in the Revel thread a few months back and that is where the whole IMD discussion came up. It ended up coming out that it wasn't the LS50 or even the R100 that performed poorly in their IMD test but the Q300, which by the way was in the MLL test with the Concerta2 M16. This was when I started taking their double blind tests with a grain of salt because they lead people to believe everything being tested is the same or up to double the MSRP of the Revels in the test but in this case the Q300 were I believe $650 and most consider them to be inferior to even the Q100.

 

[Beave]

The myth is that the distortion is IMD in the sense that two simultaneous pure tones being played will give you extra tones at sum and difference frequencies. That's not what the issue is with coax drivers.

The midwoofer excursion can affect the tweeter response - but not in the sense of creating sum and difference frequencies that aren't in the original signal. The effect, rather, is that the tweeter's dispersion changes as the midwoofer moves. So the sound power thrown into the listening space gets modulated by the movement of the midwoofer.

 

[Beave]

I'm not sure if you're on AVS as well but I was talking to a few people in the Revel thread a few months back and that is where the whole IMD discussion came up. It ended up coming out that it wasn't the LS50 or even the R100 that performed poorly in their IMD test but the Q300, which by the way was in the MLL test with the Concerta2 M16. This was when I started taking their double blind tests with a grain of salt because they lead people to believe everything being tested is the same or up to double the MSRP of the Revels in the test but in this case the Q300 were I believe $650 and most consider them to be inferior to even the Q100.

I lurk on AVS but won't post there. I regularly read the Revel thread, KEF thread, and others. I saw what you're referring to. Revel/Harman has produced a lot of good science. The results from their listening lab tests, where their speakers always win, is at least somewhat due to cherry-picking the competition. For the competing speakers, they always pick three or four that have notable flaws; and they always conveniently neglect picking competitors that have a good chance of winning. It's where their science team meets their marketing team, and it shows.

 

[KEW]

latest stereophiles has John Atkinson comparing Revel M106 vs. LS50. Interesting read as measurements somewhat comparable but different sound...worth a read.

Thanks, Randy, that'll be really interesting to read! I didn't see it on the review page - is it print only?

Sorry for late reply. Print only for now although I think at some point ends up on web.

This has probably been available online for a while now, but I figured I'd link it:

A Tale of Two Speakers

A comment by "cgh" in an online reprint of a Stereophile review caught my attention: "The [1990s] were probably the last real decade that we could reasonably bend the truth. Everything since is verifiable electronically."

www.stereophile.com

This is an interesting read and of special note, JA contrasts the differences between his Anechoic measurements and in-room measurements to reveal how much difference there was in how these speakers (which had largely similar anechoic measurements) interacted with the room! (they were, of course, placed in the same position).

 

[shadyJ]

This has probably been available online for a while now, but I figured I'd link it:

A Tale of Two Speakers

A comment by "cgh" in an online reprint of a Stereophile review caught my attention: "The [1990s] were probably the last real decade that we could reasonably bend the truth. Everything since is verifiable electronically."

www.stereophile.com

This is an interesting read and of special note, JA contrasts the differences between his Anechoic measurements and in-room measurements to reveal how much difference there was in how these speakers (which had largely similar anechoic measurements) interacted with the room! (they were, of course, placed in the same position).

A couple notes about that article. The article is an attempt to rebut the statement: "
The [1990s] were probably the last real decade that we could reasonably bend the truth. Everything since is verifiable electronically."

But the problem is he then attempts to rebut it using personal subjective experience, i.e., non-scientific, unreliable data. Something else to consider is that the Revel speakers have a wider dispersion than the LS50s, and that simply toeing them in more or less would have reduced the treble which seemed to trouble him, but without affecting the linearity of lower frequency ranges. Compare the off-axis responses of each speaker and you can see that a warm to neutral sound can be had from either speaker- depending on the angle you listen to them.

 

[KEW]

A couple notes about that article. The article is an attempt to rebut the statement: "
The [1990s] were probably the last real decade that we could reasonably bend the truth. Everything since is verifiable electronically."

But the problem is he then attempts to rebut it using personal subjective experience, i.e., non-scientific, unreliable data. Something else to consider is that the Revel speakers have a wider dispersion than the LS50s, and that simply toeing them in more or less would have reduced the treble which seemed to trouble him, but without affecting the linearity of lower frequency ranges. Compare the off-axis responses of each speaker and you can see that a warm to neutral sound can be had from either speaker- depending on the angle you listen to them.

I would have to respectfully disagree with your interpretation!
As I read it, the crux of this article is the comparison of the traditional anechoic FR measurements vs the in-room FR measurements. It is more of a snapshot than a study since it is a sample of two speakers in one room, but it does show how the similar anechoic measurements translate to in-room measurements which show more obvious differences, thus showing that the conventional anechoic FR measurement does not give a very complete understanding of what you might experience in your room.
However, to your thesis that it is subjective, I think part of his investigation was whether the differences shown in the in-room measurement were relevant (audible) which requires subjective evaluation.
I appreciate your experience and comments on the effect of toe-in; however, when you say:

Compare the off-axis responses of each speaker and you can see that a warm to neutral sound can be had from either speaker- depending on the angle you listen to them.

, I believe you are looking at the anechoic response for your comment about obtaining a warm or neutral response, while JA points out that he is in a small room with lively acoustics. Your point likely still has merit, but not so much as you might infer from the anechoic measurements.
I know I was shocked and intrigued by how the bass response was fairly similar between the speakers with close roll-off points, but in-room, the Revel (with anechoic roll-off around 51Hz) actually goes back up to -1dB at around 33Hz. Looking back at it a delta of ~6-7 dB is maintained in both measurements, but looking at the anechoic chart I would not expect that to be very audible...however, looking at the in-room response, I would expect that to be a very significant aspect distinguishing one speaker from the other!
I am not so well versed as you (or JA) for correlating measured differences to perceived audible differences, but the in-room chart adds a lot of information (if it was for my room) that is missing from the anechoic chart!

 

[everettT]

Here is a good thread ( shootout with Revel and JBL) that Toole has a lot of commentary.

Speaker Shootout - two of the most accurate and well...

www.avsforum.com

Some excellent discussions on measurements and addresses Sterophile measurements somewhere around page 9

 

[PENG]

Here is a good thread ( shootout with Revel and JBL) that Toole has a lot of commentary.

Speaker Shootout - two of the most accurate and well...

www.avsforum.com

Some excellent discussions on measurements and addresses Sterophile measurements somewhere around page 9

I remember reading the shootout article. The discussions by Floyd on that thread is very interesting.

I am not sure if Dr. Floyd is right about everything and/or wrong about something, but what he said below seemed logical at least.

"A major problem is that enthusiasts in general have not taken the trouble to find and read the existing science. They will not be guided to it by audiophile publications because for many of them the scientific findings run contrary to their business interests. Fortunately a few have acknowledged that the complete answers may not lie in "take it home and listen to it" sighted and biased subjective evaluations. But for them the lack of facilities and finance are serious limitations. So, in the absence of published comprehensive anechoic data, consumers and professionals are seriously handicapped when trying to make rational decisions. The last chapter in my new book is a 50 year retrospective on loudspeakers - lots of curves. It is clear that there were some excellent loudspeakers years ago, and some mediocre ones even today. Price is not a factor. Professionals seem to have had the greatest problems embracing measurements. Several consumer audio magazines show measurements in their reviews - not perfect, but usefully accurate, and in one case (soundstagenetwork.com) nearly so as they use my old NRCC facilities. Professional magazines almost always leave evaluations of monitor loudspeakers to sighted listening tests by individuals who have a high probability of having hearing loss. Go figure. "

He's talking about loudspeakers, so think about how some of those professional reviewers described the sound quality difference they heard between power amps or even preamps that all measured much better than the Salon2s in order of magnitudes, on sound quality related specs.

Below are some examples of the expressions they used freely in such reviews and in this case, in one single review:
- What makes the XX so special is its inherent textural sweetness and warm tonality, and it’s in these areas that the YY actually outgunned the XX.
- with ABC preamp, which is capable of dishing out the most luxurious textures I’ve ever experienced from a solid-state design.
- It is clearly a remarkable, deliciously organic-sounding low-power amplifier.....

I read such reviews for entertainment, when I get bored. It is sad that many people were influenced by those talks, that I believe could have enhanced Placebo effects and/or expectation bias. In many cases, when that happens, it may be very difficult to convince them (the affected) the otherwise..