KEF LS50 vs. Revel Performa M105

A

aarons915

Enthusiast
Ratings
14
#81
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.
 
A

aarons915

Enthusiast
Ratings
14
#82
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.
 
B

Beave

Full Audioholic
Ratings
281 2
#83
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.
 
B

Beave

Full Audioholic
Ratings
281 2
#84
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.
 

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