Revel M22 Speaker Review

[Tks]

It is an extra cost license. I can do it with REW but that is a lot of hassle right now when I have so much more to test.

Hey bossman, I was just wondering since this distortion stuff confuses me from time to time (especially when trying to wrap my head around heavily mains derived distortions, or IMD distortions, or some other kinds). When you do THD measurements for devices. It's safe to assume that is worst-case that takes all of the distortions into account right? So while we may not see how much IMD distortion is having a piece of that THD pie, we can rest assured when something like THD is under something for example like 0.1% we surly woulnd't be hearing any IMD coming through as the entirety (or lets say 95%) of the distortion artifacts right?

I am also wondering (since only someone with your experience, and mathematical prowess, among a handful of others here perhaps as well with the math know-how), how much in your experience (for DACs or Amps since you don't measure IMD of speakers) does IMD comprise itself of the entire distortion pie? Maybe you haven't taken notice to ask yourself this question up until now. I was just curious about the aproximate average makeup IMD is present if you were to subtract it's distortions from the THD pie (if such a calculation is even possible and not masked after a certain point by other distortions)?

 

[Alice of Old Vincennes]

OK I see. The M22 has an acoustic lens but no waveguide. I found Revel white paper on the concertas. Acoustic lens for 9 khz and above.

 

[amirm]

I am also wondering (since only someone with your experience, and mathematical prowess, among a handful of others here perhaps as well with the math know-how), how much in your experience (for DACs or Amps since you don't measure IMD of speakers) does IMD comprise itself of the entire distortion pie? Maybe you haven't taken notice to ask yourself this question up until now. I was just curious about the aproximate average makeup IMD is present if you were to subtract it's distortions from the THD pie (if such a calculation is even possible and not masked after a certain point by other distortions)?

It is a complicated thing that we have argued at length earlier. Studies have shown that neither THD, nor IMD impact listener preference. Between two speakers, their on-axis, off-axis and bass performance determine preference.

Now, if you had two speakers with identical frequency response and the only difference was distortion, then that would matter. But such an animal does not exist.

With respect to electronics, their frequency response is identical so then we focus on distortion differences.

Instrumentation is also different. With electronics, the distortion in my analyzer is vanishingly small, less than anything I measure. With speakers, we use a microphone that itself has distortion. In addition, I measure in a room which means there are effects from that which impact the measurements (both noise and room modes).

I do show distortion measurements as a detective tool to recognize something is happening in a speaker. For example, around midrange, increasing distortion may mean the woofer is not rolled off fast enough. What the absolute value is, is not material in that case. Just the rise and fall at certain frequency.

Longer term, I will show more distortion data. Right now, the battle is to sift through so many speakers and find the worthwhile ones at various price points.

 

[Usernome]

OK I see. The M22 has an acoustic lens but no waveguide. I found Revel white paper on the concertas. Acoustic lens for 9 khz and above.

Mind sharing? The only Revel white paper I’ve been able to find is the Concerta2 one, and it’s interesting to see.

 

[pma]

Hey bossman, I was just wondering since this distortion stuff confuses me from time to time (especially when trying to wrap my head around heavily mains derived distortions, or IMD distortions, or some other kinds). When you do THD measurements for devices. It's safe to assume that is worst-case that takes all of the distortions into account right? So while we may not see how much IMD distortion is having a piece of that THD pie, we can rest assured when something like THD is under something for example like 0.1% we surly woulnd't be hearing any IMD coming through as the entirety (or lets say 95%) of the distortion artifacts right?

I am also wondering (since only someone with your experience, and mathematical prowess, among a handful of others here perhaps as well with the math know-how), how much in your experience (for DACs or Amps since you don't measure IMD of speakers) does IMD comprise itself of the entire distortion pie? Maybe you haven't taken notice to ask yourself this question up until now. I was just curious about the aproximate average makeup IMD is present if you were to subtract it's distortions from the THD pie (if such a calculation is even possible and not masked after a certain point by other distortions)?

There is only one and only non-linear transfer function for the component under test. "THD", "IMD", these are just and only poor means trying of some description. The transfer function depends on amplitude and frequency for electronic systems, however it is much more complicated for electro-acoustic drivers and speakers. It may be a function of time (time for which the signal is applied) as well. What do you mean when you say IMD? Do you mean twin tone with closely positioned frequencies, do you mean DIN IMD, SMPTE IMD or what? These are important questions because audio frequency range is divided to several drivers in most speaker boxes. So closely spaced tuned twin tone sweep makes much sense, eventually with the 3rd tone added. Yes THD plots as shown here do not reveal much, but again, think about non-linearity as a complex function of many variables and not as a single number or plot.

 

[QMuse]

Also, do you think expensive bookshelves are not needed as surrounds?

Expensive bookshelves are overkill when used as surrounds. You can find good dipoles that will cost less and do a better job than bookshelves.

 

[andreasmaaan]

Hmm, these are actually quite poor measurements for a Revel speaker IMHO.

Broadband peaks and dips in the axial frequency response, poor off-axis behaviour, mediocre distortion. And the irregularities in the on-axis response around the XO point are actually exacerbated by the off-axis behaviour, not mitigated as they are in Revel's better speakers of this era.

Not particularly impressed I must say

 

[thewas]

Expensive bookshelves are overkill when used as surrounds. You can find good dipoles that will cost less and do a better job than bookshelves.

Toole doesn't recommend dipoles for surrounds but rather direct radiating ones or bipoles. Dipoles were a (bad) approach at early Dolby surround days when the rear channel was mono as its was encoded in the L, R signals to create a bit more width due to diffusity/comb filtering artefacts. Luckily the market has adapted now and almost no serious loudspeaker manufacturer makes surround dipoles anymore.

 

[QMuse]

Toole doesn't recommend dipoles for surrounds but rather direct radiating ones or bipoles. Dipoles were a (bad) approach at early Dolby surround days when the rear channel was mono as its was encoded in the L, R signals to create a bit more width due to diffusity/comb filtering artefacts. Luckily the market has adapted now and almost no serious loudspeaker manufacturer makes surround dipoles anymore.

Interesting..

How would you explain the popularity of CBT arrays acting as dipoles?

One would expect that well designed dipole would simply have wider and more uniform horizontal dispersion when compared to bookshelf.

 

[thewas]

The CBT arrays or a well designed dipole have not really anything in common with how primitive small dipoles were (mis-)used as surround loudspeakers. Latter were placed such that they would be radiating to the listeners their side radiation full of comb filtering to creat some pseudo diffusity envelopment.

Diagram of Various Surround Speaker Types courtesy of Dr. Floyd Toole from https://www.audioholics.com/loudspeaker-design/surround-speaker-dipole-vs-bipole

Toole has nothing against well designed loudspeakers used correctly and even used to own the bipolar Mirage M-1 but the surround dipoles were a flawed concept.

 

[QMuse]

The CBT arrays or a well designed dipole have not really anything in common with how primitive small dipoles were (mis-)used as surround loudspeakers. Latter were placed such that they would be radiating to the listeners their side radiation full of comb filtering to creat some pseudo diffusity envelopment.

View attachment 56144

Diagram of Various Surround Speaker Types courtesy of Dr. Floyd Toole from https://www.audioholics.com/loudspeaker-design/surround-speaker-dipole-vs-bipole

Toole has nothing against well designed loudspeakers used correctly and even used to own the bipolar Mirage M-1 but the surround dipoles were a flawed concept.

I was not aware that term "dipole" is used for out-of-phase speaker, I was referring to in-phase speaker, "bipole" in your terminology. Are you saying they don't make bipols as surround speakers these days?

 

[thewas]

Are you saying they don't make bipols as surround speakers these days?

I clearly talked about dipoles, thus out of phase. But also bipoles are not as popular for surround as monopoles nowadays as they don't really offer any real advantage, because its hard to widen the radiation by using 2 loudspeakers without creating comb filtering effects (and most compact midwoofers and well designed waveguided tweeters anyway radiate already quite wide).

"bipole" in your terminology

That is not "my" terminology but the correct one used by everyone.

 

[QMuse]

I clearly talked about dipoles, thus out of phase. But also bipoles are not as popular for surround as monopoles nowadays as they don't really offer any real advantage, because its hard to widen the radiation by using 2 loudspeakers without creating comb filtering effects (and most compact midwoofers and well designed waveguided tweeters anyway radiate already quite wide).

And how do they avoid comb filtering with CBTs?

That is not "my" terminology but the correct one used by everyone.

Eh, now you're pulling my leg - I meant terminlogy used in your post.

 

[andreasmaaan]

And how do they avoid comb filtering with CBTs?

Comb filtering will occur only at frequencies at which the wavelength is less than approximately 2 x the C2C distance between drivers. This means that for a CBT using closely spaced 3/4" tweeters (say with a 2cm C2C distance), comb filtering occurs only in the top octave or so.

 

[thewas]

And how do they avoid comb filtering with CBTs?

Many and very close loudspeaker drivers compared to the radiated wavelengths so comb filtering is minimised and also smeared creating an almost perfect radiation "bubble".
https://en.wikipedia.org/wiki/Line_array
Also look at the nice animation here https://en.wikipedia.org/wiki/Phased_array

 

[QMuse]

Comb filtering will occur only at frequencies at which the wavelength is less than approximately 2 x the C2C distance between drivers. This means that for a CBT using closely spaced 3/4" tweeters (say with a 2cm C2C distance), comb filtering occurs only in the top octave or so.

Aha. Well ok then, in that case you can build surround speaker for home use as a short horizontal arc with say 4-6 small drivers. If designed carefully it should have excellent horizontal dispersion and no comb filtering.

P.S. vertical dispersion won't be that good but for home use that seems less problematic.

 

[QMuse]

Aha. Well ok then, in that case you can build surround speaker for home use as a short horizontal arc with say 4-6 small drivers. If designed carefully it should have excellent horizontal dispersion and no comb filtering.

P.S. vertical dispersion won't be that good but for home use that seems less problematic.

2 of those can be mounted in the back corners of the room or on the side walls. They should be able to create a wide dispersion field for surround effects.

 

[thewas]

Aha. Well ok then, in that case you can build surround speaker for home use as a short horizontal arc with say 4-6 small drivers. If designed carefully it should have excellent horizontal dispersion and no comb filtering.

P.S. vertical dispersion won't be that good but for home use that seems less problematic.

4-6 drivers are usually unfortunately not enough for a decent array and with the horizontal array you actually will achieve exactly the opposite of what you are looking for and that is very high horizontal beaming. Line arrays like the CBT are used to narrow the radiation, not to widen it. To make it more clear, think what a larger driver does compared to a smaller one, it beams more. Thus you can think of a line array like a huge elliptic driver of the same dimension from the radiation point of view.

 

[QMuse]

4-6 drivers are usually unfortunately not enough for a decent array and with the horizontal array you actually will achieve exactly the opposite of what you are looking for and that is very high horizontal beaming.

Is that so? So if I build a full circle of drivers in a horizontal plane I will not get uniform horizontal dispersion in all directions from the speaker?

 

[andreasmaaan]

Aha. Well ok then, in that case you can build surround speaker for home use as a short horizontal arc with say 4-6 small drivers. If designed carefully it should have excellent horizontal dispersion and no comb filtering.

P.S. vertical dispersion won't be that good but for home use that seems less problematic.

Yeh, as @thewas_ said. To get wide horizontal dispersion from a CBT, it needs to be a vertical array.

The reasons such CBTs tend to have wide vertical dispersion are:

• they tend to use very small drivers
• at higher frequencies, they produce the greatest sound pressure at 90° off-axis

This is the normalised horizontal response of a CBT made up of 16 x 1" drivers spaced approx. 3cm apart. The red trace is 90° off-axis. As you can see, as frequency increases, the 90° off-axis response rises with reference to the on-axis response:

And this is the vertical response of the same array. As you can see, the vertical array narrows the vertical beamwidth, as opposed to widening it:

This is the layout of the array FWIW: