• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Revel M106 Bookshelf Speaker Review

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,448
Likes
4,209
Well, the way we usually treat a minimum phase system is when it behaves as a single minimum phase system.
When reflections come into play one should see this as another soundsource. So you could in a way still see it in minimum phase terms but with many different soundsources which individually act like minimum phase systems but the whole does not act like a single one.
So you can't apply minimum phase logic to the whole. You can't say if it measures flat (after EQ) it's not a resonant mess for instance, as it will be in an untreated room :)

The whole point of the transition region is that the small room ceases to act like reflections (and multiple sources) below it.
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
The whole point of the transition region is that the small room ceases to act like reflections (and multiple sources) below it.
Aah I'm not familiar with such small rooms. I've often read it's next to impossible to get a good bass response in a small room for studios.
What dominates below the lowest mode? Strong first reflection cancellation of the walls opposite the subs? And what freq for the lowest mode are we talking about / how small a room?
 

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,448
Likes
4,209
I mean small rooms in the sense that Toole uses the term, i.e. home hifi rooms. And he identifies the transition region for such rooms as around 200-300 Hz.
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
I mean small rooms in the sense that Toole uses the term, i.e. home hifi rooms. And he identifies the transition region for such rooms as around 200-300 Hz.
Aah yes ok transition region in that way. You will have especially strong and widely spaced modes / resonances in the bass in such rooms which will give a very bad bass response? (you will still have this region in big rooms too only lower and more space to put treatment)
Edit: Ah but I'm not going to argue with Toole's ideas again. I can sum it up that I disagree with Toole on room acoustics treatment (or his lack thereof) and his research in this area.
 

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,448
Likes
4,209
Research = evidence. Disagreeing with it = ?????
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
Research = evidence. Disagreeing with it = ?????
It isn't particularly good or convincing research :) For instance his particular home listening room where he placed thin absorption on part of the sidewalls vs bare sidewalls and then asked a bunch of people what they preferred. I mean if that kind of thing is called "research" or be any kind of basis to form an opinion on bare reflections vs absorption then I will protest like I do.
Much more research has been done by many studio designers. And their results have been checked by studio users / mastering engineers looking for the ultimate room and they have often travelled to many different finished mastering studio's based on different design concepts before they arrive at their final choice based on their experienced ears. And literally none of them, acoustic engineers / room designers and studio users / mastering engineers arrive at anything near what Toole would suggest.

And have a look at the Gearslutz.com forums for instance:
https://www.gearslutz.com/board/studio-building-acoustics/
https://www.gearslutz.com/board/photo-diaries-of-recording-studio-construction-projects/
https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/
They are all wrong? All these producers, mixing engineers, mastering engineers, etc? All these reports of people who experience vast improvements in audio quality after treatment? Etc etc.
But noo.. Toole is god, he only has to slap on a few panels in a living room, invite a few friends (of who'm one self identifies as a "mastering engineer") and record their preferences to know they're bad. :facepalm: (exaggeration but it's something along this line)
(Great work by Toole on speakers though)
 
Last edited:

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,448
Likes
4,209
None of them are designing for listening to playback in the home. Those that are, and who have based their approach on validated research, Toole is not inconsistent with.

Read the recommendations in his books. They are not recommending "thin absorption on part of the side walls", nor "bare sidewalls".

However, he is right to point out that acoustic consultants coming out of the pro audio space are not well equipped for consulting in the home audio realm, although they think they are. He wisely advises home audio enthusiasts not to listen to them or adopt their studio/pro audio solutions.

cheers
 

Absolute

Major Contributor
Forum Donor
Joined
Feb 5, 2017
Messages
1,084
Likes
2,125
Research has showed that we're insensitive to decay below about 100 hz, but become increasingly sensitive above that. This is not surprising given the amount of time it takes for us to even register low frequency sounds, but it's also not surprising that room treatment will increase the sense of punch and dynamics in the bass because it works over 100 hz as well. Especially so if we rid ourselves of some of the SBIR-related issues in the process.

I think this discussion is one of those cases where the opposites are both correct; we're both insensitive to decay in the bass and EQ is good enough in the low bass and we are sensitive to the benefits of room treatment in the bass as well due to effect over 80-100 hz.

Remember that Toole himself is not the one behind this research, he only refers to it.
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
None of them are designing for listening to playback in the home. Those that are, and who have based their approach on validated research, Toole is not inconsistent with.

Read the recommendations in his books. They are not recommending "thin absorption on part of the side walls", nor "bare sidewalls".

However, he is right to point out that acoustic consultants coming out of the pro audio space are not well equipped for consulting in the home audio realm, although they think they are. He wisely advises home audio enthusiasts not to listen to them or adopt their studio/pro audio solutions.

cheers

Something which depends on what your goal is.
If you goal is to hear low level detail better than on heaphones, to truly hear what was recorded or produced warts and all, etc. To hear audio close to perfection. Then the pro audio space is what you want.
If you want to listen to 60's rock or to dry / close recorded jazz etc and want it to sound subjectively "good" / pleasing then you want a coloured audio experience with your own room adding the space and why not throw in a tube amp with some pleasing harmonics etc. But don't think for a second you're hearing what's actually on the disk or talk about "detail" etc. Bunch of "audiophile" nonsense. Hell you may even take a speaker with relatively high HD etc, you won't be able to hear it anyhow.
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
Research has showed that we're insensitive to decay below about 100 hz, but become increasingly sensitive above that. This is not surprising given the amount of time it takes for us to even register low frequency sounds, but it's also not surprising that room treatment will increase the sense of punch and dynamics in the bass because it works over 100 hz as well. Especially so if we rid ourselves of some of the SBIR-related issues in the process.

I think this discussion is one of those cases where the opposites are both correct; we're both insensitive to decay in the bass and EQ is good enough in the low bass and we are sensitive to the benefits of room treatment in the bass as well due to effect over 80-100 hz.

Remember that Toole himself is not the one behind this research, he only refers to it.
Sure not insensitive to decay below 100Hz. Less sensitive yes, but not at all insensitive. I haven't even read research on this but can tell with absolute certainty from personal experience. On top of that, aaaaal the pro's report vast improvements in bass quality when treating <100Hz with absorption. Hell it's most of what they talk about. It's audibly totally different from EQ.

But again, I'm not going to go into this discussion yet again. For me it's like arguing against Yehova's witnesses. Sorry don't mean that to be insulting but that's really the impression I've been getting and it leads to nothing in the end.
I'm perfectly fine to disagree on this and that some of you come from a different belief / perspective. Please put all my previous posts / comments under the pro-audio perspective.
 

Absolute

Major Contributor
Forum Donor
Joined
Feb 5, 2017
Messages
1,084
Likes
2,125
Sure not insensitive to decay below 100Hz. Less sensitive yes, but not at all insensitive. I haven't even read research on this but can tell with absolute certainty from personal experience. On top of that, aaaaal the pro's report vast improvements in bass quality when treating <100Hz with absorption. Hell it's most of what they talk about. It's audibly totally different from EQ.

But again, I'm not going to go into this discussion yet again. For me it's like arguing against Yehova's witnesses. Sorry don't mean that to be insulting but that's really the impression I've been getting and it leads to nothing in the end.
I'm perfectly fine to disagree on this and that some of you come from a different belief / perspective. Please put all my previous posts / comments under the pro-audio perspective.
I appreciate that your findings might differ from the research. I'm not a scientist and can't really tell whether or not the methods used in the research is sufficient enough to find all the answers we're looking for.
But what I do know is that you can't compare EQ with room treatment without controlling that you've accounted for the frequency response in the whole listening position and not just a single point in space.

With EQ in a random point you may or may not correct the frequency response in the whole listening position, most likely not. With treatment you will see a benefit in the whole space which could likely explain differences in experience between the two.

Experiencing such a difference does not mean that the assumption that we hear decay in the low bass is correct. This assumption needs to be tested to confirm whether or not the difference is due to decay or just frequency response.
The research say it's all frequency response down low, but the issue is that we hear bass with our whole body, not just the ear.
I believe they took this into account in the study, but have you done so in your testing? If so, can you show me?

If not, how can you know you're hearing decay and not variances in frequency response?

I don't really care one way or the other, treatment is necessary to get good bass above 100 hz either way, so there's no position for me to defend here.
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
I apologize for my earlier statements. Made it too black/white contrast and I was in a bit of a grumpy mood.
I have only read parts of Toole's book "Sound Reproduction" and saw a few videos with him.
I have been under the impression that he proposes a largely untreated room as the ideal. Maybe I've gotten the wrong impression.
 

Absolute

Major Contributor
Forum Donor
Joined
Feb 5, 2017
Messages
1,084
Likes
2,125
I apologize for my earlier statements. Made it too black/white contrast and I was in a bit of a grumpy mood.
I have only read parts of Toole's book "Sound Reproduction" and saw a few videos with him.
I have been under the impression that he proposes a largely untreated room as the ideal. Maybe I've gotten the wrong impression.
I would think so. Toole in general gets a lot of flak for presenting the results of studies he himself was not part of, partially because many have not read the book and/or the studies referred to, or sometimes because the context of his writings is misunderstood. The latter being the most prominent, in my opinion.
There's somewhere between 250-300 different studies referred to in the book, so simplifying it to "Toole's opinion" is doing the audio community a massive disservice.
 

richard12511

Major Contributor
Forum Donor
Joined
Jan 23, 2020
Messages
4,335
Likes
6,700
I apologize for my earlier statements. Made it too black/white contrast and I was in a bit of a grumpy mood.
I have only read parts of Toole's book "Sound Reproduction" and saw a few videos with him.
I have been under the impression that he proposes a largely untreated room as the ideal. Maybe I've gotten the wrong impression.

I think he's more of the opinion that in an average living room, with carpet and furniture, adding further treatment may make the room too dead. "Average living room" though is a generalization, and many average living rooms could have very different sound signatures. If you've got tile floors, glass walls, granite counters, and only "modern" furniture, you're probably gonna have to add some absorption to make that room sound good, and I don't think Toole would disagree with that.
 

BingaMoon

Member
Joined
Jul 9, 2020
Messages
43
Likes
24
Weirdly enough seems like some people prefer the M16 over the M106. Any other opinions?
 

KaiserSoze

Addicted to Fun and Learning
Joined
Jun 8, 2020
Messages
699
Likes
592
None of them are designing for listening to playback in the home. Those that are, and who have based their approach on validated research, Toole is not inconsistent with.

Read the recommendations in his books. They are not recommending "thin absorption on part of the side walls", nor "bare sidewalls".

However, he is right to point out that acoustic consultants coming out of the pro audio space are not well equipped for consulting in the home audio realm, although they think they are. He wisely advises home audio enthusiasts not to listen to them or adopt their studio/pro audio solutions.

cheers

I will go out onto the proverbial shaky limb and say that the single most important thing to avoid is the standing waves that set up between two large parallel walls or between the floor and the ceiling. The room needs to be irregularly shaped, with no parallel walls. If this is accomplished, the need for sound absorption is greatly diminished, and it won't make much difference whether the absorption material/object is fixed to the walls, suspends from the ceiling, or sits somewhere in the middle of the room.

The first standing wave for two parallel surfaces occurs where 1/4 of the wavelength is equal to the distance. The next one is where 3/4 of the wavelength is equal to the distance, then where 5/4 of the wavelength is equal to the distance, etc. In other words, the wavelength (WL) of standing waves that set up between two parallel surfaces separated by distance d are given by the expression n/4 x WL = d, where n is any odd integer. Rearranging this expression, the wavelengths at which standing waves will set up between two parallel surfaces separated by distance d are given by the expression WL = 4d/n.

The "to be avoided" rule for room dimension ratios is the same as for the interior dimensions of speaker enclosures. What is to be avoided is the situation where standing waves of the same length will be associated with two (or more) of the dimensions. This obviously will occur if two of the dimensions are the same, but more generally it will occur if the expression 4d/n is the same for any two dimensions, where n is any odd integer and generally is not the same for both dimensions. If we let d1 and d2 represent any two room dimensions, and n1 and n2 represent any two odd integers, then we want to avoid satisfying the equation "4 x d1/n1 = 4 x d2/n2". Manifestly, the '4' cancels out of both sides, leaving us with "d1/d2 = n1/n2". Thus, the dimensional ratios that are to be avoided are the ratios of odd integers. This includes the cases where one of the odd integers is 1, but also the cases where one of them is 3, or where one of them is 5, etc.

The bad ratio that you are most likely to encounter with room dimensions (ignoring the floor-to-ceiling dimension) is 3:5. Fortune smiles upon you if the room available to you has a vaulted ceiling. If so, you will most likely have at least one pair of parallel walls, probably two pairs, and will need to deal with them. But most people aren't blessed with a vaulted ceiling, and will more likely have to contend with a low drop-down ceiling built within a basement corner. In this situation, you absolutely, positively want to avoid the situation where the standing waves associated with the floor-to-ceiling distance also occur in association with the distance between either pair of parallel walls. And it can potentially occur with both pairs of parallel walls, even if the two room dimensions are different.

If the ceiling height is H, then you want for neither of the other two dimensions to be equal to H multiplied by any of these ratios: 5/3, 7/3, 7/5, 9/5, 11/5, 13/5, 9/7, 11/7, 13/7, 15/7, 17/7, or 19/7. If you study these ratios for a moment you will realize that the ratios you get with a small denominator, e.g. 3, leave you with wide gaps that are usable, but that when you proceed to use larger denominators, these gaps start filling in. What this means is that while it is possible to avoid compounded standing waves (standing waves associated with more than one room dimension) at low frequency, that it isn't possible to avoid this at higher frequency so long as there are parallel walls.

Absorptive panels on the walls can be helpful for wavelengths where the panel thickness is at least 1/4 of the wavelength. Since wall panels are rarely more than a couple inches, they are typically only effective for treble and upper midrange. Why are the pyramidal cones you see in anechoic chambers so long from base to tip? Because to be effective, the height of the pyramidal cone from base to tip needs to be at least 1/4 of a wavelength.
 

TimVG

Major Contributor
Joined
Sep 16, 2019
Messages
1,181
Likes
2,573
@BYRTT

Could you process this for the M106 into your comparison set when you have some spare time? :)

1594406594840.png
 
Last edited:

Newman

Major Contributor
Joined
Jan 6, 2017
Messages
3,448
Likes
4,209
I will go out onto the proverbial shaky limb and say that the single most important thing to avoid is the standing waves that set up between two large parallel walls or between the floor and the ceiling. The room needs to be irregularly shaped, with no parallel walls. If this is accomplished, the need for sound absorption is greatly diminished, and it won't make much difference whether the absorption material/object is fixed to the walls, suspends from the ceiling, or sits somewhere in the middle of the room.

The first standing wave for two parallel surfaces occurs where 1/4 of the wavelength is equal to the distance. The next one is where 3/4 of the wavelength is equal to the distance, then where 5/4 of the wavelength is equal to the distance, etc. In other words, the wavelength (WL) of standing waves that set up between two parallel surfaces separated by distance d are given by the expression n/4 x WL = d, where n is any odd integer. Rearranging this expression, the wavelengths at which standing waves will set up between two parallel surfaces separated by distance d are given by the expression WL = 4d/n.

The "to be avoided" rule for room dimension ratios is the same as for the interior dimensions of speaker enclosures. What is to be avoided is the situation where standing waves of the same length will be associated with two (or more) of the dimensions. This obviously will occur if two of the dimensions are the same, but more generally it will occur if the expression 4d/n is the same for any two dimensions, where n is any odd integer and generally is not the same for both dimensions. If we let d1 and d2 represent any two room dimensions, and n1 and n2 represent any two odd integers, then we want to avoid satisfying the equation "4 x d1/n1 = 4 x d2/n2". Manifestly, the '4' cancels out of both sides, leaving us with "d1/d2 = n1/n2". Thus, the dimensional ratios that are to be avoided are the ratios of odd integers. This includes the cases where one of the odd integers is 1, but also the cases where one of them is 3, or where one of them is 5, etc.

The bad ratio that you are most likely to encounter with room dimensions (ignoring the floor-to-ceiling dimension) is 3:5. Fortune smiles upon you if the room available to you has a vaulted ceiling. If so, you will most likely have at least one pair of parallel walls, probably two pairs, and will need to deal with them. But most people aren't blessed with a vaulted ceiling, and will more likely have to contend with a low drop-down ceiling built within a basement corner. In this situation, you absolutely, positively want to avoid the situation where the standing waves associated with the floor-to-ceiling distance also occur in association with the distance between either pair of parallel walls. And it can potentially occur with both pairs of parallel walls, even if the two room dimensions are different.

If the ceiling height is H, then you want for neither of the other two dimensions to be equal to H multiplied by any of these ratios: 5/3, 7/3, 7/5, 9/5, 11/5, 13/5, 9/7, 11/7, 13/7, 15/7, 17/7, or 19/7. If you study these ratios for a moment you will realize that the ratios you get with a small denominator, e.g. 3, leave you with wide gaps that are usable, but that when you proceed to use larger denominators, these gaps start filling in. What this means is that while it is possible to avoid compounded standing waves (standing waves associated with more than one room dimension) at low frequency, that it isn't possible to avoid this at higher frequency so long as there are parallel walls.

Hi, a couple of things I would like to comment here.

Regarding flutter echo caused by parallel walls (which you didn't mention but, to me, is worth mentioning), this can be broken up with as little of an inch of non-parallel-ness. A slightly bowed sheet of thin ply on one wall. Vertical drapes turned slightly open. Pictures hanging on the walls with a slight downward tilt. Very easy to eradicate while still having parallel walls. Getting more formal, acoustical diffuser and absorber panels also do the job, of course.

Regarding room modes in the bass, it is a myth that parallel walls are the problem and non-parallel walls or ceiling are the solution. In the horizontal plane, room symmetry is too important at all non-bass frequencies, for non-parallel walls to be acceptable. Toole wrote, "A recurring fantasy about rooms is that if one avoids parallel surfaces, room modes cannot exist. Sadly, it is incorrect. Among the few studies of this topic, Geddes (1982) provides some of the most useful insights. He found that “room shape has no significant effect on the spatial variations of the pressure response.... The spatial standard deviations of the p2 response is very nearly uniform for all the data cases [the five room shapes evaluated in the computer model]."...." and "....for modes in rectangular and non-rectangular spaces...it is clear that both shapes exhibit regions of high sound level and nodal lines where sound levels are very low. The real difference is that in rectangular rooms, the patterns can be predicted using simple calculations.” Regarding vaulted ceilings being better than flat ceilings, not many homes have rock-solid floor and ceiling, so one or the other is going to let bass through and destroy the theoretical modal behaviour (which still exists for vaulted ceilings too). It is a theory that has been taken too far by lovers of theories.

Regarding room proportions, a room is not a reverberation chamber. Thus, analysis based on it being one is flawed, to the point of being misleading. One could argue it has some relevance between 40 and 120 Hz in small rooms (i.e. home hifi rooms), but researches in recent times refutes its usefulness. e.g. Fazenda et al (J. Audio Eng. Society, 2005) found that, "it follows that descriptions of room quality according to metrics relying on modal distribution or magnitude pressure response are seriously undermined by their lack of generality, and the fact that they do not correlate with a subjective percept on any kind of continuous scale."

Toole wrote that the 'irrefutable logic of the facts of room modes' has led to the appearance in pro audio text books of things like ideal, and undesirable, room proportions, and their widespread recitation by acoustical consultants. The fact that an acoustical consultant says so, is not, apparently, enough to make it true. Toole concluded that, "the acoustical performance of rooms cannot be generalized on the basis of their dimensional ratios and that reliably hearing superiority of a “good” one may not be possible....It is difficult to understand how this concept of an optimum room got so much traction in the field of listening room acoustics, and why it has endured."

Absorptive panels on the walls can be helpful for wavelengths where the panel thickness is at least 1/4 of the wavelength. Since wall panels are rarely more than a couple inches, they are typically only effective for treble and upper midrange. Why are the pyramidal cones you see in anechoic chambers so long from base to tip? Because to be effective, the height of the pyramidal cone from base to tip needs to be at least 1/4 of a wavelength.

You might need to revise that "1/4 wavelength" rule. The wavelength of 250 Hz is 54 inches, demanding a 13 inch thick panel by your rule, yet my 4-inch panels have an absorption factor of 1.00. In fact, at 125 Hz their factor is 0.60 -- and that is one way, so maybe 0.8-ish on a wall -- so are still highly effective, although your rule would require 26 inches of panel thickness.

But your main point, that typical 2-inch panels are no help in the bass, is well made.

cheers
 

JustIntonation

Senior Member
Joined
Jun 20, 2018
Messages
480
Likes
293
You might need to revise that "1/4 wavelength" rule. The wavelength of 250 Hz is 54 inches, demanding a 13 inch thick panel by your rule, yet my 4-inch panels have an absorption factor of 1.00. In fact, at 125 Hz their factor is 0.60 -- and that is one way, so maybe 0.8-ish on a wall -- so are still highly effective, although your rule would require 26 inches of panel thickness.

But your main point, that typical 2-inch panels are no help in the bass, is well made.

cheers

Panels are most effective 1/4 wavelenth distance from the wall as this is where airspeed is the highest.
Indeed doesn't mean they're not effective closer to the wall but their effectiveness does decrease.
Here a good calculator: http://www.acousticmodelling.com/porous.php

I don't think you can make a 4 inch thick panel which has an absorption coefficient of 0.8 at 125Hz when directly placed on a wall. (though with airgap / placed some distance from the wall it's very easy).
It's not just about thickness of the absorber, it's specifically about the distance from the wall as air does not move at the wall where it bounced off only pressure increases at the wall. But porous absorbers only absorb when the air moves. This is why you will see a higher absorption coefficient for your 4 inch panel at 125Hz when it is in free air than you will see at that freq when it's directly against a wall (for sound hitting it perpendicular)
 
Last edited:

aac

Active Member
Joined
May 17, 2020
Messages
217
Likes
163
I think he's more of the opinion that in an average living room, with carpet and furniture, adding further treatment may make the room too dead. "Average living room" though is a generalization, and many average living rooms could have very different sound signatures. If you've got tile floors, glass walls, granite counters, and only "modern" furniture, you're probably gonna have to add some absorption to make that room sound good, and I don't think Toole would disagree with that.
F. Toole is an advocate of using quite massive absorption at least on some surfaces.
 
Top Bottom