A Broad Discussion of Speakers with Major Audio Luminaries

[Newman]

I accept that a flat on-axis response and linear-ish off-axis should be pretty high on the list of priorities for good sound in a loudspeaker. However, since I'm still a bit new to the subject of speaker design, after watching some of Alain's videos (like the one below), I also wonder about many of the features/characteristics he also seems to be indexing for, like the better time domain performance of sealed cabinets, for example.

It is just not productive to emphasise design specifications over performance specifications.

Almost any design element can be done well or done poorly, so execution is more important than any 'rules' about what type of driver or cabinet or materials.

That is why Dr Toole and other key players on ASR have adopted the approach of identifying the performance specifications that correlate with listener preference. Trying to come up with a design attribute / features checklist is almost futile and very likely to lead people to poor speakers with the 'right' features.

When we look to performance first and foremost, we can then celebrate the diversity of speakers that can deliver great performance, instead of getting lost in rabbit-hole discussions about features.

cheers

 

[Floyd Toole]

Sorry to keep dragging the conversation back to nerdy science, but there is more than YouTube evidence on the topic. Here is an except from the upcoming 4th edition, also in the 3rd edition. It follows a long section with numerous references concluding that phase shifts and group delay in general, are not audible problems in practical domestic and pro monitor loudspeakers. This is contrary to numerous opinions floating around, even those with high production value video accompaniment and chummy dialogue.

"9.6.4 Phase Shift at Low Frequencies—a Special Case

In the recording and reproduction of bass frequencies there is an accumulation of phase shift at low frequencies that arises whenever a high-pass filter characteristic is inserted into the signal path. It happens at the very first step, in the microphone, then in various electronic devices that are used to attenuate unwanted rumbles in the recording environments. More is added in the mixing process, storage systems and in playback devices that simply don’t respond to DC. All are in some way high-pass filtered. One of the most potent phase shifters is the analog tape recorder. Finally, at the end of all this is the loudspeaker which cannot respond to DC and must be limited in its downward frequency extension. I don’t know if anyone has added up all of the possible contributions, but it must be enormous. Obviously, what we hear at low frequencies is unrecognizably corrupted by phase shift. The question of the moment is, how much of this is contributed by the woofer/subwoofer, is it audible and, if so, can anything practical be done about it? Oh yes, and if so, can we hear it through a room?

Fincham (1985) reported that the contribution of the loudspeaker alone could be heard with specially recorded music and a contrived signal, but that it was “quite subtle”. The author heard this demonstration and can concur. Craven and Gerzon (1992) stated that the phase distortion caused by the high-pass response is audible, even if the cut-off frequency is reduced to 5 Hz. They say it causes the bass to lack ‘tightness’ and become ‘woolly’. Phase equalization of the bass, they say, subjectively extends the effective bass response by the order of half an octave. Howard (2006) discusses this work, and the abandoned product that was to come from it. There was disagreement about how audible the effect was. Howard describes some work of his own, measurements and a casual listening test. With a custom recording of a bass guitar, having minimal inherent phase shift, he felt that there was a useful difference when the loudspeaker phase shift was compensated for. None of these exercises reported controlled, double-blind listening tests, which would have delivered a statistical perspective on what might or might not be audible, and whether a preference for one condition or the other was indicated.

The upshot of all of this is that, even when the program material might allow for an effect to be heard, there are differences of opinion. It all assumes that the program material is pristine, which it is not, nor is it likely to be in the foreseeable future. It also assumes that the listening room is a neutral factor, which it cannot be. However, if it can be arranged that these numerous other factors can be brought under control, the technology exists to solve the residual loudspeaker issue."

 

[MaxwellsEq]

These are pretty short, digestible videos btw

You can do yourself a favor: stop watching and trusting YouTube click bait and instead read.

Read AES papers or published books such as Floyd Toole's.

 

[gnarly]

In the recording and reproduction of bass frequencies there is an accumulation of phase shift at low frequencies that arises whenever a high-pass filter characteristic is inserted into the signal path. It happens at the very first step, in the microphone, then in various electronic devices that are used to attenuate unwanted rumbles in the recording environments. More is added in the mixing process, storage systems and in playback devices that simply don’t respond to DC. All are in some way high-pass filtered. One of the most potent phase shifters is the analog tape recorder. Finally, at the end of all this is the loudspeaker which cannot respond to DC and must be limited in its downward frequency extension. I don’t know if anyone has added up all of the possible contributions, but it must be enormous. Obviously, what we hear at low frequencies is unrecognizably corrupted by phase shift. The question of the moment is, how much of this is contributed by the woofer/subwoofer, is it audible and, if so, can anything practical be done about it? Oh yes, and if so, can we hear it through a room?

I can't understand why whatever went on in a recording process should effect what we want in a speaker. For me, a speaker should simply be able to reproduce whatever signal is given it, without out regard to either imperfections or perfections in the signal.
So if a particular track is either massively phase corrupted or not, I ask the speaker to reproduce it as is........without adding any further phase sift.

In the same vein, I think small room masking is also immaterial to what I want in a speaker. Why let the limitations of the listening room, be a reason to forego technical excellence? Doesn't make sense to me.

With all due respect, it seems like both of those reasons not to be concerned with phase, are more in the manner of excuses for allowing audio at large to continue to dismiss it.

 

[Alice of Old Vincennes]

I can't understand why whatever went on in a recording process should effect what we want in a speaker. For me, a speaker should simply be able to reproduce whatever signal is given it, without out regard to either imperfections or perfections in the signal.
So if a particular track is either massively phase corrupted or not, I ask the speaker to reproduce it as is........without adding any further phase sift.

In the same vein, I think small room masking is also immaterial to what I want in a speaker. Why let the limitations of the listening room, be a reason to forego technical excellence? Doesn't make sense to me.

With all due respect, it seems like both of those reasons not to be concerned with phase, are more in the manner of excuses for allowing audio at large to continue to dismiss it.

Not an excuse. Just a waste of time.

 

[kyuu]

With all due respect, it seems like both of those reasons not to be concerned with phase, are more in the manner of excuses for allowing audio at large to continue to dismiss it.

I think you're confusing "excuses" with an explanation of why it's not something to be concerned about.

 

[Alice of Old Vincennes]

I think you're confusing "excuses" with an explanation of why it's not something to be concerned about.

I suppose. I think we are on same page. It was a satire.

 

[Suono]

can't understand why whatever went on in a recording process should effect what we want in a speaker. For me, a speaker should simply be able to reproduce whatever signal is given it, without out regard to either imperfections or perfections in the signal.
So if a particular track is either massively phase corrupted or not, I ask the speaker to reproduce it as is........without adding any further phase sift.

In the same vein, I think small room masking is also immaterial to what I want in a speaker. Why let the limitations of the listening room, be a reason to forego technical excellence? Doesn't make sense to me.

With all due respect, it seems like both of those reasons not to be concerned with phase, are more in the manner of excuses for allowing audio at large to continue to dismiss it.

I think the same way

 

[Arindal]

It follows a long section with numerous references concluding that phase shifts and group delay in general, are not audible problems in practical domestic and pro monitor loudspeakers.

It would be interesting if there is any updated research on that matter from the last 25 years. Not only because in this period a lot of EDM appeared which came with synthesized bassdrum sounds which are subjectively much more transient and punchy even to their lowest frequencies. What was used for listening tests before the mid-1990s, is not necessarily relevant to this question, as the sounds themselves were produced with measures applying group delay on the lower bands (yes, even Moroder´s famous click-induced disco beats). Daft Punk have been mentioned already as pioneers of bass sound design, their work is a good example for even traditionally recorded kick drums being sampled and made subjectively ´faster´.

The other aspect is DSP active speakers appearing which are truly linear phase. I remember undergoing some comparison tests organized by K+H (now Neumann) who showed that group delay in the bass region is clearly audible with synthesized beats above a certain threshold.

When it comes to judging bass quality we should not forge that there is more than just group delay, lower cutoff frequency and SPL. Although resonance issues and long decay might be attributed to the room and its modes in most of cases, speakers seem to show differences here as well. Same with any type of frequency- or level-dependent linear distortion such as compression or expansion, and may it be in a narrow band. According to my experience this is why many compact speakers don't produce substiantially ´kicking´ lower bass even if they technically reach as low as necessary.

 

[amirm]

So if a particular track is either massively phase corrupted or not, I ask the speaker to reproduce it as is........without adding any further phase sift.

If that fix comes for free, why not. What I routinely see is that timing/phase correction comes at high cost of screwing up other parts of the response. Correct timing, whatever that is, appeals to layman so has become a major selling point for some speakers. You get products with massively screwed up phase response but hey, they got the phase right!

 

[amirm]

Why let the limitations of the listening room, be a reason to forego technical excellence?

The right word is not limitation but reality. A lot of research is conducted both in anechoic and actual rooms because the two are very different. Phase is one of those where in anechoic chamber with contrived signals, subtle audibility differences are heard but in real rooms, that difference disappears. The room is the last part of the chain that connects the speaker to your ear and it massively stomps on any phase response. Even if you build a fully padded cell, this will happen. Ergo, put your efforts in other things that matter.

 

[amirm]

I can't understand why whatever went on in a recording process should effect what we want in a speaker.

The point was being made that folks are not screaming when phase gets demolished over and over again in the production chain. If it is such an issue in just one component in our listening space, why isn't it a horror show in production?

Further, if the talent/engineer/label heard it with phase corruption, why would you want a different reproduction without?

 

[Keith_W]

I think we need @j_j to jump in with a response about phase inaudibility.

The way I see it, INTRAchannel phase distortion is audible in a free-field, and with live instruments. Griesinger has written about the proximity effect where instruments lose their focus / sense of immediacy after a certain distance where phase becomes incoherent after being distorted by reflections. As anybody who has attended a live performance of acoustic instruments will tell you, the experience of sitting further away is definitely true, although I am less confident that loss of phase coherence is the only explanation.

The real question for us, who listen to recordings in listening rooms, is whether intrachannel phase distortion is still audible after:

- it has been distorted by the cumulative effect of multiple minimum-phase devices in the recording process - microphones, mixing consoles, etc.
- it has been reproduced by minimum-phase loudspeakers
- it is distorted by the minimum-phase and non-minimum-phase behaviour of listening rooms

It has been pointed out that non-acoustic recordings do not have phase distortion (or maybe minimal phase distortion), and we have linear phase loudspeakers in 2025. So the only remaining question is whether phase distortion in listening rooms is sufficient to corrupt remaining phase information to the extent that it becomes inaudible. Of course this is a YMMV question since every listening room is different, but it is an important question that needs to be answered since that influences our choice of speakers that are narrow/wide directivity and how much we should attempt to dampen reflections in listening rooms.

Given that we have some heavyweights in this discussion, perhaps someone is aware of a study that answers the third question. For a given listening room, and given linear phase recordings and linear phase loudspeakers, does room masking sufficiently corrupt phase to the extent that it becomes inaudible?

 

[Suono]

When it comes to high fidelity, I want linear speakers, off-axis coherent speakers, and phase coherent speakers. If the recordings aren't, never mind; as for the listening room, it's up to the end user. Regarding the audibility of distortion in high fidelity, I generally have a very clear idea. In high-fidelity stereo reproduction, nothing can be left to chance. Everything is important, and some designers consider and address the issues that could distort the signal.

 

[amirm]

it's up to the end user.

It isn't. By definition your room is not an anechoic chamber so it will corrupt the phase and repeatedly so.

 

[amirm]

but it is an important question that needs to be answered since that influences our choice of speakers that are narrow/wide directivity and how much we should attempt to dampen reflections in listening rooms.

That is the issue: plenty of research shows that we enjoy certain reflections in the room. Eliminating them, and certainly making a dead room, is a detriment to good sound enjoyment. All to address something that we can't even tell if it has value???

 

[Suono]

It isn't. By definition your room is not an anechoic chamber so it will corrupt the phase and repeatedly so.

Of course, you're right, but my direct sound must be in phase. An instrument, a violin or a cello, playing in my room is in phase

 

[Holmz]

It isn't. By definition your room is not an anechoic chamber so it will corrupt the phase and repeatedly so.

How?

If the person can determine the direct sound when the earliest reflections are a delayed by a certain number of milliseconds, then whatever is happening in the room would only affect more of the steady-state stuff.
Or what am I missing here?

 

[gnarly]

If that fix comes for free, why not. What I routinely see is that timing/phase correction comes at high cost of screwing up other parts of the response. Correct timing, whatever that is, appeals to layman so has become a major selling point for some speakers. You get products with massively screwed up phase response but hey, they got the phase right!

I guess you meant to say 'you get products with massively screwed up phase response, but hey, they got the timing right!
If so, I agree! and shake my head at such marketing claims as well.

That 'got time alignment right, but not phase too', is the only example I can think of where regular frequency response gets screwed up. (regular meaning frequency magnitude-only )

Because ff time and phase alignment are both correct, it can only help the optimization of the regular response. It cannot hurt.

So it's unfair imo, to ever blame timing/phase alignment for screwing up response.
Or to say it can have a cost to other parts of the response (which really is technically impossible.)
Scientifically, i think we can only blame poor implementations.

 

[Floyd Toole]

The other aspect is DSP active speakers appearing which are truly linear phase. I remember undergoing some comparison tests organized by K+H (now Neumann) who showed that group delay in the bass region is clearly audible with synthesized beats above a certain threshold.

This has been one of the dilemmas in psychoacoustic investigations - differences can be heard (the phenomenon is "real") but preferences are not statistically reliable (the phenomenon is common in everyday life, and it is at least somewhat normalized). We live in rooms and reflected sound is part of everything we hear, even conversing across a table distorts the amplitude and phase of voice sounds, ever changing as we move around, leaning forward or back, standing, sitting, etc. Measurements indicate horrendous acoustical interference effects - amplitude and phase variations - but we are not conscious of any of them.

In recordings all these variables get "fixed" in time, we have no means of separating what is a characteristic of the sound source from that which has been added by the recording environment or the playback apparatus. The recordings are not binaural, dummy head, with head-movement-compensated playback, allowing us perceptually to perceive the sound source in its environment. The direct sound from the source to the mic and all reflections are simply added together. So we end up having discussions of the present kind.

An ABX test can reveal whether there is an audible difference. It is blind, so the result can be trusted. But it does not scale the magnitude of the perceived difference. It is there, but how significant is it in real world listening contexts? That is a much more difficult question to answer. The "laboratory" demonstrations use signals deliberately selected or electronically generated (like clicks or impulses) to magnify any possible audible effects, These are as "fast" as any real or synthesized kick drum, but they may or may not duplicate the spectrum of that signal. The perception may be different, but the effect, if there, should be audible. Then the question is: which one is preferable? That is a different question and it introduces the further question of what did it sound like to the creators? It is art.

All this brightens many an otherwise dull day . . .