The importance of time alignment for subwoofers

[Cosmik]

Not sure where this experiment might lead. Both a and b have their problems so possibly neither would sound good, and the choice might be moot.

I do not think DSP room correction is a perfect or precise solution to the messy and very complex problem of room acoustics. Nothing is. All I know is that it is a sonic revelation offering much preferred performance with recordings I enjoy. I would never be without it. And, it is cheap relative to what it achieves, in my view.

Yes, we may adapt to the sound we have in our rooms if we choose to. But, there are limits to that, which you don't seem to wish to acknowledge. I would rather adapt to sound that measurably corrects for some, if not all, of the problems in the room than a system which does not. The good may be good enough, even if imperfect. Room correction might even do some harm, but never have I heard it do so with proper calibration compared to no correction. The latter does more obvious harm in my experience.

But if there's direct sound and reflected sound and it is the effect of the reflections that you are seeking to 'correct' by modifying the signal, then you will also be forced to hear the direct sound 'corrected' will you not? It's just not doing what it is advertised to do.

On the other hand, using DSP to render the speaker itself as neutral as possible is valid and does just what it says on the tin. How many people launch into 'room correction' (I apologise for the quote marks but I have to use them!) without first getting their speakers neutral? Half the time, I'll bet, the 'room correction' is indirectly and partially correcting the speaker e.g. a subwoofer that sounds 'slow' because it is not already phase-corrected.

The only way to really modify the reflections in isolation from the direct signal is to change the room - and that's not the end of the world. And many rooms (if they have a fitted carpet!) are probably not all that bad anyway.

Edit: Off-topic (bass), but I just found Sound and Carpet - The Movie

 

[DonH56]

Some correction/measurement programs allow you to specify a time window so you can filter out (some) reflections. Be nice if more did, and made it easier on the users... Still not a panacea.

 

[Fitzcaraldo215]

Some correction/measurement programs allow you to specify a time window so you can filter out (some) reflections. Be nice if more did, and made it easier on the users... Still not a panacea.

Agreed, Don. And, I think an excessively reflective room is going be bad no matter what you do, DSP or not.

 

[Fitzcaraldo215]

But if there's direct sound and reflected sound and it is the effect of the reflections that you are seeking to 'correct' by modifying the signal, then you will also be forced to hear the direct sound 'corrected' will you not? It's just not doing what it is advertised to do.

On the other hand, using DSP to render the speaker itself as neutral as possible is valid and does just what it says on the tin. How many people launch into 'room correction' (I apologise for the quote marks but I have to use them!) without first getting their speakers neutral? Half the time, I'll bet, the 'room correction' is indirectly and partially correcting the speaker e.g. a subwoofer that sounds 'slow' because it is not already phase-corrected.

The only way to really modify the reflections in isolation from the direct signal is to change the room - and that's not the end of the world. And many rooms (if they have a fitted carpet!) are probably not all that bad anyway.

Edit: Off-topic (bass), but I just found Sound and Carpet - The Movie

What we hear in reality is the sum of both direct and reflected sound, and that combined response is what room EQ seeks to correct. Even if the speakers were perfect, the reflections still might cause response at the listening seat to be off target one way or another. If reflections do not distort the combined response in certain frequency ranges, then no correction filters are applied to those ranges. That is pretty much how all room correction systems work, and we do not hear the direct and reflected response separately, only the net combined result. The effect on just direct response is unimportant as long as the combined direct plus reflected response is more frequency linear.

As we know, there is a difference between bass response below the transition frequency and mid/hi response above. The former is subject to modal variations due to reflections, and they are not controversial. Such modal response variations are quite large in any room I have measured, as they are throughout the literature. Toole discusses this at length, as do countless others. Correction of modal issues are the key advantage of room correction, and DSP EQ is widely used by acousticians for this purpose. Passive or even active correction schemes for the bass are large, ungainly, difficult and expensive in home installations if they are to be effective at bass wavelengths.

EQ of response above the transition frequency is more controversial, and some prefer not to use it. Many EQ tools allow for correction to be turned off for those frequency ranges if desired. I prefer full range EQ with a slight downward slope with increasing frequency, myself, similar to response curves derived by Toole and many others. Measurements indicate this EQed response is superior in my room with my speakers. It sounds much better to me, as well. But, YMMV.

Yes, DSP EQ is about correcting combined response only in one area of the room, near the sweet spot. It might not be as perfectly optimized for other positions nearby or it may be optimized for an average of multiple nearby positions, with each being suboptimal relative to an EQ done separately for each individual seat. Still, as I change seats across my 3 listening seat setup, results to me sound significantly better in each case than with no EQ. There is also variability with no EQ in any case.

 

[Cosmik]

What we hear in reality is the sum of both direct and reflected sound, and that combined response is what room EQ seeks to correct.

1. Why listen in a room, then? Just sit close to the speakers or wear headphones.
2. How do you recognise people's voices when they are speaking to you in unfamiliar rooms?
3. How do you identify where voices are coming from in a room?

To me it seems obvious that we separate out the direct from the reflected sound. It isn't just a 'soup' of sound. But it's all off-topic anyway!

 

[Kal Rubinson]

1. Why listen in a room, then? Just sit close to the speakers or wear headphones.
2. How do you recognise people's voices when they are speaking to you in unfamiliar rooms?
3. How do you identify where voices are coming from in a room?

To me it seems obvious that we separate out the direct from the reflected sound. It isn't just a 'soup' of sound. But it's all off-topic anyway!

There are reasonable answers to each of these questions but, in general, they seem to be addressing only the recognition and identification of sounds and not their optimal and accurate perception.

 

[Cosmik]

I prefer full range EQ with a slight downward slope with increasing frequency, myself, similar to response curves derived by Toole and many others.

I think Dr. Toole may have modified his views over time..? He currently says:

Humans evolved while listening in reflective spaces, and are comfortable listening in them. In fact, it is now widely recognized that we perceptually "stream" the sound of the room as separate from the sound of the sources - that is what happens in live performances. A Steinway is a Steinway; only the hall changes....

...The parallel situation in sound reproduction is that a good loudspeaker is a good loudspeaker, and its virtues are appreciated in a wide variety of rooms – except for the differences in the bass region. ...

...As I said, humans, because of binaural hearing, are well equipped to deal with reflective spaces. Two ears and a brain are much “smarter” than a microphone and analyzer.

...Reflections within listening rooms are real and numerous. Some would argue that they all are problems to be eliminated. Others take a more philosophical view that they just provide information about the room, and the brain can figure it out. I’m somewhere in the middle, but leaning towards the latter. The science that has been done so far seems to be on my side.

He seems to be implying that if you go modifying the Steinway to 'correct' the room (above the bass frequencies), you no longer hear the Steinway but some other instrument with a different tonal character - which is my argument, too.

 

[Fitzcaraldo215]

1. Why listen in a room, then? Just sit close to the speakers or wear headphones.
2. How do you recognise people's voices when they are speaking to you in unfamiliar rooms?
3. How do you identify where voices are coming from in a room?

To me it seems obvious that we separate out the direct from the reflected sound. It isn't just a 'soup' of sound. But it's all off-topic anyway!

I agree with Kal.

1. Sure, that gets rid of room effects. I don't like listening either of those ways, and there are numerous downsides. Mostly, people like listening in rooms in the far field. But, if those ideas are what you prefer, then do it.

2. There are essential, recognizable tonal, speech pattern and other signatures in voices, like fingerprints or facial characteristics. Mostly, rooms do not suffienctly distort that so as to make people's voices unreconizable. However, an excessivly reflective or reverberant room might make it difficult or impossible. Also, too little reflected energy might make recognition more difficult, such as with a person outdoors at some distance away.

3. Please read up on the Haas Effect for starters. Direct sound arrives first, and usually loudest, and it provides the main directional information. Then, the presence of early reflections are masked by it, though the reflections combine with and alter the tonality of the perceived sound, though we are unaware of the presence of those early reflections. Early reflected sounds might also alter perceived location, such as a perceived widening of the soundstage with music playback when speakers are positioned to cause more lateral reflections.

 

[svart-hvitt]

I think Dr. Toole may have modified his views over time..? He currently says:

He seems to be implying that if you go modifying the Steinway to 'correct' the room (above the bass frequencies), you no longer hear the Steinway but some other instrument with a different tonal character - which is my argument, too.

Is piano recorded in anechoic chamber? Recording is of piano plus room, n’est-ce pas?

 

[Cosmik]

I agree with Kal.

1. Sure, that gets rid of room effects. I don't like listening either of those ways, and there are numerous downsides. Mostly, people like listening in rooms in the far field. But, if those ideas are what you prefer, then do it.

2. There are essential, recognizable tonal, speech pattern and other signatures in voices, like fingerprints or facial characteristics. Mostly, rooms do not suffienctly distort that so as to make people's voices unreconizable. However, an excessivly reflective or reverberant room might make it difficult or impossible. Also, too little reflected energy might make recognition more difficult, such as with a person outdoors at some distance away.

3. Please read up on the Haas Effect for starters. Direct sound arrives first, and usually loudest, and it provides the main directional information. Then, the presence of early reflections are masked by it, though the reflections combine with and alter the tonality of the perceived sound, though we are unaware of the presence of those early reflections. Early reflected sounds might also alter perceived location, such as a perceived widening of the soundstage with music playback when speakers are positioned to cause more lateral reflections.

Sure, you can second guess your hearing by assuming that it will register the early reflections as a change in tonality but not be able to work out that it is because of reflections. This assumes your hearing is like a microphone, laptop and simple algorithm.

Or you can assume that your hearing doesn't register it as a change in tonality at all, because it is not just a tonality analyser, but a 'tonality-timing-spatial' analyser moving in three dimensions (as you turn your head).

 

[DonH56]

This is all somewhat interesting but getting pretty far off the original topic. The big impact of the room for subwoofers is room modes and SBIR effects that cause peaks and valleys in the bass response at the MLP.

Recordings are performed in a room, true, but the recording may or may not reflect the room. Pianos are usually mic'd pretty close, usually with multiple mics, and there may or may not be a far-field mic to pick up room ambience. Many times ambience (reverb) is added during mixing after the original recording. I have heard more than once (and been involved with a few recordings myself) that all that "hall" sound was added later in the studio...

A number of folk, Toole included, advocate using room correction only for the deep'ish bass and not trying to correct the upper frequencies except perhaps with acoustic treatment. Flat direct sound from the speakers (which is naturally rolled off by the room) and good off-axis speaker response is key to their arguments IMO.

 

[Cosmik]

This is all somewhat interesting but getting pretty far off the original topic. The big impact of the room for subwoofers is room modes and SBIR effects that cause peaks and valleys in the bass response at the MLP.

Recordings are performed in a room, true, but the recording may or may not reflect the room. Pianos are usually mic'd pretty close, usually with multiple mics, and there may or may not be a far-field mic to pick up room ambience. Many times ambience (reverb) is added during mixing after the original recording. I have heard more than once (and been involved with a few recordings myself) that all that "hall" sound was added later in the studio...

A number of folk, Toole included, advocate using room correction only for the deep'ish bass and not trying to correct the upper frequencies except perhaps with acoustic treatment. Flat direct sound from the speakers (which is naturally rolled off by the room) and good off-axis speaker response is key to their arguments IMO.

Apologies for going off topic - it's just one of those discussions I can't resist.

 

[DonH56]

I think it is interesting but would be best split off into a separate thread. There have a been a lot of good discussions here (and elsewhere on the net -- endemic if not epidemic problem) that are nearly impossible to find later because they have nothing to do with the title of the thread.

 

[Fitzcaraldo215]

I think Dr. Toole may have modified his views over time..? He currently says:

He seems to be implying that if you go modifying the Steinway to 'correct' the room (above the bass frequencies), you no longer hear the Steinway but some other instrument with a different tonal character - which is my argument, too.

You are cherry picking with stuff out of the context of a much bigger picture.

Yes, what he says is true to the extent that your hearing system can separate direct from reflected sounds. But, that is not true of early reflections whose presence is masked by the direct sound, although those early reflections provably do modify one's perception of direct sound.

Note also what he says about good speakers sounding good in most rooms, except for differences in bass response. This is where DSP EQ becomes the "great equalizer", restoring bass frequency linearity that the room has messed up.

He does not see EQ as a panacea replacement for speakers with good performance characteristics. But, he is no enemy of it, either.

He also acknowledges elsewhere the limits to our ability to adapt to the sound we have in the room we have. If our ability to adapt were as great as you imply, then LPs are fine, tubes are fine, Bose's are fine, all in any room in the house, outdoors even. Further, any and all measured response issues of the room/speaker are fine, even if 5,10,20 dB or more. They are all fine. We'll simply adapt and get used to it.

 

[Cosmik]

He also acknowledges elsewhere the limits to our ability to adapt to the sound we have in the room we have. If our ability to adapt were as great as you imply, then LPs are fine, tubes are fine, Bose's are fine, all in any room in the house, outdoors even. Further, any and all measured response issues of the room/speaker are fine, even if 5,10,20 dB or more. They are all fine. We'll simply adapt and get used to it.

I, personally, am not saying that our hearing merely adapts. I am suggesting that our hearing is a complex analyser that seamlessly processes information in both time and frequency domains (one is derived from the other and vice versa) and doesn't need to adapt to the room because it is already equipped to 'read' the room from the off. As Toole says, it 'streams' the source and the room separately. It would, indeed, hear an arbitrarily messed-up source as messed-up and would need to adapt to that as best it could.

Just found this short article on the topic:
https://www.soundandvision.com/content/rethinking-room-correction

 

[Fitzcaraldo215]

I, personally, am not saying that our hearing merely adapts. I am suggesting that our hearing is a complex analyser that seamlessly processes information in both time and frequency domains (one is derived from the other and vice versa) and doesn't need to adapt to the room because it is already equipped to 'read' the room from the off. As Toole says, it 'streams' the source and the room separately. It would, indeed, hear an arbitrarily messed-up source as messed-up and would need to adapt to that as best it could.

Just found this short article on the topic:
https://www.soundandvision.com/content/rethinking-room-correction

Do this:

Toole also strongly advocates for calibrated DSP EQ, particularly below the transition frequency. He does that in his home system. So, which is it? If he thought we could simply adapt, would he do that?

I do not understand your jihad.

 

[fas42]

I, personally, am not saying that our hearing merely adapts. I am suggesting that our hearing is a complex analyser that seamlessly processes information in both time and frequency domains (one is derived from the other and vice versa) and doesn't need to adapt to the room because it is already equipped to 'read' the room from the off. As Toole says, it 'streams' the source and the room separately. It would, indeed, hear an arbitrarily messed-up source as messed-up and would need to adapt to that as best it could.

Just found this short article on the topic:
https://www.soundandvision.com/content/rethinking-room-correction

Good link! The quote, "A grand piano sounds right no matter where you place it, whether it’s in a concert hall or your living room. You don’t go in and start EQ’ing it for different acoustical environments." says it all - and that's what happens when a playback is working well enough.

Personally, I have been amazed at how powerful this human processing mechanism is, on so many occasions - with recordings that are in terrible shape, that sound like an aural Nightmare on Elm Street on normal systems; which can dramatically reveal their musical "soul", when the system is up to it. The recording is "full o' crap" - but my hearing dives right through the middle of all that - and extracts the core that makes it worth listening to, effortlessly.

 

[Kal Rubinson]

Is piano recorded in anechoic chamber? Recording is of piano plus room, n’est-ce pas?

Let's distinguish between a Steinway as heard in different rooms from a recording of the Steinway in any one of those rooms played in yet another.

 

[Kal Rubinson]

Good link! The quote, "A grand piano sounds right no matter where you place it, whether it’s in a concert hall or your living room. You don’t go in and start EQ’ing it for different acoustical environments." says it all - and that's what happens when a playback is working well enough.

Let's distinguish between a Steinway as heard in different rooms from a recording of the Steinway in any one of those rooms played in yet another. Shall I say it again?

 

[Don Hills]

... Recording is of piano plus room, n’est-ce pas?

Not usually. It's common to close-mike the piano under the lid, capturing the maximum direct sound and the minimum room sound. In theory, it's quite unlike the natural "live" piano sound, which includes the contribution of the other side of the soundboard and the room acoustics. In practice, it's proven to translate better when listening to the reproduction in another room.