delay in right speaker-ETC?

[tonio]

After few acoutical treatments, I noticed that my right speaker is delay vs the left. Mostly from the mids on up, and some of the peak/nulls appear to be out of phase in a ETC render.
Mix position is typical @38%. Speakers are equlateral triangle and is set up within 1". Right front corner has 2 windows.
I confirmed its not my equipment by measuring up close to the speakers

Caveat of being coupled with left rear door(to hallway) & right rear ( to dinning room ).
I made a portable panel set that goes into the right rear opening, the other doorway is stil open other than a coner trap ( whcih covers half of the opening).

Any ideas?

T

[tonio]

Thanks SAC,
Besides the windows in the front right corner, and the coupled openings all else is generally symetrical.
So plug all openings to see if they are contributing .... ah , so perhaps its a combination of the windows and left opening since the right opening is panelled up. Just guessing at this point of course.

T

[tonio]

thumbsup

I'll work on it

T

[macc]

Originally Posted by SAC

And I would be comparing the actual response to the desired ISD chosen to compliment that particular space in which the measurements are taken and the manipulation of the subsequent later soundfield.

Hi SAC,

I'm sure it would take someone more vastly experienced than I, but how would one go about figuring out 'the desired ISD'? Is it a matter of experience/practice, or is there a formula or something (I doubt it ). Just out of interest, like.

Sorry to butt in here, but it looked like you were all done so

[Still really enjoying my room by the way, but always more that can be done!]

[avare]

Originally Posted by macc

Hi SAC,

I'm sure it would take someone more vastly experienced than I, but how would one go about figuring out 'the desired ISD'?

The short answer, SAC is working on the complete one, is the specification. EBU/ITU listening room recommendations specify at least 15 ms with sound in that time at least 10 dB down. The traditional spec is 20 ms.

SAC will make it complete with the underlying pschoacoustics involved.

Andre

[macc]

Absolutely wonderful - thanks chaps.

As an aside, I'm very much enjoying my journeys into acoustics - beyond 'trap the arse off of everything', I mean

I'd like to take this chance to thank Lupo (who has been nothing short of wonderful), SAC for his detailed in insightful posts, and all the other peeps whose names escape me. Hopefully you know who you are.

I don't post a lot on this part of the forum, but I read a lot

[Dange]

Originally Posted by avare

The short answer, SAC is working on the complete one, is the specification. EBU/ITU listening room recommendations specify at least 15 ms with sound in that time at least 10 dB down. The traditional spec is 20 ms.

SAC will make it complete with the underlying pschoacoustics involved.

Andre

Where did the 20ms come from for small rooms? I've seen references to Beranek's investigations of concert halls ISDs but don't have a copy of that book.

I also look forward to reading SAC's 'long' answer!

And.. could you get a 'significant reflection' off a large mixing desk that would mess up your ISD?

[Dange]

Originally Posted by SAC

Can you? ABSOLUTELY - as well as off the bridge where, too often, speakers sit!
And forget 10 or 15 ms! These reflections are of VERY short delay.

Thanks, I've actually just read the paper from the (1982) 72nd AES convention about the history and development of LEDE and one of the first things D. Davis and R. C. Heyser found with the TEF system was the reflection from the desk....

Actually also SAC any pointers for reading on the psychoacoustics of ISD? Papers or books...

[PaulP]

Originally Posted by Dange

any pointers for reading on the psychoacoustics of ISD? Papers or books...

Floyd Toole's book has about a hundred pages on the matter.

Paul P

[tonio]

Hows about a perforated metal desk? Or would the diffusive character totally wack it out.
T

[Dange]

Originally Posted by tonio

Hows about a perforated metal desk? Or would the diffusive character totally wack it out.
T

By desk I meant the mixing desk. Say you were to drill holes in it (!!) to create a diffusing effect, maybe like the RPG bad panel. This would reduce the intensity of the reflection off the desk, therefore possibly not shortening the ISD.

[Dange]

Originally Posted by PaulP

Floyd Toole's book has about a hundred pages on the matter.

Paul P

Cheers Paul, I've had a look through it on google books.

Now I have a question, at what point does the ISD become too long? I can't seem to pin down a definitive answer...

ITU says up to 15ms.
I've seen up 20ms 'and not much more' here - Acoustics and Psychoacoustics Applied - Part 1: Listening room design | Audio DesignLine

A post of SAC's mentions 20-30secs here - http://www.gearslutz.com/board/4928170-post8.html

So if I've got this right, you can make a room seem bigger than it is by creating a longer ISD. This is done by reducing the level of the first reflections, off side walls, ceiling etc. by at least 10dB compared to the direct signal. This longer ISD allows you to hear the ISD of the room of the recording you're listening to.
You need to trigger the Haas effect within a certain amount of time by a single rear reflection or a diffuse 'reflection' field (e.g. from a QRD on back wall). However, if this is too long the reflection will be perceived as an echo.

[Dange]

I might have answered this myself, going by Haas the maximum could be up to 30ms.......

[PaulP]

Originally Posted by Dange

So if I've got this right, you can make a room seem bigger than it is by creating a longer ISD. This is done by reducing the level of the first reflections, off side walls, ceiling etc. by at least 10dB compared to the direct signal. This longer ISD allows you to hear the ISD of the room of the recording you're listening to.
You need to trigger the Haas effect within a certain amount of time by a single rear reflection or a diffuse 'reflection' field (e.g. from a QRD on back wall). However, if this is too long the reflection will be perceived as an echo.

Sounds about right. The following picture from Everest gives a good overview :

If you follow down this path you may notice that certain 'common wisdom' practices
often discussed here may act against you. Also it depends on what you're after as
many people seem to prefer a very dry environment. Dry and spacious are pretty
much opposites.

Paul P

[Nordenstam]

Prefer this one now, instead of the (older one) above:



As this one goes to show the variable nature of the phenomena. Notice that the dotted speech curve is the same as shown in the A curve in the post above.

Originally Posted by PaulP

Floyd Toole's book has about a hundred pages on the matter.

The book have been ordered. Thanks for the tip!


Have seen several mentions of 17ms as an ideal time for ending the ISD. 20ms seems pretty common, probably due to the proliferation of great concert halls having an ISD ending at 20ms. In large room acoustics, 20ms have found to be a common factor in many popular halls. Larger than this and it makes things swim around. Smaller ISD makes the room seem too small.

[Nordenstam]

PS: most of you guys have seen this thread before, just have to repeat it in case it got lost on some of the readers.

The before/after change in these measurements from my room is the most significant change in sound I've ever heard in my life:


The upper/before measurement does not have a definite end to the ISD. What I heard in the before graph was a very supressed room with a richly diffused tail. Although early reflections where supressed down to -20dB, there was no definite end to the ISD. This means that the brain latches onto the first reflection as the ISD terminator. Which, as can be seen in the graph, was only a few millisecs after the initial sound.

In the second/after graph, reflections have been suppressed further down to -24dB. The brain will hear the loud reflection close to 20ms as the ISD terminator. As far as I've gathered, this not only means that the room sounds like it's way much bigger than it is. (physically speaking, 20ms is equivalent to having the nearest wall 7 meters away. Which means my 65 cubic meter room sounds like its' about 20 times larger than it really is!) As I've gathered, part of the magic of this "trick" is that the brain effectively disregards the earlier reflections is junk/noisefloor. Effectively rendering the RFZ as an anechoich enviroment within the ISD.

In other words: one gets the clarity and definition of having an anechoich response within the first 20ms, followed by a rich and dense reverb tail.

Compare, again, to the first/above graph. The reflections are very suppressed, sure, but it's way far off from being actually anechoich. The brain will hear those reflections and it'll hear what sort of room structure the reflections correspond to. So the second graph not only have much more life and fun to it, making the room more enjoyable. It also have higher precision within the ISD/RFZ, a sort of precision that can not be had if there is no definite end to the ISD.


PS: am I doing something wrong in equating ISD with RFZ? Seems to me the terms are interchangeable..

[PaulP]

Originally Posted by Lupo

PS: am I doing something wrong in equating ISD with RFZ? Seems to me the terms are interchangeable..

They're related but I wouldn't say they were interchangeable. The ISD is a
measure of time whose value may or may not be appropriate. A room is
designed with a RFZ as a way of lengthening the ISD. Instead of simply
elliminating the early reflections as was done in a LEDE room, the room with
a RFZ may aim to send them elsewhere until the desired ISD is reached.

So the 'zone' in RFZ is not a zone in the decay graph, it's a zone in the room,
the physical space that has been shaped/treated to get a particular ISD
to appear on the graph.

Paul P

[Dange]

Originally Posted by PaulP

They're related but I wouldn't say they were interchangeable. The ISD is a
measure of time whose value may or may not be appropriate. A room is
designed with a RFZ as a way of lengthening the ISD. Instead of simply
elliminating the early reflections as was done in a LEDE room, the room with
a RFZ may aim to send them elsewhere until the desired ISD is reached.

So the 'zone' in RFZ is not a zone in the decay graph, it's a zone in the room,
the physical space that has been shaped/treated to get a particular ISD
to appear on the graph.

Paul P

Slight correction, an LEDE does have a RFZ, this is created by the absorption at the 'Dead End'. The RPG/RFZ D'Antonio design creates a RFZ using room geometry rather than absorbers


I am having a slight issue with Haas

One conclusion in the paper is 'The magnitude of the auditory "suppression effect" for echoes with 1- to 30-ms difference was found to be 10 dB, i.e., the intensity of the echo must exceed that of the primary sound by 10 dB in order to make the echo separately perceptible in the said range of delay differences.'

Where in the real world are you going to get an echo/reflection that's 10dB louder than the direct sound?

[PaulP]

Originally Posted by Dange

Where in the real world are you going to get an echo/reflection that's 10dB louder than the direct sound?

In sound reinforcement a satellite speaker can provide the equivalent of a
reflection. This can be set to any volume you want but because of Haas
you don't want it more than 10db louder (the amount of delay is important
too) or the sound will no longer appear to come from the stage.

Paul P

[avare]

Originally Posted by PaulP

In sound reinforcement a satellite speaker can provide the equivalent of a reflection. This can be set to any volume you want but because of Haas you don't want it more than 10db louder (the amount of delay is important too) or the sound will no longer appear to come from the stage.

What Paul wrote is correct. What is often (almost always) forgotten, is that the higher level delayed signal will noticeably color the sound. It just will not be noticed as a discrete signal. Somewhat irrelevant for live sound, but with our emphasis here being accuracy, I am mentioning it to be forum topically complete.

Andre

[macc]

[long post alert]

That post linked above: http://www.gearslutz.com/board/4928170-post8.html

I wish I had read that ages ago! Good thing is, I am finally starting to *get it*. And it is good. Actually, sod it - as this is about the most appropriate thread, I hope you all don't mind if I have a bit of a waffle…

I’ve just taken my first (ok, second) step in this direction and I have to say that the results are absolutely stunning.

I moved into a new room about 3 months ago - 28.5 feet long, about 10 feet wide, bit narrow but not too bad. Speakers are K+HO300, twinned with a pair of Rythmik F12G subs. I asked Lupo for some advice and he went to work, giving me the idea of building a false acoustic wall about 2/3ds of the way into the room, loading the rear with large amounts of absorption. The ‘wall’ is (currently) constructed of 2 RPG skylines stacked vertically in the middle, flanked by two angled RPG QRDs, all standing on a ‘custom’ *cough* table/bass trap affair. There’s a third QRD on its side down in front of this whole thing, and out to the sides, flanking the QRDs, are two big reflectors…. which are currently made of piled up gear boxes. I’ll be getting some bigarse wood panels soon enough. The cardboard is high end though – Maselec, K+H, etc

So, to the point. After a lot of emails with Lupo, about a zillion measurements, endless days of moving, nudging etc (you know the drill), I have ended up with an ISD that is, at its worst, 21.5dB down. This is terminated at ~21ms by a pretty big reflection, which precedes the tail. The tail itself is not perfect – and not as linear as Lupo’s! - but far far better/smoother/more linear than it was. Comparing the ETCs from ‘before diffusion’ to now show a huge increase in the general energy level in the room, much improved decay linearity, no reflections apart from the ‘kicker’ poking out (at least, none that concern me greatly), and, of course, the kicker itself.

Having had a few days listening, I have a number of thoughts. On the one hand, I think I need to define the ISD a little better. That is, I need to increase the difference between RFZ/ISD and the trigger, partly through bringing 8.5ms down and the kicker up a bit. At least, I want to. On the other hand, I have to say that it sounds truly absolutely amazing. To think that this room can sound this way… utterly incredible. More life, more envelopment and involvement, detail and depth, essentially flat down to 14Hz… life is good

Specifically in relation to this thread, after doing careful listening to/at the edges of the soundfield, I am not 100% sure if I would say the room itself feels bigger. I’m not sure that the sound is coming from beyond the boundaries. But the sound is absolutely HUGE, make no mistake. I would say that the room is 100% full of the sound, the sound reaches to the absolute extremes. It is as though the room is so full of sound that it could burst, like a tyre with too much air pumped into it. This was not the case before, when I just had diffusion. I would say that going from 'no diffusion' to 'with diffusion' was a more dramatic change, in fact it was one of the best moments I have had in a long time. But from 'no kicker' to 'with kicker' gives a significant increase in the 'scale' of the sound.

A thought hit me at a certain point; the only time I have ever felt such a sense of near-overwhelming envelopment, coupled with such accuracy, was at Masterpiece in London when attending a mastering session there recently. That's in a big £million purpose-built room, with soffit-mounted PMC BB5s etc. I had a distinct moment that I remember, when I was there. One specific sound really brought it to me - I was knocked out by the envelopment. That exact same feeling hit me again in my room, it triggered that specific memory. So, thinking about it again, maybe the sound is bigger than the room. It felt like that big room at Masterpiece, it made me feel the same way. And that room is much bigger than mine

I have more work to do of course - it never ends! – I want to kill 8.5ms a bit more which would hopefully give me an ISD that is ~25dB down. I just want the ISD to be a little better defined. I also want things to look a bit better, haha, and more diffusion would be good too. But for now? I am a very happy bunny.

I’d really like to thank Lupo (again), who has been so forthcoming, patient, and helpful. I’d also like to thank SAC (again!), who has indirectly/unknowingly helped so much. Perhaps I am preaching to the choir in this thread, but for anyone who reads this: These boys know what they are talking about. Get into ETCs. Once you understand those, the frequency response follows along. Plus you actually understand why it is changing, unlike the feeling of semi-random shooting in the dark you have when only following the FR.

Sorry for the long post and for the gushing – I’m just extremely happy. When I am back at the place I’ll post some pix and whatnot, if anyone is interested.

Cheers and thanks all!

[Dange]

Glad it's all come together macc, I'm a believer!

Has anyone done a comparision between ending the ISD with a single reflection (say off the back wall with no diffusion) compared to ending it will a diffuse 'field' I think is the best way to put it, i.e. the back wall has diffusion?

[Dange]

In Sound System Engineering - Sound system engineering - Google Books

It gives a function of the Live End of LEDE to provide the Haas effect. "A first reflection from the studio, as heard over the control room's loudspeakers, to provide the Haas effect"

So that has to be a first reflection greater than -10dB (and within 30ms) of the direct sound? This could be a reflection from the back wall, I think this is most likely in LEDE.

However if you add diffusers to your back wall are you not reducing the intensity of your reflection? What I'm getting at is it may not be within -10dB of the direct sound. But you're (theoretically) not losing any energy in the diffuser, so the 'reflection' will still arrive ~20ms, but will actually consist of lots of little reflections spaced out around ~20ms, instead of one bang on 20ms.....then due to the fact the ear integrates over time the diffuse field will be equivalent in intensity to a > -10dB reflection arriving within 20ms..................not too sure about my last statement...

Am I getting there?

[Dange]

Originally Posted by Lupo

As I've gathered, part of the magic of this "trick" is that the brain effectively disregards the earlier reflections is junk/noisefloor.

Is this is a case of amplitude/temporal post-masking, the direct signal is the masker. It's louder than the suppressed early reflections of the room, and due to temporal post-masking it's effect can last up to the first reflection that ends the ISD.....?

That seems to make sense, but then 'sense' can be sometimes useless in understanding acoustics

[PaulP]

My understanding, from intently following Lupo and G.E.'s experiments, is that
you want a clear strong reflection for the Haas kicker. You want an echo
that isn't quite an echo. Something that tells you clearly that the place is big
but without messing up the sound.

Paul P

[Dange]

I've just read The LEDE Concept for the Control of Acoustic and Psychoacoustic Parameters in Recording Control Rooms, JAES 1980, 28,4

This seems to advocate the use of diffuse ISD ending early reflections, rather than one hot reflection.