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eigenmodes calculator Reverb & Delay Plugins
Old 8th September 2011
  #1
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eigenmodes calculator

i've been running some room dimensions through the eigenmodes calculator. other than corners, a trend that jumps out is the locations of hot spots depending on freq. for eg, low freq tend to show hot spots mid wall/ceiling length, and as the freq increase the hot spot tends to go from 1/3 length wall/ceiling to 1/4 length wall/ceiling

so in a room with bass treatments already placed in corners. if looking for additional trapping in particular frequency ranges and with traps of different depths does it make sense that the deeper lower freq traps would be orientated towards the mid distances of the wall ceiling and as the traps get shallower (as in lees bass absorption) is there sense in moving those more towards 1/3 distance or 1/4 distance.

seems mid rear wall receives low freq hot spots.

then i started looking at how to implement this idea into the built outcome. what i drew ended up with a NE type environment. or a room approaching Studio C @ Blackbird if you want some reverb. (in very loose terms)

with rooms based on a RFZ design, you rarely see deep trapping on side walls? is it possible to get enough bass trapping if you only do corners in RFZ rooms. i'm wondering how this all relates

any thoughts?
Old 8th September 2011
  #2
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Jens Eklund's Avatar
Quote:
Originally Posted by gouge View Post
with rooms based on a RFZ design, you rarely see deep trapping on side walls? is it possible to get enough bass trapping if you only do corners in RFZ rooms. i'm wondering how this all relates

any thoughts?
In a LEDE/RFZ design, the entire inner shell is made to absorb the region below approximately the Schroeder frequency (but reflective above) and this shell is placed asymmetrical within the base structure (that naturally has been optimized for good modal distribution) to avoid the nodes and antinodes related to width as well. One generally wants to minimize the use of velocity based absorbers in a LEDE/RFZ (or CID) design since they defeat the purpose; to keep the energy and reintroduce it to the sweet spot after the ISD-gap in a controlled way. The only way to do this properly is to use pressure based absorbers (that reflects the mids and highs) and splaying walls to redirect the energy instead of absorbing it.
Old 8th September 2011
  #3
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great stuff jens,

you've given me a massive amount to look into there. is there a particular room volume where the shroeder frequency becomes a more affective approach to room design?

i had thought to some degree (after reading bbc pages) that velocity based treatments may be more effective for very low freq. but after stumbling across a 9 page thread on exactly that debate here i will need to go back and re think that.

what is your preference to the front room treatment. i see examples of absorbant front walls. should rfz see reflective front walls also with the wall angles controlling the isd gap. is this best achieved in a large room with soffit mounted monitors.? although wouldn't some part of the front of the room need to be absorbant to control early reflections.

when you say the "shell is placed assymetrical within the base structure" can you clarify that further for me.

cheers.
Old 8th September 2011
  #4
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Jens Eklund's Avatar
If full on LEDE/RFZ design (RFZ assumes flush mounted speakers), the front wall should (could if LEDE but not nesseseraly) be reflective but with angels so that the early reflections are redirected away from the sweat spot. The key is to keep as much energy as possible so that a termination of the ISD-gap and the semi diffuse field following it is achievable. If freestanding speakers (but probably still very close to the front wall), some parts of the front wall might need to be absorptive depending on the directional characteristics of the speakers and placement.

The inner shell is made "transparent" or absorptive for low frequencies within the modal region (below the Schroeder frequency, depending on room size). The inner shell should be positioned slightly of centre (but naturally symmetrical internally) in relation to the main frame (solid thick and heavy boundaries) in order to avoid the nodes and antinodes of all lower order modes.

All of this assumes a large space and deep pockets ... and an acoustician.
Old 9th September 2011
  #5
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cheers,

so is offsetting the inner shell a pragmatic way of varying the depth of trapping on either side of the room and therefore achieve a greater spread of frequency absorption below the schroeder frequency.? is that Fc for short?

or is it more about the position of the listener being offset from the mid point of the mode that occurs due to the width of the room?

i was hoping to ask a question re rear wall diffusion also.

for eg, if my listening position is 4m from the rear wall. that would give me an isd of 22 or so ms (asuming i need 22ms). looking at pictures of studios with more than 4m from listening position i often see 1d diffusors used on rear walls. i am wondering why this is so? is there still a need for diffusion even if ISD gaps are fullfilled by room dimensions alone.

tia.
Old 9th September 2011
  #6
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Jens Eklund's Avatar
More because of position in relation to nodes and antinodes.

Yes, diffusion is needed to create the reflection dense semi diffuse tail following the termination of the ISD-gap. 1D-diffusers is often the best choice if LEDE/RFZ design since the attenuation if incident energy is not too high (compared to 2D-diffusers).
Old 9th September 2011
  #7
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Jens Eklund's Avatar
Quote:
Originally Posted by gouge View Post
schroeder frequency.? is that Fc for short?
No, "fc" stands for "center frequency".
Old 9th September 2011
  #8
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jhbrandt's Avatar
+1 to Jens posts above..
But I never place the shell offset at all, it is always perfectly symmetrical. Your ears are never in the exact center of the room anyway. Plus, like splaying massive walls to counter modal issues, the point is moot because you are not going to have a 'perfect' modal environment in most of the rooms that we use as control rooms.
Wes Lachot has said, "It is impossible for every bass frequency to be heard at the same volume at every point in a room. This is just a reality of the physics of sound..."

Cheers,
John
Old 9th September 2011
  #9
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Jens Eklund's Avatar
If one is going to off-centre the inner (symmetrical) shell, it needs to be some distance, not just a couple of cm, in order to avoid the first node of the axial (or tangential or oblique) mode related to width.

I think no one splays rigid walls assuming it will combat modes (they hopefully learn before doing so that modes do not go away because of splayed walls, the pattern of nodes and antinodes becomes complex and the frequencies of resonance shifts but the problems remain and needs to be treated). If the wall is made more or less transparent for modal frequencies is another story. The outer shell is usually made rectangular in order to easily predict the modal behavior of it and this also results in a less expensive construction.



Quote:
Originally Posted by jhbrandt View Post
Wes Lachot has said, "It is impossible for every bass frequency to be heard at the same volume at every point in a room. This is just a reality of the physics of sound..."

Cheers,
John
+1
Old 9th September 2011
  #10
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this leads on to something else i've been contemplating. so i thank you again guys.

say i have a room where i cannot afford the real estate to achieve wes lachots 35 deg side wall and ceiling angles.

by adding absorption to deal with early reflection i am altering the absorption co-efficient of the room which will effect the shroeder frequency.

seems simple in theory but the absorption of foam/insulation usually varies across it's frequency range. does that mean a mean absorption should be used to simplify the maths?
Old 9th September 2011
  #11
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Quote:
Originally Posted by gouge View Post
looking at pictures of studios with more than 4m from listening position i often see 1d diffusors used on rear walls. i am wondering why this is so? is there still a need for diffusion even if ISD gaps are fullfilled by room dimensions alone.

tia.
the requirement is for the termination of the ISD for the haas effect - which should be as strong as possible (ive seen recommendations of the termination being no lower than -12dB below the direct signal - which can be a difficult feat!). the requirement for 1D diffusers (QRD/PRD) is because the lateral returns are more important than ceiling/floor returns for envelopment - and 2D diffusers on the rear wall will likely attenuate the returns too much (by dispersing energy in 2planes vs 1plane). the strength of the termination of the ISD is important, as well as the rate-of-decay of the remaining energy (room's total specular response) - which is another reason for QRD/PRDs which offer temporal dispersion in the time-domain.


some commentary from previous threads on this board:





Quote:
Originally Posted by SAC
the ISD termination should be a maximum of 12 dB SPL below the direct signal level. ... Up to an ISD length of ~25ms.
Quote:
Originally Posted by SAC
The preponderance of the termination as well as the exponentially decaying diffuse tail energies should arrive laterally.

To quote from Schroeder: "..research, based upon a subjective evaluation of the acoustics of 20 major European concert halls, has shown that many modern halls have poor acoustics because their ceilings are low relative to their widths. Such halls do not provide the listener with enough laterally traveling sound waves - as opposed to sound traveling in front/back direction and arriving at the listener's head in his "median" plane (the symmetry plane through his head). Such median plan sound, of course gives rise to two very similar acoustic signals at the listener's ears, and it is thought that the resulting excessive "binaural similarity" is responsible for the poor acoustical quality."

Also, to keep it short...
The purpose of the ISD termination is to REMOVE the localization cues of the later arriving energies and to reinforce the localization cues of the direct energy.
Quote:
Originally Posted by SAC
Also, in the diagram, note the delta between the separate source and image shift thresholds and compare that with the level of the ISD termination.
Quote:
Originally Posted by SAC
A late arriving reflection, if of sufficient gain, is perceived as a destructive element that skews localization and tonality. (And in a Large Acoustical Space, if after 80 ms, it is perceived as a distinct echo). Hence the use of the ETC in identifying and mitigating them and the use of the Haas kicker - the ISD termination - to reinforce the direct signal localization prominence.
Quote:
Originally Posted by SAC
As the intensity of the ISD termination has a significant impact on the sense of liveliness of the space, while the laterally arriving semi-reverberant soundfield and to the sense of space (size) of the room.

The ISD balances between the comb filter interval (CFI) featuring time delays within the first few ms (say a meter) that cause significant spatial misdirection via comb filters, and the ISD where the establishment and support of the time region capable of supporting a partial Haas effect as supported by Madsen's research.
Quote:
Originally Posted by SAC
As far as the two issues regarding orientation of later arriving diffuse energy and the psycho-acoustical requirements of relative levels of arriving energy relative to the direct signal necessary to trigger individual behaviors. (That is not to say that we know everything there is to know! But it is what research we currently have.)

Yes, it is beneficial to increase the degree of later arriving, laterally directed, exponentially decaying, diffuse energy return in that it increases the sense of space in the room. Bu this is optimally accomplished by a combination of controlled dispersion speakers minimizing boundary incidence (and including soffit mounting optimizing Q), limited strategic absorption, and the redirection of energy maximizing its content until it is diffused back into the listening position. Thus it is an issue of maximally conserving energy and minimizing losses in the finite energy supplied. Thus this also implies the judicious use of lossy diffusion as well such that reflection is the choice until such time as diffusion is strategically introduced.

The higher ISD termination relative to the direct signal within the Haas time interval both increases the sense of liveliness in the room while also increasing the Haas effect and direct signal localization process while simultaneously minimizing the destructive localization and tonality cues of any later higher gain reflections.

But as to the basic relationships as defined in the LEDE model, they have all been researched and predicated upon psycho-acoustics principles - not simply assumptions. And there is not much point of debating them anecdotally unless we have new psycho-acoustic research that either invalidates or modifies concepts that are directly supported by the implementation of the model.

With the advancement in the complexity of diffusive treatments, there has been the corresponding advance in the integration of the soundfields, but there has not been a corresponding 'replacement' discrediting of the basic psycho acoustical concepts. Instead the models have simply become more tightly integrated and complex. We are now able to generate much more complex mixed soundfields and this has enabled the various models to become more effective, as evidenced in the extreme low level and extremely complex diffusion incorporated in the ambechoic model.
Quote:
Originally Posted by SAC
My general point remains that the issues with retaining sufficient energy to reach the prescribed ISD termination levels requires judicious attention to detail at each stage of the signal process, including a careful management of boundary incidence, reflection/redirection, and a care in the optimal use of lossy diffusive techniques in the process of redirecting the later arriving diffuse energy laterally back to the listening position.
Quote:
Originally Posted by SAC
All of the variables listed as simply steps in the process whereby the energy from the speaker propagates and is either redirected or absorbed.

Our larger task is on the one hand to have only the direct signal arrive at the listening position during the ISD gap, while ALSO, redirecting the indirect energy in such a manner as to preserve as much energy as possible, to return the energy from a lateral orientation in a diffuse manner at a level within at least 12 dB of the direct signal level.

Thus, be it the over application of (broadband) bass trapping, broadband specular absorption, and/or diffusion (and less diffusion, as the process of diffusion has a relatively high 'absorptive' loss component.

Whereas it is common to hear the notion that one cannot apply too much bass or broadband absorption, this is simply is not the case with this acoustic response model! Here we require very judicious application of the treatment sufficient to tailor both the direct response as well as the indirect response.


Thus controlled Q/dispersion radiation from the speakers minimizing the need for absorption, bass trapping must be frequency specific, specular absorption must be surgical, and diffusion efficient (diffusing diffusion is a big energy loss) while also effectively reflecting/redirecting the energy such that after a suitable time it can be redirected laterally in a diffuse manner back to the listening position with sufficient gain is a challenge in energy conservation.

Each step contributes to the losses, and with each step we are faced with economizing to preserve the energy. The best term that comes to mind is "surgical" - to do just what is necessary to prevent anomalous behavior while preserving the later arriving energy.

And while the perils of excessive absorption are rather obvious in this regard, so too are the issues with diffusion - not because diffusion is bad, but rather because it is a rather inefficient process with higher losses than many would assume. And the emphasis shifts a bit from 'are the absorbers large enough', to the balance with low loss reflective and re-directive surfaces, or moving surfaces to avoid incidence entirely as was done in the RFZ implementation of the LEDE.

Its a balancing act at each step in the process.
Quote:
Originally Posted by SAC
The length of the ISD gap maximizes intelligibility during the Haas interval where multiple arriving signals are merged/smeared into one event in what Heyser called 'time smear distortion'.

I don't see that as ever being good or acceptable.

Also, in a control room or critical listening space, the ISD also allows one to experience the reproduction of the recording space in total before the incursion of the control room or listening space.

The termination of the ISD does several things as well psycho-acoustically. It provides the sense of liveliness to the listening space. Second, it aids in localization by 'removing' the localization and tonality shifting cues from later arriving signals - causing the focus and localization to lock onto the direct signal. And the later arriving exponentially decaying diffuse soundfield adds to the sense of space/size to the listening environment. This is the bonus above and beyond what a dead room affords you.

So in fairness, while its hard to say "which one", I guess one would have to acknowledge the primacy of the ISD regarding fundamental localization, imaging and intelligibility of the direct signal itself. As the termination and later arriving diffuse soundfield further augment this.

The termination and latter arriving lateral diffuse sound field further augments the localization and imaging, accurate tonality and provides a sense of space to the listening environment.
Old 9th September 2011
  #12
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Jens Eklund's Avatar
I miss SAC and his contribution to this forum :(
Old 9th September 2011
  #13
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Glenn Kuras's Avatar
Quote:
Originally Posted by gouge View Post
this leads on to something else i've been contemplating. so i thank you again guys.

say i have a room where i cannot afford the real estate to achieve wes lachots 35 deg side wall and ceiling angles.

by adding absorption to deal with early reflection i am altering the absorption co-efficient of the room which will effect the shroeder frequency.

seems simple in theory but the absorption of foam/insulation usually varies across it's frequency range. does that mean a mean absorption should be used to simplify the maths?
If you can not give up the real estate (most small rooms should not) then I would not go that route. It is always better to keep the room larger when at all possible. Though if doing a custom build, with plenty of room then go for it!
Old 9th September 2011
  #14
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boggy's Avatar
Quote:
Originally Posted by jhbrandt View Post
.....
Wes Lachot has said, "It is impossible for every bass frequency to be heard at the same volume at every point in a room. This is just a reality of the physics of sound..."
......
If we talk only about useful volume of control room and only hearing abilities, it's rather expensive than impossible, but I agree that "expensive" is similar to "impossible" in most situations. heh
Old 10th September 2011
  #15
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i had to read localhosts post several times, thanks ...... from what i can interprate from this plus other information on GS, this is where i'm at.....

above the shroeder frequency, in general, an lede room uses absorption at the front of the room and reflectivity at the rear room and listening position, as opposed to the RFZ room which uses reflectiviity to the entire room..... ok, i know that's fairly simplistic and not specific to an actual room. but the aim of this is to increase the psychoacoustic size of the room.

i guess from this most small diy rooms we see on GS are LEDE in principle. and in rooms where walls cannot be placed at optimmum angles solutions leaning towards lede are better suited.

when achieving a room with an isd gap of around 20ms or at least more than the isd gap of the recording space, lateral reflections are preferred as this allows the listener to hear the initial sounds clearly and with a defined position within the mix sound stage, the isd termination should also see a min of 20db reduction in spl (or is it 12db as SAC says? am confused). the amount of attenuation in the spl is calculated by use of the specular absorption coefficients of the specific materials or acoustic devices.

so with regards the frequencies below the schroder freq, sac mentions that to much absorption is not the goal, where as other people have said to absorb all frequencies below the schroeder freq. i find that a little confusing also. wouldn't one want to absorb only enough energy of the freqs below the schroeder frequency until a spectrum analysis shows a flat response?

also, based on an 80db playback level within a control room is the spl level of a particular freq constant at a constant decibel level? i mean can this be calculated during the design process. for eg, at 80db a 63hz sound with have an "enter amount" db level....?
Old 10th September 2011
  #16
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Quote:
Originally Posted by Jens Eklund View Post
More because of position in relation to nodes and antinodes.

Yes, diffusion is needed to create the reflection dense tail after the termination of the ISD-gap. 1D-diffusers is often the best choice if LEDE/RFZ design since the attenuation if incident energy is not too high (compared to 2D-diffusers).

hi jens, do the reflection dense tails need to support the rt60 requirments of the room.

this again seems very difficult to calculate when acoustic treatments result in a varying absorption coeffients of different frequencies.

so tfollowing on from the isd termination information above.

the room need to have all refelctions to the listener start at a particular time and end within a particular time.
Old 10th September 2011
  #17
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Jens Eklund's Avatar
Quote:
Originally Posted by gouge View Post
above the shroeder frequency, in general, an lede room uses absorption at the front of the room and reflectivity at the rear room and listening position, as opposed to the RFZ room which uses reflectiviity to the entire room ...
Quote:
Originally Posted by Jens Eklund View Post
The RFZ concept is just one way of reaching the LEDE criteria. RFZ is LEDE. Perhaps LEDE is a bad name since people assume it needs to be completely covered with broadband absorbers in front but it doesn’t. In fact, splaying walls to redirect energy instead of using absorption was done before it got a name (RFZ). The important thing is the suppression of early reflections; the ISD-gap, and the termination of it, followed by diffuse reflections. Some think that the LEDE is old and outdated but good things stick around. The car is old but still used by many and the basic criteria is the same; it takes you from A to B.
Quote:
Originally Posted by gouge View Post
i guess from this most small diy rooms we see on GS are LEDE in principle. and in rooms where walls cannot be placed at optimmum angles solutions leaning towards lede are better suited.
Far from it unfortunately. Most rooms you see on GS are close to anechoic (at least above the modal range), no termination of any ISD-gap due to overuse of velocity based absorbers only.


Check out some more threads and your questions will be answered.
Old 10th September 2011
  #18
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Jens Eklund's Avatar
Quote:
Originally Posted by gouge View Post
do the reflection dense tails need to support the rt60 requirments of the room.
https://www.gearslutz.com/board/7007412-post7.html
Old 10th September 2011
  #19
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The RFZ concept is just one way of reaching the LEDE criteria. RFZ is LEDE. Perhaps LEDE is a bad name since people assume it needs to be completely covered with broadband absorbers in front but it doesn’t. In fact, splaying walls to redirect energy instead of using absorption was done before it got a name (RFZ). The important thing is the suppression of early reflections; the ISD-gap, and the termination of it, followed by diffuse reflections. Some think that the LEDE is old and outdated but good things stick around. The car is old but still used by many and the basic criteria is the same; it takes you from A to B.

ah...... thankyou! now i get it

Far from it unfortunately. Most rooms you see on GS are close to anechoic (at least above the modal range), no termination of any ISD-gap due to overuse of velocity based absorbers only.

yep... excellent.

thanks again for taking the time to explain this all in simple terms. much appreciated.
Old 10th September 2011
  #20
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boggy's Avatar
Quote:
Originally Posted by gouge View Post
........
so with regards the frequencies below the schroder freq, sac mentions that to much absorption is not the goal, where as other people have said to absorb all frequencies below the schroeder freq. i find that a little confusing also. wouldn't one want to absorb only enough energy of the freqs below the schroeder frequency until a spectrum analysis shows a flat response?
LEDE design (full) absorption of back/side walls is defined for all frequencies below:

f= 3*c/a (*)

c - speed of sound
a - smallest room dimension

This means that for ordinary room with smallest dimension of 2.5m we need a full absorption (or full transmission to outdoors) of all frequencies below 408Hz. So, yes, of course, this will give us a fairly flat low end frequency response (with fully absorptive front wall), in this particular room. For all frequencies above this we need reflection nature of back/side walls (diffusion, ISD gap, etc...)
There is nothing about "too much absorption"... so, making side/back walls acoustically transparent/absorptive for all frequencies below 3*c/a needs serious and huge bass trap for sure.


(*) - "The LEDE (TM) Concept for the Control of Acoustic and Psychoacoustic Parameters in Recording Control Rooms" , D. Davis, C. Davis, 63rd AES Convention, 1979
Old 10th September 2011
  #21
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thanks boggy,

is there a volume where you believe davis to be more appropriate to schroeder? much of a muchness?

i also have realised one of my errors in my comments above. where i was clumsily trying to ask a question about DB attenuation but was confusing a lot of ideas and it made no sense.

i guess my question relates to modes that occur above the davis/schroeder frequency. they will need absorption to control them. is there a way to calculate the amount of attenuation required for these frequencies prior to measurment of the built outcome?

cheers
Old 10th September 2011
  #22
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boggy's Avatar
Quote:
Originally Posted by gouge View Post
thanks boggy,

is there a volume where you believe davis to be more appropriate to schroeder? much of a muchness?
It's more important how low you will go with absorption in the room... this is a challenging task... if you start from Schroeder frequency, "Davis frequency" or "my" 250Hz for all small rooms, isn't really that important... (IMHO)
Old 10th September 2011
  #23
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cheers boggy,

i noticed your post re the myroom also :-)

john brandt has a paper on his site also where he looks at modal resonances at different frequencies, 250hz or there abouts seems to be a very important crossover point as well.

also highlights that my question above should not have read "absorption to control them".... :-)
Old 10th September 2011
  #24
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Quote:
Originally Posted by gouge View Post
i guess from this most small diy rooms we see on GS are LEDE in principle. and in rooms where walls cannot be placed at optimmum angles solutions leaning towards lede are better suited.
attenuating the early specular reflections (to create the ISD-gap) can be done with absorption or redirection (splayed walls; geometry). the reason why splayed walls are preferred is because there is a finite amount of energy in the room, and while you want to suppress any energy within the ISD-gap, you want to termination of the ISD-gap to be as loud and dense as possible. absorption at first-reflection-points removes precious specular energy from the room which could otherwise be used for the dense, diffused termination returns.

Quote:
Originally Posted by gouge View Post
when achieving a room with an isd gap of around 20ms or at least more than the isd gap of the recording space, lateral reflections are preferred as this allows the listener to hear the initial sounds clearly and with a defined position within the mix sound stage, the isd termination should also see a min of 20db reduction in spl (or is it 12db as SAC says? am confused). the amount of attenuation in the spl is calculated by use of the specular absorption coefficients of the specific materials or acoustic devices.
you are combining different elements, here..

if you choose an ISD-gap of 20ms, you also choose what your requirement is to attenuate any specular energy that arrives within this gap (eg., -20dB). this means you need to attenuate any early specular reflections to -20dB or more of the original signal - for the 20ms ISD-gap.

once this anechoic period in time is over (the RFZ ISD-gap), then energy begins to arrive back at the listening position. this is referred to as the 'termination'. you are terminating the anechoic ISD-gap (eg, the anechoic response is now "finished"). where SAC says no lower than -12dB, that means that the termination (in gain) should be no more than -12dB lower than the original signal. this is for psycho-acoustic triggers such as the haas effect - which SAC describes in the quotes above as to the importance of it regarding localization).

after the termination comes the decay of the energy within the room. as it continues to reflect off boundaries, it will lose energy until completely damped. how this energy decays (the rate of decay) is another important factor.



in the bottom graph, you can see the original signal, the ISD-gap (RFZ) where no 'early specular energy' impedes, and then the termination where energy finally hits the listening position - and then the decay of that energy until it is fully damped.

so you're looking at three separate elements (to keep things simple):

  • ISD-gap (anechoic period in time (ms) after the original signal for which all specular energy is attenuated) - eg, 20ms ISD w/ all energy no louder than -20dB of original signal
  • termination of ISD - first loud specular reflection to terminate the ISD-gap and to trigger haas effect (localization cues, determine "liveliness" of room) - "no lower than -12dB"
  • decay - determined by dense, diffused sould-field and the rate at which that energy decays (determine perceived "space" and "size" of room)
again, the reason for splayed walls vs absorption at early reflection points is because you need all of that precious energy for the termination of the ISD.
Old 10th September 2011
  #25
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Quote:
Originally Posted by Jens Eklund View Post
I miss SAC and his contribution to this forum :(
What...??? He's gone....???

OK, I know he could sound like an ass sometimes but in most of the cases he was right. Could someone contact him to compel him into making a new account and educate/justmakeussmarter/enlighten us for a few months/years more before he gets kicked out again???
Old 10th September 2011
  #26
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SAC was one of the few here you could learn from.
What surprises me though is how little the info about LEDE and psychoacoustics is easily available. Even in D. Davies' book ("Sound System Engineering"), there's not much written about it.
Old 11th September 2011
  #27
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boggy's Avatar
Quote:
Originally Posted by gouge View Post
cheers boggy,

i noticed your post re the myroom also :-)

john brandt has a paper on his site also where he looks at modal resonances at different frequencies, 250hz or there abouts seems to be a very important crossover point as well.
......
I agree that this crossover point is very important, but I have experience with rooms where is bass trapping go only down to about 100Hz... then even if you try to bring back reflections in room from 1000Hz and up, there is no real effect of this, because you still have in a small room at least one or two LOUD room modes below 100Hz that destroy whatever other you try to improve. There is nothing to do except to start from the beginning and to greatly improve bass trapping at low frequencies...

This is a reason why my priorities are in this order, because it's much worse if you "forget" to absorb frequencies below 100Hz than missing a "right crossover point", or at which frequency you need to stop with absorption....
Old 12th September 2011
  #28
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@ localhost^^^ thanks. that cleared that up nicely.

@boggy^ cheers, leads me to a question though. with your myroom design, you've used the 1khz design frequency, how low does the diffusion go with your design? i wondering about the diffusion of the lower frequencies just above the your 250hz bass trapping?
Old 12th September 2011
  #29
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with reference to lede/rfz and the maths/philosophy designers are using to calculate room outcomes,

i started reading up on the subject. stumbled upon the ESS type rooms. can anyone confirm whether the isd gap termination calculations still apply with ESS rooms? i am assuming that an ESS room still requires an appropriate termination time and all freq below the schroeder/davis/boggy/brandt etc crossover still require full absorption.

tia.
Old 12th September 2011
  #30
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boggy's Avatar
Quote:
Originally Posted by gouge View Post
.............
@boggy^ cheers, leads me to a question though. with your myroom design, you've used the 1khz design frequency, how low does the diffusion go with your design? i wondering about the diffusion of the lower frequencies just above the your 250hz bass trapping?
1kHz is designed lowest working frequency for air transparent diffusers. Below this frequency absorption begin to be larger than about 0.6...
Diffusion just above 250Hz is not needed because room is too small. If you use diffuser design with 250Hz lowest working frequency you need to have minimum distance from diffuser of 4m, this means that useful width and lenghth of the room must be 8m min. (useful means "after treatment"), and useful height of ceiling must be about 6m (height of ears included). Because this reasons, it is decided not to build diffusers that can go to lower frequencies than 1kHz, and fortunately, this frequency range is very useful for diffusion psychoacoustically.

MyRoom design is developed because people needs to have a good acoustics even in small rooms, but this is not a rule, MyRoom design may be implemented in much larger room too (with much better results, of course), so, in this case, diffusers may work from lower frequencies, but room must be proprotionally larger.
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