Spot treating a room at mirror points theoretically seems useless

[Jens Eklund]

Originally Posted by OpusOfTrolls

Now, applying absorption to the said area will just kill flutter. Because of the minimal surface area absorption in use, will also maintain the reverberant field.

"I would think the trained Acoustician" would know that a reverberant field does not exist in SAS (Small Acoustical Space).

Also, instead of absorption, you can simply redirect early energy away from the sweet spot using geometry (as in the RFZ solution for LEDE) thus making it easier to reach the desired level of termination of the ISD-gap and the following (semi) diffuse sound field.

[OpusOfTrolls]

So it's not a perfectly diffuse sound field, sue me. It beats out any other form of specular treatment!

[Jens Eklund]

Originally Posted by OpusOfTrolls

So it's not a perfectly diffuse sound field, sue me. It beats out any other form of specular treatment!

Que?

[kasmira]

Holy hell localhost. Bookmarked. Wonderful post!

Sent from my SCH-I535 using Tapatalk

[DanDan]

+1, a great post. But remembering context. In the quest to entice a newby or even a client to do some or even any, treatment I find the mirror convinces them, and works well enough, while the ETC looks pretty daunting. More importantly, checking with ETC, I have never discovered stronger reflections than the nearby side and overhead ones located by mirror.
Similarly there is great correlation here Desktop Reflection Revealed But worth noting that there is still plenty of reflection from the desktop when the image has gone from the mirror.
So Mirror is the screwdriver, ETC is the Makita.
However Lupo has shown, by ETC, that it can be beneficial to angle these ZWR panels redirecting some energy that is being reflected rather than fully absorbed. Worth remembering Gullfo's angled hard or partly hard cloud also.
DD

[Glenn Kuras]

Originally Posted by DanDan

+1, a great post. But remembering context. In the quest to entice a newby or even a client to do some or even any, treatment I find the mirror convinces them, and works well enough, while the ETC looks pretty daunting. More importantly, checking with ETC, I have never discovered stronger reflections than the nearby side and overhead ones located by mirror.
Similarly there is great correlation here Desktop Reflection Revealed But worth noting that there is still plenty of reflection from the desktop when the image has gone from the mirror.
So Mirror is the screwdriver, ETC is the Makita.
However Lupo has shown, by ETC, that it can be beneficial to angle these ZWR panels redirecting some energy that is being reflected rather than fully absorbed. Worth remembering Gullfo's angled hard or partly hard cloud also.
DD

As we point out here. Using ETC is great but most don't have the background so the mirror trick is fine.
Early Reflection Points Definition

[hsal]

Good post on using ETC Local, to be bit nitpicky, the amount of lateral reflections is related to width of the room, LEDE/RFZ certified rooms build from the ground up are wide rooms, and will have a much more benificial incidence angle than narrow (domestic) rooms.

It would be interesting to get some polar energy time measurements of LEDE/RFZ rooms with different width, in order to actually measure the incidence angle.

Normal energy time curve measurements does not show the incidence angle of reflections.

[localhost127]

yes, but the context of the post with respect to the OP was regarding the emulation of such specular responses (NER, LEDE/RFZ) within their existing rooms for "setting up a room for accurate monitoring" - not certification of a room built from the ground-up.

a user who chooses to attenuate high-gain early arriving indirect signals that are destructive to accurate localization and imaging, yet still wishes to reintroduce energy to the listening position as a laterally arriving, semi-diffused decay field is essentially emulating the LEDE specular response, as stated previously.

[jim1961]

Originally Posted by hsal

Normal energy time curve measurements does not show the incidence angle of reflections.

The 23ms ISD gap terminating peak is at 110 degrees (assuming front is 0, back is 180, and directly right and left to be 90)

[hsal]

Reflections can have very different trajectory and yet have the same arrival time, ETC only measures arrival time, not incidence angle, let`s not get into semantics

yes, but the context of the post with respect to the OP was regarding the emulation of such specular responses

IMO it is constructive to undermine that even though a correct
isd gap is possible, the actual perception might be completely different due to higher percentage of "mono reflections", reflections arriving with very small time difference at the two ears.
inter aural time difference is used for localisation of sounds below 800hz and down to appr 80 hz.

[jim1961]

Originally Posted by hsal

Reflections can have very different trajectory and yet have the same arrival time, ETC only measures arrival time, not incidence angle, let`s not get into semantics


IMO it is constructive to undermine that even though a correct
isd gap is possible, the actual perception might be completely different due to higher percentage of "mono reflections", reflections arriving with very small time difference at the two ears.
inter aural time difference is used for localization of sounds below 800hz and down to appr 80 hz.

It seems to me that a room with a ISD gap below -20db and a strong termination need only consider the incidence angle of the termination energy given that very little of the other reflections are actually being heard.

In a non-terminated room, them your point regarding angle of incidence becomes much more important I think.

In my case, the terminated energy is controlled so that the terminated energy you hear on the left is coming from the left speaker, and visa versa.

Mono or reversed (left speaker delayed energy arriving at your right ear) energy arrivals one would think would change your perception of room boundaries at the very least. I had one setup where I had the reversed scenario. My impression was that you still got that "live" feeling, but room boundaries and size were rather indistinct. Sometimes instruments panned heavily to one side would seem to get a bit smeared sounding in their localization.

[hsal]

It seems to me that a room with a ISD gap below -20db and a strong termination need only consider the incidence angle of the termination energy given that very little of the other reflections are actually being heard.

The "termination" is the first wave of reflections arriving from the diffusors placed at the backwall, it seems illogical to me that these reflections will have a lateral incidence angle (from the side) in narrow rooms.

[localhost127]

Originally Posted by hsal

Reflections can have very different trajectory and yet have the same arrival time, ETC only measures arrival time, not incidence angle, let`s not get into semantics

polar envelope time plot provides direction, gain, and time-of-travel/distance.

and determining which boundary is incident of the measured energy within the ETC (via blocking +/- string method) thus informs the user of the incident angle. or must we now account for operator error ?

Originally Posted by hsal

IMO it is constructive to undermine that even though a correct isd gap is possible, the actual perception might be completely different due to higher percentage of "mono reflections", reflections arriving with very small time difference at the two ears.
inter aural time difference is used for localisation of sounds below 800hz and down to appr 80 hz.

i fail to see the relevancy of your tangent with respect to the OP's questions and initial discussion regarding "setting up a room for accurate monitoring.". do you have anything further regarding the provided commentary on utilizing the ETC to identify the reflections (vs using the mirror), or the emulation of the LEDE or NE specular response to achieve the OP's goals?

[jim1961]

Originally Posted by hsal

The "termination" is the first wave of reflections arriving from the diffusors placed at the backwall, it seems illogical to me that these reflections will have a lateral incidence angle (from the side) in narrow rooms.

Thats because my room isnt your typical LEDE / RFZ room.



Brown = QRD
Black = Absorption
Grey = deflector

This pic is only generally accuarate, but it shows how I am getting what I am claiming. There are omissions, like the back wall is not reflected forward due to more deflectors there, ect.

[hsal]

polar envelope time plot provides direction, gain, and time-of-travel/distance

?

polar energy time measurments (PET) is different from normal ETC measurements where you use an omni mic, you use cardoid for PET measurements.

a normal ETC does not give enough enough info in order to determine incidence angle of reflections using a typical setup with diffusors on the backwall imo,if one look at the posts in this thread, one will see that it is hard to trace even specular reflections.


My initial point was that room dimensions is a fundamental parameter, and if you change the ratio, for instance using narrow LEDE rooms then it can become a totally different beast all together

p.s seems like we go into old habits no point to continue imo

[localhost127]

Originally Posted by hsal

polar energy time measurments (PET) is different from normal ETC measurements where you use an omni mic, you use cardoid for PET measurements.

you didn't imply any hardware limitations when you made your statement - hence why the reference was made - the individual ETCs are combined into the PET.

and you conveniently left off the 2nd half of my statement in your response regarding "normal ETC".

Originally Posted by hsal

a normal ETC does not give enough enough info in order to determine incidence angle of reflections using a typical setup with diffusors on the backwall imo,if one look at the posts in this thread, one will see that it is hard to trace even specular reflections.

sorry, but i do not buy your claim that is "hard to trace even specular reflections" with the ETC utilizing the blocking and/or string method. it's a ridiculously simple yet elegant process. do you find it not effective in tracing the source of the incident indirect energy as measured within the ETC? what do you recommend for the OP besides the mirror?

[hsal]

you didn't imply any hardware limitations when you made your statement - hence why the reference was made - the individual ETCs are combined into the PET.

?

PET measurements requires a pretty large investment in measuerement equipment. Polar Energy-Time Curves (PET)

"hard to trace even specular reflections"

yes higher order reflections, it was used as an example.

early specular reflections can easily be traced, as soon as diffusors are introduced it is a much more complex task, even more complex than higher ordr specular reflections.

what are we actually discussing here?

I simply stated that narrow (domestic) LEDE rooms have less benificial incidence angle for reflections than wide LEDE/RFZ rooms,it is logical imo

what do you recommend for the OP besides the mirror?

From the picture it looks like a rather small and narrow room (I assume it is his room in the picture)

in order to determine possible design options, I think it is benificial to get the actual room dimensions .

For tracing reflections, mirror trick goes along way, ETC is nice to use in order to double check if one have the time to learn the program, one can have reflections caused by diffraction off surfaces etc that the mirror trick will not identify

[localhost127]

Originally Posted by hsal

From the picture it looks like a rather small and narrow room (I assume it is his room in the picture)

diagram was borrowed from here:
RealTraps - Creating a Reflection-Free Zone

Originally Posted by hsal

For tracing reflections, mirror trick goes along way, ETC is nice to use in order to double check if one have the time to learn the program, one can have reflections caused by diffraction off surfaces etc that the mirror trick will not identify

yes, but the OP already sees the limitations of the mirror (hence the title of thread and first post)...

utilizing ETC to identify sources incident of high-gain early arriving indirect specular energy is not all that difficult. usually the most difficult part of the process is getting one to understand why the hardware loopback is necessary - and its configuration within REW.

[hsal]

I think as a general rule one needs to know dimensions of the room before suggesting design philosophy.

quote localhost:

there are of course other methods, but LEDE (RFZ) and NER are two that can be fairly easily emulated within your room. regardless of the specular response, LF/modal region issues are still relevant and must be addressed (but this is somewhat independent of the specular response - even though treatments may still need to take into consideration each aspect).

Fully agree on the point of adressing LF/modal region issues.