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SBIR Virtual Instrument Plugins
Old 13th March 2017
  #421
Gear Nut
about 5-6cm because there is a foam on that wall 5cm thick.. So , it´s touching...

May be is because the ceiling path?
in that position, I have no treatment on the ceiling to absorb the ER from monitor to listening position

Last edited by esencia; 13th March 2017 at 07:51 PM..
Old 13th March 2017
  #422
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Small

Touching is touching. I use masking tape or a little rubber buffer to prevent scratching. 5cm would show quite a difference in LF response. Also I really don't think foam could be doing anything useful there.
RealTraps - Front Wall Absorption
I expect the acoustic centre of the SMR or the acoustic source of the 100Hz would be mid woofer, placing it effectively quite a bit further from the FW.
But as things stand clearly go with the test result and try different distances and even heights and widths. That blue graph doesn't look bad at all to me.

This has been mentioned before but it's a long thread. These nulls are not always associated with just one boundary. So it can be confusing.
The best way to resolve this IMO is to test with intention. Try those speakers at 1.5M and lets see if the frequency of the null(s) rises or falls.
Ditto ceiling or floor suspects. NB, if you have a ceiling reflection as the primary or sole cause of a dip, moving the mic towards the 'virtual source' on and above the ceiling, will change the frequency of that dip. Ditto floor, side walls......

DD
Old 14th May 2017
  #423
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I want to raise a problem of floor SBIR - in my, well damped room, it's may be the last unwanted reflection. It's well noticeable from Impulse Graph on my REW's.

So, i found two solutions, that can help solve this problem:

1) Create shields, perpendicular to floor surface, that redirect floor beam to absorbers on a front/side walls.

But it have some difficulties:
a) In my case, i can made panel 0.66 m height * 1.05 m wide (i think golden ratio here will be very opportunely). It will works only from ~340Hz. Bigger shields will affect direct sound from speakers, and we can't allow this
b) I think, that shields can adding something to room acoustic, not just "Floor SBIR redirection".

Ssory for newbie drawing, but schematically you can understand, what i'm have on mind.
Shields go right from floor to height of lowest edge of speakers cabinet (or some below if needed). Of course, we can mount some absorbers on shields, on side that closer to speakers.
Shields locations - right 1/2 distance from you to each speaker(ERZ).


2) Next solution - is to mount big angled shield right on floor surface, between you and speakers. So, it will works like an angled table desk, but much effective size, than first solution. For example, i can use 1.25x2.5m shield. Of course, you can locate absorbers under it, and trying to use composite materials, to weaken LF reflection, that goes through you to rear wall. What about MF reflections - they should fully redirect from listening position.

But some questions - how low should work this system? what is the compomise between added angle and redirection efficiency?


Join the discussion, or leave links, where we can see similar solutions.
Thanks for attention.
Attached Thumbnails
SBIR-2.jpg   SBIR-123.jpg  
Old 14th May 2017
  #424
Gear Nut
Quote:
Originally Posted by TTRESHH View Post
I want to raise a problem of floor SBIR - in my, well damped room, it's may be the last unwanted reflection.
Are you listening (control room) or recording (live room)?
If listening, you'll ideally want to absorb it. Adding any reflector merely slightly moves the point where the reflection happens and hence the position of the peaks and nulls. You can't "reflect away the sound", without making the reflector angled away from listening position so that any reflecting angle is blocked (iow, if you were to place a mirror on it, you would not see the speakers in the mirror at all).
Old 14th May 2017
  #425
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Quote:
Originally Posted by Antti H View Post
Are you listening (control room) or recording (live room)?
It's my control room, where i try to mixing and critically listening.

Quote:
Originally Posted by Antti H View Post
(iow, if you were to place a mirror on it, you would not see the speakers in the mirror at all).
Not so difficult - achieve angle, that won't allow to see speakers in mirror.

It's the only one condition? So, getting necessary angle and rigidity, we can reflect all frequencys right from wavelenght that comparable to the size of shield?
Old 15th May 2017
  #426
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Quote:
Originally Posted by TTRESHH View Post
It's my control room, where i try to mixing and critically listening.
...........
For critical listening and mixing rooms, hardwood and reflective floor is mandatory, especially because mix translation. And yes, reflections from floor exists and our brain reacts naturally to it, as it is used to. We are humans, not two legged microphones with FFT transform in the brain and simple listening criterion borrowed from telecommunications. We are used to floor reflection influence, because we are born in similar spaces, and genetically inherit from human history.

So it is not that simple as expected, otherwise people will do critical listening and mixing in anechoic rooms where floor reflections virtually doesn't exist, as from walls and ceilings.

So, if you like a better frequency response, please look here:
Speaker placement methods and keep your floor reflective (and wooden, oak, ash, lacquered...)


Old 15th May 2017
  #427
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Reflexive floor ?

I put on the floor japanese tatami with a thickness of 7 cm plus a carpet. My celling is not treated.

Highly recommended
Old 15th May 2017
  #428
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Quote:
Originally Posted by boggy View Post
For critical listening and mixing rooms, hardwood and reflective floor is mandatory, especially because mix translation. And yes, reflections from floor exists and our brain reacts naturally to it, as it is used to. We are humans, not two legged microphones with FFT transform in the brain
What you mean, when saying "and our brain reacts naturally to it, as it is used to"? Brain doesn't pay attention to this reflection, until they didn't exist, and when we hear no floor reflections, then we go panic? (Psychoacoustic, may be...)

But if we are sensitive to this comb filtering comes from below reflection, it will distort overall sound image.
So, if to build in an extreme this "mix translation" idea, there is no need in control rooms - because listener's always have floors, untreated walls, low celling and often very modest speakers...


Quote:
Originally Posted by boggy View Post
So, if you like a better frequency response, please look here:
Speaker placement methods and keep your floor reflective (and wooden, oak, ash, lacquered...)

Why I so concern about floors reflections...
Because in my CR they comes in first 3ms and it's much stronger, than others reflection.
Attached Thumbnails
SBIR-whynotfloorsbir.jpg  
Old 15th May 2017
  #429
Gear Nut
Quote:
Originally Posted by boggy View Post
For critical listening and mixing rooms, hardwood and reflective floor is mandatory, especially because mix translation. And yes, reflections from floor exists and our brain reacts naturally to it, as it is used to.
Ok, I'm going to bite:

1) Why would a single random comb filter be necessary to mix translation? Given that the comb filtering frequency (first notch and interval between notches) is pretty much guaranteed to be significantly different in a typical living room (with speakers on one wall and listening position on the opposite) compared to mixing with nearfield monitors (distance likely less than half of the living room situation), what possible mechanism would be at play that would explain this somehow helping the translation?

2) Floor reflection comes from the direction of speakers and hence doesn't help with spatial image. It is also identical for both ears, thus significantly hindering brains ability to use interaural differences to filter out the effect. For the case of near field speakers, the time delay is about 2-3 milliseconds, so much too short to give any kind of size cue (in fact likely short enough to be impossible to differentiate from the attack of the instruments themselves). What other mechanism than comb filtering could there even be at play?

3) How would it help for what nowadays constitute probably more than half of listening situations: headphones and cars?

4) Anechoic room is a completely different situation as there's zero (by definition) early or late reverb and complete lack of echoes to sounds caused by the listener themselves (giving the audible impression of floating in vast emptiness).
Old 16th May 2017
  #430
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Quote:
Originally Posted by TTRESHH View Post
What you mean, when saying "and our brain reacts naturally to it, as it is used to"? Brain doesn't pay attention to this reflection, until they didn't exist, and when we hear no floor reflections, then we go panic? (Psychoacoustic, may be...)
Yes, psychoacoustic, brain can ignore this one reflection because it is used to do this every day in the normal life. Ground reflection is common phenomenon.

Quote:
Originally Posted by TTRESHH View Post
But if we are sensitive to this comb filtering comes from below reflection, it will distort overall sound image.
Yes, but only if the brain will work as common DSP with fast Fourier transform... We are more complicated/powerful than mathematical signal transform, or any mathematical model we use to describe signal processing or acoustics.
Quote:
Originally Posted by TTRESHH View Post
So, if to build in an extreme this "mix translation" idea, there is no need in control rooms - because listener's always have floors, untreated walls, low celling and often very modest speakers...
Even trained in production, brain cannot (easily) overcome untreated reflections from ALL walls. It is just few people I know who can mix in untreated, or mildly/wrongly treated rooms...
So, skill is needed for mixing, but it is also easier without too much reflections. The last connection with reality you describe, it is reflective floor.
Modest speakers are defined with small Auratones.
Also treatment is needed to give you a better feel during work, decrease time needed to get results what you like, and lower your tiredness, and absorptive floor won't help with that.
So, people have problems they can bear with it, and other they cannot... we need to find balance, and not to kill every comb filter literally.
Quote:
Originally Posted by TTRESHH View Post
Why I so concern about floors reflections...
Because in my CR they comes in first 3ms and it's much stronger, than others reflection.
One way is to "fool" the brain with diffuse reflections from the other walls... So, this one becomes less pronounced/destructive... We can ignore diffuse reflections much easier. Even if it is not probably logical, ceiling diffuser may help.

People need reflections, but people do not need a low frequency "hell" in the untreated (small) room. We need a reflective floor, diffuse reflections are easily processed in the brain, and can mask the floor reflection, so, this is a main reason we invented a hybrid diffusion principle in MyRoom Design Mark II



Last edited by boggy; 16th May 2017 at 10:05 AM..
Old 16th May 2017
  #431
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Quote:
Originally Posted by Antti H View Post
Ok, I'm going to bite:
....
Why?!

I tried to answer in the post above...


Old 16th May 2017
  #432
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Northward's Avatar
Quote:
Originally Posted by Antti H View Post
Ok, I'm going to bite:

1) Why would a single random comb filter be necessary to mix translation? Given that the comb filtering frequency (first notch and interval between notches) is pretty much guaranteed to be significantly different in a typical living room (with speakers on one wall and listening position on the opposite) compared to mixing with nearfield monitors (distance likely less than half of the living room situation), what possible mechanism would be at play that would explain this somehow helping the translation?
Tip of the iceberg:
1) "1. When head tracking is not possible, an environment with a single floor reflection is a canonical environment in that it reduces reversal rates by more that 40%, decreases the bias of azimuth errors on the average by 30% and does not increase elevation errors. Adding reverberation to that environment does not significantly change the localization accuracy.
2. When head tracking is used, then an environment that includes a floor reflection as well as head tracking is canonical. For most subjects, the reversal error rate was the lowest in such an environment, and on the average was 65% lower than for dry sound and 40% lower than for the canonical environment without head tracking. The bias in azimuth errors was also reduced further by 15% from the canonical environment without head tracking and the elevation errors were slightly reduced." source: 'On the design of canonical sound localization environments" Eric J. Angel, V. Ralph Algazi and Richard O. Duda.

Removing the floor reflections creates a lot more problems than it solves. Difference in speaker height has little to do with the effect floor has on our perception. Don't forget that in a listening environment, it's not only the speakers that interacts with the floor. Every other noise source is, and we are sensitive to all of them.

Quote:
Originally Posted by Antti H View Post
2) Floor reflection comes from the direction of speakers and hence doesn't help with spatial image. It is also identical for both ears, thus significantly hindering brains ability to use interaural differences to filter out the effect. For the case of near field speakers, the time delay is about 2-3 milliseconds, so much too short to give any kind of size cue (in fact likely short enough to be impossible to differentiate from the attack of the instruments themselves). What other mechanism than comb filtering could there even be at play?
2) See PDFs. Too long and complex to resume/type here.

Quote:
Originally Posted by Antti H View Post
3) How would it help for what nowadays constitute probably more than half of listening situations: headphones and cars?
3) Since when are cars a reliable mixing environment? There is no depth or stereo image to speak of, even in cars with a DSP corrected systems and a "driver optimized" mode. Cars are also a small ER dense, secondary correlated and uncorrelated mechanical vibrations fest. Mixing nightmare.

Headphones translation is fairly poor in the headphone -> speaker direction except the frequency response in the LF that can help when the studio's LF response isn't sufficiently performant. Mixing on headphones only will not allow proper translation - starting with judging amounts of reverb and spacial localization. They have a limited use in pro studios. Also see PDFs attached for further clues as to what's behind all this.

Quote:
Originally Posted by Antti H View Post
4) Anechoic room is a completely different situation as there's zero (by definition) early or late reverb and complete lack of echoes to sounds caused by the listener themselves (giving the audible impression of floating in vast emptiness).
In your point 4) you partially answer your own question 1)
Quote:
Originally Posted by Antti H View Post
1) Why would a single random comb filter be necessary to mix translation?
Attached Files
File Type: pdf AES113_5714.pdf (532.6 KB, 79 views) File Type: pdf Begault_1996_Audible_Inaudible.pdf (36.1 KB, 49 views) File Type: pdf Bech.pdf.pdf (169.7 KB, 76 views) File Type: pdf fnins-08-00451-01.pdf (6.38 MB, 52 views)
Old 16th May 2017
  #433
Gear Nut
Quote:
Originally Posted by boggy View Post
Why?!

I tried to answer in the post above...
You've restated your original assertations. I'm looking for evidence and / or explanation of the mechanism. Specifically, why a single very short specular reflection would be required (instead of general diffuse reflections which don't cause comb filtering).

Further, why would this floor reflection be necessary, but reflection off the console / mixing desk is generally considered bad? Or are you saying that the general advice is wrong and console reflection is not a problem?
Old 16th May 2017
  #434
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Quote:
Originally Posted by Antti H View Post
You've restated your original assertations. I'm looking for evidence and / or explanation of the mechanism.
Music production is a creative process, not a mathematical equation, science (IMHO)

These opinions came from my experience, I share only that here.

Still, you need an evidence why the reflective floor is needed for better mix translation? At the same time, better mix translation "fact" is also just an opinion, yes, subjective/objective... no evidence.

So, what we can do to find an "evidence" of my opinion, except concentrated opinions/experience of professionals or habits, I asked for?

Quote:
Originally Posted by Antti H View Post
Specifically, why a single very short specular reflection would be required (instead of general diffuse reflections which don't cause comb filtering).
Mostly because a strong diffuse floor is not practical in the control room.
Quote:
Originally Posted by Antti H View Post
Further, why would this floor reflection be necessary, but reflection off the console / mixing desk is generally considered bad? Or are you saying that the general advice is wrong and console reflection is not a problem?
You try to take my words out of context. I never said that all comb filters from reflections are "healthy", this one from the floor we need because we are used to it in everyday life (I wrote this again)

I tried to be precise,
and also:

- Mixing desk reflections are even more pronounced than floor reflections, because the shorter reflection path.

- People aren't used to suppress mixing desk reflections in brain in everyday life.



Last edited by boggy; 16th May 2017 at 04:24 PM..
Old 16th May 2017
  #435
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Northward's Avatar
Quote:
Originally Posted by Antti H View Post
You've restated your original assertations. I'm looking for evidence and / or explanation of the mechanism. Specifically, why a single very short specular reflection would be required (instead of general diffuse reflections which don't cause comb filtering).
Auditory system can't process, calibrate and locate to diffused reflections effectively. Because of both temporal and geometrical diffusion, and as a result much lower level too. Some of the papers I uploaded in my previous post explain some of that phenomenon - even if for some indirectly.

Quote:
Originally Posted by Antti H View Post
Further, why would this floor reflection be necessary, but reflection off the console / mixing desk is generally considered bad? Or are you saying that the general advice is wrong and console reflection is not a problem?
Very different frequency spectrum and intensity. Different brain interpretation and correlation of stimuli.
Old 17th May 2017
  #436
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Northward, boggy, seems that your point of view is rather reasoned, and close to truth. Thank you for having time and efforts to share it with me. XXI Century - great time, when peoples can discuss topics all over the world, beautiful.

But I'm going to make some expiriements with my angled floor shields, only for satisfy my curiosity, trying to think soberly with an psychoacoustic, not across.

My redirectional devices doesn't affect range below 600-700 Hz, so it will be situation, when floor SBIR exist, but brings some few to overall sound. May be, it's impossible to find nice-sounding compromice.

Remains only to install, deinstall, install, deinstall, until ears-brains-mind can draw a conclusion, where i can find more transparency and details, or which option sound unnatural and coloured. Good luck.
Old 17th July 2017
  #437
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Quote:
Originally Posted by DanDan View Post
Cheers Andre.
This one is a little more interesting IMO. For clarity I show only 4 curves.
The Null frequency shifts downwards as the speaker is moved away from the Front Wall in 10cm increments.
Green to Red to Black. IMO suggests one of the two walls on axis, F or B in dominant. The directlon of the frequency change points to the Front Wall.
However, you can't beat blocking.
A LF MiniTrap is inserted between the speaker and the wall. The Blue.

When the speaker further from the FW, the MiniTrap was tried close to the speaker, close to the wall and in between. No effect.
So FWBIR can be tamed with a 100mm trap, but only when Wall Trap and Speaker are as close as possible.

Attachment 283333
I tried inserting a 100mm panel of Rockwool behind my speakers (which are as close to the wall as possible) and it made absolutely no difference to the massive and very focused dips I was seeing in my FR with REW.

Does SBIR happen at 3/4 wavelength as well as 1/4? I realize the question I am asking may not be valid as we seem to have come to the conclusion that SBIR does not exist in the classical sense...

Last edited by chrismeraz; 17th July 2017 at 10:51 AM..
Old 17th July 2017
  #438
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Quote:
Originally Posted by chrismeraz View Post
I tried inserting a 100mm panel of Rockwool behind my speakers (which are as close to the wall as possible) and it made absolutely no difference to the massive and very focused dips I was seeing in my FR with REW.

Does SBIR happen at 3/4 wavelength as well as 1/4? I realize the question I am asking may not be valid as we seem to have come to the conclusion that SBIR does not exist in the classical sense...
That would suggest that your issue is not related to that surface. Try putting it on the floor inbetween the speaker and sweet spot. Also, note that the panel (assuming velocity based) needs to be at least 1/2 wavelength (at least) wide in relation to the frequency you're trying to absorb.
Old 17th July 2017
  #439
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Quote:
Originally Posted by chrismeraz View Post
I tried inserting a 100mm panel of Rockwool behind my speakers (which are as close to the wall as possible) and it made absolutely no difference to the massive and very focused dips I was seeing in my FR with REW.

........
Ummm, I placed there 40-60cm thick combined absorption treatment on all walls and ceiling...



Measured frequency response at the listening position in situation you see above:




Old 17th July 2017
  #440
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Random

Quote:
I tried inserting a 100mm panel of Rockwool behind my speakers (which are as close to the wall as possible) and it made absolutely no difference to the massive and very focused dips I was seeing in my FR with REW.
Yup, as time passed, I have also experienced that more often than the success seen in my example. It seems that sometimes to often the FW is not the dominant contributor to the nulling.

A typical panel trap is quite small relative to the wavelengths involved, plus the distance from the speaker would appear to determine how much of a 'shadow' is cast. Most advice concurs that speakers should be as close to or as far from the FW as possible. With all of that I cannot not see much point in moving the speaker a bit away from the FW, creating a BIR issue, then trying to fix it with something which rarely works. If it is far from the FW there is no point at all in trying a relatively small trap.

DD
Old 2 weeks ago
  #441
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ReDRuMx's Avatar
Sorry to revive an old thread, but I've been exploring wave propagation and the Huygens principle, so I have a thought regarding SBIR. Would like to know what folks here think

Let's say we have a "room" with only one hard surface - the floor, and we are considering reflections from this surface. The speaker is 1m above the floor, and the listening spot is 1 m away from the speaker, 1m above the floor. This would cause cancellation at around 140 Hz ( Floor/Ceiling Reflection Calculator ).

In this case, I also see the only possible "cause" of SBIR as coming from the "mirror point" (Left image in first post of this thread).

But let's consider we have covered the mirror point with a small 100% absorbent patch, measuring 20 cm2, or have a hole in the floor of same dimensions. Have we solved the SBIR at the offending frequency? Obviously not, because low frequencies are not rays.

But we have "removed" the mirror point (first arrival), so the same sound now reaches the listening spot a bit later.

The "notch" is attenuated a bit firstly because we removed some energy, and secondly because we have "delayed" the arrival of the reflected sound.

I know that I'm not saying anything new and revolutionary really, but thinking about it this way makes it clear to me that an SBIR notch doesn't necessarily need to be caused by a mirror point, and shows how it actually works

P.S. - In the case it's not clear to someone how covering the mirror point "delays" the reflection, just imagine the extreme example. Imagine we remove the floor, leaving only a small patch of the floor right below the speaker. Now the (omnidirectional) reflection source is this small floor patch. From the perspective of the microphone, this is obviously "delayed" when compared to the mirror point reflection. Considering the mirror point provides a reflection 180 degrees out of phase for this particular frequency, it is easy to understand that this new reflection will not be 180 degrees out of phase, but will still probably be in the "deconstructive interference" range. This also explains why the absorbent patch needs to be large relative to the wavelength of the offending frequency.

Last edited by ReDRuMx; 2 weeks ago at 07:25 PM..
Old 1 week ago
  #442
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Definition

I am a bit lost Red. I am not sure what you mean by mirror point reflection.
Many of the text books etc. refer to virtual images of the speaker. Each one of these is obviously caused by a reflecting boundary. As I, or the mic, sees it, the path from every image speaker is longer than the direct. So I can't see how removing any of them, by removing or making absorbent the boundary, could be said to introduce a delay. I am probably not following your rhetoric or terminology.
DD
Old 1 week ago
  #443
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Quote:
Originally Posted by DanDan View Post
I am a bit lost Red. I am not sure what you mean by mirror point reflection.
Many of the text books etc. refer to virtual images of the speaker. Each one of these is obviously caused by a reflecting boundary. As I, or the mic, sees it, the path from every image speaker is longer than the direct. So I can't see how removing any of them, by removing or making absorbent the boundary, could be said to introduce a delay. I am probably not following your rhetoric or terminology.
DD

I'll make a drawing when I find some time, I suck at drawing
Old 1 week ago
  #444
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Quote:
Originally Posted by DanDan View Post
Many of the text books etc. refer to virtual images of the speaker.
DD
Forget about the mirror image, it's obviously a MODEL, as we don't have speakers in floors obviously It is a helpful model, but I'm trying to figure out reality.

Please check the two images I posted and tell me if it makes my point any clearer.

If someone needs proof that the mirror point is the shortest path - Shortest Path Problem - GeoGebra

NOTE: In the "floor only below speaker" example, the reflection will be quieter than in the "mirror" example, but that's another point.
Attached Thumbnails
SBIR-screen-shot-2018-01-07-21.15.51.png   SBIR-screen-shot-2018-01-07-21.18.23.png  
Old 1 week ago
  #445
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Quote:
Originally Posted by ReDRuMx View Post
Forget about the mirror image, it's obviously a MODEL, as we don't have speakers in floors obviously It is a helpful model, but I'm trying to figure out reality.

Please check the two images I posted and tell me if it makes my point any clearer.

If someone needs proof that the mirror point is the shortest path - Shortest Path Problem - GeoGebra

NOTE: In the "floor only below speaker" example, the reflection will be quieter than in the "mirror" example, but that's another point.
Mirrored speaker for boundary reflections is model of the reality. We need nothing more "real" than that. If you like to do more in depth analysis, try to include actual (and real!) reflection coefficient (frequency dependent) of the boundary, and/or add loudspeaker radiation characteristic to the same model.

Old 1 week ago
  #446
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Quote:
Originally Posted by boggy View Post
Mirrored speaker for boundary reflections is model of the reality. We need nothing more "real" than that. If you like to do more in depth analysis, try to include actual (and real!) reflection coefficient (frequency dependent) of the boundary, and/or add loudspeaker radiation characteristic to the same model.

Hi Boggy. I wasn't saying that the mirror model is not sufficient, or that it's wrong, I was just trying to understand it more deeply.

What I'm simply saying is this:

In your first illustration, if we "removed" the floor and left just a small part of it right below the speaker, the reflection would arrive a bit later than if we had the entire floor surface below.

In a bit more depth: In my below illustration, the frequency being created is very low, and is omnidirectional. When it reaches the floor patch below, the reflection is also omnidirectional, because the floor surface is very small compared to the wavelength of the signal.

Does this illustration make it clearer?

P.S. - The "mirror model" holds true if the floor is homogenous, unbroken.
P.S. 2 - I'm aware that this reflection will be much quieter than if the whole floor was "present", but that's not the point here.
Attached Thumbnails
SBIR-screen-shot-2018-01-08-14.06.27.png  

Last edited by ReDRuMx; 1 week ago at 03:17 PM..
Old 1 week ago
  #447
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Party

Eventually I get it. Clearly the floor bounce is the shortest bounce path for HF. But I am not so sure about LF. We place a virtual image directly underneath the speaker. But when there is a reflecting boundary, surely this image has turned into a wide wavefront. So, removing the floor removes the HF bounce. But I reckon it also removes a large chunk of the equally early LF.
Interesting, but where do we stand?
DD
Old 1 week ago
  #448
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Quote:
Originally Posted by DanDan View Post
Eventually I get it. Clearly the floor bounce is the shortest bounce path for HF. But I am not so sure about LF. We place a virtual image directly underneath the speaker. But when there is a reflecting boundary, surely this image has turned into a wide wavefront. So, removing the floor removes the HF bounce. But I reckon it also removes a large chunk of the equally early LF.
Interesting, but where do we stand?
DD
Partly what I meant but... It isn't the case that the mirror point is the first reflection only for HF. It is the first (earliest) reflection point for LF also. But if the mirror point is "removed", LF will still reach the listening point (diffraction, see Huygens principle), but with a slightly longer total path!

Edit: BTW, in my illustration, the floor isn't completely gone, there is a small patch of it beneath the speaker. Obviously there would be no reflection at all without the floor
Old 1 week ago
  #449
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Early Riser

Yes indeed, earliest LF too. It is an interesting mental exercise, but I don't see a practical application or advisory coming from it. I mean, we kinda need the floor, for the time being in any case......
Your fans will be aware of another brain teaser you posted regarding +6dB summing of two speaker mono. The concept of 'Radiation Impedance' came into view. In terms of cancellation rather than reinforcement, this would seem to very much apply to the 'Speaker' BIR in particular.
DD
Old 1 week ago
  #450
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Quote:
Originally Posted by DanDan View Post
Yes indeed, earliest LF too. It is an interesting mental exercise, but I don't see a practical application or advisory coming from it.
Heh, considering I've been down with a cold this past week, I could have just spent the time watching reruns of Two and a Half Men for example. I'd say exploring the Huygens principle is a more worthwhile endeavor As with any scientific exercise, it's hard to say in advance if it's going to have strict practical applications. But the kinds and frequency of exercises one chooses to partake in, tells something about the participant, no? I like it, even if I'm (possibly) bad at it

Anyway, I would say that in this particular case, we are talking about more than merely a mental exercise. If what I described is correct, it makes me understand reality in a bit more detail. That's always good, no?

The revelations here for me are:

1. A SBIR dip in FR doesn't necessarily need to be coming from a mirror point. This was always more-less clear to me, but now I have a better understanding of why, and what are the limitations.
2. It is clear to me exactly WHY placing an absorbent patch at a mirror point is not sufficient, and how the size of the absorbent relates to the wavelength of the SBIR frequency.


Quote:
Originally Posted by DanDan View Post
I mean, we kinda need the floor, for the time being in any case......
I chose the floor example because it was the easiest for me to visualize and draw, but you can just as easily rotate the viewing axis by some angle, and realize that everything said here applies to any other reflective surface, such as side walls or the ceiling.


Quote:
Originally Posted by DanDan View Post
Your fans...
Is there a fan club? lol


Quote:
Originally Posted by DanDan View Post
...will be aware of another brain teaser you posted regarding +6dB summing of two speaker mono.
Well to be honest, that really wasn't a brain teaser. It was a simple question, but the answer is obviously either complicated, or no one here knows it, or I'm to dumb to recognize and understand that some of the offered answers were correct.


Quote:
Originally Posted by DanDan View Post
The concept of 'Radiation Impedance' came into view. In terms of cancellation rather than reinforcement, this would seem to very much apply to the 'Speaker' BIR in particular.
DD
And you say there's no practical implication? This is all very interesting, and obviously very much connected.

TBH, for me the origin of this particular "exercise" was when I began trying to figure out why low frequencies were omni-directional, and why do they diffract more easily. But true, people usually tell me that I ask one why too many
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