OC 703 faced? - Page 7

Sorry, but I don't get it. What does directivity have to do with it? You're saying that a reflection arriving in the time interval that is disruptive to our brain from the front wall will be LESS disruptive than one arriving from a side wall? Whatever the source, is it not equally disruptive given similar amplitude in similar time? And, why should there be spectrum variance here? The reflection should follow the source from a spectral perspective, unless there's something in the path acting as a filter right?

"Likewise, if a reflection is broadband, I might not find it objectionable (or even notice it), since it could be reinforcing the direct sound."

Again, I don't get it.

If the reflection has sufficient energy and arrives within time defined as disruptive, why would you find it "not objectionable" based on the spectrum involved "broadband"?

Thanx, as long as we keep the benefits in perspective and not treat it like some magic bullet.
A measurement tool that displays energy over time is more valuable in a situation where you're targeting all energy/reflections within a particular time range, like a studio, than reflections based on direction and spectrum, like a living room. You don't see designers of home theatres and music listening rooms that post on AVS talk about the Haas kicker the way posters on GS do. [BTW, what happened to all that talk about the Haas kicker? Seems to have quietly faded away.]
But you're doing something similar by suggesting generalized ETC measurements without any caveats. Problem is, the strength of a reflection (how tall the spike is in an ETC measurement) is affected by the frequency content of the reflection. At least the Mellor/Hedback paper mentioned earlier talks about using bandpass filtered ETCs rather than a generalized one.
Only if your objective is to supress all reflections within a certain time period, like when designing a studio. That's where a measurement that gives you energy over time, without caring about the spectrum of that energy, is most useful.

who here is insinuating that a 'tool' which details a user how specular energy is impeding the listening position is a 'magic bullet'?

the tool in context of this thread is with regards to the 'defined goal' of attenuating an early specular reflection - and verification once 'treatment' (be it an absorber or reflector or diffuser) has been procured and placed to confirm that the 'treatment' resolved the identified and measured 'problem' sufficient to the user's criteria.

it also identifies other sources of incident energy that may otherwise not be so obvious as that of 'large boundaries' - such as edge diffraction or specular reflections from other objects or surfaces within the room. is the ETC not sufficient for such identification?

why is it we never see such vicious confrontation on this forum when another user recommends "the mirror-trick"? yet recommending the actual tool for the job to verify that the absorber is placed properly and is sufficiently attenuating the specular reflection across the entire listening position (be it single seat or multiple rows) brings about all sorts of confrontation...


who are you to say what information regarding the room's specular response is 'valuable' or not? who are you to say or insinuate what the acoustic response should be of a user's room? do inherent issues within small acoustical spaces change based on the function of the room?

whether one allows early reflections to impede the listening position or not is not the discussion. the acoustic response a user is looking to achieve in their room is not the discussion. whether a user is looking for an accurate, critical listening space or a pleasing listening space based on 'their' subjective tastes, is not the discussion. instead, it's about using a specific tool for a specific job. if you want to discuss differing acoustic responses, then by all means start a new thread.


if a particular user has made the decision to attenuate early reflections (and implemented 'treatments' accordingly), then by nature you are creating an 'effectively anechoic' response at the listening position for a specific amount of time (inter signal delay) - such that any energy arriving within this time gap is below the human detection threshold and thus, not processed. unless the room is completely damped, then eventually, specular energy will be reintroduced to the listening position. this is essentially the 'termination' of the 'effectively anechoic' time-period. with the use of diffusers, the 'haas kicker' can indeed be of a diffused termination. the problem is, the diffused returns will (by nature) by lower in gain than a specular reflection termination - as such, if one wants to adhere to the psycho-acoustics for the termination (haas trigger) to remove the localization cues from the later arriving specular energy in the room and force the brain to 'lock-on' to the direct signal, then the termination (trigger) needs to be of sufficient gain. this is why you may find reflectors being used in place of absorbers at early reflection points - to maintain and preserve as much of the finite, specular energy in the room as possible such that it can be managed appropriately based on the user's desired acoustic response.



precisely as stated as early as post#10. the lower energy has longer wavelengths containing inherently more energy. it is also very likely that the lower specular region will be more 'off-axis' than the HF (highly directional) content (speaker dependent) ... as such, the focus with regards to attenuating (absorbing) early specular reflections with porous (velocity-based) insulation is that the absorber needs to be effective down to the lower specular region. hence, why 'thin' absorbers are not recommended, as they simply 'filter', 'EQ', 'color' the reflection by attenuating the HF band and allowing the low-mid specular energy to persist - and why one should measure to determine the effectiveness of their absorber at attenuating the 'entire' specular reflection (and this is why attenuation is with respect to overall gain - NOT frequency).


first of all, i am not sure why you feel particular acoustic responses that look to address fundamental issues of being constrained to small acoustical spaces (where time domain takes precendence) - is somehow limited to 'studios'.

tell me, what is the 'goal' of a 'studio'?
why do you feel that a particular user may not wish to achieve or implement an acoustic response of a 'studio'? if you want to discuss differing acoustic responses, then by all means do so in a new thread. but please refrain from introducing such debate and distractions from this discussion which is about the (already chosen) decision to absorb early reflections, and how to verify that such goals are being sufficiently achieved.

Not according to toole, who referenced many past efforts that generated similar results. They found that listeners often don't mind, and sometimes prefer, pure lateral reflection from sidewalls. Reflections from other directions may not produce the same result.


Very few speakers have a similar spectral balance at all angles. This refers to the common discussions around here about directivity, polar response, power response, etc. If a speaker's frequency response is dramatically different at 30 degrees and 60 degrees (and many are), reflections from those angles will likewise have very different spectral content. Dragon mentioned this previously in this thread I think.

Often the off axis response of a speaker will dictate the use of absorption vs diffusion.

The "something" acting as a filter is the "something" the reflection is reflecting from! When sound strikes an object some is reflected, some is absorbed and some passes through ... there's a timbre shift and, not often talked about, a frequency shift and, in some frequencies a delay (more of a delay than in other frequencies). To get even more anal, while talking about how much of what is absorbed (or not) by 1, 2, or 4" of fiberglass (regardless of the angle of incidence) is completely ignoring the effect of the underlying strata. (You don't have a piece of fiberglass, you have a composite for which the fiberglass panel just happens to be the first layer.)

Ok, I've read and seen posts previously about off-axis response. So if a speaker has poor off axis response, why would I want to hear a reflection that has a spectral shift? Don't we want to hear the direct signal without the shite?

You may not want to hear the reflection. Many have questioned whether toole obtained the results he did because the speakers used were relatively well behaved off axis.

im sorry, sdurani, but your entire post is null and invalid with regards to a user's simple and defined design requirement to attenuate (absorb) a broadband specular reflection.

it has nothing to do with studios, listening rooms, living rooms, laundry rooms, ... it has to do with attenuation of specular reflections and the measured verification of the effectiveness of the procured 'treatment' - be it an absorber, diffuser, reflector (specular re director), etc...

spectral issues with regards to the ETC tool are irrelevant when one's defined goal is to attenuate the entire broadband reflection. the gain and the attenuated gain after the treatment has been placed is the focus of discussion.

there is no conspiracy of 'studio folk' from GS that have suddenly 'infiltrated' AVS ... there is just a much higher SNR on that forum with regards to acoustics and physics, as the studio world is much less forgiving than the home listening environment. problems there are presented with measurements - and iterations of treatments and their results are presented back to the community from those that wish to share and 'give back'. physics do not change based on the 'label' or 'purpose' of a room.

you continue to debate about the usefulness of the ETC with regards to other problems or scenarios that are not even being discussed here - which is a blatantly and obvious distraction. just because you have chosen a particular acoustic response, of which the ETC (simply one tool in the toolbox) may not directly apply to your particular scenario or the particular information regarding your room's acoustic response that you are attempting to identify - does not invalidate the tool's usefulness in other scenarios.

simply put - you are in disagreement with the usefulness of a particular tool for an application that is not even relevant of this discussion or the identified goal.

if you have input, i would love to see you present any self-quotes of your own commentary in recent threads where a user or novice has opened the discussion regarding attenuation (absorbing) of early specular reflections - such that you clearly outlined for the user how to best approach solving the user's request and what tool(s) the user may use to verify that their procured 'treatment' has truly and objectionably addressed the original issue.

Because it doesn't exist, except as a description of insecurity. When you point out the limitations of the basic mirror trick, no one calls it a "vicious confrontation". When I point out the limitations of simple ETC measurements, you label it "vicious".
It's not the discussion you want to have. But that doesn't mean listener preference has no place in a discussion about addressing reflections. These systems are being set up for listeners, human listeners, not an audience of microphones.
It's not about what I feel. I was merely pointing out that ETC was rarely discussed at this home theatre forum until folks came over from a studio forum.
If my posts in this thread are bothering you, then report me to the moderator and/or put me on your ignore list.

could you please elaborate on how one would choose or select design characteristics of a diffuser based on a particular off-axis response?

"diffuser" is a very loose term which can have many distinct capabilities (spatial dispersion? temporal dispersion? bandwidth? hybrid absorber/diffuser?).

one must also be mindful of a "diffusers's" performance with regards to how it is placed within the room - since first-order reflection points in a typical rooms generally mean that angle of incidence is around +/- 45*, the "diffuser's" bandwidth, cut-off frequency, lobing, etc the "overall polar response" can change dramatically vs that of normal incidence.

and more importantly - the root of this whole thread - with regards to your statement above, how does one objectively measure the effect an absorber or diffuser has on the specular reflection once the treatment has been placed? what and how do you recommend a user or novice of this forum to go about identifying that their problem has been solved and the treatment is acceptable?

and even more importantly, since this thread is rooted in thin absorbers of which attenuate HF specular energy only - do you also (when recommending diffusers at first reflection points) - also design said diffusers such that the are effective throughout the entire specular range?? if a diffuser has a LF cut-off of ~700hz, is that not essentially tantamount to a thin absorber? as the lower specular range (with longer wavelengths and more inherent energy) not even "see" the diffuser and reflection off the boundary as if it were a flat wall?

and/or if one is using a hybrid absorber/diffuser - how does one measure the effectiveness and what would you recommend the 'end-state' response of the treatment look like?

right - mitigating the need for "side wall absorption" !!!

that is why such conclusions are so contradictory!!

if the speaker is well-behaved such that off-axis energy (side-wall reflection) impedes the listening position low enough in gain, then absorption/treatment may not even be required!

hence - the usefulness of the ETC to objectionably measure the reflection's gain (based on speaker off-axis response, boundary impedance, angle of incidence, etc) - to verify whether any such problem exists in the first place such that 'treatment' is required !

absolutely zero substance regarding the topic or any responses to my direct commentary that is regarding acoustics.
casually side-stepped and instead chose to focus on "human communication" and irrelevant nonsense that is not related to acoustics.

we are discussing a particular tool's job for a particular (and clearly identified!) problem.

just answer the question - if a user has a design requirement to fully attenuate a broadband specular reflection - then how does the "spectral lacking" of the ETC matter?


may i suggest you re-read the first 3 posts in this thread.


then by all means - before the ETC was being "discussed" or "recommended" - how on earth were you objectionably verifying or communicating to a novice how to objectionably verify that their procured treatment was truly and sufficiently addressing the original problem that it was procured for ?!

In his final paper (which I have been trying to get you to read), he cites published research going back to the 1950s that describe early reflections improving speech intelligibility. Obviously, that research didn't involve him nor any of Harman's various brands of well behaved speakers. There are similar citations to research on the effects of early reflections, timbre, spaciousness, listener preference, etc. Most of the paper is a clearing house for past research, not stuff he did on his own.

These views aren't limited to Harman/Toole. The Dirac (room correction) white paper starts the discussion of early reflections with the following quote: "There seems to be consensus in the field that some early reflections actually help make speech more intelligible. However, it is also well documented that reflections within 5-10 ms of the main pulse in typical listening rooms are above the level where the primary source shifts or spreads (even when just listening to a single primary source). Reflections from the front and the rear (within ±40º) are perceived as detrimental to sound quality, whereas side reflections (within reasonable levels) often improve the perceived sound quality."

It certainly helps to use speakers with decent off axis response if you want to take advantage of early lateral reflections. As for absorbing them, James Moir of the BBC once said: "if a room requires extensive treatment for stereophonic listening there is something wrong with the stereophonic
equipment or the recording. The better the stereophonic reproduction system, the less trouble we have with room acoustics."

To that end, see this post from Hedback regarding a conversation he and Mellor had with Toole.

Alright, I have one last question before I rest my brain. A simple yes or no would suffice:

Q: Can a reflection (from whatever surface, independent of frequency) arriving at the listener in <20ms of direct signal, and containing an energy level at 90-100% of the direct signal, provide ANY positive psycho-acoustic benefit to the listener?

What part of the ETC measurement showed the reflection to be broadband?

please apply some reading comprehension before replying to my commentary. here is my quote again -


where in that statement did i insist the ETC provided measurement of the broadband signal? you're distractions are becoming blatantly desperate.

you continue to prove you cannot directly answer my statements that a particular tool (ETC) is more than adequate for the design requirement of a user wishing to fully attenuate (absorb) a specular reflection across the listening position.

the fact is - it doesn't matter what the spectral content of the reflection is (based on speaker response, impedance of boundary, angle of incidence) - if the goal is to attenuate the early specular reflection then the spectral content of the reflection is irrelevant. the goal is merely to attenuate the entire reflection with respect to gain - and the ETC is the tool for the job.

you cannot simply focus on the topic of discussion regarding a particular tool to provide a particular measurement based on a particular design requirement.

this is tantamount to you saying a hammer is not an appropriate tool to build a house with because you believe a house is not the ideal living quarters that a person should live in. you're attempting to distract and inject a debate regarding differing acoustical responses, when the topic is regarding a CHOSEN acoustical response (attenuate early reflection) - and what tool is appropriate for verifying that procured treatment is adequate in addressing the measured problem.

if you wish to discuss acoustic responses, then by all means start your own thread. but please refrain from the blatant distractions when a member of this forum has made the decision to attenuate (absorb) early reflections and the proper tool for the job is provided.

Then how do you know the reflection is broadband?

sdurani,

in the context of this thread (post #1 and post #3, which you may wish to brush up on) - of which the design requirement is a specific and defined goal to attenuate (absorb) an early specular reflection ... i have insisted that the ETC response is the appropriate tool to measure the gain of the reflection as well as the attenuation once the treatment (in this case, a velocity-based porous absorber) has been procured and placed.

please dictate how the ETC is not an acceptable tool in such a scenario.
please dictate how spectral information is at all relevant when the goal is to attenuate the entire reflection (regardless of what 'broadband' content it may contain).

edit: i don't even need to respond anymore ... i can just repost my original questions of which you blatantly ignore; such as:


then by all means - before the ETC was being "discussed" or "recommended" - how on earth were you objectionably verifying or communicating to a novice how to objectionably verify that their procured treatment was truly and sufficiently addressing the original problem that it was procured for ?!

if i am fortunate to have a (relatively) large room - such that first-order reflections naturally arrive at ~20ms after the direct signal - should i deploy reflectors to artificially induce 'early reflection' to the listening position?

and if so, what gain and arrival time should such criteria be?

Food for thought, courtesy of Keith Yates:


http://www.hometheater.com/content/l...and-play-right

Lol, yeah, I've started it a few times but never make it through. Not sure why. But I'm aware of his citations and the body of prior work. I was just pointing out that this objection has been raised. To be honest, I'm not sure what to make of this research as it contradicts my own in room perceptions. I don't know whether to attribute that to placebo/bias, listener training/experience, adaptation, speaker design, or something else.

Freudian slip?

Audyssey dsx does this digitally via wide speakers. I don't know if there are any examples of implementation in large spaces, but I thought it was worth pointing out that the idea isn't without some traction.

Ah, now it's "regardless of what 'broadband' content it may contain". In that case, your entire scenario starts from a false premise. Since you don't know whether the reflection is broadband or not, then you don't know whether the goal is to attenuate the reflection or not.
Actually, that is a good question, along the same lines as the one asked by test4echo101. In over a decade that this forum has been around, how on earth was anyone able to place treaments in their home theatres with any effectiveness without using ETC? Either: everyone who was using treatments had no idea what they were doing OR surgical precision in placement isn't all that critical in consumer listening spaces.

would you please elaborate on what "decent off-axis response" represents? your perceived definition of: "decent" - or objectionable polar responses of "decent"?

if one were to apply an acoustic model such that 'early lateral reflections' are identified as a design requirement, what polar response is recommended via proper speaker selection?

if the ETC is irrelevant (eg, "not the proper tool for the job") in such a scenario - then what should my time-domain responses look like with regards to frequency?

what is the 'ideal' early reflection? what is the ideal time arrival and what is the ideal gain with respect to direct signal? what criteria should i design my room around?

if i were to implement 'treatments' that were essentially staggered reflectors , such that i were able to induce 15 separate early reflections (each spaced 1ms apart) - would this add to spaciousness and perceived quality? what is the limit on 'good' early reflections? is there a limit such that too many reflections within a time interval will start to degrade perceived quality?

Similar shape to the direct response but with the higher frequencies naturally attenuating as you move further off-axis. Nothing more complicated than that.
Why do you feel ETC is irrelevant?

based on your logic, a user would build the room, measure the spectral content of the reflection, AND THEN choose the acoustical response of the room (after it has already been constructed). i think not.

you can dance around the topic all you want. you are simply incapable of answering even relatively simple questions with regards to acoustics.

did you dig through your history yet such that you can produce any self-quotes / commentary where you gave a novice advice regarding this topic? ... where, if a novice had a design requirement to attenuate a specular reflection - that you offered advice on what tool can provide objectionable measurement once treatment has been applied?

the real issue here is i am not arguing against logic or measurements or objectionable data - but instead your feelings. as such, human nature will always prevail.

what does that even mean?
so - you are not able to provide any polar responses? ...i thought so. more vauge commentary with little to no substance.

on a related note - with regards to off-axis response and the broadband nature of specular reflections ... should you not also be considering the material of the boundary and the acoustical impedance of the boundary such that the reflection's spectral content is maintained?

what is the point of a speaker having "decent" off-axis response if the boundary dictates what spectral content is preserved in the reflection? why is it that i have YET to see you even recognize this fact? do you assume every user's boundaries are 100% reflective? have you dumbed this topic down to the point where you completely and mistakenly forgot to take into account the acoustical impedance of the boundary?

OOPS.

Remember, we're talking about consumer listening spaces, not studios. So most of us are starting out with a room that is already built. And yes, I would choose whether to treat or not, let alone what type of treatment, based on the contents and direction of the reflection.

The point is to take advantage of lateral reflections, so having off-axis response that is similar to the direct response (but tilted down, naturally) is helpful. It doesn't have to mimic the direct response precisely, as long as it doesn't look too different. Just looking for consistency, so that when the direct sound and reflections combine, it doesn't make drastic changes to the sound of the speaker.