[docaudio]

HI,
I have a couple questions about measuring studio proper areas. It seems that you would take several readings with the speaker and mic in various positions because, unlike a control room, the sound source position would vary. But are there some specific places that one should place the speaker and mic? Also, should there be a calibration done to the speaker itself? It is only "standing in" for live instruments or voices, so it seems to me that you would want to eliminate any of it's coloration from the measurement (just like the sound card calibration)
Thanks!
-Bill

 

[SAC]

I am guessing by your reference that you are referring to trying to determine some quality in regards to a live recording room?

Yes, there are limits to trying to simulate an 'instrument' with a speaker. The polar dispersion and Q, etc, will significantly influence a myriad different qualities within the space where the total response is largely conditioned by the interaction of speaker and the bounded room..

But I also get the feeling that you are focusing upon the frequency response, which is perhaps the most limited view that one can have in this respect.

Rather, you should be concerned more with the energy dispersal and how that energy behaves with respect to the boundaries. Therefore you are much better off viewing such energy dispersal in the time domain. From this perspective you can see how the energy disperses and how it interacts with boundaries, is returned to the space (with respect to gain, arrival time, degree or lack of spatial and/or temporal diffusion diffusion).

This view will necessarily be conditioned by the acoustical impedance of the boundaries encountered.

The time domain will provide insight into this behavior and the results. The frequency response will provide no insight into the above mentioned characteristics - and as such provides no basis for actionable causal evaluation or adjustment.

As far as does the polar dispersion and Q of a speaker matter? Absolutely! And this is a variable often simply ignored as we begin to evaluate speakers within a room! And even worse, many begin to design a room simply figuring that any speaker they like can be "inserted here".

The fact is, proper design BEGINS with not only a speaker with a well defined spatial dispersion and Q, but the designer's knowledge of such character! As a speaker's dispersion within a bounded space is critical in determining what early reflections will be generated that contribute directly to potentially anomalous behavior, it is critical that this interaction be anticipated and defined!

In other words, it makes NO sense to design a room and then to simply plop a speaker with an unknown or inappropriate spatial response into the midst and expect the room to perform as expected!

This issue is a critical and FUNDAMENTAL issue in such acoustical response models as the Hidley/Newell Non-Environment rooms and the LEDE concept. But it is also a subject that one seldom ever hears mention in all of the focus upon room design and measurement on forums. And as such, this constitutes a rather major MISTAKE in the design process. The irony is that such room models are built 'around' specific speaker responses, in order to compliment them. They were not designed and built simply so that one could plop whatever speaker they wanted on a bridge and mix - as is SO commonly done!

This supreme irony: Many have some anechoic frequency response that they can pullout with which to impress friends regarding their choice of speakers (which, by the way is very handy the next time you install them mounted in a free field suspended in the center of an anechoic chamber!). But how many have an ACCURATE assessment of the actual polar response/Q of their speakers? And how many of the measured responses actually take into consideration the intended spatial loading and mounting of the speakers in a real defined space?

I'll take such spatially defined energy dispersion data over a frequency response any day!

And for the speaker room interaction, aside from the fundamental addressing of low frequency modes, give me the Envelope Time Curve (ETC) ANY DAY! But all is not lost, as the printouts of the frequency response are handy as drink coasters. :rofl2:


(That just might make some stop and think about just how they determined the best(sic) speakers to buy the last time out, doesn't it? And PLEASE do not tell me that anyone intended to bridge mount their speakers and to simply go out of their way to introduce critically destructive early reflections!)

 

[docaudio]

I guess the gist of my question was how critical is the placement of mic and speaker in measuring a room with REW, or is it more important to place the mic and speaker in the same position when you do follow up measurements - after room treatment. So the concern is not so much the initial tests, but how well the follow up tests improve things.

 

[SAC]

I guess the gist of my question was how critical is the placement of mic and speaker in measuring a room with REW, or is it more important to place the mic and speaker in the same position when you do follow up measurements - after room treatment. So the concern is not so much the initial tests, but how well the follow up tests improve things.

Again, you must first define your intentions. Proper answers follow from a well formed question.

First is the issue of the intended use.

In a live recording space you are creating responses - essentially like an FX generator, ranging from dry (devoid of reflections) to very live with high levels of reflections dependent upon a multitude of positions. And different regions of the room can exhibit different responses depending upon the design goals.

This differs from a control room, which has a much more rigidly defined design goal and a defined listening position.

In a live room measurements are made in defined positions. The response will be particular to that position. And in a live room, different placements will generally have different responses - intentionally. You measure various positions with the intention of creating different local responses.

You do not take 'before' measurements in one place and 'after' measurements in another place (or with speakers and mic located in different positions) and expect to be able to make any kind of valid comparison for agreement. Room and system behavior is position specific. This will only verify differences. If one is not trying to design specific locations in a room to have different responses, utilizing multiple measurement positions in the process of trying to tune a response relative to a particular spot makes no sense in any space regardless of intended use, as you are not comparing apples with apples.

One other possible usage option may be that one is trying to extend the uniformity of a listening area through the use of a distributed listening system. This opens a while other can of worms as there are a different set of design methodologies for planning distributed sound systems. However, if one is attempting to do this without employing distributed systems, you might consider averaging specific measurements (those where this can be done) and creating a mediocre but 'acceptable' distributed response - meaning that it is neither non-optimal nor non-worst-case. I don't recommend this approach, but some attempt this and find it acceptable. Some measurement systems are designed specifically with this capability as an option, such as SysTune and SIM.

One other scenario where multiple position measurements might be made as a part of a preliminary evaluation of a space is when one encounters an unknown space where one is unable by experience based pattern recognition to have an idea of what the expected behavior will be, or if the space is simply too complex to reliably predict the response with a high degree of confidence. In this case one might take several measurements in potential listening positions and/or with different speaker positions in order to get an idea of what arrangement may present a response correlating more closely to a desired response behavior - thus using the room to make the design goal a bit easier to achieve.

So, I hope that covers a few of the potential situations and intended uses that might condition how/where/why preliminary measurements are taken.

But in all cases, once one has an idea of what response model is desired, one measures in the same spot both before and after to determine if progress and to provide final proof of performance verification the desired response is achieved.

I hope this shotgun approach to many possible uses has perhaps hit upon the case has covered the scenario you intended to address... If not, providing much more specificity in the desired use will help to be able to provide a methodology for the process of making the necessary measurements.