Nulls

audioguy · Oct 19, 2010

RBFC said:
Here's some specs that may assist you....

http://www.gikacoustics.com/absorption.html

Lee

Lee: You are the best. I had been on their web site with another house/room and when I looked this morning, what did I find but ---- lo and behold, they are located here in Atlanta. I will call them this morning. Stay tuned (just don't ever buy the service of Rives Audio!!)

microstrip · Oct 19, 2010

Audioguy,

I have used this calculator with great success. It reproduces the room modes of my room perfectly.

http://www.hunecke.de/en/calculators/room-eigenmodes.html

A cheap but useful software to model RT60 is Cara - Computer Aided Room Acoustics

http://www.cara.de/ENU/index.html

Good luck!

audioguy · Oct 19, 2010

microstrip said:
Audioguy,

I have used this calculator with great success. It reproduces the room modes of my room perfectly.

http://www.hunecke.de/en/calculators/room-eigenmodes.html

A cheap but useful software to model RT60 is Cara - Computer Aided Room Acoustics

http://www.cara.de/ENU/index.html

Good luck!

Thanks. The Hunecke calculator is very interesting but does not show nulls (at least if it does I can not interpret where they are). I think I'm now moving in the right direction based on the input I got from Nyal. I am trying to get hold of GIK to get some advice from them on the best way to treat the problem.

I must say that it really annoys the heck out of me that the designer of the room will not assist in this process since he has said probably 10 times "it's not the room"!!! To me, given all of the evidence to the contrary, his attitude clearly demonstrates either massive incompetence and/or just REALLY crappy customer service.

microstrip · Oct 19, 2010

audioguy said:
I have one (a null) that is VERY detrimental to the sound in my room and am trying to determine from which dimensions it is generated (the null is not in the bass region -- it is located in the sweet spot of between about 200 hz and 350 hz). I'm pretty sure I know but am looking for confirmation.

I just went back to read the first postings - rule number one before posting! (Rule number two - make no exceptions

! )
According to the dimensions of your room the range of frequencies of your problem is out of the range dominated by the room modes - this zone should end around 120 -140 Hz in your room, so spreadsheets and room calculators based in resonances are useless! The frequencies you refer are in the zone where diffraction and diffusion prevail - you really need advice from an expert!

audioguy · Oct 19, 2010

The owner of GIK Acoustics is on the way to my home now. I will keep you posted !!!!!

RBFC · Oct 19, 2010

Not to plagiarize the movie, but Good Luck Chuck!

Lee

audioguy · Oct 19, 2010

This is apparently going to be an iterative process. We r going to try one thing and if that doesn't work we will move onto the next. Great customer service and I have yet to actually buy anything.

It makes Rives Audio lack of customer service even more obvious.

mauidan · Oct 19, 2010

audioguy said:
This is apparently going to be an iterative process. We r going to try one thing and if that doesn't work we will move onto the next. Great customer service and I have yet to actually buy anything.

It makes Rives Audio lack of customer service even more obvious.

It would be interesting to see before and after room measurments, from the GIK visit.

Kal Rubinson · Oct 19, 2010

audioguy said:
This is apparently going to be an iterative process. We r going to try one thing and if that doesn't work we will move onto the next. Great customer service and I have yet to actually buy anything.

Yes on both accounts. OTOH, you should consider a measurement tool of some sort to verify/inform what you hear. I do not if you have anything but the cheapest is an RS meter with TrueRTA or RoomEQ Wizard.

Kal

mauidan · Oct 19, 2010

Kal Rubinson said:
Yes on both accounts. OTOH, you should consider a measurement tool of some sort to verify/inform what you hear. I do not if you have anything but the cheapest is an RS meter with TrueRTA or RoomEQ Wizard.

Kal

If you check his profile, you'll see he has a TacT RCS 2.2XP.

Kal Rubinson · Oct 19, 2010

devert said:
If you check his profile, you'll see he has a TacT RCS 2.2XP.

That'll do.

audioguy · Oct 20, 2010

Kal Rubinson said:
Yes on both accounts. OTOH, you should consider a measurement tool of some sort to verify/inform what you hear. I do not if you have anything but the cheapest is an RS meter with TrueRTA or RoomEQ Wizard.

Kal

I have REW, XTZ, a TacT and a SigTech. Last night I installed a GIK monster trap on the ceiling just in front of the listening position. The measurements before and after were identical. More importantly (and sadly) the sound did not change either. Next (I think) is to try another product (I don't know the name but it is a QRD diffusser mounted in front of a monster trap) on the rear wall. I think he was talking about using 4 or 5 of them.

Kal Rubinson · Oct 20, 2010

audioguy said:
I have REW, XTZ, a TacT and a SigTech. Last night I installed a GIK monster trap on the ceiling just in front of the listening position. The measurements before and after were identical. More importantly (and sadly) the sound did not change either. Next (I think) is to try another product (I don't know the name but it is a QRD diffusser mounted in front of a monster trap) on the rear wall. I think he was talking about using 4 or 5 of them.

A bass trap will do less on the ceiling than in a corner and, up there, it will be little more than a panel absorber. The diffuser will not fix a null, either.

audioguy · Oct 20, 2010

Kal Rubinson said:
A bass trap will do less on the ceiling than in a corner and, up there, it will be little more than a panel absorber. The diffuser will not fix a null, either.

All corners are already trapped. I currently have RPG Skyline diffusers on the back wall (at the recommendation of Rives). This next step is to replace the Skylines with this GIK product that is a combination QRD Diffusor/Monster Trap. The "guess" is that the null may be coming from the back wall (which is a stud wall up against concrete in a basement)

Observation: After having a number of visits and consultations with room acoustic folks, the process of fixing a very specific room problem is apparently a bit of hit and miss application of scientific principals. No one has been able to say: "do this and the problem will be addressed". It has been (by three different knowledgeable individuals) more of "let's try this and if that doesn't work, we'll try that". I find that interesting.

RBFC · Oct 20, 2010

It's very difficult to predict the density of a given room boundary, or its absorptive characteristics. Therefore, it becomes hard to predict the performance of a known product placed on those walls, etc. Unfortunately, most calculation models assume some amount of "fixed" values for walls, etc.

Lee

Kal Rubinson · Oct 20, 2010

audioguy said:
All corners are already trapped. I currently have RPG Skyline diffusers on the back wall (at the recommendation of Rives). This next step is to replace the Skylines with this GIK product that is a combination QRD Diffusor/Monster Trap. The "guess" is that the null may be coming from the back wall (which is a stud wall up against concrete in a basement)

Observation: After having a number of visits and consultations with room acoustic folks, the process of fixing a very specific room problem is apparently a bit of hit and miss application of scientific principals. No one has been able to say: "do this and the problem will be addressed". It has been (by three different knowledgeable individuals) more of "let's try this and if that doesn't work, we'll try that". I find that interesting.

Agreed. If the null is fairly frequency-restricted, you might consider trying a tuned membrane trap for it. Something like the RPG Modex Plate.

Gregadd · Oct 20, 2010

Trial and error is the way most scientific problems are solved. Haven't you watched "House?"

Nyal Mellor · Oct 21, 2010

audioguy said:
Observation: After having a number of visits and consultations with room acoustic folks, the process of fixing a very specific room problem is apparently a bit of hit and miss application of scientific principals. No one has been able to say: "do this and the problem will be addressed". It has been (by three different knowledgeable individuals) more of "let's try this and if that doesn't work, we'll try that". I find that interesting.

This is very true, and it is because we do not have 100% correlation of measurements to subjective sound quality impressions. We have a set of heuristics (i.e. principles) that say 'to get good sound' do x, y and z with room acoustics. In most cases applying these principles will solve a room's acoustic issues. But not in all cases as you have observed. Thanks to the work of people like Floyd Toole we are learning more and more about how to relate measurements to subjective impressions but there is still a gap.

Some considerations:
-the first step is identifying the problem. Often this is a process of elimination and in this we must try and link subjective sound quality impressions to measurements or what we can visually observe about the acoustic design of the room
-the second step is to apply the most often used fix. Most acousticians will have a 'go to' solution for a particular issue, and this may be different from person to person. At a reflection point behind the listener one person may use a thick absorber another may use a diffusor.
-the third step is to listen. Does that solve the problem? If not then
-the fourth step is to work out if a) did we really identify the right problem or b) do we need to try a different solution

This is typical engineering in my opinion!

microstrip · Oct 21, 2010

Did you take RT60 measurements with 1/3 octave resolution of your room? Or are you just relying on listening tests?

audioguy · Oct 26, 2010

microstrip said:
Did you take RT60 measurements with 1/3 octave resolution of your room? Or are you just relying on listening tests?

I have taken more measurements than a scientist working on the space shuttle flight - way more !!!

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