John Sayers' Recording Studio Design Forum Archive

Project started , reducing drums SPL first!

some new measurements ,
Instead placing the sub woofer in one corner and the mic in the opposite corner I decided to measure in a different more realistic way.

measurement mic ( drums overhead )
sub woofer: (bass drum,)
speaker : (on top of the sub-woofer looking up toward the ceiling just like snare drums or tom tom projects the sound toward the ceiling...)

1) blue line, 20 lenrds bass traps, floor to ceiling in each vertical corner , 1 in each horizontal wall/ceiling corner

2) yellow line, same 20 lenrds set up + 8 pound 4" in front of the lenrds floor to ceiling in each vertical corner

3) red line, 8 pound 4" floor to ceiling in each vertical corner + 20 lenrds in all horizontal wall/ceiling corners ( NO lenrds behind the 8 pound !)

Some how...by ears I like more when 16 of the lenrds are behind the 8 pound panels in the 4 vertical corners...
I guess the measurement look better too....
As far of low end there is not improvement with more coverage when all the 20 lenrds are exposed toward the room ...
looks like it's better to use the lenrds to fill up the space behind the 8 pounds..
Any suggestion to improve further this 4 floor to ceiling corners?

pictures

Timo,

You must be the most persistant guy on the face of this earth.
I think this is somehow a very positive quality, but scary and tiring for the rest of the world.......
You're the kind of guy, if you want someting, one better gives it directly if only for ones own piece of mind (self protection). (joke).

Just a question.
Your first measurement picture you showed:

Did you fix your y-axis?
Are this 3 measurements which you somehow combined afterwards?

Measurementment tools often have the property, when you don't calibrate your input, with either a calibrator to set the absolute level right, or fix that input based on an arbitrary level, that every individual measurement will calibrate itself to an own auto-level.
That way you loose the relativety (relationship) between measurements.

I find it a bit strange that these differences in absorption don't translate better in the levels on the y-axis.

Have you taken this into account?
Just wanted to know, because it can influence other measurements you showed as well ( you know, .... the ones on these +/- 500 other pages related to your room).

I start really wondering, and it just occurs to me that you didn't trust your measurement tool either for the absolute level measurements of your drumkit therefore reaching for your radioshack SLM ???????

If this should be the case, and without overdoing it, search how to calibrate your measurement tool (help file or manual), set up a noise (it can be interesting to compare pink and white noise, but standard pink), measure it with your radioshack, then measure at exactly the same spot with your measurement tool, without altering any variables, and fix the calibration level to the level given by your radioshack.
To know how exactly to do this: read your help file.

And be aware that your Radioshack gives weighted results. To have it correct the weighting in your measurement tool and on your radioshack should be the same (FLAT, dB(A) or dB(C))
Since I don't know your measurement tool and have no idea if this all causes trouble for you, just use a pure 1000 Hz signal with a frequency/noise generator. In that case this setting doesn't matter because FLAT, dB(A) and dB(C) are all exactly the same at this frequency.

Eric_Desart wrote:Timo,
Just a question.
.

OK,
1) I did the measurements one after another all saved in the same file, they appear already combined in the "all measured" window that I use to save as image file.....( the program I use is the Room EQ wizard , free download here
http://www.hometheatershack.com/roomeq/

2) I never take only one measurement, I always take several measurements to make sure they are all similar, than I keep only one or two of them for each different absorption experiment and then I open them all together in the "all measured window" ...easy to compare and save as immage file.
In that window I can make the measurement look taller or wider and that effect all the measurements at the same time , that's what you mean for y-axis...?

3) yes I did my best to follow the program instructions and I calibrated with the radio shack sound meter at 75 dB , the program has it's own sound generator for calibration, I can calibrate using only sub-woofer or only speaker etc ..and the radio shack sound meter is in C weighting as suggested by the help file....

3) I said I don't trust the measurements because my room is not empty or a testing room, also everything change drastically depend where I place the sub or speaker or the measurement mic ! In fact now I decided to measure from the overhead drum mic position placing the source ( sub and speaker) where the real source ( drums ) will be...
for recording I never put the recording mic or the drums in the corner..I don't like how things sound there...
also sometime by mistake I stumble on the measurement mic stand!

P.S. anyways I'm still measuring.. only because I'm curious too see how the acoustic material I have works in the room.
The Lenrds tend to be very transparent .. it's like they are not there at all..
But I do ear the difference in fact my drums sound better when the lenrds are behind the 8 pounds....!

Timo,

Stupid question.

Since you did the calibration, which is good:
Can you add a measurement of your empty room?

Due to the small differences I have the feeling that you have more or less absorbtion already (which could be very possible with your construction).

It calls for time but it should be possible to reverse calculate the absorption you have in your room.

One of the main thing we experienced by comparing Chunks and panels in the corner is the explicit peak at around 100 Hz for the panel.
Hence while the chunks are more expensive in the comparison material and cost versus efficiency (per sabin you pay significant more than for the panels stradling the corner since you need 3 times as much material for 100 mm panels) the chuncks excel by giving a smoother curve.

The panel behaves peacky, a bit like a tuned absorber.
Bob Golds at the time made a related joke that, since that peak look rather fixed, we should design our rooms to match that peak.

Therefore one can assume that the panels with the LENRDs behind them will more behave as the chunks, and become nicer and smoother broadband.

But if you notice what you noticed now, is it really important to find the answers, which you can't find via the forum anyhow (the local stuff - your walls, tiles and so on, which you assume will go away by not speaking about them).

You know how you get a pleasing result: The panels with the LENRDs behind them. You have these so do it that way:
You need more: apply the same on your ceiling/wall edges.
You don't have LENRDs enough. It doesn't matter fill those gaps with cheaper low density wool.

It's even possible that your 8 pound will enhance this peacky membrane like behavior.

Hence use what you can conclude already, without wondering about the why, and proceed.

The LENRDs will not go as low as the larger panels or chunks, not for the traditional argument you hear anywhere, but mainly because they are smaller and can't go that low in frequency. That's a given.

And start adding a cloud and wall absorbers as needed. And paint these tiles again with thick paint if you're worried about the highs.
And think about that plastic foil.


And FEEL and LISTEN. Your measurements don't look so bad you know.

Timo

Here you find the comparison between just panels, the chuncks and the MegaLENRDs (Auralex)
http://forum.studiotips.com/viewtopic.php?t=536

The PANELS and CHUNKS are OC 703 (but can be other material as well)
Notice the dip with the panels. I'm not going into details what this is but it is related with the fact that you have wavelength related absorption combined with some membrane effect, and these 2 curves from these 2 phenomena don't overlap enough. While the chuncks smooth this behavior in a better manner.

The CHUNKS and the MegaLENRDs have EXACT the same section.
Hence and you can see that the MegaLENRDs beat the CHUNKS.

The problem however is that the MegaLENDRs are expensive things (are really large compared to the LENRDs, but equal to the CHUNKS).
But it also shows that foam in this case is NOT worse than OC 703 in this application, even somewhat better.

Hence the general comment used anywhere, foam (in itself) is no good for the lows is plain wrong.
One uses foam for anechoic rooms as well, where low frequent behavior is very important versus measures.

NEW MEASUREMENTS BEGIN HERE

Eric_Desart wrote:Timo,
Can you add a measurement of your empty room?

I just completed all the new measurements, I re calibrated, removed some stuff from the room, studied the help file again etc... everything look good to me ...

The sub woofer, speaker and mic, they are at about at 38% of the room in the drummer sweet spot area... I prefer to measure the real things... instead measuring the corner...

The grey line is the empty room, all the measurements include the grey line for reference...

*grey line, empty room (not really empty but without acoustic treatment )

*olive line, 16 Lenrds, 4 in each vertical corner floor to ceiling

*violet line, 8 pound 4" mineral wool floor to ceiling in all 4 vertical corners

* cyan line, combination 8 pounds with Lenrds behind, floor to ceiling in all 4 vertical corner

* blue line, 8 pound 4" floor to ceiling in all 4 vertical corners plus 16 Lenrds in the horizontal ceiling wall corners

P.S. This corner stuff is unpredictable! It just turn things around, Also, why all this if just for the 100Hz? ...
That simple 4 inc foam hearing test room sound great.

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P.S. This corner stuff is unpredictable! It just turn things around, Also, why all this if just for the 100Hz? ...
That simple 4 inc foam hearing test room sound great.

Timo,

just 100Hz?

from your graphs, 68, 90, 110Hz are all smoothed out! Don't forget you are using a 10dB per unit vertical scale. Use a higher definition and it will be more obvious.

If you are fond of drums, double bass and piano, this area is so vital in the quality of the sound. Its where it's all going to "boom" together in an despicable mess, or where some notes are going to "hide" (if there are problems)

I thought the idea of your new treatment objective, per Eric's advice, was to bring down the SPL of your room.

My guess is you would be doing that making sure that the frequency response remains reasonable. If it improves (as is the case) then better!!

I'll take a look at the dimensions of your room for the total surface area (I am a straight metric guy, inches and feet mess me up )

About that ear testing room, there is much more to it than just the 4 inches foam.

Cheers,
Jean

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