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Help, ETF doesn't show difference measured with CD+RS meter!


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#1 of 6 OFFLINE   Dennis B

Dennis B

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Posted July 26 2002 - 06:18 AM

I finished my first TubeTrap-like 16"x4' bass trap last weekend and have been testing it during this week. I started off with a listening test and I needed only 5 minutes to hear a remarkable improvement in sound.

So I moved on to the scientific testing phase Posted Image, started with my self-burnt CD with tones every other Hz and measured the freq response with a RS SPL meter from 20 to 200 Hz. BTW, I modified my RS meter so that it reads flat in the bass frequencies.

I used Excel to plot it and there it was, a graph showing significant improvement around some of the room modes.

So far, so good. Then I started measuring with ETF5, and strangely no difference came up at all. So I took the trap out of the room, measured the room again, then brought it back in, another measurement and... nothing!

So now I'm thinking the trap "broke" or I didn't take valid measurements before, so I repeated the procedure with the CD and the RS meter, and I got exactly the same curve as before, clearly showing the differences.

Could someone please help me understand why ETF is not showing what's going on, even being it so clear that I can hear it?

Thanks!

#2 of 6 OFFLINE   Pete Mazz

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Posted July 26 2002 - 06:56 AM

What test did you run in ETF and what gate timing did you use.

Pete

#3 of 6 OFFLINE   Dennis B

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Posted July 26 2002 - 07:01 AM

I ran the LF test and used the default gating (10ms, I believe). Thx.

#4 of 6 OFFLINE   Rick Guynn

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Posted July 26 2002 - 08:28 AM

I think you would probably need arounn 60 ms gating if you are looking at the lower octave.

Which graph are you looking at? If it is the low frequency response, you may be only seeing the direct sound. Try looking at either the waterfall or using the time slices in the low-freq plot to see if the resonances you had die out quicker now.

RG

#5 of 6 OFFLINE   Dennis B

Dennis B

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Posted July 26 2002 - 09:31 AM

Rick,

Actually I was already using 100 ms gating, sorry.
When looking at the waterfall or using the time slices, I can see the differences now.

Thanks! Posted Image

#6 of 6 OFFLINE   Pete Mazz

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Posted July 26 2002 - 02:05 PM

It might show up with a 200 ms gate time.

Pete