Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 431 - AVS Forum
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post #12901 of 12912 Old Yesterday, 04:08 AM
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Originally Posted by Audionut11 View Post
I'm not jumping to anything markus. I've sparked discussion.
That's good but I've been through this discussion multiple times so please forgive me if I don't sound as enthusiastic as you might expect. Rest assured that I know all those references down to the single papers.

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"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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post #12902 of 12912 Old Yesterday, 04:24 AM
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That's good. Because being over enthusiastic leads to mistakes.

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post #12903 of 12912 Old Today, 08:09 AM
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I have a new sub so have been taking some measurements recently. I noticed something interesting that had never occurred to me before, not sure if this is stating the obvious to everyone else but thought I'd comment anyway

This is the raw response of my sub in my completely untreated room, I have grown to know and love that 40Hz spike



the 60Hz null goes if you move the mic a few cm so ignore that for now

I was just doing some quick compression testing so 1 PEQ filter & a few sweeps later produces



I stopped at this point as my door frame was creaking! distortion for the top sweep



Notice the substantial elevation in distortion around 20Hz in the 2nd harmonic and ~13.3Hz in the 3rd harmonic & note how it falls either side of that frequency. If the sub was being overdriven (I know it's not, the drivers are not even working that hard) then you'd normally see distortion continue to escalate as frequency drops. My thinking is this is an artefact of using EQ to tame a mode, i.e. the EQ targets the fundamental frequency only but the mode still exists and still serves to amplify the harmonic distortion from lower frequencies. Hence you see this "artificial" (but still real) boost in distortion. This sounds plausible to me, any thoughts welcome though.

This made me think about building a tuned bass trap to tackle the 40Hz mode instead, not sure whether it will be practical in my room but worth investigating anyway. Does anyone have any experience of building/using such a thing?
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post #12904 of 12912 Old Today, 10:50 AM
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3ll3d00d,

I am not sure how meaningful measuring the sub by itself is. When listening, your hearing everything going at once. Are there other subs or just the one?

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post #12905 of 12912 Old Today, 12:25 PM
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3ll3d00d,

I am not sure how meaningful measuring the sub by itself is. When listening, your hearing everything going at once. Are there other subs or just the one?
It is a single sub that has 2 18" drivers. I was really looking for clean output capability here BTW.
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post #12906 of 12912 Old Today, 12:29 PM
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It is a single sub that has 2 18" drivers. I was really looking for clean output capability here BTW.
(2) subs with (1) 18" in each would have offered more versatility.

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post #12907 of 12912 Old Today, 12:36 PM
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For sure however the positions I have in my room, for a 2nd sub, provide no appreciable benefit with respect to smoothness of response.
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post #12908 of 12912 Old Today, 01:17 PM
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Quote:
Originally Posted by 3ll3d00d View Post
My thinking is this is an artefact of using EQ to tame a mode, i.e. the EQ targets the fundamental frequency only but the mode still exists and still serves to amplify the harmonic distortion from lower frequencies.
At those frequencies (and especially at that volume! ), the Rockwell figurines in my family room start to dance around. I'm assuming that that causes most of the distortion I get on my graphs.
You say your room is "untreated"; is there "stuff" around that could be vibrating/rattling/moving?

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Did you really need to quote that entire post in your reply?
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post #12909 of 12912 Old Today, 01:50 PM
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Quote:
Originally Posted by 3ll3d00d View Post
This made me think about building a tuned bass trap to tackle the 40Hz mode instead, not sure whether it will be practical in my room but worth investigating anyway. Does anyone have any experience of building/using such a thing?
I did an evaluation of GIK Acoustics Scopus tuned traps a while back. the report is here:


Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs
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post #12910 of 12912 Old Today, 03:45 PM
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ok guys I bought new UMM mic with calibration file of 90 degrees. I was following the guide to copy the sensitivity factor. The first line that needs to be copied, is it the whole line with quotes, just the number, .... ??? Assuming the line is
"Sens Factor =-12.444dB, SERNO: 123456"

exactly what part needs to by copied over (please include double quotes as well if that needs to be copied)?
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post #12911 of 12912 Old Today, 04:38 PM
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Originally Posted by SherazNJ View Post
ok guys I bought new UMM mic with calibration file of 90 degrees. I was following the guide to copy the sensitivity factor. The first line that needs to be copied, is it the whole line with quotes, just the number, .... ??? Assuming the line is
"Sens Factor =-12.444dB, SERNO: 123456"

exactly what part needs to by copied over (please include double quotes as well if that needs to be copied)?
The whole line. Page 53 of the guide actually has an example.
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post #12912 of 12912 Old Today, 10:40 PM
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The whole line. Page 53 of the guide actually has an example.
Thx. Yes the guide has it but it was confusing. I shows a highlighted part that doesn't highlight whole line. Plus it says
"Copy this sensitivity factor".

Therefore I got confused since the line has two parts Sens Factor and Sensor:----

But now its clear. Thx a bunch.
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