RE: Looks Very Interesting

Posted by emailtim (A) on September 22, 2023 at 10:36:06

In Reply to: RE: Looks Very Interesting posted by Barry on September 22, 2023 at 09:26:35:

The Vertical Spectrogram is basically a topological chart (mountain ridges and valleys) that you can adjust for depth contour detail.

It is very helpful because it shows the frequencies constituting the reflections where the bottom chart does not. Both are useful, but for different details.

The bottom chart shows you the exact dB level of each peak, but not what frequencies are causing it. This one is only showing the 4ms peak, not the 9ms peak which is off the right side of the chart. I started testing with 1 poly, so could only test 1 reflection at a time, not all 4 reflections.

The Vertical Spectrogram also details time alignment of your multiple drivers and subs (black dashed line). People who align their subs by other means would be surprised to view this plot after thinking they dialed in their subs. It is well worth getting familiar with.

I would have assumed the same as well, but [1-7]kHz includes the most sensitive range in human hearing so it is a critical region. Ideally, your room reflections should be down 20dB within 20ms (4 and 9ms are well within that range). The 2nd plot easily shows this range (amplitude and time) as well as which peak time is the worst offender (1st to treat).

The closer the reflections are to the direct sound, the more they smear the clarity. In my scenario, it also destabilized the soundstage by mixing the channels.

I blocked various sides of the microphone (with a tripod and heavy folded quilt), remeasured and compared plots to identify where the reflections were coming from using the 4 and 9 ms as hints at which reflections to try identifying first.

After the reflection sources were identified as cross and cross-side, I realized as I twisted my head, the leading ear would cross the tangential of one channel's reflection and then the other channel (another variant of "head in vice", but caused by the room, not the speakers).

On tangent would dictate the soundstage. Switching between the left and right channel with the leading ear explained the sound stage shift. The tangential effect could further be exaggerated by cupping the leading ear (helpful tool) making it more directional.

According to some studio designers and anechoic measuring engineers, polys have a natural sound and specify QRDs for the rear because of the phase scattering. QRDs can also make time aligning speakers harder because the measurements show altered phase from the QRDs.

John/REW has a beta thread with weekly releases of the newest REW development. I recommend grabbing the latest development version which has a lot of nice new features/bug fixes and found it to be quite stable.

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2022/03/30 Historical Records CENSORED

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Follow Ups Full Thread

Topic - Polys revisited - emailtim 19:41:06 09/19/23 (24)

One wonders if the sound have more air if the panels were removed. Nt - geoffkait 04:14:19 09/27/23 (4)

RE: One wonders if the sound have more air if the panels were removed. Nt - emailtim 08:05:12 09/28/23 (3)

RE: One wonders if the sound have more air if the panels were removed. Nt - geoffkait 09:51:26 09/28/23 (2)

Didn't you just say you used an SPL to measure room nodes ? - emailtim 14:16:23 09/28/23 (1)

Yes, I use an SPL meter to map out the room. - geoffkait 10:07:58 10/05/23 (0)

Plants are not good for the sound. - geoffkait 04:28:01 09/23/23 (11)

RE: Plants are not good for the sound. - Scholl 05:20:21 09/24/23 (6)

RE: Plants are not good for the sound. - geoffkait 07:54:13 09/24/23 (5)

RE: Plants are not good for the sound. - Tre' 17:55:43 09/26/23 (4)

RE: Plants are not good for the sound. - emailtim 08:21:11 09/28/23 (2)

must be he has a magic nasty plant too - Story 08:42:23 09/28/23 (1)

RE: must be he has a magic nasty plant too - emailtim 09:20:10 09/28/23 (0)

The only thing to fear is fear itself. - geoffkait 03:01:44 09/27/23 (0)

Those are not plants - emailtim 11:16:44 09/23/23 (3)

The Carpenters and the Beatles? Yup, that's Japan. Nt - geoffkait 12:27:17 09/23/23 (2)

Do your really think that this is the best place to air your prejudices? Nt - Tre' 17:37:15 09/23/23 (1)

You're right - geoffkait 03:15:45 09/27/23 (0)

Looks Very Interesting - Barry 13:12:35 09/21/23 (6)

RE: Looks Very Interesting - emailtim 15:25:31 09/21/23 (5)

RE: Looks Very Interesting - Barry 09:26:35 09/22/23 (4)

Mounting orientation - emailtim 11:24:00 09/22/23 (0)

RE: Looks Very Interesting - emailtim 10:36:06 09/22/23 (2)

Thanks so much! - Barry 15:26:54 09/22/23 (1)

REW Early Bird Release - emailtim 15:38:11 09/22/23 (0)

Follow Ups

RE: Looks Very Interesting - emailtim 10:36:06 09/22/23 (2)

Thanks so much! - Barry 15:26:54 09/22/23 (1)

REW Early Bird Release - emailtim 15:38:11 09/22/23 (0)

RE: Looks Very Interesting

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