DIY flush mount speakers

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Eric Best
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Re: DIY flush mount speakers

Post by Eric Best »

I had been measuring with the output from my laptop. I just connected my soundcard and did some more measurements. Let's just say my measurement mic does not have problems above 10k.

Here is the new nearfield measurement of the speaker.
single speaker from 20inches.png
Here is measurements for each speaker individually from the mix position.
left and right from the mix position.png
Here is a mono test signal from both speakers from the mix position.
both speakers from mix position.png
I think when I start doing REW stuff I'm going to find issues at 80hz.
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Re: DIY flush mount speakers

Post by Eric Best »

I wonder how much not having a bezel on the right speaker effects the measurements.
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Re: DIY flush mount speakers

Post by Soundman2020 »

Your graphs at the mix position look pretty much they way I'd expect from a typical room. What treatment do you have in there right now?

I'd love to see the measurements taken in REW, so I can see all the other things that are happening, not just the frequency response. That's important, of course, but only a small part of the picture.
I wonder how much not having a bezel on the right speaker effects the measurements.
I would imagine that it is having a quiet significant effect, especially in the low end.


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Re: DIY flush mount speakers

Post by Eric Best »

Sorry this took so long. The picture below show all of the treatment that I have for the room.

The wedges on the sides are a hard surface facing the mix position but are filled with rockwool which is open facing the speaker. I have two similar wedges on the ceiling angled to reflect to the back of the room, but with the front open and filled with rockwool. The back wall has 1/2" drywall with 4" of rockwool and hangers as shown.
control room layout.jpg
I made an error on the dimensions, it should be 17'6" width 11"6". In front of the mix position, the height is 7'6" behind it is 6'8".

I am planning on doing measurements tonight. Should I post those here, or go back to my original studio build thread?

Thanks again for all of your help!
Last edited by Eric Best on Fri May 05, 2017 1:41 pm, edited 1 time in total.
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Re: DIY flush mount speakers

Post by Soundman2020 »

I am planning on doing measurements tonight. Should I post those here, or go back to my original studio build thread?
I would suggest posting them here, and putting a link at the end of your build thread that leads here. Or do it the other way around: Post them on the other thread, and put a link here, at the end of this one, going back to your build thread. If you want, I can lock this thread after you post the link to the other one, so nobody else can mess it up with additional comments: they would have to go to the other one to comment.

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Re: DIY flush mount speakers

Post by Eric Best »

With some help from Glymur (Curt), we measured the room.

Here are links to the mdat files

Baseline from the mix position https://www.dropbox.com/s/h4f7c8t2nygyu ... .mdat?dl=0

Measurements moving from the front of the room to the mix position https://www.dropbox.com/s/8ih6ozzl3oavt ... .mdat?dl=0

The mix position to the back https://www.dropbox.com/s/ji0uw287xv8z7 ... .mdat?dl=0

Here is SPL from the mix position.
SPL from mix position.JPG
The waterfall
waterfall from mix position.jpg
And the rt60
rt60.jpg
Obviously we have an issue at 80hz :)
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Re: DIY flush mount speakers

Post by Eric Best »

A couple of pictures.
me with measurement mic.JPG
measurement front of room.JPG
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Re: DIY flush mount speakers

Post by Soundman2020 »

I downloaded your files, but there's something very strange going on there: I suspect the data is not valid. The SPL curves look fine and normal, but the rest is way off.

Also, your RT60 graph does not match what I'm seeing! This is what I get:
eric-best-faulty-rt60-graph.jpg
Which is pretty much impossible in any room! I'd find it REALLY hard to accept that your decay times are essentially zero for everything below 100 Hz! :shock:

Your waterfalls look weird too: Even the one you posted is mighty strange: It clearly shows decay times of around 100 ms or less, yet the RT60 data shows over 300 ms, and the actual calculated RT60 is also around 300-something... so there's an issue here for sure! I thought it might be data corruption in the file download, so I downloaded again, but it's the same.

Are you SURE you calibrated correctly, using your sound level meter? Did you really see 80 dBC on your meter while running those tests? It looks a lot like you calibrated incorrectly:
Eric-Best-faulty-WF-FS-high-noise.jpg
The white horizontal cursor line is a rough estimate of the background noise level in your room, as seen by REW, and I'm pretty sure it is not 52 dBC in real life! You'd be VERY disappointment if your isolation was that bad.

My guess is that something went wrong with your calibration procedure, and the tests were done at a level that is way too low, but that REW still identifies as 86 dBC.

Please check your calibration procedure...

What hand-held sound level meter are you using here? Is the meter itself calibrated? Good batteries? In good condition? Just some thoughts...

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Re: DIY flush mount speakers

Post by Eric Best »

Which measurement did you take the rt60 from. I cant find one that matches.

The spl meter we used to calibrate was the one with the Omnimic system.
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Re: DIY flush mount speakers

Post by Soundman2020 »

Which measurement did you take the rt60 from. I cant find one that matches.
Mix position, baselline, both left and right speakers.

The other two (Left only and right only) are equally invalid:
eric-best-faulty-rt60-L-graph.jpg
eric-best-faulty-rt60-R-graph.jpg
I uploaded the same file to one of my servers, so you can download it and compare to the original. It might be data corruption, but I don't think so, as the waterfalls you posted look equally invalid. You can find it here: http://spartanew.digistar.cl/SayersForu ... eline.mdat
The spl meter we used to calibrate was the one with the Omnimic system.
As far as I know, Dayton does not manufacturer hand-held sound level meters. They only make mics and test software. I'd suggest that you get a real SPL meter, such as an Extech or Galaxy, or some such, and calibrate again. Even an app for your cellphone, such as AudioTools, would at least give you a semi-reasonable estimate of the real SPL levels in your room. Not accurate, of course, but good enough to do a basic check. Try that now, to see what you get. I suspect that you are not really getting the levels that REW thinks you are getting.

Here's a spectrogram from your right speaker:
eric-best-faulty-SP-R-graph.jpg
That's just meaningless mush. Here's what a typical spectrogram looks like for a partially treated room:
typical-SP-2.jpg
Here's what the low-end waterfall for that same room looks like:
typica.WF.17..500-2.jpg

And here's the full spectrum waterfall for it:
typica.WF.20..20k.jpg
And here's the RT60 graph (same room):
typica.RT.20..20k.jpg
All of the above are similar to what I'd expect to see in your data. Not the way it looks in your graphs. I chose that MDAT file at random from among the large number I have, but that's typical of most of them. Your data is way, way noisy.

Before doing anything else, you need to figure out what's wrong here, and fix it! You can't make room treatment and tuning decisions based on flaky, suspect data.

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Re: DIY flush mount speakers

Post by Eric Best »

I downloaded what you have for my data from you link and for the rt60, this is what I got.
screenshot rt60 mix position.JPG
This may not be good, but it is very different from what you are getting.

I included the whole screen so we can compare and make sure we are looking at the same files.
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Re: DIY flush mount speakers

Post by Eric Best »

I will re-calibrate and try again tomorrow.

I know this is frustrating, but thank you for all the help.
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Re: DIY flush mount speakers

Post by Soundman2020 »

This may not be good, but it is very different from what you are getting.
You are using one-octave smoothing. Switch to 1/3 octave.


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Re: DIY flush mount speakers

Post by glymur »

Today I learn the value of fresh batteries. Thanks for the info Stuart, much appreciated.
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Re: DIY flush mount speakers

Post by Eric Best »

Here are new measurements.

https://www.dropbox.com/s/a8rie5wtsukp5 ... .mdat?dl=0

https://www.dropbox.com/s/d48on2o4wq7tc ... .mdat?dl=0

https://www.dropbox.com/s/dqiorkt96zm0e ... .mdat?dl=0
SPL from mix position 3.jpg
waterfall from mix position 3.jpg
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spectrogram 3.jpg
rt60 3.jpg
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