Could you take a look at these measurents for acoustics please - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 9 Old 04-12-15, 04:47 PM Thread Starter
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Could you take a look at these measurents for acoustics please

These are for a small studio control room so I want it quite dry with a low decay time. I've been experimenting with rew and have lots of gik panels and have been using the realtime analyser (with white noise as it seemed to represent a more similar result to the sine sweep than pink) for the last few weeks. I include the mdats. I did not have an SPL meter this week, but they are quite close to 75 db. The measurement mic is a superlux ecm 999 which is suposed to be very flat and quite reliable and consistent build - I dont think ill go as far as to get it calibrated just yet. Speakers are PMC tb2s+ with rotel amp. There's so much more to learn and thanks for the fantastic software. Any tips and insights appreciated (the phase graphs were particularly ineffable to me) :












Last edited by Gusss; 04-14-15 at 06:30 PM.
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post #2 of 9 Old 04-13-15, 04:44 PM
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Re: Could you take a look at these measurents please

You can ignore the phase plot.

For the RTA make sure you have the mode on one of the RTA settings (e.g. 1/48 or 1/24), not on Spectrum, then you will find the result with Pink noise will look correct - use the generator's Pink PN signal with these RTA settings:



The measurements have very good signal to noise, all working well there.

As for the results, certainly seems to fit the desire for a 'dry' room. Both channels have some ringing around 52 Hz, that might be improved by moving your listening position or the speakers back or forward a little - try moving the mic about with the Pink PN playing to see. Both channels also have a significant reflection at about 4 ms, which corresponds to a path difference of about 4.5 feet - might be the floor, ceiling or desk I guess, could be worth tracking down what that is.

For more informed views on treatments and their use worth trying the folk in the Home Audio Acoustics forum.
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post #3 of 9 Old 04-13-15, 05:41 PM Thread Starter
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Re: Could you take a look at these measurents please

Quote:
JohnM wrote: View Post
You can ignore the phase plot.

For the RTA make sure you have the mode on one of the RTA settings (e.g. 1/48 or 1/24), not on Spectrum, then you will find the result with Pink noise will look correct - use the generator's Pink PN signal with these RTA settings:



The measurements have very good signal to noise, all working well there.

As for the results, certainly seems to fit the desire for a 'dry' room. Both channels have some ringing around 52 Hz, that might be improved by moving your listening position or the speakers back or forward a little - try moving the mic about with the Pink PN playing to see. Both channels also have a significant reflection at about 4 ms, which corresponds to a path difference of about 4.5 feet - might be the floor, ceiling or desk I guess, could be worth tracking down what that is.

For more informed views on treatments and their use worth trying the folk in the Home Audio Acoustics forum.
Thanks for your feedback. I've spent quite a lot of time (weeks in fact) taking impulse responses and using the RTA making tiny adjustment to speaker positioning and listening position - I think thats about the best spot for the speakers TBH as moving them from there causes large problems elsewhere - listening position is limited in where I can be but I will try with the pink noise moving the mic. I was wondering if that 52 hz might be the low frequency buzz my computer puts out ? It could also be the speakers - PMC seem to have a characteristic bump in low frequency on a few models that Ive seen measured. In 4 ms sound travels 1.36 metres. So I need to look for something that makes the sound travel an extra 1.36 metres - thats going to be something pretty close to the speaker right ? I have no table or desk in front of the speakers - there is a high ceiling so I think that would be further than 1.6 metres so it could be the floor but then the distance from the speakewr to the floor and to the measurement mic is more than 1.36 metres. I wonder.... It could be the side wall - that has got 1st reflection panels but maybe they need to be thicker. Is there any way of telling which frequencies are being reflected? Also could you move this thread to the hoime acoustics forum ? I notice there's a lot more response there to this kind of thing. Thanks again.

Last edited by Gusss; 04-13-15 at 07:18 PM.
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post #4 of 9 Old 04-14-15, 02:27 PM
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Re: Could you take a look at these measurents for acoustics please

Floor is possible, depends how close the sepakers are to the mic. Remember you can visualise the sound as travelling like a ray that gets reflected at the floor (or whatever surface it hits) so it is travelling along diagonals, the extra distance it travels compared to the direct path is actually much less than the combined distance from the speaker to the floor and from the floor to the mic. For example, suppose the mic is 5m from the speaker and both speaker and mic are 1m from the floor. The direct path is 5m, the path via the floor is 2*sqrt(2.5*2.5+1*1) = 5.39m, only an extra 39 cm. If the mic was only 2m from the speaker the distance via the floor is 2.83m, so still only 83 cm more than direct.
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post #5 of 9 Old 04-14-15, 04:52 PM
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Re: Could you take a look at these measurents for acoustics please

Are you doing anything in your room aside from speaker positioning to raise the signal to noise ratio?
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post #6 of 9 Old 04-14-15, 05:30 PM Thread Starter
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Re: Could you take a look at these measurents for acoustics please

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Kiddcabbage wrote: View Post
Are you doing anything in your room aside from speaker positioning to raise the signal to noise ratio?
Hi,
If I understand your question correctly speaker positioning won't really change the signal to noise ratio. What would affect that would be getting an amp without a fan and a quieter computer - however I am not recording in the control room so its not really an issue I just tune that out and it doesn't effect mixing at all even when quiet . Industry standard for a control room is 20db ambient noise - Ive got that for most of the spectrum except said computer noise - at some point I will get round to changing the fans and getting an amp with a heat sink . In terms of preamps,converters etc all my equipment is professional industry standard equipment such as RME and has negligible noise.
In terms of room treatment I have many GIK and home made traps which I spent a long time positioning whilst staring at the real time analyzer. Incidentally due to all the white noise and sine sweeps I am now quite deaf so getting the room right is completely pointless

Last edited by Gusss; 04-14-15 at 06:34 PM.
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post #7 of 9 Old 04-14-15, 05:38 PM Thread Starter
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Re: Could you take a look at these measurents for acoustics please

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JohnM wrote: View Post
Floor is possible, depends how close the sepakers are to the mic. Remember you can visualise the sound as travelling like a ray that gets reflected at the floor (or whatever surface it hits) so it is travelling along diagonals, the extra distance it travels compared to the direct path is actually much less than the combined distance from the speaker to the floor and from the floor to the mic. For example, suppose the mic is 5m from the speaker and both speaker and mic are 1m from the floor. The direct path is 5m, the path via the floor is 2*sqrt(2.5*2.5+1*1) = 5.39m, only an extra 39 cm. If the mic was only 2m from the speaker the distance via the floor is 2.83m, so still only 83 cm more than direct.
Yes you are quite right. I wasn't thinking straight. So 4 ms = 1.36 meters but thats on top of the direct distance. I think that means 3 meters + 1.36 = 4.36 - that could be the floor. Hmm an acoustic panel on the floor ? Is that a thing ?
Also - on the phase plot - I know Im being insistent - does the straight line mean the end of 360 degrees ? Comon reveal the secrets of the phase plot John ..... Im pretty sure something that was badly phase aligned would show up in that right ? Like if you had one of the speakers with the cables the wrong way round ?

Last edited by Gusss; 04-14-15 at 06:33 PM.
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post #8 of 9 Old 04-15-15, 01:57 PM
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Re: Could you take a look at these measurents for acoustics please

I knew a guy who ripped out a big square of his flooring and put a bunch of homasote underneath him (with some flooring on top of it). Not really the cheapest or least intrusive solution though. Other people have made raised floors in their control rooms so they can isolate the floor from the room and treat it as well.
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post #9 of 9 Old 04-16-15, 05:32 AM Thread Starter
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Re: Could you take a look at these measurents for acoustics please

Quote:
Kiddcabbage wrote: View Post
I knew a guy who ripped out a big square of his flooring and put a bunch of homasote underneath him (with some flooring on top of it). Not really the cheapest or least intrusive solution though. Other people have made raised floors in their control rooms so they can isolate the floor from the room and treat it as well.
I think it is indeed the floor - amazing what you can tell just by looking at a graph ! The reason - whilst using the RTA I noticed there was not enough top end so I angled the speakers down - this equalised the frequency response a lot and solved a 10 db dip in the highs and high mids but must be causing the floor reflection (Ill test when I get back) . I could angle the speaker snormally but then the dip would return so maybe some floor panels. My control room is begining to look like an Escher painting.....
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