My graphs - advice appreciated - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 28 Old 08-31-08, 11:04 AM
union1411
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Re: My graphs - advice appreciated

graph looks prettier when i cross to 120 hz. less sharp dips in the 60-90hz range. i wonder if that's because i'm using the mbm-12. Dynamic EQ is on in this graph.

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post #22 of 28 Old 08-31-08, 11:36 AM
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Re: My graphs - advice appreciated

should I turn off Audyssey entirely when measuring? is that the best way to reveal what my room's problems are? well, since i have Audyssey in my receiver, then i would think i should turn it on because i'm using these graphs to see if i need extra EQ (like BFD or 8033 or whatever) and/or treatments. correct?


this is my graph with Audyssey on (120 hz xo; using mains and MBM-12; no Dynamic EQ)




and this is with all Audyssey off


post #23 of 28 Old 08-31-08, 11:53 AM
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Re: My graphs - advice appreciated

Quote:
Wayne A. Pflughaupt wrote: View Post
It's best to keep your output levels 40-50 dB above the noise floor, and the graph's floor should be a good reflection of the room's ambient noise floor. A 45 dB lower graph limit is fine for frequency response readings, but kind of high for a waterfall, since most domestic rooms have ambient levels at least 10-15sd dB lower.

Thanks but I'm curious about the fact that my SPL reading on REW is around 57 db when there is no signal through my receiver - like right now while everything is idle. So, isn't 57db my noise floor? I live in NYC


this is my waterfall with no Audyssey on. Mains and MBM-12 are on. apologies if graph isn't set correctly. these waterfalls are finicky.

35db floor you recommended




i have no idea if this means traps will make a significant difference or not.


this is the 45db floor


Last edited by union1411; 08-31-08 at 12:05 PM.
 
post #24 of 28 Old 08-31-08, 02:11 PM
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Re: My graphs - advice appreciated


Quote:
Thanks but I'm curious about the fact that my SPL reading on REW is around 57 db when there is no signal through my receiver - like right now while everything is idle. So, isn't 57db my noise floor? I live in NYC
Keep in mind that the meter in C weighting has fairly flat response down to about 40 Hz. Also keep in mind that it can only register one figure, and that will be the frequency that is the loudest.

Take a look at your graph, especially the highlighted 50+ Hz area:


My graphs - advice appreciated-low-frequency-background-noise.jpg


Notice that the 50+ Hz signal is not decaying, like the rest of the signal is. I'll bet if you re-frame the waterfall with a 600 or 1000 ms window, you'll see that it doesn't decay there, either. In other words, its a steady-state signal that's not coming from your HT system (notice the way it "emerges" from between two peaks).

What it is is background noise from some other source - which in NYC could be just about anything. That's what your SPL meter is registering - notice it's at or above the 57 dB figure you registered...

Quote:
i have no idea if this means traps will make a significant difference or not.
If you use enough of them, bass traps will deliver a faster rate of decay, as these graphs show:






That said, your waterfall doesn't look bad, with everything above 50 Hz pretty much fully decay'd by 300 ms. That's nearly twice as fast as the top (no bass traps) picture above.

Regards,
Wayne



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post #25 of 28 Old 08-31-08, 02:42 PM
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Re: My graphs - advice appreciated

thanks for the reply

also, by staring at the graph for a while, i think i understand it more now. in my first graph at 300ms, above 100 hz, basically nothing is above 50 decibels. so that seems pretty good to me. bass traps are pricey - and i don't want to ever do DIY again after i buily my screen - so i think i'll hold off on them for a little while. i'm probably better off spending the $$ upgrading my svs than buying bass traps at the moment.
post #26 of 28 Old 09-01-08, 03:19 AM
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Re: My graphs - advice appreciated

Quote:
union1411 wrote: View Post
did some more measurements

as i suspected from watching movies, Dynamic Eq (not to be confused with Dynamic Volume) via Audssey is boosting the bass. and i was careful to check the SPL level when switching back forth from dynamic so the sweep would still be at 80db. left the mains on
You will not be able to get a representative measurement from any "dynamic" features using a swept sine, the nature of the signal is very different from anything a dynamic feature might be configured to process, different sweep lengths and end frequencies (and hence different rates of frequency change during the sweep) could give very different results. A better idea might be to use the RTA graph with the Periodic Pink Noise test signal, that would give you a view of the dynamic response with a signal that has content across the band.
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post #27 of 28 Old 09-01-08, 07:00 PM
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Re: My graphs - advice appreciated

Thanks. Does your post apply to regular Audyssey settings as well? In other words, running REW and leaving Audyssey on but turning Dynamic EQ off.
post #28 of 28 Old 09-01-08, 07:24 PM
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Re: My graphs - advice appreciated

Quote:
Does your post apply to regular Audyssey settings as well?
No, the Audyssey filters will be similar to a BFD EQ filter. It isn't dependant on the sweep.

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