First up graphs, advice appreciated - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 22 Old 01-30-09, 08:13 AM Thread Starter
 
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First up graphs, advice appreciated

First measurement. Room has some bass traps and touches of other treatment. Thoughts? Im just trying to learn to interpret these things. Obviously a big problem between about 60Hz and 260Hz.

Two channel studio monitoring, no sub. Only gone up to 3K due to RS meter. Only the left channel is measured here for the moment
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post #2 of 22 Old 01-30-09, 08:59 AM
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Re: first up graphs, advice appreciated

What are your speakers and sub? Are you planning on using an EQ for the sub?

Room effects and a gradual roll-off of the speakers can contribute to the low output in the 100 to 200Hz region. Then comes the conundrum. If you want SPL at the low end, you have to jack up the sub, but then that peak at 60Hz will be noticeable and boomy.

If you do choose to EQ, you can tame that peak and raise the level of the sub for good results.

I have a similar problem in my setup: my mains roll off a tad above 80 Hz leading to low output in the high-bass region.
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post #3 of 22 Old 01-30-09, 11:52 AM
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Re: first up graphs, advice appreciated

Well, since this a studio with two channel monitoring, with no sub, then your effect on the monitors is limited to positioning of the speakers and treatment. Usually the listening position in front of the mixer board is fairly well fixed, so I suppose you have to start playing with the monitors to get the smoothest response, or get them near-field enough to help remove the rooms influence. Hopefully you're able to add treatment behind and overhead.

You'll want to change the scale of your waterfall to 15Hz to 100Hz (max 200Hz) and change to LOG mode so you can see the waterfall the same way that you hear (logarithmically) and to help to expand the lower octaves where you want to see more of what's happening.

For your response plot use horizontal scale of 20Hz-3000Hz.

EQ is usually a no-no for mixing, so that's out, but you should be able to get it a lot better than it is now...

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post #4 of 22 Old 01-30-09, 05:22 PM
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Re: first up graphs, advice appreciated

Sorry, missed that about the sub and studio (no coffee this morning).

Bruce's suggestions are good:
Nearfield -- use the IR windowing feature in REW to eliminate reflections from the measurement
Treatment -- help smooth out the response, especially in the low end.
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post #5 of 22 Old 01-30-09, 05:50 PM Thread Starter
 
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Re: first up graphs, advice appreciated

thanks guys, Ill experiment and see what I can come up with.
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post #6 of 22 Old 01-30-09, 06:58 PM Thread Starter
 
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Re: first up graphs, advice appreciated

ANthony,

What exactly is IR windowing. Im looking as we speak but havent found it yet... Ok I have found it, just investigating what it does and how I should set it
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post #7 of 22 Old 01-30-09, 10:35 PM
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Re: first up graphs, advice appreciated


Never used it so I can't tell you how it's done, but "what it is" is a super-quick, snap-shot measurement that shuts off the signal before it has a chance to start echoing around the room. The result is a measurement akin to anechoic.

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post #8 of 22 Old 01-31-09, 06:28 AM
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Re: first up graphs, advice appreciated

Quote:
Nearfield -- use the IR windowing feature in REW to eliminate reflections from the measurement
Quote:
What exactly is IR windowing.
Quote:
shuts off the signal before it has a chance to start echoing around the room
But, in this case, you don't want to alter the IR gating, since the gating puts a limit on the lowest frequency and the resolution of the response. For example, if you were trying to limit reflections from surfaces 1 meter away to eliminate comb filtering when high frequency testing, you might use a 6msec gate (d=(time*speed)/2), but this would limit the lowest frequency of usable response information to 167Hz (1/gate time). Not much use in this case where we're measuring 20Hz-3KHz. The default windows are much better for this low to mid frequency testing.

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post #9 of 22 Old 01-31-09, 09:23 AM
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Re: first up graphs, advice appreciated

That is true, windowing lowers your effective frequency, but you can allow second and third reflections to keep the window longer and still see the lower octaves. You start introducing some comb filtering, but you get the extended response.

When I test speakers in my basement, I have to do this since it's not that big of a room and there's no way to make it truly anechoic (it's also my theater, and bar, and game room). Just another lever to play with for testing. Usually, though, I'm only interested down to 60 or 80 Hz.

What are the dimensions of the studio? That might give some insight as to the peak/valleys. Construction? (concrete, drywall, etc).
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post #10 of 22 Old 02-07-09, 06:32 AM Thread Starter
 
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Re: first up graphs, advice appreciated

Ok, small improvement, but not in the area Im looking for! Two speakers here, the left only was lost when the comp. crashed.

I cant get anywhere near enough more trapping I dont think to help the low bass. So Im now thinking other trap types for solutions. Helmholtz got a wide enough Q in some form?

Purpose built $$$ studio's aside, I.E your typical make shift room for mxing, how close to flat can one be realistically trying to achieve.? Within 10db be a nice job? I need to know where the finish line should be.
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