Now what? Please give comments - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com
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post #11 of 67 Old 08-06-07, 09:02 PM Thread Starter
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Greg
 
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This seems a bit weird

Forgive me for breaking the suggested graph limits but I had to show you guys this. Here is my sub only. I did not think I was getting any response below about 30 Hz. It looks like a huge dip. Is this normal below 20 hz???

Can this be fixed with a BFD?

Incidently, my crossover has two settings - 12 dB/Octave (normal) or 36 dB /Octave (special for THX subs). I have it set to normal or 12dB/octave.
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post #12 of 67 Old 08-06-07, 09:20 PM
 
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Re: Now what? Please give comments


I dunno – typically a “real” null is pretty narrow. That thing’s more than 2-1/2 octaves wide.

Quote:
Can this be fixed with a BFD?
I have my doubts, unless you have something like 30 miles of headroom. If not, it’s impossibly deep - 30 dB!!! Aside from that, the lowest filter setting the BFD can be set at is 20 Hz. Sure, you could affect lower with a really wide filter, and then EQ down everything above 30 Hz, but as noted, you would have to have a sub system – both amp(s) and driver(s) - that’s totally loafing right now, using maybe only 5-10% of their capability.

I’m can’t help but think there’s something we’re missing. I can’t say I’ve ever seen anything quite like this. Not in a corner, anyway... Are there any gaping holes in the wall - bar pass-through, doorway, etc. – near the sub?

Regards,
Wayne



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post #13 of 67 Old 08-06-07, 09:27 PM Thread Starter
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Re: Now what? Please give comments

Quote:
Wayne A. Pflughaupt wrote: View Post

I dunno Ė typically a ďrealĒ null is pretty narrow. That thingís more than 2-1/2 octaves wide.


I have my doubts, unless you have something like 30 miles of headroom. If not, itís impossibly deep - 30 dB!!! Aside from that, the lowest filter setting the BFD can be set at is 20 Hz. Sure, you could affect lower with a really wide filter, and then EQ down everything above 30 Hz, but as noted, you would have to have a sub system Ė both amp(s) and driver(s) - thatís totally loafing right now, using maybe only 5-10% of their capability.

Iím canít help but think thereís something weíre missing. I canít say Iíve ever seen anything quite like this. Not in a corner, anyway... Are there any gaping holes in the wall - bar pass-through, doorway, etc. Ė near the sub?

Regards,
Wayne
Well I do have a lot of headroom left. My sub is at about 15 to 20 percent of capacity. I bet I could easily boost it up to get the 15 Hz to 75 dB. But wouldn't that blow out every thing else?
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post #14 of 67 Old 08-06-07, 09:30 PM Thread Starter
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Re: Now what? Please give comments

Quote:
Wayne A. Pflughaupt wrote: View Post
I’m can’t help but think there’s something we’re missing. I can’t say I’ve ever seen anything quite like this. Not in a corner, anyway... Are there any gaping holes in the wall - bar pass-through, doorway, etc. – near the sub?

Regards,
Wayne

No gaping holes. I do have a basement window that is in the room, but it is small (typical basement window). The window is closed, and I have linacoustic lining the walls. The position of the sub is fairly close to the corner - just the right side of the left speaker. When I move the sub around the room I get, in general, the same response.
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post #15 of 67 Old 08-06-07, 09:48 PM Thread Starter
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Re: Now what? Please give comments

Wayne,

Here are 50 percent, 75 percent and 90 percent in that order:
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Now what?  Please give comments-75-percent.jpg  

Now what?  Please give comments-90-percent.jpg  

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post #16 of 67 Old 08-07-07, 03:58 AM
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Re: Now what? Please give comments

The information below 20hz is not actual output from the sub. As the response drops into the noise, the meter calibration file compensates (as it also drops) and applies its opposite compensation.

See in your graph where the cal file drops past 10Hz and carries lower (because C-Weight is incorrectly turned on). This offers increasing compensation, and as the actual signal enters the noise, the meter file creates the strange rising signal.

Your usable response goes a little below 20Hz.

Below I show a couple graphs of a small sub I own.

You can see from the impulse response where the signal enters the noise about ~45dB down.

Then see the associated frequency response plot (with the exaggerated vertical scale) that is created from that impulse response, and you can see where the signal is down about ~45dB, but then begins to rise. This isn't signal - it's noise.

Generally you determine where your sub signal enters the noise and set your bottom horizontal axis to that...... For most people, that horizontal scale is about 15Hz.... The LLT guys use about 10Hz....


Now what?  Please give comments-rising-level-impulse.jpg
Now what?  Please give comments-rising-level-c.jpg

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post #17 of 67 Old 08-07-07, 08:27 AM Thread Starter
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Re: Now what? Please give comments

Quote:
brucek wrote: View Post
The information below 20hz is not actual output from the sub. As the response drops into the noise, the meter calibration file compensates (as it also drops) and applies its opposite compensation.

See in your graph where the cal file drops past 10Hz and carries lower (because C-Weight is incorrectly turned on). This offers increasing compensation, and as the actual signal enters the noise, the meter file creates the strange rising signal.

Your usable response goes a little below 20Hz.

Below I show a couple graphs of a small sub I own.

You can see from the impulse response where the signal enters the noise about ~45dB down.

Then see the associated frequency response plot (with the exaggerated vertical scale) that is created from that impulse response, and you can see where the signal is down about ~45dB, but then begins to rise. This isn't signal - it's noise.

Generally you determine where your sub signal enters the noise and set your bottom horizontal axis to that...... For most people, that horizontal scale is about 15Hz.... The LLT guys use about 10Hz....


brucek
Thanks, Bruce. So based on that I should set my lower limit of frequency back to 15 and try to equalize that. You mentioned that C-weighting is incorrectly turned on - do you mean below 15 Hz? I assume I should have it on for measurements and that it is not relavant below the limit of my small sub.

Who are th LLT guys? I did not understand the reference.

From my graphs of 50, 75 and 90 percent, would a BFD help to tame things with my sub?

Thanks again for the help.
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post #18 of 67 Old 08-07-07, 10:02 AM
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Re: Now what? Please give comments

Quote:
So based on that I should set my lower limit of frequency back to 15 and try to equalize that
You should set the axis on your graphs to horizontal of 15Hz-200Hz and the vertical to 45dB-105dB. The third (blue) plot you show is quite good. The natural low end extension is a bit below 20hz. That's good. You can't equalize below 20Hz with a BFD. Either way, there's no upside to trying to boost below a subwoofers rolloff at the bottom end.

Quote:
You mentioned that C-weighting is incorrectly turned on
The C-weight check box in REW is only active outside the limits of the meter calibration file. It should be turned off.

Quote:
Who are th LLT guys? I did not understand the reference
Many members here have built LLT's. See the DIY subwoofer and Soundsplinter sections in the forum..
LLT explained

Quote:
From my graphs of 50, 75 and 90 percent, would a BFD help to tame things with my sub?
You have a very good response. I wouldn't try and equalize it.

brucek
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post #19 of 67 Old 08-07-07, 01:37 PM Thread Starter
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Re: Now what? Please give comments

Quote:
brucek wrote:
You should set the axis on your graphs to horizontal of 15Hz-200Hz and the vertical to 45dB-105dB. The third (blue) plot you show is quite good. The natural low end extension is a bit below 20hz. That's good. You can't equalize below 20Hz with a BFD. Either way, there's no upside to trying to boost below a subwoofers rolloff at the bottom end.
ok. I will reset the graph limits. That last graph (blue) is just a result of me turning up the gain on the sube to about 90 percent of the total. I did not set the levels before I took the reading. I just did a quick check levels before the test and it said ok. Maybe that's all I need to do?
Quote:
brucek wrote:
The C-weight check box in REW is only active outside the limits of the meter calibration file. It should be turned off..
I don't understand. I am using the radio shack analog meter, aren't I supposed to have the C-weight box checked? Is it different for just measuring the sub? I think I am missing something. Could you please explain?
Quote:
brucek wrote:
Many members here have built LLT's. See the DIY subwoofer and Soundsplinter sections in the forum..
LLT explained.
I will check this stuff out. Thanks for the clarification.


Quote:
brucek wrote:
You have a very good response. I wouldn't try and equalize it.

brucek
That's good news. I just need to get it dialed in with my mains.
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post #20 of 67 Old 08-07-07, 01:56 PM Thread Starter
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Re: Now what? Please give comments

One more question. I am running everything through my ICBM for bass management. I did those readings (green red and blue graphs) with my crossover set to 60 Hz. It looks like it is not working correctly. Shouldn't I have a drop off just before 60 Hz? From the graphs, it looks like it's set at about 120 Hz.
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