First Sub Measurement. Advice Appreciated. - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 9 Old 04-09-14, 01:20 PM Thread Starter
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First Sub Measurement. Advice Appreciated.

Hi everyone,

I'm new to the forums and to REW, but after a bit of tinkering, I was able to run my first measurement. I'm still not sure of what I'm looking at here, so I'd like to hear what those of you who know what you're doing think.

This is of the sub only (mains were disconnected), a PSA XV15, connected to a Pioneer VSX-820 receiver. The crossover is at 80 Hz. I played with the phase a bit, and the current setting (0) resulted in the shallowest dip at 30 Hz.

Many thanks,
Josh
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First Sub Measurement. Advice Appreciated.-rew01.jpg  


Last edited by Josh865; 04-09-14 at 02:17 PM.
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post #2 of 9 Old 04-09-14, 02:10 PM
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Re: First Sub Measurement. Advice Appreciated.

Hi Josh,

Congratulations on getting a viable measurement ( & posting it with the correct formatting ) !

Your sub-woofing experience will be a whole lot better if you find a way to ( at least mostly ) fill-in that trough that's centered at ( a frequency,slightly higher than ) 30 hz .

I'll leave it to others to detail ( or for you to research ) the various approaches ( along with their pros & cons ) to accomplish this.

Here's a ( very ) brief summary of approaches ( though by no means comprehensive ) ;

(i) EQ ( boost the frequencies within the area of the hollow / likely the worst choice )
(ii) Room Placement ( move that sub-woofer to a location that gives a better response / should be the first thing done )
(iii) add more sub-woofers ( placed in various locations within the room to pressurize the room more smoothly )

The whole point of having ( & using REW ) is to get visual feedback , after you change an important parameter ( such as moving the sub location &/or adding some EQ ).


Last edited by EarlK; 04-09-14 at 05:15 PM.
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post #3 of 9 Old 04-10-14, 03:23 AM
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Re: First Sub Measurement. Advice Appreciated.

Basically what Earl said

Sub placement, even listening position can make a difference specially if you are restricted in sub placement.
Use REW RTA for this then use the sweep measurements to fine tune.

Does the Pioneer have EQ for subs, if so use this to fine tune after placement.

This approach applies to mains as well.

Bring the mains in as well with the sub after finding the best possible sub and mains postilion.

Generally when EQing from 0-250hz you are EQing the room (influence), from 250hz - 20,000hz you are EQing the speakers.
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post #4 of 9 Old 04-10-14, 07:34 AM Thread Starter
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Re: First Sub Measurement. Advice Appreciated.

Thanks for the help, guys. I was able to play around with the placement a bit last night, and was quite surprised with the impact the different locations had on the measurements (I always heard sub placement was a big deal, but I never realized just how big). After trying out five different locations, I ended up with the attached measurement.

Interestingly, no matter where I put the sub, the dip around 30Hz remained, even after playing around with the phase adjustment. Is it likely I'm out of luck there, given that none of the different locations eliminated it?

I don't have any way to EQ the sub (and the receiver doesn't do it), but would like to add a miniDSP to bring down the peaks.

Thanks,
Josh
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First Sub Measurement. Advice Appreciated.-newsubposition.jpg  

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post #5 of 9 Old 04-10-14, 08:25 AM
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Re: First Sub Measurement. Advice Appreciated.



The curve ( above ) is a much better curve ( for EQing purposes ) than ( below ) ;



Before you give up on sub relocation , you might try positioning the sub at the ( LP ) listening position ( you'll need to move a chair or couch obviously ) & then move the mic ( instead of the sub ) to various positions .

FWIW, I've never done this myself / but I've read it works .

If you post your .mdat file, I'll in turn post a ( hypothetical ) EQ curve derived from your first measurement .

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post #6 of 9 Old 04-10-14, 09:00 AM Thread Starter
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Re: First Sub Measurement. Advice Appreciated.

Quote:
EarlK wrote: View Post
If you post your .mdat file, I'll in turn post a ( hypothetical ) EQ curve derived from your first measurement .

Thanks so much! I've attached the mdat file with the first graph.

I also attached a second mdat file that includes measurements from the other positions I experimented with (and from which the second graph I posted was pulled). If you would be willing to take a peek at those and see if any of the curves there are even better, that would be much appreciated.

Thanks again,
Josh
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post #7 of 9 Old 04-10-14, 09:49 AM
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Re: First Sub Measurement. Advice Appreciated.

Hi Josh ,

Here are the EQ filters as promised . This exercise demonstrates the effectiveness of using REW to EQ the 20-75 hz region ( using an appropriate target level of 78db ) .

The first pic shows filters dedicated to the Behringer 1124dsp unit ( I turned off 1/2 of the filters generated since I felt they were superfluous ) / while the second is using filters meant for miniDSP's 96K unit .

If sub-sonic info below 20hz is important to you ( & it's not to me ) / you might ( manually ) add the necessary filters to bring those areas up a bit ( though I wouldn't recommend it, since frequencies below 20hz are more than likely below the tuning frequency of your sub & boosting below the "box-tuning" is generally frowned upon ) .

Be aware that EQing ( or boosting filters ) will reduce the headroom of your amplifier ( by the amount of boost applied ) .
- I've moderated the amount of "boost" applied .

Attached Thumbnails
First Sub Measurement. Advice Appreciated.-bfd-filters_c_.png  

First Sub Measurement. Advice Appreciated.-minidsp96k-filters_b_.png  

Attached Files Modified Fikter Set for BFD.req (4.1 KB)  MiniDSP 96K Filters.req (2.0 KB) 

Last edited by EarlK; 04-10-14 at 12:26 PM.
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post #8 of 9 Old 04-10-14, 12:06 PM Thread Starter
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Re: First Sub Measurement. Advice Appreciated.

Thank you for taking the time to do this, I really appreciate it. That looks like a considerable difference, so I'll have to add something to do the EQ'ing sooner rather than later.

Thanks again,
Josh
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post #9 of 9 Old 04-10-14, 04:32 PM
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Re: First Sub Measurement. Advice Appreciated.


Quote:
EarlK wrote: View Post
Be aware that EQing ( or boosting filters ) will reduce the headroom of your amplifier ( by the amount of boost applied ) .
- I've moderated the amount of "boost" applied .
Actually, boosting or cutting is academic; any EQ reduces headroom.

For example, Josh’s baseline graphs had response ( at 45-55 Hz) peaking at ~82-83 dB. The subwoofer level (relative to the main speakers) was calibrated based on that peak. But after equalizing, even with a number of negative-gain filters, the sub’s maximum output is reduced – notice that it’s now down in the 77-78 dB range, 5 dB lower than before. Well, guess what? Now you’re going to have to increase the sub’s output level to compensate. So say “goodbye” to the headroom you thought you saved by minimizing boosting!

Regards,
Wayne





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