Measurements, Help My Theater - AVS Forum
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post #1 of 24 Old 09-29-2013, 09:17 AM - Thread Starter
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Just received a UMIK-1, time to get started with a prelim evaluation of my theater sound!
Some Background:

Room is 18x25x8, theater is on one side, speakers firing along the 18' dimension making the actual theater space about 18x13 with the left side open to the rest of the room.
Gear is an underpowered F-20 sub, 300 watt plate amp on a UM-15 rated for 800W, Fusion 10 Pure for LR aimed just in front of the LP, no center, SL and SR are some small bookshelf polks all powered by an AVR for now.
No room treatments.
No gear for EQ.

Set up REW with a sound card cal and UMIK cal file from minidsp. For starters I did 4 sweeps from 15 to 20k with this unfortunate result:

1/12 smoothing


1/6 smoothing


The suckout at 50hz is enormous mad.gif

I suspect that I need to do some nearfield sweeps of each speaker and then some sweeps of all speakers across alternate LPs.
I am a total newb to this stuff so the primary purpose of this thread is to gather advice from you guys that have done these measurements with success and know how to evaluate/correct issues.

Also, is there a way to measure the delay for each speaker using REW?

Thanks in advance for the help.

Edit: Xover to sub is at 80hz
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post #2 of 24 Old 09-29-2013, 11:17 AM
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Do a sweep 10-100 with no smoothing.

Then do the L/R with no subs and 1/6 smoothing.

You may be able to tame the null by moving the sub around. I achieved great results just moving 6" at a time. Sometimes it doesn't take much.

You measure the delay with the ETC function. Use the ASIO drivers and an HDMI cable to make it easy.

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post #3 of 24 Old 09-29-2013, 06:46 PM - Thread Starter
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More Measurements:

This is the best response I could get out of my sub by moving it around under the screen. This includes phase.

Here is L/R combined response


Here is an overlay of R and L. Green is Right. Purple is Left


Here are full 10-20k sweeps at different LPs. Red is the Main LP
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post #4 of 24 Old 09-29-2013, 07:15 PM
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That peak from 5 to 6khz puzzles me.
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post #5 of 24 Old 09-29-2013, 07:17 PM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

That peak from 5 to 6khz puzzles me.
LOL, just sent you a PM, guess it worked!
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post #6 of 24 Old 09-29-2013, 07:58 PM
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Try measuring at 85db, 60db is a bit on the low side, someone talking in the background would throw the chart off.

I like to measure my subwoofers to at least 25% excursion at infrasonic, which is over 100db.
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post #7 of 24 Old 09-29-2013, 08:44 PM
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What's happening between the L&R. The left looks terrible by comparison.
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post #8 of 24 Old 09-30-2013, 06:05 AM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

What's happening between the L&R. The left looks terrible by comparison.

The only difference that I know of is placement. The right is wedged into a corner and the left only has a wall behind it.

Should I take close mic measurements to verify the response of each speaker? To do this do I measure the CD and the woofer separately or put the mic halfway between the driver center points and a few feet back?
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post #9 of 24 Old 09-30-2013, 08:13 AM
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As a baseline, it's always useful to look at the low frequency anechoic response of the speaker and subs. To do this, do a nearfield. Put the mic about 1" away from the woofer dustcap and take a sweep at fairly low volume. High is better, but don't clip the mic. Do that for your subs as well if you can.

You could also take a measurement just below tweeter height about 2 or 3 feet away, but you'll get the floor reflection and possibly more reflections. Here's my outdoor measurement of the Pure.



You can see a little wrinkle in the response at 5 to 6khz. I mentioned this a few posts up. I'm puzzled because it's so big on yours and you've used smoothing where I didn't. It could be a reflection is making this worse. It could be that a few db of eq may be useful there.

Anyways, once you have the baseline measurements, you can start to compare them to your room measurements and ask the tricky questions. Why is there a peak at 5khz? Why is there a suck out at 2khz and 50hz?. Etc.

EDIT - Oh ya and chop off your graphs at 10hz since your data doesn't go lower. It'll make it easier to read.
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post #10 of 24 Old 10-01-2013, 06:18 AM - Thread Starter
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Worked on this some more, turns out I was using V5.01 of REW when I needed to be using at least V5.01 Beta 14 for use with the UMIK-1. So I downloaded V5.01 Beta 17 and remeasured everything including nearfield on my left/right. I didn't have long enough usb cord to do the sub nearfield but I do have measurements done by Lilmike on my F-20.

Here is Left/Right independent and together, the combined response is offset by 10db for clarity



Nearfield woofers and tweeters on left/right with left/right components offset a bit. These are not level matched between tweeter and woofer to avoid mic clipping.


thoughts?
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post #11 of 24 Old 10-01-2013, 08:08 AM
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Well the nearfields look about what I'd expect. The LP measurements seem to show a lot of treble reflections though. Are you sitting up against a couch or something. Maybe a wall right behind your head? Is the mic lying on the seat cushion?
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post #12 of 24 Old 10-01-2013, 08:48 AM
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yeah...the nearfields look fine.

what are you doing with the microphone at the listening position? how is it setup? take a picture.

Listen. It's All Good.
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post #13 of 24 Old 10-01-2013, 08:59 AM
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you have an extra roll of phase on your sub. disable the low pass on the plate amp if possible. if not possible set it to the max setting and let the avr high pass do the filtering.

that might be screwing up the integration with the mains as well.

Listen. It's All Good.
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post #14 of 24 Old 10-01-2013, 09:18 AM
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The nearfield between 1-4khz looks a bit off even still.


But if you apply room treatments you will get closer to the nearfield response, which is definitely better than what your walls are doing to the sound.
Otherwise fullrange EQ is about all you can do, short of putting this in a different room, such as a dedicated theater.
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post #15 of 24 Old 10-01-2013, 09:32 AM
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Hard to evaluate that region in the NF. Same with below 100hz where the ports start to take over.
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post #16 of 24 Old 10-01-2013, 05:22 PM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

Well the nearfields look about what I'd expect. The LP measurements seem to show a lot of treble reflections though. Are you sitting up against a couch or something. Maybe a wall right behind your head? Is the mic lying on the seat cushion?

Yes, I set the mic right on top of the recliner headrest to get the diaphragm (or whatever the mic uses) as near to where the center of my head would be as possible. The end of the mic was probably about 2 inches away from the headrest.

LTD, will try to post up a picture later of the setup. I cant disable the low pass but I do have it turned all the way up. The low pass, 80hz, on the AVR was active for all measurements.
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post #17 of 24 Old 10-01-2013, 05:25 PM - Thread Starter
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Quote:
Originally Posted by BassThatHz View Post

The nearfield between 1-4khz looks a bit off even still.


But if you apply room treatments you will get closer to the nearfield response, which is definitely better than what your walls are doing to the sound.
Otherwise fullrange EQ is about all you can do, short of putting this in a different room, such as a dedicated theater.

I agree with the room treatments. I think that will be my next move for this space. I will probably move the screen to a different wall eventually also where none of the speakers would be backed into a corner.
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post #18 of 24 Old 10-01-2013, 08:18 PM
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Ah ok. That's to close for the mic. What you're seeing is strong reflections at high frequencies. Try to move it further away if possible. Where your head will actually be. Or ignore the >500hz response.
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post #19 of 24 Old 11-11-2013, 09:22 AM - Thread Starter
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Update: I have moved the screen to one of the short walls and put up some DIY acoustic panels. I plan on taking measurements today, with and without the panels up. I can easily tell the difference with the panels, and it is GOOD cool.gif Movie dialogue is very clear, don't have to crank the volume on quiet scenes anymore and even my wife made a comment on how good music sounded in the room.

Before I start taking the with/without panel measurements I need to integrate my sub as best I can without EQ. How should I do this? I have set the L/R distances on my AVR as well as for the sub, but I added the horn path length to this distance, about 14 feet I believe, is this right for setting up a horn sub? Do I just take low end sweeps and adjust the sub distance one foot at a time to gain the smoothest FR?
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post #20 of 24 Old 11-11-2013, 08:27 PM - Thread Starter
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Here are the goods:


Left and Right Front Speakers separate plus sub


Left and Right Front Together with Sub


Waterfall of sub and mains (sorry about the quality, can't seem to make it any better)


I also did alot of sweeps optimizing the distance setting for integrating the sub, makes a much bigger difference than I expected. In the end I only adjusted the distance setting of the sub by 1 ft. It did help reduce the 80-90 hz dip.

Didn't get a chance to do the measurements without room treatment, but I suspect it could have been much worse. Anyone have ideas on what could cause the large peaks and dips?

The waterfall is still not so pretty with that 41-42 hz ringing. Not sure if this can be knocked down by further treatment.

Here are a few pictures of my very unfinished room, maybe it will help identify some of the FR issues.






Would love to get some suggestions on this. Thanks
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post #21 of 24 Old 11-13-2013, 06:12 AM - Thread Starter
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No Takers?

C'mon, I know we have ALOT of talent around here! biggrin.gif

I'm looking for suggestions on sub placement, acoustic panel placement, possible floor/ceiling cancellation issues. What do you think?
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post #22 of 24 Old 11-13-2013, 06:25 AM
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I think you should probably go here:

http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs#post_22790110

and continue this discussion there.


Downloadable FREE demo discs:
http://www.avsforum.com/t/1475769/de...ently-authored 

Did you really need to quote that entire post in your reply?
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post #23 of 24 Old 11-13-2013, 07:33 AM
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Your FR looks pretty good. Depending on how you draw the line +/- 5db from 500Hz on up in-room is not too bad.

You have the normal SBIR jaggedness below 500Hz which could be improved with some acoustic treatment.

First identify all high gain reflections within 20ms and within 20dbs of original impulse. Locate offending reflection point within room and treat with appropriate BB absorption or your choice of treatment. For this read ETC tips in the REW thread here and on HTS.

You have a strong room mode at 45Hz, significant trapping will be needed to address properly. Ideally some floor to ceiling corner traps in all available corners.

As possible get the speakers appropriate stands there is lots of vibration present in sub enclosures especially non-opposed ones. Until stands are done do some decoupling of the speakers from the subs like open cell foam or other material.

Horn subs often need a little EQ even with a room that is cooperating. The F20 is not an exception in my experience.

Overall the FR looks pretty good, worth being proud of! smile.gif

Don't waste time reading signatures.....
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post #24 of 24 Old 11-13-2013, 08:57 PM - Thread Starter
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LastButNotLeast, thank you for linking that thread. A little overwhelming but I did do a thorough read on the REW 101 pdf found in one of the posts. Excellent information that I wished I would have read before taking any measurements. smile.gif

NicksHitachi, thanks for the detailed response. Now that I know better how to measure and interpret impulse I will definitely be identifying those reflections. I do have 3" thick safe n sound behind each speaker, at first reflection points and two on the back wall, still need to space them off the wall a couple inches. I have 2'x4'x6" "traps" in each vertical corner, plan on doubling that to go floor to ceiling eventually.

Also agree on the need for sub EQ, when lilmike came to measure my F20 the response was great but a horn is still a horn, and from what I understand virtually all of them require some EQ to flatten the response. At some point I will be getting a pro amp and mini dsp for this.

As it is right now, i'm pretty happy with the sound, it is much much better than before treating the room.
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