Using REW to setup B&K PEQ and notch filter

[Jarrod]

Hi,

I have a B&K Ref50 and plan to use REW to optimize its EQ settings for my room. In the past I've done this using the internal test tones and the RS meter but that is a real pain. REW sounds like a much more fun and accurate way to do it! Looking for feedback before I get too far into this....

By way of test equipment, I've got an ECM8000 and a EURORACK UB802 mixer with phantom power. I was planning to use this mic for measurements with the ECM8000 calibration file on the download site. I also have the Radio Shack SPL meter to calibrate the SPL reading (old-school version). I plan to use the software on my MacBook Pro 17" with the internal sound card.

I was able to get REW version 4.11 properly setup on the Mac. I measured the frequency response of the internal sound card (graphs posted below), and created the sound card calibration file.

At 48kHz sampling on the input and output, I got this response:



I switched to using 44.1kHz sampling on input and output and got this, which is much better:



Does it matter if I use 16, 20, or 24-bit audio? For the internal sound card calibration I used 24-bit.

Am I on the right track? Does it sound like I have everything I need?

Thanks!

[brucek]

Yeah, the 44.1K sampling looks fine for the soundcard cal file.

Be sure to download the ECM8000 cal file from our site.

brucek

[Jarrod]

My new sub (Outlaw LFM-1 EX) is on the FedEx truck for delivery today

My current sub is a Velodyne DLS-3500 with an 8" forward-facing driver and slot port underneath. I am considering keeping this subwoofer to use in a dual config with the new Outlaw sub.

I measured the response of the Velo tonight in two locations. The first location (red) is on the left wall, about 8 feet from the front of the room. The second location (green) is on the front wall, next to the center channel (underneath the TV inside an open-air stand that I custom built).



I always had the Velodyne sub in the first (red) location, long before there was a place to put it on the front wall. The new Outlaw sub is going to have to go in the red location, as there really isn't any other place to put a box of this size in our room. So the Velo is definitely staying in the green location!

By the way, do I need to make a calibration for my mixer (Eurorack UB802)?? Right now I have the ECM8000-cs.cal and my soundcard/loopback calibration files loaded. What is the best way to go about calibrating for my mixer's response?

Thanks,

Jarrod

[brucek]

I am considering keeping this subwoofer to use in a dual config with the new Outlaw sub.

I'm assuming the new sub will have better extension than the existing sub. If that's the case, then it's an extremely bad idea to keep the challenged sub in the mix. You're wasting the extension of the new sub. Only subs with similar response should be mixed.

What is the best way to go about calibrating for my mixer's response?

Create a new soundcard calibration with the mixer in the loopback in place of a loopback cable.

brucek

[Jarrod]

Yeah, the new sub should have usable energy down to 16Hz. I was hoping to be able to set it up to mesh with the existing sub at around 30-40Hz.

I think I'm gonna need help including the mixer in the soundcard cal file. I did what seemed obvious to me (plugging from soundcard out to line in on the Mic channel, then from mixer tape out to soundcard input) and did not get any input signal.

[JimP]

That's sure is a nice sound card response curve but from what I read, it was recommended that we use external sound cards. This might very well be the exception, but I think I'd try to find out if its good enough.

The other thing is that on the Ref 50, you only have the capability of using a single notch filter without much latitude for the Q which isn't given as a Q setting. You really need more flexability and need to look at other manual eqing options.

Getting back to including the mixer in the sound card calibration file, you'll need some connector adapters. You'll want to convert the microphone xlr input on the mixer to go into the stereo line in 1/8" connect on your sound card. The outputs on the mixer also have to have 1/4" to 1/8" adapters and cable.

I've gone through multiple 8200 mics and have used the generic files on most of them. I've always had that question in the back of my mind just how accurate the mic file combination might be. You might want to either get your calibrated or get one that's calibrated from the form member whose selling mics and files. Sorry, don't remember his name.

[Jarrod]

Jim,

I'm not clear on what you are saying. It doesn't make sense to me that the XLR mic input on the mixer should be connected to line in on the sound card. Did you mean that the line/headphone out on the sound card should be hooked to the XLR mic input on the mixer? What about phantom power - would I leave it on in this scenario? I have no clue how the mic preamp would be expected to interact with a line-level input from my computer.

I do need to hit guitar center this afternoon and get some 1/4" to RCA adapters so I can get whatever I need then. As I mentioned, right now I'm using the tape out on the mixer to get back to line in on the sound card, because I don't have the right mix of cables and adapters to use the Main Out as is shown in the cabling help file. The tape out uses RCAs. Not sure what affect this has (I'm a total neophyte when it comes to using mixing equipment).

Thanks for the input!

[JimP]

Jarrod,

My bad...you're correct in that the XLR mic input should be connected to the sound card's line out. You do use the phantom power supply and be sure to turn your gain on the mixer all the way down and slowing bring it up when adjusting levels.

Don't know if using the tape/cd in/outs matter. I use the main outs. That is a good question though.

[Jarrod]

Ok, thanks again Jim. I think I know what I need now. As soon as FedEx delivers my sub (I have to be here to sign for it) I'll pick up some adapters. I'll go ahead and get a few 1/4" to RCA adapters so I won't have to worry about the tape out question - they will be useful adapters to have anyway...

[JimP]

...and the XLR adapter.

Trying to intergrate those two subs can be a real headache (been there, done that...gave up). I'd suggest trying to get the new one optomized and after you're happy with it, then see about adding back the other one.

[Wayne A. Pflughaupt]

brucek wrote:

I'm assuming the new sub will have better extension than the existing sub. If that's the case, then it's an extremely bad idea to keep the challenged sub in the mix. You're wasting the extension of the new sub. Only subs with similar response should be mixed.

Ordinarily I'd agree with you on this, but don't you feel that in this case the small sub (green trace) will help fill in the hole that the Velo will have (red trace)? More power and deeper extension won't eliminate the hole he's going to have at 37 Hz in that location...

Regards,
Wayne

[brucek]

XLR mic input should be connected to the sound card's line out.

No, when connecting a mixer into the soundcard calibration loop, you connect the soundcard line-out to the mixers line-in (on the UB802 the line-in is directly below the MIC XLR input connector). Then the mixers main-out is connected to the soundcards line-in. That's the loop.

You require a couple (1/4" TS to RCA adapters) to accomplish this.

Yes, this hookup bypasses the mic preamp part of the mixer, but it has been established that the mic preamp has negligible effect compared to the line stages in the mixer.

Simply setup the dials approximately as shown below, except the mic isn't used and the phantom power is of course turned off.




brucek

[Wayne A. Pflughaupt]

JimP wrote:

Jarrod,

My bad...you're correct in that the XLR mic input should be connected to the sound card's line out.

We typically don't recommend trying to include the mic pre-amp in the soundcard calibration. Often it's problematic. brucek's tests on the UB802's mic pre-amp has shown that it's virtually flat anyway.

Regards,
Wayne

Edit - looks like brucek hit "send" before I did - LOL

[Wayne A. Pflughaupt]

JimP wrote:

Trying to intergrate those two subs can be a real headache (been there, done that...gave up). I'd suggest trying to get the new one optomized and after you're happy with it, then see about adding back the other one.

I assume you're talking about measuring and equalizing each sub independently? Have you tried the "Sonnie method?" He measures and EQs their combined output and says it works great. Kinda makes sense I guess, when at the listening position you're hearing them both together anyway...

Regards,
Wayne

[Jarrod]

Ok guys, thanks for the additional input. Sounds like I'll skip the XLR adapter and continue to use the mic line in to receive the signal from the soundcard. Now to figure out why I didn't get any signal when I did it this way the first time....

My subwoofer arrived with defective driver So, no woofage until I can swap in the replacement that the manufacturer is shipping today. Hopefully I'll have everything I need by the weekend...

[Jarrod]

I picked up a pair of 1/4" TS to RCA adapters after work and am now able to measure the response of my UB802. Earlier I was using stereo 1/4" TRS to stereo 3.5mm adapters that I had laying around and these must not be wired in a way that brings the right channel back to the soundcard.

Black is the soundcard by itself and blue is the UB802 in the signal path (both with the soundcard calibration loaded). +0.5/-2.0dB from 5 to 20k is pretty clean.



Thanks for getting me straightened out on the wiring.

[Jarrod]

JimP wrote:

The other thing is that on the Ref 50, you only have the capability of using a single notch filter without much latitude for the Q which isn't given as a Q setting. You really need more flexability and need to look at other manual eqing options.

Yeah, obviously I have no expectation of getting really far with the Ref50 built-in EQ but it is better than nothing. I think the new Ref70 has three notches, which is a lot more useful. I may end up with a BFD at some point but if I can get this new subwoofer in decent shape with my existing equipment then I'll put that expense off for a little while.

Just being able to do reasonable measurements for placement and crossover settings is helping a lot. I am already shocked to see dramatically I improved the bass response at the listening position by simply moving my old sub to the front of the room.

[JimP]

Congrats on getting this far. It looks like you only have a very slight drop over the subwoofer range. That's the way its suppose to work but knowing rather than assuming helps put your mind at rest.

One thing though in brucek's photo of the mixer, use a xlr cable and some kind of tripod, mic stand,etc. to get the mic in at the correct position for either single or multiple readings.

I also have an interest in a Ref 70 upgrade from my Ref 50 but will wait until the high rez audio upgrade actually shows up. Its already questionable whether or not it'll show up as its already so late. I'd like to believe that B&K is financially strong enough to endure the economy but who really knows. They're also some other features I'd like to have that may not be in a completed Ref 70 such as some form of steady sound, dynamic eqing for sub and room eqing for the other speakers.

For the short term though, with the popularity of the new SVS equalizer, you might be able to find pretty good deals on the Velodyne SMS-1 and the Behringers.

[brucek]

+0.5/-2.0dB from 5 to 20k is pretty clean.

Yeah, looks about the same as my plot with the UB802. It's not going to alter the measurements you take that much since the response of the mixer is so good, but you may as well have the response built into the soundcard cal if you can.....

brucek

[Jarrod]

JimP wrote:

Congrats on getting this far. It looks like you only have a very slight drop over the subwoofer range. That's the way its suppose to work but knowing rather than assuming helps put your mind at rest.

Thanks. Yes, I am a scientist by profession and so "assuming" doesn't get it done for me

One thing though in brucek's photo of the mixer, use a xlr cable and some kind of tripod, mic stand,etc. to get the mic in at the correct position for either single or multiple readings.

I've got it on a mic stand, with the mic pointed at the front of the room, angled toward the ceiling at a ~30 degree angle.

I also have an interest in a Ref 70 upgrade from my Ref 50 but will wait until the high rez audio upgrade actually shows up. Its already questionable whether or not it'll show up as its already so late. I'd like to believe that B&K is financially strong enough to endure the economy but who really knows. They're also some other features I'd like to have that may not be in a completed Ref 70 such as some form of steady sound, dynamic eqing for sub and room eqing for the other speakers.

Yeah my thinking is the same as yours. I have never been one to buy equipment on promises - they seem to fall through all too often for various reasons. I have been really happy with my Ref50 so would be interested in the Ref70, but also have wondered whether or not a small company like B&K can weather this economy. Also, I'm not sure how the Ref70 can be a very successful product in the marketplace if they don't add some form of semi-automated room EQ. Even sub-$1000 receivers have this feature now.

For the short term though, with the popularity of the new SVS equalizer, you might be able to find pretty good deals on the Velodyne SMS-1 and the Behringers.

I'll keep my eye out. I haven't really spent any time understanding what the strengths and weaknesses are on these different units, other than that I know the SMS-1 can do its job without an external software such as REW. Not sure that's worth the extra $$$ to me since I've already got the REW setup.

[JimP]

If you do go the route of the SMS-1, I've found that room measurement and filter calculations are better handled by REW, then manually entered into the SMS-1. That way you can even do an average of several mesurement positions and use REW to average them. You also have extra memory slots for doing house curves etc.

[Jarrod]

My replacement woofer arrived this afternoon. I installed it and the new sub is working now

To remind folks of the setup here: I've got a small 8" Velodyne subwoofer located at the front of the room (I'll call this location 3). My new sub is an Outlaw LFM-1 EX and I'm testing it in two locations (I'll call these locations 1 and 2). Location 1 is on the left wall, about 8' from the front wall (red traces). Location 2 is on the left wall, about 5' from the front wall (green traces).

To increase the number of variables further, the outlaw sub has two user-selectable tunings: 25 Hz (Maximimum output mode - I'll just use "MO" for short) and 20Hz (Maximum extension mode - I'll just use "ME" for short).

All of the measurements are done with L+R fronts plus the subwoofer, using an 80Hz crossover.

Here is the trace for the little Velodyne sub at location 3:



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Here are the traces for the Outlaw sub with the MO tuning at the two locations described above:



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And here are the traces for the Outlaw sub with the ME tuning at the two locations described above:



As expected from the measurements I posted several days ago for the little Velodyne sub at location 1, you can see that the new subwoofer has some big room cancellation going on from between 35 and 50Hz. My hope is to integrate the old sub (at location 3) to fill in this hole. So here we go....

Here are the traces for both subs playing simultaneously, with the Outlaw sub in MO tuning at locations 1 and 2:



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And here are the traces for both subs playing simultaneously, with the Outlaw sub in ME tuning at locations 1 and 2:




I am feeling pretty lucky at this point! It seems obvious which setup I should use as the baseline for setting the B&K notch filter (both subs on, Outlaw in location 1 with ME tuning - the last graph in this post). And the even better news is that location 1 has the most WAF.

[Jarrod]

This will give you a feel for what the Ref50 pre/pro gives you to work with. It has a notch filter which can be set in 2Hz increments from 20Hz up, with a variable "width" of up to +/- 17% of the frequency it is centered on. It also has a low-pass shelf filter, which lets you specify a frequency below which will be boosted by as much as 6db, or cut by as much as 18db. Here is what that looks like using 30Hz as the cutoff frequency (the red graph is no shelf applied).



So what I'm thinking I want to try to do is boost the frequencies below ~50 Hz and apply the notch to tame the peak at 60Hz.

[Jarrod]

Botched attachment - see next post

[Jarrod]

With the sub crossovers defeated, I get the smoothest response with the notch filter set at -11dB centered on 62Hz with a width parameter of 51.7-72.3Hz (the max width for the notch), and the low-pass shelf set for +3dB below 70Hz.



The sweep sounds pretty smooth with the EQ set like this. I can hear the peak at 25-30Hz, but it isn't that bad and everywhere else sounds great to my ear. I'll play some music and movies for awhile and see what I think.

I do not know what the drop out at 111Hz is about - this appears any time I engage the notch filter, and seems to be independent of the location or amount of correction applied. Strange, but it doesn't seem to be audible.