# Phase questions, REW graphs, help?



## chrisp9446 (Sep 5, 2009)

Hi all. I finally found some more time to fiddle with my sub (Epik Sentinel) and eq (BFD 1124). I'm using a radio shack SPL meter.

I'm going to be taking some more measurements after changing crossovers, etc., but between the two EQ'd graphs, which do you think would be preferable? I don't really have any choice in moving the sub's location (WAF, corner, where no one can see it), so I'm probably going to be stuck with one of these. I am currently using my receiver for crossover control and the crossover is set at 80hz.

The only phase control is a switch on the sub (0°/180° only).

0° before EQ:







0° after EQ:







180° before EQ:







180° after EQ:








It looks like there is some cancellation at the crossover (80hz) with the phase set at 180°. That would normally tell me that I should use 0° for the phase, but when I do that, there are significant cancellations that occur >100hz. 

From that, I have two questions:
1. Which will have a bigger impact on my overall listening experience?
2. Is it possible to correct either one without room treatments?

Thank you in advance for any help.


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## tonyvdb (Sep 5, 2007)

Position of the sub is crucial to getting a smooth response and I would retry the test after you have moved it to a different spot.


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## chrisp9446 (Sep 5, 2009)

tonyvdb said:


> Position of the sub is crucial to getting a smooth response and I would retry the test after you have moved it to a different spot.


I appreciate the suggestion, and I agree that positioning is critical, but this is the best "wife-approved" location I could find in the room. There were only a few spots that could work, and this was the one that gave the best response out of those. 

In our next house, we'll have a dedicated HT room, but for now I have to make do with keeping everything in the living room.

That being said, I understand I may not get an ideal freq response, but I want to understand how to get the best I can with what I have.


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## tonyvdb (Sep 5, 2007)

You can install some bass traps in the corner behind the sub as that could help. Not sure if the ascetics of the room would change allot going that route.


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## chrisp9446 (Sep 5, 2009)

tonyvdb said:


> You can install some bass traps in the corner behind the sub as that could help. Not sure if the ascetics of the room would change allot going that route.


That could be a possibility. Which of the peaks/nulls (or in general which kind of peaks/nulls) would bass traps there help control?


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## tonyvdb (Sep 5, 2007)

I'm no expert in that area but Im thinking that you would help with the area around the 50-120Hz range. I am sure someone with better knowledge will chime in here to give you better advice with this.


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## glaufman (Nov 25, 2007)

If we're tlaking about the commonly DIY'ed OC703 or rock-wool traps either straddling or completely filling the corner... the higher in frequency you can push the problem areas the easier it'll be to treat ... The lower in frequency you want the traps to be effective the larger they have to be, i.e. the more they'll protrude into the room...

That being said, I don't think traps will be significantly effective in removing phase cancellations from multiple sources.

I would suggest running a scan of the sub alone. If some of those dips in the 40-160Hz range go away, then I would try using the distance setting on the AVR to fine tune the phasing... but that being said, if you've got the WAF for traps, they almost always have a beneficial effect on some of the peaks and dips, just less as you go lower in frequency.


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## chrisp9446 (Sep 5, 2009)

Thank you all for the help so far. 

I've gotten some scans of my subs only (disconnected wires to the mains) and the mains only (turned sub off), but there seem to be some weird things going on. First off, my receiver H/K AVR 254 apparently uses 12db/octave for the crossovers, so that's one reason why my graphs look different. But the crossovers in general seem to be screwy...

Here is the sub only. Even though the 12db/octave isn't standard, it seems to follow it pretty well. 









Here's where it gets weird. This is what I plotted when I turned off my sub, changed nothing else on the receiver, and got a plot of just the mains. 









I'm not really sure what to make of this. It doesn't even follow the 12db/octave crossover at 80hz. It seems more like it follows what would be a 30-40hz crossover (40hz x-over shown below). My mains are Polk Monitor 60's (supposedly can reach 38hz), but I don't know why the receiver would be playing them close to full-range. 








I know this opens up a whole new can of worms, but it seemed very strange to me. Is there any way the receiver could tell that the sub is off and decide to play all freq's through the mains? Everything is still plugged in, but the sub was turned off...


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## glaufman (Nov 25, 2007)

Unlikely. What's more likely is that the acoustics of the room are skewing the response you're seeing so it looks like it's doing something that it's not.
Does your AVR have preamp outs for the mains that you can use as the input to the soundcard so you can see exactly what the crossover is doing?


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## chrisp9446 (Sep 5, 2009)

glaufman said:


> Unlikely. What's more likely is that the acoustics of the room are skewing the response you're seeing so it looks like it's doing something that it's not.
> Does your AVR have preamp outs for the mains that you can use as the input to the soundcard so you can see exactly what the crossover is doing?


Yeah, it does. I don't really like what I'm seeing in my graphs, though. I can't tell if I'm doing something wrong with REW/setup, or if my AVR (Harman Kardon 254) is just really screwed up. I know it's not a high class receiver, but I would have thought it would know how to crossover material. I double checked that my crossovers were all set to 80hz to make sure I'm not crazy, and they are.

Sub preamp out:







Front Right preamp out:








:huh:


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## laser188139 (Sep 19, 2009)

You are right, it is a puzzle why the sub crossover in the receiver's preout does not appear sharper. 

The main preout being flat could be explained by the mains being set to Large and the sub mode being configured to LFE+Main. (Or whatever the equivalent terminology is in the HK.) 

If the main is set to Small, you should see the crossover there. 

Bill


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## glaufman (Nov 25, 2007)

Here I go saying +1 to Bill again... :T


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## glaufman (Nov 25, 2007)

Sometimes that feature is called "double-bass"


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## chrisp9446 (Sep 5, 2009)

I agree, and that's what I thought, but I can't figure out for the life of me why the receiver is doing that.

Here is the configuration screen for the crossovers:








All of the crossovers are set to 80hz, but for whatever reason, the receiver (=:devil doesn't care. I shot an email to HK's technical support, but I don't have high hopes for a great response.


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## chrisp9446 (Sep 5, 2009)

glaufman said:


> Sometimes that feature is called "double-bass"


Yeah, on this receiver, you can set it to LFE+Main. But, to do that, you have to first set the mains to "Large," and then make a change in the previous menu. Maybe there's a firmware glitch that got it stuck true, though?

(Also, please don't mistake my short answers as not appreciating the help. I know forums can often be hard to convey emotion, especially with short responses, so I am very grateful that you guys are around to help troubleshoot my issues  )


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## laser188139 (Sep 19, 2009)

Besides the normal crossover settings, some receivers offer a second set of 2ch stereo settings. I know my Denon does. So it may be possible that your receiver is seeing the 2ch connection from REW and using a different speaker configuration than the primary one you showed in the picture. (I did not see an Owner's Manual on the HK support site that might answer these questions.) 

Bill


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## chrisp9446 (Sep 5, 2009)

laser188139 said:


> Besides the normal crossover settings, some receivers offer a second set of 2ch stereo settings. I know my Denon does. So it may be possible that your receiver is seeing the 2ch connection from REW and using a different speaker configuration than the primary one you showed in the picture. (I did not see an Owner's Manual on the HK support site that might answer these questions.)
> 
> Bill


Good catch! After some digging in my Owner's Manual, there is an Analog Bypass mode that disables bass management. It's not set directly, but through a combination of other settings (it's activated when "Tone Control" is off...go figure). 

After going to "DSP Surround Off Mode," where it is 2-channel with bass management active, here is what I get from the front preout:








It now follows the standard 24db/octave crossover at 80hz, though the signal is still very noisy. When measuring preouts, should I have to turn the volume all the way to -0db to get a clean signal? The only reason that I'm hesitant is that the preouts don't output signal when I disconnect the speakers, and I don't want to run test tones at -0db through the speakers...


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## laser188139 (Sep 19, 2009)

I'm not sure why you would need to turn the volume up so high to get a "clean signal" on the preouts. I've not had that issue with the Denon. There, I've looked at the preouts to get a clearer idea what Audyssey is generating for equalization, so I turn Audyssey equalization Off, calibrate the preout level to read 75dB in REW, run a sweep for a baseline, then turn Audyssey equalization on and run a sweep of the preout again. This has worked for me at pretty near any reasonable volume level.


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## chrisp9446 (Sep 5, 2009)

Hmmm...

I'm not sure what the problem is, then. Should I disconnect the banana plugs from the fronts to the receiver before running REW through the preout? 

If that is really what the receiver is coming up with to send to the fronts, it's no wonder why my EQ efforts have been so difficult...


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## glaufman (Nov 25, 2007)

Did you have Audyessey or something similar on while running this scan? The preout should be a VERY clean looking signal. That trace looks more like an acoustic response of the room than the electrical response of the preamp. At least we're making progress...
If you've turned the volume all the way up, it's possible you're clipping something somewhere...


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## chrisp9446 (Sep 5, 2009)

No, I had disabled the EZSet/EZEQ because it doesn't seem to be nearly as good as Audyssey. I have been running these tests at around -25db on the receiver. 



glaufman said:


> That trace looks more like an acoustic response of the room than the electrical response of the preamp.


Yeah, that is what worries me. I'm not sure if there is some additional setting in the receiver that's gone haywire or if there is some interference introduced once the signal is in the cable to the soundcard...(I'm at work so I can't run any scans 'til this evening)


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## glaufman (Nov 25, 2007)

Fair enough... when you get home run a new scan of the sub-preout... if it's gone haywire, then maybe play with the settings or the connections... if it's still clean, then maybe play with the settings or the connections...


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## chrisp9446 (Sep 5, 2009)

I changed the input device in REW from "Default Device" to "USB Audio Codec," and started getting some slightly more realistic preouts. I don't know why I had to switch it now...it had always seemed fine before. I'm still concerned with how far off from target they are, though. 

Sub preout:








Front Right preout:








With the front right, it flattens out from 200hz-1000hz, but it still slopes up towards 5hz between 20hz and 5hz when I did a 5hz-1000hz scan. As far as settings, I read through the manual again and I think I've changed everything I can...


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## glaufman (Nov 25, 2007)

Any chance your tone controls are messing with things? (either in the AVR or the soundcard)?


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