Can REW be used to help set sub distance in receiver?

[lovingdvd]

It seems that my sub may be a tad out of sync delay-wise (perhaps less than a half second behind) even thought I added 1 foot to the distance per the instructions.

When I used YPAO their software said my sub was 7.5 ft away. According to my measurements its only 6 feet away. So I'm using 6+1 for 7 feet in the receiver now.

Anyway I was wondering whether REW can be used in some fashion to determine whether there is any delay, and if so, to adjust it.

If not, are there any techniques that can be used such as audio tracks/patterns that can be played while adjusting to try and get it synced by ear? Thanks.

[brucek]

When I used YPAO their software said my sub was 7.5 ft away

I don't know much about YPAO software, but I guess they are using the microphone and deducing speaker distances with that.

That's fine, except you have an even more accurate device called a tape measure that doesn't have to worry about reflections and algorithms to know the exact distance. Simply measure the distance and enter it into the speaker distance setup in your receiver. It is wise to add the extra foot for the BFD though..

brucek

[lovingdvd]

brucek wrote:

I don't know much about YPAO software, but I guess they are using the microphone and deducing speaker distances with that.

That's fine, except you have an even more accurate device called a tape measure that doesn't have to worry about reflections and algorithms to know the exact distance. Simply measure the distance and enter it into the speaker distance setup in your receiver. It is wise to add the extra foot for the BFD though..

brucek

Right this is what I did. I measured 6 feet, plus added a foot. However it still seems like there is a bit of a delay.

So I am wondering if there is a graph or feature within REW that can help me determine this. Or if not perhaps there is some sort of test pattern like an intermittent "boom" that covers frequencies played in the main and rear so I can experiment with different settings.

[DrWho]

To see this in REW, you would need to look at the Energy-Time plots. As you change the distance setting on the sub, you should see peaks shifting back and forth. The goal would be to have a single peak centered around 0ms instead of two peaks.

[Wayne A. Pflughaupt]

When I used YPAO their software said my sub was 7.5 ft away. According to my measurements its only 6 feet away. So I'm using 6+1 for 7 feet in the receiver now.

This isn’t uncommon, from what I understand, as the phase shift introduced by many crossovers are essentially time domain issues. That’s why an automatic system like YPAO “sees” the sub at a greater distance. Also, equalizing adds its own phase shift, we’re often told, so the YPAO might be seeing that, too. You should probably stick with the YPAO adjustment, unless you can determine that it’s really off.

Regards,
Wayne

[JohnM]

You can't determine absolute time delay in REW, it places the peak of the impulse response at 0. To measure delays some reference is needed, e.g. a loopback on the other input of the soundcard, the software can then measure the relative positions and place the impulse peak accordingly. The important thing, however, is not the absolute delay but the relative delays of the various channels, if you make a measurement of sub and main together then problems in their relative time delay would show up as offset peaks in the impulse response or energy-time curve, as Mike said, but the sub has rather a broad peak due to its limited bandwidth, it can be hard to see the individual peaks (much easire when measuring a pair of main speakers full range). You will also get dips or bumps in the frequency response through the crossover region if the time delay is wrong, but it can be difficult to separate these from room effects.

[lovingdvd]

Wayne A. Pflughaupt wrote:

This isn’t uncommon, from what I understand, as the phase shift introduced by many crossovers are essentially time domain issues. That’s why an automatic system like YPAO “sees” the sub at a greater distance. Also, equalizing adds its own phase shift, we’re often told, so the YPAO might be seeing that, too. You should probably stick with the YPAO adjustment, unless you can determine that it’s really off.

Regards,
Wayne

YPAO showed 7.5 feet before I had the BFD in line. With BFD now connected and filters engaged, I think it'll be an interesting experiment to see if YPAO changes its recommendation. I've read in many places to add a foot to the measurement to account for its processing delays, so it'll be interesting to see if it now comes back at 8.5 feet or what. I'll keep you posted.

[catnip]

I just spent the weekend with the latest version of REW (very nice John!) and spent some time playing around with the sub distance (in the receiver speaker setup) to determine the impact on frequency response around the crossover region. I found that incremental one foot changes (+ and -) from the measured distance plus the 1 foot BFD electronic delay, made very obvious changes in the crossover region. I observed this with sub only and then all speakers running. It was quite easy to use the distance setting to help minimize the peaks/dips and was far better than just using the initial measured distance. Here is the final result:
01-27-2007 x-over result.jpg

[lovingdvd]

catnip - looks very good. So this is with a house curve of about +8dB at 20 to 0dB at 80? It would be great if you could get the 20-28 range up another couple dB. Not suggesting a gain filter (since they are talked about as being so bad, although I've used a few small ones myself for this very thing).

Thanks for the tip about the sub distance and using it to smooth things around the xo point. I hadn't tried that on purpose. Although after reading this it dawned on me that after raising my sub distance by 0.5 feet I did notice it seemed to make things even smoother.

[brucek]

It would be great if you could get the 20-28 range up another couple dB.

There is no reason to, he wouldn't hear the difference........

Good resposne Chuck..

brucek

[lovingdvd]

brucek wrote:

There is no reason to, he wouldn't hear the difference........
brucek

What is that? Would he *feel* the difference than? From what I can see on the chart, he essentially has a flat response from 20-40hz before it then finally starts to slope off. Whereas I thought the idea is that you want it to actually follow the house curve starting at 20hz? I thought the 20-30 range was quite important?

I ask because I made a similar tweak to make sure I have a response that follows the curve the entire way. Now I'm wondering if that is necessary

[Wayne A. Pflughaupt]

What is that? Would he *feel* the difference than?

Not really. You hear the most difference (improvement) from eliminating the worst peaks and depressions. Chasing every little ripple in response, you typically can’t tell the difference in that one way or another. We tend to do it anyway, because we can, and because we want a nice, “pretty” picture to present on this Forum, to impress all our mates. I’ll confess I’ve done it myself, so consider this “do as I say, not as I do.”

For instance, our system is in the family room, so every other room of the house opens up to it. I initially plotted response and equalized with all doors closed. Well, it’s seldom around here that all the doors are closed, so that’s the way we end up listening, with some of them open. Readings with the doors open is noticeably worse than with them closed, but in actually listening you can’t tell a difference.

Regards,
Wayne

[brucek]

I thought the 20-30 range was quite important?

Actually, our house curve expert, Wayne P says that a good house curve begins rising at the crossover until it gets to 30hz and then is flat from there down....


house_combined.jpg


brucek

[lovingdvd]

brucek wrote:

Actually, our house curve expert, Wayne P says that a good house curve begins rising at the crossover until it gets to 30hz and then is flat from there down....
brucek

Interesting. Currently I have +8dB 20 to +0dB at 80. Do you think its worth doing over with +8dB 30 +-dB 80? I am VERY happy with how it sounds now. However if its possible I'd hear and improvement by switching it I'm happy to try tweaking it. But based on what you mentioned earlier it doesn't seem like this would make a noticeable difference?

[brucek]

it doesn't seem like this would make a noticeable difference?

You're probably right........

[lovingdvd]

brucek wrote:

You're probably right........

This brings up an interesting question. What then are the different types of house curves worth experimenting this that would result in a noticeable difference? Perhaps someone can suggest three. One would be to use say +8dB at 20 or 30hz with 0dB at 80 hz. What would be two more?

This way we can play with say three different types of curves and see which one gives results best suited to our taste.