SVS + Polk RTIs

[jesyjames]

Hey guys. I've recently upgraded my PSW350 to an SVS 20-39+.

My current set up is:
RTI38s
CSI40
FXI30s
SVS 20-39+
Denon AVR-1803

I'm trying to find the best spot for the sub and have been doing some frequency plots on it using test tones.

Things are very smooth except for one problem area.

For whatever reason, I get a substantial db loss between 80-100hz. I've tried different placement issues and that effected the curve, but there wasn't a placement that helped that gap.

I have the receiver crossed over at 80hz, the sub's crossover set to "disabled" and turned to 120hz just to be safe.

I did notice that when I changed the phase from 180(which was the proper setting for the polk sub) to 0, that I gained about 8 db in that range. But the dropoff still seems sharp to me. Is there an intermediate step that would be better for me to set the phase at? Obviously it's a dial so I can put it anywhere between 0 and 180. What have other RTI/SVS owners found to be ideal?

If you could take a look at my frequency response graph, I'd appreciate it.

Of all the spots I've tested, this really seems to be the best in terms of low end oomph, and flat response...

I have the digital RS meter and applied the correction factors... I'd been told they were the same as the analog.

Thanks.

[Loud & Clear]

What happens when you set the Denon's crossover to 100Hz?

[jesyjames]

Not much. Before I adjusted the phase I'd get about 10db gain... now that I've changed the phase it gives me the 10db gain and changing the crossover doesn't seem to do a whole lot.

[Dr. Spec]

All SVS phase controls seem to be wired reverse polarity. Why, I don't know - Tom V explained it once in a different forum and I didn't catch his post.

Anyway, definitely leave it set at 180. My 20-30PC+ did exactly the same thing, and so does my PB2+. Don't worry about leaving the filter at 120 just to be safe - the Disable switch does the trick.

I prefer 80 Hz as the crossover, but don't go any lower than that or you will lose the top of the LFE channel on HT as the 1803 sums it with the other low passed bass.

Is the graph shown with the phase set at 180?

1) Just to be sure, double check to make sure each RTi38 is wired in phase with respect to each other.

2) And I agree, you might try 100 Hz with 180 and see how that graph looks.

3) Mess a little with the 38's location-wise and see what happens.

4) Move the meter two feet laterally in either direction and see what happens.

OK, what are your impressions compared to the PSW350?

Doc

[jesyjames]

Do you mean 0 instead of 180? When I had the phase set to 180 is when I was getting dips into the high 50 db range.

180 is what I had my polk sub set at and that was the best setting. So if they really are reversed then it should be zero(and that's what my graphs indicated).

One thing I'm unclear one when I'm charting these response charts is how should I have the speakers hooked up?

Do you guys unplug your mains so you are only testing the sub?

I've tried that, and I've tried running in stereo mode which crosses the speakers over(or so I suspect).

I'm going to play a bit with the position of the 38s. For whatever reason that has never crossed my mind.

One thing I was wondering about, is that since I have the sub calibrated about 4 db hot would that account for some of the difference in the 70-100 range? It would make sense as the sub is running a few db higher than the mains would be... and then at that point where the mains should start kicking in they will be at a lower volume rating.

I'll post a review once I get everything calibrated. This big null area is troublesome. I don't remember having it with the other sub, but it's definetly possible it's always been there.

[jesyjames]

well this is interesting. Moving the speakers amounted to nothing.

Moving the meter two feet laterally in either direction amounted to db reading exactly where it should be...

as I can't move my couch I'm not sure where this puts me. I'm going to replot the frequency response with the new listening position being to the side of center on the couch.

Truthfully if there's two of us watching a movie no one is in the middle anyway.

How wierd.

[Airplay355]

im sorry to hear that, even if i didnt sit in a place where bass was weak id still be pissed off to know that it existed lol

my couch and my bed, where i watch movies, are all in nice bass heavy spots :D happy happy for me lol

[Loud & Clear]

One thing I was wondering about, is that since I have the sub calibrated about 4 db hot would that account for some of the difference in the 70-100 range?

Einstein had a theory.

[Dr. Spec]

Just to be clear, both my 20-39PC+ and my PB2+ have (by far) the least dip at the crossover frequency when set to 180 degrees. And my 800's are not wired out of phase.

Setting my 20-39PC+ to 0 degrees resulted in a 8 dB dip at 80 Hz. Set it to 180 and poof, it's gone. Same thing with the PB2+.

Rooms are funny things. The acoustics will be all over the board, but overall I know people who would KILL for a in-house curve like that. You have a bit of irregularity near the crossover region, and even that goes away when you move the meter to a slightly different location. It probably won't even be audible.

And yes, running the sub hot will of course accentuate the curve below 80 Hz and this might be affecting your overall impression of how significant any problems in your crossover region are, because they really are minor.

Run the phase at whatever setting gives you the least dip (180 for me) at the crossover point, and obviously run all your speakers on small. Try 100 Hz or 80 Hz and pick whatever works best and gives the smoothest transition. Definitely run the sweep in stereo mode only with just the 38's and the other surround channels shut off.

So, what are your impressions of the 20-39PC+ as compared to the PSW350?

Doc

[tryrrthg]

Doc,

Isn't there a way to reverse the phase again by switching the + and - wires on the sub? I think I read that at the HTF, if you switch those you can get 90 and 270 phases. is that true?

[Dr. Spec]

Originally posted by tryrrthg
Doc,

Isn't there a way to reverse the phase again by switching the + and - wires on the sub? I think I read that at the HTF, if you switch those you can get 90 and 270 phases. is that true?

Maybe an EE can chime in here, but AFAIK, reversing the polarity on a phase switch does nothing but make 0 180, and 180 0. The PC+ has a variable phase control from 0-180, but in my experience it is wired reverse polarity, but I don't know why. Regardless, if all you have is a 0/180 switch, that's all you'll ever get.

Doc

[BeginnersLuck]

Originally posted by Dr. Spec
Maybe an EE can chime in here, but AFAIK, reversing the polarity on a phase switch does nothing but make 0 180, and 180 0. The PC+ has a variable phase control from 0-180, but in my experience it is wired reverse polarity, but I don't know why. Regardless, if all you have is a 0/180 switch, that's all you'll ever get.

Doc

You are correct!

-BL