Can you adjust the phase between subs and mains?

Originally, I used a Paradigm X-30, later the SMS-1, on my Servo-15. The advantage of the latter is the visual display that makes the tweaking easy.

Kal

I'll second the Velodyne SMS for the same reason as Kal. I'd also note that the 2 controls on the SMS; "phase" and "polarity" (I'm not sure how 180 degrees of phase differs from polarity) were absolutely critical to achieving smooth integration of subs and mains in my system. I was PEqing and tweaking the x-over points/slopes trying my way toward a flat response on video and couldn't get it quite right until I flipped polarity. Instantly, I got a great, almost flat line through the x-over frequency and the results are dramatically audibly superior to the earlier settings.

Marty

"I'm not sure how 180 degrees of phase differs from polarity."

"Dumb question, but what's the difference? Don't they both insert a time delay?"

Polarity is a simple inversion of the electrical signal across all frequencies and is either 0deg or 180deg. All of the signals are inverted in phase with this.

Phase, however, is frequency sensitive in that delaying a signal by a finite time will change differently the phase of each frequency, measured in degrees. For example, delaying a signal such that a particular frequency F is shifted 90deg with respect to the original signal will shift by 180deg the signal at 2F and by 45deg the signal at 0.5F.

Kal

Kal,

That explains my experience in which the offset 180 degree phase setting and inverted polarity setting on the SMS yielded very different results.

Marty

Yes. The phase shift adjustment is, afaik, centered on 80Hz, the nominal crossover but the phase change would be different below that. With a polarity inversion, everything would be 180deg changed.

Kal

Ken,

Well that explains EVERYTHING !!!!

When I looked at your system I simply couldn't figure out why the roof of your house was still there. I mean why doesn't it simply blow off?

Be warned! With the kind of high quality parts and superb build of your speakers if you do actually ever get the phase precisely right between the subwoofer and your front three channels then as they say "Houston, We have lift off"

Shadorne,

Phase was one of the most important points I had to address when building the speakers. The more drivers you use, the greater chance you'll have phase issues.
All the drivers in the three front towers are time aligned with respect to each other. By using only active crossovers throughout I greatly reduced the phase anomalies associated with passive xovers. It also made level adjustments much easier without wasting power.

Having the subs behind the front towers presented a phase issue that was addressed by the time delay settings for each speaker by the Krell processor.
While it enabled me to dial in the distance from my ears to each of the speakers, in feet, it offered no fine tuning. The Phaser should be the fine tuning device, when I finally get around to hooking it up.

The subs xover at 60 hz at 24 db per octave. An spl measurement for maximum level using a 60 hz signal at the listening position should do the trick. How it will sound at any other spot in the room will be interesting but inconsequential.

Using a self powered sub with the adjustments incorporated has got to be the cat's meow but being a DIY guy, that option didn't exist. I'm looking forward to hearing the difference the Phazer will make, I think I'll try it tonight.

Ken

Ken,

The phazer device appears to be just a variable delay. I don't think it does any more than the delay setting in your DSP amp. If you want to perform phase compensation across the bass between the mains and subwoofer then you'll need to examine the phase of each speaker design (F3) and build phase compensation into the active circuits going to each speaker so they match.

At the listening position (far back) you have a lot or room modal reflected energy affecting your test signal - you might be better off nearfield to make precise phase adjustments - just two cents.

Shadorne,

You're exactly right!. It goes just before the bass amps and shifts the phase from zero thru 180 degrees and will also invert the phase to allow adjustment thru a total of 360 degrees of one full cycle. I guess it's the same as if the processor allowed infinite spacial adjustment rather than just in full measured feet; ex 15, 16, 17 feet etc.

I'm going to check the results at various distances to see what happens, good suggestion!

Ken