Velodyne SMS-1 PROPER phase adjustment

[Bob_Collins]

Most articles I've read concerning how to set the phase correctly when using the SMS-1 say to adjust for the flattest response at the crossover point, or for the cleanest transition at the crossover point, which in most cases would be 80 Hz., however, isn't the whole point of getting the phase properly adjusted to get your subwoofer and main speakers properly "timed" so they are not cancelling out each other?

Shouldn't you adjust the phase control to give you the flattest response across the entire spectrum below AND at the crossover point? I've noticed that the phase adjustment can introduce some deep cuts in the below 80Hz. response, as well as introduce some large peaks. Also, whether I run my speakers (Klipsch RF-7s) at LARGE and in mixed mode output (both the sub and front L/R speakers produce the low end bass) versus running them at SMALL where they are rolled off and all low end content is fed to the subwoofer, has a direct result on the flattest response, and thus what I believe to be the proper phase adjustment.

Example: Running all speakers at SMALL, flattest response output from the SMS-1 display graph before any EQ applied, phase = 45 (positive). Running front L/R at Large and sub set to mixed, flattest response output from the SMS-1 display graph before any EQ applied, phase = 165 (negative).

Am I correct in that the phase control should be used to give the flattest overall response and not just try to "optimize" the crossover setting?

[Klipschguy]

Most people adjust their phase for maximum output. I disagree. Setting it for the flattest in room response usually sounds much better, IMHO. I use my sub's phase control to flatten out a 40hz hump which is intrinsic to my listening room. With the "room boom" dialed out, the bass takes on an incredibly tight quality. Much tighter with the sub than without (Cornwall mains). You can do it all by ear, but a meter is best (followed by slight tweaks by ear). A continuously adjustable phase control is a very valuable feature for sub integration.

Andy

[Jay481985]

doesn't the sms-1 cross the mains at 70 hertz?

Also I agree with tuning to flatness not maximum output

[Klipschguy]

What kind of slope is the 70Hz high pass?

Regardless, the crossover frequency can still generally be smoothed using the phase control. Room nodes play a big part too. I personally like using a little constructive "destructive phase interference."

You can also experiment with running the mains rull fange. It takes some trial and error to get a system optimally tuned to the listening room. Have fun with it!

A meter and test CD helps. The ear is the final authority.

Andy

[formica]

Two main reasons for adjusting phase at crossover:

- The Phase inherently varies with frequency... regardless if you are looking at subs or tweeters.

- The area which cancellations will occur is where two different speakers are playing the same frequency out of phase.

This creates problems when using two speakers to reproduce a

significant frequency range. They will be in phase at some

frequencies, and out in others. The idea behind adjusting the

phase at the crossover point is based on having ideally the two

speakers types (mains and subs) only overlap in this region.

This can be done by running mains as small and crossing over to the sub

at a typical frequency like 80Hz, or using the mains as large and

adjusting the sub's xover according to the natural roll off of the

mains.

Well, that's the ideal...

ROb

[DrWho]

This issue comes up rather often, so instead of retyping everything I went ahead and created a PDF with diagrams...maybe you'll find it helpful.

subsettings.pdf

[Klipschguy]

If maximum output is your goal, this PDF gives a good description of how to do it. Good for movies, but it may not be the best for music/critical listening. I actually set my set phase for max output for "effects type movies" and conversely, best flat in room response for music (and DVD's requiring tonal accuracy). Really, when you get the music right, movies will still sound good; the reverse is not usually the case.

[DrWho]

Technically this procedure results in almost perfect phase alignment and a flat transfer function

through the crossover region. Max SPL = flat response...any deviation

and you are reducing output in the crossover passband. I only mention

this because you make it seem like "max SPL" is a bad thing when really

it is ultimate ideal goal.

Now if there are peaks in the crossover region - they are going to be

the result of some other issue unrelated to the crossover and should

ideally be accounted for directly. You can

certainly band-aid a peak in the response in the middle of the

crossover region, but chances are the peak decays differently in the

time-domain and has a Q different to that of the crossover - which is

why I intentionally left it out of the pdf. I'm not saying it doesn't

work or should never be used, but in a system with good speakers and an

acoustically treated room you should never need the trick. Also, the

subwoofer(s) need to be within 1/4 wavelength from both mains in order to avoid very different results from happening at different listening positions.

Nevertheless, if you find the need to mis-align the phase to reduce a

peak in the crossover region, you should still go through the steps listed out in

the pdf to give yourself a starting point.

I am curious though why you feel the need to return to the non-flat

frequency response when watching movies. I would think it would reduce the

perceived low frequency extension of the system - what crossover point

are you running?

[Klipschguy]

DrWho,

It is a good starting point, and your input is always appreciated, however many rooms will have a big fat nodes which make the bass boomy (as you know). My room has one at 40Hz. Setting my sub at max output per your PDF results in +12dB peak @40Hz. It probably wouldn't happen outside, or in an anechoic chamber, but it does in my listening room (according to my meter).

For my particular situation I get the flattest response by running my Cornwalls full range, placing the sub between the mains (or pretty close) and using the phase control to null the 40Hz peak - it does this VERY well.

Since the Cornwalls fall like a rock below 40Hz, the sub comes back on line to give me +1Db @ 25Hz. Flat @ 40Hz (all relative to 1000Hz) . The room boom is gone and the Cornwalls sound much tighter with the sub than without because the room node has been nullified. Indeed, the best response is at my listening position, but the overall efect is postive elsewhere in the room.

Also, I like to set my sub's phase control for max output for "effects type" movies because the 40Hz peak makes explosions more exciting - especially for the kids. I feel free to break the rules of audio at times. Most movies I leave it alone, i.e. Walk The Line sounds much better in the "music mode."

I am not trying to knock your technique, I am just trying to give other ideas which can be used to tackle the often difficult job of sub integration. That is why I said "Experiment and have fun" in one of my earlier posts. Cookbook recipes are nice (and often the best way to go), but many times people use the recipe to the letter and tell themselves "that is the best it can be!!!" when in fact they are not even close.

Andy

P.S. 40Hz is my lowext crossover point, If it went to 30Hz it would also be useful for tuning that nasty 40Hz node!!