[Housteau]

I just finished building my new listening room, actually an expansion and renovation of my previous one.  My next trick will be to properly place and tune my 4 piece system to its new space.  I want to integrate my sub bass columns to the mains for an optimally phased wave launch.  As far as standing wave and acoustics I am in pretty good shape and have a good understanding of those issues and controls.  So, getting the speaker listener interface in good starting positions, which they are close to now, is not so much the issue.



What I am not sure about is the crossover values to use for this.  I will be using a digital type crossover with several choices.  In the past I have used both the Butterworth 12 and 18 as a low pass feeding those sub bass towers and allowed the mains to roll off naturally starting around 68 Hz, and ignored the phase issues.  I was very pleased with the sound, but I didn't really believe it was fully tweaked for optimal performance.  However, this time around since I have been given the chance to start all over again with a nice new room with better acoustics, I want to do this crossover and settings as correct as possible.

This time I thought it would be best to roll off the mains as well.  I was thinking a good crossover point will be between 70 and 80 Hz for both.  If I use a Butterworth 3rd order as both a low and high pass how does that 270 degree phase shift add up?  I have several was to correct this with use of delays and separate phase controls, but to prevent such delays would of course be best.  What is the best way to approach this?  Should the high and low pass be of the same 3rd order slope?  Should I use a 1st order?  In the resulting phase mismatches how much may the sub bass towers lag the mains in ms?


 

[JohnR]

Hi, you'll need to be able to measure it to get things correct. With that said, if your mains  are sealed (?) and are rolling off naturally at ~70 Hz then that's effectively a second order (Butterworth) filter. Adding a second order highpass at the same frequency will turn it into a 4th order Linkwitz-Riley, then set the bass lowpass to 4th order LR.

Looking at your arrangement, I'd be inclined however to put the bass-mid crossover up higher. Say... 120 Hz. In that case you can use whatever crossover slopes on both sides. Set the delay on the mains initially to match the physical offset and then measure and tweak...

[Housteau]

Hi, you'll need to be able to measure it to get things correct. With that said, if your mains  are sealed (?) and are rolling off naturally at ~70 Hz then that's effectively a second order (Butterworth) filter. Adding a second order highpass at the same frequency will turn it into a 4th order Linkwitz-Riley, then set the bass lowpass to 4th order LR.

Looking at your arrangement, I'd be inclined however to put the bass-mid crossover up higher. Say... 120 Hz. In that case you can use whatever crossover slopes on both sides. Set the delay on the mains initially to match the physical offset and then measure and tweak...

The bass section of the mains (approx. 70 - 280 Hz) is sealed.  My older Infinity system was crossed over @ 120 Hz.  I had not considered that high a crossover point for this one by VMPS though.  I guess the reason is mainly because the designer (Brian Chaney) felt that 70 Hz region was best in his testing.  But, I see no reason I cannot experiment around that now.

I had used the distance offset for time in my previous set-up, but had not taken anything into account for the crossover.  I guess what I am not fully understanding is the time (phase) lag due to the crossover selection.  Shouldn't that lag be added to the difference in distance between the two sections in order to create a correction and have the system in proper phase?

[JohnR]

I had used the distance offset for time in my previous set-up, but had not taken anything into account for the crossover.  I guess what I am not fully understanding is the time (phase) lag due to the crossover selection.  Shouldn't that lag be added to the difference in distance between the two sections in order to create a correction and have the system in proper phase?

I've generally found that adjusting the time delays based on "pre crossover" distance (or measured delay) works out pretty well. It hasn't always, but with your bass modules not that far from the mains and out from the wall, my guess is that it would. IOW add the crossover after adjusting the delay. Bass is not always predictable though...

[Housteau]

I have been thinking about higher crossover frequencies.  I am away from home right now and so I have the opportune time to plan out this tuning in process, both pros and cons.  I am thinking that with my room at 21 ft. wide, my bass towers can be placed an optimal distance from the side walls to have them on the ideal 1/5 dimension from those boundaries not to excite room modes.  But, that then places the higher range units nearly spot on the ¼ distance, which will highlight the standing waves of that dimension, both a positive pressure zone and negative depending upon the fundamental.

So, as I see it geometrically, it would be an advantage for the bass towers sitting in ideal spots to carry more of the frequencies normally troubled by room modes, rather than having them assaulted being located further from the side walls in the higher range mains.  Room modes are generally more forgiving to the frequencies above 100-120 Hz.  So, this is certainly worth a try and something I just never thought about before.  Thank you.

[Housteau]

  Room modes are generally more forgiving to the frequencies above 100-120 Hz. 

What I meant was that in my particular room, being 21 ft wide, the fundamentals most harmful are below 100 - 120 Hz.

[SetterP]

Killer rig, but is that Hans Solo cryogenically frozen on your back wall?

[Housteau]

Killer rig, but is that Hans Solo cryogenically frozen on your back wall?

The artist that made that is Patrick Miller as a self sculpture, but his full inspiration did in fact come from Hans Solo being frozen in carbonate.  Back in the day most of his sculptures were science fiction and fantasy based.