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Subwoofer X/O frequency experiments

I have really been going crazy trying to find the best X/O frequency for my elaborate 6-driver subwoofer set and my three Maggie MG1.6. I finally had the thought that the optimum frequency depends on the kind of music being played. So I bought an electronic crossover that I can locate in the listening room and make various adjustments (including X/O frequency) while music is playing. (My old X/O was located in the cellar with my power amps, and the frequency can only be changed by plugging in a different module…not very convenient for experimentation). Initial tests confirm what I thought.

First I played a CD of Wurlitzer theatre organ music. Heavy duty bass! No doubt that the best results were with the X/O set to 300-400Hz. Not all subwoofers can do 400 Hz, but mine can. Interestingly when I cranked it up to about 800Hz harmonic distortion became evident, but not unpleasant…it sounded exactly as if the organist had pulled out another stop. Organ pipes produce very pure tones, and little pipes are played simultaneously (via stops) so as to produce harmonics and make it sound nice. I did the same thing electronically. Sort of “tube amp sound”.

Next I played a Mozart Symphony DVDA (MDG 940 0967-5). Again this is a massive complex sound source, mostly loud, and 130 Hz or thereabouts seemed best.

Last I played a DVDA Emmylou Harris, Producer’s cut (Warner R9 78174). On this one anything over 50 Hz was bad. It has the usual pop music bass line, probably exaggerated to sound better on inferior systems.

I know that the audiophile party line is that the subwoofer should be crossed over where the main speakers roll off, generally below 50 Hz. This is a “safe” bet if you have to pick one frequency and stick to it. Been there, done that. However, I suggest that there is (or ought to be) a significant overlap of frequencies that both the main and the subwoofer can reproduce well, and that the optimum X/O varies depending on the music.
eldartford
eldartford OP
4,262 posts
 
Davehrab...What you explain is the conventional wisdom, and what I described as a "safe bet". In many, but not all, cases significantly higher X/O sounds better.
davehrab's avatar
davehrab
380 posts
 
... "safe bet".....

Eldartford, I'm surprised at you. A man who works with precision guidance controls using a "safe bet".

Would you accept a "safe bet" if you where targeting that "Russian school filled with 18 year old blond women".... I think not!!

I should have prefaced my comments by saying they applied mainly to box speakers, in fairly rectangular shaped rooms.

Now, with your Maggie's or any other panel or Stat's type speaker ... all bets are off.

Certainly the room can cause "anyone" it's share of the problems. I think the sub sometimes takes the rap for a bag room. It only takes a few bad room modes, in the mid and upper bass, to give that sub a reputation for being slow, bloated, and a-musical.

After you go through enough subs, with the same results, you come to realize it's your ceiling's 7 foot height that is causing a 70hz peak, and maybe the last 3 subs weren't really the bad guys.

Tough challenge seem the sub to the mains, and then that package to the room.

>>"my elaborate 6-driver subwoofer set"<<

Man thats AlottA warheads

Dave
eldartford OP
4,262 posts
 
Davehrab...Hey, those Russian babes really got to you! I am sorry to say that they are about 21 by now, but still quite desirable.

With regard to "safe" design decisions, military stuff is much more conservative than commercial. The consequence of error is worse (like that Chinese Embassy). Our chips, for example are larger and run slower than commercial functional equivalents (but they can fly through a nuclear fireball and still work).

My recent observations are based on planar speakers, and an unusual subwoofer array, but I think that similar results will be seen with box speakers. The important factor is a subwoofer that doesn't conk out at 100 Hz, but you would want that anyway even if you crossed over at 50 Hz.
gregm
3,395 posts
 
The important factor is a subwoofer that doesn't conk out at 100 Hz...
True, especially to avoid sub drivers' distortion as the frequency goes up.
Generally speaking, I've noticed that most of us use subs as woofer complements, i.e. to offer extra energy that's lacking in the 90-40Hz region -- rather than to introduce energy in the 16-40 region.
The difficulty with most subs is, drivers cannot reproduce both (say) 16Hz & 300Hz (about 4octaves!) signals at the same time w/out some form of distortion and major difficulties in blending with the sats. They hit mechanical & electrical limitations. With the sub set high the resulting sound in the room may "sound" pleasing at first, but, the reproduction anomalies quickly show up in classical music (to cite one example).
eldartford OP
4,262 posts
 
Gregm...What you say suggests that the subwoofer should really be two-way, 20 to 50 and 50 to whatever, and I agree with this. Each of my three subwoofers consists of two drivers, 15" and 12" driven by separate power amps, and I have actually tried the two-way subwoofer thing. It doesn't seem worth the trouble, so I use both drivers through the full SW range so as to take advantage of maximum cone area to minimize cone excursion. Perhaps because the cone excursion is much less than most SW, my drivers (remember there are six of them)don't have the IM distortion problem which you describe...not to any noticable extent.
"Blending" with the main speakers is also not a problem even with the higher X/O frequency. My SW are located directly (2 ft) behind the MG1.6, and off the floor so that their sound goes through and around the Maggies, just as if the Maggies were producing it.
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