W/M/W alignment for bass?

[will33]

Reading some m/t/m quasi-D'Appolito stuff about lobing, control over room reflections etc. but can't seem to figure out if it would be of any benefit lower in frequency like a 12-6-12 setup. It wouldn't be a real D'Appolito anything really, just something different, I'm really not sure what slopes are even used in my 800rb's crossover, could find out. When I flip my top cab over so the mid is about a foot lower, I can still hear it fine up close to the rig. Doesn't seem to be any disadvantage to doing this but is there really any advantage?

 

[BurningSkies]

Here's what I do for much of the time:

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[will33]

Here's what I do for much of the time:

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Right. Your rig is a good deal taller and higher performance than mine. I would imagine it's a benefit just to get that hot mid out of your ear. Can't figure out what it might do to dispersion patterns, etc., or if it would even matter in a live bass rig. May do it anyway, just for something different, as long as there isn't a real downside.

 

[BurningSkies]

It was suggested to me by Greenboy through a few conversations that we had. It also is suggested when people have two mids (and a reverse baffle) so that it puts the mids aligned vertically and close to each other. I don't think it does much to damage your end output since the speakers are crossed over and representing different frequencies, and the 15's are still roughly the same distance apart.

It very much keeps that screaming loud 6" speaker out of my ear, while I can still hear it plainly, and means what I'm hearing when I'm standing on top of my rig (on a tight stage or small room) is closer to what is going on in the room. Otherwise I find that I'm attenuating my mids much more than needed.

 

[will33]

Well, it seems the 800rb's crossover specifics aren't exactly readily available info. One of my search results was a thread at Bill's site where somebody was trying to pin down some problems with his. Some of the plots look like they could be 12db/octave but they're hard to read and that guys wasn't functioning properly, being an octave or more short of the goal at higher settings. Mine may not line up exactly with the label numbers, but sounds like a much wider range than that, at least somewhat close to the 100-1k it's supposed to have.

 

[will33]

It was suggested to me by Greenboy through a few conversations that we had. It also is suggested when people have two mids (and a reverse baffle) so that it puts the mids aligned vertically and close to each other. I don't think it does much to damage your end output since the speakers are crossed over and representing different frequencies, and the 15's are still roughly the same distance apart.

It very much keeps that screaming loud 6" speaker out of my ear, while I can still hear it plainly, and means what I'm hearing when I'm standing on top of my rig (on a tight stage or small room) is closer to what is going on in the room. Otherwise I find that I'm attenuating my mids much more than needed.

Ya, mine doesn't run that hot, but still, when I set things right from out in the room, it sounds pretty middy/bright on stage. But I've just come to expect that with any cab when carrying the room with it.

 

[billfitzmaurice]

is there really any advantage?

The same advantage as in a hi-fi MTM, vertical pattern control.

 

[will33]

Cool, thanks Bill.

 

[will33]

So, from what I've read of this alignment, with certain crossover slopes, there should be a pretty good null zone when I stand close to the cab, more than there would be from just figuring off-axis angle and beaming of the cone?

I take it a true vertical pattern is needed to get this? When I just flip my top cab over, the mid is still off center and I can still hear it clearly up close.

 

[billfitzmaurice]

So, from what I've read of this alignment, with certain crossover slopes, there should be a pretty good null zone when I stand close to the cab, more than there would be from just figuring off-axis angle and beaming of the cone?.

No. There are many misconceptions about the MTM alignment, this is one of them. I have a pretty fair understanding of them as a colleague of mine at AudioXpress magazine, and at Speaker Builder before 2001, is Joe D'Appolito, who invented the MTM. The radiation pattern is independent of the crossover slope.

 

[will33]

No. There are many misconceptions about the MTM alignment, this is one of them. I have a pretty fair understanding of them as a colleague of mine at AudioXpress magazine, and at Speaker Builder before 2001, is Joe D'Appolito, who invented the MTM. The radiation pattern is independent of the crossover slope.

Aha.....thanks.

I'll have to dig up wherever I read that and correct them.
Some hi-fi site.
I guess the guy incorrectly identified pattern control as a null zone when he stood up off his couch.

 

[billfitzmaurice]

Aha.....thanks.

I'll have to dig up wherever I read that and correct them.
Some hi-fi site.
I guess the guy incorrectly identified pattern control as a null zone when he stood up off his couch.

Well, of course the pattern control of the woofer output only extends as high as the woofer response, which is determined by both the corner frequency, slope and Q of the filter. But the actual action of pattern control is defined by the cone size and CTC spacing.

 

[BurningSkies]

Aha.....thanks.

I'll have to dig up wherever I read that and correct them.
Some hi-fi site.
I guess the guy incorrectly identified pattern control as a null zone when he stood up off his couch.

I often get a head rush when I get up off the couch too...

 

[will33]

As always, very informative and helpful, Bill. I'd read a bunch of stuff about certain crossover slopes defining the D'Appolito alignment and couldn't comprehend it. Then found other stuff about Mr. D'Appolito modifying the alignment with steeper slopes or something that seemed to contradict what I'd read earlier. Couldn't make heads or tails of it.

 

[will33]

I often get a head rush when I get up off the couch too...

That may have as much to do with it as anything.

Whatever site this was I swerved into down some internet rabbit-hole, these guys were trying to define what was a "true D'Appolito alignment" and what sort of cheaper versions would simply be refered to as "mtm". The crossover slope used was one of their defining factors, but I guess they were mistaken. It's one reason I was trying to find out what slopes my amp uses trying to predict what would happen with that driver alignment.

 

[DukeLeJeune]

The original MTM article by D'Appolito specified a horn-loaded tweeter and third-order crossover slopes, as this resulted in more unifom vertical coverage than 2nd or 4th-order slopes.

If I remember correctly, in theory even-order crossover MTM's have symmetrical nulls above and below the horizontal axis, whereas odd-order crossover MTMs result in each woofer producing a single null in one verrtical direction only; for example, the upper woofer produces a null above the horizontal plane, while the lower woofer produces a null below the horizontal plane (the nulls could also be on the opposite side of the horizontal plane from their respective woofers, depending on the tweeter polarity). The good news with the odd-order crossover is, the woofer that's not nulling in that direction fills in the response where the other one is nulling, so the net pattern in the vertical plane is more uniform. At least, that's my recollection of the theory.

D'Appolito's landmark article was actually predated by the Meridian M2, which was a highly innovative, compact MTM active system. I believe the M2 came out in 1981, two years before d'Appolito's paper.

Given that D'Appolito himself has designed commercial systems that do not adhere to the guidlines in his original paper, I'm not sure where one would draw the line between what is and is not a "true D'Appolito alignment".

 

[billfitzmaurice]

Given that D'Appolito himself has designed commercial systems that do not adhere to the guidlines in his original paper, I'm not sure where one would draw the line between what is and is not a "true D'Appolito alignment".

He admits that strict adherence to his original guidelines aren't necessary.

 

[Jeff Scott]

D'Appolito's landmark article was actually predated by the Meridian M2, which was a highly innovative, compact MTM active system. I believe the M2 came out in 1981, two years before d'Appolito's paper.

IIRC, I bought a pair of RTR speakers in 1979 that had a D'Appolito configuration. Perhaps he allowed his concepts to be put into speakers systems before his paper was published?

 

[T-Bird]

Hi.

IIRC, I bought a pair of RTR speakers in 1979 that had a D'Appolito configuration.

Care to elaborate?

The physical arrangement of the drivers, or the electromechanical design?

AFAIK, ( I obviously wasn't around reading about speakers back then ) the 70's were the awakening period in Hi-Fi speaker systems as we know it today, and everything was being researched by multiple parties all over the world. Some got their names on the eyes and ears of the general public, some are known only to the die-hard Hi-Fi nerds .


BTW, has anyone here tried the D'Appolito approach with a Driverack type of control rather than the quite elaborate passive cross-over it requires?

Regards
Sam

 

[billfitzmaurice]

BTW, has anyone here tried the D'Appolito approach with a Driverack type of control rather than the quite elaborate passive cross-over it requires?

Regards
Sam

The MTM does not require an elaborate crossover. A standard 2nd order LP/3rd order HP works well. The only caveat is that for best results the crossover must be purpose designed for the drivers used, and to really get it right the crossover point also compensates for the baffle step. But those factors apply to all well designed speakers, not just MTMs. The advantage to a good DSP active crossover is being able to quickly dial in the best combination of corner frequencies and slopes, rather than going through the involved process of choosing components with a passive.