Variac said:
and it bothers me that the designer can't seem to decide the precise box size
Is one thing deciding the alignment of a driver for yourself,
another telling other people what alignment to use when
there is such a spread of choice for that particular driver.
Try it yourself.
sreten.
I can't figure out what you are saying here.
All I was saying is that I was considering building the Eros, that Navin linked to, dicovered discrepancies between his written instructions, and the dimensioned drawings and hesitated, to try to resolve these, (which were actually pretty small differences I guess )
I think the designer was tired of discussing the speaker and just kept saying that there were no inconsistancies when others also pointed them out.
I then got distracted by another design.......
All I was saying is that I was considering building the Eros, that Navin linked to, dicovered discrepancies between his written instructions, and the dimensioned drawings and hesitated, to try to resolve these, (which were actually pretty small differences I guess )
I think the designer was tired of discussing the speaker and just kept saying that there were no inconsistancies when others also pointed them out.
I then got distracted by another design.......
>speed of sound 1180ft/s. 1180*12/11 = 1300Hz. that means polar interfereance starts at 1300hz.
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Hmm, this assumes a ~102 degF temp. Not uncommon in a prosound app, but ~1130-1135ft/sec is more realistic in a typical HIFI room. BTW, polar interference begins as soon as two point sources are shifted out of phase, it just reaches a point of unacceptable comb filtering beyond ~1WL.
Here's a nice little treatise on MTMs: http://www.birotechnology.com/articles/VSTWLA.html
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>Also, the narrower focus of MTM is claimed by some to help imaging since it cuts off more reflections from the side walls of the room, so maybe as in all speaker design, there is a trade offf? stage width for imaging?
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Of course, though the trade off of limited off axis response is an increase in both sounstaging and imaging, just listen to a large FR driver that beams over a considerable portion of its BW, or large 40-60deg horn system.
GM
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Hmm, this assumes a ~102 degF temp. Not uncommon in a prosound app, but ~1130-1135ft/sec is more realistic in a typical HIFI room. BTW, polar interference begins as soon as two point sources are shifted out of phase, it just reaches a point of unacceptable comb filtering beyond ~1WL.
Here's a nice little treatise on MTMs: http://www.birotechnology.com/articles/VSTWLA.html
====
>Also, the narrower focus of MTM is claimed by some to help imaging since it cuts off more reflections from the side walls of the room, so maybe as in all speaker design, there is a trade offf? stage width for imaging?
====
Of course, though the trade off of limited off axis response is an increase in both sounstaging and imaging, just listen to a large FR driver that beams over a considerable portion of its BW, or large 40-60deg horn system.
GM
Some homework on MTM inter-centre spacing
Did some looking up of some MTM kits, thanks to Variac's pointer to Zalytron.com. It almost appears that they are the single largest collection of MTM kits around. Here are some data points I found.
The Seas Thor kit seems to be a top-quality (will this qualify as "high-end"?) design. It has an xo freq of 2.5KHz and an inter-centre spacing between M and T of 152mm, or about 6". Double this and you get the M-to-M inter-centre spacing.
Ditto, the Seas Odin Mk III. Both this one and the Thor seem to use the same set of drivers, BTW.
The Froy Mk III has a lower xo (2.2K) and a smaller distance (133mm instead of 152). So it's done both the things to reduce comb filtering as per prescribed text. The Froy is using smaller midbass units, so it can easily reduce the spacing. The xo freq lowering is a different matter. It's interesting that all three use the same Seas Millenium, and if it can go as low as 2.2K on the Froy, I guess it could have done that on the other two. Yet, the designers seem to have left the higher xo freq in the other two.
The Aria 7 kit uses two Focal 7K4411 woofers and Focal TC120TDX tweeter, and has an M-to-M inter-centre spacing of more than 12 inches. Xo freq: 3KHz. (I believe the Aria series was designed by Joe D'Appolito himself?)
The Aria 5 too has a 3Khz xo freq, but has smaller midbass drivers and a shorter M-to-T distance (4.75").
Interesting....
I am sure in my design I can get the inter driver spacing to be less than 152mm (M-to-T). And my xo freq will be 2.5K, if I stick to what I've decided so far. It appears that with this set of values, there isn't too much lobing or other audible problems with the THor and Odin. Does this mean it'll be good enough for me? (And thanks, Variac. )
Did some looking up of some MTM kits, thanks to Variac's pointer to Zalytron.com. It almost appears that they are the single largest collection of MTM kits around. Here are some data points I found.
The Seas Thor kit seems to be a top-quality (will this qualify as "high-end"?) design. It has an xo freq of 2.5KHz and an inter-centre spacing between M and T of 152mm, or about 6". Double this and you get the M-to-M inter-centre spacing.
Ditto, the Seas Odin Mk III. Both this one and the Thor seem to use the same set of drivers, BTW.
The Froy Mk III has a lower xo (2.2K) and a smaller distance (133mm instead of 152). So it's done both the things to reduce comb filtering as per prescribed text. The Froy is using smaller midbass units, so it can easily reduce the spacing. The xo freq lowering is a different matter. It's interesting that all three use the same Seas Millenium, and if it can go as low as 2.2K on the Froy, I guess it could have done that on the other two. Yet, the designers seem to have left the higher xo freq in the other two.
The Aria 7 kit uses two Focal 7K4411 woofers and Focal TC120TDX tweeter, and has an M-to-M inter-centre spacing of more than 12 inches. Xo freq: 3KHz. (I believe the Aria series was designed by Joe D'Appolito himself?)
An externally hosted image should be here but it was not working when we last tested it.
The Aria 5 too has a 3Khz xo freq, but has smaller midbass drivers and a shorter M-to-T distance (4.75").
An externally hosted image should be here but it was not working when we last tested it.
Interesting....
I am sure in my design I can get the inter driver spacing to be less than 152mm (M-to-T). And my xo freq will be 2.5K, if I stick to what I've decided so far. It appears that with this set of values, there isn't too much lobing or other audible problems with the THor and Odin. Does this mean it'll be good enough for me? (And thanks, Variac.
)
navin said:
Isn't the premise of the MTM design that the output sums to reduce lobing with reasonable M-T spacing and a standard filter?
IIRC, Joe D'Appolito's Speaker Builder article (early 80's) showed that with 3rd order filters the output sums to pretty even vertical dispersion. I think he also showed a 4th order LR filter produces a pretty strong central lobe.
I think you are right!
Select the new Odin kit at
http://www.madisound.com/
and you will discover that it is also designed by D'Appolito.
Brian GT made a pair of Odins and likes them a lot. They are certainly intended to be high end.
Select the new Odin kit at
http://www.madisound.com/
and you will discover that it is also designed by D'Appolito.
Brian GT made a pair of Odins and likes them a lot. They are certainly intended to be high end.
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