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In Reply to: RE: Summary article on importance of transients over pitch posted by Satie on September 17, 2014 at 12:01:43
The MTM arrangement does not require any particular crossover. In fact, the original D'Appolito scheme did not use a 4th-order acoustic network. It was designed as a 3rd-order network to facilitate a less abrupt change in power response. I've seen the MTM arrangement implemented as everything from 1st-order to 4th-order. :)
The MTM arrangement has some disadvantages but the primary advantage outweighs many of those.....IMO. The twin woofers add to a 6db sensitivity increase which generally matches that of many stock tweeters. Thus, you can usually design a crossover network with minimal/no attenuation on the tweeter and have system sensitivity approximately 6db higher than an MT version with the same drivers.
On the Froy design, the CR is not part of the notch filter and the system impedance curve follows that of a typical MTM implemented this way. There is no impedance leveling network employed on the Froy design. If there were you would see an LCR series network connected in shunt with the input terminals.
All LR4 crossovers exhibit a 360 degree phase shift. It has nothing to do with the drivers unless the crossover point is fairly close to the driver native acoustic roll-off point. You can see an excellent example of this with the Froy design.
Cheers,
Dave.
Follow Ups:
I should have said that it is better executed with a steep XO (acoustic and electric combined) slope and has a narrow vertical sweet spot. My friend with the Focal Utopia has to choose chairs with the right height to match the angle of the speakers.
Thanks for correcting me but I still don't see the 4rth order network in the Froy schematic.
It's 4th order acoustic, not electric. You have to take driver characteristics into account. And if it were 4th order electric in this case it wouldn't be really 4th order. It would be higher order. You need a good computer program to get the transfer function you want. If you just take nominal driver values and do a textbook crossover, you get nothing like what you think you are.
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