Die 18 dB hat der Joe schon lange verworfen, siehe Interview:
"Andre,
I'm up to my behind in alligators right now. You're right, there is much bad folklore on the MTM configuration. People seem to forget that the basic reason for the MTM is to stabilize vertical polar response with respect to frequency. This is accomplished by the geometry alone, regardless of interdriver phase relationships, interdriver time delays due to lack of time alignment or crossover type.
Beyond that, you can examine via simulation, just about any crossover configuration you want. Different crossovers will yield different vertical polar patterns, but all patterns will stay centered on the central axis defined by the central driver, usually a tweeter. In-phase (even-order) crossovers will have off-axis nulls in the vertical direction. The depth of the null and its angular location are a function of the crossover frequency, the interdriver spacing and the crossover order. Laying MTMs on their side
for center channels as you see in so many home theater systems can lead to poor horizontal coverage with in-phase crossovers.
One of the popular myths is that one must use an odd-order crossover to get the benefits of MTM. Nothing could be farther from the truth. The off-axis null with in-phase crossovers is of great benefit in reducing floor and ceiling reflections. Odd-order crossovers have a 90 deg inter-driver phase shift at crossover and generally do not produce off-axis nulls with time aligned drivers. They are more sensitive to lack of time alignment, however, and may in this case also produce off-axis nulls.
My original paper on the MTM covered most of this in great detail, but few people bother to read it. I really don't have time now to say more on this topic. The short essay you suggest will have to wait till I get back from Greece in mid April."
Best regards,
Joe D'App"
Die Con WG trennt akustisch auch etwa mit 24 dB (MT-HT). Und - wie grün markiert - empfielt er (außer bei liegendem Center) auch Weichen, die in Phase sind, wegen der Auslöschungen, um Reflektionen zu verhindern. Das habe ich auch so getestet und als besser empfunden.
Ach ja, und wenn der Joe das als wesentlich nennt, ist ein LS ohne diese Auslöschungen NICHT in seinem Sinne. Man verschenkt Potential. Sorry.
"Andre,
I'm up to my behind in alligators right now. You're right, there is much bad folklore on the MTM configuration. People seem to forget that the basic reason for the MTM is to stabilize vertical polar response with respect to frequency. This is accomplished by the geometry alone, regardless of interdriver phase relationships, interdriver time delays due to lack of time alignment or crossover type.
Beyond that, you can examine via simulation, just about any crossover configuration you want. Different crossovers will yield different vertical polar patterns, but all patterns will stay centered on the central axis defined by the central driver, usually a tweeter. In-phase (even-order) crossovers will have off-axis nulls in the vertical direction. The depth of the null and its angular location are a function of the crossover frequency, the interdriver spacing and the crossover order. Laying MTMs on their side
for center channels as you see in so many home theater systems can lead to poor horizontal coverage with in-phase crossovers.
One of the popular myths is that one must use an odd-order crossover to get the benefits of MTM. Nothing could be farther from the truth. The off-axis null with in-phase crossovers is of great benefit in reducing floor and ceiling reflections. Odd-order crossovers have a 90 deg inter-driver phase shift at crossover and generally do not produce off-axis nulls with time aligned drivers. They are more sensitive to lack of time alignment, however, and may in this case also produce off-axis nulls.
My original paper on the MTM covered most of this in great detail, but few people bother to read it. I really don't have time now to say more on this topic. The short essay you suggest will have to wait till I get back from Greece in mid April."
Best regards,
Joe D'App"
Die Con WG trennt akustisch auch etwa mit 24 dB (MT-HT). Und - wie grün markiert - empfielt er (außer bei liegendem Center) auch Weichen, die in Phase sind, wegen der Auslöschungen, um Reflektionen zu verhindern. Das habe ich auch so getestet und als besser empfunden.
Ach ja, und wenn der Joe das als wesentlich nennt, ist ein LS ohne diese Auslöschungen NICHT in seinem Sinne. Man verschenkt Potential. Sorry.
- man muss den Elektronen also doch vorgeben, was sie zu tun haben 
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