high cross point d'Apolitto

[SunRa]

Hello,

What are the problems when crossing a MTM, d'Apolitto configuration at more than 3Khz?

[SY]

Horizontal dispersion, same as when you cross over anything too high. The lower driver's pattern starts narrowing, then as the upper driver comes in, the polar pattern spreads out. You see this in off-axis measurements as a large dip and peak. As a consequence, the reverberant energy (and thus power response) becomes very non-flat and the speaker will sound colored in anything but a very absorbent room.

[sreten]

Hi,

The vertical lobing of an MTM is much worse that an MT, and gets
worse the higher you c/o.

Also the vertical dispersion of an MTM is poor compared to an MT,
this "focussing" is claimed to be an advantage for HT, again it
gets worse the higher you c/o.

/sreten.

[SunRa]

SY, sreten,

Thank you for the reply.
While I did a more careful search on the subject, I found myself wondering if a digital crossover would allow me the higher cross point by delaying the drivers signal. This way I could emulate a coaxial design, with no lobing problems. Aditionaly the space between drivers will be reduced and the tweeter mounted to help the delay.

Furthermore, a dsp would resolve crossover and driver phase related problems.

All this I think I could implementate with brutefir and drc. Do yo think the trick could hold up?

[SunRa]

Well, no one can give me a hint here?

[planet10]

In an MTM the maximum XO is determined by the centre-to-centre spacing of the 2 Ms. The only way to get a higher XO to work well is to use smaller Ms.

dave

[bjorno]

....hint here?

b

1(1)

[SunRa]

planet 10 and bjorno,

thanks for the input. Well I've used the same program to simulate this, only that I've set the distance between drivers near 0. The reason is that I think I can emulate this effect by delaying the signal to the drivers so that I have virtualy no distance between. I wonder if someone tried something like this...

I know Linkwitz uses some kind of delay to his Phoenix baffle (an MTM also), but I don't know if this is his objective..

[HiFiNutNut]

Hi,

I think in the Xdir the distance refers to the actual physical distance between the tweeter and the woofer.

What I am not sure is the "Woofer Phase lag". Is it calculated from the tweeter offset to the driver distance? or is it the actual phase difference of the two drivers taking into account of the XO network, baffle step response, and the natural driver rolloff characteristics?

I found that when the "Woofer Phase lag" is around 90 then the polar response can be acceptable even if the driver distance is a bit longer or the XO point higher. When it is around 0 then the polar response is totally unacceptable. How can this happen? Why people do time-alignment then? But what is the definition of "Woofer Phase lag" in the first place?

I hope the experts can shed some lights.

Bill

[tinitus]

As far as I know you will have to cross lower than 2khz to get a true d`appolito alignment, and use very small mids to get them close enough, and you will have to use steep filters because of the low cross point

Coherense is often forgotten, which means that the mids should play highs of the same quality as the tweeter, and the tweeter should play the mids of same quality as the mids does - just like the bass needs to play mids of same quality as the mids does, and so forth ... kind of logical, isnt it
Its possible but not easy

Remember that with MTM you will need to have tweeter precisely at listening height or theres a big risk of phase problems - generally I dont like it because it results in a very tall speaker, but with the use of multiple drivers you may have to use such designs

Another option could be the use of a wide front, which would make the small drivers act like bigger ones with loss of disspertion .... and maybe more coherent