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Re: horn stuff and final conclusions

Hi Wayne

When you look at the polar plots, keep in mind the size of the enclosures, because the horn mouth is the entire front side of the enclosure, the
td-1's for there size have about the highest directivity and "front to back" ratio possible.
Most all speakers of similar size radiate significantly more energy outside the pattern than the td-1.

Being on Art Bell's radio show was weird, and I was really sleepy by the end.
Boris the film's director talked me into it and being on the Laura Lee show.
Too much voodoo for me though, While it was a cool trip and very interesting, some of the new age stuff gets a little thick.
If you didn't, read the article in Live Sound, it kind of gives the flavor of the place.


I have to keep this short but there are a couple points.

Your say that the horn does not load above the low cutoff (true) set by mouth size and above some frequency, hence hf roll off (not true).

Look at the radiation resistance curve for any shape horn and one finds that it is a "High Pass filter", not a low pass filter.
It has NO inherent high cutoff (and there isn't one on the graph), once the horn is "large enough" , it presents the radiation resistance of air above
that frequency.

The horn presents a more or less CONSTANT acoustic load above the low cutoff so saying the Unity doesn't "load" over a broad band is
wrong.
The compression driver we use can only produce a constant acoustic power to about 2 - 2.5 KHz because of its moving mass to motor strength
ratio and this fall off in acoustic power is what is compensated with the network.
Again, this roll off has NOTHING to do with horn loading or not loading, it is the particular drivers electromechanical properties.
Different drivers give different roll off points, it IS the driver not the horn.


You talk about the drivers being a moving target and wandering around in time.

The Unity design does not free one from what the drivers do in the operating band, to what ever degree the acoustic phase is not zero or
changes, the drivers do move around in time, like any other speakers drivers.
What I did was to try and make the mid and lower sections as close to zero as practical in the operating band so it "moves" very little.
At zero degrees the drivers only have fixed delay which can be determined, there is no movement in time from that delay.
The compression driver is also fairly highly acoustically loaded and in the lower part of its range where the radiator has mobility, it is near zero as
well.
Look at the plot I am sending, it shows a near perfect alignment in time and near zero acoustic phase (fixed acoustic position vs frequency).
Hey, where should I send it by the way.
Think how different that is compared to a direct radiating point source at its -90 degree avg. phase or multiple sources in multiple physical
positions.

Your concern about parallax or interference from adjacent sources is valid, however the spacing involved and operating frequencies are such that
it is not an issue. The polar plots for example are 5 degree, 1/6 octave measurements and if there were interference as you describe, it would
seriously effect the polars.
One thing the Unity does is produce the radiation pattern of a single source even though there are multiple drivers, this is only possible because
the drivers are "close enough" to let it happen.

Wayne, the Unity isn't a miracle, it is my current best shot at eliminating the interference and time issues present in nearly all other multiway
speaker systems. You have to think of this from my perspective for a second. My job has mostly been building weirdo transducers, many for
acoustics.
For 17 years i worked under a rule that we should not use conventional drivers for anything so what ever we sold, it used a driver we made.
At Servodrive when I went to work directly for them 3 years ago, I suggested we start with conventional drivers to get the company going.
I gave this Unity design some good thought but on the other hand it is not as difficult as some of the things in Acoustic levitation.

The thing is , they DO work, the significant success in difficult rooms has sparked a quiet fire in the Church Sound market, nothing available
commercially stands up to a side by side demo in quality or intelligibility.
Cleveland Symphony Orchestra's Blossom Park had a new sound system installed.
The contractor measured all the boxes in consideration and picked a Meyer box, about $8,000ea.
A friend of the contractor told him about the td-1 and brought one by to play with.
Not only did the td-1 give the best RT-60's and intelligibility indexes but the Conductor said "THAT BOX, NO SUBSTITUTIONS" when he
heard them side by side with the others. There are now 57 td-1's in Blossom park.
I know your not going to buy one but I hope you can hear one eventually, they really do work.

Got to run, let me know where I should send the plot.
Cheers,

Tom

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