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RE: Unity Horn w/ B&C DE25-16, BMS 4550 o TAD2001?

Posted by tomservo (M) on May 20, 2010 at 08:28:01

In Reply to: Unity Horn w/ B&C DE25-16, BMS 4550 o TAD2001? posted by keto on May 20, 2010 at 06:57:34:

Hi
The unity horn that Lambda sold under license was one of the first horns of that type I had designed (now 11-12 years ago) and came with the De-25 hf driver.

Here is one as applied by a DIY builder;
http://www.cowanaudio.com/unity.html

I know later on, I also did a crossover for a TAD 2001 back when Paul B had them but I would have to look.
The BMS 4550 is a very good hf driver that I use in many of our products at work, it has two things which make it very useful. First, it’s internal origin is also a conical horn, even a one inch driver is large enough to cause directivity or if the wavefront is the wrong shape, radiates higher order modes, bouncing off the walls internally. That driver produces an expanding wave front internally unlike many that produce a plane wave at best or a self interfering pattern at worst. Generally, on a conical horn, the BMS will also have a higher sensitivity up high and down low, on that horn, the hf sensitivity would be a couple dB higher, it tolerates lf excursion better and has a little more headroom...
So far as CD compensation, understand that IF one could make a perfectly constant directivity horn, it’s frequency response will exactly reflect the acoustic power vs frequency that the driver produces.
ALL compression drivers exhibit an acoustic power roll off up high (above 2 to 4KHZ) and all of them have a lower limit set by the suspension stiffness and excursion.

The only ways to get “flat response” is to use a horn that constantly narrows as the frequency climbs (a curved wall horn) or use a filter to correct the drivers efficiency and make it flat again.
Toole and others have shown listeners prefer CD radiation as the reverberant sound field tends to have a response shape similar to the power response so a flat power response AND flat listener response is preferred.
The goal of the Unity was to combine the mid and hf ranges in a way that they combined into one source, for that, the dimension has o be less than about one quarter wavelength, just like the distance required for sub woofers to add coherently. There have been advances but they could be adapted to that horn.

So far as “active vs passive” understand, for flat response, the real or maximum sensitivity is limited by the efficiency of the system at say 15KHz or where ever you choose as your upper limit of flat response. The correction filter attenuates the mid band where the sensitivity is much higher.

So, the questions that come to mind are what measurement gear do you have /or have access to and / or do you live near Chicago or Atlanta?
Best,
Tom Danley

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