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Unity Horn Curves

Here are some curves for the Unity Horns.  The frequency response curves are done with 12th octave smoothing, the least amount possible and with a one sided Bingham window taper for the MLS (again least amount possible).

I was told that there is evidence of noise being present in the graphs, well I will admit that I have about the opposite of an anechoic environment, there is constant noise here in my shop as I can hear it myself (so I know the microphone can hear it).  This means that the true curves for SPL are probably much smoother than these, at worse case, they are at least equivalent.  We also did the curves with much less smoothing than is typically used in the industry.  I consider using alot of smoothing a way of "smoothing" over the truth.  Smoothing can hide alot of problems with a speaker, and I have NOTHING to hide here.

Before heading further realize that no horn will be as flat in the frequency response as a standard dome tweeter.  The horn by way of its acoustic loading however will give a near flat acoustic phase response.  This is where dynamics and realism are to be found, and is what horn fans are so fond of.

This horn has a super flat frequency response though, in both the on axis and off axis!

I have been learning alot about horns recently, and one thing odd is that no matter the compression driver I use, it has a flatter response (on the Unity Horn at least)  at 15 degrees off axis and the on axis is the roughest area.  I highly recommend for critical listening to be done with the horns at a slight angle to you.

This is a Constant Directivity Horn which is the best shape possible!  How can we say this?  First a Constant Directivity horn has an off axis that closely matches the on axis, ALL other horn shapes cannot do this.  Rather they (Tractrix, Exponential, etc.) reduce the directivity at higher frequencies which not only kills the off axis frequency response, it gives that "head in a vice" super small sweet spot.

The Unity Horn because of its linear off axis response actually

IMAGES!!!

Yes this horn images quite well, the sweet spot is super large, you do not have to play "musical chairs" to hear what the speaker is doing!

(Musical chairs is when there is only one good seat is in a room in front of the speakers, and everybody has to take a turn sitting in it.  I know many of you have experienced this)

Rather now get a wide couch and everybody will be happier, including perhaps the "significant other" who usually has the final say on your speaker selection.

Second the Constant Directivity Horn has the lowest "throat distortion" of ANY horn be it Tractrix, Exponential, etc..  Proof of this is found in the incredibly low T.H.D. measurements that many amplifiers would be proud of!  Read the distortion measurements below yourself.

DISTORTION MEASUREMENTS

As reported by Tom Danley the inventor of the Unity.

"The measurements were taken with a HP Dynamic signal analyzer and in some cases involved subtracting the real and imaginary parts of the amplifier distortion from the real and imaginary parts of the speaker distortion (as amp distortion can either increase or decrease speaker distortion depending on phase)."

At 112dB at 1 meter T.H.D. of Unity Horn

300 Hz = .477%

600 Hz = .194%

1200 Hz = .386%

2400 Hz = .967%

4800 Hz = 1.5%

Read the above again, this was taken at a full 112dB, no other speaker can match this incredible specification!

Now something that a dome tweeter would love that is near impossible for it.  The compression tweeters on these horns do NOT roll off in the off axis above 10Khz.  Compare the curves above 10Khz and you will see the tweeter response stays very even no matter the angle to the horn.

IMPORTANT

Off Axis on this horn is the same whether you are to the right, left, up, down, or any point in between.  This is unlike most speakers other than true coincident co-axials (Most Tannoy, Seas coax, etc.)  Most standard 2-way speakers have ugly dips in the response moving from just left to right, up and down is even worse as the angle of the 2 individual speaker elements is always different unless it is a true coincident source speaker.

B&C VERSION

The following is the B&C version of the Unity.  What is unique with the Unity Horn is that there is a small null in the output at 4Khz in the on axis caused by the midbass input holes.  The effect can best be described as looking at a flashlight with a small black dot in the middle.  This null lowers in level the further off axis you move on the horn and is generally not discernable since it is less than an octave wide.  Higher smoothing levels would eliminate this from the measurements.

 Remember the part before about hiding things?  The typical 3rd octave smoothing that is so prevalent in other company's speaker measurements would hide this null completely. 

There was alot of concern about padding down the B&C Unity by way of a L-Pad.  Crossovers are very sensitive to the dynamic impedance of the driver that they are on, and the original crossover for the horn did not allow for easy SPL adjustments.  We changed the crossover 5/17/01 to allow for this, and to eliminate a wide shallow dip that was found in the response from 1~4Khz.  Now the tweeter portion of the horn acts like a straight 9 ohm resistor, and the midbass acts like a straight 8 ohm resistor.  You can now adjust the SPL without changing the curve of the horn.  Simply pad down the tweeter and midbasses separately.

The following shows the symmetry of the crossover point which is found at roughly 1066Hz, the tweeter is reversed polarity to show this. No matter what speaker you are using, it can be tested in the same manner to see if the crossover slopes are done correctly and match each other properly.  This is a test that can separate a non-optimal design from one that is near perfect.

This is the only speaker system I have ever measured that had the same crossover null on axis and off axis, it is truly unique.

This shows that the Unity Horn has near the same amplitude and phase output from both sets of drivers no matter what the listening angle is.

This translates to good imaging and a super wide sweet spot!

I admit that I am a perfectionist and I tried to also notch the small bump in impedance at 1.5KHz, but there is already a notch circuit to lower a LARGE impedance rise at 3Khz.  Adding the additional notch at 1.5Khz dropped the impedance below 1.5Khz to very low levels no matter what I tried.  As is the impedance is very smooth and is now very tube amp happy.