This thread is titled as a comparison of my 1 Inch Trachorn and Greg's 2 Inch V-trac Bruce Edgar type wood tractrix horns, but in reality, it's a comparison of a 1 In driver and a 2 inch driver. The horns are really two of a kind. The JBL driver was an 8 Ohm 2426h. The BMS is a 16 Ohm 4692 midrange.  

I did three instrument test. NO, one of the test was NOT a listening test! I will leave that to others. My instruments have no bias about the matter. I obviously do!

The tests:

Both drivers were driven from a 100W McIntosh amp from the 4 Ohm tap. The input tones were clean to greater than 60 dB down.

1-Frequency response of the two horn / driver combinations one over the other. Both show 110 dB sensitivity over the 400-6000 Hz range we are interested in.

2-Harmonic distortion of a single 550 Hz tone at 3 levels. There was virtually no distortion to the 4400 Hz tone on either driver, so I didn't plot it.

3-Intermodulation distortion if two simultaneous tones of 550 Hz and 4400 Hz at three levels. The 4400 Hz tone is 8 dB lower than the 550 Hz tone. I think this is to compensate for the Fletcher-Munsen laws but I'm not sure. The 550 Hz tone is 100 dB SPL at 2 feet. These frequency and level settings were used by PWK in one of his publications. He says they represent 90 dB SPL at the usual home listening position. I also tested at 100 and 110 dB SPL at 1 meter. This is LOUD! I did the test wearing ear-plugs!

 A segment of PWK's article is below.

 
Here's the frequency response of the two drivers. The mike was 1 meter from the mouth of the horns. The levels are true sensitivity of the driver in dB SPL at 1 meter for 2.83V input (1 w into 8 Ohms). The marker is at 300 Hz. The Vtrac and BMS combination obviously goes lower. The JBL driver is a full-range driver, so it goes higher.

 
I did a paste-up of the three level setting plots for each driver. The lowest level is in the background. This harmonic distortion of a 550 Hz sine wave tone.

Here's the JBL 

 Here's the BMS:

 
I did a similar paste-up of the three levels if intermodulation distortion plots. Lowest level is in the background.

Here's the JBL:

 Here's the BMS

My personal opinion is that the 1 inch and 2 inch drivers have virtually the same distortion levels at living room listening levels. When the volume level goes up the clear winner is the 2 inch driver. I believe that 2 inch drivers are for movie theaters and audiophiles who must have the best no matter the cost. For the vast majority of we mortals who live in houses, a 1 inch driver is fine!

Here's details on the horns and drivers:
The JBL 2426 1 in driver:  http://www.jblpro.com/pub/components/2426.pdf
The BMS 4592 2 in driver:  http://www.lataudio.eu/HTMLs/BMS/4592NDL.htm

The horns:
The Trachorn 400:  http://www.alkeng.com/trachorn
The V-Trac:  http://www.dcchomes.com/Gregsaudio.html

NOW: Somebody tell me why the horns in PWK's article shows so much lower distortion than what I measure!  I'm quite sure my mike isn't overloading. Moving it away from the speaker does not reduce the distortion products, just the level.

Al K.

Fantastic job Al and I completely agree with your conclusion.

Al,

Have you tried to duplicate PWK's test using his horn and driver?

Bob Crites

 Bob,

Yes, I did test the stock stuff. Look at the back plot. It's the K500 horn (Belle Klipsch and K55V). This paste up is dated Nov. 2004:

Hey AL

I believe the BMS's intermodulation distortion plots  lowest and middle level plots are reversed.

Do you have the ability to do ETF (waterfall plots)? My experience is drivers can exhibit similar standard frequency response curves yet when you look at their behavior in the time domain you begin to see were the drivers obvious tested differences can be seen to correlate with what is heard to some extent.

mike tn

edit: Looking closer at the low versus the middle BMS's IM plots maybe I'm wrong but the spike at 1100Hz is higher for what is shown as the lowest level plot while the middle level plot shows it to be lower in level which I wouldn't expect.

 I looked at the BMS IM plots. They seem to be in the right order. 100 dB at 2 feet in back. 100 dB at 1 meter in the middle and 110 dB at 1 meter on top.

The problem with the distortion products is the room response. I had to do all the plots twice because I had the horns facing a wall. Reflections were giving me realy goofy results. I turned it so that it pointed at the dining room doorway. That improved the results a lot. The answer would of course be an anechoic chamber!

Al k.

Al Klappenberger:

The answer would of course be an anechoic chamber!

Thanks for all the info, Al.

Bruce

  Are these drivers both fabric diaphragms?

 The JBL and BMS are both titanium.