So I finally found another pair of EVM 15L drivers, so I didn't have to rob my main system of one (see Avatar) and finished building my first prototype horn, which is, after several dozens of iterations in Hornresp, is finally here.
I'm happy to report that it measures very much as predicted. Put the microphone at the edge of horn mouth and ran Frequency Response plots, same as I did with the FH-1 bin a while back. The FH-1 is similar to a Belle Klipsch/LaScala bass bin, but larger, more ruggedly built (for PA) and ugly as sin.
Now keep in mind, in my case, both bass horn cabinet use EVM 15L woofer, which is the preferred woofer by Dr. Bruce Edgar. This woofer has fairly high resonance for a 15", but it's low Q and low mass paper cone with minimal coil inductance give it superior high frequency response in the 300-400 Hz. range where I'll be handing off to the K402/1133 combo at about 300-320 Hz.
The plots shown in the image are 1/48th octave resolution from REW (no smoothing) was used. The FH-1 had a 2.5 Mh Klipsch choke on it at the time of the measurement, so it rolls off more in this plot than it would without it. Nonetheless, the main reasons for designing this new bass horn was to extend the bass to 60 Hz. with the same driver and keep the 300-400 Hz response intact.
As you can tell from the RAW curves, with the FH-1 (green) I had to do a 141 Hz, -5 db PEQ to knock down the peak in the FH-1 as well as adding a +10 db boost at 61 Hz. to get any sort of bass below 100 Hz, down to 60 Hz.. Needed to this to mate up with my DTS-10 Tapped Horn Subwoofers, which are best below 60 hz.. The red Quarter Pie curve shows I don't need to do this anymore.
So far, it looks like I have succeeded at lowering the bass response acoustically by making a 5 ft. horn (which I'm calling "Quarter Pie") vs. a 2.8 foot long horn for the FH-1. I will also be lowering the 6 ft. height of my horn "stack" down to about 5 ft. or so, bringing the tweeter much closer to my ears when seated in the sweet spot. It also looks like I got a MUCH smoother horn in the process also. The distortion should also be lower because I will NOT need any kind of bass boost at all, so 10 db less power should translate into at least 10-16 db less IM distortion.
The green is the FH-1, the RED is the new Quarter Pie Bass Horn. They are RAW Frequency Response Plots with NO smoothing and NO Equalization of any kind. An EVM15L driver was used in both. The smoother, flatter curve of the Q-Pie is pure acoustic response of a better horn on the same driver. Mission accomplished.
Edited by ClaudeJ1, 06 March 2014 - 09:18 AM.