In this blog post I feature a full set of measurements on the ES-290 Biradial Wood Horn with the JBL 2446H compression driver. I then test custom carbon fiber diaphragms against the stock titanium units. I then test damping material in the rear chamber.
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The ES-290 Biradial is constructed from solid walnut hardwood and measures 69cm wide x 30cm tall x 30cm deep not including the throat adapter. The throat adapter adds another 10.4cm to the overall depth. The throat adapter is long enough that other drivers can be accommodated.
For set up in my living room since this is the largest space I have available. I set my Datyon UMM-6 at 1 meter distance from the horn to conduct the measurements. I also placed the microphone at the horn mouth for some of the distortion measurements. I used a custom built rotary table for the speaker. The mic stays fixed and the speaker rotates for the off-axis measurements.
I began my testing by conducting an impedance sweep. The lowest impedance peak is at 300Hz while there are a number of other peaks at 450Hz, & 700Hz. Upper treble breakup starts to occur at 13kHz. This is to be expected considering this is a 4" titanium diaphragm.
Impedance sweep of JBL 2446H with ES-290.
I then conducted an on-axis frequency response. Since this horn has a 300Hz cutoff the effect of room gain is a constributing factor to the overall response. So to factor this in I've conducted two measurements.
- Four Pi (all first reflections >2 meter distance)
- Quarter Pi (Horn located in normal listening position 1m from floor and rear wall)
Four Pi Frequency Response
Below is the on-axis frequency response 1 meter distance with the stock JBL 2446H compression driver.
On-axis Frequency Response JBL 2446H with ES-290 Biradial (Four Pi with 1 meter mic distance)
I then moved the horn to a Quarter Pi location that would be the typical location in a listening room.
Overlaying the two responses shows the typical boost provided by the one pi placement.
Compare 1 pi (Blue) and 4 pi (Grey) Frequency Response (1/3 smoothed 1 meter mic distance)
I then measured distortion using a 1 meter mic distance. I decided to take a second set of measurements with the mic located at the horn mouth.
Percent Distortion for ES-290 Biradial and JBL 2446H (1m mic distance)
I then conducted the same measurement however with the mic placed at the horn mouth.
Percent Distortion for ES-290 Biradial and JBL 2446H (Mic located at horn mouth)
For those interested I've shown the same measurement as above however with the distortion vertical scale changed from percent to dB from the fundamental. Notice that third harmonic distortion is a full -68dB down at 1kHz (See highlighted yellow in chart below). That's a very respectable result.
Db Distortion for ES-290 Biradial and JBL 2446H (Mic located at horn mouth)
Off-Axis Coloured Polar Map
I then conducted off-axis measurements using my rotary table. I decided to conduct the measurements all the way out to 90 degrees off axis.
Off-axis coloured polar map for ES-290 Biradial Horn (90 degrees off-axis)
For reference I've shown the same measurement but only out to 60 degrees off-axis.
Off-axis coloured polar map for ES-290 Biradial Horn (60 degrees off-axis)
Additionally I've shown the same measurements in the normal frequency response plot overlay.
Off Axis Measurements, 0° Red, 15° Green, 30° Blue, 45° Grey
I conducted burst decay at 1 meter and at the horn mouth.
Burst Decay for JBL 2446H and ES-290 Biradial (1 meter mic distance)
Burst Decay (35dB vertical scale) with mic at horn mouth
Rear Chamber Modification
In order to deal with the breakup that starts at 13kHz I decided to install alpaca wool in the rear chamber. I did not have any 30ppi open cell foam to use and so I decided to use the alpaca wool. I suspect that the open cell foam would be even better performance from other tests that I've done.
Alpaca wool installed in the rear chamber of the JBL 2446H
I then conducted the same measurements to see the impact of the wool.
Overlay of frequency response with and without the wool
Impedance comparison with wool (Blue) and without (Green)
Burst Decay comparison between no wool (left) and with wood (right). Mic located at horn mouth.
Testing Carbon Composite Diaphragms
Working with a colleague we've built prototypes carbon epoxy composite diaphragms. My colleague manufactures high performance sporting goods such as wind surf boards. These diaphragms use the same technology as the products he manufactures on a regular basis.
Carbon Epoxy Composite Diaphragm, custom made for the JBL 2446
Frequency Response (Carbon Diaphragm)
Frequency Response Carbon Composite Diaphragm on JBL 2446
Frequency response overlay Carbon Composite (Red) against Titanium (Green)
Distortion (Carbon Diaphragm)
Distortion sweep for carbon composite diaphragm
Burst Decay (Carbon Diaphragm)
Burst Decay comparison Titanium (left) against carbon composite (right), 25dB vertical scale
Subjective Listening Impressions