Fostex T925A Super Tweeter with ES-2000 Circular Horn
This blog post looks at adding a 2kHz horn lens to the Fostex T925A super tweeter. The horn lens is my a prototytpe ES-2000 circular horn that I had on hand and requires little modification to integrate. I will feature some acoustical tests comparing the stock driver against using the ES-2000 horn. The ES-2000 Circular horn measures 15cm (6") in diameter and is CNC machined from solid walnut.
About the Fostex T925A
The Fostex T925A horn super tweeter is designed to sit on top of your existing speaker. The tweeter is 108dB and can be used from 5,000Hz to 40,000Hz. The tweeter features an Alnico magnet.
Information on the Fostex T925A can be found here.
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| Fostex T925A mounted to ES-2000 Circular Horn |
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| Fostex T925A |
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| Clay putty added to smooth transition |
I had to add putty to fill a small gap between the horn and the driver.
Measurements
Frequency Response
Below is the frequency response comparison. The horn lens is adding another +3dB of sensitivity in the region around 5kHz. After EQ this would translate into lower distortion.
Step Response
The horn cleans up the step response after the initial impulse response.
Burst Decay
The burst decay doesn't show any noticeable improvement with the horn.
Off-Axis Polar Map Frequency Response
Definitions:
Lower Treble (4kHz-10kHz)
Upper Treble (10kHz-20kHz)
The horn provides better coverage pattern matching between the lower and upper treble. I've zoomed in on the area of concern and highlighted the difference with a red dashed line. Without the horn the driver is going to have excess lower treble energy into your listening space (early reflected sound). You will struggle to get the 'air' because of the imbalanced power response between the upper and lower treble. The horn lens balances out this relationship and allows the upper treble to have the same energy into the room as the lower treble, which subjectively translates into more 'air'.
Conclusion
The horn offers some small improvements over the stock driver. In a system where every last ounce of performance is required, then there is strong rationale for the horn.
For custom built-to-order horns contact Joseph_crowe@josephcrowe.com
Originally published at Crowe Audio.