In this blog post I introduce the Prince Edward Collection of vintage inspired DIY plans (files and drawings). To introduce the new collection I feature a new spiral horn inspired by the Western Electric 22A horn from the 1920's.
Initial Idea
While testing the ES-290 biradial horn in my lab I ended up just listening to the horn on its own while I worked away on my computer. Normally I would listen to a pair of decent stereo desktop speakers at my workstation. However the reverberant and non-direct sound from the biradial horn (covering 300Hz-8kHz) was much more dynamic and enjoyable than the sound reproduced by my desktop speakers. It then occurred to me that it would be interesting to produce a dedicated mono horn that covered even greater frequency range, perhaps from 200Hz.
Obviously this would not be audiophile sound quality, but more a vintage sound that was effortless and dynamic albeit with some moderate horn coloration...or so I assumed.
I designed and printed a prototype horn featuring a 40cm x 20cm mouth and a 80cm path length providing a 165Hz Fc.
Once all the pieces were printed I decided to apply some primer and hammertone paint for a vintage appearance.
Testing Various Drivers
RCF ND350 1" Compression Driver
The first driver to test was the RCF ND350. The response is ungated a 1m, just so that I can get some resolution in the low frequency result. The response is surprisingly smooth until 5kHz where we see a drop in output. This tells me the horn wants to load very low and is not providing much horn loading gain above 5kHz. The result is still surprisingly positive.
I then printed a small adapter ring and mounted the Fostex FE83NV shown in green below. I've kept the RCF overlaid in red. Generally we see the Fostex loading down to 160Hz although the response is quite irregular. 
Almost for fun I tried the 19mm fullrange from Peerless. This also required a small ring adapter before firing into the 25.4mm (1.00") throat. The response is unexpectedly smooth providing output down to 330Hz. 
Overlaying the Peerless with the Fostex FE83NV shows a much more linear response through the vocal range. This is likely a result of the small driver size with minimal disturbance entering into the horn.
I then decided at this point to measure the off-axis behavior. We see good control down to 600Hz with about a 90 degree coverage window. Treble narrows at around 8kHz.
Better than a center channel?
Sound Dynamics RTS-C2B-2
It occurred to me that it would be interesting to see how this compares to an average center channel since this could be used as a sound bar or center channel.
The Sound Dynamics RTS-C2B-2 exhibits a major suck-out in the midrange where directivity narrows to only 40 degrees. This means the midrange would disappear if moving more than 20 degrees off-axis.
The Sound Dynamics RTS-C2B-2 exhibits dominant third order harmonic distortion through the midband (0.54%, 1kHz, 85dB for 1m).
I then printed a ring adapter for the Fostex PW80K and tested the response. This provided strong response down to 200Hz but lacked treble output. A phase plug would be required to extend the treble which is not covered in this blog post. The response is relatively smooth however through the midrange.
Harmonic distortion is extremely low through the midrange at only 0.04% for H3. This is the same test signal level of 85dB conducted with the center channel earlier. We see distortion rise in the lower midrange however this is predominantly H2. 
This one provided similar results as the Fostex PW80K.
Distortion was also measured at the 85dB test signal level. 
Making a 0.05L sealed rear chamber for the Peerless.
I then made a 0.05L sealed rear chamber for the 19mm fullrange Peerless driver. This is what I thought simulated well in terms of a reasonable QTC. The rear chamber would help improve the power handling and keep distortion low.
Below is the result of with and without the rear chamber.
Distortion with Chamber, 85dB 1m
