Unity horn build

first off i fitted a protection bulb and polyswitch in series as protection for the beyma cd1014fe HF driver. also fitted an 80uF cap as HP for the mids. still waiting for the coils to finish the passive network. filter settings are posted above.

bulb is a 24V 50W osram halogen. cold resistance is 1.5R and calculated full power resistance is 12R - so ratio of cold to hot resistance is only 1:8 which is lower than usual. polyswitch is one of these:

played around turning the volume up quickly and the polyswitch seemed to cut out at moderate volumes before the bulb started glowing as planned.

played a few tracks at full volume with earplugs in as it was insanely loud. was putting 3*800W amp channel into 1.4",4*6", and 2*10". at higher volumes there was a lot of colouration of the upper treble and severe chuffing from the reflex ports. examining with the mic and signal generator confirmed this. frequencies above 5kHZ showed high levels of distortion up to 20kHz at a level approaching -10dB of the signal at high volumes. the chuffing distortion was coming from the ports from the rear of the bass drivers. the output from 120Hz to 260Hz from  the other ports did not have significant distortion even at full volume. the mids seemed relatively clean but might try making the shorts shallower to increase HF extension.

the beyma cd1014Fe was the cheapest 1.4" I found so have ordered a Paudio BM2-D740 for comparison. going to try some flared 2" port tubes rather than the current 36mm holes to reduce the chuffing.

will have it out at St Pauls carnival in Bristol if anyone is interested.

those aren't quite the finished article as I have since added flying point brackets and handles.

I have abandoned using tee-nuts. a coach bolt with a couple of normal nuts and a washer works fine and if it does start to spin the nuts and end of the bolt are always on the driver side and accessible to pliers.

this was the most complex build I have ever done but seems to have turned out well thanks to my new festool saw and guide rails. I just used PVA on most of it as the joints were so close polyurethane didn't seem necessary.

Beautiful!

at the moment the rear woofer ports are the same size as the front woofer ports. the response is falling off at about 100Hz and then there is a shelf that extends down to 40Hz. I think if I make the ports about 50% bigger should raise the tuning and the output of the port to make it -3dB at about 65Hz.

major differences from the first prototype are that there is no wasted volume inside making the rear volume of the woofers much bigger. have used 12" rather than 10" woofers. changed the throat geometry a bit so that it is an exponential expansion which matches the compression driver throat angle at one end and the angle of the conical horn at the other.

response of the new compression driver is very different to the BM-D740 which means re-design of the crossover. a compression driver that rolls off a 6dB per octave from 1kHz can easily be made flat with the right capacitor but the new driver is fairly flat to 7kHz anyway.