An appointment with the devil

[Timber_MG]

So gentlemen, that which was supposed to be playing at DIY Audio Fest was called into life yesterday (and given a rough coat of primer the day before). Unfortunately I don't have picures to display just yet (they will no doubt surface sometime soon) One thing is sure: the system is showing a lot of promise.

The system details:

Subs + W-BM-MT-BM-W configuration per side

Sub: 2x 18" Bass reflex, tuned 38Hz and amped with Behringer EP2500 (1.2kW per 18) 98dB sensitivity each

Bass: 2 x 18" cardioid (Effective d ~750mm), system efficiency 104.5dB falling 6dB/oct below ~100 something Hz, specially damped cab with 2.5:1 compression ratio amped 1 bridged EP2500 per 2 modules (2 per side)

Lower Mid: 2x 15" Midrange (76gm mms), open baffle (for now), system efficiency >103dB falling 6dB/oct below ~200Hz amped by one channel of Behringer EP2500.

Mid-Tweeter: 19" diameter 80 degree horn loaded with a 1.5" large format compression driver

Last night the system was given a baptism of fire in an open air-concert with the additional help of another pair of subwoofers. The sound was quite exceptional for the 20 minutes time I had to do a controller setup and the added bonus is that the system is so directional above 70Hz that the PA was virtually not very audable on stage (there was still something between 70-230Hz but highly attenuated due to the cardioid character)

Crossover config (from memory):

Subs:
Butterworth 4th order HP on subs 35Hz
Bessel 4th order LP 70Hz

Bass:
Butterworth 4th order HP 73Hz
LR-4 LP238Hz

Mid:
LR-4 HP 238Hz
LR-4 LP 1 kHz (also works well at 738Hz)

Mid-Tweeter:
LR-4 HP 1 kHz

There was some EQ needed for the cardioid and the tweeter, but otherwise the system is fairly flat (iirc there was a slight correction for the open baffles somewhere).

Unfortunately the system was run very loud, even though it doesn't particularily sound it, even with peaks @ 20m likely exceeding 115dB. The wine at the soundie didn't particularily help either ;-)

There were lots of compliments about the sound, but nobody took my utterings that this was my hi-fi very seriously.

[kay]

Well some people don't know you to believe you I'd love to hear it though... where do you actually find the space to use it?

[Timber_MG]

For now it will probably first reside in my room until I am happy with a couple of tweaks (both cosmetic and sound) and then (apart from perhaps a live gig or two) take up residence in the fest venue (in a month or so becasue I am still borrowing my electronics to the church and don't want to move between venues that often.

Its modular nature (it's 2.4m high, three pieces) makes it moveable (the heaviest module is the sub as seen at DIY-Fest)

This is a system that could be powered by flea-power amps (chip-amps might not suffice for enough headroom for live music playback)

If I were to add to this system, I'd probably make up some 18" horn subwoofers, but for live work outdoors up to 30m throw I am happy with the system.

[Timber_MG]

Quick update, a woofer (in my case doubling up as sub too) in four corners vs only a single makes a large difference in controlling an unruly room. Want to experiment with six LF sources.

[chipwelder]

Well... can't think of an unexcited room node there... but can you switch the amps on without going deaf... I mean you can't use much more than two watts without getting into serious spl in a room...

[Timber_MG]

I am quite busy tomorrow and I can certainly not risk a sweep with any sort of resolution at 1:30 in the morning.

You'd be quite surprized at how evenly the room gets excited. Four corners is similar to three decorrelated random bass sources in the room and I will end up with six LF sources in this room. Easily superior to a single "well placed" sub.

And yes, seing amp lights indicates sane (normal long term) listening levels. When the controller's -40dB lights spring on I know I am getting into serious listening or a recording with some headroom.

I am having a little bit of trouble with the integration of the open baffle 15s, currently just letting the horn do 300Hz and up with the 15s doing just an octave below. The baffle still sings a little, so the 300Hz x-o helps a little in that regard.

Lots of tweaking left before it's presentable, starting with a damped baffle. Amps have a relay that engages once the amp has settled.

[chipwelder]

You are a kind neighbour...

Good luck with tuning, two 15" going up to 1kHz... how does the dispersion stay wide enough to match the horn?

[Timber_MG]

Open air it is perfect horizontally (and sufficient vertically) and that is all that matters. In the home I am running a single 15 and crossing anywhere between 300Hz and 1khz.

[Timber_MG]

Oh, and the 15 is quite happy up to 3k5, though I don't cross anywhere near there (atm ~850Hz)

[chipwelder]

I can't believe there is no cone break-up at that frequency... or that it still behaves pistonically... how much do they cost?

[Timber_MG]

I never said no break-up. It starts mildly at 1k4 but has very well behaved cone (correctly terminated) that is +/- 2 odd dB up to 3k5 where it dies. I have used it sucessfully crossed 1st order electrical 1k5.

There are many such cones available from 18Sound, P.Audio, Beyma, B&C, DAS, RCF, the list can go on a lot more.

Pistonic behaviour is not a prerequisite for using a speaker in a certain range, it's derrived acoustical properties however are more important.

[chipwelder]

Would like to hear it when you are happy... although chances are we are never happy with our toys for more than a week...

[Timber_MG]

Will let you know when I am happy.

[Timber_MG]

Today it got its first stereo setup, crossed 150 and 760 with commendable room-response. I will post some plots a little later to demonstrate what 4 dipoles can do for room balance and modal excitement.

[kay]

You are a kind neighbour...

Kind or not... I still wouldn't want him as my neighbour with that kit