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Old 28th October 2010, 12:27 AM   #1
dave251 is offline dave251  United States
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Default Line array for PA use, part II

So I've been using my little line array cabs for a few months now, and couldn't be more pleased with the results. Most of it has been solo vocal/guitar work, but have done a couple of larger groups.

So, the limitations: I've noticed, even though I've been able to eliminate monitor cabs, that I'm not getting quite the high frequency dispersion I'd like...begins to sound a bit dull as you move off axis more than about 45 degrees. If I really want to run the gain up, I can get plenty loud before feedback...but I lose the "bright" that I'd get from a floor monitor. Hmmm...

So I've been working on a "stackable" small format design and would like some input.

One 6 1/2" woofer @ 8ohms, 94dB sensitivity
Three dome tweets/series wiring( 8ohm--24ohm total ) at a rated sensitivity of 91dB.

I'm wondering if this configuration will match up correctly for sensitivity. I'll be using a simple 1st order x-over...

These cabs will be designed to "stack" up to 8 units high...that way the player can take however many he needs into the venue.

Thoughts, recommendations, appreciated.

Here's my first thread on the cabs I designed last spring:
Line array for PA use
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Old 7th November 2010, 01:55 AM   #2
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I built some PA cabs that your ideas remind me of. I used six 6 1/2" Soundlab full rangers, rated around 91dB efficiency, aluminium voice coils with whizzer cones. When I first tried out in a test box the high range sounded off, so I removed the whizzers.When I finally got around to building them I used six in a small sealed box of around 35Litres, I added a 6" piezo horn using a first order crossover at 5 kHz. The box was made of some special plywood-with braces tight up to the driver magnets, very solid construction. Using 6 drivers put the power handling up to around 300 watt, with the usual multidriver increase in sensitivity up to around 98-99dB. How did they sound, surprisingly good- not bass below 100hz, but much smoother sounding than the usual 12"+ horn combination. As there is no crossover in the main range it was essentially a full range speaker with a supertweeter.The disadvantage was the drivers have a soft foam suspension and a pop from a microphone would make the cones jump like crazy. To get around this problem I used the speakers with 75hz high pass filter in the Mackie mixer I was using. Other times I used them with 18" 100w subs crossing at 150hz (12db octave slope) and they had no trouble keeping up with the subs. The layout was 2 drivers wide by 3 drivers (like Bose 802) high with the horn jammed in between. The cross bracing in the boxes was probably why these cheap speakers sounded so good, they were very solid. I always wanted to build another as a line array as I have 12 drivers spare. this would probably sound similar but with much wider horizontal dispersion and less vertical-reducing ceiling and floor reflections.
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Old 7th November 2010, 02:14 AM   #3
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Sorry I realised I did not really answer your questions, instead I enthused about my old speakers! The tweeters will retain their voltage sensitivity connected up in series, and will be a reasonable match (3db less) than your woofer.The advantage is in power handling though, the domes will have 9 times the power handling capacity wired in series like that-in voltage terms each will only see 1/3 of the amplifier voltage. When I built my cabs I used 1st order crossover with an extra damping resister across the tweeter, this forces the load to become predominantly resistive, and will suppress the fundamental resonance of your tweeters. I used a 25w 8ohm resister in parallel with my tweeter and a 4uF capacitor in series for 5khz crossover. I have built other types of cabs since then using expensive pro drivers but I still prefer these because of there non fatiguing midrange sound.
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