Second build


2015-11-19 4:48 pm
After building the smaller 2.1 system, I found the paper "A Method for Designing a Compact Back Loaded Horn Loudspeaker System", by Martin J King. See:

There is a drawing in the paper that made it look easy to build. It seems "Compact" in the title is a relative term - these speakers are much larger than the last set, but I guess they are small in terms of "folded-horns".

I made two modifications to the design in the paper:

-) An 8" sub-woofer and 75W amplifier is added to one enclosure

-) Rather than one 5-1/2" front-facing driver, there are four smaller drivers with angled about 22 degrees off vertical.

To accommodate the four drivers, the width was increased from 8" to 11-3/8", and the height from 38" to 44.5" (including about an inch for the feet). The face holding the four drivers is constructed effectively as a hip roof, in an uneducated attempt at treble dispersion. A small 60 w/ch amplifier is added at the top of the enclosure with the sub-woofer, where the plate amplifier is added to the back. Here's a picture:


Here is a picture with the removable sides off:


The sound is pretty good (better than the first build, most agree). It would be nice to measure SPL/Frequency response and make those nice graphs that I'm beginning to appreciate. Parts-Express has a solution for about $100. I could buy that but I was wondering if I could buy a half-way decent microphone and use some "freeware" on the computer instead.

Also, a second question, if I may - I ran the system at about 5/8 max volume for 10-15 minutes. Then I tried a song with a lot of bass at about 3/4 volume. No distortion noticable, but the subwoofer amp cut out - pretty sure it was the thermal overload circuit, as it continued working about an hour later. The unit felt warm buy in no way hot. Is this expected? Should I think about trying to return the unit, or is this just the nature of thermal overload circuits?

Any input would be appreciated.

-Mike MacIsaac