trying out a large port low tuned reflex - average power?
I had some MDF left over from another project so decided to test build a large slot port 29/30hz tuned reflex for the 18sw115. I wanted to try doing a full rebated build using just the router and track saw, so I made a jig so that 'IF' I like the performance I can build some from ply for my little rig.
The goal was not ultimate SPL, but a focus on 25-65/70 with a clearsish response to at least an octave above at 135/140. The cabinet is a washing machine sized 288L, as thats the largest I wanted to go - plus I could always install it in the kitchen for an awesome kitchen party 😅.
The reflex volume is 133L gross with a port area just over half sd at around 640cm2 and 1.1-1.2m-ish in acoustic path length. I'm going for a small volume low tuning which will result in a non flat response, but with the aim of using a low shelf instead of a high pass to protect the low end and flatten it out and keep the delay as low as possible (DSP assisted reflex).
I've measured some used 18sw's using DATs and used the hornresp semi inductance model, interestingly with both drivers the fs comes in above spec sheet despite having been abused in hogs before. I'm not sure which to believe, but either my measured values or spec sheet gave usable responses so it was worth a try.
So ... My question ... How long before I melt a coil? the hornresp model peaks at 3.4kw at 30hz 126db 1m 2pi, the question is how this will average out? The power levels drop off fast and by 40hz are no problem, but then its being crossed low at 65hz so the average will still be fairly high. Comparing the filter to other designs, they seem to do similar with around 3-4db max boost around fb.
I can't wait to get this outdoors and some proper measurements made. Initial testing on a t.racks dsp 4x4 and one channel of a teac a-h300mkii and it really sounds great.
Hornresp came out pretty damn close, the port resonance wasnt quite right but everything else looks good. Akabak BEM also matched hornresp when using the spec sheet figures, but more accurately modeled the port resonance a few hz lower as it really came out. I wasn't sure on the measured values for the 18sw in akabak so cant compare there.