Midrange compression driver development

So I would imagine you are planning to use a compression driver to fill in the gap (4 kHz - 5 kHz) housed on a 60 x 40 horn to keep things uniform (seamless)?

Best Regards,

Great to see someone doing some proper R&D! Well done for taking the step! 

I just wondered, have you got any pictures of your measurement set up and how you have analysed the data? The measurements of your driver on it's own are making me suspicious and you may be measuring reflections rather than your horn, and compression/phase bung. Both look great by the way!

Cheers,

Sam

^^^^^THIS!!!^^^^^

You write the throat is 80mm 50cm^2, consider that a standing wave in the throat would have its first null at ~2140Hz, which ligns up almost exactly with the first measured null.

In the simulation, did you do a full BEM analysis of waveguide including horn?

Thanks for all the replies! They sparked more thoughts on the matter for sure! In a few days i will post more pictures of the complete CAD model of the driver, the phaseplug and the horn. Hopefully this will clear thinks up a bit.

After many suggestions of, in my eyes, knowledgeable persons to expand the centre of the plug, this will probably be my next try in getting a flatter FR. But first i will try the new plugs with slightly different channel entry positions. This test will probably be done tomorrow, so i can update you on that in a few days, too.

Thanks :) 
Yes, a standing wave at 80mm would have a null at that frequency. That could be a possibility. But i have to ask why there should be a standing wave there and not at all other parts of the horn with different dimensions? Would it just be because of the miniscule part of the throat were the outer walls change from a negative to a positive expansion and create a zero expansion segment by diong that?
Would the only effect of the plug-extension be then to block the path for this particular standing wave until the outer walls of the horn start to expand?

Lots of questions, but i am excited to learn more!

For the simulation: i did a full bem analysis in AKABAK of the membrane (with the shape as close to the real one as a pair of calipers and some tricky measuring could get me) driving the compression-chamber (just the shape of the membrane and surrounds shifted by 2mm to the front) then the phaseplug (with interfaces at each end) connected to a model of the horn in use, which is then coupled to the outside via another interface. All that in 4pi with 180° polar measuring points at 1,5m distance.
I did some pre-meshing of my models in gmsh and remeshed certain parts again in AKABAK if they needed a finer mesh as indicated by the standard deviations calculated by the solver.

I didn't use the model of the horn in the simulations for the initial design of the phase plug. For that i used a model of a plane wave tube (with a 100% absorbant boundary at one end) and later a conical horn shape with the same boundary at the end. <- this was just to get a more accurate look at the achievable FR.
But after my phase plug was designed, i simulated it with the horn that i had from previous tests. <- just as with hf compression drivers, the horn shouldnt be critical for the performance as long as there is no large impedance missmatch at the throat

An interesting project - but really shows that the physics is difficult and simulations obviously have some severe limitations. Measurement and experimentation is the way - but also, in the end, using a decent DSP unit with several parametric corrections may be the only solution. And generally, the simplest. 

You can really drive yourself mad trying to tweak and tweak and tweak. Ultimately a bit of a waste of time. There has to be a point where you say enough is enough, and just use some electronics to get the thing sounding good. All the big manufacturers do that, even going back decades. 

I just picked up some EV S200's that a friend found while clearing out his shed! I really love those cabs, but they also need their processor to really sound good.