A midrange horn project - opinions and proposals

First, hello everyone. I've been reading this forum for quite some time, but now I felt it's time to register.

So, after reading Klipsch's paper on loudspeaker distortion and doing some simplified tests myself, I decided that horns are the way to go. I've bought a pair of Eminence Alpha 6 (at the moment playing in my bedroom on small OB-s and already very pleasing:) ). 300 Hz conical flare is on paper (or actually on hard drive). But before I incarnate this project any opinions and proposals are welcome, to further refine the design. Also, I have not enough time and money for extensive prototyping, so I'm trying design principles that (according to information found after extensive data digging on Internet) are proven to work and keep it as simple as possible.

So, here are the details:

Primary goal is as good sound as possible, ear-piercing SPL is secondary.

9x9 cm rectangular throat with phase plug (4 cm diameter initially, so throat area 68cmˇ2, compression ratio 1,86. Phase plug final shape and size is determinated by some experimentations)

1600 cmˇ2 mouth (40x40 cm), terminated with a foam or other similar material roundover to ~50x50 cm to smooth out the response and reduce mouth reflections back to throat.

Horn lenght 31,2 cm (36,2 inc. roundover)

Back chamber as small as possible, no larger than 2 litres. Intended bandwith is 300 to 3000 Hz, or as high as possible. 2...2,5 kHz will do it also, but not below 2 kHz. Fairly large throat gives me a chance to experiment with various phase plug shapes and sizes.

Dispersion is approx. 50 degrees.

Tweeter coaxially mounted in the mouth, at first trying to reuse my ol'trusty piezo array (a là Bill Fitzmaurice), compression driver with horn if that doesn't work well enough.

They will be used in a multitude of roles - as my main hi-fi, for house parties, some band practice and occasional discos and lives, mainly closed parties in smaller venues up to 200 persons max. Proper bass support is to come next year (at the moment I have to stick with some "leftovers" -  two 2x8", which are enough for home and band practices), for time being I can always rent (some Altec 816 style midbass bins that are around here would to the job). This is my hobby, just for fun and self-education and I'm not planning to make any money from it (yet).

A concept image


And Hornresp graph


Schematic diagram


So, all opinions and proposals are welcome

I've done some research on horns and am aware of various methods to terminate mouth correctly. Again, roundover is the simplest and most accessible method. I got the foam idea from reading about an experiment where you make an improvised horn fom a rolled up magazine, talk into it and compare the sound with and without mouth termination made of a towel that is rolled up and wrapped around mouth.

I've considered non-axisymmetric construction, but  I don't want to make it wider - it's roughly 50x50x50 cm cube and seems to be optimal as far as doors, pole mounting (a compromise solution with horn on the pole and one or two 15" subs covering 50...300 Hz on the floor) and stacking goes (I live on the 8th floor and have to consider elevators). Also, my piezo array won't fit if I make the cab lower.

I also considered tractrix etc but conical is the simplest (and arguably sonically one of the best) flare rates, also gives good control over dispersion so I'll go with this.

I've double-checked the excursion figures, and with smaller than 2 litre back chamber it's OK even without crossover.

Front chamber volume is estimated to be 100 cmˇ3 or less. Again, experimantation with phase plugs will be done.

Construction shall begin in September. I'll try to get a camera and post some pics of the process. Also I'll try to make some plans up and post them here.

Actually one more question about group delay - it always looks quite horrible with any horn on Hornresp graphs, but I quess it's not really relevant, right?

Here's the GD graph with 2 L back chamber (black) and 0,5 L chamber (light grey):


At first yes, my idea was to extend the mouth with foam or something similar, but guess I'll make that last bit of flare from plywood and cover with foam. Or maybe try to get some foam like used for air filtering in amp air intakes and such and make a plug of several layers that also doubles as speaker grill (and also hides those "nasty piezos" from snobbish eyes:D)?

Then, another idea - to extend the horn with eg. styrofoam and apply some acoustic foam over it and also ~10 cm into the main flare?

Thanks for the info, _djk_, those look interesting boxes (although foxit reader goes bananas when trying to scroll daown the first PDF).

Anyway, I threw some plans together (my CAD skills are not the best, actually these are the first CAD plans I've ever made): http://www.speedyshare.com/952908459.html.

have a look at the OAP audio coaxial horns. They use dense foam on the end of the 10inch horn and have a very nice TAD 2inch coaxially mounted.

the second immage isn't jeff robinson horn?