EAW BH760

Dear Speakerplanners, I have finished my works on EAW inspired box. I shall build it during upcoming summer, untill then any feedback is wellcomed.

I want to share the project right now in case anybody makes it before me and shares thoughts on how theory works in practice. Moreover - nobody is perfect, I could miscalculated something that trained eyes catch in seconds.

Finally - something aimed at copying finished as separate design in its own rights, possibly better than orginal project. I learned a lot that way, maybe this inspires other ppl. Yes, you can make stock designs better! You are not that limited as engineers of big companies. You do have time to do things more in complicated way (see my bends against EAW's), you do not have to count inches of plywood, you do not care that much for weight and size.

Lots of hornresp experimentation brought me to the opinion that EAW BH760 is a big trade-off. They tried to reduce the box size at the SPL curve expense, thus their box needs serious equalisation to sound fine (go check their website!). What they did to make the mouth area biggest (to increase lowdown response) is a hybrid cone, 3 conical segments that try to average expotential cone. This models rather  badly regardless speakers. Add to this not very carefully designed bends and you meet  harsh sounding box that is believed to work properly only at really high spl's and in groups of four at minimum (this is popular oppinion among pro sound companies).

I still liked the 3 segment bend horn idea and decided to find out what can be done if I do not limit myself with volume that much, and stress sound quality rather than highest gain @35hz.
I modelled many speakers, to find out the best for the purpose. The main discovery was that huge range of speakers seem to model well for optimal 1/4 WL cone. Only parameter that needed update to keep flat SPL was a back chamber volume. So remark number one - if you want to use my design with other speakers then leave the bent cone untouched. Put your speaker in Hornresp and find out right back chamber volume, then update the dimmension in my project. The rest of calculations (eg bends) are already done for you ;). General rule here is more rear chamber volume - flatter SPL at expense of group delay and vice-versa. Try everything between 50 - 150 litres.

I calculated the design for Eminence Delta 12" LFA because they are robust, and quite cheap to buy http://eminence.com/proaudio_speaker_detail.asp?web_detail_link=DELTA-

  Other speakers that go well with this design are Delta Pro 12" and LAB 12" both more expensive. Only advantage here is that they could work with significantly smaller rear

chambers (Delta Pro 12" = 80 liters vs. 140 liters for 12" LFA). Since box volume was not that important for me I bought 4x12"LFA's for circa 300$ little used (for that you get 2 Lab 12" if lucky).

In the final desing I had to compromise the ideal SPL curve a little to conform to limitations coming from bending the whole thing into cuboid.
I decided not to follow the hybrid EAW way and stick to traditional straight conical design that roughly looks like this:

Finally the list of raw rectangle panels to order from Castorama or other vendor with CNC is here ;)