Chris A Posted December 23, 2015 Share Posted December 23, 2015 Note that Geddes fills the entire "waveguide" (horn) with foam in order to attenuate higher order modes (HOMs). Chris 1 Quote Link to comment Share on other sites More sharing options...
jwgorman Posted December 23, 2015 Author Share Posted December 23, 2015 Hey Denny, Yep, I noticed that. I do not possess the skills to do that You still at the Rock? Joe Quote Link to comment Share on other sites More sharing options...
Chris A Posted December 23, 2015 Share Posted December 23, 2015 (edited) I decided not to use foam inside the horn because I thought it might affect the geometry too much. Instead I stuck felt on the surface covering about half the depth of the horn. I also stuck a strip of open cell foam around the outside of the mouth. The effect on the frequency response is shown in the attached graphs. The measurements are at 80cm with no crossover attached. I didn't like the effect on the sound produced by the felt but I have stuck with the foam around the horn mouth. Robert Looks like all you need to do is to add a little boost starting at 14 kHz using the foam around the mouth. The effect of the foam seems to tame some of the peaks and valleys--except as noted above 14 kHz. It makes me wonder if Geddes' approach might work, too. I'll have to find a large amount of foam for a K-510 and try it to see what happens with just a K-69-A up to 20 kHz (I'm crossing over to a Beyma CP25 at 8 kHz presently, because of the chattering of the K-69-A just above 10 kHz). Geddes mentioned that the foam density is somewhat critical, but it seems to me that if the resultant output is simply EQed back to flat response after foam insertion, it doesn't matter if it might be a little too dense or slightly less dense than optimal. EDIT: I found Geddes' patent (US 7,708,112, May 2010). He states that 20-30 pores-per-inch (PPI) foam density is optimal. Chris Edited December 23, 2015 by Chris A 1 Quote Link to comment Share on other sites More sharing options...
jwgorman Posted December 23, 2015 Author Share Posted December 23, 2015 Very interesting Chris. Quote Link to comment Share on other sites More sharing options...
djk Posted December 24, 2015 Share Posted December 24, 2015 "You still at the Rock?" For the time being, the company is making a serious effort to get the old dogs to quit. What are you up to? Quote Link to comment Share on other sites More sharing options...
jwgorman Posted December 24, 2015 Author Share Posted December 24, 2015 "You still at the Rock?" For the time being, the company is making a serious effort to get the old dogs to quit. What are you up to? Well, glad you're still there. Yeah man, that past couple of weeks I heard about a lot of old timers retiring. I left the Rock 4 years ago. When I was Test Lead on US Navy P3, and PE on Taiwan's P3 CNS/ATM upgrade I was always the oldest guy in reviews! If I'm the adult supervision, I need to go somewhere else I'm working in the Railroad industry now for a company that spun off the Rock in 1998. Still in Cedar. David Guckenberger stopped out to my place a couple of weeks ago and we spun vinyl and CDs and listened to the Khorns. Talked about the days of glory at The Audio Room. Take care and Merry Christmas. Quote Link to comment Share on other sites More sharing options...
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