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DIY 225 Hz tractrix horns. Lots of pics!


capo72

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DOC....Chuffing for a HF horn??? come on its a compression horn design...

Chuffing in the sense of random chaotic motion of air - not as in the

audible air swooshing sound typically associated with overdriven ports.

Are you saying that it is impossible to introduce turbulence to higher

frequencies?

Do,nt forget to collect some good professional Not the cheap

crap. testing equipment along the way....and dont throw away the

mistakes.

I'll have to wait for that when my purpose of measuring actually

requires more reliable resolution. But at the same time, I remind

myself that all the audio giants had far less measuring capability back

in their day - and they whipped out some insanely awesome designs. I

don't pretend to be as good as they are/were, but I can still try to

apply methods to work around the limits of the measuring capability. Heck, gotta start somewhere.

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I can do some chuffing on a Tuba..... When good measuring equipment comes along dont pass up the chance to aquire it. Some of the early guys had to make there own....Like PWK s famous string and coil to measure complience of a cone...But he also had to buy and collect his wiggle tube measuring instruments.

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Really nice work on those horns Jeremy, it'll sound great when you get it all together.

Mike/Maron -- below posted at the Asylum back in 2002 by DJK

For all intents and purposes horn distortion is a function of how hard you squeeze the air and how much bandwidth you try and cover.

I'm going to use a Klipschorn as an example that we all love/hate.

The K55V (Atlas) midrange driver has a 5/8" (nominal) throat. This driver (and most drivers) have a 10:1 compression ratio. Distortion is proportional to pressure per square unit of area and the square of the bandwidth in octaves (bandwidth to be covered later). Loosely put: a 2" throat has over 10X the area that a 5/8" throat has and thus the air distorts less. Dedicated midrange drivers also exist that have lower compression ratios, ie: 2~5:1 rather than 10:1 or higher. For a given sound pressure level the larger the throat and the lower the compression ratio, the more 'relaxed' or 'easy' the sound is.

The shape of the horn throat is also important. Long narrow necks on horns also suffer from air overload.

I remember the first time I heard this sound. It sounded like somebody was frying bacon in my horns. Some describe it as 'quacking'. It wasn't the crossover. It wasn't the amplifier. It was the air in the throat of the horn. Replacing the horn with a different type allowed a big increase in level before the same thing happened again. This time it was the air between the diaphragm and the phase plug. Horns without long necks generally have limited dispersion at high frequencies and drivers with lower compression ratios generally have less high frequencies too. Going to a two way top end gets rid of the problems (the square of the bandwidth thing goes away too).

People that are interested in the square of the bandwidth thing should refer to figure 7.8 Acoustic Engineering, Olson. "for constant sound power output, the distortion is proportional to the frequency"... "the nearer the frequency is to the cutoff frequency (of the horn) the smaller the distortion"..."for a certain allowable distortion the power output is directly proportional to the area of the throat".

The problems of frequency intermodulation distortion due to variations in the volume of air between the diaphragm and the phase plug also become moot with a two way top end.

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Thanks Dean. That's trippy that you get the least amount of distortion at the Fc of the horn - I wonder if that's because at Fc the horn has its greatest efficiency. I wonder how that plays out with the K402...

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  • 3 weeks later...

As an update to all who are interested, I have purchased some equipment to get some frequency response measurements on these horns. I'm still trying to work out the bugs on my measurement rig, and i'll get some charts posted as soon as I figure it out. I've also started working on the direct radiator bass bins for my 18" JBL 2245's. I just received some of Bob Crties' tweeters via Greg Roberts. I will be doing some testing with these as well as some JBL 077 tweets, maybe some JBL 075's also. I think Bob's have a big advantage in that they will reproduce quite a bit lower than the JBL's, and since my mid drivers reproduce down to 300hz, they just don't cover the high end as well. I can't wait to get to the point where I can get all this stuff tested. Unfortunately that may be a little while off as my work has picked up, so between 12 hour work days and taking a couple classes at the local community college, and the kids activities, my time is pretty limited. I will give it my best though! Thanx to those of you who have followed along or helped out along the way.

Jeremy

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Unfortunately that may be a little while off as my work has picked up, so between 12 hour work days and taking a couple classes at the local community college, and the kids activities, my time is pretty limited. I will give it my best though!

Jeremy

Wow Jeremy... don't you think you could also squeeze in a few hours on a part time job to help pay for all the audio gear, too? [8-)] There will come a day when you will wonder how you did it all. More than anything, make sure you spend time with the kids.

Bruce

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Not much to tell yet. GotHover built some of these horns and sent one to JWCullison for some testing. You can read about it in his thread about 2" 223 HZ Tractrix horns. I just sent him one of my JBL 2482 drivers to do some testing on that horn. He should be getting it tomorrow and probably have some results within a week or so. I have some testing equipment, but have had no success getting good data. I gave up for a while but the fire has been relit recently. This project has moved down the priority list for me, but I may get back to it soon. I just need to figure out how to add a few more hours to the day.

Jeremy

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