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HornResp

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Posted on July 24, 2020 at 06:30:29
ACMINC
Audiophile

Posts: 25
Joined: April 13, 2012
I have a pair of EV 1823M and T350's. I want to make conical wooden horns for both. I already used Hornresp to model my mid-bass and bass horns. However I can not find the data needed to enter into Hornresp for these drivers. Should I just follow the basic rules of horn design instead? Length of horn, and circumference of horn = lowest freq wanted. What is the rule for the throat? Of course if anyone has the parameters for these 40 year old compression drivers that would be much appreciated too

 

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RE: HornResp, posted on July 24, 2020 at 09:53:38
Paul Eizik
Audiophile

Posts: 2120
Joined: September 15, 2001
ACMINC

I have EV 1823M's and T350's too. I also have Hornresp but to be honest I've never actually used it. I'n not sure what specs Hornresp is asking for but the specs on the EV 1824M Engineering Data Sheet are rather basic: 8 Ohms; minimum crossover freq. 400 Hz @ 12 dB per octave; 104 dB sensitivity. Hornresp can sometimes ask for rather obscure specs which you would have to guesstimate or derive yourself by testing.

A horn is most efficient when the length of the horn is equal to one half of the wavelength of the lowest target frequency you want to reproduce. It's not necessary for the entire wave to fit inside the horn as the half wavelength is a high pressure area and this is what the horn will be loading/ affecting at the low end. So working from this we use: 13500/F. Tthis is where F is that frequency in Hz, and 13500 is an approximation of the distance sound travels in inches per second, and the answer is that particular wavelength in inches. So using 500 Hz (which is where I cross my 1824's): 13500/500=27 inches, and dividing this by 2=13.5 inches which is the optimal horn length for this frequency. The mouth of the horn should be nominally equal to, or greater than the circumference of a circle similar to the full wave length of the lowest frequency. It's best to oversize the mouth and my square tractrix horns are 11 inches per side: 11 X 4=44". This works for the curved wall tractrix horns I have but you would need to oversize a conical horn quite a bit to get a comparable bass extension as the conical horn tends not to load the bass as low as comparable curved wall horns as Olson has shown us. I believe that Hornresp can allow for this in sizing a conical horn. Anyway that's the bad news, the good news is that experimental conical horns are quite easy to construct and modify from cardboard or fomecore from the art supply store, and you can test them with Room Eq Wizard/REW and a suitable test mic.

If I understand your intention correctly, I would avoid trying to build a conical horn for the T350. Designing the phase plug part is rather tricky to put it mildly. Some years ago I tried to design a tractrix horn for some EV STR350's and the phase plug was the part that got me stuck as the low/mid response was good on my horn but I couldn't get the highs with my home made phase plug that the stock horn and phase plate had, though it was a learning experience. At any rate make sure to get the 1824's and T350 in phase by at least aligning the voice coils on the vertical plane and making a streamlined ramp going from the bottom of the T350 mouth to the top end of the mid horn mouth. This won't make the sound drastically different but it will tighten up the stereo image quite a bit as it mitigates destructive reflections off of the mid horn back towards the T350. BTW the T350 should be mounted with the long horn dimension in the vertical position for broadest horizontal coverage which may seem counter intuitive but the T350 is a diffraction horn employing "waist banding"/ squeezing the coverage pattern as the low end response of the smallest dimension of the horn mouth part collapses and squeezes the response of the larger dimension of the horn mouth area.

Paul

 

l agree with Paul, leave T350 as-is. nt, posted on July 24, 2020 at 13:17:46
Coner
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Posts: 3703
Location: S.W. Washington state, USA
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nt

 

RE: HornResp, posted on July 25, 2020 at 15:48:33
ACMINC
Audiophile

Posts: 25
Joined: April 13, 2012
I guess that I should not have just said "conical" horns. I really meant "round" and not 4 sided. I am going to go either exponential or tractrix (But round). So I am guessing that you have a 3 or so segmented horn to approximate the tractrix curve. Hornresp does not provide results without t/s parameters. So how did you determine how long each segment should be? Did you use cardboard to test your horns? Or did you decide that anything is better than the 8HD Diffraction horns! My 45 year old 1823M's were crossed over with EV 8X and 36X crossovers. So who am I to second guess the manufacturer? Besides I don't need to go down to 500Hz because my mid-bass covers 150-800Hz

 

RE: HornResp, posted on July 26, 2020 at 08:29:35
Paul Eizik
Audiophile

Posts: 2120
Joined: September 15, 2001
Ken

I'm Hornsesp curious but I'm really just an interested by-stander as I don't have a job for it now, so I can't help you there. My tractrix mid horns are square horns with 4 sides. I built them out of fomecore which is a piece of styrofoam between two sheets of plasticized paper which can be formed into curves by scoring the top sheet and styrofoam with an exacto and then bending so the bottom sheet acts like a hinge. I built them following Bruce Edgar's seminal Tractrix Horn article from Speaker Builder magazine which is still available I believe on VolvoTretter's website. They immediately crowded out the big McCauley cast aluminum PA mid horns I was using which had replaced some 8HD's before that. I use home made first order series crossovers now with ASC oil caps and air core foil inductors. I once compared my square horns to some round Edgar "salad bowls" at a friends house, and the Edgars were nominally the same dimensions as mine, and I really couldn't hear a difference. I tried some smaller experimental horns out but none of them performed as well as the original 13.5" long ones. I let the drivers and horns frequency response measurements tell me where the crossover point should be and I cross my 1823s' and 1824M's at 500 Hz on the bottom, but your milage may vary of course. Square horns are easier to make than round horns and, since I couldn't hear a difference, I remain in the square camp. Square horns are also easier to integrate with the aforementioned ramp which streamlines the tweeter with the mid, and is non-negotiable once you've tried it in my opinion.

I would definitely do the midrange project first and see how you like it. When Voigt designed the original tractrix horn he wanted to make the smoothest possible curve from the horizontal plane to the vertical mouth, and a draftsman told him that this was a tractrix curve. It's easy to draw a tractrix curve with a flexible ruler you can get where they sell drafting supplies, if you know the length of the horn and mouth size.

About the only useful modification you can make to the T350 is to remove the bug screen which will make it measure slightly better, but whether this is actually audible is hard to say. The advantage of the T350 is how low you can cross it, as it had to be able mate with the EV mids which didn't go as high as the Altec and JBL's.

Good Luck and let us know how it goes

Paul

 

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