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Horn fixer upper

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julius111 View Drop Down
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    Posted: 17 September 2021 at 7:58pm
Hi, 
long time reader, first posting… maybe i could get some advice on my horn “restoration” project from some knowledgable people here, i would appreciate

from my youth i have these folded horns, dynacord fe 100 lo. except an old scan of the technical data i have nothing on info. they used to have evm 15lo pro line inside, before i had them.


yep, there is some plastic pipe where it used to have what looks like cardboard…

i will be setting these up next weekend for an event of a friend, for free. so my plan is to put RCF LF15N401 in, which are the only drivers i have on hand. my knowledge of ts parameters is limited but it looks to me like it could work, and the sound is okay. not super low, but punchy.

have not really put a lot of power into them, tested them with a small amp. i am concerned though that the ports could be to small considering the much bigger xmax on the new speaker. before & after closing the port temporarily, i made measurements, close range, with that behringer mic. far from perfect, but maybe someone can see a trend in the data? (spl is not calibrated)


red is standard, green with ports blocked. 

my intention is to run them on a macrotech 2400,
lo cut 40-50hz 48db
x-over 90-120 hz to electro voice S1503ER
with t.racks 206

any input on how to achieve the best results would help.

thanks! & cheers.



Edited by julius111 - 17 September 2021 at 8:00pm
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 17 September 2021 at 11:17pm
From the picture it's bit hard to tell the tube diameter, but to my eye the grey one seems to be 50mm sewer pipe. Why not use 75mm, for example 22,5 or 30 degree elbows at driver plate and bit more length straight pieces inside the back chamber?

Model the rear chamber in win isd and try to achieve same tuning with larger pipe diameter. Start with longer than needed, measure, and cut to lenght. Glue and screw to position. Use screw pilot holes.

Tune seems to be somewhere near 35Hz?

Simple red-neck-tech solution.LOL
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smitske96 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 17 September 2021 at 11:28pm
If the measurements are valid, I would definitely not use it that low.
It's -10dB @45Hz (80Hz reference), even as a dedicated kick bin it looks poor.
If you have a driver like the LF15N401 I would defo look for something else, would be a waste for the driver.
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julius111 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote julius111 Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2021 at 7:34am
hi andy, thanks for your feedback. i am hesitant to make any permanent modifications, it’s more the „mac gyver“ approach to get some sound on short notice. i think i heard the air flow through the ports when increasing power, but i might be wrong?

i have looked at win isd and hornresp a few years back, pretty sure i won‘t learn all that until next weekend ;)

hi smitske, thank you for your response. i know it‘s a mismatch, it‘s just all i can work with. trying to get the most out of it, so my question is if i sacrifice efficiency for sound quality, or will i ruin the sound completely? i feel it‘s not enough sub anyway to match the full output of the tops.

if it‘s a totally stupid idea to put the RCF in even just for the weekend, i might call in some favors and built cubo15… 
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2021 at 8:39am
Just compared EVM-15L and RCF LF15N401 datasheets. There seems to be almost 3 times more Xmax.

Not even talking about Xmech......

Maybe try them back chamber temporary closed with some ply scrap pieces if using RCF drivers? Compensate with eq as needed.

Can you measure the impedance graph in original state tubes open and tubes closed? That would reveal the intended exact back chamber tune.


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julius111 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote julius111 Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2021 at 12:05pm
the measurement with ports open was done with the other enclosure, which is original, except the driver. i‘ve now got the amp and will do some a/b testing.

could something really bad happen if i close the ports? mechanically or thermal?

while electrovoice does not produce the evm any more, i‘ve read numerous times that you can buy clones, are they any good? then i wouldn‘t need to change the ports. i am thinking of 3d printing a replacement with the exact length and diameter of the originals.

in any case, thanks for the input!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2021 at 12:20pm
Edit. 

Edited by Contour - 18 September 2021 at 12:21pm
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 18 September 2021 at 12:26pm
Hi Julius

In your second picture, You have measured frequency response, not an electrical impedance.....

edit

In RCF there's so huge mechanical limit of 52mm p-p, that I suspect You can not trash them too easily.

Those pipes appear to be too small for such large displacement driver as RCF, that reflex part tuning could go screwed if extreme power is used. On the other hand rear enclosure volume is not that large, that will lower the port airspeed somewhat. And port in horn throat may add up small amount in acoustical loading of ports.


Edited by AndyWave - 18 September 2021 at 12:40pm
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julius111 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote julius111 Quote  Post ReplyReply Direct Link To This Post Posted: 21 September 2021 at 1:09pm
One last follow up to this… i‘ve had to check out how and why to measure impedance, and then decided to not do this. while i do appreciate your answer, and i like to learn new things, it seems even if i pull it off, i am not sure i can do much anything before next weekend :/

so i did what every professional would do, fix the plastic pipe with hotglue and hope for the best.

i‘ll try stacking and putting one top on them. i am sure they are much louder now than original, looking forward to hearing them in the location.

cheers! J.
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