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250-4k horn

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Augusts View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Topic: 250-4k horn
    Posted: 21 March 2021 at 4:28pm
Hello

I am planning to construct a mid freq horn for an 8" Oberton 8NMB250v4

What do you think?  I am using an exponential horn flare. Its depth is 350mm

I will try to do a phase plug next





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JulianDA View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JulianDA Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2021 at 11:28pm
250-4k is, to say the least, pretty challenging if you want to have an even dispersion in that range. Did you try to simulate it in akabak or a similar software? I even struggle to get good directivity from 200-2k with a phaseplug in front of the driver...
That said, your horn looks rather decent with a nice curved geometry, but i would try to eliminate the sharp edges at the mouth, since they will be the cause for diffraction und reflection of soundwaves back into the horn. This will result in peaks and dips in frequency response and the onset of resonances over the length of the horn, which in turn will have a bad impact in the time domain (i dont know the rigth word in the english language, but you will see it in the burst decay and that can lead to an unpleasant sound)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2021 at 11:30pm
Well said saiar!

Thank you for commenting
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Post Options Post Options   Thanks (0) Thanks(0)   Quote VECTORDJ Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 2:23am
The hard part is 2k-4k. Please show Us the Phase plug design and real life testing. Thanx....


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Augusts View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 8:09pm
Julian, do you mean the sharp edge of the perimeter at the very end of the mouth or the not so sharp corners towards the end of the mouth?

I simulated the horn in hornresp, as far as it could be simulated. Have not got my head around akabak


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 8:25pm
The phase plug is probably going to be just a round cilinder with a cd horn at the end. I still have a long way to go until testing. Ill be routering this baby out of polystyrene for testing, then adjust, then another routering to make a negative. then fiberglass 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 10:31pm
How big is the Horn's mouth? It seems you are basing this design on Quarter-space. This may be fine for bass horns. However, for midrange horns, if the mouth is not big enough to play 250 Hertz at a substantial level, you are looking at the bulk of your SPL will hover around 500 Hz, with a box offering a mere 350 mm in depth.

I might add with the loudspeaker you are considering offering around -3 dB @ 5 kHz (all courtesy of the Le) you may want to consider finding a driver that reaches to around 7 kHz if the goal is  4 kHz.


Best Regards,


Edited by Elliot Thompson - 22 March 2021 at 10:34pm
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Augusts View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 10:37pm
Thanks for commenting.

The mouth is around 3000sq/cm

Hornresp shows promising results
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 10:53pm
The radius of the mouth nears 250 Hz full-space, which is good. You will definitely be relying on equalisation once, you go below 500 Hz due to the limited depth of the horn.

Best Regards,


Edited by Elliot Thompson - 22 March 2021 at 10:55pm
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Augusts View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 11:05pm

This is a sim on axis. I think the phase plug could sort things at 2-4 kHz
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 11:21pm
Originally posted by Augusts Augusts wrote:


This is a sim on axis. I think the phase plug could sort things at 2-4 kHz



The graph correlates to what I mentioned in regards to the limitation of the horn's length. Remember, -3dB is half the power. So anything below 500 Hz will rely heavily on equalisation. Also, the loudspeaker in question is not suited for the application for, you should not have such a drastic decline from 1 kHz - 2 kHz. The driver's Le is the problem.

Try a different loudspeaker.

Best Regards,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 22 March 2021 at 11:37pm
Your goals of a coaxial mid/HF horn are the dream, if I could design a phase plugged mid horn that could play from 250-4k with a compression driver in the phase plug I would.

The issue is that getting a mid horn to play from 250-4k is a serious challenge, not impossible but seriously difficult. As VectorDJ said above, the 2-4k is the hardest part. Simply putting a phaseplug looking object in the centre of the horn will not get you there. 

I had a go at designing a mid horn but gave up when I realised how involved it was going to be. The process of tweaking a cad model over and over, then simulating it over and over was soul crushing.


I suggest you read this thread https://forum.speakerplans.com/xtro-flare-redevelopement-thread_topic98310_page1.html

A lot of the images are missing which is a shame but there is some really good information there. After all that work, all those AKABAK 3 simulations, they ended up with a horn that could play from ~300-2k.


Take these tips with a grain of salt as I have never actually successfully designed a mid horn but this is what I would do:

-There are worse choices than the 8NMB250v4, but there are also better ones, as I understand it, more EBP is better in mid horns, a popular driver in the past has been the 8PE21 but I would use a closed back driver like the 8NSM64

-I would use AKABAK 3 to simulate the horn and the phaseplug, hornresp tells you pretty much nothing when it comes to these kinds of horns, they are very sensitive to small changes in geometry, which you can not simulate in a 1d simulation program like hornresp.

-While your goals are the dream, I would target a much lower xover point and use 1.4 inch compression driver to meet it. This is just far more achievable. 

Keep working at it, I think its a cool project! If you keep posting updates here, I'm sure people will help you out and will enjoy following your progress.
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