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

Thank you for commenting

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

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,

The mouth is around 3000sq/cm

Hornresp shows promising results

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,

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,

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

Yes i mean the perimeter on the hornmouth. You have to keep in mind that all sudden changes in acoustical impedance (i.e. flarerate) will produce diffraction effects which can be interpreted as new point-like "sound-sources" which then will radiate omnidirectional and therefore also back into your horn, causing resonances.
Another thing to keep in mind is the big spike in groupdelay on the tuning frequency of a horn. In an optimal world you dont want to have this spike in the used range of the horn. At lower bass frequencies the groupdelay is less noticeable, but in the mid-range it can be problematic. So a really good midrange horn should be tuned ~1 Octave lower than the desired crossover frequency. But this leads to really big horns...there is a compromise to be found somewhere inbetween big enough and to small 

But on another note: you can listen to the advice of citizensc, he knows his stuff regarding horns and akabak ;)

 

I am now learning Akabak

Do you know why it could be that tha phase plug is absent in the BEM section but visible in the General- Mesh section?

Sorry i cant answer that question on the fly since i am not that deep into akabak at the moment (there is alot of other stuff to be done in my life :D ), but maybe citizensc has encountered a similar problem?


But your directivity plots dont look to bad :) For easier comparison of plots i would advise you to normalize your plots. There should be the option "normalize to x-axis" in VACS-Viewer under "processing" (or "postprocessing"). After that you can choose your dB-steps as indicated by the different colours to show the -6dB Point better. 

I do not know how to do a simulation like that with the horn. Could you give me some keywords?

That said look at the pm 60 90 streach the fane design a bit and squeeze it a bit to fit that 18 sound horn and two drivers. Quite similar. Not saying that is was the inspiration for the pm in anyway shape or form. But fane say in the book stick a comp in the middle. If you want.

Hello,

For a 3-way, 15"+8"+CD I'm thinking of using the Oberton 8NMB250v4,

the specs look very good.

If you have purchased them, how do you judge them ?

Regards,

Danny

They are excellent drivers, the response is smooth up to 5kHz, I would compare them to BMS.

Thanks,

I will put them in my basket :-)