Synergy/ MEH Horns and Port Length, size, form

Hi

I am planning my first meh horn.

What is clear to me is the position: position should be max lamda/4 from next diafragma of the tweeter and ports should be in the corner's.

But what about port size und port form? I found somebody who said: size max ~1/8 of SD is this correct?

In my case it could be necessary, to make the ports a bit longer and diagonal, to make sure, that i keep the max lambda/4 rule.

Is it OK to drill the holes not 90° into the plate?

I have attached a picture. The red part is a diagonal port. Frequency range would be 100Hz to 500Hz.

Thx a lot and greetings

Christian


Port.PNG
 
I found somebody who said: size max ~1/8 of SD is this correct?
I use a max "area compression ratio" of 10, or 1/10 per your point of view. The tradeoff is acoustic efficiency. Look at the Harry Olson or Leo Baranek texts in the horn sections (Acoustical Engineering, Acoustics) for more detail on this subject.

The only concern of elongating ports is that the port length is constrained by something like a quarter wavelength at the crossover frequency, e.g., 3.4" (8.6 cm) at 1 kHz, so however long you choose to make them is basically not of great concern. I believe this is what you are referring to as "lambda/4" (although I'm not sure).

Is it OK to drill the holes not 90° into the plate?
Yes. Look at the Danley Jericho horn or any folded horn design. The tradeoff is local resonances, which you can adjust using a different mounting plate with slightly different port geometry/angle, if necessary, if an unwanted resonance or cancellation appears.

Chris
 
Hi Chris,

Thx for reply!

The only concern of elongating ports is that the port length is constrained by something like a quarter wavelength at the crossover frequency, e.g., 3.4" (8.6 cm) at 1 kHz, so however long you choose to make them is basically not of great concern. I believe this is what you are referring to as "lambda/4" (although I'm not sure).
OK... that seems to be the same rule lake we have for Port position.

To be more flexible i am cutting my horn and will remodel the mouth... so maybe no need to make them longer ;)

Christian