Horn throat adapters - do they destroy the sound?

[AevilMike]

Hi everyone.. I'm in the middle of building a set of La Scala clones and am fighting with myself over an issue dealing with the mid horn. I'm planning to build wooden tractrix horns and mate them with  a pair of A-55G mid drivers. 

I'd like to build my horns with a 2" throat for possible future upgrades to a 2" driver, as well as making it a bit easier to sand and paint inside the horn.. the 1" throat horn design has a long thin neck and I can foresee trouble getting in there with paint and such.

My quandary surrounds the mating of the A-55G driver to a 2" throat tractrix horn.. I can buy adapters that go from the 1-3/8" thread to a bolt on 2" exit.. but is it going to destroy the sound?

Anyone have any experience with those adapters, or just some good old uninformed opinions?

Cheers!
Mike

Edited April 5, 2019 by AevilMike

[Tarheel TJ]

I did the same thing you are considering.  I bought some 2" horns and needed to use my K-55s for a while until I could upgrade to a 2" driver.  It worked fine and sounded good to my ears.  I never measured it, but it certainly didn't destroy the sound.

[Dave S]

I have been reading about this topic for a few weeks now and I will admit I am no expert on the subject but do read opinions of those who claim to be.  🙂  Long story short, what I have gathered is as long as you do not throttle the orifice of the horn you are good.  The exit diameter of the A-55 G seems to be 11/16 of an inch which is the same as the entry diameter of the Klipsch K 700 and K 701 horns. The 701 horns used with the K 53 driver has a reducer cone which fits around the phase plug of the driver so first 1.5 inch of the horn is actually more a part of the driver design.  The 700 horns are exactly the same dimension once you get past the rear 1.5 inch of the horn.  The concern about that reduction of diameter and then opening up again is that it may introduce distortion.  It would seem that if your adaptor has a smooth transition in diameter to your horn, all should be good.  

[Chris A]

I recommend using modeling clay and the outer diameter of a suitably-sized socket wrench socket to smooth the modeling clay via precessing the socket around until the clay is smooth and takes on a nice full radius shape into the horn throat's radius angle--sort of like a section of an oblate spheroid or "quadratic throat" radius that Peavey used to market.

 

What this does in minimize the creation of "higher order modes" (HOMs) in the throat of the horn at or near the transition from the throat adapter to the horn throat.  The resulting sound should be a little cleaner and without a harsh "frying egg" sound at higher SPLs.

 

In general, you want to avoid sudden transitions in the throat in more than one place, i.e., the transition of a compression driver into a K-510 or K-402 horn is okay...but a long slot that transitions suddenly into a edge shape will begin to create problems above 4 kHz in terms of that harsh sound.

 

Chris

[ClaudeJ1]

28 minutes ago, Chris A said:

I recommend using modeling clay and the outer diameter of a suitably-sized socket wrench socket to smooth the modeling clay via precessing the socket around until the clay is smooth and takes on a nice full radius shape into the horn throat's radius angle--sort of like a section of an oblate spheroid or "quadratic throat" radius that Peavey used to market.

 

What this does in minimize the creation of "higher order modes" (HOMs) in the throat of the horn at or near the transition from the throat adapter to the horn throat.  The resulting sound should be a little cleaner and without a harsh "frying egg" sound at higher SPLs.

 

In general, you want to avoid sudden transitions in the throat in more than one place, i.e., the transition of a compression driver into a K-510 or K-402 horn is okay...but a long slot that transitions suddenly into a edge shape will begin to create problems above 4 kHz in terms of that harsh sound.

 

Chris

Better yet, use a Tweeter above 4 Khz.