Horn Flare/driver throat mismatch causing big FR dip?

[dabbler]

Thanks, dabbler. Seems like a fairly successful mod. 3 questions-

1. What do you mean by 'inner rim'? The throat?
2. Do you have any pics?
3. Did you plot any graphs w/ all blu-tak mods, but w/o the foam?

Thanks- Kent

I mean the rim of the mouth. The blue tack needs to sit inside the rim slightly because the voice coil former is almost touching the mouth on the outside edge.

I didn't save all the measurements however I can say that that foam made only a small difference compared to the blue tack on its own.

 

[Cal Weldon]

The mouth of a horn is the exit point. The throat is where you mount the driver.

 

[dabbler]

Yes, the blue tack is on the mouth

 

[CLS]

?

For a coaxial, the mouth of the mid-high horn is the cone edge (surround) of the woofer section, isn't it?

 

[Cal Weldon]

I guess. It was something said earlier that had me confused for a minute.

"the voice coil former is almost touching the mouth"

I thought he was talking about the tweeter former so I temporarily assumed he had the two backward. My bad.

 

[dabbler]

?

For a coaxial, the mouth of the mid-high horn is the cone edge (surround) of the woofer section, isn't it?

The image below should explain what I am trying to say. It compares a Tannoy dual-concentric to a generic coaxial unit. The Beta 12CX is similar to the diagram on the left (though not exactly the same). We basically have a small horn surrounded by a second larger horn (cone) i.e. the transition isnt smooth and we can't really say it is one horn. In the case of the Beta 12CX the "HF" unit is conical and has a smaller diameter mouth than the one shown here.

An externally hosted image should be here but it was not working when we last tested it.

The blue tack is attached to the mouth of the "HF" unit. I attempted to smooth the transition between the "HF" and the "LF" (cone) by "filling" the gap as much as possible however the voice coil former protrudes between the 2. So I ended up using the blue tack to round over the sharp edge of the "HF" horn.

Hope this clears things up.

 

[CLS]

Thanks for the explanations. 🙂

I've never seen a Beta 12CX in person, the pictures on the web pages can not reveal such detail (let alone the mesh dust cap... ).

But I'm still curious about the horn mouth treatment - is blue tack touching the cone? I hope not! Or it adds a roll-back lip like a LeCleac'h? But even then, there's trapped sound energy here between horn and cone 🙁

 

[CLS]

OK, I found this:

AudioVidioPhilia: Building a pair of Adire HE12.1 Speakers

In this picture:
http://cognitivevent.com/images/he12_vctrim_500.jpg

The author mentioned about the VC former, too.

By that picture, I think the construction of the Beta 12CX should be more like a Tannoy type (instead of a Altec 605 type). Except for the overly protruding VC former, I see the 'terminus' of the tweeter section is not in a continuous curve alone the cone. I'm afraid it must be very hard to 'fix' the problem by add-on mods. 🙁

 

[dabbler]

CLS, you are correct. I did this experiment a while back and have forgotten exactly how it looks under that dust cap. Cutting back the VC former would be one way to smooth the response I guess. It would also allow modification of the horn but as you say its still not perfect.