TH-18 Flat to 35hz! (Xoc1's design)

[m R g S r]

Try contacting Tom Danley. Others have mentioned that he has been helpful with technical questions in the past.

[Djim]

Hi Martin,

I think there are two problems with your model:

1. The air in the horn is not running like a 'flow' but the air molecules bounce against each other.
2. There are no pressure points after the throat in an expanding horn.

When the frequency drops below the excursion dip in your picture, the right side of the driver becomes unloaded first (distance versus frequency). Therefore I prefer centre loadings with a (cone)volume make up.




Since this is not always possible another way is to close half of the throat (the half on the left side in your picture) so that the soundwaves from the cone all have the same distance to S2.



The 'S' form is needed to follow the curve of the cone and dome of the driver.

This way the S2 becomes again the centre point of pressure and both sides of the driver are more equally loaded.

[BP1Fanatic]

Excellent illustration! The 1st pic looks like the CB's people are building on speakerplans.com.

[Xoc1]

Hi Djim
Thats an interesting solution.
An obstruction like that would have to be offset from the baffle plate to miss the driver excursion, which could be quite a distance, given the X mech of some of the drivers available.
I have never seem that used in a DIY TH speaker. Do you know of any practical examples?
I like that you have taken account of the shape of the cone.
The cone shape must make quite a difference to the cross sectional area of the throat, as the air molecules bounce into each other across the offset face of the speaker.
Regards Martin

[m R g S r]

I don't doubt you djim, but if the shape made that much of a difference to the cone, why aren't people destroying drivers due to uneven pressure on the cone in every TH that doesn't have the S-shaped covering? Is it because the compression ratio is low enough And the cones are stiff enough to resist deformation?

[Djim]

Hi Martin,

I think it was djk who showed an actual picture of an existing example in some thread. It reminded me of its true function since it is an old trick used by several companies in the past (maybe also today, I don’t know) for 'problem' horns in a time that cones were not enforced with fibres or other exotic materials.

When the throat isn’t optimal loaded, which is the case in most horns and TH’s (I mean different speeds of particles along the throat line) it can end in complex behaviour at max excursion.

About its optimum form, with your advanced 3D modelling skills you should be able to optimise it in relation to the form of the cone/dome. If it is the answer for all mechanical problems at high excursion I don't know yet.

Hi mRgSr,

I don’t have all the answers, but the stability of the mechanical characteristics are very important to drivers that have to operate around their max excursion. You have experienced that difference in quality yourself

[scameron78]

Originally Posted by Djim

Hi Martin,

I think there are two problems with your model:

1. The air in the horn is not running like a 'flow' but the air molecules bounce against each other.
2. There are no pressure points after the throat in an expanding horn.

When the frequency drops below the excursion dip in your picture, the right side of the driver becomes unloaded first (distance versus frequency). Therefore I prefer centre loadings with a (cone)volume make up.




.

this picture looks like the Cyclops cabinet.

[djk]

"an actual picture of an existing example in some thread."



Cerwin Vega B36 style as made by B52.

"this picture looks like the Cyclops cabinet. "

Frazier made step-horns dating back to the 50s, RCA made some too.

[Djim]

Thanks Djk, that is the picture I was looking for.

[Djim]

Hi Martin,

Danley seems to use another approach. Some owners describe the Danley throats as having a "V" shape. Such "V" shape has two advantages:
1.) The "V" shape opening is closing towards the end of the driver probably to equalise the pressure.
2.) The second advantage of the "V" shape seems to be that the horn length from S1 to S2 is at least 3 times the diameter of the driver. By positioning the driver more away from S1, the pressure/loading differences between the two sides of the cone becomes smaller.

(The picture is meant as an example of the principle and is not a realistic representation of any Danley's TH's)