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

[NEO Dan]

Originally Posted by CRESCENDO

Sounds like you are thinking of implementing just one ring (with or without the V-shape?). Where are you thinking of putting the one ring?

This is the general idea:

[CRESCENDO]

Interesting...

[tb46]

Hi NEO Dan,

Post #591: "...general idea..."

The "V-shape w/ the flat" in blue already takes care of the cone correction. Also, this method only applies if there is no throat chamber with reduced (e.g.: same as S2) throat to horn coupling port (Ap1/Lpt in Hornresp).

Regards,

[Djim]

Hi Dan,

It’s difficult to predict exactly what is going to happen but one thing for sure, you are adding a relative high compression factor (this is what you want to prevent as much as possible). I can't see it will correct the S2 position either, sorry.

Since there seems to be some sort of confusion about the different elements needed, I’ll sum them up:

A) Cone Volume Correction for correcting the extra volume the cone is creating in the first section of the horn/pipe. This correction needs to be placed carefully and can’t be simplified to just a flat surface. There is a relation between correction/distance/cone. It also doesn't need to be perfect (shape-wise) since it is used for subs with relative long wavelength.


B) Wavelength Correction between the two edges of the driver. Because the driver is mounted at a 90 degree angle into the horn/pipe, one edge of the driver sits more close towards the mouth than the other. The distance differences between the two edges is causing phase shifting problems and maybe it even shifts the lowest resonance upwards a little. If people want to know about it search for phase plug as used in mid-horns for instance. It has a similar function.

Both elements are used by Danley, who is also an authority in old school horns for those who didn’t know. The reason I mention this is because both correction are used by old school designers. In other words you can search for those sources yourself.

The difficulty is to integrate them both at the same time. In a symmetric fold system with centre position of the driver it easy to do, but for the 'classic' SS15 folding it needs some clever thinking.

My earlier suggestion of using a S-shape opening for the speaker baffle allows this phase shifting correction (and repositioning of the S2) but needs less cone volume correction, and probably on just one half of the driver since it will be covered halfway by the S-baffle.

[weltersys]

Originally Posted by Djim

Since there seems to be some sort of confusion about the different elements needed, I’ll sum them up:
A) Cone Volume Correction for correcting the extra volume the cone is creating in the first section of the horn/pipe. This correction needs to be placed carefully and can’t be simplified to just a flat surface. There is a relation between correction/distance/cone. It also doesn't need to be perfect (shape-wise) since it is used for subs with relative long wavelength.

B) Wavelength Correction between the two edges of the driver. Because the driver is mounted at a 90 degree angle into the horn/pipe, one edge of the driver sits more close towards the mouth than the other. The distance differences between the two edges is causing phase shifting problems and maybe it even shifts the lowest resonance upwards a little. If people want to know about it search for phase plug as used in mid-horns for instance. It has a similar function.

Wavelength size does matter, phase plugs are needed at mid and high frequencies.
As Tom Danley has often pointed out, as long as two sources are within about 1/4 wavelength of each other, they will sum coherently.

At 100 Hz, as long as the leading edge and trailing edge of the cone exits are within around 34 inches of each other, (just a bit under a meter) "phase shifting" is a non-issue.
Even as high as 200 Hz, there is no problem whatsoever in this regard with an 18" driver.

At 200 Hz, any "Flat to 35 Hz!" TH will have problems far worse from the combination of the front and rear output, totally swamping the approximate 15" leading edge to trailing edge path length difference of the radiating surface of an 18" driver.

C) The "stub" on the throat side of the "V" used in various Danley TH serves a function other than described in your "A" or "B" summation.

Art

[CRESCENDO]

Originally Posted by Djim

The difficulty is to integrate them both at the same time. In a symmetric fold system with centre position of the driver it easy to do, but for the 'classic' SS15 folding it needs some clever thinking.

My earlier suggestion of using a S-shape opening for the speaker baffle allows this phase shifting correction (and repositioning of the S2) but needs less cone volume correction, and probably on just one half of the driver since it will be covered halfway by the S-baffle.

And it also creates more pressure as well, right?

What about incorporating cone volume correction with your other throat idea? I assume it will need "less cone volume correction" like above. Maybe it'll work a little better with it.

[NEO Dan]

I think at some point you need to decide if you want to make something exactly like a model or if you have other priority's like reliability. IMO obscuring the driver cutout with the S or other oddly shaped restrictive cutouts is a sure route to cause problems. I would expect to implement a disc above the cone that would be no more restrictive than S2, and of course the volume correction would also be accounted for.

[Djim]

Originally Posted by weltersys

C) The "stub" on the throat side of the "V" used in various Danley TH serves a function other than described in your "A" or "B" summation.

If he didn't imply those functions and maybe only uses impedance correction, I find it difficult to believe the driver will hold at the power ratings he is claiming.

[Djim]

Originally Posted by CRESCENDO

And it also creates more pressure as well, right?

Yes, the S-baffle also introduces a (low) compression ratio.

Originally Posted by CRESCENDO

What about incorporating cone volume correction with your other throat idea? I assume it will need "less cone volume correction" like above. Maybe it'll work a little better with it.

Probably the pyramid-shape baffle makes it too complex to use correction of the cone volume.

Originally Posted by NEO Dan

IMO obscuring the driver cutout with the S or other oddly shaped restrictive cutouts is a sure route to cause problems.

It was an idea to work from and it probably doesn’t even have to go half way to find the right balance. It's just for correcting the position of S2 to the centre with the smallest amount of compression possible.

Originally Posted by NEO Dan

I would expect to implement a disc above the cone that would be no more restrictive than S2, and of course the volume correction would also be accounted for

I don’t see how you can compensate the volume any longer in a correct way.

[Djim]

Originally Posted by weltersys

"phase shifting" is a non-issue.

Okay, Phase shifting is probably not the correct term but if Danley doesn't use a similar approach how is it possible to expect linear cone movement of both edges of the driver at high excursion when their position is separated by the diameter of the cone? Also both edges seem to have a different distance towards S2 since it looks like S2 it is not centred in the middle of the cone in this fold-type enclosure. Also, both edges have a different position in the horn/pipe and seem to be loaded differently...