Geddes on Waveguides

[gedlee]

Originally posted by graaf

please at least make it CLEAR - the answer is "NO advantage"?

best regards,
graaf

In general I don't see much advantage to a changing cross-section in the waveguide, certainly not from circular to square. Circular to elliptical I could understand - if done right!!! - but not to square.

[gedlee]

Originally posted by MaVo
Hi JLH, i wonder if the distance between both horns will lead to increased interference, lobing, combfilter effects. Gedlees speakers have a smaller distance between both sources. I dont know guidelines to figure out if this is a problem in this case, so if someone knows better, please clarify.

These were all good posts and good work. I do think that the larger waveguide and horn might have polar response problems because of their size. Lobbing cannot be avoided, but it can be minimized and spacing is the critical thing. All these tradeoffs - sorting them out is indeed a real task.

What I would ask of JHL - why don't you try my approach first and see how you like that. It far easier to impliment that what you are proposing and you just might find that it changes your mind about the dynamics of a direct radiator. If you still aren't satisfied then you can add in your Tractrix horn, but at least you will have a well established basis for a comparison.

[tinitus]

Originally posted by gedlee


Circular to elliptical I could understand - if done right!!! - but not to square.

That good news as I and friend are going to make a mould fore a big glassfiber elliptical horn/waveguide ... also because it looks cool ... probably in a couple of years

[MJL21193]

Originally posted by gedlee



Insults are seldom an effective way of making friends. And don't claim that it was a joke. Good jokes don't make fun of people.

No insult intended, just a comment from the sidelines.

We need to lighten up a bit.





Humility: The defining characteristic of an unpretentious and modest person, someone who does not think that he or she is better or more important than others. Synonym: humble

[KSTR]

Originally posted by angeloitacare
i have drawn a tractrix lower midrange horn with 27" size at the mouth, and a oblate spheroid midrange horn with 20" mouth, and 10" deep. When the two horns are time aligned, the vertical mouth distance one to the other is about 13". How might this discrepance affect the perceived sound and integration of the two channels?

I'd think it's always best wrt to a consistent time behaviour vs. radiation pattern to align the mouths on the baffle, not the diapraghms... which means, when the HF part comes out to be ahead of the bass as it is here, the HF must be delayed... hard to do in a passive/analog XO. This is another point where the approach in Dr. Geddes' Summa is well balanced, he has the bass before the HF in time and that is easily taken care of in the XO. And both parts are integrated onto a single baffle which, besides of more benign diffraction issues in general, is quite probably making off-axis time behaviour very consistent to on-axis, at least in the sideways dimension.

Therefore, another +++ from my side, too...

- Klaus

[gedlee]

Originally posted by MJL21193


No insult intended, just a comment from the sidelines.

We need to lighten up a bit.

It was insulting and YOU do need to lighten up.

[angeloitacare]

I'd think it's always best wrt to a consistent time behaviour vs. radiation pattern to align the mouths on the baffle, not the diapraghms... which means, when the HF part comes out to be ahead of the bass as it is here, the HF must be delayed... hard to do in a passive/analog XO. This is another point where the approach in Dr. Geddes' Summa is well balanced, he has the bass before the HF in time and that is easily taken care of in the XO. And both parts are integrated onto a single baffle which, besides of more benign diffraction issues in general, is quite probably making off-axis time behaviour very consistent to on-axis, at least in the sideways dimension.

hi Klaus

there is no baffle. While with time aligned diaphragms the distance on axis to the listener is the same, off axis, the reverbant sound takes different paths, when the mouth is not aligned. Crossover delay is another chapter... I am not interested in comparisons between the two designs - summa - and lower midrange horn configuration in a multihorn system , they are two worlds, but the best method of horn alignment each to the other.

[tinitus]

the "super-ellipse" by Piet Hein
Its a beautiful shape ... wonder if it would make wonderful sound too

[soongsc]

Originally posted by gedlee



...
What I would ask of JHL - why don't you try my approach first and see how you like that. It far easier to impliment that what you are proposing and you just might find that it changes your mind about the dynamics of a direct radiator. If you still aren't satisfied then you can add in your Tractrix horn, but at least you will have a well established basis for a comparison.

I second this proposal. Most perceived limitatiodynamics heard in direct radiators are the more more complicated wave generated from various parts of the diaphram which are evident when looking at off-axis response. This normally does not exist if the xo point is below the beaming point in lower frequency drivers.

[JLH]

Angelo,

I find in real practice you can have the two horns/wave guides much closer than what your picture shows. It is a subjective call as to how close they can be. For the most part, the mid-range wave guide’s sound reflection off of the back lip of the mid-bass horn just becomes indirect sound. However, you still don’t want too much reflection.






Klaus,

You make some very good points. My problem is I’m an Analog man and very much dislike digital devices and artificial time delays. In my past installations, I have had very good success with time aligning the diaphragms in a vertical arc. The convergence at the listening position becomes very good with this method. Of course, I have never done it with an OS wave guide before. I’ve only done this with tractrix horns. I’m unable to tilt the horns in the image, so I just drew lines to show how they should be tilted along the vertical arc.





Dr. Geddes,

Thank you for your reply. You make a good argument for the direct radiator. However, I’m still not sure if there is one made that has the punch I’m used to. In addition, since I’ve always used horns all my amplifiers are of the low power tube type. My most powerful amplifier is 6.5 Wrms. Maybe a Karlson coupler would be an interesting compromise?



Some of the few direct radiators I know I could live with are unobtainable at a reasonable price. The Western Electric 728B, the original Altec 515A, and a few Klangfilm woofers are just a few that come to mind. Earl, do you have a suggestion for a good direct radiator?

Thanks, JLH