Hello Soongsc,
You asked me to explain what means:"découpe plane d'une facette" in my spreadsheet one can use for the calculation of axial horns.
In this version of the spreadsheet an option is the calculation of a "gramophone style" horn. The horn is made from the edge to edge assembly of many facets (or petals). Each facet (or petal) can be cut inside a sheet of plywood, cardboard or metal using the coordiante of the points under the title "découpe plane d'une facette".
Also about "profil d'une arête de facette" this was added at the request of someone who want to build profiled rigidifiers to add at the back of every edge between 2 facets (or petals) in a gramophone style le Cléac'h horn.
Best regards from Paris, France
Jean-Michel Le Cléac'h
You asked me to explain what means:"découpe plane d'une facette" in my spreadsheet one can use for the calculation of axial horns.
In this version of the spreadsheet an option is the calculation of a "gramophone style" horn. The horn is made from the edge to edge assembly of many facets (or petals). Each facet (or petal) can be cut inside a sheet of plywood, cardboard or metal using the coordiante of the points under the title "découpe plane d'une facette".
Also about "profil d'une arête de facette" this was added at the request of someone who want to build profiled rigidifiers to add at the back of every edge between 2 facets (or petals) in a gramophone style le Cléac'h horn.
Best regards from Paris, France
Jean-Michel Le Cléac'h
soongsc said:
A Small Request for the Moderators
A small request for the DIYAudio moderators: could the JMMLC discussion (and the recent associated postings) be moved over to the new thread?
As Dr. Geddes has mentioned, this is his thread, and there is lots to discuss about the OS waveguide and the overall Geddes system design philosophy without digressing into other areas. As one of the most notorious thread-starters myself, I feel this would be the courteous thing to do.
A small request for the DIYAudio moderators: could the JMMLC discussion (and the recent associated postings) be moved over to the new thread?
As Dr. Geddes has mentioned, this is his thread, and there is lots to discuss about the OS waveguide and the overall Geddes system design philosophy without digressing into other areas. As one of the most notorious thread-starters myself, I feel this would be the courteous thing to do.
I thought I'd post a comparison between measurement and BEM. The measurement has equalization.
BEM of the second wave guide
Measurement of the second wave guide
BEM of the second wave guide
An externally hosted image should be here but it was not working when we last tested it.
Measurement of the second wave guide
An externally hosted image should be here but it was not working when we last tested it.
On the topic of the foam inserts and people suggesting reduced resolution, would lining the O/S waveguide with 1/4" 30dpi foam not have much the same percieved effect without "losing resolution", or a complete waste of time?
Also, does the foam attenuate the low end of the WG+CD much? And if so, does it greatly affect the added sensitivity (and thus the ability to use a lower XO point)?
Also, does the foam attenuate the low end of the WG+CD much? And if so, does it greatly affect the added sensitivity (and thus the ability to use a lower XO point)?
I haven't read every post closely but there's been talk of loss of resolution from the foam plug. What's the basis or the thought process behind this claim? I've been thinking about this and I don't see how the foam can have an adverse effect on "resolution". If anyone has a different understanding or some insight into this I would like to hear it. And before we have a discussion on this I would also like to see a definition (or something close to it) of what that vague and often miss-used and misunderstood term - resolution, is.
I don't want to be contentious here but just throwing feelings and hunches out there without some sort of a valid theory based on the mechanics involved can't be very useful.
I think you reduce a lot of the high order non-linearities in a tweeter, which those who are used to typical dome tweeters are use to, and they perceive a loss of detail and "air". But then now I am making unsubstantiated conjectures.
Myself, I am happy to loose that "sparkle", as that sparkle is catching at first and fatiguing eventually.
Myself, I am happy to loose that "sparkle", as that sparkle is catching at first and fatiguing eventually.
musical noise said:
The people making these claims aren't trying to be useful. They have a "hunch" that something in the path of the wavefront is bad. I've heard this all my life. It use to be horns were "bad" because they interfeered with the wavefront. Then when this was resolved and now it is the foam. There simply is no more science to say that something in front of the wavefront is bad than the bogus theory that electrical components, AKA the crossover, in front of the driver are bad. Both can be very effective if done correctly. The fact that they are often done wrong is not proof that the concept is faulty.
Well, I can't say what happens with each and every speaker. But all speakers I have listend to sounds a bit muffled with speaker grills on. I think the effects of foam will be evident if the same curves on the Summa's were shown without the foam. However, I don't think this data will ever been shown.musical noise said:
I would say, put grill cloth in front of your speakers, if you don't hear a difference, then don't worry about it.
But the whole point is that the Summa is "equalized" WITH the foam in place. That's very important especially in light of the fact that all open cell foams have varying absorption coefficients with frequency. This is also true for regular grill cloth material albeit to a lesser degree but that's only because it's much thinner.
Put more simply, the muffled sound is due to the greater rate of absorption with increasing frequency. When you equalize and restore this high frequency content the end result should be indistinguishable from the original. Me thinks its all in the frequency response.
Up to now, what I'm finding is that the OS type expantion handles the high frequency control quite well, the traditional horn expansion controls directivity and HOMs at the mid frequencies quite well. So really, a more complicated curve will yield better results, and could possibly reduce the need for foam. But the whole thing really needs quite a bit of work and could be very driver dependent design.
Why would you need to equalize differently for each angle? This is not apparent from the geometry of this waveguide - quite the opposite. The waveguide is basically a conical beyond the OS transition just past the throat. As such the wave is perpendicular to the side walls and its frontal shape forms part of a sphere's surface. All points on that surface are equidistant from the throat and because of the shape of the foam plug (I guess it doesn't bulge out for no reason) all such points will travel the same distance through the foam.
Can't see a variation of absorption with respect to angle.