Quarter wavelength point of interaction synergy horn

[nc535]

I'm using Google Sketchup, which is free and fairly intuitive, with lots of tutorials and help online. If you can draw it, with each separate piece of wood a "component" than you can build it, you might even be able to get it CNCed, you can use the protractor tool to measure angles and then label them with text, ....

Makes sense ? Are you saying have the 12" mid driver inside the box and the other 3 segments of the horn outside? You could do that for the ultimate in simplicity or you could wrap the sides all the way around the horn, which I did in my 2nd dwg. If you put more of the volume under the horn, as you are proposing, then you lift the horn up closer to ear level. This is a generally a good thing except then your floor bounce null will be a lower frequency and harder to get rid of. If you keep the horn low, then you should probably tilt the whole assembly back a bit to point the axis of the horn at your ears.

 

[bwaslo]

The horn isn't going to do anything for the bass frequencies, so I wouldn't put the reflex ports into it just to keep it a 'Synergy'.... minimize the diffractions possibilities.

I'm also a little doubtful that synergy apertures near the thoat, that would let you crossover up at 800Hz would also pass enough bass for you from the 12" woofer. That would be a lot of compression. Best model it in HornResponse and check before you make sawdust.

 

[nc535]

Yes, the sound will be equally spaced around the horn axis, and would remain so in an axisymmetrical guide but individual components won't necessarily travel axially. As you say, the range is limited. A point source (which implies a cone based waveguide) can be achieved if the wavefront has an effective focal point that coincides with that of the waveguide's conical asymptote.. In this case it is being taken care of only by the acoustically small space.

Witout this constraint, reflection at the smaller throat wouldn't necessarily align to create a complete cancellation notch, though the reflection may amount to a point source.

Your definition of a point source is apparently geometry based: that there is indeed a single point from which the sound appears to emanate.

I think that may be too strict to apply to a Synergy horn. Many of the horns we build have astigmatism and still are considered point sources. I know XRK would take issue with you because he made a Synergy with a Tractrix profile, which was in no way cone based.

Perhaps we are speaking loosely when we call these point sources; more precisely they have a certain desirable point source behavior.- that they act like a single full range driver when observed,listened or measured from different angles. (e.g. no lobing). Whether the apparent source is indeed a single point or a fuzzily defined acoustically small region near the apex of the horn is immaterial.

 

[bwaslo]

As you get lower in frequency (and as wavelengths get larger) a relevant size of a "point" gets bigger, less specific.

But I don't consider that "point source" means linear or minimum phase, just that the radiation into airspace is similar to that from a point, while keeping similar spectral shape. Of course, for a Synergy horn, that space doesn't include the half that is behind the horn!

 

[AllenB]

Your definition of a point source is apparently geometry based: that there is indeed a single point from which the sound appears to emanate.

Making a speaker 'disappear' includes removing secondary sources of sound such as diffraction, which give audible clues to the shape of the speaker in time and space, and this can be achieved by aiming for point source behaviour so that in band sound is radially supported as from a single point, however that is achieved.

Point source waveguiding geometry can be divided/limited in frequency or space. Where the wavefront doesn't conform to said part of full space, diffraction is possible. It doesn't have to be axisymmetrical, but doing otherwise is technically difficult at the top end.

Tractrix is a graceful curve that spreads diffraction in a way that reduces its audibility. That is one way to do it well, I won't say it's ideal (but not much is). I have chosen to use the LeCleach profile in the past in a few horns, specifically for its DI transition in the lower midrange where it offers a couple of other benefits.

 

[AllenB]

that they act like a single full range driver when observed,listened or measured from different angles. (e.g. no lobing).

You seem to be saying that lobing is a bad thing (which it sometimes can be), although achieving consistent directivity through a conventional crossover is normal practice when done properly, and comes down to more or less the same principles as mentioned here.

I think the full range driver analogy betrays the physical scope of what constitutes a z-axis, as Bill has pointed out.

 

[nc535]

I agree completely - each point of diffraction is another apparent source. Diffraction is inconsistent with point source behavior.

I like LeCleach also and have some idea of its benefits from having just reread the entire LeCleach thread. I don't know if I would prefer a multiple LeCleach solution to a single Synergy with a less ideal profile, however. That new Celestion driver that covers 300 Hz to 20Khz might be a good driver to pair with a LeCleach horn - one of the variations with constant directivity, of course

 

[nc535]

You seem to be saying that lobing is a bad thing (which it sometimes can be), although achieving consistent directivity through a conventional crossover is normal practice when done properly, and comes down to more or less the same principles as mentioned here.

I think the full range driver analogy betrays the physical scope of what constitutes a z-axis, as Bill has pointed out.

Our posts passed each other in flight.

I make no moral judgements about lobes. In fact I have a couple on my ears. I have heard and heard of some pretty good speakers that don't emulate point sources. It just seems to me that having a good wide range apparent point source with constant or at least consistent directivity makes the rest of the system design task easier.

 

[AllenB]

Yes, good thread. If hornresp is to be believed all LeCleach (f and T) horns will beam. One cannot be crossed to another however unless the room is taken out of the equation, nor is one an ideal transition into a room as a self contained unit. But they well support a smooth transition into full space, hence my choice as a way to gracefully 'give-up' on the directivity at the low end of the controlled spectrum, or at the far end of some waveguides.

 

[AllenB]

It just seems to me that having a good wide range apparent point source with constant or at least consistent directivity makes the rest of the system design task easier.

Fair enough. I haven't found either way to be 'easy'. For my mind covering from the hundreds of Hz and up with a single unit is what makes it easier, which I believe is a common goal.