What kinds of results might be expected if a cone driver were simply flush-mounted from the front of a conical horn, so that the driver's overall diameter becomes the throat area? This would be in opposition to the usual practice of mounting the driver to the backside of a more restrictive throat, through a rear access panel. An example of such would be the Meyer Sound MSL-4, with the optional phase plug removed.

Intuition implies that the cone's HF would sag, roll off and beam sooner than with a conventional throat, with more possible internal reflections, which means a lower crossover point. A considered application would be a horizontal trap of no more than 30-40 degrees, in an attempt to put the predicted beaming to some use.

The advantages: No double-walled cabinet construction, no rear access panel, no protruding rear chamber to obstruct array angles.

What are the disadvantages, and do they outweigh the upside?

As always Wayne, I truly appreciate the time you take to answer my tedious barrage of questions, but I also invite other forum members to take a crack at me. I mean, if anyone feels that I'm monopolizing the forum, please let me know and I'll back off a bit!

Has anyone else (besides Peavey and Meyer Sound) tried this idea?

The driver does some things that interact with the horn as a system. It also does some things independently. Two of those that are relatively independent of the horn are cone breakup modes and certain forms of collapsing directivity. These things aren't completely independent of the horn, as the acoustic load placed on the cone by the horn is different than the acoustic load of the cone in free air. This modifies cone flex, and breakup modes shift as a result. Collapsing directivity can be caused by a horn, particularly those that have curved walls and narrow throats. But even without a horn attached, a driver will enter breakup and it will begin to beam at some frequency.

As the cone enters its breakup mode region, it becomes more efficient. It's behavior is less controlled, and response may become too peaky to be usable, but some drivers have reasonably well-behaved breakup modes that can be used to extend response past what the driver would do as a rigid piston. Parts of the cone move independently of the rest of the cone, and they move like ripples on a pond. These modes are resonant, so the speaker is pretty efficient though these bands.

Another thing that happens at relatively high frequency, is that the driver starts to become directional. When wavelength is approximately equal to diameter, the pattern is roughly that of a 90° conical flare. As frequency rises, the pattern grows more and more narrow. As directivity collapses, the energy becomes more and more focused. So on-axis SPL increases as a result.

These two things combine to make on-axis output significantly higher than the power response of a rigid piston. The diaphragm is no longer rigid, so mass-rolloff loses its meaning at some point. This is because the whole mass of the cone is not moving in unison. The concept of mass-rolloff is still right, but the mass that's moving isn't rigid anymore. It acts more like a lumped group of mass-spring systems. So the system just becomes more complex than what can be represented by a rigid piston. And since directivity is collapsing, on-axis response is greater even if power response stays the same. If power response is falling but directivity is rising at the same rate, then on-axis response will remain flat. If power response doesn't fall off quite as fast as directivity rises, then the on-axis curve will show rising response.

Some drivers looked very good on throatless horns in hornresp, so I'd consider making one if I thought hornresp was relatively accurate.

I think this is a good question though. I've heard a lot of discussion about waveguides lately, but not much about cone, particularly midrange, waveguides.

• Breakup modes and collapsing directivity

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I know I'm sounding like a broken record, but I'd suggest modeling with Hornresp. I think you'll find general trends that way. Seems to me like one thing that was consistent between systems I liked with 1:1 throats was high BL drivers. I was looking for HF extension, so massive cones weren't good. Ligher cones with powerful motors were the ticket for that application.

I think you'll also want to consider directivity and breakup modes. This is unrelated to the basic pistonic model, but on a straight horn with the entire diaphragm exposed, it will definitely play a big part in overall response. There is no front chamber to attenuate HF, so whatever the cone does will be presented to the horn. And when frequency is high enough that the diaphragm radiation pattern becomes more narrow than the horn wall angle, then the horn system will begin to have collapsing directivity even if the horn wall angles are straight. That will increase on axis SPL. The horn will no longer have constant directivity at that point, but it may provde some acoustic EQ, boosting the upper end of the on-axis response curve.

The 10Pi must have been a storage shed! Might we please see some history on it? How does one go about avoiding standing waves, and do they occur more readily in a conical horn because of its symmetry?