High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ High Efficiency Speaker Asylum ]

---

[ Alert Moderator ]

---

Agreements and disagreements

Posted by EGeddes (P) on January 24, 2006 at 12:38:17

In Reply to: Re: horn signature - whats left after proper tailoring? posted by tomservo on January 23, 2006 at 19:04:38:

Tom

I thought that I would note where we agree and where I disagree with your comments.

" The wider the horn wall angle for a given size mouth, the lower the frequency where pattern control is lost. The larger the horn mouth, the less energy is radiated say 90 degrees of axis even at 20KHz.."

I'm not sure that I agree with the second comment. I find that the LF control point for directivity depends only on the mouth diameter and yes I agree it always narrows and then widens again going lower in frequency through this point. My experience is only with waveguides and not other device so there may be differences there.

"the working portion of the “horn” and to significant degree, the portion that governs directivity, is within the driver itself. An abrupt or “too large” transition to a larger angle than that internally, produces the HOM’s. To minimize these effects, one must keep the exit diameter (acoustic size) consistent with the horn wall angle its connected to."

This is oh so true, and in fact the generation of HOM goes down into the phase plug itself at these higher frequencies. The phase plugs for most compression drivers are designed such that they generate HOMs in the plug itself (Bob Smiths analysis was wrong.) I have found that the slope of the waveguide walls must match the slope of the driver at the junction point to minimize the HOMs. There must not be discontinuities of area or slope. I think that this may be what you said or meant to say, but you talked only about the diameter not the slope.

"If one had a horn that had constant directivity, then one would still see the drivers inherent power roll off."

Hardly ever appreciated is the fact that a horn cannot be CD if it has a flat axial response (unEQ'd). I can't tell you how many times I've seen so-called CD horns with flat axial responses (NOT!). If the device is CD then the axial response, and everywhere else, must fall as the drivers power response must also fall (above the mass break point). Again NO horn or waveguide can be CD and flat on axis at the same time - it is physically impossible. I think that we agree here.

"If one had two horns of identical response etc on axis, one being CD the other exponential etc *, then on axis, they would sound nearly exactly the same."

This is where I have the strongest disagreement. It depends on the waveguide design and how many HOM's are generated as these can be quite audible. A device with lower HOM's will sound better than a device with high HOM's even if the two do have the same axial response. But then there is also the reverberant response to consider which is still a big factor even on axis unless the room is anechoic. That makes the comparison even more complex and cannot be done without a consideration of the room and its direct to reverberant ratio at the listening point.

One test that is quite revealing is to have two people stand in front of the speakers about half way between the listener and the speakers. Wat is heard is the reverberant field. If it is not spectraly nuetral then the off axis response is not the sam as the on axis one. This also shows just how much reverberation field there actually is in a room. I came across this one time when I had my eyes closed and I perceived a small shift in the image. I opened my eyes to find someone walking past me in ront of the speakers. I was amazed at how little difference this made - it was not at all obvious.

"Off axis, this system sounds nearly the same spectrally as on axis but of course there isn’t a stereo image off axis."

I disagree here too. I agree with the spectral sound being constant off axis, but not about the stereo image. My speakers are actually designed to be toed-in such that a central listener is off axis of both speakers and the stereo image is quite good - perhaps the best that I have heard. And this image is maintained across a fairly large area. This has to do with the amplitude decreasing from the closer speaker and increasing from the one farther away as the listener moves from side to side. This helps to offset the time delay situation which cannot be corrected automatically.

"To combat this, it is normal to have a short mouth section which has about a 30% greater angle than the rest of the horn to combat this narrowing. "

I put a large radius at the mouth which helps to control the narrowing effect (see my book) but also reduces reflections at the mouth and diffraction from the waveguide edges.

"Mating to the adjacent drivers is a problem with horns, one has to have two sources less than about 1 / 4 wl apart in order to have unilateral addition. "

This is virtually never possible and one must deal with the innevitable lobes that will occur in the response in the plane containing both sources. Even in my system, which has maticulous detail paid to the polar response at the crossover the DI dips in the vertical plane - which is unavoidable. (Except in a coax, but then the waveguide is too small to be effective, which is a bigger problem than the crossover lobes.) In my speakers there are two holes vertically, one above and one below the central axis. They are set to be at about the floor and ceiling bounce angles to help with these problematic reflections, but they are also diminished by the off axis location of the listener.

I think we agree on more than we disagree, but there were a couple of significant points that differ on.

Thanks for the writup Tom

Earl Geddes

This post is made possible by the generous support of people like you and our sponsors:

VH Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---