From: Tom Danley
Sent: Tuesday, May 05, 2009 5:56 PM
Subject: From Tom Danley
I hope you don’t mind the intrusion, it was suggested I could answer your questions.
“Still, I did not hear the Danley’s tapped horns and I have no idea what he is trying to do.”
Well I can explain and hopefully it will make sense.
When you make a bass horn “too small’ and by that I mean a mouth that is significantly less than a wl in circumference in full space and by making it a quarter wavelength long instead of ½ wl., you have a number of tradeoffs.
By making the horn shorter, only a quarter wave long at the low cutoff, you prevent the system from having high electroscoustic efficiency conversely you’ll find that the short bass horn does reach efficiency until it’s about an octave above low cutoff, again where it is a half wl or greater. The classical horn, needs to have the driver at the motional maxima, which begins at a half wavelength.
Also, one finds the response of such a horn typically droops off instead of being “flat” down to the low corner. When the mouth is made smaller in area, then one finds the horn’s modes become increasingly revealed by the reduced radiation resistance (which fully damps them in a larger horn).
When you make the horn mouth a convenient size (too small), then you have a response curve with a large peak defining the low corner, with a deep valley then another peak with a series of smaller and closer together peaks after that.
It is the magnitude of these peaks and dips which define how small you can make a horn.
Acoustically, what you see is where there are peaks, there is the maximum acoustic loading on the driver, the point where the motion and impedance is minimum.
Where the deep valley is, there is little load on the cone, motion and impedance are maximum.
The quarter wavelength bass horn can’t be efficient down low because the driver’s parameters that are ideal for operation where it is ½ wl long or longer, are totally different than those needed for the quarter wave mode which is a motion minimum instead of motion maximum (1/2 wl)
The Tapped horn idea began when I was thinking about the quarter wave length reflection that places a notch in the response of the side mounted drivers (as used in the synergy horns), that notch defines where the usable upper response corner is.
I wondered, “what happens if I substitute a source of the opposite phase for that reflection” Having that source already available in the drivers rear radiation, I made a computer model.
It took a long time before I had anything I felt like building, but occasionally I would see predictions of a nice sensitivity.
The Tapped horn idea is that you use a driver which can efficiently drive the quarter wavelength mode which defines the low corner. This driver is too massive for efficient horn loading normally.
At the low corner, the front driver is approaching 90 degrees out of phase from the radiation at the throat. The acoustic load is nearly entirely on the throat side of the driver at the low cutoff. As the frequency climbs into the range where one has the deep valley, now the shorter wavelength means the front and rear radiation are separated by 180 degrees of path length and now are additive in the horn.
“When everything is right” (the horn dimensions and driver parameters), then where the valley was, is now flat, filled in by the added radiation load on the cone.
Compared to a vented box, these typically have about half the group delay for a given low corner and they often have a roll off slope between a vented and sealed box.
In a conventional horn, one normally sizes the rear volume to put the Fb somewhat above the system low corner. The drivers suspension spring is in parallel with the box compliance or spring. By choosing the horns hyperbolic or shape, one can adjust the acoustic mass the horn presents to the driver as you approach the low corner. The proper relationship between the two results in “reactance annulling” which lowers the low corner to its lowest value.
In the Tapped horn, the acoustic mass in the horn also exists but with no rear volume, the drivers suspension spring does the entire job. As a result the ideal Fs for a Tapped horn is usually the better part of an octave above the low corner.
Anyway, like a normal horn, once you have “all” the parameters right, they can work very well and provide flat smooth response, like a much much larger horn..
I don’t know if there are home bass horn systems that are measured in half space 1W/1M or have real response curves at all, but here are a couple tapped horns which one could compare to.
Granted these are made for movie theaters and large-scale sound and are big and ugly but the up side is they are absolutely loafing when used in the home.
On the other hand, there are some hifi “horn people” who are finding our stuff nice in the home.
You might find the SH-50 interesting; it can reproduce a square wave from about 260Hz to about 2900Hz, a span covering all three sets of drivers. There are no lobes at crossover or anywhere else and appears to be one source in time and space with nearly constant directivity down to it’s mouth dimension governed pattern loss.
In large spaces the rooms problems are much more formidable, hence all the focus on directivty and no interference between sources etc. the time coherency seemed like an obvious target which as taken over 10 years to zero in on.
Something you may have noticed too, as you make a speaker better and better in time, it becomes harder and harder to estimate how far away it is, if you stand in front of it with your eyes closed. What I am hearing consistently is that a system, which does not deliver audible clues, that “shout” where it is in depth when listened to singly, provides a more faithful center image and stereo image.
Anyway, don’t want to ramble, hope this helps explain the Tapped horn.
You may post this if you wish.
Try a couple of these outdoor uncompressed two channel recordings on your horn system, go to the bottom of the page here;
Play softly at first, NO compression, large dynamic range, deep bass on the fireworks recording.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche