Hi guys
A bunch of people asked questions, I will try to answer.
I don’t think it would be fun or fair to just explain how to build a Tapped horn although Walt seems very close.
Rather, what I can do is to mention a few “clues” or things, which lead to the approach.
When working with the Unity and later Synergy horns, it was clear that the acoustic passageway called a horn could be driven from a location other than at the “small end” with only a few differences in operation, all of which can be modeled.
The bass reflex approach provides a phase inversion (at resonance) which allows the rear radiation to be additive with the front.
This approach depends heavily on a high Qb in order to have a high Q in operation, horn loading a port produces a significant acoustic load which greatly alters the Qb.
Bottom line is the port stops working properly if significantly loaded by the horn.
The real problem with a horn that is too small is that the radiation load presented to the driver changes too much vs frequency, in a perfect horn (the kind assumed in horn theory) the radiation resistance is constant.
Peaks in the output are normally associated with dips in the impedance which causes “more” power to be delivered, producing the peaks.
The Tapped horn approach can be smaller because at the low cutoff, the drivers appears to have a smaller radiating area (but the same motor), which raises the electrical impedance, lowering the peak.
Above the low cutoff peak, the driver can appear to have as much as twice its original radiator area (still on the same motor) which raises the dip by having a greater area / load.
The idea in the patent application is that the drivers acoustic source impedance tracks the horns acoustic load impedance (when everything is right) which results in a MUCH flatter response and greater efficiency than a conventionally driven horn the same size could produce.
One cool benefit of the approach is seen when one compares the group delay of a Vented box and Tapped horn with an identical low cutoff.
The PB-12 tower for example has a measured group delay which hovers around “zero” down to about 30 Hz.
A vented box with the same low cutoff would already have about 10 –12 ms GD at 30 Hz. One can picture the effect of GD more clearly when you recall that this is like moving your speaker to the rear in time at a rate of 13.5 inches per millisecond of delay.
The other effect of the Tapped horn can be realized when you consider that alone, the driver in the Tower has a sensitivity of about 88 dB 1 W while it is a minimum of 95 dB 1W 1M when in the Tapped horn.
If you guys are inclined to and are near Atlanta, call the shop and go get a demo and see what you think.
Best,
Tom Danley
Danley Sound Labs
Stephan, So far as why is the Sky Blue?, I would guess it has something to do with the fact that liquid oxygen is also sky blue.
Liquid oxygen has gotten a bad rap too, look what you can do with it.
Hungry? Fire up the bbq. Yumm.
http://www.doeblitz.net/ghg/