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Old 25th July 2006, 03:36 PM   #1
e-side is offline e-side  Netherlands
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Default horn-loading: 100% efficiency ?!

Is it possible to get 100% efficiency when using a cone driver in a horn system?

In Leach's paper eq. 31 gives the efficiency for a maximum sensitivity design, when Ral (eq. 30) and St are set to the correct values.
Eq. 31 can be written as:

N (Wh) = (0,5*(((Wl*Wh)^0.5) / (Wl+Wh))) / ((1/(((Wl*Wh)^0.5)*Rae*((1/((Wl*Wh)^0.5))^2 / Mad))) - (((Wl*Wh)^0.5) / (Wl+Wh)))

For example, with the following parameters:

Mmd = 0,01515 kg
Sd = 0,012469 m^2
(Bl) = 13,04 T.m
Re = 10,8 Ohm

and a cutoff frequency of 70Hz (Wl becomes ~439), then you'll see that N=1 for Wh ~ 1120 (Fh = 178)

This means an efficiency of 100%, together with maximum sensitivity accross the horn's bandwidth.

Did I make a mistake in my calculations or is this a design with very nice properties??
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Old 25th July 2006, 03:44 PM   #2
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The horn system would need to radiate 360 degrees to be technically 100 percent efficient
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Old 25th July 2006, 04:27 PM   #3
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Also, in theory this is all well, but in practical situations it will be different I suppose...
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Old 25th July 2006, 05:03 PM   #4
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I have used TAD compression drivers (and others) in large 180 cycle flare tratrix horns and it sure seems within a certain area they are purely efficient - off axis it's quite a bit different -

Probably the most efficient midbass system I've had is this one with a compression driver down to 80 hz - below that was three horn loaded 18's across the front wall

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Old 25th July 2006, 08:16 PM   #5
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"Is it possible to get 100% efficiency when using a cone driver in a horn system?"

No; it would take a diaphragm with zero mass and wire with zero resistance.

IIRC the theoretical max is 50% for a horn.
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Old 25th July 2006, 09:01 PM   #6
Pano is offline Pano  United States
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Quote:
Originally posted by noah katz
IIRC the theoretical max is 50% for a horn.

And I've heard that horn!

Western Electric 15A Horn, 1950s vintage Westrex Driver.
Very close to 50% efficient. But only within its angle of dispersion. Was about 115dB/1W/1M.
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Old 25th July 2006, 09:11 PM   #7
Rocky is offline Rocky  Norway
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Quote:
Originally posted by Magnetar
...with a compression driver down to 80 hz...
Is this some sick goto/ale drivers with sportscar prices or are they something I should know about? Compression down to 80hz.. Jeez.. That would be the perfect midbass mates for my 350Hz TAD
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Old 25th July 2006, 09:56 PM   #8
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Quote:
Originally posted by Rocky


Is this some sick goto/ale drivers with sportscar prices or are they something I should know about? Compression down to 80hz.. Jeez.. That would be the perfect midbass mates for my 350Hz TAD

Nope, Emilar EC600 - when loaded in the right horn they go pretty low. I had them in the BIG Emilar mid horn on the floor and they did pretty well. Around 112 db/w/m from 80 to 3k. They use a 6" aluminum diaphram and a mylar surround.


Click the image to open in full size.

They are hard to find and not too expensive. The Community M4 is simular as well as the Adamson. I had the Adamson and didn't like it as well. It uses a 10" kevlar diaphram.

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Old 25th July 2006, 11:29 PM   #9
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"Very close to 50% efficient. But only within its angle of dispersion."

Efficiency is not determined by SPL on a particular axis; it's total acoustic output power/electrical input power
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Old 26th July 2006, 08:15 PM   #10
e-side is offline e-side  Netherlands
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Quote:
Originally posted by noah katz
"Is it possible to get 100% efficiency when using a cone driver in a horn system?"

No; it would take a diaphragm with zero mass and wire with zero resistance.

IIRC the theoretical max is 50% for a horn.
I did make a mistake in my calculations, in my example Qmc becomes negative, so the calculations aren't correct. I already made a new efficiency formula, which seems to work well. Now I'm able to calculate a maximum sensitivity design with a chosen efficiency.

Maximum efficiency point for my drivers occured at ~67%. Anyway, 50% is enough for me
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