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Horn phase [message #42497 is a reply to message #42490]

Mon, 15 September 2003 02:22

Wayne Parham
Messages: 18787
Registered: January 2001

Illuminati (33rd Degree)

I think it was good to point out the distinction between acoustic impedance and electrical impedance. There is a reflection of acoustic impedance in the electrical impedance though, through the mechanical system. The acoustic load modifies the mechanical load which then in turn causes an effect in the electrical load.

The best examples are those that that are highly loaded acoustically, i.e. horns. I've noticed that horns exhibit electrical peaks where the horn's acoustical load becomes more reactive. The acoustic phase angle of horn forms a rippled curve, which is caused by the changing acoustical reactance and resistance. It acts very much like a series of resonators and as such, generates ripples in the acoustic impedance curve. These are translated into the mechanical system and, in turn, in the electrical system. So while acoustic impedance is not the same thing as electrical impedance, there is some inter-relationship between the two.

The relationship between phase and impedance is determined by the following formula:

θ = ArcTan i / r
where,

θ is the phase angle
i is the imaginary or reactive impedance, and
r is the real or resistive impedance

Considering this, you can easily find the phase where impedance is known.

So let's look again at the response chart for a horn:

You can see that the horn is intended to be used from 40Hz to 400Hz, so that's the region of interest. You'll notice that the device is quite reactive, meaning that it has non-zero phase. And it isn't trivial - It is a significant amount. For example, phase θ = 65° at 55Hz, 45° at 110Hz, 30° at 200Hz and 20° at 400Hz, where the horn has reached upper cutoff. Phase isn't consistent either, but instead is a series of ripples representing large closely-spaced changes in phase. You'll find this reflected in the electrical impedance, where you'll see ripples in the impedance curve.

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[Message index]

		Subwoofer Group Delay and such. Long post, but I hope its interesting, maybe :P By: Adrian Mack on Fri, 12 September 2003 02:13
		Aren't we By: mollecon on Fri, 12 September 2003 05:59
		Possibly... but heres another thought By: Adrian Mack on Fri, 12 September 2003 10:28
		An attempt at an answer... By: mollecon on Fri, 12 September 2003 13:03
		fl, fb and fh By: Wayne Parham on Fri, 12 September 2003 15:18
		Impedance Peaks relating to damping and GD By: Adrian Mack on Fri, 12 September 2003 17:03
		A short comment. By: mollecon on Fri, 12 September 2003 19:35
		An even shorter comment By: Adrian Mack on Fri, 12 September 2003 22:37
		Choices and optimizations By: Wayne Parham on Fri, 12 September 2003 23:28
		Re: Choices and optimizations By: Adrian Mack on Sat, 13 September 2003 01:25
		Re: Choices and optimizations By: Wayne Parham on Sat, 13 September 2003 03:39
		Cool. By: Adrian Mack on Sat, 13 September 2003 08:35
		Re: Cool. By: Wayne Parham on Sat, 13 September 2003 17:22
		Re: Cool. By: Adrian Mack on Sun, 14 September 2003 00:45
		Re: Cool. By: Wayne Parham on Sun, 14 September 2003 01:37
		Re: Cool. By: Adrian Mack on Mon, 15 September 2003 01:22
		Ah, I figured most of it out By: Adrian Mack on Mon, 15 September 2003 01:40
		Pneumatic loading By: Wayne Parham on Mon, 15 September 2003 07:14
		Re: Pneumatic loading By: Adrian Mack on Mon, 15 September 2003 08:14
		Re: Pneumatic loading By: Wayne Parham on Mon, 15 September 2003 08:44
		Sowy for budging in again By: mollecon on Sun, 14 September 2003 16:39
		Horn phase By: Wayne Parham on Mon, 15 September 2003 02:22
		Re: Horn phase By: Adrian Mack on Mon, 15 September 2003 06:32
		Re: Horn phase By: Wayne Parham on Mon, 15 September 2003 07:54
		Almost... By: mollecon on Sat, 13 September 2003 16:33
		Electrical, mechanical and pneumatic properties By: Wayne Parham on Sat, 13 September 2003 00:25

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