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Re: About 4-Ohms for 40 ft loop of 30 AWG

KS,

It is my understanding that long and lengthy dissertations concerning speaker wire are verboten on this forum. The two references provided earlier address the speaker wire issue with a degree of objectivity not likely found elsewhere. There scope is not limited to PA settings, so an assertion to the contrary does not constitute a basis for ignoring them or the findings contained within them.

I have addressed your comments reproduced here as paragraphs [1], [2] & [3].

Regards,

WHG

[1] Yeah, but this horn has no appreciable T/S parameters to speak of (Lowthers with "off-the-chart" numbers) and they do not operate near any resonant cutoff frequency because the horn cuts it off before the driver does.

Comment: The horn driver has a set of parameters, and they are important. Never identified them as T/S parameters. That is solely your characterization. By the way, T/S parameters are nothing more than a recast of the electrical, mechanical, and acoustical parameters of the driver/enclosure system (horn included). To suggest that such a system has “no appreciable T/S parameters” is utter nonsense, even for those using Lowther drivers.

[2] So a lot of high frequency horns are like this, which is also a lot like tweeters. Tweeters are not designed with Qts in mind when crossed over well clear and above where Qts takes effect. And that's why it's still okay to use series resistors in tweeters and midrange drivers for attenuation purposes and still have good transient behavior.

Comment: [Qts], the quality factor of the driver alone, is not mentioned in my post. [Qt] for the system of driver, driver/amp circuit, back and front chambers, phase plug and horn body is addressed there.

[3] So I don't know exactly how series resistance is playing the only role in INCREASING the damping down of this horn that controls the cone better and allows more detail to pass through at middle and high frequencies. According to this argument the opposite if anything should have happened. It "should" have gotten more sloppy and less distinct, but then again Qts is not a factor really.

Comment: You need to reread my previous post. What is clearly implied there, is that system [Qt] is raised when the sum of [Re]+[Rg] is increased, which is the same as saying system damping is reduced. The last part of paragraph [3] parrots this finding. So, no issue anymore! Right?

Note also, that given the band pass nature of horn loaded systems, increasing [Qt] also reduces system bandwidth characterized by [wl] & [wu].
[Qt] = [w0]/([wu]-[wl]) = (1/([Rae]+[Rac]+[Rat]))*([Mac]/[Cat])^(1/2)
where,
[w0] - system resonance ([wl]*[wu])^(1/2)
[wl] - lower frequency bound (-3 db point)
[wu] - upper frequency bound (-3 db point)
[Rae] - Acoustical Resistance that models electrical loses
= ([Bl]^2)/{([Re]+[Rg])*([Sd]^2)}
[Re] – circuit loop DC resistance) including voice coil and leads
[Rg] – source DC resistance

Notes:

(1)Other parameters given here can be considered constant for the purposes of this discussion.

(2)The above characterization is for the mid band response of a horn system.

(3)HF horn response is modeled using the second system resonance associated with the front cavity. Again [Re] & [Rg] play a significant role (See [Rae] definition above).

[wa] = (1/([Mac]*[Caf])*(1+([Rae]+[Rac])/[Rat])^(1/2)
– resonant frequency

and

[Qa] = ((1+([Rae]+[Rac])/[Rat])^(1/2))*{([Rae]+[Rac])*(([Caf]/[Mac])^(1/2))+(1/[Rat])*(([Mac]/[Caf])^(1/2))}^-1
– system Q for low pass model

[Qa] = 0.5 is a typical value for best results.

(4) An ideal piston movement is assumed for modeling the driver diaphragm. At the onset of diaphragm breakup modes, some irregularity in response will be noticed that becomes severe when [Qt](or [Qa]) is sufficiently increased. In this model the effect of voice coil inductance is considered negligible at the frequencies of concern.

(5) For a fuller treatment of horn/driver modeling, see the following reference:

[043] Title: Introduction to Electro-acoustics and Audio Amplifier Design, Second Edition.
Publication: Kendall/Hunt Publishing Co., 1999, ISBN 0-7872-6093-2
Author: W. Marshall Leach, Jr.
Abstract: This book is an outgrowth of a senior level elective course in audio engineering that the author has taught to electrical engineering students at the Georgia Institute of Technology. The first part of the book covers basic acoustics as it pertains to the field of audio engineering. Remaining chapters, address the application of the tools of electro-acoustics, to the design of loudspeakers, their enclosures, crossovers, networks, acoustic horns, and audio amplifiers.
URL: http://users.ece.gatech.edu/~mleach/ee4026/notes.html





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