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Re: From Wayne Parham - Re: Patentable claim

Hello Tom!

Thanks for responding. I have always liked the belt-driven woofer that you make. There is really no other way to get single-digit frequency performance from a bass subsystem other than using a very large linear motor or a rotary motor and pully arrangement like yours. Industrial control and robotic actuators use things like this and I've always thought it would be great to build loudspeakers with these kinds of motors. Linear motor in 1970's-era disk drives are suitable for the task as well. So it's neat to see someone build a device for the sub-audio band like the Servodrive.

I'm just not as impressed with the Unity.

You wrote:

> > For one, Lambda Acoustics was issued a license to build and sell
> > Kits for the DIY crowd.

Yes. I understand that Lambda is licensed to build the Unity.

> > Beyond both of our companies using the same wood blank for the
> > horn and us supplying the mid drivers, they are different and
> > otherwise unrelated, the interior shape of the horn is different
> > (and the crossover is different).

Are you inferring that Lambda's does not perform properly because it is different than yours? Why do they need to be licensed then? Licensing requires a financial relationship; Why would they pay you for something that does not work?

> > I know that sounds odd to offer something like that to the public
> > but I have always been a DIY'r and have in the past managed to get
> > the Contrabass released as a DIY project for those willing to tackle
> > assembling a rotary motor driver.

Not at all. I do the same, and offer DIY kits as well as finished designs.

> > I would guess that the measurements you keep harping on and on
> > about (Their own measurements of the device prove my case.) were
> > on Lambda's web site as we have not removed anything in some time.

That may well be true. They were response charts published for the Unity horn device.

> > Again, as it must not be clear to you , Lambda and SoundPhysicsLabs
> > are a separate company each with there own crossover design and
> > proprietary flare shape.

So does the Lambda speaker require licensing or not? Is it a Unity horn?

> > You also keep referring to some previous conversation that you had
> > with Mark from a position of having debating the merits of the
> > design. Although he now works for the company, he didn't at the
> > time you corresponded with him, I am not familiar with the
> > write-up you linked to and had never heard of you or your speakers
> > until this thread began (brought to my attention by Mark).

Yes. The charts posted showed a definite diffraction anomaly from the Unity horn.

> > In your rant about "why it can't work" you also go on to cite the
> > conditions in which acoustic problems do occur and yet you go one
> > to put mental fences up which prevent a solution being visible to
> > you.

I respect you and I like the Servodrive. But I do not find merit in claims of "unity summation" and "perfect phase" for the Unity device.

> > In making your conclusion you also ignore the phase shifts and
> > frequency responses associated with the acoustic paths and "what
> > happens" when one increases the radiating area of a horn driver
> > (such as in the unity at crossover). When drivers are so closely
> > coupled, it is FAR more complicated than you describe and one has
> > to deal with ALL of that when coming up with the electrical network.

One of two conditions must be true in your Unity horn, having a difference in distance between its three subsystems. As Sam pointed out on this thread, you have an HF subsystem further from the listener and an LF subsystem closer to the listener, both in relation to the MF subsystem. This means that you must have one of two conditions:

1. Constantly changing phase response, that moves further away from the listener as frequency goes up.
2. Discontinuities in phase response that break rapidly as crossover is made between drivers.

> > Like they say, what good is a patent if there aren't trade secrets
> > to back it up. I can give you a clue though, a fixed distance offset
> > corrects the phase when the total phase difference between the
> > upper and lower sources (everything, the drivers, the crossover,
> > the acoustic path) yields a phase slope which doubles in its
> > degrees for each octave increase in F.

Do not patronize me, Tom. You imply that I do not understand diffraction issues caused by path lengths and reactive circuits. I've done a great deal of analysis and that's why I object to the claims made by you and your associates in regards to the Unity device.

My analysis is shown in the document at www.PiSpeakers.com/Speaker_Crossover.doc . It is a thorough examination of the behavior of reactive circuits used in loudspeaker construction, and includes analysis of phase.

Another document that describes these issues and draws the same conclusions was published published in volume 31, number 6 of the AES Journal. It is called " Improvements in Monitor Loudspeaker Systems ," and was written by David Smith, Don Keele and John Eargle. The paper discusses frequency division between components, passive compensation networks for compression horn tweeters, positions in space where phase response is true and off-axis angular positions where it becomes destructive and causes frequency anamolies. So I believe it is relevant to this discussion as well.

> > You are not thinking "outside the box".

Not to be a smart ass, but since "the box" is the laws of physics, you're right - "I'm not thinking outside the box."

Wayne Parham

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