High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ High Efficiency Speaker Asylum ]

---

[ Alert Moderator ]

---

Re: Wave shape

Posted by tomservo (M) on September 9, 2003 at 21:00:24

In Reply to: Re: Wave shape posted by Wayne Parham on September 9, 2003 at 14:46:42:

Firstly, I do want to differentiate my self from your “we” view of loudspeaker operation.

I would also have replied to the “spoor post” too but Rod has apparently cut off any possibility of reply.
I will ask Pat to forward me your e-mails you sent to the office incase you still can’t remember who threatened legal action to who.

You are still suffering from a misconception about the basics here and my explaining it yet another time to you will make no difference to you as your various position on things always seems set in 9 bag concrete.
On the other hand, while you rarely reply to any of my technical points, I know others are reading this too and would encourage anyone who is curious to root around and find out themselves.

While my words have never persuaded you about anything I know of in the past, perhaps some words from a few of the all time great’s in the loudspeaker engineering area would.
For example, in the book “Theory and Design of loudspeaker enclosures” by J.E.Benson he describes the basic woofer this way on page 77. Benson’s work is used in Thiel and Small’s papers in the AES loudspeaker anthology fwiw .
Snipped > “but the frequency is sufficiently high in practical cases for the motional impedance to behave substantially like pure capacitance, or in other words, for the diaphragm motion to be mass controlled”

Or how about this one from “Electroacoustics, The analysis of Transduction and its historical background”
Published by the American Institute of Physics for the Acoustical Society of America”
In the Chapter called Electrodynaic Transducers, page 145 it says;
“The effective mass is correspondingly defined so as to yield a total inertial reaction force which lags Velocity by 90 degrees in phase.”
A further explanation of how this happens is found on page 153
While knowledge of the “mass controlled” was known in some circles from the development of the Rice Kellog transducer and the reason why it this way is on page 81

Given I have had a TDS system which can measure real acoustic phase at my disposal for about 20 years and have very publicly presented measurements to both AES and ASA, why in the wide world of sports would I say something so openly and blatantly that you say is obviously not true?

On the other hand, you do not take acoustic measurements (or at least you didn’t the last time this came up) that would reveal the facts about acoustic phase to you first hand. You ignore the “uncomfortable” parts of how things are. I would encourage you to look but I will be surprised if you can find any hard technical references which support the “we” view of driver operation.
It is a fact that the acoustically small point source (like a woofer) must have an acceleration response if its amplitude is to be flat.
That acceleration response is caused by the drivers mass dominating the system and when above Fb and below Rmin, it’s acoustic phase lags by a nominal - 90 degrees.
Because acceleration is force against mass and current is force and sound is proportional to acceleration, one can look at the current waveform’s phase with respect to input voltage and see the general shape of a drivers acoustic phase curve.

I would ask you to consider the following thought experiment.
You have two loudspeakers, one is a small direct radiator, the other is an efficient bass horn
You measure the response and they are essentially the same from say 40 Hz to say 200Hz with the horn being more efficient.

One is a resistively controlled device, one is a mass controlled device (the direct radiator).
They have the same response curve but is the acoustic phase the same?
Remember, one is resistive dominated, the other is reactance dominated.
Think hard, reactance does what to phase and resistance does what to phase.

A clue, the flat part of the response is actually the falling slope of the mass filter corner and phase (for a 1 pole low pass filter) reaches what well above the corner ? ans ~ -90 degrees

The part your not seeing is that the reason for the need for such a slope is because the radiation resistance change with frequency BUT there is no phase shift associated with it, it is just a changing resistance.
The acoustically small point source speaker on the other hand is a mass controlled filter with a corner F at the low cutoff. Anywhere its flat above Fb and below Rmin , you are on the slope of the filter response and getting the resulting phase nominal –90 degree shift.
A highly loaded horn on the other hand does not have the nominal –90 degree phase shift being resistively controlled.

TD

This post is made possible by the generous support of people like you and our sponsors:

VH Audio

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---