Nearfield Bass Shootout

[Pete B]

History is loaded with examples of people who invented things and then either chose not to patent them or if they tried, did so incorrectly and had their patents invalidated. IIRC, Vilchur's patent on AS was invalidated, mostly because of errors resulting from his not using an attorney, and today nobody holds a valid patent on the technology. Subsequent to that, Vilchur chose not to try to patent his dome tweeter, and today nobody holds a patent on that, either.

Some friends of mine at the Xerox Palo Alto Research Center (PARC) used to have a digital counter on a wall that displayed a calculated estimate of the profits Xerox had lost over the years by not patenting many of the things originally developed at the center (the window/folder based GUI and the mouse being the most famous). The last time I visited there (about 10 years ago), the total was in the hundreds of billions of dollars.

If you ever get the opportunity to visit PARC, try to avoid being the first person to inject the word "patent" into any conversation unless you enjoy watching grownups cry.

A lot of excellent research came out of PARC. We used one of their tricks to hide the pipelining

at the microcode level when I worked in CPU design.

[Pete B]

Understand it? Certainly they are aware of it but understanding is another matter. I find I need to re-read most of the landmark papers every couple of years and still pull out new concepts or at least re-familiarize myself with them. Like you probably, I go all the way back to typing in Program Woof in Fortran, into a terminal, to have it spit out a crude response curve: marvelous stuff at the time.

In the last couple of years I've learned more about woofer/box science while trying to create high output very compact subwoofers. Certainly its the large signal, not the small signal issues that create the challenges.

The first step along that path was viewing the woofer and enclosure as a system rather than just assuming that "more magnet is good". The AR1 was one of the first steps there, but Jenson and RCA were in there too. (And don't make me prove that RCA invented the acoustic suspension system, imagine the flames!)

Second guess: is it Burl Ives?

David

Program Woof! http://ieeexplore.ieee.org/xpl/freeabs_all...rnumber=1162409

I got that running on one of the first IBM PCs (8088) with 160K floppy drives and no

hard drive around 1981. The only FORTRAN compiler available for it was on something

like 5 or 10 floppies that you had to feed in every time you compiled, LOL, talk about

slowwwwww! And it was loaded with bugs! Microsoft bought it of course.

I should have run it on the VAX-780 at work that had an excellent FORTRAN

compiler but I wanted to have it running at home.

Brings back memories!

[kkantor]

I'd like to point out a couple of things:

1- Unless the speakers are used at ear level, asymmetrical lobing is generally a >good< thing. It's a useful tool in the designer's bag of tricks.

2- The effective crossover slopes are a combination of driver response and crossover response. Since most drivers are used somewhat close to their natural rolloffs, predicting polar patterns really definitively can be tricky.

(I suspect you know this stuff well, but I though it might be worthwhile to add as a footnote.)

-k

PS- a couple of years ago, I posted a simple application called "Baffler" that we wrote at International Jensen for sandboxing driver placement, radiation patterns, etc. It might be in a library here, but I'll dig it up and upload it. The UI is rather primitive by modern standards, but it's easy to use, and only takes a few minutes to get the hang of.

Generally, even order electro-acoustic XO's are in-phase at the crossover point and therefore

have symmetry in the polar pattern when properly designed. D'Appolito proposed the MTM

configuration to make odd ordered electro-acoustic XO's have a symmetric polar pattern. Indeed,

any network will provide a symmetric pattern when the driver layout has geometric symmetry as

with the MTM:

http://www.aes.org/e-lib/browse.cfm?elib=11762

The MTM configuration solves a problem with odd ordered networks, it does no harm with even

ordered networks. D'Appolito makes this clear in his abstract: "a simple geometric arrangements of

three drivers in a two-way loudspeaker is shown to eliminate lobing error independent of interdriver

phase relationships"

My brother (older) suggested this configuration to me when he was about 17 years old and I was

about 12, LOL! He didn't write a paper about it as he thought it was obvious. I had built my first 2-way

speaker, held it at arms length in front of me and noticed a change in output around the crossover

point as I rotated it. I noticed asymmetric lobing. He drew phase plots to figure out what was going

on and then suggested adding another driver. He even pointed out that in-phase networks did not

have asymmetric lobing.

[speaker dave]

Here it is in Villchur's own words:

http://www.stereophile.com/interviews/105v...hur/index1.html

Professor Wadsworth ( http://dx.doi.org/10.1121/1.409268 )

at WPI where I studied loudspeaker design made a point of explaining

that a key feature claimed by Villchur was to have the driver suspension 10 times more

compliant than the air spring. This ratio is alpha in T&S theory; he was specifying an alpha

of 10. Wadsworth pointed out that only the very early designs came even close to an alpha

of 10 and that AR's own later designs were closer to 3. He pointed out that it was not practical

to manufacture such highly compliant suspensions. I did not review the patent at the time, or

ever since, but I did read Villchur's late 1950s AES paper were an alpha of 10 was mentioned.

His point was that an alpha of 10 is not required to provide reasonably low distortion. He also

pointed out that the large VC overhang was as, if not more, important.

Hi Pete,

The Stereophile interview was interesting with regard to the patent situation. AR sued EV but the case was tossed due to prior art by RCA. Although I quoted the RCA research, I didn't realize there was a patent. In fact, Preston and Olson have 3 pages of patents if searched by google. I think the relevant one is 2,490,466 for odd multiple suspension woofer variants. (Plural Compliant Members, there is a punch line in there somewhere): "Since a linear suspension is not available, the distortion may be reduced by reducing the effect of the suspension impedance..."

So the AR patent centers more on the surround than the high compliance woofer and predominance of cabinet stiffness. In the end, the value of the patent is frequently more the marketing benefit of a perception of advanced tehnology. Defending patents in court is seldom worth the money required. Use the patent for bragging rights and move on.

The EV point of view is outlined in an article in Audio magazine (March 1959) Design of the Wide Range Ultra Compact Regal Speaker System. They take a number of questionable potshots at AR including stating that domes are inferior to horns, box stiffness is highly nonlinear, etc. They do point out correctly that simply reducing or even removing the suspension stiffness of a high efficiency woofer will not get the system resonance down significantly. Your alpha of 3 case will, in the end, only have a resonance about 15% higher than an infinitely compliant woofer. In the end the essential feature of acoustic suspension systems was that driver mass was considerably increased over the norm at the time.

In a consumers mind, acoustic suspension makes a better invention than "relatively heavy cone".

David

[kkantor]

Hi Pete,

The Stereophile interview was interesting with regard to the patent situation. AR sued EV but the case was tossed due to prior art by RCA. Although I quoted the RCA research, I didn't realize there was a patent. In fact, Preston and Olson have 3 pages of patents if searched by google. I think the relevant one is 2,490,466 for odd multiple suspension woofer variants. (Plural Compliant Members, there is a punch line in there somewhere): "Since a linear suspension is not available, the distortion may be reduced by reducing the effect of the suspension impedance..."

So the AR patent centers more on the surround than the high compliance woofer and predominance of cabinet stiffness. In the end, the value of the patent is frequently more the marketing benefit of a perception of advanced tehnology. Defending patents in court is seldom worth the money required. Use the patent for bragging rights and move on.

The EV point of view is outlined in an article in Audio magazine (March 1959) Design of the Wide Range Ultra Compact Regal Speaker System. They take a number of questionable potshots at AR including stating that domes are inferior to horns, box stiffness is highly nonlinear, etc. They do point out correctly that simply reducing or even removing the suspension stiffness of a high efficiency woofer will not get the system resonance down significantly. Your alpha of 3 case will, in the end, only have a resonance about 15% higher than an infinitely compliant woofer. In the end the essential feature of acoustic suspension systems was that driver mass was considerably increased over the norm at the time.

In a consumers mind, acoustic suspension makes a better invention than "relatively heavy cone".

David

Agreed about patents. In addition to marketing uses, patents seem very important to investors/acquirers. They are seen as somehow protecting their investment, validating a company's concepts, etc. Also, they are convenient as a "fungible" part of the valuation. What I am getting at, is that since EV clearly wanted to exit AR, sooner or later, he was wise to try and accrue at least some IP.

-k

ps-

http://classicspeakerpages.net/library/aco...ecial_sections/

[Zilch]

More data: Dahlquist DQ-10 and original "large" Advent Utility, both on the eWave 1.5 mH/12 uF lowpass, and both ostensibly employing the same woofers. The DQ-10 has an interesting triple-chamber construction inside; I'm hoping Ken can explain that next time he comes by....

[Carlspeak]

More data: Dahlquist DQ-10 and original "large" Advent Utility, both on the eWave 1.5 mH/12 uF lowpass, and both ostensibly employing the same woofers. The DQ-10 has an interesting triple-chamber construction inside; I'm hoping Ken can explain that next time he comes by....

I was told once by the outfit that services DQ woofers that the DQ woofer is slightly different than the Advent. They said something about the VC being different.

Truth or fib?

[Zilch]

I was told once by the outfit that services DQ woofers that the DQ woofer is slightly different than the Advent. They said something about the VC being different.

Truth or fib?

The dust dome is larger, but that may be all.

Perhaps Pete knows....

[Pete B]

The dust dome is larger, but that may be all.

Perhaps Pete knows....

I have no experience with the Dahlquists, however I'm told that they

are the same from a performance and very close from a construction

standpoint. This is from someone who's worked on both.

We have seen a Dahlquist masonite woofer with a 1980 data IIRC, which

is well past the time when Advent made them.

[Carlspeak]

I recently refoamed a pair of DQ-10 woofers. Attached are the WT3 test reports, FYI.

Pete, can you spot any glaring differences with your Advent masonite woofer data?

Olivers_DQ10_woofer_refoam_B.doc

Olivers_DQ10_woofer_refoam_A.doc