Who followed AR with the dome tweeter....

[Andy]

I know AR introduced the hemipherical tweeter in 1958 and got a U.S. Patent on it in 1962, # 3,033,045. Who was the next speaker maker to use a dome tweeter ?

[tysontom]

>I know AR introduced the hemipherical tweeter in 1958 and got

>a U.S. Patent on it in 1962, # 3,033,045. Who was the next

>speaker maker to use a dome tweeter ?

I believe that Fisher was the next with the Bill Hecht-designed fabric-dome tweeter, but it came several years later. The concept of a dome radiator was not new; most compression drivers, dating back to the late-1930s and 40s used a hemispherical diaphram made of aluminum or phenolic resin, but they propogated sound into a "phasing" plug and then into an exponential horn of some description. What was new in the AR-3 was the use of a dome tweeter that was optimized to be a direct-radiator device. It is also interesting that the hard-dome tweeters, typical of the AR-3 MR and HF and the tweeter in the AR-3a, had superior dispersion over soft-dome devices, but at the expense of efficiency.

--Tom Tyson

[Andy]

Thanks Tom, I would guess that AR having the Patent, had control over who in the industry could use a dome tweeter, (Do Patents last 7 years?) In 1969 Winslow Burhoe started EPI and they promoted their Dome tweeter pretty heavily. He had worked for KLH in 1966. Today, Burhoe has a company called Direct Acoustics. Their website www.directacoustics.com lists a research laboratory based in Weston, MA. I don't know where the speakers are made, but maybe New England made loudspeakers are alive and well!

[tysontom]

>Thanks Tom, I would guess that AR having the Patent, had

>control over who in the industry could use a dome tweeter, (Do

>Patents last 7 years?) In 1969 Winslow Burhoe started EPI and

>they promoted their Dome tweeter pretty heavily. He had worked

>for KLH in 1966. Today, Burhoe has a company called Direct

>Acoustics. Their website www.directacoustics.com lists a

>research laboratory based in Weston, MA. I don't know where

>the speakers are made, but maybe New England made loudspeakers

>are alive and well!

Few companies initially understood the merits of the dome tweeter, and for that reason there were no competitive companies using the dome tweeter for a few years until Fisher, I believe. Making a dome tweeter was one thing; having it perform with smooth and uniform on- and off-axis response was quite another thing, and very difficult for most speaker manufacturers. The cost of dome tweeters was higher than cone speakers, and so forth. However, once the industry began to see the very high critical acclaim of the AR-3 and its subsequent commercial success, there was pretty quick migration to that technology. It was also during the AR-3's peak years that AR's market-share numbers grew so rapidly. The two main advantages of the dome tweeter are (1) wide dispersion and (2) rim-driven diaphram.

Properly maintained Utility patents issued prior to 1995 lasted for 17 years. After 1995 that period changed to 20 years, and some patents can be extended. Incidentally, when a patent expires it cannot be renewed, nor can the item be re-patented. It become the public domain. Burhoe was an AR alumnus, as were most of the New England loudspeaker people. Burhoe's contribution was the inverted, or concave, phenolic-dome tweeter. It's performance was quite good, but I'm not sure of the advantage of the concave construction vs. conventional convex shapes.

--Tom Tyson

[soundminded]

Tom, would you know what factors AR attributed the superior dispersion of its dome tweeter to? Was it the size and geometry of the dome itself? Does the mesh screen in front of it play a role? Is there some other factor? When the Snell IIIi was introduced at a trade show, I asked one of the reps why there was a small piece of styrofoam glued to part of the front of it. I was told it was to improve dispersion. Various "acoustic lenses" have been tried by other manufacturers including those with concentric rings and with small baffles directly in front of the cone which are supposed to improve dispersion. I was very impressed by the graph showing output only 5 db down at 15 khz 60 degrees off axis for the AR tweeter. Are there any contemporary tweeters in its league? I haven't seen any, most are at least 10 db down.

[tysontom]

>Tom, would you know what factors AR attributed the superior

>dispersion of its dome tweeter to? Was it the size and

>geometry of the dome itself? Does the mesh screen in front of

>it play a role? Is there some other factor? When the Snell

>IIIi was introduced at a trade show, I asked one of the reps

>why there was a small piece of styrofoam glued to part of the

>front of it. I was told it was to improve dispersion.

>Various "acoustic lenses" have been tried by other

>manufacturers including those with concentric rings and with

>small baffles directly in front of the cone which are supposed

>to improve dispersion. I was very impressed by the graph

>showing output only 5 db down at 15 khz 60 degrees off axis

>for the AR tweeter. Are there any contemporary tweeters in

>its league? I haven't seen any, most are at least 10 db

>down.

Well, the size is obviously the most important element, but I believe the flush-mounting is also very important: many dome tweeters today use a cavity or small "semi-horn" to increase efficiency, but these cavities cause reduction of the off-axis performance. Hard-dome tweeters are better off-axis than soft-dome versions, as measured, and I think this is due to the tendancy of soft domes to flex at high frequencies. There may be other reasons. The mesh in front of the midrange drivers was originally put in place to hold the fiberglass pad, which was put on the outside of the 2-inch AR-3 dome to "counteract" the forces of the fiberglass pad under the dome. One of the problems of the original AR-3 midrange dome was the tendancy to "pop" out of the gap under high-output conditions, and the fiberglass under the dome -- placed for cavity damping -- put pressure on the dome that helped it pop out of the gap. The tweeter also had this problem, but it had less power fed to it. Roy Allison came up with the idea of placing fiberglass on the outside of the 2-inch dome, and the screen was used to hold it in place. Later 1-1/2-inch domes did have a dispersing pad placed under the screen, but I don't know how much effect this had on dispersion.

I am aware of several designs that used dispersing rings or pads or other devices to aid in dispersion. The University "Spericon" tweeter, for example, used a tiny plastic ball in front of the dome to help dispersion. The problem with that tweeter was the recessed nature of the dome itself. The only tweeter that I am aware of superior to the AR-3a tweeter in dispersion is the Allison tweeter.

Fig. 1 below shows the Hiquphon 3/4-inch fabric-dome tweeter in anechoic on- and off-axis measurements. It is a very smooth tweeter as can be seen by the on-axis response curves, and it is one of the "darlings" of the current high-end loudspeaker trade. It falls short in off-axis response -- if integrated-power response is important -- when compared to the AR-3a 3/4-inch tweeter. Fig. 2 below are the well-known AR-3a 3/4-inch tweeter family of response curves, far superior to the Hiquphon tweeter off axis. The graph scale somewhat favors the Hiquphone, too, so the tweeter shows fewer response variations.

http://www.classicspeakerpages.net/dc/user_files/1247.jpg

Fig. 1 Hiquphon OW1 3/4-inch soft-dome tweeter with a recessed dome.

http://www.classicspeakerpages.net/dc/user_files/1248.jpg

Fig. 2 AR-3a 3/4-inch hard-dome, flush-mounted tweeter family of curves

--Tom Tyson

[roundhome]

Hello Tom and Ken do we have a AR 303 tweeter graph to compair to the above?

thank you

Jim

[Steve F]

"The only tweeter that I am aware of superior to the AR-3a tweeter in dispersion is the Allison tweeter."

Of course, as Tom well knows, the Allison tweeter (and midrange) was a truely unique design. Its voice coil was halfway up the diaphragm (rather than at its periphery), so that the radiator behaved much like the ideal "pulsating hemisphere." I've always like audio critic/writer David Moran's description of the Allison tweeter: "Strangely unimitated." Quite true. It's a driver with better dispersion than a conventional dome, and no particularly vexing manufacturing complications that would make the cost prohibitive. Incredibly clever, common-sense engineering.

As to the dome patent, Ken Hecht later patented the SOFT dome tweeter and brought suit against Boston Acoustics sometime in the late '70's or early '80's when they began to manufacture their own 1" soft dome in-house. (The very first mid- and higher-priced BA's used purchased tweeters--Vifa's, I believe. And the lower-priced BA's like the A40, HD5, HD7 used either Tonegens or inexpensive French tweeters.) But as BA's sales and market share surged in the early '80's, they became a juicy target for less successful companies like Hecht's Phase Technology.

Steve F.

[kkantor]

I don't. Sorry.

[kkantor]

1- To the extent that the radiating area changes with excursion, leading to what you analogize to the pulsating sphere, you get intermodulation distortion. With a pulsating sphere, the radiation impedance doesn't change with "excursion," but with a half-sphere, it does.

2- Mass and sensitivity are today considered more important than getting a few more dB at 20 KHz, 60 degrees off-axis.

3- The old Audax polycarb, and the similar Tonegen "Ultra 12" were centrally driven. So are the current Peerless and ScanSpeak "ring radiators."

4- I could be wrong, but I thought the original BA 1" tweeters were based on the design that Moses Gabbay did for the AR 28s, etc. ?

[kkantor]

I believe it was Kates who proved conclusively that the radiation pattern of a dome was the same, whether convex or concave. Someone did! Inverted domes have the advantage of being more finger-proof. On the other hand, they potentially reduce Xmax, which is relevant if you are trying to implement a lower xover.

[Steve F]

>1- To the extent that the radiating area changes with

>excursion, leading to what you analogize to the pulsating

>sphere, you get intermodulation distortion. With a pulsating

>sphere, the radiation impedance doesn't change with

>"excursion," but with a half-sphere, it does.

>>4- I could be wrong, but I thought the original BA 1"

>tweeters were based on the design that Moses Gabbay did for

>the AR 28s, etc. ?

Hi Ken,

The "Pulsating hemisphere" isn't my description of Allison's tweeter; that's why I put it in quotes in my previous post. I don't remember if it was from Allison's lit or perhaps some review, but that's how someone else described it.

Since Moses came to BA from AR very shortly after BA was founded (he arrived at BA around 1979 or 1980), I'm sure he brought a lot of AR's "tribal knowledge" with him. The AR 1" dome in the later 14's, the 15, the 28, etc. was not exactly a hard tweeter, nor exactly a "soft" (textile) tweeter. But then again, neither was BA's 1" polyamide dome. It wasn't the classic textile soft dome either, so it remains puzzling as to why Hecht would have sued BA and not AR over his 1" soft dome patent.

In any event, given the years-long Yankees-Red Sox/Ali-Frazier-type rivalry that Andy always felt towards AR, it's not surprising that he didn't make it well known that BA's 1" tweeter may have been based on Moses' work at AR.

Steve F.