Right, speakers are pretty tough to nail down with measurements alone. For example, the design of the tweeter has a whole lot to do with the sound -- a titanium dome and a soft dome may have similar on axis response, but off axis will affect the sound. My current favorite tweeter is the Linaeum:



These defy the theory of most tweeters -- they act as a line source and so they have amazing dispersion, but at the same time, they have huge radiating surface area, so they move the air "effortlessly" and sound really really clean and clear. They are dipoles, and the sound "migrates" along the four flexible plastic strips; so they are nearly 360 degree.

These are my current main speakers, and their enclosures are frustratingly mixed -- the main box is a single piece cast aluminum which is great, but the front panel is molded ABS (maybe fiber reinforced?) and it can resonate with things like grand piano music. I have a modified powered woofer (from RS) that sounds very good, but is almost completely missing the bottom octave (below 40Hz) -- I'm pretty sure they have filtered it out in the amp... I put 2 ounces of epoxy glue on the woofer cone, and the "transparency" of these speakers is astonishing -- they play the original acoustics of the recording with ease.

I paid $300 total for all three speakers, brand new...

Sounds like a new enclosure project just begging for your attention, Neil!

What is the xover freq? Are xovers & amps built in?

I'm in wholehearted agreement with you regarding dispersion. A constant dispersion pattern over the entire frequency range -- that is the ideal, imo. If it varies a lot with frequency, results are inconsistent and not as convincing. Either dipole or omni is better than simple forward firing.

The most fundamental problem with 99% of conventional speakers is that they are omnidirectional in the bass, but much more directional higher up in frequency. 20~100 Hz tones fire in every direction almost regardless of bass driver/enclosure design, but by middle C (260Hz, center note on the piano), on most box speakers, it is usually not better than... maybe 3~6 dB down 45 degrees off axis, and at least -10 dB by the time you get to 90 deg. This varying polar radiation "excites" room resonances in different ways at different frequencies, and we human beings easily hear the discontinuities. It's one of the reasons that you can usually tell in seconds whether the music is live or canned.

Ah -- I found it, Neil: Radio Shack Optimus PRO-LX5 II -- right?

SPECIFICATIONS
Frequency Response ............................................................ 80–25,000 Hz ±10 dB
Power Handling ........................................................................... 65 Watts (RMS)
Maximum Power ................................................................................. 130 Watts
Impedance .............................................................................. 8 Ohms (Nominal)
Speaker Complement ........ 5-Inch High-Compliance Woofer and 2-4-Inch Di-Pole Tweeter
Dimensions (HWD) w/Front Grille ................ 105/8 ´ 61/4 ´ 71/4 Inches (27 ´16 ´18.5 cm)
Weight .................................................................................. 8 lb 6 oz (3.9 kg)

Mine are the second generation, just like the one in the picture (they made three different versions). They are branded RCA and I think LX-55 was the model number? And yes, some epoxy to fill in the plastic ribs would be the thing. The last version had yellow "Kevlar" midrange cones and were called LX-550. Those specs look about right.

I've rewired the innards with AudioQuest solid core wire, and I left the simple (first order?) crossover in place. They are not powered -- I'm using my B&K ST-140 and Audible Illusions 2c. The woofer is powered (75watts?) and it has a 10" driver, which I added the 2 ounces of epoxy to both mass load and stiffen the cone. Using my Stereophile bass test tone CD, the response below 40Hz is almost non existent. The little 5" midranges put out more sound at 20Hz than the woofer does...

These speakers replace my beloved Snell Acoustics Type E II's. The Snells had stupendously good bass -- only 6dB down at 31.5Hz (after long tuning sessions). I used a tight bundle of drinking straws cut to the length of the bass port to slightly dampen the lowest output, and they were placed so that they were different distances from all the surrounding room surfaces. I talked to someone at Roy Allison's company called RA Labs, and I got a copy of his program that helped determine the various relationships.

The Type E II's have a rear firing tweeter that was phased in over the top octave(s), and they were pretty good for "typical" 2-ways with dome tweeters. But, the Linaeum tweeter is a work of sonic art.

[Edit: thanks for splitting this out, Mike. I'm just sad that the Linaeum tweeter is not available anymore; let alone at bargain prices...]

Oh these tweeters go way back. When they were in a Radio Shack model (probably a rebrand of what you have) they were considered a best buy by audio magazines (you needed a little something to address the boomy bass, but even so.) Lineaum was a speaker brand in and of itself back in the day.

Overall there's a tendency for soft domes to not be hard as nails, while metal tweeters fall more in the aggressive territory.

The main problem with most tweeters are the capacitors used. They are usually electrolytic, the worse possible choice. They simply behave very badly from an electrical standpoint, and replacing them almost always makes the speaker far more pleasing without losing any highs. Some people may perceive of losing harshness as losing highs, but that's not the case. (As much as you like yours Neil, what if it got that much better?)

There are many capacitors that will do a far better job and they may cost $3 to $5 each. For a small bookshelf speaker that single capacitor may be the entire crossover network. Why do they do this? Well you don't put a $3 cap in a $100 retail speaker. Such a speaker needs to cost $20 in labor and materials, so $3 is way over the top. That's the nature of business.

http://forum.audiogon.com/cgi-bin/fr.pl ... &zzlinaeum

Frankly due to availability and personal choice I would choose a ribbon tweeter over anything else, and a full blown ribbon speaker if money and space allows.

http://www.aurasound.com/index.php

Nothing at this site suggest they still deal with this tweeter. Such designs come and go, no matter how good they are, due to demand. The capabilities are frankly a bystander of their success, not the cause. Recall betamax? Posts referring the tweeter date back to 2005.

Ceramic tweeters are still in rage right now. A really interesting design I've seen is the powered driver, and by that I mean it doesn't use conventional magnets for the magnetic field it uses a coil with current flowing through it to create the magnetic field, and it's far stronger than anything in use today. There's only 1 manufacturer currently doing this, and you don't want to know what such a driver costs (I wonder if they make a dozen a year at this point) but I believe sound and speaker efficiency are through the roof, allow low powered class A electronics to make loud and wonderful music.

This speaker company also uses a unique tweeter in many of their models.
http://www.roundsound.com/reference-35-speakers.html

Here the tweeter is in the middle:
http://www.roundsound.com/reference-strada.htm

The world is full of interesting people, I'd enjoy talking to this guy.
http://jeffsplace.me/wordpress/?p=914
Holy Xxxxx

Another famous tweeter back in the day.

http://en.wikipedia.org/wiki/Air_Motion_Transformer

Pics:
http://www.google.com/images?hl=en&q=he ... 04&bih=579

Hey Neil,

Do you recall this tweeter?

http://www.canuckaudiomart.com/view_ima ... _id=694580

No Aris, I have not seen that particular unit. It looks a lot like Gallo Acoustics, mention above.

Looks like that system may have a soft-dome midrange driver (probably made by Dynaudio).

I had a pair of the 2nd gen ESS ATM1 (1a?). circa... 1980? Eventually dumped everything in them except the tweeters. Used them for a long time from ~1000Hz and up in a 2-way active xover / biamped transmission line tower with 2 7" Focal drivers on the bottom, one firing forward, one back -- to duplicate the dipole of the Heils. They were very good, but a bit too big. Sold them off early 90s. The disconnect between the AMTs and the rest of the sound was always there... and at some point I just tired of the sound. Amazing that the AMT drivers are being sold for $350 each now. A lot more than what I got! It is possible to build them at home. I recall a distant friend doing this back in the day. Not so different in detail from an electrostatic, but way easier because the diaphragm is tiny in comparison. Also, the precision of manufacturing tolerances does not have to be as great as w/ conventional tweeters. It is an ingenious design. Maybe with newer high efficiency magnets, it could be made a lot smaller, too.

Not surprisingly, asking the low frequency driver to reach 1000Hz is a bit much. It never stopped Altec Lansing however. Placing a crossover frequency in the midrange frequencies is also asking for trouble.

The "Voice of the Theater" speakers met the requirements of the day, high efficiency and bass extension with puny single ended amps. Puny in terms of power, wonderful sound quality.

Not for my 7" Focals. They were flat to ~2.5kHz. Dispersion did not narrow appreciably till above 1500hz.

You're talking rather recent tech, things didn't work so well for a long time. Altec tried to pull the same stunt with a 12 inch woofer, and many other companies did no better.

IM distortion is more likely with an amp with a low damping factor.

One reason many planars have certain qualities is that they eliminat cross over frequencies in the critical midrange. I suspect the disconnect you noticed was that the two drivers didn't have the same "speed" at the cross over frequency, where both should be working together and both are down only "3 dB."

Speaker design is so complicated, and each solution is really only a compromise, adding it's own problems while mitigating others. I gave up on it during the research phase.

http://en.wikipedia.org/wiki/Tweeter

Covered here are various tweeters, including electrostatic. I believe Janszen (not Jensen) was one of the first to do a 'stat tweeter in a rather plain bookshelf speaker.

The most common and by far absolute worst tweeter ever invented is the piezoelectric tweeter. Its in PA systems, as it tends to be indestructable, which is more than what you can say for what this freakish device will do to your hearing.

At the other end of the spectrum are ribbon tweeters, which can be had all the way in price to

http://www.google.com/products/catalog? ... DsQ8wIwAg#

Of course there are other ways to get ribbon tweeters:
http://analysisaudiousa.com/products.php