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Different between LST and LST 2?

Guest Tube747

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The original AR-LST ("Laboratory Standard Transducer") was introduced in late 1971 as AR’s attempt to offer a quantifiable, repeatable, accurate acoustic reproducing device, suitable for use in recording studios and other applications where known, verifiable accuracy was required.

Since ferro fluid-cooled tweeters did not yet exist in 1971, AR used multiple (4 ea.) 3/4" tweeters and 1 1/2" midranges to achieve the high levels of power-handling needed for its intended application. AR also had a design goal of achieving a virtually flat acoustic power response over a 180-degree solid angle (hemisphere) when the speaker was mounted very close to the wall behind it. They considered the radiation patterns of the MF and HF radiators and then calculated the angles of the cabinet side panels to minimize any interference/cancellation between those drivers, while being able to achieve the wide MF/HF dispersion needed.

The LST was perhaps the most breathtakingly accurate speaker ever devised up until that time in the history of consumer electronics, and is still more than remarkable even by today’s standards. The reviews in Stereo Review, Audio, and High Fidelity were amazing. High Fidelity summed it up when they said of the LST’s name that the speaker "could lay claim to such an auspicious title with complete authority."

The LST used a 6-position autotransformer spectral balance control that kept the midrange level unchanged, while raising or lowering the tweeter/woofer balance in 1 dB steps relative to the midrange. Position 1 had a slightly elevated tweeter level with a slightly lower woofer level; 2 was nominally flat; 3 thru 6 progressively raised the woofer by 1 dB and lowered the tweeter section by 1 dB. According to AR, positions 5 and 6 approximated the balance of the AR-3a with its controls set to ‘normal.’

The speaker was an unexpected commercial success at its (very high for 1971) price of $600 ea. As with most companies, AR tried to capitalize on the original LST’s success by coming out with a second model.

The LST-2, introduced in March 1974, used a 10 " woofer instead of the LST’s 12," and 3 ea. of the mids and tweeters instead of 4 ea. (Interestingly, the LST-2 used a midrange and tweeter in the forward-facing front panel, while the LST had all four of its midranges on the angled side panels with just two tweeters and the 12" woofer on the front panel. The forward-facing mid of the LST-2 gave that speaker a very slightly more "forward" character than the LST.)

The other major difference was that the LST-2 had a 3-position autotransformer instead of a 6-position control. The LST-2 had a retail price of $400 ea.

I used the LST-2 for almost 10 years as my main speakers and found them to be quite excellent—neutral, room-filling, and very easy to listen to.

Steve F.

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Guest Tube747

Dear Steve,

Thank you very much for the valuable information!! I read somewhere from this forum, it says that LST is very hard to drive, and having a tuffy impedance down to one ohm load (minimum).

So is this speakers suitable for solid state or tube amplifier? Do you know the sensitivity of the LST? Actually, what is the nominal and minimum impedance of the LST?

Don't you think 50 watts tube or solid state amplifier capable to drive the LST?

Rumour has it that the AR9 is a better loudspeakers against the LST, is that really true?

Thanks Again!

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