Vintage 3a close mic'd and FF measurements

[Carlspeak]

I recently did some close mic and far field on axis measurements on a vintage 19,XXX ser. speaker. The measurements were done with the drivers in situ in a 3a cabinet and xover functioning. The woofer was an Alnico version with cloth surround and #7 coil. With one exception, the the roll offs of the drivers were similar to those shown in the library copy of the 3a driver's separate responses http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_other/ar-3a_series_frequency_resp/. However, it was noted the roll off of the midrange above 5000 hz (red curve in right pic below) was much shallower than shown in the library test. I would have thought the shallower roll off should have been higher in light of the series 50 uF (LP) capacitor and series #1 coil (HP).

Note also the very good HF extension of the tweeter out to almost 20 kHz. I haven't seen this stellar a performance before in such a vintage (1968) 3a.

The second response test shows the 1 meter on axis system response. The measurement is gated @ ~300 hz and each vert. div. is 5 dB. Here we see a gradually declining 6 dB/octave response from 300 hz on up. Not surprising to me is the observation that my measurement looks similar to some of those done by Roy Allison in his co-authored study of numerous home installations of 3a speakers http://www.classicspeakerpages.net/library/acoustic_research/special_sections/additional_ar_documents/the_sound_field_in_home_lis/.

[ligs]

Very interesting.

About 3a midrange rolloff, the crossover schemcatics I have seen all had a 0.044 or 0.1mh choke in series with the midrange driver.

[Carlspeak]

Good catch ligs, I forgot about the #4 series coil. I revised my post accordingly.