View Full Version : Heathkit AS 21 Crossover Question

12-09-2014, 10:49 AM
I'm running a pair of Heathkit AS 21 with McIntosh C30 preamplifier and MC 240 tube amplifier or MC 2505 SS amplifier.

The problem is that the EQ in the preamplifier must be set as follows in order to obtain correct response (more or less):

30Hz ~ +10dB

150 Hz -4B to flat (depending)

500 Hz ~ -6dB

1,500 Hz -12dB (max cut)

10kHz ~ +10 dB to +12 dB (max boost)

These settings must be used to approximate response from pair of Boston Acoustics T1000 with EQ at flat settings.

The crossovers are completely original to the speakers with nothing ever done to them. I checked with Bob Crites but he said he does not do crossovers for Altec. Does this sound like crossover issues and if so, who works on crossovers for this speaker?

12-09-2014, 02:54 PM
One naturally wonders about your test setup.

Some of those numbers are not surprising. Some are, a little.

12-09-2014, 03:46 PM
Great Plains Audio is the place to go for Altec, they may be able to help you:



12-10-2014, 09:16 AM
Thanks for the suggestion, fpitas.

I spoke with the gentleman from Great Plains this morning.

The bottom line is that there is nothing he can do in this case and that the response characteristic I am experiencing is typical of this model.

He also mentioned that the driver compliment of this model is the same as the Malibu & 9844 monitor which was also helpful.

Thanks again.