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AR 1.5" Dome for AR-3a and AR-5 Characterization

Pete B

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I'd like to measure an AR-5 type 8 ohm 1.5" midrange if anyone has a spare to loan.  I'll post the .zma

file here for general use.  I'm also interested in the physical construction in case anyone has disected

a dead one or would be willing to donate dead ones for me to do.

I'm curious about the specs for these midranges, I have a pair of 4 ohm from AR-11 which I believe the

same as the AR-3a type.  I'm also interested in the physical construction, again if anyone has a dead

one to donate for analysis.

I measured a pair of AR-11 mids many years ago and am reposting them below, I'll remeasure them and 

post .zma files here.

AR-11 Midrange (200010-1) Measurements 9/17/05:

Midrange #1:

Red label indicating that this was replaced

Date code : 561 8018

Fc = 464.6 Hz

Re = 3.15 ohms

Qe = .92

Qm = 3.15

Qtc = .71

Midrange #2:

Appears to be original

Date code: 561 7812

Fc = 514.9 Hz

Re = 3.18 ohms

Qe = 1.04

Qm = 3.17

Qtc = .78

The impedance curve looks primarily like a simple sealed system with a fundamental resonance of 12.9 ohms at 521 Hz. Impedance is 4.0 ohms in the pass band at 3 kHz. There is a very small secondary peak of 4.27 ohms at 1098 Hz.

Neither the midrange or tweeter utilize rear chambers and it is clear that the acoustical response is part of the crossover network. The midrange Fc being close to the crossover point, and the Qtc of .7 could form one section of a Linkwitz-Riley 4th order response. The acoustical response being one 2nd order section and the electrical being the other if properly designed.

The large increase in impedance suggests that ferro fluid was not used in these drivers.

I don't like the idea of an acoustical filter in front of the dome, however the construction of this midrange appears to be very well done.

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Robert, ra.ra kindly provided this drawing of the 200044 1.5" midrange that was used in the AR-58s.

It includes ferro fluid and does not include a screen or front fiberglass pad but otherwise is likely

the same, can anyone confirm this?   The older mids did not include the glued on "Semi-horn", 

item 10 in that drawing.

The diagram mainly provides construction details and notes but does not include actual dimensions or

tolerances.  Still a great diagram.


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