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AR's test proceedures


teknofossil

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AR used a fairly standard method of measuring individual drivers as part of the development process and also for on-going QC reasons. From the beginning up through the early 90s, individual drivers (tweeters and mid-range drivers) were tested in one of several calibrated anechoic chambers or in the case of woofers, measured out doors in cabinets buried in the ground, flush with the surface. Woofers were also measured in Harvard University's large anechoic chamber, and the calibration curve from that was established for AR's in-house anechoic chambers to correct for AR's chambers not going down to sub-sonic frequencies; thus, AR was able to use in-house chambers to measure woofers even though these anechoic chambers were not truly anechoic down below 100-200 Hz or so.

Drivers were tested with crossover in place, and even though system frequency response was useful, individual driver performance was considered paramount and the subsequent power-response measurements were made both with spectral analysis in anechoic chambers and also in reverberant and semi-reverberant chambers.

Testing for frequency response of individual drivers, the procedure was standardized. A good example was the AR 1-1/2-inch midrange dome used in the AR-3a, LST, 5, AR-10, AR-11 and many others.

The test specifications were as follows:

1. Voice-coil terminals were tested for proper polarity, such that a positive signal applied to the "+" terminal will cause the dome to move away from the magnet structure.

2. Speaker is tested for buzzes, rattles, rubs, chips in gap, and any other form of distortion when 6-volt input is applied at all frequencies within its operating pass band.

3. DC resistance is tested (e.g., the 4-ohm dcr should be 2.3-3.5 ohms).

4. The driver is tested on a flat baffle with front board flush with 180-degree (2Pi) solid-angle radiation baffle, facing an anechoic environment (into anechoic chamber).

5. The measurement microphones -- B&K calibrated measurement condenser microphones -- were placed 1 meter from the driver on its axis. An input of 2.83 volts is applied across the crossover network into the driver.

6. Efficiency is tested to fall within 88 dB +/- 1 dB SPL re .0002 microbar.

7. Low-frequency rolloff 6 dB +/- 1.5 dB down from average level on axis at 525 Hz.

8. High-frequency rolloff 3 dB, +/- 0.5 dB from average level on axis at 5 kHz to 8 kHz.

9. Maximum peak of 2.5 dB and/or maximum dip of 2.5 dB from average level.

--Tom Tyson

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