19 Element Mic Test Using Yamaha Mixer

Element Arrangement

19 Panasonic WM-64K wired in parallel. (see schematic) The noise is uncorrelated and only increases by 13db, but the correlated audio increases by 26db. A 13 db increase in S/N ratio.

The WM-64K spec for S/N is 58db. We should get 71db S/N.

Off axis, especially at 90 degrees, we should get some comb filtering at wavelengths near the WM-64k capsule size.

See John Conover's page using the WM-61A.

This mic and an Earthworks M23 were placed very close (see picture) and the sound (hand claps) and noise were recorded and used to determine relative sensitivity. BTY, here is a sensitivity conversion tool.

Shown here as RMS Power, the 19 element mic consistently produced 12.5 db higher signal than the M23 which has a sensitivity of -30.5db/Pa (30mv/Pa), so this mic sensitivity is -18db/Pa, or 126 mv/Pa.

Here is the spectrum of the hand claps used for comparative sensitivity test. The M23 signal was boosted 12.5db so that the RMS power was the same in each channel.

The 19 element mic has about 5db rolloff at the high end.

The recorded noise amplitude, A weighted, of both channels was multiplied by 20db and played back to the RTA.

The noise for both mics is shown to the left. There does appear to be some 60hz products in the our mic that is not in the M23, however they are still less than the noise level of the M23.

The M23 spec for self noise is 22db SPL. Since we are 8db lower, then this mic self noise is 14db SPL. At 115db_max SPL we have a dynamic range of 101db, and S/N ratio re 94 dB SPL = 80db.

This mic has 12db higher signal and 8db lower noise, thus we have a 20db better S/N ratio for a specific SPL.

frequency response and phase of 19 element mic.

Driver: AKG240 headphone clamped over mic. Test setup B*

* Same as test setup B except that Phones are clamped over mic and no plastic ear canal is used because we used headphones instead of ear buds.

Intermodulation distortion form two tones, 300hz and 400hz Driven by AKG240 headphones @ 77db SPL. The are 600 ohm phones, so -10 dbm = 0.1mw. Test setup B*

Intermodulation distortion from two tones, 300hz and 400hz of reference channel, the headphone amp of the UA-1EX used to drive the AKG240.

It appears that the IM is produced by the headphone amp of the UA-1EX.

Test setup B

Total harmonic distortion of 19 element mic, driven by AKG240 phones @ 72db SPL. Test setup A

THD measured with DSSF5E.

frequency response and phase of 19 element mic.

Driver: Sony CD350 headphone clamped over mic. Test setup A*

* Same as test setup A except that Phones are clamped over mic and no plastic ear canal is used.

Intermodulation distortion form two tones, 200hz and 300hz Driven by Sony CD350 headphones @ 1mw (97db SPL) . These phones are 32 ohm phones, with sensitivity of 97dbSPL/mw. (1mw into 32 ohms = .179 vrms.)

Test setup A*

Intermodulation distortion form two tones, 200hz and 300hz Driven by Sony CD350 headphones @ 79db SPL . The are 32 ohm phones, with sensitivity of 97dbSPL/mw, thus power = 0.028mw. (0.028mw into 32 ohms = 0.03 vrms.)

Test setup A*

Total harmonic distortion of 19 element mic, Sony CD350 headphones.

Test setup A*

THD measured with DSSF5E.

Remaining work: We need to do some free field test of this mic. I need to build the apperatus.