Monday, November 15, 2010

Powys SASS "Lite" vs. Crown SASS-P/MKH-20's

Vicki Powys, of New South Wales, Australia, made some refinements in her SASS "Lite" array and to illustrate her progress with the design made simultaneous dawn recordings in the Bush of New South Wales, Australia. To me, the comparison suggests that one can very closely approximate the sound impact of a pricey array with a fraction of the cash and DIY labor. Here are the equipment particulars and a QuickTime Movie comparison:

Crown SASS-P body
modified with 2- Sennheiser MKH20 mics ( Diffuse Field EQ turned ON)
Sound Devices 702 Recorder, Record level "60"
2 x MKH20 mics with Diffuse Field ON
No Low Cut
Lycra windshield

DIY SASS Lite Narrow #2 
with PIPMics "Twin" capsules (two on each channel; PIP)
Olympus LS10 Recorder; low sensitivity; record level 10
No Low Cut
Lycra windshield + Beanie

 click on image to enlarge
Download QuickTime comparison Movie [.zip 12 mb] 

The same arrays were also included in her outdoor pink noise test and sound and silent versions of the localization test can be evaluated here:

 click on image to enlarged animation
Download QuickTime comparison Movie with sound samples [.zip 12 mb]

Comments Rob D. November 16, 2010:

The only significant difference I can detect by-ear between the two arrays in the recordings is slightly more "body"/lower frequency representation in the SASS-P body mod with the MKH-20 mics. This difference might be lessened if harder boundary surfaces were employed in the DIY mic. See Paul Jacobson's polar plots below where the lift <1000 Hz is greater for unfinished wood.

The harmonic shift between the pink noise samples is not detectable in the spectrum of the sounds presented in the field recordings. I think this shift is the result of the unique tonal balance presented by the capsules and not problematic coloration. If we think of each capsule/array as a filter or producing an unique tonal balance, these "curves" cause some bands of pink noise to get boosted and others to become attenuated. The net effect is some notes get louder and others get softer-- thus a shift in key. 

Pink noise confuses my ability to evaluate overall tonal "balance" so I used the visual sonogram displays in analyzing the test using pink noise. The greater low-end response of the SASS-P/MKH-20 mod is evident in the field recording sonogram but not in the pink noise generated sonogram by the portable CD player. This is not at all surprising considering its 4" speaker.

It appears that SASS-P/MKH-20 mod has more response from 3K to 4.5K Hz from the 12 to 2 o'clock positions.  The SASS Lite's response is better in the 5500 Hz to 9500 Hz range at most angles. Probably due to the Diffuse EQ option on the MKH20's, there's more response above 12K Hz at most angles and especially from 10:30 to 2:30. It looks like much of the extra brightness with Vicki's current SASS Lite configuration is associated with sounds arriving from 2:30 to 3:30. There may be some evidence of this in the field recording that Vicki can pick-out.

The most audible change in the pink noise comparison is the SASS Lite's greater response between 1K Hz and 3KHz.
The effect starts at 10:30 and increases to 1:30. From 2:00-3:30, it disappears. Its not standing out to me in Vicki's field sample but settings with more distant subjects and "airyness" might make this difference more apparent. The difference is not just between hard and soft boundaries because the capsule sizes differ. Paul Jacobson's comparison of the 10mm "Jack Mics" placed in SASS-P dimensioned unfinished wood and foam boundaries might be better for isolating the hard soft boundary differences:

click on image to enlarge animation

At some point we might want to compare the self-noise and phase performance of single 10mm capsules to the "twin" sets Michael Rooke made for Vicki. I assume the twin capsules use series or parallel wiring to take advantage of the higher PIP voltage of the LS-10 and increase output.  

I am not struck by a huge noise performance difference in the recordings. The < 500 Hz input noise we've detected with the mic pre of the LS-10 is not surfacing noticeably.  There is proportionally more soft background "grunge" in the Lite/LS-10 sonograms between 500-1000Hz. Perhaps the input noise is effectively masked by the background sounds she happened to record? (Note LS-10 owners that Vicki uses special recorder settings to get lower input noise performance).  Those with better high frequency hearing than mine can probably hear more self-noise difference above 10K Hz. Under that, the considerable high-frequency content in the setting seems to be masking the potential 4 dB(A) difference in self-noise ratings  [MKH-20's at 10dB(A) and Pip Mics at 14 dB(A)]. The high gain associated with the quiet conditions would normally reveal a difference this large, so the twin capsules may be improving self-noise performance.