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Measurement Details

AmplifierPowersoft Digam K20-DSP+AESOP
Outside Temperature72 F
Date TestedMay 22, 2015
Settings & Equalization25Hz Butterworth 24dB/Octave High Pass Filter (For High Power Measurements)

Notes

The measurements of the OS-Pro start off with the impedance response, which shows that the DC resistance is down near 2.1 ohms but quickly rises and reaches a minimum of about 3.6 ohms at 39Hz. The rest of the 25-125Hz bandwidth is 4ohms or greater. The sensitivity measurements with 2 volts applied at 1 meter and 20 volts applied at 10 meters show that the JTR spec of 103dB is dead on in my opinion. The measured peak in sensitivity is actually about 108.5dB at 100Hz which a lot of manufacturers would claim as the system sensitivity but the broad band average over 35-120Hz is about 103dB which is quite high. This is what JTR claims as the sensitivity. The overall frequency response shows a little bit of the roughness that is typical of horn loaded bass systems. However the response was within +/-4dB from 34.5-115Hz which is quite reasonable. The factory spec is a little bit tighter at +/-3dB over 37-121Hz but otherwise this is pretty close agreement. It is interesting that the measured response seemed to be shifted down in frequency just a hair from the factory specs as evidenced by the low end extending to 34Hz instead of 37Hz and to about 115Hz up top instead of 121Hz. Regardless the agreement between the two is quite close. The combination of high sensitivity and 4ohm or higher impedance mean that the OS-Pro should not be a difficult load for most amplifiers. The time domain measurements indicate that in general the OS-Pro is well behaved. There is a bit of extra group delay near 35Hz where it reaches about 1.5 cycles briefly, however the waterfall decay shows that this frequency bandwidth has decayed by about 32dB in around 200ms so it is not likely to be audible. The group delay below about 25Hz can be ignored as this is below the effective range of the system and getting down into the noise floor.  There is a slight issue at 100hz, which corresponds with another peak in the OS-Pro’s response, where there is increased group delay and notable ringing. After applying a bit of a notch EQ to flatten the response in this area and applying the typical 80 or 90hz low pass filter this should be patched up somewhat.

The long term output compression measurements start with the application of a 25Hz, 4th order, Butterworth high pass filter to prevent excessive driver excursion in the deep bass and a tiny 1.05 volt drive level which causes the OS-Pro to produce about 90dB at 50Hz at 2 meters. During the next 30dB worth of increases in output, delivered in 5dB steps, the OS-Pro responds in a linear manner and just starts to show about 1dB of compression with a 33.2 volt input which causes the OS-Pro to produce about 120dB at 2 meters. A further 5dB increase in drive to 59 volts and output levels near 125dB the OS-Pro just starts to reach about 2dB of output compression over some parts of the bandwidth. A 3dB increase was used for the next measurement resulting in a drive voltage of 84 volts. At this point the OS-Pro was producing around 130dB over a large part of its bandwidth using a very long duration sine wave sweep and output compression had reached 3dB over a few areas of the bandwidth. Additionally there was some distress noise from the cab down in the 25Hz region indicating that the driver excursion may be getting out of hand. As with the Growler a slightly more aggressive high pass may have allowed the cabinet to be pushed a bit further with this demanding test type but with compression reaching 3dB in a few places it is unlikely that going much further would be worthwhile. During the 84 volt sine wave sweep the OS-Pro produced some of the loudest SPL levels that have been recorded during this type of test.

The distortion measurements for the OS-Pro with a 10.5 volt input show less than 3% THD above 30Hz. Likewise at the 18.7 volt measurement the THD is low staying under 5% above 30Hz. Increasing the voltage to 33.2 volts results in the THD rising a bit but still staying under 9% above 30Hz. The next  increase in the drive signal to 59 volts results in a moderate increase in THD with 10 to 14% from 25-45Hz which is still acceptable and less than 10% THD above 45Hz. The final, loudest 84 volt measurement shows another jump in THD to the range of 15 to 30% in the 25-50Hz octave and 15% or less above that point. This may seem a bit high but considering the output levels being produced and the fact that the distortion is nearly all 2nd harmonic it is actually not bad at all. In fact the 2nd harmonic distortion is the dominant distortion harmonic over the entire 25-110Hz range. The 3rd harmonic rears its head in a few spots but it is well down for the most part.

The CEA-2010 short term burst output measurements are impressive. This cab is primarily focused on output at 35Hz and above so it does not put up huge deep bass numbers. It does manage to eek out a passing 16Hz result though, with a score of 92.7db on about 28 volts drive and with the 3rd harmonic limiting. The output improves a bit to about 99dB at 20Hz where again the 3rd harmonic is the limitation. At 25Hz the OS-Pro would take a bit more voltage and produced a passing SPL of nearly 112dB with 69.3 volts applied. If the distortion limitation was thrown to the wind the OS-Pro would burst about 5dB higher from 16-25Hz but with 50-60% THD. At 31.5Hz the OS-Pro starts to be in its intended bandwidth and records a solid 125.2dB on 112volts. The OS-Pro was pushed a bit further at 31.5Hz but it made some audible distress noises so testing was halted after getting just 0.2dB more out of it. Once up near 50Hz the OS-Pro was able to take everything the bridged K20 had in a very short burst and started putting up huge numbers. At the 63, 80 and 100hz bands it actually broke 140dB and the microphone had to be moved back to 8 meters for the measurements to ensure ample headroom in the mic preamp!

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