To the listening test review
Doing things together is always the best way. For this reason, last morning, with my friend and colleague Mauro Simolo we prepared the set-up to measure the impedance trend of the Gato PM6 speakers. Armed with oscilloscope, sinusoidal generator and reference resistor, we started the detection of the Vap VRr/frequency correspondences that are, respectively, the tension values detected on the speakers clamps and on the reference resistor. Based on these tension values you can then calculate the impedance of the loudspeaker.
Ready, set, go. Starting from the lowest frequencies, up to the highest parts of the audio range, with paper and pen, at each frequency, we wrote down on a chart all the values.
Then we inserted the data in a spreadsheet chart in order to calculate the impedance and get the Frequency/Impedance chart represented here below:
What can I say? The impedance is enough irregular and rich of substantial changes all along the range considered for the measure.
Let us try to recognize the various zones to understand how the filter of a speaker works with a 1/2 way in the low range, trying not to be intimidated by a nonlinear impedance chart.
In the Gato PM6 speakers, the manufacturer has pushed a lot the low frequencies and in my opinion, they are very powerful, but at the expenses of what? Of an impedance quite difficult to drive! The sudden slope, due to the filter configuration between a high midwoofer and a low midwoofer, requires amplifiers with strong outputs in order to contrast the rapid current increasing, which is due to minima of impedance, just 2.4 ohm, between 30 and 40 Hz and between 100 and 200 Hz.
This happens because underneath a certain frequency the two midwoofers are configured like two components in parallel.
The substantial difference between a "2.5" way system and a two-way and subwoofer is set by the filter.
In the two-way plus subwoofer, the midwoofer is provided with a high cut off point and it realizes an ideal crossover with the subwoofer, or the system cuts off at -6dB at the crossover frequency with the subwoofer.
Pay attention, we are talking of a passive subwoofer with a crossover filter!
In the "2.5" way system, there are two identical midwoofers and, at electric level, the filter is configured in such a way that the 1/2 way, the low midwoofer, picks up the signal directly at the ends of the high midwoofer by applying a further low-pass filter. The series coil makes diminish the resistance at the decreasing of the frequency and applies at the high midwoofer ends a parallel frequency that brings the impedance to values that are lower than the nominal value.
This slope has nevertheless a very audible advantage. At the decreasing of the impedance, what follows is a constant increasing until doubling the low frequency emission area and, in our case, until it is the equivalent of the surface of a 10/11-inch woofer.
Components
The Gato PM6 system has components by SB-Acoustics, a 1.2-inch, eight ohm ring tweeter and 6-inch, eight ohm Midwoofer with bass reflex loading.
Design considerations
As I know the components, I consider it as a good compromise. The 6-inch midwoofer gives great performances in low frequency, the SB-Acoustics produces a 4-inch midwoofer that can go down to 40 Hz: so the choice to add a further 1/2 way means more acoustic pressure in the low range giving to the Gato PM6 speakers a better power handling.
Driving
The Gato PM6 speakers have, as I told before, a quite difficult and not very regular impedance. For this reason it has to be taken into account the fact that the amplifier should be very generous in current in order to avoid that in the slopes with very low impedances there will be a too high current need for the possibilities of the amp.
Final considerations:
It is not difficult to find nowadays amplifiers with the needed requirements. Therefore, the designers instead being worried about the 2.4 ohm in low frequency have focused on more balance on the bass notes. They deserve an attentive listening session!
Official technical specifications:
Type: 2½-way floorstanding speaker
Frequency response: 34Hz-25kHz -6dB
Sensitivity (2,83V): 90dB
Recommended power amplifier: 50 to 300W
Nominal impedance: 4ohm
Connectors: Gold plated 4mm Plugs, bi-wire
Drivers:
High frequencies 38mm Ring Radiator, powerful ferrite motor and optimised chamber
Mid & Low frequencies 170mm papercone, low loss suspension, motor with shorting rings and optimised voice coil
Low frequencies 170mm papercone, low loss suspension, motor with shorting rings
Dimensions: 200x1020x370mm (WxHxD)
Weight: 28kg, 61.73lb
Official Italian dealer: to Il Tempio Esoterico website
Official current price in Italy: 2,990.00 EUR
Associated equipment: to Mauro "OutliNero" Simolo's system
