Comparison of frequency response with and without series
resistor
The measurement distance was slightly over 3 meters. I
put some carpet and foam on the ground between the speakers and the mike panels to
suppress reflectionssome (see picture of the measurement setup
below). In low-mid-, high-mid and tweetercircuit a 3.3 ohm
resistor was inserted, while on the bass drivers I put in a 1.5 ohm resistor as these are two 8 ohm drivers in parallel. All
measurements were done using Speaker Workshop version 0.98 and
were smoothed with 1/4th octave.
From this chart you see that a 3 dB drop in level is apparent as can be expected, but the drop is much less near the woofers' resonance as there the impedance is much higher. The overall impression was that the loudspeakers sounded a lot more bass heavy, giving the speakers a "warmer" sound, which can be expected. My first impression was also that there was an improved stereo image, but after removing the resistors and listening to the same tracks again this impression proved false. Overall one can say that with the resistors being present the sound was more "tube like", probably because the considerable bump of nearly 3 dB in the lower bass region. I do not consider this to be an improvement.
Here a 1.5 ohm resistor was put at
the input of the original passive crossover filter of the
ME1's. As these are MTM's with the two 8 ohm woofers put in
parallel, the impedance is 4 ohm below the crossover frequency, rising to 8 ohm (theoretically) above. Crossover frequency is about 2700
Hz.
Here you see another influence from
the added resistor : the range from about 1 kHz to about 4 kHz becomes
less attenuated. I don't know what this means in terms of sonic character, but it sounded rather unpleasant to me. In the
bass range we see again the same effect as above : in the
resonance region of the bass drivers the output is less attenuated compared to the overall 3 dB, so again this made the
speakers sound "warmer". The bass became rather uncontrolled
and excessive in my opinion. From both measurements it's clear
I have a strong resonance mode of my room around 60 Hz.
Difference between the frequency
responses without and with a series resistor for the active
4-way speakers :
Difference between the frequency responses without and with a series resistor for the ME1 passive speakers :
of the active speakers because of the presence of the filter.
A picture of the measurement setup.
