p { margin-bottom: 0.25cm; line-height: 120%; } I recently acquired a pair of Philips AD1256/M8 full range speakers. With the knowledge that a suitably large open baffle would not be conducive to domestic bliss, I have paired them with some New Zealand-assembled alnico magnet Plessey 12U50 speakers which have a good bass response and were often used in guitar amplifiers.
These speakers were produced in Melbourne by Plessey Rola and many of the parts were taken over by Lorantz Audio Services whose owner had been the development engineer at Plessey at the time it ceased production. While technical data for the 12U50s is no longer available, Mikhail from Lorantz very obligingly sent me a datasheet for the A308PA50 which was made using Plessey parts.
Overall, the Philips/Plessey combination is pleasing, with acceptable levels of bass, and a really clear sound. The one drawback is that the AD1256 speakers have the full-range tendency for rising sound which makes the combination a little fizzy at the top end. I have tried quelling this with a choke (values between 0.3 and 0.8 mH) and also bypassing the choke with a resistor (about 12 ohms). While the tone profile is much improved, there is some sibilance at some frequencies, which I put down to the choke shifting the phase of the AD1256 speaker.
Currently, with the Philips/Plessey combination, with about 2 dB of attenuation and a Zobel network on the Philips and no choke, sounds good, but could be better.
My knowledge of crossovers is challenged, as are my powers of guesswork. Any thoughts?
Philips AD 1256/M8 Fullrange Loudspeaker Measurements Data and Information Full Range
These speakers were produced in Melbourne by Plessey Rola and many of the parts were taken over by Lorantz Audio Services whose owner had been the development engineer at Plessey at the time it ceased production. While technical data for the 12U50s is no longer available, Mikhail from Lorantz very obligingly sent me a datasheet for the A308PA50 which was made using Plessey parts.
Overall, the Philips/Plessey combination is pleasing, with acceptable levels of bass, and a really clear sound. The one drawback is that the AD1256 speakers have the full-range tendency for rising sound which makes the combination a little fizzy at the top end. I have tried quelling this with a choke (values between 0.3 and 0.8 mH) and also bypassing the choke with a resistor (about 12 ohms). While the tone profile is much improved, there is some sibilance at some frequencies, which I put down to the choke shifting the phase of the AD1256 speaker.
Currently, with the Philips/Plessey combination, with about 2 dB of attenuation and a Zobel network on the Philips and no choke, sounds good, but could be better.
My knowledge of crossovers is challenged, as are my powers of guesswork. Any thoughts?
Philips AD 1256/M8 Fullrange Loudspeaker Measurements Data and Information Full Range
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Trow out all the components and put an acoustic band pass filter in front of the Phillips. Dense open cell foam with a vertical one inch slit could be a start.
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