I bought some second hand B&W DM4s (early 1970s) which have very good mid/low frequency reproduction but have lost their high frequency performance (muffled/reduced cymbals, guitar string scratch, speech sibilance, amplifier hiss etc) compaired to the fantastic top end I remember hearing on others (the reason for buying them!). The high frequency drive units (Coles 4001 & Celestion HF1300) are producing sound in their appropriate frequency ranges, ie they are functioning & not blown. Have applied frequency sweep to speaker inputs & viewed signals with scope through xovers to drive unit contacts and appropriate signals appear at the drive units. Can the drivers themselves lose their upper frequency performance over time (diaphram gets brittle etc)? I replaced the HF1300s with a second hand set bought off ebay with no marked difference so either they have the same problem or its the 4001s or xovers. Could the capacitors in the xovers have aged? they appear to be good quality polypropylene film not electolytic. The diaphrams on the 4001s look OK, no cracks etc. I see you can get replacement diaphrams but the coil wires are very fine & I'm not sure I'd like to take a soldering iron to them. I see you can pick up DM4s on ebay for ~£100 so not sure if buying new 4001s at £45 each is worth the punt!
I have tried connecting both types of driver in place of the Trio tweeters in some old Trio (Kenwood) LS-202s and they are not nearly as good at the top end as the orginal Trios (this may not be particularly valid as the Trios are 4ohm on a much more basic x-over).
I might try experimenting with shorting out coils & capacitors in the xover but dont want to damage the drivers by putting too low frequencies up them, so advice on this appreciated.
Any thoughts?
I have tried connecting both types of driver in place of the Trio tweeters in some old Trio (Kenwood) LS-202s and they are not nearly as good at the top end as the orginal Trios (this may not be particularly valid as the Trios are 4ohm on a much more basic x-over).
I might try experimenting with shorting out coils & capacitors in the xover but dont want to damage the drivers by putting too low frequencies up them, so advice on this appreciated.
Any thoughts?
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