The RL 850 pictured above has a treated paper 8" driver which may be a good, if not perfect, match.
There are four pairs of these speakers currently available on UK ebay, going for around £35 a pair. Probably not to be found in Australia though.
Thanks Galu.
If the RL 850 was 'Made in England', maybe the RL 870 refers to the Danish built version.
Visual difference include 3 fixing screw holes on the 870's Tweeter faceplates, & smaller cone dust cap on the 870's Woofers.
Also the 870's paper cone seems to go back more deeply.
Other differences might include crossover build and country of manufacture?
I've realized, I have a pair of 8" B&W BZ200/16 Bass/Mid drivers on hand.
To fit them, I'd need to route the woofer hole in the face plate approx 7.5mm
Also the top of the basket surrounds would cover approx 4mm of the lower part of the circular face plate belonging to the tweeters.
The B&W's are heavier (maybe better quality) than the original Rotel Woofers.
Would the crossovers need to be revised?
Also would the Rotels loose their resale value??
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Even if both original woofers were working, the value of your RL 870 speakers would only be that which someone would be willing to pay for them - well built though they may be!
You haven't confirmed that your RL 870 has a sealed enclosure, as I suspect it does. Some external photos would be nice.
The B&W BZ200/16 mid bass drivers were used in parallel pairs in the B&W DM 220 sealed box loudspeaker - so each will have a nominal impedance of 16 ohms.
So, good for sealed box use but, at 16 ohm, the B&W drivers will be a mismatch for the Rotel crossover.
Cliff, please measure the dc resistance of a B&W driver (and remember to subtract the resistance of your meter leads) in order to confirm or deny my nominal impedance figure.
A single one of those B&W drivers is suited to a sealed box volume of 25 litres.
What do you estimate the volume of one of your Rotel enclosures to be?
A single one of those B&W drivers is suited to a sealed box volume of 25 litres.
What do you estimate the volume of one of your Rotel enclosures to be?
No, Allen, I am asking Cliff to measure his potential replacement B&W drivers, not his original Rotel ones.
I believe the B&Ws have an impedance of 16 ohm, but require that to be checked.
I believe the B&Ws have an impedance of 16 ohm, but require that to be checked.
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Sorry for tardiness in reply.
Recovering from surgery.
The RL870's are sealed boxes, & fully stuffed with material.
The side enclosure panels are well braced with 16mm panels glued in position and almost entirely covering the sides.
I roughly measured the internal lengths of the boxes 210mm x 220mm x 440mm = 20,325.
The B&W BZ200/16 mid bass drivers measured 1.9Ω and are listed on line as 16Ω drivers.
The shorted Meter measures 0.5Ω
Photos attached are one of the existing XO's belonging to the RL870's.
Recovering from surgery.
The RL870's are sealed boxes, & fully stuffed with material.
The side enclosure panels are well braced with 16mm panels glued in position and almost entirely covering the sides.
I roughly measured the internal lengths of the boxes 210mm x 220mm x 440mm = 20,325.
The B&W BZ200/16 mid bass drivers measured 1.9Ω and are listed on line as 16Ω drivers.
The shorted Meter measures 0.5Ω
Photos attached are one of the existing XO's belonging to the RL870's.
Attachments
I wish you a quick recovery, Cliff.
However, the Rotels may take longer! 😉
16 ohm drivers should not show a resistance of 1.4 ohm. If you have measured this correctly, then the potential B&W replacement drivers are toast.
As a double check, have you performed the battery test on these drivers?
P.S. The 20 litre enclosure volume is the same as that of the Rotel RL 850. I've discovered it used a British Elac mid/bass driver.
However, the Rotels may take longer! 😉
16 ohm drivers should not show a resistance of 1.4 ohm. If you have measured this correctly, then the potential B&W replacement drivers are toast.
As a double check, have you performed the battery test on these drivers?
P.S. The 20 litre enclosure volume is the same as that of the Rotel RL 850. I've discovered it used a British Elac mid/bass driver.
Thanks Galu.
Update: Sorry, reads 11.9 & 12 (not 1.9)
It might be my Meter skills.
The battery test resulted in a pop & healthy movement of the cones.
Positive to postive results in an outward movement of the cones.
I set the Meter to 200 in the Ω section for the test.
Maybe it's where I connect the terminals.
Choice includes: COM, & 1000VDC 200mA MAX, & 10A DC
Where should I connect the terminals on the Meter?
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Coil and transformer short circuits can be troublesome things.. even to the point of causing (further) damage in some cases.
There's nothing to say that the battery test won't give you a result but IMO it means little. Ideally you'd do an impedance sweep but with this measured short it's unlikely to look normal. There may be simpler listening tests you could do but you'd be putting your amp at risk.
There's nothing to say that the battery test won't give you a result but IMO it means little. Ideally you'd do an impedance sweep but with this measured short it's unlikely to look normal. There may be simpler listening tests you could do but you'd be putting your amp at risk.
My hunch is that Cliff isn't using his multimeter properly.
Cliff, perhaps you should show us a picture of your multimeter.
Usually, an Ω symbol is found on the same multimeter socket as the V and mA symbols. Plug the red test lead into that socket and the black one into COM.
Then the 200 Ω scale has to be selected with the rotary control.
Cliff, perhaps you should show us a picture of your multimeter.
Usually, an Ω symbol is found on the same multimeter socket as the V and mA symbols. Plug the red test lead into that socket and the black one into COM.
Then the 200 Ω scale has to be selected with the rotary control.
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Now we're cooking! Add one third of 12 onto 12 and we have the nominal impedance of 16 Ω.
These B&W drivers could be suitable as replacements in your 20 litre sealed Rotel enclosures.
The problem is adapting the crossover.
If you're keen to experiment, you could start by replacing the current iron-cored inductor with one of twice the value.
Right, past my bedtime!
These B&W drivers could be suitable as replacements in your 20 litre sealed Rotel enclosures.
The problem is adapting the crossover.
If you're keen to experiment, you could start by replacing the current iron-cored inductor with one of twice the value.
Right, past my bedtime!
I'll have to remove it from the XO and place a meter on it.
Here's the current schematic.
Should I interfere with the cap/resistor?
The current 3.3µF Cap reads 4µF & ESR 0.85Ω
Attachments
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It might be my meter.
It gives me Cap results but doesn't recognise the Inductor.
I would replace the electrolytic capacitor, but not the resistor.
P.S. It would do no harm to any of the components to try out the replacement mid/bass driver with the existing crossover before going to the expense of buying a new iron-cored inductor of twice the inductance.
Who knows, you might like the resulting sound balance with the current inductor.
P.S. To get accurate measurements you must lift one leg of the inductor or other component in order to effectively remove it from the circuit.
EDIT: I see you said you would remove the inductor to measure it, so that's OK.
P.S. It would do no harm to any of the components to try out the replacement mid/bass driver with the existing crossover before going to the expense of buying a new iron-cored inductor of twice the inductance.
Who knows, you might like the resulting sound balance with the current inductor.
P.S. To get accurate measurements you must lift one leg of the inductor or other component in order to effectively remove it from the circuit.
EDIT: I see you said you would remove the inductor to measure it, so that's OK.
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