advertisement


B110 (SP1209) Buzzing.....may need a replacement or repair?

What would happen if I used 8ohm units as a pair? The guy from Wilmslow said he would suggest the Monacors as replacement units and despite being labelled as 8ohm, they run closer to 6ohm in reality?? It's something I don't understand at all. The other thing I don't understand are crossovers. I thought they diverted the different frequency ranges to each speaker so if the crossovers are correctly set for a three way (treble, mid and bass), why would the introduction of a new mid driver possibly necitate a crossover change?
 
Using two 8 Ohm units in parallel would be fine electrically, but because you have two units covering the same frequencies, you will get problems of phase canellation etc. Not really recommended.

If you used 6 or 8 Ohm instead of the correct 4 Ohm unit, the crossover point will change, it will tend to crossover lower than the specified frequency. Also, all other things being equal, you will also get a drop in output level.

Obviously, the best solution is an exact replacement unit. Failing that it's worth looking for a Polypropylene coned unit of the same size, and also 4 Ohms.

This may be difficult, I think the Monacor may be worth trying. I may be wrong, but I think there is a Monacor with adjustable impedance (dual coil) and is should be possible to get 4 Ohms.

I still think the transformer solution with a suitable unit is viable. As mentioned, look at the Rogers LS2 for a driver.
 
The crossover is designed specifically round the impedance curve and frequency response of the driver.

If you use a different driver, the midrange response shape will be different; for example if the new one has a higher impedance than the old at high frequencies, there will probably be overlap between midrange and treble, plus changes to phase, so you will probably get a peak in response there.

Sophisticated designs like the R107 have a lot of optimisation in the design, so that the sum of the outputs of the drivers adds up to a smooth response; the crossover paths to the individual drivers take the driver details into account.
 
KC Cantiaci said:
... despite being labelled as 8ohm, they run closer to 6ohm in reality?? It's something I don't understand at all.
Click to expand...

In simplified terms:

Impedance (AC) = Resistance (DC) + Reactance (AC)

Resistance varies moderately with temperature, reactance varies considerably with frequency - which is useful as it allows us to make filters for crossovers, etc. Ideal inductors and capacitors have NO resistance at all, their impedance is purely reactive. Ideal components do not in fact exist...

Most 8 ohm drivers have a voice coil (an inductor, with a certain amount of unavoidable capacitance too, suspended in a strong magnetic field) exhibiting a resistance of about 6-6.5 ohms. The reactance adds with that (vector sum) to give an overall impedance value of about 8 ohms for most of the frequency range of interest. It is only a nominal value, it will be exact at usually two specific frequencies and thereabouts for a (hopefully broad) bandwidth in the middle of the driver's working range.
 
The thing is, the label "8 ohms", or "4 ohms" is only a nominal value.

You have to measure the actual impedance, and see what it is at the frequencies where the crossover operates.

As a last resort, crossover component values can be changed to compensate.
 
If you've sent off the offending B110 for repair, hopefully that will be the end of it. Otherwise the only way to really get a proper replacement would be to find a pair of knackered 107s and part them out for spares.
 
Yank said:
If you've sent off the offending B110 for repair, hopefully that will be the end of it. Otherwise the only way to really get a proper replacement would be to find a pair of knackered 107s and part them out for spares.
Click to expand...

I agree.....but I suspect I'm one of many probably looking to do the same thing. I can' recall ever seeing a knackered pair of 107's, at least not on eBay..... but maybe I've missed them. I have a constant search looking for Kef 107 and associated parts but I've never seen a B110 SP1209 come up. The flip side is you're buying an unknown quantity and they could be damaged/worn as well. Hopefully, the repairer will do a good job and I'll be back on track. I'm sorting out the posting of the offending item now but I'm wondering whether to send the other one off or wait until that goes?? At least I've got a spare pair of mids to use in the meantime ;)
 
Trouble is that the Falcon B110 is Bextrene coned and what is wanted, I believe, is Polypropylene.

Maybe Falcon could provide that.
 
You must log in or register to reply here.


advertisement


Back
Top