Bi-amping Mordaunt Short MS40

[iUSERTLO72p]

Hi all,
Just picked up these floorstanders on the cheap, however, I'd like to Bi-amp. Mordaunt Short has Bi-wire terminals fitted to these units that consist of a pair of 6" woofers and a tweeter. Close inspection shows the dust cover on the top woofer is not fixed to the cone, but they are on the lower driver. Question is, do I connect one amp to the bottom driver and the other amp to the top driver and tweeter or one amp for the woofers and one for the tweeter?

Either way, I'd like to install an active crossover into the mix, so whats best?

Is this a 2 way or a 3 way??

Cheers iUSERTLO72p

[iUSERTLO72p]

Okay, no replies yet. Do I need to give you more info? I was only concerned about the top driver not having its voice coil attached. Normaly a 2 way would be obvious, and I'm not Tri-amping. Maybe I could go either way, and I could keep the tweeter passive.

Google doesn't throw up much.

Cheers iUSERTLO72p

[5th element]

It looks like they are a 2.5 way loudspeaker, although they could possibly be 3 way.

Whatever they are it doesn't matter, MS only provide two pairs of terminals for you to wire them up with anyway.

What these do I have no idea. One set could power the tweeter and the other the two mid/bass drivers. Or one set could power the tweeter, the upper mid/bass and the other set the lower mid/bass.

You can easily figure out which configuration this is by only applying power to one set of terminals at a time and noticing which drivers get powered up.

Bi-amping is always better then nothing, going active is the icing on the cake, but its not really that simple a job. If MS have designed the passive xovers well, then just throwing a text book active filter at it would probably be worse then what you've got now.

With regards to modification, as in, can you alter them to be tri-wired? Well you'd either need to get a copy of the xover, or open them up and see how everything is wired.

If its a 2.5 way, there is a possibility for the .5 way driver to be powered AFTER the upper of the two mid/bass. This means that modifying them for tri-amping would be out of the question, unless you want to get measuring the driver units yourself.

With regards to the dust cap issue, from the poor pictures I've managed to google up, it appears the upper driver has whats known as a phase plug. A solid cone of usually plastic or metal, thats fastened to the top of the pole piece and does not move with the cone.

In a 2.5 way loudspeaker, the upper of the two mid/bass drivers handles the midrange and the bass, whilst the lower of the two drivers covers the bass and lower mids.

[Cloth Ears]

Without knowing the specific speakers, I'd agree with 5th. The tweeter will come off one of the pair of terminals, the two 6" drivers will come off the other. You'll probably find that the lower (in more ways than one) woffer will probably be low-passed (~6dB/octave) at approximately the baffle-step frequency (maybe 3-400Hz for these speakers). The other will match the low-pass on the tweeter.

Bi-amping is a definite possibility, as this can be done without any changes to your speakers. The easiest way is to get 2 matching stereo power amplifiers and use one to run each speaker. OR, use one stereo power amplifier to drive the mid-bass and one to drive the tweeters (in this case, the amplifiers do not have to be the same make and model). Both power amplifiers should run full-range in this set-up.

Problem: how to direct the same signal to the power amplifiers. You may be lucky in that your pre-amplifier might have 2 pairs of outputs, of you may have power amplifiers that also have output RCAs, so the signal can be sent on to the other amplifier. If you're using solid state, then you would probably be able to 'split' the signal, using a 'Y' RCA splitter, as the halving of the output impedance 'probably' won't have a great deal of effect on the sound.

For going active, you would probably have to do a detailed inspection of the passive crossover - as this would have to be removed. Going active with a 2-way active x-over would mean that you would need to keep the passive low-pass for the second woofer in place (probably not a problem, as it's likely to be a single inductor). you might also want to investigate using a single (very very small value) cap in series with the tweeter to prevent the 'pop' of the amp (or more likely the active xover) turning on causing the tweeter to blow.

Have fun!

[iUSERTLO72p]

Mmm, thanks for replies. I think I need to delve further. If I find some T/S parameters of the woofers and the Fs of the tweeter, maybe a Linkwitz crossover could be realised. Will pop over to Rod Elliotts site for some detailed look at crossover theory. Then hit the fridge for a 4 pack, stick on some Pink Floyd and fancy I'll tackle it later.

Seriously, I'll take a look at the crossover today, then I can proceed from there.

Many Thanks

iUSERTLO72p

[ashok]

Best thing for you to do now is bi-amp this unit as you are already commited to having extra power amplifiers. All you need is speaker cables and two stereo power amplifiers and a pre-amp.

Doing an active crossover is FAR more complex , and will take much more time and money.

Do the bi-amp scheme first which in itself will be very satisfying. After that you can slowly go about trying to change to an active scheme. It WILL take time and as you have never done it before there will be a (long ? ) learning curve !
Cheers.

[Cloth Ears]

Originally posted by ashok
Best thing for you to do now is bi-amp this unit as you are already commited to having extra power amplifiers. All you need is speaker cables and two stereo power amplifiers and a pre-amp.

Doing an active crossover is FAR more complex , and will take much more time and money.