Speakers only playing high freq through tweeters

[skibum]

Morning,

Probably a dumb question, but here goes.

Recently bought some Mission 780 speakers through ebay to use in the garage set up. Wired them up to my amp and they only seem to be playing through the tweeters and therefore at high frequency. The new speakers are bi-wire, so I connected another cable up (twisting the two cables together at the amp end and then having the separate cables connect to each of the 4 posts on the speaker) and same issue.

I've not used bi-wireable speakers before so is there something I am doing wrong?
Is there normally an Amp setting or something I need to do?

Or have I bought some dodgy/broken speakers?

[Crackie]

The speakers should have a pair of flat metal links between the connectors. See the attached pic.
https://www.google.co.uk/search?hl=en&site=img...
Are the links there ?

Assuming you connected to the top pair originally, have you tried connecting the bottom pair instead; this should give you bass/mid only and no high frequencies.

Your description points to both crossovers or both bass drivers being blown; this is possible but unlikely unless they've both been badly abused.

Edited by Crackie on Wednesday 1st June 13:24

[pc.iow]

https://www.youtube.com/watch?v=TxQqWSnsHoA

[skibum]

The connecting strips are present.

I've tried every possible combination. single pair of wires to top posts and then to bottom posts. I've also tried bi-wiring with/without the connectors.

Hmmm - starting to think they're knackered.

Love the sketch btw.

[NDA]

Sounds very odd.... if the connecting strips are there, then you should be able to connect to either pair of terminals.

The connecting block on the 780's is easily removable - can you unscrew the assembly and gently pull out and inspect?

It's also worth very gently pushing the bass drive units in and out with your fingers (spread out so that you're gently pressing in the entire unit). You shouldn't feel any resistance or hear any scratchy sounds. A blown drive unit should still produce some sound however - but it's worth seeing if they've been over driven.

What did you pay for them?

[megaphone]

If they're blown it will ether be the bass drivers or the crossover that's gone. Are the bass drivers moving in and out freely when you push them by hand? No scratching or rubbing?

You can remove them quite easily, stick a test meter across them and see if you get a reading, probably around 8 ohms. If not they're probably blown. You can also test with a battery across the terminals, a 9v is easiest, touch it on and off to see if the cone moves.

[Crackie]

skibum said:

I've tried single pair of wires to top posts and then to bottom posts.

Hmmm - starting to think they're knackered.

Was there no sound at all when connected to the bottom terminals ? If so crossovers and/or bass drivers have been fried.

[schmunk]

Have you connected the speakers out-of-phase? That'd significantly reduce the bass output.

[skibum]

I've checked and both bass drivers seem to move without any resistance or scratching sounds at all.

I've taken the panel off the back and all seems connected and fine.

If I wire up the speakers to the bottom pins only, without the connecting plates in place, I get zero sound.

Not sure what wiring out of phase means. Do I need to review the Youtube video again

[Crackie]

skibum said:

I've checked and both bass drivers seem to move without any resistance or scratching sounds at all.

I've taken the panel off the back and all seems connected and fine.

If I wire up the speakers to the bottom pins only, without the connecting plates in place, I get zero sound.

Not sure what wiring out of phase means. Do I need to review the Youtube video again

I can't find an online circuit diagram for 780 but looking at this picture http://lowestoft-stereo.co.uk/items/Mission/780-mk... it looks like the crossover components for bass are only in parallel with the driver. The inductor and cap values point to the grey wires being for bass driver and the grey wires are soldered to the terminals; if there is zero sound when connecting to bottom pins then the bass drivers are open circuit.

Have a google search for blown 780 bass drivers......... unfortunately others have had similar problems.

Out of phase means the wiring on one of the speakers is reversed; the resulting sound from speakers cancels rather than adding together. The zero sound you have from the bass drivers is nothing to do with phase.

Edited by Crackie on Thursday 2nd June 07:27

[jmorgan]

Pop a speaker out to see if the cross over is there?

[Le TVR]

skibum said:

Morning,

Or have I bought some dodgy/broken speakers?

Very likely, Mission replaced vast quantities of these bass speakers under warranty and even the replacements failed soon after. See what resistance you measure across the bass speaker connections they will probaby be open circuit.

[skibum]

Thanks all for the responses.

I paid £65 for them on ebay and collected them locally. As such I've been back in touch with the vendor and we've arranged to head back to his to test them out on his setup as he says that they worked fine earlier in the year. Will see what happens.