Advice on rear ported speakers "rasping"

[Phil Bishop]

Thanks Antony, I had not thought of this. By the way, I am biwiring and also bi-amping. Is there another permutation, that is reversing the +ve/-ve on just one speaker (both sets of terminals) to see if that makes any difference?

Epos have got back to me and have not added much, apart from to check that tweeter wires inside cabinet are not touching port. They have recommended removing tweeter to check. Is this safe, i.e., I assume there is no seal I will be breaking? I guess if they are asking me to do it, it must be OK. Thanks again, Phil.

[anthonyTD]

Thanks Antony, I had not thought of this. By the way, I am biwiring and also bi-amping. Is there another permutation, that is reversing the +ve/-ve on just one speaker (both sets of terminals) to see if that makes any difference?

Epos have got back to me and have not added much, apart from to check that tweeter wires inside cabinet are not touching port. They have recommended removing tweeter to check. Is this safe, i.e., I assume there is no seal I will be breaking? I guess if they are asking me to do it, it must be OK. Thanks again, Phil.

hi phil,
should be fine to remove the tweeter as these are not sealed cabinets.[ported]
just make sure when replacing the tweeter to do up the screws evenly, and not too tight.
if you cannot find anything obvious, then it could be that the voil coil is damaged due to excessive heat from either large amounts of clipping [amplifiers running out of steam] or prolonged high volume use causing speech coils to distort and rub...

[Phil Bishop]

Thanks Antony, I have generally been using two recently serviced 125W Audiolab 8000Ms so I would have thought clipping was unlikely, although I grant I don't fully understand this phenomenon. I do play music at relatively high volumes, but for relatively short periods (no more than an hour at a time) and not at "party" levels and not loud enough for the neighbours to complain! To see whether they are damaged, I guess all I can do is return them to Epos - they are under guarantee. Phil.

[Filterlab]

To check the voice coil; push the bass driver gently and with even pressure back and forth. If there's a rough grind to the feel then chances are it's damaged, if it's super smooth then it's fine.

[Phil Bishop]

Rob, Seems super smooth to me. I can't imagine I have damaged the speakers. When I get a chance I will remove tweeters and check for wires near port (as recommended by Epos) and also muck around with the phasing a bit. Thanks for advice, Phil.

[anthonyTD]

To check the voice coil; push the bass driver gently and with even pressure back and forth. If there's a rough grind to the feel then chances are it's damaged, if it's super smooth then it's fine.

i agree with rob,
this is the only way of checking realy without test equipment!
let us know the outcome, also, if this test dosent show anything obvious, [be gentle, and use even presure at oposite sides of the cone] this test will not rule out the posibility of the speech coil windings having come loose on their former due to excesive heat but this would be an extreeme fault! my advice would be to try a diffrent amp and see if the problem is still present at similar volume on the tracks you know.
regards,anthony,TD...

[Filterlab]

Rob, Seems super smooth to me. I can't imagine I have damaged the speakers. When I get a chance I will remove tweeters and check for wires near port (as recommended by Epos) and also muck around with the phasing a bit. Thanks for advice, Phil.

No problem. I'm glad your voice coils are fine, it's a rare problem these days but when it does happen it can be expensive to sort.

Good luck with the phase checking!

[The Grand Wazoo]

From The Grave

Any more thoughts on chuffin', socks & voice coils?

[Rare Bird]

Ports used to augment the bass performance of smaller speakers DO "chuff and whooffff" and even those with drinking straws in can do so too (some Mission 737R's I once owned did this spectacularly). In the case of early Spendor BC1's the port was little more than a hole in the baffle and the sound from this hole was known as a "honk" all at one frequency and gave a lumpy bass with huge distortion, only minimised with certain amps with huge amounts of damping.

Quite a few speaker used the drinking straw method, i think the Mission ports was more proffesionally manufactured than others.

[Macca]

There was a piece in Hi-Fi World back in the 90s (may have been in the DIY supplement) in which NK experiments with ports. IIRC he tapes a plastic funnel (the kitchen type) onto the end of a port to improve it's behaviour, which he confirms with measurement. Not sure what issue or what 'speakers he was using.