[Stuart]

Hi Danny, thank you for sending me the two servo subs, both arrived in perfect order. I have a small problem though, as discussed on the phone, the subs sound great at low volumes, but if turned up so that they move +-10mm p-p they  sound like they cant handle the power being fed to them. there seems to be a mechanicle distortion noise comming from inside the drivers. one is worse than the other. I have discussed this in length with Brian from Rithmik and have carried out  a number of tests with him. he has the same driver in his lounge and says his is quiet. could i have a set of faulty drivers. the boxes are air tight and are about 1.6cu.f. Please help with ideas. Does any one else have this problem. The sound is like the drivers are reaching their limits at about 5 - 10mm p-p and is unpleasant to listen to.

[Danny Richie]

You have a long way to go before they reach their limits.

All so far have been dead quiet.

You might check and see if you internal wiring is close to the cone and getting hit when the exertion is long enough to reach it.

[nodiak]

Another possibility - I once built a sub and had an air leak that sounded very unpleasant at loud volumes. Once sealed it was fine. Fwiw my GR/Rythmic sealed sub bottomed out very lightly in the first few hours but never again at the same levels.
Don

[Stuart]

Hi Danny

I have tried bith drivers out of the boxes and both make the same noise it sounds as if it is comming from under the spider. When you place the drivers bake in the boxes the noise is amplified. the noise starts at only+- 8 to 10 mm p-p. any ideas. all wiring checked and ok.

Best regards,

Stuart ( South Africa )

[rythmik]

Hi Danny

I have tried bith drivers out of the boxes and both make the same noise it sounds as if it is comming from under the spider. When you place the drivers bake in the boxes the noise is amplified. the noise starts at only+- 8 to 10 mm p-p. any ideas. all wiring checked and ok.

Best regards,

Stuart ( South Africa )

The way I would test the system is to use a pure sin wave at 20hz at free air and 40hz in box.  Be sure to use 20% duty cycle. That is test 10 secs and rest 40secs. This will allow you to test at full power level and not to be considered as abuse. I also have my oscilloscope connected. Make sure to float the ground at the scope as the negative terminal is not a true ground in servo (it is connected to ground via a 0.2ohm resistor).  In particular, the free air test would tell us more in terms of what happen. What you should see is the driver able to make more than 25mm in free air at 20hz without audible noise.

[Hank]

Dirt between the V.C. and magnet?  Dislodged pieces of adhesive due to the probably not smooth "ride" all the way to South Africa?  Rare, but it's been known to happen.  I once had a mid-woof that was noisey, and when I removed the dust cap and slid a Post-It Note down around the VC, the adhesive caught some fine particles that were intermittantly being caught between the VC and magnet.  Upon removal, the problem was solved.

Just Sherlocking a bit.

[Danny Richie]

when I removed the dust cap and slid a Post-It Note down around the VC, the adhesive caught some fine particles that were intermittantly being caught between the VC and magnet.

It must have had some 3M adhesive on it. 

I am most puzzled because he has the same problem with two woofers. I look forward to hearing a little more on this.

[Hank]

Well, we certainly don't use Acme brand adhesive when we make Post-It Notes.
Statistically, it would normally be just about impossible to have two like that, BUT they both did ship all the way to South Africa, and I imagine were thrown around quit a bit between here and there.  Yep, this will be interesting.

[Stuart]

Thank you Danny and Hank,

I will run the test that Brian has recomended over the weekend with a friend, he has a signal generator and a scope. I hope all goes well and that the problem is a simple one. Iam glad im not alone on this one and appreciate all the input from you chaps. will let you know how the tests went. Have a good one!   

Regards

Stuart            (SA)   

[Stuart]

Hi Danny,

Sorry I have not been in touch for a while! things at work have got out of hand. I would like to give you some feed back on the mechanical noise from the servo subs. They have about 100 hours on them now and sound really FAB. There is still some mech noise but you can only hear it when the mains are turned of. They are very musical and warm sounding. I originally built these sube for a friend but have decided to keep them for myself until a later date. I have the two of them in my HT room and together they reach realy low with good spl. With music they are on their own and doubt that there are many subs as musical as these. I have built better boxes for them and after talking to Brian, have made these boxes 1.6cu.f the noise has all but gone. I think these drivers will only work in a given size ie 1.5 to 1.6cu.f as they rely heavily on the internal pressure to keep the cones under controle. The previous boxes were nearly 2cu.f and the drivers did not like that at all. Hope you have good after show sales!!! You look a lot younger in the photo than your voice sounds, hope you take that as a compliment!   

Best Regards,

Stuart          South Africa