VC bottoming out? Air leak? Need some help!

[REIER]

Now I need some serious help, I feel like I have tried everything and I cant figure out the problem.

The story:

I have a 12v portable PA system. I use a 200ah lifepo4 batterybank, a pioneer mono gmd9601(500w@4ohm) with 2 tham15 (15ps100) for subs and a gmd8604(300w@4ohm x2 bridge) for tops. I blew two drivers last summer bcs someone turned on the bass boost (50hz). They never recovered from that. I played around with amplifier gain on the mono amp afterwards, and toasted them. Kind of an experiment as much as an accident.

I bought two recone kits and a new driver and built a new box. The first reconed sub sounds nice in the new cab, but the second (2) reconed sounds like its bottoming out. Not like a rub, more like a solid clank when I turn the volume a little bit up. I took it out of the cab, the clank is getting more pronounced, sound like a metallic rattle. I think for my self, maybe it could be the dust cap is off centre. So Im cutting of the dust cap, recentering it, rattle is still on board.

Here comes the weird part. I open the new 15ps100 . It says on driver it is tested before shipping. Mount it inside tham 15, and rattling/clank is here as well. I take it out of the box and try it open air, it rattles even more like a snake. I try my other amplifier, same sound. I put the brand new 15ps100 in the other cab, same sound. I go back to my first reconed sub, testing both amplifiers, and works like a charm.

Made a filter setting on minidsp, cut off at 38 and 110 hz. No improvement. Now I'm frustrated and getting creative. I go back to the driver with recentered dustcap, and try to find out if it is a misaligned voicecoil after reconing. I put on a clamp, and add force on frame until I hear rubbing sound, and release, and rubbing sound goes away. Try this again for 3 new angles, and I conclude it is not a rub, more like a bottoming out sound.

Now I'm out of ideas. The driver is rated for 700w rms and amp 500w, and the sound was there right at the beginning. I cannot remember this sound from before I blew them, but who knows. Maybe I wasn't so critical as I am now. But there is definetely something fishy going on.

Do drivers bottom out in free air always? Is this normal when pushed maybe 100 or 200 watts on music program? I have inspected amps with multimeter, no DC from amp terminal. Resistance on speaker terminals is perfect, so not blown driver.

I have an event coming up in a couple of days, and I did not expect so much hassle. I am getting quite anxious to say the least. Very new to diy pa, and feel like I have put on too big of a challenge. Now I am asking for help.

Regards

Kristoffer

(posted on another forum aswell)

 

[afa]

Check to see if the magnet assembly has worked its way loose from the basket, because the screws can come loose and the glue/silicon that is inbetween the mating surfaces is insufficient to maintain a hold (some times the glue/silicon is there to stop potential vibrating noises from ill fitting metal to metal contact and the screws provide all the holding power)
cheers, Arthur.

 

[Brian Steele]

Perhaps something is wrong with the new cab you built and it's resulting in the drivers being damaged.

 

[REIER]

Afa, thank you, I will check when im back in the workshop. Brian, the new cabinet is the only one working. Thanks for your answer. This is interesting, Can you explain how the cabinet could damage the driver?

 

[Brian Steele]

Afa, thank you, I will check when im back in the workshop. Brian, the new cabinet is the only one working. Thanks for your answer. This is interesting, Can you explain how the cabinet could damage the driver?

If the driver's cone or surround come into contact with the any part of the cabinet when the driver is mounted is one way that the driver could get physically damaged. You will see the marks on the cone though.

Check where the spider is glued to the voice coil former and where it's glued to the basket. Also to see that the tinsel leads are not coming into contact with the cone.

 

[JMFahey]

I bought two recone kits and a new driver and built a new box. The first reconed sub sounds nice in the new cab, but the second (2) reconed sounds like its bottoming out. Not like a rub, more like a solid clank when I turn the volume a little bit up. I took it out of the cab, the clank is getting more pronounced, sound like a metallic rattle.

Then it´s definitely clanking.
Not sure bwhat kind of recone kit you got, either all spare parts in a box or a preassembled VC, spide, cone, tinsel wires, cone edge assembly.
If the first, you may have set the VC way too low (assuming speaker face up while reconing) so it easily hits the back plate.

If the second, still some adhesive can seep through along the VC body and make a hard bubble (once cured) which hits the front plate.

In any case, both make speaker impossible to use.

Free air testing only worsens the problem.

Here comes the weird part. I open the new 15ps100 . It says on driver it is tested before shipping. Mount it inside tham 15, and rattling/clank is here as well.

Then you have a cabinet problem.
Or you applied some impossible to reproduce EQ.

I take it out of the box and try it open air, it rattles even more like a snake. I try my other amplifier, same sound.

Acoustically unloaded soft suspension speakers are easily damaged.

I put the brand new 15ps100 in the other cab, same sound.

Still suspecting cabinets or wonky signal.

I go back to my first reconed sub, testing both amplifiers, and works like a charm.

Maybe the first one was reconed properly, the second one was not.

Made a filter setting on minidsp, cut off at 38 and 110 hz. No improvement.

Whyb did you choose those numbers?

Now I'm frustrated and getting creative. I go back to the driver with recentered dustcap, and try to find out if it is a misaligned voicecoil after reconing. I put on a clamp, and add force on frame until I hear rubbing sound, and release, and rubbing sound goes away. Try this again for 3 new angles, and I conclude it is not a rub, more like a bottoming out sound.

I suspect the same.

Now I'm out of ideas. The driver is rated for 700w rms and amp 500w,

Power rating takes second seat to excursion limits and poor acoustic loading.

and the sound was there right at the beginning. I cannot remember this sound from before I blew them, but who knows. Maybe I wasn't so critical as I am now. But there is definetely something fishy going on.

Bottoming out is not subtle at all; if you didn´t hear it, then it was not present.

Do drivers bottom out in free air always? Is this normal when pushed maybe 100 or 200 watts on music program? I have inspected amps with multimeter, no DC from amp terminal. Resistance on speaker terminals is perfect, so not blown driver.

Count on that, not a valid test.

I have an event coming up in a couple of days, and I did not expect so much hassle. I am getting quite anxious to say the least. Very new to diy pa, and feel like I have put on too big of a challenge. Now I am asking for help.

Just to pass next event, why don´t you turn off fancy DSP processing (which might do more wrong than right) , any Bass Boosting, "improving", etc. , and apply just a simple, strong 50 or 55 Hz highpass?

In theory, you should not hear clanking under such a "safe" EQ.

Then with more free time, you polish your current design.

 

[REIER]

So, I never got to answer this, I totally forgot about it. Thanks to all you for your help. In the end it was JMFAHEYs comment on my dsp settings that made all the difference, thank you. I choose those numbers because I had read it somewhere that those where suitable numbers. But I adjusted the hi-pass to 48 hz, and they started to behave nicely. Feel a little bit embarrassed that I did not think of this before. This comment section saved the party! thanks!