AutoTuba dead driver; Any ideas on possible causes?

[monekh]

Hey all,
Im a friend of Monekh's, just posting from here as had difficulties signing up for the forum.
This is my first ever speaker build and i'm not super informed on the topic so please forgive any ignorance in the question...

Heres my little story; I finished my Auto tuba build about 3 weeks ago and have been so happy driving about with it, sounded great and the build was alot of fun.

i built it at max width for a single 10 inch driver, so with 19inch wide panels. I used the Dayton Audio DCS255-4 (4ohms with rms handling 200watts). and powered it with a Pioneer GM-D8701 1600W Mono Class-D Car Amp with Bass Boost Remote. (so with a rms of 300watts at 4 ohms)

This weekend just gone we had an outdoor gathering with about 20 friends and I was playing music out the car with the boot open. had been playing electronic music for about two hours at a volume higher than i'd normally listen to inside the car when suddenly without any dramatic pop or bang the autotuba stopped playing. The amp hadn't gone into protect mode and no fuse broken, eventually i opened up the port door and smoke/steam came out! and the paper cone was visibly broken. No sound can be produced with this driver now at all. Im waiting for a replacement driver in the post, but definitely want to get to the bottom of what happened before i re set-up and use it again.

The Bass amp i have been using is fine. I chose this amp as I had read you should overpower your driver a bit and i had also heard that the pressure of a hornloaded design increases 4ohm impedance to about 7 ohms.. so figured the 300watts would effectively be lower (maybe here is my mistake) ( and for sure writing this now i am becoming more aware this wasn't the most accurately calculated matchup of amp and speaker :/)

Here's some details that may be helpfull with trouble shooting this situation:
- the autotuba was not high passed only low passed
-The gain on the amp was set just over the halfway mark ( which on this amp is marked with the word "normal")
-The bass remote on the amp had been cranked up to full - not by myself (bass remote details listed for that amp are Level:0 dB to 18 dB and (Bass Boost Frequency 50 Hz)
- The car had been running the whole 2 hours, idling, acting as a generator as i have no leisure battery, But the driver died just as, or, just after i reversed the car back a few meters to reposition it in relation to the group of revellers)
-I have definitely previously played music at the volume we were listening at this sad occurence, but probably never that loud for that long.

hmmmm thats all i can think of , but if anyone has any ideas of what happened, or what i can do to prevent it happening next time round, any input would be much appreciated.

Ta,

Kai

[Bruce Weldy]

Too much power for the xmax. Too much heat over that period of time. Too low with no high pass creating too much excursion.....

All of those could cause the problem. The auto tuba is designed to play in the car with cabin gain - when you open up the car, you are asking a lot of it to play low and loud for extended periods.

[Bill Fitzmaurice]

The bass remote on the amp had been cranked up to full - not by myself (bass remote details listed for that amp are Level:0 dB to 18 dB and (Bass Boost Frequency 50 Hz)

18dB of bass boost equals fifty times the power. The AutoTuba should not require any bass boost.

[jimbo7]

I had my system setup in similar fashion as how we do pro audio systems here. With a multi meter connected to the amp output and no speaker, turn up the volume of a ~20-40hz tone all the way and then set the gain to just under the max voltage of the speaker. That's with everything turned up; even the bass boost knob. This way if someone cranked the music to 11 it wont blow the amp or speaker since you set it just below max threshold (unless the amp settings were messed with).
(Yes, I know we should do this with a driverack and not the amp. This is just an example for the car audio world)

To play devil's advocate, it could've been a bad driver. I've "blown" a few speakers from a certain brand that shall not be named. But in your case it sounds like a jerk touched your stuff and now you gotta buy a new Dayton.

[Radian]

...what i can do to prevent it happening next time round

Connect a digital volt meter across the sub, and watch the level during playback. Keep it under 8-10V rms. High pass filter set @ 40-45HZ would also be prudent.

[Bill Fitzmaurice]

The DCS 255-4 will take 20v when high passed at 40Hz. At 20v it will deliver 120dB, which should be plenty.