Thanks TLS Guy. Well it sounds like this will take awhile to fix. Ill need to dig up my warranty as well. Its a shame, I really enjoy the servo, though I was ignorant to the fact that high SPL is so much harder on them.
Yes it is a pity. However I think it calls attention to the fact that may be it is time to review the causes of speaker destruction. So I going to take the liberty of your speaker failure as a teaching opportunity.
The first point that I would make is that every mechanical and electrical device has a point of destruction.
There is an old adage that is as follows: - "Do speakers have to be large?" No but it helps!" To which I would add, it helps an awful lot!
So what's the deal?
Well there is a direct inverse relationship to driver sensitivity, and therefore efficiency, and LF extension This becomes particularly acute as enclosure size is reduced.
As has been stated often, for every 3db reduction in sensitivity, the power required to produce the same spl has to double. That means twice the heat liberated in the voice coil.
Now a small sealed sub will have an over all sensitivity in the low 80s. However it is worse than that, as the sub will start rolling off 12 db per octave somewhere between 40 and 50 Hz. In order to be a useful sub, a boost of 12 db per octave has to be applied to give response to the low forties. So say a sealed sub is down 3db at 44 Hz without Eq, and that would be good performance, then to be 3 db down at 22Hz, we have to apply four times the power to the driver at 22 Hz than at 44 Hz, and that means four times the heat.
Also in a sealed sub the driver's rear radiation is lost. There is no port output.
Because of the powers involved distortion is high, and this is where the servo helps.
Now sealed subs can be built with a very narrow resonance, low Q. So that can produce a non resonant sounding bass.
A ported sub will have much higher sensitivity and efficiency and produce higher spl with less heat stress on the driver. However the bass by the very definition of ported principle is resonant. By careful design this can be tamed but not eliminated. However taming it also reduces bass spl. The other problem is that below box resonance the driver quickly decouples from the box and is easily damaged due to excessive cone excursion.
Now loudspeakers are destroyed by thermal damage (heat), and signals that cause the driver to exceed its mechanical limits.
Mid range drivers and tweeters are pretty much only disturbed by thermal damage.
So how can damage be minimized? Well first of all by avoiding playing systems really loud. If they are small speakers then being really moderate with volume.
Choosing speakers with higher, rather than lower, sensitivity, that generally involves choosing larger speakers over smaller ones. Remembering that if you have a design where a lot of Eq is required, being especially cautious.
Choosing systems where the power is spread between multiple voice coils. This is a good reason to use multiple subs.
Use infrasonic filters that have a steep roll off with ported subs.
In choosing speakers that have mid range drivers MTM has an advantage, as there are two drivers rather than one.
One can not leave this issue without a discussion of program, which plays a huge role in speaker destruction.
First of all rock/pop. This music is to a large extent produced electronically and so significant energy can be placed in pass bands where acoustic instruments do not have significant energy. This plays a big role in tweeter burn out.
High spl. levels can be maintained longer, because there is no limitation of human effort.
This genre of music is often highly compressed. If it is played loud, then the drivers get no chance to cool off, significantly increasing the risk of thermal damage.
In classical music, with the exception of the pipe organ, prolonged high spl is limited by the physical effort required from the players.
This limits the risk of thermal burnout. This music is not usually compressed significantly in digital format. The big risk is woofer mechanical damage from things like sudden forceful bass drum strikes. The sudden bass drum strike in Uranus, in Holst's planets suite, has spelled death to many a woofer voice coil former.
The pipe organ, can and does, destroy any and all types of drivers.
The instrument is not dependent on the physical effort of the performer, a point frequently made by J.S. Bach. So there can be sufficient energy in the range of all drivers in a speaker system and cause thermal damage to all of them.
It might be of interest to know how I approach this as a designer.
First of all, I'm not selling anything, which is hugely liberating. This allows me to work with the laws of physics and not fight them.
First of all I prefer to use multiple voice coils. All things being equal, I would choose two ten inchers over a 15 incher. Now this bass system has four voice coils to spread the load over. A TL design was used, with a Qt of 0.5, so the bass is non resonant, with 12 db per octave roll off. Now Eq is required to reach the last octave.
Efficiency is 93 db 2.83 volts 1 meter. So I only need one third of the amp power than a system with 84 db sensitivity for the same spl. I'm using a total of 400 watts on the front bass system which would be the same thing as using 1200 watts if the system was only 84 db sensitivity.
Not only that, I chose drivers with a powerful motor systems, and the amps can only power them to 2/3 of their rated continuous power. It so happens the drivers have metal cones, and that helps get the heat away from the voice coils quickly minimizing thermal compression and damage.
In fact the bass amps barely ever get more than slightly warm. Yet in big explosions a shock wave is produced that you feel by being hit hard in the chest with it. All this is done with minimal effort, with the cones barely moving, and very large air movement from the large area ports.
The mid range also uses two drivers per speaker, with big motor systems and metal cones, minimizing the chance of thermal damage and thermal compression.
I mention this, because speakers are relatively simple to understand.
I see many members with the technical skills to build fine home theaters. With a little study, they could produce systems that did not push against the laws of physics too. If the builder and designer of the space is also the speaker designer, even very large structures can come to fit in the space aesthetically with a little planning.
Really a home theater is really a tinkerer's perfect play ground, and with a little study and experiment systems produced that can put off the shelf systems to shame no matter what they cost.
That is why I'm a constant advocate of DIY systems.
