Any speaker with a coil attached to a paper cone, where the magnetic core is inserted into the coil (paper-sleeve bearing may exist from the cone), is by definition an inductor.

I disagree with that definition.
Of course it has inductance but that doesn't mean you define it primarily as an inductor.
A speaker is more a linear motor as Colin55 stated.
Motors do have inductance but they are not normally called inductors.
The word "inductor" is typically only used for devices that are purposely designed to have inductance, not where the inductance is incidental to the design..

 

My pair of "100 W speakers" used a 1 A normal blow fuse to protect the 30 W dome tweeter. Usually it gets hot and scratchy with use. I usually used a 1-1/4A fuse.

My amp (about 100 W/c) uses a 3 A AGX fuse in series with the speakers.

I think you really want to monitor two failure modes. Too high of a signal. Fast-acting fuse. AND... monitor voice coil temperature (polyfuse?).

Maybe, another interesting way is to use a power resistor in series and monitor temperature.

With a Noton OP-amp and some other ones, the voltage can exceed the supply, Use peak detector with a small delay and then if it continues, then kill the speaker output until the levels return to normal.

Hopefully, the amp does DC speaker protection.

 

Maybe, another interesting way is to use a power resistor in series and monitor temperature.

Resistance in series with a speaker causes it to resonate like crazy and sound like a bongo drum. At resonance the voice coil moves far enough to damage it. The amplifier has an extremely low output impedance that damps the resonance.

Hopefully, the amp does DC speaker protection.

The speaker instructions recommend a highpass filter which will not pass DC and low frequencies.

 

Shimra01:
1) What voltage and power settings is the transformer on each speaker?
2) Sketch the recommended highpass filter you used.
3) Does the sound system have EQ that can overpower low frequencies?
4) The little 4.5" speaker and its transformer cannot produce low frequencies.
5) The transformer'd speakers should never be connected in series.
6) Please post a spec sheet for the 250W amplifier.

 

The transformer on the speaker has a few settings to reduce its power, why weren't they used??

Note that there is an 8 ohm version of the speaker that does not include the transformer. I wonder if perhaps it doesn't have the protective device, either.

I suspect that the tone controls or equalizer gets the bass cranked to the max with some regularity, which makes the problem especially difficult to deal with without actually modifying the existing equipment. A high pass filter would probably need to be fairly high order to be reasonably certain of doing the required job.

 

The BOSE website does not list that speaker. Maybe it was not reliable so they discontinued it?
40W of pink noise is a lot of power for a tiny little 4.5" speaker tying to produce bass sounds.
The speaker enclosure is ported which makes the cone motion uncontrolled at low frequencies.
250W on a speaker rated at 40W is an enormous overload.

 

This place must be a coffee house or maybe a bar where the staff, and probably the customers prefer very loud music. The quality of music is probably not terribly important. Why not use a T Pad? Adjust it so there is no clipping even with the amp turned up to the highest level.

 

I disagree with that definition.
Of course it has inductance but that doesn't mean you define it primarily as an inductor.
A speaker is more a linear motor as Colin55 stated.
Motors do have inductance but they are not normally called inductors.
The word "inductor" is typically only used for devices that are purposely designed to have inductance, not where the inductance is incidental to the design..

You can call it any label you like, but as long as an inductive coil is being used as the sole electromotive force to move the cone-- it's an inductor. 'Linear motor' although valid, is just a colorful term that actually confuses, rather than adds clarity. Like calling someone who cuts the lawn an Arboreal Engineer.

But all that is neither here nor there- I'd like a part number for the OPs speaker.

 

This is why I want more information from the OP, we don't know what kind of speaker he has.

The detailed spec's for the speaker was posted as a link in post #22. It is here:
https://assets.bose.com/content/dam...ical_data_sheet/tds_fs_ds_40f_loudspeaker.pdf

 

I would think if you run the amp output into the 70V primary of the speaker transformer, and select the 20W option you will have plenty of protection. It may not be ideal but smoking the speakers is a lot less ideal.
I don't like loud so running 100V in and the output on the 2.5W would be even better

 

The Original Poster did not come back to say if he has speakers without the transformer.