Bose 802 series III technical review why there are PTC there

Full range
A full-range loudspeaker drive unit is defined as a driver which reproduces as much of the audible frequency range as possible, within the limitations imposed by the physical constraints of a specific design. The frequency range of these drivers is maximized through the use of a whizzer cone and other means.
A capacitor will act as a HPF, blocking the low frequencies, thus protecting the tweeter. Perhaps I don't understand your question, but a PTC will do nothing to protect the speaker in the event of a crossover malfunction, which is the entire point of using a capacitor.
PTC will work as sensor temperature
unless it is thermally coupled to the voice coil
Specifications
Bose flagship loudspeaker
Indoor or outdoor use
Speaker ideal for vocals and instruments
240W RMS/480W peak power handling
Panaray 802 III Loudspeaker
Frequency range: 55Hz to 16kHz ±3dB
Sensitivity: 91dB-SPL @ 1W, 1m (pink noise)
Maximum Acoustic Output: 114dB-SPL @ 1m(pink noise), 116dB-SPL @ 1m (IEC3 noise)
Dispersion (-6dB point, average, 1-4kHz) Horizontal 120, Vertical 100
Long-Term Power Handling: 240W continuous
Impedance: 8 Ohms nominal
Dimensions (HxWxD): 13in x 20.5in x 12.5in(33cm x 52cm x 32cm)
Weight: 31lb. (14kg)
group of bose 01 are
Bose 101 Bose 202 Bose 301 Bose 401 Bose 501 Bose 601 here Bose 701 Bose 801 Bose 901 final
parallel JBL

[@KevinWorrell]

If you look at the arrangement of the capacitors, you will quickly note that they are parallel to four drivers and in series with the other four. These shift the phase of the high frequencies and provide directivity of sorts to the output. Additionally, the PTC is a thermal switch that resets once it has opened. It opens and shuts off the flow of electrical current when it's temperature is reached, and this is in order to protect the voice coils of the drivers from burning. One final note, the passive filter in this speaker is not meant to be the only filter. If you run this speaker without the external EQ it will sound terrible, without any bass and extremely shrill. Definately a terrible sounding box without the external equaliser.

[@Ratso_au]

If anyone is rebuilding these, I tested the PTC from my series II 802’s and found them to be equivalent to a RXEF050. I replaced the Polyswitches with these and installed new capacitors with great success

[@JNElectrics]

great ide

[@magnosantos6807]

Good afternoon ! Which capacitor did you use? I can't find capacitors with the same value.

[@Ratso_au]

​@@magnosantos6807 Bearing in mind I've got series II's & referring to the series II service notes, I used 5.1uf (corresponding to C1) and 20uF (C2) capacitors. In addition to rebuilding the shading circuit, I tested all the drivers and replaced the foam behind the baffle. Links to the manual and capacitors below

[@AudioElectronicsChicago]

Great