Scumback Speakers wrote: ↑Mon May 04, 2020 2:54 pm
Speaker power handling is based on the melting point of the voice coil former material. The signal power sent has a voltage to it, roughly 36w on a 50w 1987 Marshall cranked up to 8-9 on a NMV amp circuit. in my 50w, that's around 95w output, resulting in 36 volts at the cab speaker jack. I've measured that myself. 100w will be more, but I haven't done that measurement in the shop, so I can't say exactly what that voltage is.
Thanks, but I don't understand your calculations. Are you talking about Vrms and Wrms? I ask you because a sine wave gives:
36 Vrms into 4 Ohm makes 324 Wrms.
36 Vrms into 8 Ohm makes 162 Wrms.
36 Vrms into 16 Ohm makes 81 Wrms
36 Vpp into 4 Ohm makes 162 Wrms.
36 Vpp into 8 Ohm makes 81 Wrms.
36 Vpp into 16 Ohm makes 40,5 Wrms
Scumback Speakers wrote: ↑Mon May 04, 2020 2:54 pmI break in speakers with a variac set at about 12 volts for 20-36 hours (M's around 20, J's around 25, H's around 36) since the heavier the magnet, the more magnetic force on the coil/cone/etc and it takes longer to break them in due to the cone not moving as far, or as easily in a lighter magnet.
Thanks again, assuming it's 12 Vrms you break in speakers at 18 Wrms for 8 Ohm speakers and 9 Wrms for 16 Ohm speakers at 50 Hz.
I will sketch an idea on how to do it reducing the noise emitted outside, I'm curious to know if it's something already done.
Scumback Speakers wrote: ↑Mon May 04, 2020 2:54 pmOf course, there's a limit of how much power a 1.75" voice coil can handle based on the former size/wire, etc.
I guess this is due to the thermal power dissipated by the coil and the capability of the coil to dissipate the power outside (forced convection due to the speaker moving, and irradiation towards the magnet.
So there will be a limit of temperature at which the wire of the coil melts because the delta temperature needed to dissipate the power between the coil and the magnet is too high.
Scumback Speakers wrote: ↑Mon May 04, 2020 2:54 pmBut a square wave using fuzz/boosts/similar pedals often presents a signal that will make the speaker "hang" in it's excursion and not return to it's base position.
I guess that this is due to the fact that the power of the signal is higher (assuming the same Vpp), so the excursion of the speaker is higher, so it goes out of the admissible "swing".
Scumback Speakers wrote: ↑Mon May 04, 2020 2:54 pmTypically, the bigger/heavier the magnet, the power handling goes up slightly since the magnet acts as a heat sink to soak up some of the power in your signal to the speakers, but usually no more than 10-20% more.
Thanks, yes by increasing the magnet you increase the surface area that can dissipate heat through (almost natural) convection, and due to the fact that convection is proportional to the heat transfer coefficient that is about 5 to 25 W/(m^2 xC), to the surface area and to the delta temperature, by increasing one of the three you reduce the others (considering the same watts), so being the heat transfer coefficient stable, by increasing the size of the magnet you reduce the temperature of the magnet and then the temperature of the coil.