I'm an amateur electronics experimenter/enthusiast. I have an 8-ohm super tweeter from JBL (sold in Brazil as model ST200) whose RMS power with passive crossover is 100W @ 8kHz. It's quite a large tweeter the size of a low-power woofer. So, physically, it seems capable of delivering such power level.

I designed a simple amplifier to drive the said tweeter from the small signal coming from a signal generator, a 555 oscillator, etc. I represented the speaker in the simulator (LTSpice) with a 160uH coil (measured with an LCR meter). The power supply delivers 44VDC. The simulation showed that the current flowing through the coil is about 4A RMS (varies a bit with frequency) with the amplifier set at about 80W (output stage is composed by 3x 2N3055 power transistors in parallel and sharing the same heat sinker to prevent thermal runaway).

Before risking popping my expensive speaker, I did a bit of duckduckgo search and I found that super tweeters typically use 38-37 AWG wires in their voice coils. This is consistent with some calculation I did based on coil geometry data in the tweeter's manual.

According to this (https://www.powerstream.com/Wire_Size.htm), a 38 AWG wire safely handles only about 110mA. I'm likely missing something, but the only way to push 80-or-so watts through that is by using hundreds of volts in the power supply, which doesn't seem right. According to the part's datasheet, the bobbin in made with polyimide which can stand 220°C (428°F). So, the question is, what am I missing or misconceiving? Is it possible for the voice coil to withstand 4A RMS @ 8kHz for a minute without exceeding that temperature? I admit I don't know how to do the thermal calculations. I appreciate any help with that.

After reading this other question: Why has my tweeter speaker burned up? , I scratched my head over whether the power rating in the datasheet refers to the sound system's or the part's. In the former case, most of power actually goes to the woofer, and only about 4-6W should go through the tweeter.

  • \$\begingroup\$ A tweeter is Never Ever fed continuous full power. NEVER drive a tweeter with a tone, use real music (not rock) or vocals. Your tweeter is rated at 140W RMS or 200W peak. The peak power of 140W RMS is 140 x the root of 2= 198W. \$\endgroup\$
    – Audioguru
    Commented May 18, 2023 at 15:02
  • \$\begingroup\$ A single-ended amplifier powered from 44VDC might produce a sinewave that is 42V peak-to-peak which is 14.85V RMS. Then the power in an 8 ohms load is 27.6W and the RMS current is 1.86A. But if the amplifier output is bridged and drives BOTH speaker wires then it can produce 100W RMS into 8 ohms. \$\endgroup\$
    – Audioguru
    Commented May 18, 2023 at 15:08


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