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I'm going to assemble portable speaker system, think street musician or small open-air party. It needs to run for 2 hours. 100W-rated RMS speaker is enough from my experience, from same experience it can run that long with required loudness from small bike battery, someth. like 10Ah. Given that lead battery is unlikely to discharge more than 50% of its capacity - I understand that 60 watt-hours is how much energy I need for a gig.

Xiaomi mi battery has very appealing price, and at 77 Wh , should theoretically do the job, I found how to get it to output 12V.

I'm not going to use DC-AC invertor, I'm either modifying powered speaker to run on 12V power, or would get car amplifier.

My question is -- would 1.5A that I can get from power bank be enough to power the speaker, particularly at peak loads, when the base gets loud.

If not, is there a way to work around it -- like putting high-capacity capacitor in the power line, or stacking 2 powerbanks.

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    \$\begingroup\$ 100W at 12V is 8.3A (but allow for 10-15A to leave a margin). 1.5A at 12V is only 18W. I can't read Chinese, but given that it "has a very appealing price" there's also a good chance it can't actually do 1.5A (they could be lying). \$\endgroup\$
    – user253751
    Jan 23, 2018 at 0:24
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    \$\begingroup\$ The speaker is rated for 100W RMS, but that is largely irrelevant. How much power does it dissipate in your application? You've asked if a powerbank can provide sufficient current. Without knowing how much current you intend to draw, that's impossible to answer. Powerbanks are so cheap that it's probably simplest just to try it. \$\endgroup\$
    – vofa
    Jan 23, 2018 at 0:52
  • \$\begingroup\$ My experience says that at 12 volts you need a 10 amp supply for each 100 watts of output. Don't forget there are conversion losses in the car amplifier as it converts 12 volts to (usually) +/- 50 volts or so. Cost is not bad for 100 watts. \$\endgroup\$
    – user105652
    Jan 23, 2018 at 1:37
  • \$\begingroup\$ @immibis, I've checked the reviews of this particular one and it's tested to be quite close to specs. \$\endgroup\$
    – Gleb
    Jan 23, 2018 at 17:17
  • \$\begingroup\$ @vofa, actually the drawn current is what I'm hoping to get as an answer. I'd be happy to get to ~90 Db of SPL next to a speaker. But I do not know how the volume and hence the power is distributed in a typical song or speach -- are there huge spikes of drawn current, and is it(or can it be) smoothed out within a typical amplifier. \$\endgroup\$
    – Gleb
    Jan 23, 2018 at 17:23

1 Answer 1

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You'll get best results by using different strategies to maximize "loud time" depending on the content:

  • If this is a single musical instrument (e.g. a guitar) then your best bet would be to find a high-efficiency speaker (105 dB/W @1m is not uncommon for guitar speakers) and a high-efficiency guitar amp like this one. Most of the efficiency of this setup comes from not amplifying the frequencies outside of the guitar's range. This same general approach works for different single instruments (and voice) with some tweaking of the amplifier and speaker.

  • On the other hand, if you're doing a sort of PA system where the sound is full-spectrum (e.g. prerecorded music), you'll want to reproduce a broader range of frequencies, and you'll pay for that in terms of either overall loudness or battery life.

  • Low (bass) frequencies require a lot more energy in order to be perceived as loud, so some careful selection of program material can help extend your run-time. Choose content with short bursts of bass rather than long drawn-out bass.

  • Finally, adjust your pre-amplifier equalizer settings to avoid amplifying (especially bass) frequencies that either (a) don't match your speaker or (b) don't sound good in the space. A lot of "good sounding" small speakers (Bose is famous for this) make heavy use of this technique.

One last thought: depending on the loudness you're aiming for, some of the newer wireless speaker systems might be sufficient, even though their rated wattage might be more like 5-20. The correlation between wattage and perceived loudness is roughly logarithmic, and so a (huge, power hungry) 100W amp is only about 4x louder than a 1W amp.

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  • \$\begingroup\$ +1 for smart answer. Yes, if the OP was driving bass bins he would need 1,000 watts or more. Yet OP implies a much more modest output, yet still have bass? At least you covered all the bases. \$\endgroup\$
    – user105652
    Jan 23, 2018 at 3:53
  • \$\begingroup\$ The audio is close to full-spectrum, with drums and vocals. People have to hear the drum, or double-bass when it's there, I have to get at least 80 Hz for the rhythm. I do have sound processor with parametric equalizer and plan to use it \$\endgroup\$
    – Gleb
    Jan 23, 2018 at 17:15
  • \$\begingroup\$ I've used pair of those yamahaproaudio.com/global/en/products/pasystems/stagepas150m/… , and can say that it would be quite enough for my needs. It states just 20W of power consumption, is it realistic? \$\endgroup\$
    – Gleb
    Jan 25, 2018 at 10:23

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