Simple question for pocket amp speaker

[zener]

I'm planning to build a pocket LM386 amp with maybe a 3"-4" speaker.
What speaker wattage would you recommend to run off a 9v for a "long time"? (Not really long as in years. Something like, "oh, you're still running, huh?). Or does speaker wattage has something to do with a batt's life. BTW all speakers I can get are just of 8 ohms.

[Bernt]

Zener!
The speaker wattage rating only means one thing: how much power you can give it before it gives up. It does not even tell you how loud it is, that depends on the efficiency of the speaker. For a LM386 1Watt would be enough.
Kindest regards, Bernt.

[tcobretti]

I'm kinda dumb when it comes to this stuff, but lower ohmage would make the amp louder, right?

I've read about adding resistors to a speaker to raise its impedance, is there any ghetto fix to lower a speaker's ohmage?  It doesn't seem likely but seemed like an interesting question

[Nasse]

:? You should look for a speaker with high efficiency. If you can find data about dB/W or something you can get the knowhow

Speakers manufacturers publish data of their speakers features, like freg range, power rating and Thiele/Small parameters like resonant frequency etc. etc.

In general (not always) speakers made for musical instruments and PA are somewhat more efficient than hifi speakers. Good 12" guitar speaker can have values like 99 dB/1W and some hi-fi speaker is 89 db/1W.

Bigger cone area helps always to give more volume at little power. Sometimes efficient speakers have bigger magnets.

I once connected 1 watt amplifier to my 2x12 cabinet with 2x50 watts huge ceramic magnet elements. Sounded amazingly loud at full blast... until burned the chip, no cooling enough, funny smell... perhaps the big speakers "kicked back" poor amp too much... :oops:  :roll:

[Mike Burgundy]

IF you assume the amp is putting out the *same voltage*, then yes, power does increase when you use lower impedance. Thats Ohms law, straight and simple.
Couple of catches though: if you use a real-world amplifier, it's not going to be a true voltage-amp, plus the powersupply might sag, plus you might overheat the amp, exceed it's ratings, etc.
You want to know how much power the amp can drive at what impedance, then select a speaker of that impedance (8 or 4, whatever - it might be better to go for 8 if the amp cant supply too much current) that can handle that ampount of power or preferably more
Putting a resistor in series with a speaker will form a resistive devider with that speaker. Current through both is identical, but voltage is distributed between them in relation to their respective resistances (well, impedances).
The total system will have increased impedance, yes.
The resistor is taking the place of a second speaker (remember - add impedances...)
Comparable: parallel - lower impedance, Voltage remains the same this time, current is devided.
Everytime you replace a speaker with some sort of resistive element you lose ouput power - a resistor doesn't make noise. It does make a lot of heat though.

[tcobretti]

I have this weird little Kramer pocket amp thing (think cheapo kramer rockman) that somebody gave me ten years ago and I've never messed with.  I recently fired it up and was surprised that it actually sounds ok in a jcm900 kind of way.  I opened it up and it's based on a LM386.  For some reason I found that surprising.  It doesn't make any power, though.  I hooked it to a speaker and it was barely audible.

[christobean]

I'm kinda dumb when it comes to this stuff, but lower ohmage would make the amp louder, right?

I've read

pretty much, the lower the ohms the louder/more amplified it is.  a good example of this is with headphones, try listening to a pair with 32ohms then plug the same source into a pair with 24ohms