Design fun or design complications?
Don't you want to build a good-sounding sound system, not design all the circuits? Then go to www.ti.com and select one of their many bridged class-D audio amplifier ICs.

 

wow, that escalated quickly...

Yes im following your suggestions and im currently reading myself into Class-D amplifiers, as i didnt know much about them before.
Also the next step will be to stabilize my voltage from the power source which is going to be a battery. I'm also working every day so i need some time for all that.

I appreciate all your help and of course also the constructive criticism towards that project.

 

Most audio amplifiers do not have and do not need a voltage regulator. As the battery voltage drops which causes clipping distortion then simply turn down the volume a little. If you use a voltage boosting circuit then as the battery voltage drops its current increases which causes more voltage drop which causes more current ..... a vicious loop. Plan the battery so that the amplifier plays loud enough without clipping when it needs replacement or needs a charge.

 

Most audio amplifiers do not have and do not need a voltage regulator. As the battery voltage drops which causes clipping distortion then simply turn down the volume a little. If you use a voltage boosting circuit then as the battery voltage drops its current increases which causes more voltage drop which causes more current ..... a vicious loop. Plan the battery so that the amplifier plays loud enough without clipping when it needs replacement or needs a charge.

I totally get your point and would happily avoid using a voltage regulator if there is a valid alternative. So how would i do that considering i want to charge it via USB and still have an output of 12V for the Class-D Amp?

 

I do not know why or how you selected 15W per channel. That is a lot of power from a miniature portable device.

A Texas Instruments TAS5421-Q1 mono bridged class-D amplifier IC produces 12W into 4 ohms with low distortion when powered from 12VDC. It is 85% efficient so the boost converter must provide 17.5W which is a total of 35W for stereo.
A single Li-Po battery cell can easily charge from USB and its voltage drops to 3.0V when it should be disconnected from its load. The boost converter also might be 85% efficient then for an output of 35W at 12V then its 3V input must be 41W then its 3V battery current will be 13.7A!

The battery will be expensive, large and heavy of you want it to drive the amplifier for a few hours. Do you need that much power?

 

I do not know why or how you selected 15W per channel. That is a lot of power from a miniature portable device.

A Texas Instruments TAS5421-Q1 mono bridged class-D amplifier IC produces 12W into 4 ohms with low distortion when powered from 12VDC. It is 85% efficient so the boost converter must provide 17.5W which is a total of 35W for stereo.
A single Li-Po battery cell can easily charge from USB and its voltage drops to 3.0V when it should be disconnected from its load. The boost converter also might be 85% efficient then for an output of 35W at 12V then its 3V input must be 41W then its 3V battery current will be 13.7A!

The battery will be expensive, large and heavy of you want it to drive the amplifier for a few hours. Do you need that much power?

that's what im not sure about.. how much power do i actually need.. i currently have a 2.5 Watts mini speaker.. Its loud, but it doesn't have much bass. After i was done doing my calculations i thought a 6-10 Ah LiPo should do the job. But maybe you're right and i could downgrade a little.

My initial setup was:
2x 3" Subwoofers each 5 Watts
2x Mid Range Drivers each ~2-3 Watts
1-2 Tweeter(s) each 1W
using a TPA3122 as amplifier

That might actually be an overkill for such a small speaker. so i could probably do 1x Subwoofer too then we're talking roughly 10-12 Watts which seems decent.

Correct me if I'm wrong, but i need +12VDC voltage for that TPA3122. This assumption is the reason for the voltage regulator to get up to 12 volts.

 

You are looking at the voltage boost backwards. You should use a 11v lithium battery and use the boost circuit for the charging (5V to 12v conversion). Then you have a much higher quality audio for the output since there is no boost circuit humming in the background during the boost.

 

You are looking at the voltage boost backwards. You should use a 11v lithium battery and use the boost circuit for the charging (5V to 12v conversion). Then you have a much higher quality audio for the output since there is no boost circuit humming in the background during the boost.

that is what i was also thinking about, thanks for confirming that i will look into going that way

 

A tiny 3" speaker is used in a clock radio.
Madisound sell hundreds of speakers and they have a Hi-Vi brand model M3N 3" speaker that costs $12.40US. It is rated at 15W nominal or 30W max peak power. Its resonance is fairly low for its tiny size at 91Hz then in a suitable enclosure it is flat down to 100Hz which is in the upper bass. To get down to 50Hz it needs a bass boost of 16 times the power of higher frequencies. It plays 100Hz well because it has a long-throw design. Because it is small with a long-throw and flat response down to 100Hz it is not sensitive. Its sensitivity is only 82dB (1W/1m) so bass boost cannot be used. It is probably one of the best little low frequency speakers but it is recommended as a midrange. It is 8 ohms.

Hi-Vi also make a similar 4" woofer that can play frequencies down to 55Hz or 40Hz with some bass boost. It needs a 4l sealed enclosure.

I made a little woofer using a 4" speaker and with some bass boost its sensitivity was not too low and it produced frequencies down to about 50Hz which makes it an ordinary woofer, not a subwoofer.