DIY bluetooth speaker

SentinelAeon said:

I mentioned a few times that my amp is 2x25W, not 2x50W !

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As AG has pointed out, using 4 ohm speakers will (try to) double the power.

But why ?

SentinelAeon said:

But why ?

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Ohms law - do the maths - if you half the resistance the current will double.

I know that but it says it supports 4 ohm speakers. What kind of 4 ohm speakers do i need to have then ?

SentinelAeon said:

I know that but it says it supports 4 ohm speakers. What kind of 4 ohm speakers do i need to have then ?

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Whatever are most efficient (as you want it as loud as possible) - but you need to reconsider your entire premise, you've been working on using 8 ohm speakers but have now suddently said you're using 4 ohm ones. You need to design the power supply accordingly, the rating of the chip for 4 ohms requires a lower supply rail than for 8 ohms.

Ok so i need to suply less power to the chip ? Meaning less batteries in series ? Well that also means new charger. I might just go and buy some 8 Ohm speakers then, it sounds easier. Or just connect this cheap speakers and drive them only until i hear crackling, will that tell me when i drive them to loud ? I got them for 5 bucks

SentinelAeon said:

Ok so i need to suply less power to the chip ? Meaning less batteries in series ? Well that also means new charger. I might just go and buy some 8 Ohm speakers then, it sounds easier. Or just connect this cheap speakers and drive them only until i hear crackling, will that tell me when i drive them to loud ? I got them for 5 bucks

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When the amplifiers melt will tell you when you run them too loud, the lower supply voltage for 4 ohm speakers is there to prevent the chip destroying itself.

As you've designed it for 8 ohms, get some 8 ohm speakers - or if you've got enough 4 ohms ones, put them in series pairs to make 8 ohms.

Ok, i will get some 8 ohm speakers, about 30W 8 ohm if possible.

I got another question. I got all the spare parts for my smaller bluetooth speaker. On ebay it says its for 4, 6 or 8 ohm speakers but now i read some reviews where it says its for 8 ohm speakers. Sadly i dont have 8 ohm speakers, only 4 ohm so i am wondering, if i put 2 4ohm speakers in series will that be ok ? How will volume compare to between 2x 8ohm speakers and 4x 4 ohm speakers (2 and 2 in series) ?

Yes, you can happily put the 4 ohm speakers in series to make 8 ohms, it will also effectively double the power handling of the speakers (as each one gets half of the power). Assuming the 8 ohm and 4 ohm speakers are identical (other than their voice coils) the 2 x 4 ohm speakers should be louder, as you've got more cone area to move air.

Ok thank you for your answers,

I got another questions. I know this little amp i got is 2x6W, meaning 12W. Therefor i am assuming 12W should be safe. Lets say i put multimeter between batteries and amp and measure current. It will be run by 1 3.7V battery, i will also measure voltage of the battery. So as i said, 12W is safe. If i measure voltage and current, if voltage * current is equal or less than 12W its safe ? I am asking because i want to test 4 ohm speakers also since it says its for 4 ohm also. And i will put volume to low and then slowly increase volume until i hit 12W. Should that be ok ?

Only recently you said your speakers are 4 ohms, I assumed 8 ohms and all my calculations were for 8 ohm speakers.
It looks like you are reading ebay instead of reading the datasheet for the TDA7492 amplifier IC. ebay knows nothing about detailed electronics.

The datasheet shows a graph of maximum output power into a 4 ohm speaker with various power supply voltages and at 1% and at 10% distortion.
With a 22V supply and 10% distortion then the output power is 50W, not 25W. If you bought a cheap Chinese Bluetooth amplifier then it might not have enough cooling for 25W per channel.

Parts Express sell a little 2.5" 20W speaker as 4 ohms or 8 ohms. Because it is small it needs bass boost to produce low frequencies. Then the bass will have maximum power of 20W and the midrange and highs will have less maximum power.

Try it and see - will the amp even run off 3.7V?.

You certainly won't get anywhere near 6W even if it does.

With a 13.8V supply (car battery) you can get a MAXIMUM of 4W in to 4 ohms with a single ended amplifier, or 16W for a bridged amplifier (effectively twice the supply voltage, 27.6V).

Power output is determined primarily be supply voltage and speaker impedance, the only contribution of the amplifier is if it survives or not.

Actualy my last question was for this module:

https://www.ebay.com/itm/5V-6W-6W-2...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

So about checking wattage, should that be ok ? Amperage * voltage, measuring with multimeter ?

Like I said, try it and see, the 6+6W is entirely imaginary anyway, it won't provide anything like that much.

Please provide a link to the little amp that is 2x6W. If it is powered by only one Lithium cell at 3.2V to 4.2V (3.7V average) then it probably has an output of
2x6 Whats which is about 2x 0.6 Watts into 4 ohm speakers.

Ali Express also knows nothing about electronics and sells a 2X6W amplifier that uses TWO PAM8403 stereo ICs that produce 3 Whats per channel with horrible distortion into 4 ohm speakers when the supply is 5V (less power with 3.7V). The missing details do not show that it probably drives four speakers.

The no-name-brand ebay Bluetooth amplifier has no details. Do you notice that the IC numbers are rubbed off so we cannot see the detailed datasheet?
It seems to have a 5V USB connector that will charge a single 3.7V lithium cell to 4.2V but then does it use the 3.7V to provide a much lower power to the ICs or does it have a built-in voltage booster so that the ICs get 5V for its rated 2X6W?

ebay also shows a PAM8403 "5W+5W" amplifier with a battery holder for a single 18650 lithium battery cell. The datasheet for the PAM8403 shows 3W per channel with horrible distortion into 4 ohms when the supply is 5V, or 2.5W with less distortion. It shows only 1.3W with less distortion into 4 ohms when the supply is 3.6V.

I think ebay sells "peak power" which is double the RMS power but still with horrible distortion. Usually an amplifier volume control is turned down so that there is no horrible clipping distortion but then the power number is less.

If you feed a continuous tone into both channels loaded with speakers then you can measure the battery voltage and current and multiply them to see the power including the heating power. But since you do not know if the ICs produce high heating or low heating then your power numbers do not make much sense.

HF69B is the name of amp thingy.

I connected this amp to many 4 Ohm speakers and it was very silent. I tried single 4 ohm or 2x 4ohm in series, both gave me distortion at high volume (it was 3, 5 and 10W speakers, 10W were by far the most silent ones, its almost unreal, its like 1W, not 10W).

Anyway dont know if i told you, i converted old 2x3W bluetooth speaker by suplying 4 ohm 12W speakers and it was of decent volume. Now i connected this HF69B thingy to 12W 4ohm speakers and it is even better. It will be more than enough for until i get the mighty 2x25W thing. I am really happy with it, it looks very ugly but had 4 parallel cells. I do have a step up 50W also, and since this speaker can be powered by either battery OR micro usb, i was thinking of using a step up to suply 5V to it. And then just use a cheap module for charging the batteries.

Anyway, i am happy, it is so much fun doing this projects and it is so cheap i am not afraid for anything to burn out. There is only distortion when i put it to absolute maximum, otherwise it plays nice.

Ok, enough about this weak 2x6W. Lets talk about 2x25W. I will be using 6S to give me 21-25V. SO now i should get some good 8ohm 25W+ speakers and that will give me maximum i can get from amp ? Would u say there is even sense to use stepup to suply steady 25V to speakers, or is 21-25V good enough and its not worth to bother ? I do have a step up at home though so wont cost me anything.

Thank you for helping me with this projects. Fun i have doing them alone is worth the money i spend on it

Speakers are also rated with imaginary numbers. Radio Shack sold good-sounding Minimus 7 speakers rated at 40W. I bought a pair and used them in my car which had a 14V battery. A woofer blew up and it was marked "5W Korea".

I am pretty sure this speakers are way out of my budget. Remember, if i was willing to pay, i would buy JBL. I will buy second hand speakers and hope for the best. They are very cheap since ppl replace car speakers and sell them cheaply.

Stepping up the voltage heats the voltage stepup circuit which wastes battery power.

Have you seen a review of the 2X25W cheap Chinese circuit? I saw a YouTube review of the 2X6W circuit you have and it said there are many complaints of the Bluetooth shutting down when the volume is high and if the speakers are less than 8 ohms.