DIY bluetooth speaker

[SentinelAeon]

Well i tested it with 4P batteries and it doesnt shut down. But for this thing i plan to use external charging (low/high protection) and use step up to suply 5V directly to the board (through microusb). SO far it didnt shut down, we will see how it goes. Like i said, its like 4 bucks board so even if i burn it with 4 ohm speakers, its all worth it for me testing and studying.

 

[SentinelAeon]

Btw you mentioned step up burns energy. My step up is supposed to be 88% efficient. Since i have so many batteries i dont care about 12% being wasted, final product will play for many hours.

I decided i will make 2 speakers, 1 built around that cheap 2x6W amp, the other big brother around 2x25W.
For the small one i decided i will power it the same way as some guy in video on youtube. What he did is get a cheap board for charging 1 battery, that takes care of over/under charge. Then i will use step up to change 3.2-3.7V to 5.1V. Then i will connect this directly to microusb leads as he did in the video. And obviously i will use this 4 ohm 12W speakers, because i just tested them again and this thing is LOUD. Really loud.

 

[SentinelAeon]

I ordered this:

https://www.ebay.com/itm/DC-DC-3-7V...:g:otcAAOSwxx9b4PwQ&LH_BIN=1&autorefresh=true

Its a charger and step up in 1. It says max discharge is 2A so i will be walking a thing line. If the amp is 2x6W and you say it is always less, so lets say it is 10W altogether. And i dont know at what voltage this 2A apply. If it applies to 4.2V * 2A = 8.4W so this is not 10 or 12W. In anycase i will be walking a fine line, but its like 90 cents a piece. I am also wondering, if i somehow cool down this chip with heatsink, will this help it survive those 10 or 12W ? But i wouldnt know which chips to cool down, i guess i could just try which ones are getting hot

 

[audioguru]

It is obvious that the amplifier cannot produce 6W per channel into 4 ohms with a supply that is only 5V.

6W into 4 ohms requires a peak-to-peak voltage of 13.9V. If the amplifier is bridged then with a 5V supply, the output per channel into 4 ohms is only 2W before it has severe distortion. It is the 5V supply that limits the output power. If the supply is about 8V then the amplifier will produce 6W per channel at low distortion into 4 ohms but the voltage stepup circuit has a 2A maximum battery discharge current and the 5V supply limit for the amplifier prevents it.

 

[SentinelAeon]

Ok so there should be no problems. I tried measuring current also and at almost maximum volume it was about 0.3A. Which not only would support your findings of 2W instead of 6W, but it is amazing also how loud the speaker is at that low current. If that 2x25W is anywhere close to that, it will be a total overkill.

 

[audioguru]

A multimeter is made to measure 50Hz or 60Hz electricity, not higher audio frequencies.
Music and speech are not continuous enough for a multimeter to measure the level, a continuous 50Hz or 60Hz tone is needed.
But a speaker has a low frequency resonance that increases its impedance which reduces its power.

Assuming that you are feeding a continuous tone at about 400Hz so that the speaker is 4 ohms and that you are measuring battery DC voltage and DC current, the battery voltage and current will fluctuate at the signal frequency which might reduce or increase the measurements.

You said you increased the volume to maximum. The real maximum output level is when the output distortion suddenly increases due to clipping and the position of the volume control could be high or low. An output higher than where distortion suddenly increases is full of harmonics that add to the actual true output power. Some amplifier and speaker manufacturers lie about the true power by saying "peak power" or "maximum power" without saying how much distortion there is.

Maybe you play acid rock "music" that is already full of distortion. Then you cannot hear when your amplifier has reached its true maximum output power.

The distance of a speaker from your ears vastly affects the loudness. The sound level from a speaker is usually measured at a distance of 1 meter.

 

[SentinelAeon]

Thank you for your reply, u obviously know much more about this things than me. OK so the simplest way for me to measure real wattage is to use 60Hz continuous sound ? That will be very unpleasant but i would like to at least compare the 2 amplifiers i have.

 

[audioguru]

No. The 4 ohm speaker resonates at a low frequency so its impedance will not be 4 ohms but it will higher which causes its power used at that frequency to be much less. The 4 ohm 2.5" speaker from Parts Express is 4 ohms only at 400Hz to 600Hz.

Of course the signal must be a pure sinewave and you need good hearing or an oscilloscope to see when clipping is reached.

 

[Nigel Goodwin]

Thank you for your reply, u obviously know much more about this things than me. OK so the simplest way for me to measure real wattage is to use 60Hz continuous sound ? That will be very unpleasant but i would like to at least compare the 2 amplifiers i have.

As AG mention3ed, that's much too low - the standard frequency used is 1000Hz, or sometimes 400Hz.

 

[SentinelAeon]

Ok i am a little confused now, can i measure it with multimeter or not ? Right now i dont have very tiny speakers connected, they are about 10cm diameter

 

[Nigel Goodwin]

Ok i am a little confused now, can i measure it with multimeter or not ? Right now i dont have very tiny speakers connected, they are about 10cm diameter

No, you need an oscilloscope and an audio oscillator - but there's little point measuring the power, you're only going to be disappointed, and knowing what power it is won't make it any louder.

 

[SentinelAeon]

Ok, i will just trust the modules i guess. And again, this "2x6W" is extremely loud, it was in front of me and i could actualy feel the air blowing into my face, it was not pleasant at all Anyway, now its down to waiting for all the parts so i can build that 2x25W monstrosity. I am looking for 8 ohm 25W+ speakers now and after i have all the parts, i will go buy some nice cheap thin wood and make that JBL killer of mine ^^

 

[audioguru]

If you use a 4 ohm or 8 ohm resistor for a load instead of a resonating speaker, and you use a pure sinewave signal at a 50Hz or 60Hz then you can measure the output voltage and current with an ordinary multimeter. Slowly turn up the volume until you hear the amplifier producing clipping distortion. Then multiply the AC voltage with the AC current to determine the output power.

 

[audioguru]

You do not use cheap thin wood to make a speaker enclosure. The top and bottom, sides and ends of the enclosure must not vibrate with the speaker sounds. Also, the volume of the enclosure should match the detailed spec's of the raw speakers. The detailed spec's can also be used to calculate the volume of a port for the enclosure to produce deeper bass frequencies.

 

[SentinelAeon]

I know all that but like i said, priority is small, compact and cheap. I will carry this speaker with me in my backpack and weight and size is important. Sound quality is less important, though i certanly wouldnt say no to big bass.

I just wanted to let you know that i used this new "2x6W" speaker outside yesterday and it was a blast. I got the best compliment i could get as a DIY speaker creator: "please just turn the volume down a notch". Meaning it was powerfull enough outside near 20 tipsy people playing beer pong.

Due to this speaker being powerfull enough, i decided i will keep this 2x6W until i build 2x25W. And then i will try to sell 2x6W cheaply to cover some of the components of 2x25W.

I plan to change a few things on my 2x6W. First of all, new enclosure with bass hole. I need to add a on/off switch(cause right now its on the board itself so i need to keep a hole in the speaker box to change it). Right now its powered by 4 bateries in parallel. This is sufficient BUT i plan to power the speaker from microusb port (remember, it has 2 choices, u can power it by 3.7V battery OR microusb 5V). I will use 4P batteries, use a step up to 5.1V and connect this step up directly to micro usb. And i will use another chip for charging 3.7V batteries (speakers board has over charge protection but doesnt have undercharge protection, while that board i will use has it both)

I know that this goes against everything you belive in, regarding speaker enclosure, sound quality, etc. But bear with me, i want this to sound as best as possible but still be highly portable and as light as possible.

 

[audioguru]

Using a hole in a speaker enclosure instead of a calculated port tube will probably result is less bass than having no hole.
Will you add bass and treble tone controls?

 

[SentinelAeon]

There is no bass and treble tone controls in plan, at least not yet. I wanted to use port tube, but calculating will be a problem like i said, if i want speaker as little as possible, calculations will be way off. I am working on 2x6W speaker now since i am still waiting for parts for the bigger 2x25W. This is how i plan to connect things:

 

[audioguru]

Beside the switch, the pcb is labelled On and Off. In the OFF position the amplifier will be turned off.
Guess what the amplifier does when you turn the switch ON.

 

[SentinelAeon]

You completely misunderstood my question. First of all, on/off is kind of a lie, because even though it says OFF, its actualy ON in case u suply power through microusb, like i will. And second, i am asking which pins do i need to connect to make it on and off. For instance if i want power to microusb (falsely labeled as off), i need to make connection between which pins ? The middle one and the left one ? ON 1 side or both sides ?

 

[audioguru]

You have the connections instructions, I don't.
I guess the micro-USB is used to charge a single 18650 battery that can power the amplifier with an output of about 1W per channel into 4 ohm speakers, or +5V can power the amplifier to 2W or 3W per channel from your voltage stepup module.

There is a jack marked "Charging". Is that for a single 18650 cell and/or for powering the board from 5V?

Nothing in the ad for the amplifier explains the function of the on-off switch so maybe it simply turns the bluetooth and amplifier on and off. I guess the charging for the single 18650 connected to the amplifier is always connected to charging, even if the switch is turned off.
Maybe one side of the switch is for the amplifier on and off and the other side is for the Bluetooth on and off.