DIY bluetooth speaker

Logitech makes cheap low power audio products.
A cheap low power speaker makes distortion when it is fed too much power.

A speaker resonates like a bongo drum. But the extremely low output impedance of a sold state amplifier damps the resonance. Speakers in series do not have much damping from the amplifier so they sound boomy, something like a bongo drum.

Since an amplifier has an extremely low output impedance then its output voltage does not change when its load impedance is changed. If the output is 12V RMS with no load then it will also be 12V with an 8 ohm load. Your "25W + 25W" amplifier produces 18W into 8 ohms per channel when its supply is 21V. It will overheat if you use a 4 ohm speaker because the current is doubled. I can't remember if your amplifier shuts down if it gets too hot.

Ohm's Law says that if the voltage is the same from the amplifier but the resistance (or speaker impedance) is doubled then the current is halved.
Power= Voltage x Current so then the power is also halved. Halved power is only a little less loud because our hearing's sensitivity is logarithmic so we can hear a pin drop or hear a nearby jet airplane.

If you double the voltage into a resistance or impedance then the current also doubles. Then the power is almost 4 times.

Right now i am using either 21V or 25V (meaning 5 or 6 batteries).


Ok so driving 4 ohm speakers is not ok. I will try tomorrow experimenting with all the speakers i have. I will see what happens if i connect in series "woofer" speaker and full range speaker, they are both 4 ohm meaning 8 ohms together. I was thinking even what happens if i connect "woofer" speaker AND 2x 4 ohm full range in series, thats together 12 ohm. Do you think there would be less distortion ? Like u said, more resistance, less current -> less volume ergo less distortion.

Btw look at this amp:

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Its dirt cheap and its supposed to be very powerful. I will test it with 25.2V power and some strong speakers. What i like about it is that it has volume switch for each channel, so i can put it lower to make sure it doesnt cause to much distortion

Nvm, i thought this was to good to be true. It is missing bluetooth .. Can u help me find something like 2x50W with screw volume control and bluetooth for low price ?

A good audio amplifier (like you have) datasheet shows that its distortion is extremely low until its output level reaches as high as it can go, then if higher produces severe clipping distortion.
A cheap speaker plays well until too much power causes its coil to crash against its magnet structure causing severe distortion. Sometimes a cheap speaker causes distortion when its coil moves outside the linear magnetic gap producing distortion.

The datasheet of the TPA3116D2 recommends a 26V max supply and shows it with a 21V supply producing 50W per channel into 4 ohms at a horrible 10% clipping distortion. With a 21V supply it produces about 37W per channel into 4 ohms with low distortion or about 22W per channel into 8 ohms at low distortion.

The ebay Chinese TPA3116 Bluetooth 2.1 Amplifier has tiny little heatsinks so I bet it overheats. It does not say it can survive driving 4 ohm speakers so maybe its output is peak (double the real power) very distorted 50W per channel into 8 ohms?

I found this amp, it would be great but it has buttons instead of screws for volume. And since this will be inside the speaker i will have no access to buttons. And once batteries run out, the buttons will be at their default volume so this is useless for what i need

I ordered this amp and will see how it works. It only has 1 volume thing but its better then nothing. My plan is to find out the point where i can have volume on mobile phone at 100% and use this dial to lower volume on the board itself, to have no distortion. Then glue the dial in place.

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The high power amplifiers have small heatsinks that rely on ambient airflow for cooling. The amplifier will probably overheat inside your little speaker.
It looks like the new Bluetooth Amplifier has a stereo volume control but they do not say so.

I will add a fan that starts spinning when temp of heatsink is above 60C. Well the picture shows the volume control, so if it comes without it, i will refund it.
The wierdest thing, yesterday i connected my 2x25W amp to DC power suply. And i pluged that power suply into watt meter. Ok, so i connect and it shows 5W power usage. Even though no music was playing, there was no buzzing or anything. Then i put speakers quite loud and it increases wattage to 7W. Now mind you, at that point the music was VERY loud. And i simply do not belive that it was doing only 2x3W, there i no way. 3W is laptop speaker and this was LOUD.

Something new i am working on, mainly testing how this speaker from woofer works together with this huge passive radiators. Tomorrow the product should be finished and it will be my speaker until i get better parts and design it from scratch with better speakers. I used a case from center speaker from 5.1 system. Bass is already a lot better then it was with my previous speaker. But i still hope that it will improve once i add another passive radiator to the other side and fill all the holes

A fan must blow cool ambient air, not the hot air inside the enclosure. I do not think you will play it loud enough to need a fan.

Adding the second passive radiator might make the bass less because the spec's for the woofer and passive radiator and size of the enclosure must all be matched together in a complicated calculation, not at random.

I just read the history of the Harman Kardon company in Google. I owned and worked with many of the products mentioned but I never bought anything that is a Harman Kardon. In 1953 Harman and Kardon started their company with an investment of 5 thousand dollars each and on 2017 it was sold to Samsung for 8 billion dollars.

I tested the speaker today. Mind you, this is not a finished product ! There was still tiny holes somewhere because when i move the speakers slowly inside, passive radiators should go out and stay out, instead they dont move. They only move if i push speakers inside fast. But already this has a lot better bass then previous speaker. My mobile phone wont record the bass well though. Also on the video u can see what happens if i go over 90%. The woofer starts cliping. I didnt know why at first but then i googled. Its from logitech S-220 cheap system and its RMS is 9W. Though i still dont know why killawatt shows im using only 9W power all together but apperently its to much for this woofer. I plan to get some similar woofer, similar size, but rated like 30W. That should be great. When music plays passive radiators move, though they will move more when i seal all the holes:

Killawatt is slow and measures average power. But music has short duration high power peaks that are not shown on killawatt.
If the woofer's spec's, the passive radiator's spec's and the enclosure's size are not calculated and matched to make good bass then when the woofer moves in and out during bass tones, the passive radiators will cancel its sounds instead of adding to the sounds.

I guess i was lucky because when i hold the membranes still, there is less bass. Hmm, but those calculations for passive membranes are so tough ... i dont like those kinds of calculations :/

Btw, for my future speakers, how would such mini woofer work:


It says response 70- 6.000Hz. And i would connect it to the left channel and connect a full range speaker to the right channel. Would that be a lot worse then doing the capacitor and coil thing to only send bass to 1 speaker and highs to the other ?

Maybe when you hold the passive radiator still it acts like a huge hole in the enclosure.

A passive radiator works the same as a tuned port (bass reflex) but takes less space in the enclosure.
Look at Bass Reflex in Wikipedia in Google.

The amplifier for a bass reflex speaker (port or passive radiator) should have a filter with a sharp cutoff to cut very low frequencies since at very low frequencies the woofer seems to have no enclosure reducing its motions.

The sensitivity of the Peerless tiny woofer is low and it rolls off all bass frequencies instead of having a flat frequency response.
You should mix together the left and right channel signal sources with two resistors to make mono.
Then you must cut bass frequencies at input of the amplifier of the full range speaker and cut high frequencies at the bass amplifier to avoid phase cancellations caused by two speakers beside each other playing the same sounds.

But the problem is i am using this amp that has bluetooth on it, i cannot do anything to the signal before it reaches the board itself. The only option would be to buy separate amplifier and separate bluetooth board

Btw i just noticed something. JBL charge 3 uses 2 identical small speakers, full range speakers or full range woofers or something. And JBL charge 4 uses only 1 speaker. And i can confirm that its playing ok, its only to quiet for my needs. So how about i just go with 2 identical small 3" speakers ? Maybe find something in the area of 40W and range from 60Hz (same as JBL) to i dont know, 10.000 ?

Two 3" speakers do not produce good bass, have low sensitivity and need a larger enclosure than a 4" woofer that does produce good bass and has good sensitivity.
Only deaf old people cannot hear the octave above 10kHz. And young people who played with guns or acid rock "music".

The JBL Charge 4 has an output of 30W. 40W is only slightly more that most people will not notice. Double the power sounds like only a little more. 10 times the power sounds like twice as loud.