DIY bluetooth speaker

I am sorry but i still do not understand. If we talk about the amp i posted. Is it better to run it at 21V or 25V ? I use 30W speakers at 8 ohms. What voltage would be the best compromise between being loud and being clear. I am very new to all this.

You bought ebay cheap Chinese junk with lies or poor translation in their ad.
Your amplifier uses a TDA7492P that has a small metal tab on its bottom that is supposed to be soldered to a large grounded copper area on the pcb for its heatsink. Yours does not show any copper on the top of its pcb then it has no heatsink and it will overheat.

Please read the datasheet for the TDA7492P rev 6:
1) With copper-on-the-pcb-top as a heatsink, a 20VDC supply and an 8 ohm speaker with 10% of horrible distortion= 25W.
2) As above but with 1% distortion that is still heard= 20W.
3) As above but with low distortion= 18W.
The datasheet never shows a supply higher than 20V.
Do not operate your amplifier continuously at full power (a siren in a movie). It will probably overheat and mute or shutdown. Overheating a number of times will damage it.

ebay shows amplifiers they claim are the better (50W + 50W) TDA7492 (metal on top) without the P but they might be lying about it too. They show a heatsink on top of the IC but other people who bought it said they used bathtub caulking instead of thermal adhesive.

Ok so if i understand you correctly at 20V 8ohm i get 10% distortion 25W, if i want 1% distortion i need to use LESS voltage to only produce 20W or less and that way distortion will be lower ?

With a 20V supply, an 8 ohm speaker and the volume turned up way too high so the output is clipping like crazy, the output is 25W.
With the 20V supply and the volume turned down but high enough to produce and hear 1% distortion, the output is 20W.
With the 20V supply and the volume turned down more but as loud as possible with low distortion, the output is 18W.

If you use a lower power supply voltage then clipping distortion will occur at a lower power output.

The datasheet shows that with a 12V supply and an 8 ohm speaker, the power at 10% distortion is 9.5W, the power at 1% distortion is 7.2W and the output power is even less at low distortion.

Ok thank you, now i understand. This should not be an issue because we usual listen to the music at not maximum level, because at maxximum level in many songs u can hear distortion. We only ever listen to it at maximum volume when ppl at our party drank a bit to much and by then, nobody really cares much about quality, they just really want that "1" song they really love.

Btw, i know what i bought is a cheap chinese amp, but to give you my honest opinion, i am still impressed with it. The sole fact that i can assemble a working speaker for 20 dollars or less and i am no expert in electronics, i learned what i know myself online and by trial and error. It is still fantastic to me. I wouldnt use that amp at home when i listen to classical music, i have better sound system for that. But if a person goes camping, that is an impressive thing. Maybe that is just me, i am hugely impressed when a person can assemble something and it actualy works. Ofcourse it is no match for expensive speakers made by ppl who are really good at that, but the sole fact that as far as loudness goes, my speaker went toe to toe or even won against 200+ dollar speakers, well, that makes the engineer in me really happy.

I thank you for your help, i learn something new everytime i visit this forum

Songs usually do not cause distortion. Turning up the volume too high for the amplifier (and its power supply voltage) causes distortion.
Turning up the volume too high produces a lot of high frequency harmonic distortion that can damage your tweeters and damage your hearing.

I am glad that you like your amplifier and speaker. Years ago, I made an amplifier and speakers for the beach. It did not cost much but it sounded much better than the expensive ghetto blasters that were there.

The only fault i could say about the speaker is its size. It is more then twice the size of JBL charge 3 and JBL charge 3 is plenty powerful for my needs. I will look into some smaller speakers and passive radiators, etc. and see if i can make it smaller.

I have a question about passive radiators. I read somewhere that passive radiators need to be at least 1.5x the size of speakers in order for them to work. Is that true ? Because i have seen some speakers where passive radiators were the same size as speakers or smaller and worked (u could hear bass dissapear when u removed the passive radiator and bass came back when u mounted it in)

SentinelAeon said:

The only fault i could say about the speaker is its size. It is more then twice the size of JBL charge 3 and JBL charge 3 is plenty powerful for my needs. I will look into some smaller speakers and passive radiators, etc. and see if i can make it smaller.

I have a question about passive radiators. I read somewhere that passive radiators need to be at least 1.5x the size of speakers in order for them to work. Is that true ? Because i have seen some speakers where passive radiators were the same size as speakers or smaller and worked (u could hear bass dissapear when u removed the passive radiator and bass came back when u mounted it in)

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The bass disappeared because you had a massive hole in the cabinet when you removed the passive radiator, if you sealed the hole it would then be infinite baffle, and work 'reasonably' well.

I've always been somewhat dubious about passive radiators, and essentially it's just a variation on a port - most I've ever seen are identical in size to the bass unit, in fact I don't think I've ever noticed one where it wasn't the same size?. Often it's just an identical speaker, minus the magnet and voice coil.

A large woofer has a low resonant frequency. Below resonance the bass frequency sound levels are reduced.
A little woofer is cheap and has a much higher resonant frequency unless its cone is heavy and then it needs a strong coil and magnet (which are expensive).
A sealed enclosure increases the resonant frequency of a woofer, but properly blocks the out-of-phase sounds from the rear of the woofer from cancelling the bass from the front.
A port on an enclosure also has a resonance that adds to and is at a lower frequency than the woofer to enhance the bass low frequencies.
A passive radiator is a mechanical port and performs almost the same as a port.

Thank you for the information. I am very new to both port and passive radiator so i am learning as i go. On another forum of audio experts they explained to me that in order to get a bass using port, i need special calculating tool to calculate dimensions (volume) and port placing and many other things. I installed the program but it was far over my head, it even wanted some data about speakers i didnt have nor understood.

The reason i keep mentioning passive radiators is simple - as i said i want to make smaller speaker (JBL charge 3 size) so passive radiators are the only way i can tacle bass this way. And i am just amazed how much better bass on little charge 3 is compared to my 2-2.5x bigger speaker, even though i added passive radiators. Now granted i will never make the same speaker as JBL, there is a whole team of engineers working on it, have better knowledge, better equipment, better parts .. but as an engineer myself (different field though) i just cannot give it a rest when i see a challenge. Challenge in how much can i increase bass and keep the speaker portable. It makes me wanna get a broken charge 3 just to put it apart and carefuly inspect what they did and how.

What i learned so far about going bass way with passive radiators (correct me where i am wrong and add where necesary):

1) The enclosure has to be completely and i mean completely air tight
2) radiator size >= speaker size
3) someone mentioned something about each speaker being in its own compartment as oposed to 1 simple square box ?
4) the heavier the passive radiator, the better the bass (i simply guessed that because in 1 video i saw a guy adding coins to passive radiators for weight, dont know if its true)

Please continue to help me in my adventure of improving my speaker

Most half-decent raw speakers have detailed spec's and even post a recommended enclosure design.
Two speakers in the same enclosure are silly for making stereo. They are too close together for you to hear stereo directional effects. Instead the enclosure can be used for one larger speaker and the stereo amplifiers can also be replaced by one better amplifier.

A speaker and a passive radiator must work together as a team. If you add weight to the passive radiator then it needs more speaker/amplifier power to drive it which causes some frequencies from the speaker to make less sound level causing the passive radiator to sound like a one musical note bongo drum.

Another question. I saw some homemade bluetooth speakers on youtube and they got quite good bass with passive radiators. And 1 thing i noticed in certain video is that speakers move a lot more then my speakers. The speakers i have (30W) are loud but the membrane moves probably 3 times less then the speakers i saw on the video (i think with same amp). Could you maybe explain to me what is the positive of speakers being able to move more. Also i noticed that the passive radiators move a lot more then on my speakers. I was wondering if its possible that on my speaker i left some tiny gaps somewhere in the speaker and that is the reason air is moving in and out of those gaps, could this be the case ? But i have no idea how to find those gaps ;/ Anyway here is an example of DIY speaker with better bass than my speaker and those speakers and passive radiators really move a lot. Im thinking of ordering similar speakers but 8 ohm ones:

The little woofers in the video have a large flexible surround and a large magnet. Their cones move a lot producing good bass.
Since the cones on your speakers do not move as much then they produce less bass loudness. Are your speakers "full range" or woofers?

If you have gaps in your speaker enclosures then the speaker cones will move MORE, not less. The sounds from the gaps are from the rear of the speakers and will cancel sounds from the front of the speaker cones, which also happens when a speaker has no enclosure.

With the same amplifier, 8 ohm speakers produce low power, 4 ohm speakers produce twice as much power and 2 ohm speakers produce 4 times as much power if the amplifier can drive 2 ohms. The woofers in the video are 3 ohms.

The amplifier in the video is a TPA3116 that produces about 40W at low distortion into 4 ohms with a 21V supply and might produce 50W into the 3 ohm speakers used.
Your amplifier is the TDA7492P that produces only 18W at low distortion into 8 ohms and cannot drive 4 ohms or 3 ohms at higher power.

The person who made the speakers might have been lucky that the spec's for his woofers match the spec's of the enclosures and the spec's of the passive radiators.

This are my existing speakers, i plan to get some different speakers this time:

**broken link removed**

And this are the speakers from video, on another audio specialist forum, they told me that i need a speaker with more rubber around it. With rubber i mean the thing that allows the cone to move (rubber connecting speaker case and the cone). And looking at this speaker, it really has more rubber - as they told me that allows it to move move in and out and are less likely to fart (i am guessing this is not a technical term, thats how they called it when speaker isnt distorting but kindof "farting", they said distortion is usualy limit of amp, farting is limit of speaker). Ok so speaker from video with more rubber:


I also have to decide whether i will use existing TDA7492P amp, or some other amp. This TPA3116 from the video is in similar price range. And what i like about it is those 2 "screws" that control how loud each speaker is. So this way i could just put on some loud music, set it to maximum on my mobile phone and then move those screws to the level where i dont hear distortion anymore. If u know what i mean, lets say those 2 screws on 100% and my mobile phone on 100%, lets say it produces to much distortion. And then i would move screws to 90% and sound would be pleasant. Then i would never have to worry about distortion anymore, since those screws will be inside the speaker and once sealed, no one can touch them. This is the amp i was looking, obviously i would have to get speakers with different impedance. But i just noticed its without bluetooth so thats kind of a problem. And the amp from video has bluetooth but it only has buttons for setting volume. I would prefer screws, so that once i set them, they stay like that forever. Or maybe i could use some other methods to make sure that when volume on mobile phone is on 100%, that there is no distortion. Amp i was telling u about:

Bass is 20Hz to about 150Hz. The Visaton speakers resonate at 130Hz so they will produce almost no bass.

The AliExpress 3" expensive, Chinese, no-name-brand, no details, no spec's speaker is the one in the video.
The datasheet for the TPA3116 IC from Texas Instruments shows 50W + 50W into 4 ohm speakers with horrible 10% distortion when the supply is 19V and is about 40W per channel at low distortion when your battery is fully charged at 21V. When your battery voltage is low at 16V and should be disconnected the amplifier output power is about 25W per channel at low distortion into 4 ohm speakers.

The AliExpress speakers used in the video are 3 ohms that Texas Instruments says is a little too low. They will be fine if you do not play at full blast.

Your phone has an amplifier that will produce extreme distortion if its output level is too high. The TPA3116 amplifier also produces extreme distortion if its output level is too high or if is fed distortion from your phone.

Maybe the AliExpress speaker produces no high audio frequencies which is why tweeters were used in the viseo.

audioguru said:

Your phone has an amplifier that will produce extreme distortion if its output level is too high. The TPA3116 amplifier also produces extreme distortion if its output level is too high or if is fed distortion from your phone.

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He's building a bluetooth speaker - the audio never passed through the phone analog audio stages!


Think of how the speaker cone affect the air around it; at high frequencies, it does not take much movement to create pressure waves as the inertia of the air itself means it has nowhere to move to.

At low frequencies it can just flow out the way, so it takes much more cone movement to give a reasonable level pressure increase or decrease - and those pressure variations in air are "sound".

The ones you have do have a roll-style surround, but the metal basket is a simple cone close behind the drive cone; they are not particularly long travel. The other ones you link to have a parallel section back from the flange that the whole cone can travel back in to; they are a specific long-travel design.

They are like the ones in the JBL unit I posted the photo of earlier - those also have the parallel section in the basket; though the ones you link to are larger at rather higher power rated.

Thank you for all the advices. The speakers i have now were quite cheap, about 13€ a piece. Could i find some smaller speakers around that price that would move more and be better for what i am building ? Maybe 15€ a piece ? They even dont have to be 30W, they can be smaller, 20W maybe. Also i am thinking of just using a pvc pipe this time instead of wooden enclosure.

A "Cheap" speaker usually means poor performance, poor quality and a short life.

I understand that, i am trying to find something of a good price/perf ratio. Because if i buy more costly equipment then i might aswell go spend money on a new JBL speaker. If you have any recomendation of a good speaker i would like to hear it. With wide rubber, made for small speakers with passive radiators

Sorry, I do not use tiny speakers. Parts Express online has many speakers, some good and some fairly cheap.
Most tiny speakers have a resonance frequency too high (above 50Hz) to produce good bass.
The enclosure increases the resonant frequency but a tuned port or passive radiator reduces the resonant frequency of the system down to the speaker's natural resonance without an enclosure. But the low frequency drop-off is steeper.
A tuned port works the same as a passive radiator but a port uses up some enclosure volume.