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DIY bluetooth speaker

Nigel Goodwin

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Well the picture explains a lot - such as why your speakers in series aren't moving the same - presumably because they aren't identical speakers.

You also need the left and right in their own enclosures, not all in a single common enclosure.
 
Yep, like i said, this is full of mistakes. The next speaker i make will only use 2 drivers and i will measure all those parameters to give me the optimal size of the enclosure and port and such. But all in all i am happy. I also added heatsinks to the 3 parts of the amp that are heating and i added a fan that starts running at 45C.
 

audioguru

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Most Helpful Member
I think you got the old Rev 5 version of the TDA7492 that needs a heatsink if the supply is 25V and you play it loud.
The IC has thermal protection that shuts it down if it gets too hot then begins playing again after cooling. But don't rely on the protection going on and off over and over because then the IC will fail with thermal fatigue.

It is too bad the frequency response of your successful speaker is not great because then it obviously sounds cheap.
 

audioguru

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Most Helpful Member
It is silly to make a small speaker in stereo because the speakers are too close together to make stereo.
A single mono speaker will produce more bass than two stereo speakers in the same size enclosure.

The TDA7492 IC has a metal pad on its bottom that is where a heatsink should be attached. Without using your voltage booster then it should be fine playing 18W per channel.
 

audioguru

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Most Helpful Member
Fairly small raw speakers are made that produce most of the frequencies we hear but usually a larger woofer is used for low frequencies and a much smaller tweeter is used for high frequencies. A crossover network made with inductors and capacitors keeps the high frequencies out of the woofer and keeps the low frequencies out of the tweeter. It looks like you have a woofer and a tweeter in series which is NEVER done.
 
I have some more questions. The amplifier i have. I am still not clear if i can run it at 25V ? Because on ebay it says 25V. So lets say i add heatsinks and a fan (i did all that in my first speaker, added heatsinks and a fan that starts at 45C) and some 30W 8 ohm speakers, can i run it at 25V or will i burn it ? And another question. Lets say i want to use 4 ohm speakers instead of 8 ohm. What would be the highest safe voltage to run them ? I will write questions again like this:

1) with one 8 ohm speaker on each channel, can i run it on 25V if i add heatsinks and a fan ?
2) if i useone 4 ohm speaker per channel, what would be the max safe voltageif i add heatsinks and a fan ?
 

audioguru

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Most Helpful Member
Do you believe ebay of the TDA7492 manufacturer's website? Is your IC the old one that is marked TDA7492P?
The datasheet is not from ebay and it says the old TDA7492P can use 8 ohm speakers and a 25V supply if the IC has a heatsink ON ITS BOTTOM then the output power and heating will be high if the volume is turned up. It might destroy your cheap little speakers.

The old TDA7492P can use 4 ohm speakers if its supply is never higher than 22V then its output power will be 40W per channel and the IC will need a pretty big heatsink ON ITS BOTTOM.

A heatsink on its plastic top will be almost useless. The chip is mounted on its metal bottom.
 
Thank you for your answers,

40W per channel for my 2x25W doesnt sound healthy. What voltage would i need to use to drive 25W per channel with 4 ohm speakers ? As for heatsink on the bottom it sounds funny because my board has absolutely nothing on its bottom, its just a green plastic plate. Should i just mount it there ? I am getting a heat measure gun in about a month, i will be able to measure what heats most then. Until then i can just touch.

Btw i tested the speaker for a few hours on its max setting and its working ok. People were very happy about the speaker and they all wanted their "1" song on it. For a moment i thought i lost my mobile phone and was searching for it like crazy only to find out my friend had an "innocent" smile on her face and was typing something into a phone that looked remarkably similar to my own.
 

audioguru

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Most Helpful Member
The bottom of the TDA7492 IC has a metal plate that its chip is mounted on as shown in a photo on its datasheet. The metal plate attaches to a heatsink somehow. Since the IC is already mounted on its pcb then a heatgun cannot reach its metal plate to measure temperature. The IC should shutdown if it gets too hot.

The Rev 5 datasheet has a graph showing 4 ohms power output, supply voltage and distortion. For 25W into 4 ohms at low distortion the supply must be about 20V but if the volume control on your phone is set too high the output will be 41W at 10% distortion or if turned up more the output will be 60W at higher distortion.

Here is the old Rev 5 datasheet:
 

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I already sold the speaker and am now waiting for new parts. I already got visaton FRS7M 8 ohm 30W speakers which are said to have good performance per watt. Which will be ok to use in my 2x25 or 2x50W system. I will write with more questions as soon as i get the needed parts.
 

audioguru

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I knew it. The tiny speakers produce no bass. In a huge enclosure they cutoff at 220Hz. 3.5 octaves of sounds will be missing.

I looked up the speakers in Google and the 1st ad said 30 Whats! (from Amazon who knows nothing about speakers).
The manufacturer Visaton has a maximum continuous power rating of only 8 Watts. Your old style Rev 5 amplifier will produce 28 real Watts per channel into 8 ohm speakers when the supply is 25V so let us know how long the speakers survive.
 
So what about this data:

 

audioguru

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Most Helpful Member
With its missing bass sounds it is NOT hifi and it is NOT full range.
Its sensitivity is more than many little speakers but less than larger speakers.
With an added woofer or sub-woofer then the tiny speaker will sound fine until the overpowering destroys it.
 
How would i overpower them if they are 30/50W speakers and i would be using 2x25W amp ?
I got a lot of usefull help on this forum but sometimes it sounds almost as you wished that things didnt work well. I sold the speaker so fast not because i didnt like it (though it was to big for my backpack) but because my friend liked it so much that he just wanted to have it. And that earned me enough money for 3 or 4 more speakers like this. My next speaker has to be smaller because portability is a must, carrying this speaker for half an hour wasnt pleasant. I admit more bass would be nice, but i didnt hear any complaints when ppl wanted "just 1 song" on the speaker. And side to side with 300 dollar JBL extreme, my speaker was just as loud, if not louder. Obviously quality and bass wasnt same since it was a 12 dollar speaker. But we had lots of fun with it and it was playing all evening and better part of night and batteries lasted a lot longer than we could.


Again, i thank you all for your inputs, but instead of negative thoughts i think you all should be happy for what i accomplished with soo little money, thats what its all about when doing DIY. Otherwise just spend a fortune and buy a pro stuff. Budget. Portability. That is what matters to me.
 

audioguru

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Most Helpful Member
The speaker you talked about two days ago is smaller and lower power than the speaker you talk about today. Which one do you have?
 

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audioguru

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Most Helpful Member
You should have two threads. One thread about the low voltage battery powering the low power amplifier driving the smallest low power speakers, and a second thread about the higher voltage battery and much higher power amplifier driving the larger speakers.
I think they will sound much better if you add some bass boost.
 

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