Some questions regarding a cheap BT speaker build

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Erlas

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Joined 2018
#1
Hello everyone,

So I want to build a cheap(ish) bluetooth speaker just to gain new skills and knowledge about speaker building. Of course it would be awesome if the end product would sound somewhat decent aswell 😀 But to achieve my goals I need to overcome this problem: So here's my part list:

Amp: XH-M531 XH M531 20W x 2 DC12 15V For Yamaha Digital Amplifier Board Stereo HIFI Class D Audio Amplifier Board YDA138 E -in Instrument Parts & Accessories from Tools on Aliexpress.com | Alibaba Group
crossover: GHXAMP 50W 2 Way Crossover Audio Desktop Speakers Treble Bass Frequency divider For 3"inch Speaker 4 8OHM 3.3KHzZ 2PCS-in Speaker Accessories from Consumer Electronics on Aliexpress.com | Alibaba Group
full range: GHXAMP 2PC 3inch 8OHM 20W Woofer Bass Speaker Neodymium Multimedia Home Theater Desktop Rubber Speaker For SONY Loudspeaker DIY -in Portable Speakers from Consumer Electronics on Aliexpress.com | Alibaba Group
tweeter: Aiyima 2pcs 3 inch Hifi speaker treble tweeter fever horn 4ohm 8ohm 20W High power tweeter board 74mm-in Portable Speakers from Consumer Electronics on Aliexpress.com | Alibaba Group

and my question is: is this setup any logical? I still have a hard time understanding what crossovers to choose or what wattage the tweeters should be.. maybe you even notice more poor descisions and I would like to know about them! Thank you for your help.
 
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#2
It will work. Just do it.

Power supply? BluTooth? (I may have missed these; I don't read German.)

The point of the crossover: a real WOOFER has to be big to move a lot of air. A good tweeter has to be small to move quickly. You want to send your lows to the woofer and your highs to the tweeter.

The "funny" thing about your selection: your woof and tweet are "the same size", both nominally 3-inch. Well, actually the working part of the tweet is half the size of the woofer. In "real" systems we tend to more like a 4:1 range of woof:tweet. The MGM theater system was 15" woofers with 3" tweeters. Many older hi-fi systems were 10" woofs and 2" tweets. A car-stereo "2-way" may be a 5" woof and 3/4" tweet.

I would not expect much bass from a 3-inch any further than I can reach. For desktop systems I have been pleased with such systems. In a living room, for my music, I tend to at least 10" and have used an 18" woofer.

In this size level, _I_ would pick a nice 4-inch full-range such as FE-103 or some car-speakers (which may be super low cost). IMHO a cone this small has plenty of highs, and avoids the problem of making the highs balance the lows.

Or if you must go 2-way, I would just use a 5uFd NP cap in series with each tweeter. This will keep the bass from slapping/burning the tweeter. A real woofer will fall-off about the point that the cap-coupled tweeter picks-up. (Your 3-inch "woofer" may have plenty of tweet.)
 
#3
PRR said:
It will work. Just do it.

Power supply? BluTooth? (I may have missed these; I don't read German.)
Click to expand...

For my power supply Im planning to use a 3S 18650 battery pack with a bms of course, and charge it with a 12.6 charger. (step up to 14v for the amp)

For bluetooth im planning to use this board:
CSR8645
1x CSR8645 APT-X Hifi Bluetooth 4.0 Receiver Board 12V For Car Amplifier Speaker | eBay

which seeems quite nice becouse it would work of the 12 volts, so I dont need any aditional buck converters, and it also integrates a ground loop isolator which is ideal for me.

And yes I agree that my woofers may be a little to small, but I couldnt find any others with the same output power and bigger size like 4" or something like this (for cheap), that would work fine with this 20+20w amp.
Also I dont like the 3" size of the tweeters even though the working part of them is half the size, but i tried to match the wattage and the impedance of the tweeter with the full range (and im not sure if its the right thing to do)

anyway, thank you for your reply!

Edit:
sorry if the links were german, Im not even from Germany, and if i open them my self, they are in english 😀
 
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#4
#5
Beware that the amp chip (two of them on your board) is only rated at 1x10W at 8 ohms (which your woofer is and I'm guessing you ordered the 8 ohm version of the tweeter too), and that's at 10% THD+N distortion. 10% distortion is terrible so you'll never want to use it that high so you probably only have something closer to 2x5W usable power, which is a bit on the low side considering the speakers probably aren't that sensitive either.

You might want to rethink the amp choice. I'd go with something more powerful, and if you haven't bought speakers yet going for 4 ohm ones will get you some more power out of the 12V drive voltage.

Make sure the input sensitivity (gain) is high enough on the amp you choose as well, that Bluetooth chip puts out ~0.6v RMS, and many amps require more than that to get full output, meaning that even turned to max they might not play loud enough, but you'll still get the negative effects of turning them up (eg. the noise will be turned up).

The crossover specs look strange too, it says 4ohm 8ohm, but the parts values for the same frequency and slope crossover is very different from 4 ohms and 8 ohms, so the 3.3Khz is only true for one of them. You might want to look around for something else, or use something like the Parts Express crossover guide for component values to use to build your own (here you can also see plainly how different the values for 4 ohms and 8 ohms speakers are).

EDIT: Just saw your latest post, no idea regarding the drivers since I've never seen any of them, but if you're going to use a prebuilt crossover you'll want to make sure to choose drivers with the same impedance, ie go with 4 ohms for both or 8 ohms for both and similar, then get a crossover for that impedance.

EDIT2: All my data for the amp and bluetooth chip comes from looking at their respective datasheets, always a good idea to look at before buying stuff.
 
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#6
PMental said:
Beware that the amp chip (two of them on your board) is only rated at 1x10W at 8 ohms (which your woofer is and I'm guessing you ordered the 8 ohm version of the tweeter too), and that's at 10% THD+N distortion. 10% distortion is terrible so you'll never want to use it that high so you probably only have something closer to 2x5W usable power, which is a bit on the low side considering the speakers probably aren't that sensitive either.

You might want to rethink the amp choice. I'd go with something more powerful, and if you haven't bought speakers yet going for 4 ohm ones will get you some more power out of the 12V drive voltage.

Make sure the input sensitivity (gain) is high enough on the amp you choose as well, that Bluetooth chip puts out ~0.6v RMS, and many amps require more than that to get full output, meaning that even turned to max they might not play loud enough, but you'll still get the negative effects of turning them up (eg. the noise will be turned up).

The crossover specs look strange too, it says 4ohm 8ohm, but the parts values for the same frequency and slope crossover is very different from 4 ohms and 8 ohms, so the 3.3Khz is only true for one of them. You might want to look around for something else, or use something like the Parts Express crossover guide for component values to use to build your own (here you can also see plainly how different the values for 4 ohms and 8 ohms speakers are).

EDIT: Just saw your latest post, no idea regarding the drivers since I've never seen any of them, but if you're going to use a prebuilt crossover you'll want to make sure to choose drivers with the same impedance, ie go with 4 ohms for both or 8 ohms for both and similar, then get a crossover for that impedance.

EDIT2: All my data for the amp and bluetooth chip comes from looking at their respective datasheets, always a good idea to look at before buying stuff.
Click to expand...

Thank you for the heads up! I didn't order any parts yet so thank you for warning me about the amp. I didnt know that it only outputs 10w at 8ohms (Ill have to start looking at datasheets).
So I guess if i want to use the same 20w drivers that i listed above, I should search for an amp that outputs 20w at 8 ohms.
Also thanks for letting me know that i should match the impedance of the tweeter and the full-range, ill keep that in mind.

One more question: some tweeters have the so called "bass blocker" capacitor, in my understanding that capacitor is like a crossover, so if Im already planning to use a prebuilt crossover, then the tweeter should be without the bass blocker cap or it doesnt matter?
 
#7
Correct, if using a crossover you don't need the blocker (which makes a 1st order high pass filter btw) since the crossover handles that.

You might want to look at the Class D section for ideas on what amps you could use. Eg. something like a TPA3116 amp driven at 14V could work well.

To get an idea of power output for a given supply voltage and speaker impedance check out this post and the replies below it: TPA3116 amplifier power. It'll give you an idea on powerdraw from the batteries and you'll see that to get your desired 20W at decent distortion levels 4 ohms speakers are the way to go for a 14V supply voltage.
 
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#8
PMental said:
To get an idea of power output for a given supply voltage and speaker impedance check out this post and the replies below it: TPA3116 amplifier power. It'll give you an idea on powerdraw from the batteries and you'll see that to get your desired 20W at decent distortion levels 4 ohms speakers are the way to go for a 14V supply voltage.
Click to expand...

Thank you! I read through the thread you told me to, and found this useful formula to calculate the output wattage W(RMS) = V^2/(2Z).
So as you said, with the TPA3116 chip theoreticaly i could get ~24 w per channel with 14v supply voltage and 4ohm impedance.
But as I understood, in that thread, they were not talking about a 2way per channel setup, so if I want to use a 20w rated fullrange and a 20w rated tweeter per channel using a crossover, does the formula change? Would the 14v still be enough to drive a fullrange and a tweeter per channel?

Sorry if my english is bad, hope you understand what im saying 😀
 
#9
The crossover basically splits the power sent to the speaker between the drivers (and adds some thermal losses too). So yes, neither speaker will see 20W, but the rating on the speakers only dictate what the speakers will handle before melting basically, so you don't want to send them their full rated power anyway (which is probably overstated as well).

If you want a specification for how loud a speaker will play for a certain input, you'll want to look at the sensitivity, usually shown in 2,83V/dB/m or 1W/dB/m.
 
#10
You could first go with a single full range speaker and forget about the tweeter? Do some experiments after you have built the most basic solution. And with a small speaker you really don't gain much with two channels/stereo, well maybe then if you install them in opposite sides, so you get sound to both ways.

In my opinion it's really hard to get everything right at the first time, so that's why I'm suggesting full range and maybe even a mono amplifier in the beginning.

And make the supply as simple as possible, I would go for 4S because those step up modules might give some interference. And the 3S battery will go below 12 volts pretty quickly, because it's only 12,6 volts when full... and will go down to 9 volts when you should recharge it.
 
#11
Nenola said:
You could first go with a single full range speaker and forget about the tweeter? Do some experiments after you have built the most basic solution. And with a small speaker you really don't gain much with two channels/stereo, well maybe then if you install them in opposite sides, so you get sound to both ways.

In my opinion it's really hard to get everything right at the first time, so that's why I'm suggesting full range and maybe even a mono amplifier in the beginning.

And make the supply as simple as possible, I would go for 4S because those step up modules might give some interference. And the 3S battery will go below 12 volts pretty quickly, because it's only 12,6 volts when full... and will go down to 9 volts when you should recharge it.
Click to expand...
Well you see, I actually already built a simple speaker like that, well it was dual channel but with no tweeters, crossovers. Everything was pretty straightforward, but the only issue i had was determining the right amount of voltage that i should supply the amp, that would be best for the speakers that i was using. But now i think i know how to pick the right amp and how to pick the right voltage (thanks to this thread), so thats why I want to go slightly more advanced and try to build a dual channel, fullrange-tweeter setup even though i might fail ..

Edit:
Also im planning to separate the two sides of the speaker enclosure for the right and left channels.
And im in progress of looking for other full range drivers that would be 4inches in diameter, so that the full range-tweeter ratio would be 4:1 in size (PPR pointed this out in this thread), so that this setup would be worth the struggle 😀
 
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