DIY bluetooth speaker

[Nigel Goodwin]

Well that kind of sucks. Its so cheap, i was really happy.

Don't worry about it, it's another one of AudioGuru's pet hates - there are millions of similar tweeters working perfectly well in PA systems all over the world. The 15W of the other tweeter isn't an issue, as the crossover massively reduces the available power going to the tweeter - and you must not use them without a suitable crossover (even if it's only a simple series capacitor (of a suitable value).

 

[SentinelAeon]

Right now i plan to use woofer on left channel and tweeter on right channel. And i would use capacitor of value so that tweeter will only play from 2000Hz and up. So will the tweeter survive that ?

 

[Nigel Goodwin]

Right now i plan to use woofer on left channel and tweeter on right channel. And i would use capacitor of value so that tweeter will only play from 2000Hz and up. So will the tweeter survive that ?

If you're only using a single capacitor, I would tend to try and go higher (as it's a crap filter) - but it's not easy to calculate, as a piezo doesn't have a 'fixed' impedance. Piezo's are self filtering anyway (but a capacitor won;'t do any harm), you should also fit a series resistor to limit current through it (10 ohms should be OK).

Why are you using them on different channels?.

 

[audioguru]

If you connect a resistor in series with the tweeter then the total resistance is higher causing the total power to be lower. 50W into 8 ohms is 20V RMS which is 56.6V peak-to-peak that can be produced buy a bridged amplifier powered from about 25VDC or 26VDC.
Connect a 6.8 ohms resistor in series with the 8 ohm tweeter then the total of 14.8 ohms draws 27W. The 8 ohm tweeter gets 14.6W and the resistor heats with 12.4W when playing a constant tone at maximum output. The series capacitor to reduce frequencies below 2kHz will be 5.4uF. Of course the tweeter will play at -10.5dB but it is probably more sensitive than the woofer anyway.

 

[Nigel Goodwin]

If you connect a resistor in series with the tweeter then the total resistance is higher causing the total power to be lower. 50W into 8 ohms is 20V RMS which is 56.6V peak-to-peak that can be produced buy a bridged amplifier powered from about 25VDC or 26VDC.
Connect a 6.8 ohms resistor in series with the 8 ohm tweeter then the total of 14.8 ohms draws 27W. The 8 ohm tweeter gets 14.6W and the resistor heats with 12.4W when playing a constant tone at maximum output. The series capacitor to reduce frequencies below 2kHz will be 5.4uF. Of course the tweeter will play at -10.5dB but it is probably more sensitive than the woofer anyway.

Just to confirm for the OP - nothing in this post applies to piezo tweeters, AG is referring to moving coil ones.

 

[SentinelAeon]

HORN:
Ok so this horn tweeter poses another problem, it is big and i will have to calculate its volume to add to the enclosure, which wont be simple cause i doubt i can find any data on the speakers. It says that the speaker itself already has protection and doesn't need capacitors. And since its rated at like 50W with maximum of a crazy amount, i will only use resistor in series if i think its to loud compared to woofer.

NORMAL:
I also ordered 4 more normal tweeters for about 4€ a piece. Its rated at 10W, aliexpress title actualy says 15W, so that maybe maximum. Here i will use capacitors to cap its frequencies and also add a series resistor to makesure its not blown. It seems to work ok with 2x25W amp even if its rated at 10W(15W). But 2x50W, i wouldnt be so sure.

As to why i am using them on different channels: i found an awesome cheap amp of 2x50W with volume button. It is stereo. I know the right way would be to do a crossover with 2 tweeters and 2 woofers but sadly if i do that, i will make zero profit on the speaker or might actualy end up losing money. So ofcourse, the best way would be to find 1 100W mono amplifier. I ordered some but will need to test them. Like i said, this 2x50W, its like 2-3 euros and to me its awesome. When i make myself a better speaker, i will use 2 woofers and 2 tweeters. Also just another thing i want to add. First when i got this amplifier, i was sure i want to use its full power of 2x50W. But it can be misleading. If i only use 2x25W, i will barely notice the difference and it will draw 2x less power. And i can very easily do that, look at this chart, i can control power usage with voltage and with impedance of speakers. So i ordered 3S and 4S BMS with balance which was quite cheap and easy to connect, and i will just do like 3S2P connection and that means i can use my not so good batteries. Cause with 2x50W = 100W and 25V,i could theoreticaly need 4A and 4A would drop my batteries so low BMS would cut them off. I tested the batteries. On 1A draw, they have capacitory of 1500-2500mAh, depending on the battery. On 2.5A draw, they only have 100-800mAh. But if i use for instance 12.6V with 4 ohm woofer and 8 ohm tweeter, theoretical this is 32W total, which is max of 2.5A. But since i have batteries in series also, that splits to half, which is 1.25A, which all my batteries can easily handle. This is real good news to me and i doubt buyers will notice difference between 2x25W, 2x30W and 2x50W. Ok, so here is the chart from that amp:


12V--8 ohms/12W+ 12W, 4 ohms, greater than 20W + 20W
15V--8 ohms/18W + 18W, 4 ohms/greater than 30 + 30W
19V--8 ohms/32W + 32W, 4 ohms/greater than 45 + 45W
24V--8 ohms/38W + 38W, 4 ohms/greater than 50 + 50W

Ok so for instance, for the horn setup, i can do 24V or 16.8V since horn will survive. But for the other 15W tweeters, i can just do 12.6V or 16.8V and since tweeter is 8 ohm it will only draw a maxximum of 12W or 18W. Which i think it should survive, or i could just add a tiny resistor to be safe.

 

[audioguru]

A 3S lithium battery is 12.6V fully charged. A bridged class-D amplifier output will be about 24V p-p which is 8.5V RMS. Then the output power is 9W into 8 ohms or 15W into 4 ohms per channel. The amplifier datasheet probably says the output power with massive distortion that you do not want.

A 4S battery is 16.8V fully charged. Then the amplifier output power will be 16W into 8 ohms or 27W into 4 ohms.

Since your amplifier has only a bluetooth input then you cannot add its channels to make mono. I think the average maximum power from the amplifier will be close to only one channel output power.

 

[SentinelAeon]

I will need to do some testing. I measure with killawatt the total power draw. I know its not correct measure cause music is higher than 50Hz and killawatt cant keep up. But i tested this amp with a 3 ohm speaker and i reached an impressive 60W on 1 channel. I know this is overdriving amp, i just did it for testing purposes. And only in that unnaturaly bass amplified song, which is nowhere near a normal song.

I will obviously have to do a lot of testing. Sometimes numbers arent all. For instance, i will try 12.6V and test it. Maybe it will be loud enough as it is ? Then i will test 16,8V and see how it compares.

My biggest problem as u can remember was finding a nice cheap woofer. And that TCP115 is really great for its price, also i have all speaker data so its easy to calculate port and i dont have to deal with passive membranes and hoping for a stroke of luck.

I will keep you posted on how my testing goes. Btw, just for the fun of it, i ordered some amplifier without bluetooth. And then i ordered a bluetooth board. So connected together, i get a bluetooth amplifier, but good thing about this is that there are a lot better and cheaper amplifiers that arent bluetooth. For instance i can simply buy a 100W mono and do a crossover. Or i can buy stereo one, that has a separate volume knob for each channel. So i can easily tune them, for instance reduce volume of tweeter. And i tested it on my amp with the button - using a button to reduce volume isnt like a resistor - i will not be using power for heating the resistor. If i put volume knob on 50%, i reduce the power draw by 50%.

 

[SentinelAeon]

If i have 38W per channel and 8 amp speaker. How big would a resistor in series need to be to limit that wattage to 15W ?

 

[audioguru]

An amplifier that produces 38W into 8 ohms has an output of 17.5V RMS which is 50Vp-p so the bridged class-D amplifier is powered from 26VDC to 28VDC?
Maybe the 38W is Whats and not Watts?
Which amplifier and what power supply voltage?

Maybe the speaker is 8 ohms, not 8A? Then 38W into 8 ohms is a voltage of 17.5V RMS. 15W into 8 ohms has a voltage of 11V RMS and a current of 1.37A.
Then the resistance in series with the tweeter has 17.5V - 11V= 6.5V and has 1.37A and is 6.5/1.37= 4.7 ohms. It heats with 9W.
The series capacitor to cut frequencies below 3kHz is 4.2uF. Use 4.7uF for a -3dB cutoff frequency of 2680Hz.

 

[SentinelAeon]

It will be like 25V and sheet says 38W at 8 ohm speaker (8 ohm obviously, not 8 amp lol). I have capacitors ready to cut everything under 2700Hz yes. As for resistance ... i just thought of a simple way. I will simply plug the tweeter into an amplifier. Then use killawatt to measure how much wattage it uses. Obviously amp standby uses some wattage but anyway, the point is, when i get over 15W, i can add resistor. And i increase its value until at full volume it is like max 20W.

 

[audioguru]

I have owned and used many tweeters in my life but have burned out only one, my first one when I was a teenager. I set the speaker in my open window and fed continuous 19kHz to the amplifier. Then I went for a walk to hear how far it would go. It stopped working. It was rated for 25W and I fed it only 6W.

 

[SentinelAeon]

So what was the reason it burned out ? Freak accident ?

 

[SentinelAeon]

Btw, this appears to be the tweeter i ordered:

https://www.hdic.com.hk/?topclassid=11&classid=182&id=371

 

[audioguru]

Your tweeter is rated at 10W. Then it can play vocals or music from a 10W amplifier. But they are Chinese Whats.
My first tweeter was American and burned out because I played continuous high frequency sound, not vocals or music.
Many people burn out tweeters because they play loud very distorted rock "music".

 

[SentinelAeon]

Hmm. Well i will need to be careful then, good thing the tweeter is really cheap and in my previous speaker i was really happy with its performance. It would be great if i could find a decent tweeter for like 5€ from a good store, like soundimports. But all i found under 5€ there was that crazy horn thingy that will barely fit into my case. I would feel much better if i found a cheap tweeter like this that could handle at least 25W. Then i wouldnt have to worry that much. Cause resistor infront of tweeter is fine but that is lost battery life in the form of heat

 

[Nigel Goodwin]

Hmm. Well i will need to be careful then, good thing the tweeter is really cheap and in my previous speaker i was really happy with its performance. It would be great if i could find a decent tweeter for like 5€ from a good store, like soundimports. But all i found under 5€ there was that crazy horn thingy that will barely fit into my case. I would feel much better if i found a cheap tweeter like this that could handle at least 25W. Then i wouldnt have to worry that much. Cause resistor infront of tweeter is fine but that is lost battery life in the form of heat

You don't have any issue - simply feed the tweeter via a proper crossover and it won't receive anywhere near it's rated power. The important thing is the crossover frequency, and how sharp the cut-off is - you should use at least one capacitor and one inductor really - if you crossover too low the cone will move to much, and break the wires to the coil. Also, the lower you cross over, the higher the percentage of power goes to the tweeter.

 

[SentinelAeon]

Like i said, i havent got my 100W mono yet so for now i have to do tweeter on left channel and woofer on right channel. Not optimal i know, i am still waiting for the amplifier. Such a shame though cause i really love this 2x50W amp.

Anyway i did a little test. I used 7uF on the tweeter to do crossover at about 2800Hz. Then connected it to my 50W amp, put on some music and slowly increase the volume. The maximum value i recorded was 7W and keep in mind my amp + external DC power suply together eat about 3W. So i should be more than safe, if there is such thing as safe in cheap chinese tweeter trade.

The tweeter is quite loud, after a few seconds of listening to it at maxximum volume, i started hearing strange distortions in my ear and my head started spinning. Such high frequencies, i certanly dont want to be near when someone will drive it at maxximum.

 

[Nigel Goodwin]

Here's a page you should have a look at:

How much power handling do I need for a high frequency driver? | Eminence Speaker

You may need less power handling from your high frequency driver than you might expect! High frequency drivers will only see a small percentage of system power, if a proper crossover network is used. The woofer section sees the brunt …Continue reading

www.eminence.com

Bear in mind that these kinds of figures are based on 'average' music - which is why you (and AG) could kill tweeters if you apply a high power continuous sinewave above the crossover frequency.

 

[SentinelAeon]

Thank you, that link put my mind to ease and somehow goes together with my killawatt observation. I wont use any high power continuous sinewave, just normal music. Lets hope it will live long and prosper, if not, i have a cheap replacement at home. It would really suck to need to install extra resistors that would act as heaters and steal my battery life.

The new speaker is almost finished, i am just painting the case now, cant wait to see it in action. Its a 2.64L calculated with TCP115, obviously the ending enclosure is a tad bit larger, 3,04L to be precise, to adjust for all the things inside the speaker and port volume. I made a neat little excell sheet that helps me with all the calculations, like which parts i need to cut. Cause otherwise i always cut wrong, like i forget to include thickness of the wood, etc.