# Different Pass filters for different speakers.

Apr 26, 2017
38
I recently ordered 5 amplifiers from Aliexpress which are all the same kind - TDA2030A. Ive got some speakers lying around that i could build a speaker out of. I havent come up with a design yet where im exactly going to put the speakers, but ive got a box for the speaker and the speakers themselves, the amplifiers havent came yet. In the mean time, my design is - have a speaker for low freqs at the bottom, middle ones at the middle of the box, and the highs handeled by 2 small tweeters from a car that i salvaged some time ago. All the amplifiers output the same amount of wattage and freq range, i want to use 3 amplifiers in total - 1 for the lows, 1 for the mids, and 1 for the 2 car tweeters, but the problem is, how can i filter out the unneeded frequencies for each speaker, i know how to do it for tweeters - just put a capacitor before the tweeter, but how can i filter out the audio for the remaining 2 speaker kinds and what should be the freq range for each speaker that i should use ( For example - 0 - 300hz for sub )?

#### Audioguru

Sep 24, 2016
3,639
A very cheap speaker uses only a capacitor feeding the tweeter in its crossover network. The cutoff slope is very gradual so a lot of low frequencies are still poorly produced. Since you have an amplifier for each type of speaker then you need an active crossover circuit that uses many resistors and capacitors for sharp cutoffs and some opamps.

The datasheets of the speakers will show recommended frequency ranges so that the woofer does not shriek and the tweeter does not groan. The woofer should have an enclosure designed for its detailed spec's.

Here is a link to an audio site and a 3-way active crossover network: http://sound.whsites.net/project09.htm

#### kellys_eye

Jun 25, 2010
4,775
You could also use active filters at the input to the amplifiers. These can be made with far more accurate (and steep) responses.

Look into 'reflex cabinets' too - the best speaker systems have cases that actively assist in sound reproduction using internal baffles, wool etc.

Apr 26, 2017
38
A very cheap speaker uses only a capacitor feeding the tweeter in its crossover network. The cutoff slope is very gradual so a lot of low frequencies are still poorly produced. Since you have an amplifier for each type of speaker then you need an active crossover circuit that uses many resistors and capacitors for sharp cutoffs and some opamps.

The datasheets of the speakers will show recommended frequency ranges so that the woofer does not shriek and the tweeter does not groan. The woofer should have an enclosure designed for its detailed spec's.

Here is a link to an audio site and a 3-way active crossover network: http://sound.whsites.net/project09.htm
It seems like that in the 3-way schematic, only 1 amplifier is being used, how can i make it to run on 3? Also, i didnt descibe this before, but each of the speakers have their own wattage, the one that im going to use as a sub is 25W, the mids are 120w max and the tweeters - well.... i dont really know about the tweeters, all i know they are aftermarket and come from a car.

#### kellys_eye

Jun 25, 2010
4,775
As I said above.... use one amplifier for each speaker and fit active filters at the amplifier inputs such that they only pass (and amplify) the range of frequencies you want. You can make quite 'steep' filters using RC networks or even better ones using a simple op-amp configured as a filter.

Since the human ear does not have a linear response to frequency there is a tendency to construct speaker systems with different power outputs for the three bands (low, mid and high) and have the frequencies that you are less capable of hearing boosted more than those that you can easily hear i.e. sub 300Hz would be higher power than the 300Hz-10kHz (say) range and over 10k the amplification would be increased again to compensate at the higher frequency end.

All you then do is parallel all the amplifier inputs and feed the outputs straight to the speakers of interest.

#### BobK

Jan 5, 2010
7,682
To do this right you would need to know the frequency tesponse and sesitivity of each of the drivers. Since they are random things you have lying around, that seems unlikely.

Bob

#### Audioguru

Sep 24, 2016
3,639
It seems like that in the 3-way schematic, only 1 amplifier is being used, how can i make it to run on 3?
Where does this active crossover circuit have only one output? It has 3 outputs, high to the tweeter amplifier, mid to the midrange amplifier and low to the woofer amplifier.

Also, i didnt descibe this before, but each of the speakers have their own wattage, the one that im going to use as a sub is 25W, the mids are 120w max and the tweeters - well.... i dont really know about the tweeters, all i know they are aftermarket and come from a car.
The Aliexpress TDA2030A amplifier costs only $0.74US and produces an output of only 2W into an 8 ohm speaker when powered from 12VDC. If the speaker is 4 ohms and/or of the supply is higher than 12VDC then the IC will overheat because its heatsink is cheap and tiny. Why does Aliexpress say that the output power is 18W?? Why do you think that a speaker rated at 120W will draw 120W from a 2W amplifier?? Why buy electronic items from the cheap Chinese website Aliexpress that knows nothing about electronics?? #### Attachments • Aliexpress TDA2030A amplifier.png 537.1 KB · Views: 108 Last edited: #### Audioguru Sep 24, 2016 3,639 Since the human ear does not have a linear response to frequency there is a tendency to construct speaker systems with different power outputs for the three bands (low, mid and high) and have the frequencies that you are less capable of hearing boosted more than those that you can easily hear i.e. sub 300Hz would be higher power than the 300Hz-10kHz (say) range and over 10k the amplification would be increased again to compensate at the higher frequency end. Wrong. Except at very low levels, a healthy human ear hears from 20Hz to 20kHz perfectly. Old people like me (72 years old) have high frequency hearing loss that is corrected with my hearing aids. Different speakers have different sensitivities then you adjust the volume controls on the amplifiers so that the lows, mids and highs sound balanced. If the speakers have an awful frequency response then maybe an equalizer can make them sound better. All you then do is parallel all the amplifier inputs Wrong. The active crossover circuit feeds the amplifiers inputs separately. #### GamingAddict Apr 26, 2017 38 Where does this active crossover circuit have only one output? It has 3 outputs, high to the tweeter amplifier, mid to the midrange amplifier and low to the woofer amplifier. Ok, sorry about that, i thought that you need to put an amplifier before the circuit, not after. The Aliexpress TDA2030A amplifier costs only$0.74US and produces an output of only 2W into an 8 ohm speaker when powered from 12VDC. If the speaker is 4 ohms and/or of the supply is higher than 12VDC then the IC will overheat because its heatsink is cheap and tiny.
Why does Aliexpress say that the output power is 18W??

Why do you think that a speaker rated at 120W will draw 120W from a 2W amplifier??

Why buy electronic items from the cheap Chinese website Aliexpress that knows nothing about electronics??
1. im aware of that it might not be 18W, cause, well, its aliexpress and its china. Also, im not getting only 1 circuit, im getting 5 in a bulk.

2. If i want to use the amplifiers in a ''''custom built'''' amp and use them on higher voltages than 12 volts, its not really a big problem for me to take an old heatsink, drill holes, tap them, unsolder the ICs, solder wires to both - the ics themselves and the boards, and screw them to the heatsink. Im not sure, but i can bet that they all together cant exceed 50W Thermal Design Power, those 3 words are usually used for pcs only, but why not use them here.

3. Ive never thought that, and i completely understand that the speaker would never run on its max with this amplifier.

4. 2 words - theyre cheap. Dont say that you have never ordered atleast something thats related to electronics from ebay/aliexpress.

#### Audioguru

Sep 24, 2016
3,639
Ok, sorry about that, i thought that you need to put an amplifier before the circuit, not after.
A quick look at the datasheet of the TDA2030A shows that its maximum allowed output current is 3.5A peak so that its maximum output power to a 4 ohm speaker is 22W if the supply voltage is 36V.
But the maximum allowed output current for an opamp is only about 0.02A then its output power to a 4 ohm speaker is 0.0008W which is nothing. The TDA2030A is a power amp and the opamp is a very low power amp.

If i want to use the amplifiers in a ''''custom built'''' amp and use them on higher voltages than 12 volts, its not really a big problem for me to take an old heatsink, drill holes, tap them, unsolder the ICs, solder wires to both - the ics themselves and the boards, and screw them to the heatsink.
What about replacing all the tiny resistors with larger more powerful resistors what about replacing all the capacitors with larger higher voltage capacitors? Replace the entire amplifier board if you want more power than only 2W.

Dont say that you have never ordered atleast something thats related to electronics from ebay/aliexpress.
I have never ever bought cheap poorly made or fake Chinese junk from ebay, Amazon, aliexpress or Bangood.
I buy genuine electronic parts from authorized distributors like Digikey and Newark.

Apr 26, 2017
38
A quick look at the datasheet of the TDA2030A shows that its maximum allowed output current is 3.5A peak so that its maximum output power to a 4 ohm speaker is 22W if the supply voltage is 36V.
But the maximum allowed output current for an opamp is only about 0.02A then its output power to a 4 ohm speaker is 0.0008W which is nothing. The TDA2030A is a power amp and the opamp is a very low power amp.

What about replacing all the tiny resistors with larger more powerful resistors what about replacing all the capacitors with larger higher voltage capacitors? Replace the entire amplifier board if you want more power than only 2W.

I have never ever bought cheap poorly made or fake Chinese junk from ebay, Amazon, aliexpress or Bangood.
I buy genuine electronic parts from authorized distributors like Digikey and Newark.
Well, okay, you got me about those china electronics, but still! Some pretty well known Electronics youtubers buy parts from aliexpress/ebay, like Great Scott! and Aftotechmods ( not really sure ).

According to STMicroelectronics TDA2030A chip datasheet, the absolute maximum it can take is 22 Volts, so there is no way it can take 36V and output 22W of power. Also, in the datasheet, i found a schematic for 3-way amplifier, and ive got some parts at home, and i could take some, with permission of course, from my electronics lessions, so, from 1 way, i think this thread is done.

#### Audioguru

Sep 24, 2016
3,639
The datasheet for the TDA2030A says that its absolute maximum supply voltages are plus and minus 22V which is a total of 44V!
Its power is spec'd at 18W with low distortion into 4 ohms when its supplies are plus and minus 16V which is a total of 32V. At 10% distortion the output into 4 ohms with the 32V supply is about 22W.
A graph shows 17W into 8 ohms when its total supply is 40V.

I think your cheeep little Aliexpress amplifiers will be quickly destroyed if the supply is higher than 12V and the output power from each is higher than 2W.

Apr 26, 2017
38
The datasheet for the TDA2030A says that its absolute maximum supply voltages are plus and minus 22V which is a total of 44V!
Its power is spec'd at 18W with low distortion into 4 ohms when its supplies are plus and minus 16V which is a total of 32V. At 10% distortion the output into 4 ohms with the 32V supply is about 22W.
A graph shows 17W into 8 ohms when its total supply is 40V.

I think your cheeep little Aliexpress amplifiers will be quickly destroyed if the supply is higher than 12V and the output power from each is higher than 2W.
Well, theres really only one way to find out - by hooking them up to a large heatsink, by desoldering them and pushing in 36 volts, cause thats the highest i can go with the equipment ive got. Then if you can, recommend me a proper Audio amplification IC from the TDA series or something like that, and one thats not SMD, cause, im really not into SMD soldering.

#### Audioguru

Sep 24, 2016
3,639
The small cheap Aliexpress amplifiers are designed to be powered from 12VDC. The tiny resistors and tiny low voltage capacitors will release their "magic smoke" if you increase the supply voltage.

There are many fairly old TDA amplifier ICs in through holes packages because their design is class-AB which gets fairly hot. Texas Instruments make many modern amplifier ICs but they are in tiny SMD packages because they are class-D which does not get hot. Texas Instruments purchased National Semiconductor and sell some of their LMxxxx amplifier ICs.

Apr 26, 2017
38
The small cheap Aliexpress amplifiers are designed to be powered from 12VDC. The tiny resistors and tiny low voltage capacitors will release their "magic smoke" if you increase the supply voltage.

There are many fairly old TDA amplifier ICs in through holes packages because their design is class-AB which gets fairly hot. Texas Instruments make many modern amplifier ICs but they are in tiny SMD packages because they are class-D which does not get hot. Texas Instruments purchased National Semiconductor and sell some of their LMxxxx amplifier ICs.
Sorry for the late answer, but yeah, i started to think of that too. Recently i remembered that my dad gave me his old car radio, that stopped working. It got a pin code on it, and he forgot it. I took that apart, and searched every IC on alldatasheet.com, and found out that theres 2 audio amps on the circuit board, both of them are TDA7375s and are fairly simple to hook up, so i might do that.

Apr 26, 2017
38
I just found this schematic online, and this is what i might make.

The only thing i dont understand is - what is SL and SR ?

#### Audioguru

Sep 24, 2016
3,639
SL is surround Left and SR is surround Right. Most cars have 4 speakers, 2 in the front doors and two on the rear shelf. I have never heard surround sound in a car.

The output power with the 15V supply shown and 8 ohm speakers is about 2.6W per channel and into 4 ohm speakers the power is about 4.5W per channel. If two amplifiers are bridged then the output capacitors are not needed and the power into an 8 ohm speaker is about 9.1W and into a 4 ohm speaker the power is about 15.8W.

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