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Videos / How to Use Speakers and Amplifiers with Your Project

A popular question that we get all the time is ‘How do I choose a speaker or amplifier to go with my project?'

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Hey guys, how you going Sam here from core electronics and today I want to answer a couple of questions that we've had from people who are trying to integrate audio into their project so how to use speakers and amplifiers either in their existing project or how to pick new ones for a whole new project so we're going to take a look at some of the terminology that's used for audio devices so that I feel like once you understand the terminology and what all the different phrases mean that's really easy to go in out and pick the correct amplify the correct speaker for the project that you're trying to work on and then I'll go through and recommend some of my favorite products that I'd recommend for different applications or projects so first up we'll look at amplifiers first and then speakers.
So I've just got a little 20 watt, well little but powerful 20 watt stereo amp board here but more on that later so an amplifier wattage you'll often see well, in fact, you'll always see amplifiers rated in watts which are a measurement of the amount of power they are able to output not the amount of power they consume because that's a combination of amplifier efficiency versus output power...anyway its output power output watts and you don't need to worry about watts as a product of voltage and current like you would with you know a typical power draw measurement what's is simply a measurement of power. So amplify wattage is the amount of power it can output.
Then we have the amplifier classes so you'll see on amplifier boards they might say Class A you know Class C, Class D, Class A/B all these different letters and that just refers to the topology the type of circuit that the amplifier is using and different circuits give you different efficiencies so obviously the input power required compared to the output power so how efficient they are converting their electrical supply into output power you know losses, waste such as heat and efficiency as well as sound quality so generally speaking and a Class A amplifier is the least efficient, best-sounding amplifier and as you go through and up right through to generally Class D amplifiers where we stop there but there also extremely common especially for DIY projects when you're talking about class-a amplifiers you really talk about high-grade audiophile level amplifier topologies, which aren't used in DIY maker or even most project boards at all so pretty much every amplifier board we have a lot of them are from Adafruit are class D amps and you're not going to notice sound difference when we're talking about the sort of project that most of us are making until you get to really high-end audio sort of stuff.
Next up is amplify interfaces so what sort of interface it accepts either is the audio input or as a form of control so most amplifiers are simple analog boards they take an analog input your signal and it can either be a differential signal or just a single signal with a ground so you'll either see it as input plus minus which allows for a differential signal from a differential supply or it will be, it might just say input and ground in which case you've just got to be careful about what type of input you are feeding it based on the supplier. A board I recommend further down, for example, the Adafruit 2.5 watt mono board accepts both a differential and non-input so you can really pick and choose what you're getting but just something to keep in mind when you're going from your source to your amplifier.
The other thing is whether it has a digital interface or not, some amp boards specifically designed for Raspberry Pi's for example will have a digital perhaps an iOS interface other ones this guy just accepts analog audio in but it also has an I2C interface for volume control which is pretty handy so different interfaces on different amplifiers something to be aware of and of course power supply it sounds fairly common sense but make sure you match up the voltage for your amp and if you're using little boards like this you're not going to need to worry about having heaps of current on tap most power supplies even battery-powered ones for the single figure what amplifiers and even you know this 20 watt amp could probably run on a battery power supply if you design it well so nothing to worry about there especially at these low wattage level amps.
So that is all about amplifiers in a nutshell and now we're going to take a look at how you need to match those with your speaker.
So we have the speaker wattage now the speaker wattage is how much power the speaker is able to handle the speaker is able to handle I should say so a larger speaker can handle more power a small speaker can handle less power [Head exploding noise] what I know bear with me so a really big speaker can handle lots of power and that's because it literally has bigger coils it's put together more meatily because a speaker is really nothing more than using the motor phenomenon with as an electromagnet so there's a coil and there's a magnet here and when you apply a voltage to it when you have a current running through it it creates this magnetic field and the whole idea is it pulls the cone of the speaker back and forth which moves the speaker which causes these pressure waves and there's a lot of physics behind it but electro-magnet creates linear motion from an electrical signal that's how speaker works so a more heavy-duty speaker has much heavier winding because it's a beefier unit. Now how does that match up with our amplifier wattage well there's a lot to it especially if you're going into hi-fi and high-end audio systems where you're matching all these different specs but it's pretty straightforward when you're dealing with smaller units. General rule of thumb is have a higher rated speaker than the output amplifier power so it doesn't always mean that the amplifier is going to put that much power up but that's just its capacity so you want to make sure that you're speaking can handle that leave a little bit of room for error for example this is a 3 watt speaker in a project a sound buzzer I was using I used a 2.5 watt amplifier says a little bit of head room there which is ideal to make sure that you don't damage anything so that's pretty much a general rule of of thumb is make sure it's at least matched and give yourself a little bit of wiggle room.
Next up we've got passive vs. powered speakers or active speakers and this one's really straightforward if you're having to use an amplifier for your speaker and your speaker just has two tabs on it and it's a passive speaker and it requires an amplifier to drive the speaker powered speakers such as once you find for phones, computer accessories are powered by a USB or an external power supply pretty much just take a line level input you know I could put a head phone jack. Line level is just a specific definition for a signal type of signal but we're always going to be talking about passive speakers and you know in the amplifiers when we're talking about these things so just ignore active speakers we're just talking about passive speakers.
Now speaker impedance in ohms this is the other big one you want to watch out for I can see on the back here now if you can read that it says four and then we've got the symbol for ohms three watt so speaker impedance. So impedance is a bit like resistance but for AC signals and as we serve a speaker consists of a winding of a coil and that coil is going to help determine the impedance of the speaker so imagine you've got a battery this is how I like to think of it because it can be really confusing when people are talking about matching impedance let's say you've got a battery hopefully we all know that you can't just short out the battery and stick a wire across there you have to have a significant resistance or a load in order for the battery not to you know to draw too much current and explode may not explode but you get the point and it's the same thing with the speaker if an amplifier output is rated for let's say 8 ohms a minimum of 8 ohms and you attach a 4 ohm speaker then it's a bit like shorting out to the output of an amplifier it's not designed for that and most amps are going to have a speaker rating and impedance rating again the 2.5 what mono amp I was talking about before has a either a 4 ohm or an 8 ohm speaker generally 4 8 and 16 are the most common speaker impedances so just just stick to what the amplifier spec says and you'll be fine go outside of that you probably won't be fine just stick to it especially don't use a lower impedance speaker than the output of your amplifier.
Speaker wiring this is another easy one if it's mono F then you can connect the terminals of your speaker to the outputs you don't really have to worry about the polarity of it just going to determine the phase of the speaker ie if it's pushing when it should be pulling and that's that's not a huge deal but look it's got plus or minus its got plus or minus they just match it up easy as that and if you do don't attach more than one speaker to the same terminal otherwise you can run into issues especially with these passive speakers and if it's a stereo amplifier you want to use separate channel so that is should always have separate solder pads or terminal blocks to connect the two speakers up to.
So I mentioned there are a few different products that I recommend for different projects one of which I've been talking about the whole time the mono 2.5 watt Class D amplifier from Adafruit, it's awesome I've got those three amplifiers here and I have recommended combining it with this speaker it's a really great combination then stepping up you've got a stereo 3.7 watt class D audio amplifier it more power its stereo really good and then if that's not enough for this guy that I'm holding right here twenty watts monster class D audio amplifier at stereo so each channel is capable of handling twenty watts it's awesome it's got IVC connectivity it's got all this you can control volume with either an onboard potentiometer or you start you solder to the pins or with a serial signal as I said it is really really cool but you're going to need to make sure that you've got speakers that can handle it and that is the Big Bertha of you know DIY maker amplifiers that we carry.
So that is a bit about speakers and amplifiers things you need to watch out for we've taken a look at all of the common terminology and the thing is there's so much science and physics and complexity in this area especially once you dive into high and you know audiophile level matching and amplifiers and products but as far as the kind of the kind of signals that we're going to be using the level of amplifiers and speakers and things like that you don't need to over-complicate you don't need to worry about whether it's a Class D or a Class A amplifier just pick one that has the amount of power you need for your project don't about matching decibels compared to RMS compared to how long you know the real perceived loudness of the speaker look just get you a little three watt amplifier test it out and if it's not loud enough get a bigger one otherwise get a small one make sure you match your speaker off and that's all I had for you today guys hopefully you can take this and create some really awesome projects if you're only if you do have a project or you know something you're working on which does use some of these gear and you found this useful then leave a comment down below we'd love to hear from you and be sure to check out some more of our other tutorials and projects I'll see you next time guys.                                                  

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