I was curious if the dfplayer can be used with a speaker whose specifications are:
300W MAX
20W NOM
8 ohm of impendance
I saw that most people use speakers of 3 W and 4 ohm so i'm not sure if using one of this power will burn the MP3 module. I'm feeding the module with 5v (using an Arduino).

I'm new to this site so let me know if this isn't the right forum for questions like this!

 

Hi ash,
Welcome to AAC.
I have used the MP3 module on 20Watt rated 8 ohm speakers, no problem, of course the actual audio power output will as per the MP3 specification, they sound OK

E

 

The speaker power rating is just the maximum power at which it can operate without damage.
It has nothing to do with the load on the amplifier, as that's determined by the speaker impedance.
You should not operate an amplifier with a speaker load below its rated impedance, but above that impedance is okay.

 

Welcome to AAC.

To understand the reason it is OK to use these speakers you need to know at least a little about what the specifications mean. It will help you make decisions like this in the future for yourself.

300W MAX is the absolute maximum rating. Ratings labeled this way by the manufacturer are the limits the device can experience without permanent damage or failure.

Sometimes this rating will include a time limit or temperature. Devices can often handle vey large peaks for short periods that will damage them if extended, this is about heating, so a temperature may also be included. Devices might be derated, that is, have reduced ratings for higher temperatures as they can tolerate less additional heating in such a case. Low temperatures can also affect ratings for other reasons.

You will find absolute maximum ratings for every component.

20W NOM is the nominal or ideal rating. It means the speaker will perform best, most closely meeting its other specifications like distortion and frequency response if used with this much power. This is a best case but doesn’t mean less or more won’t work well enough for any give use.

You will find something like a nominal rating for every component though some are rated by normal minimum, maximum, and typical. This maximum differs from the absolute maximum in that it is the top of the normal operating range. These numbers can also be affected by temperature and so often have a specified temperature (or range) at which they are valid.

Both of these are specified in Watts, which is a measure of power. Watts are the product of Volts and Amps. The formula is \( \mathsf{W=V \times A} \). Power is the amount of work that can be done, so all things being equal, delivering higher power would be louder in the case of speakers.

Be very clear that the speakers themselves are loads. That is, they use electrical energy and transduce it to acoustic energy. So, they will never add to a signal, they always represent a loss due to inevitable inefficiencies found in every component. The will have an efficiency rating though and a speaker with a higher efficiency will convert more electric energy to acoustic, being louder for a given input. This all about “wasting” less of the input as heat.

8Ω is the impedance of the speaker’s coil. Impedance is the tendency for the coil to resist the application of the signal. It is akin to DC resistance, but it is about AC instead. Impedance is complicated and changes with frequency. It’s worth learning about, but for our purposes here it can be understood as how hard the amplifier has to work to drive the voice coil. (This is a very simplified but functional version of the truth).

This means that an amplifier that has an 8Ω output impedance will perform closest to its specifications with a matching speaker, but also that if you were to connect it to a 4Ω speaker it would not be able to be turned up fully without additional distortion. Conversely, a 4Ω amp on an 8Ω speaker will not be able to drive it to the same volume as the expected one.

So the rules for specifications in general are like this:

• A supply that exceeds the voltage rating of the load is going to do damage because it is the supply that determines the voltage that will be present in the circuit.
  
  
• A supply that exceeds the current rating of a load is not a problem because it is the load’s resistance combined with the supply voltage that determine this the current that will flow.
  
  
• A supply with an insufficient voltage rating connected to a load will not power it, but also won’t be harmed or do any.
  
  
• A supply with an insufficient current rating (but sufficient voltage) connected to a load can be damaged by it since it is the resistance of the load that determines the current.

Translating these into corollaries for amps and speakers:

• An amp that exceeds the power rating of a speaker can damage it if it is made to deliver too much power.
  
  
• An amp that has a lower power output won’t harm a speaker but may not be able to drive it to a useful level.
  
  
• An amp with a higher impedance rating connected to a speaker can be damaged by if it is made to exceed its own maximum ratings by increasing the gain to the point of overheating the output stage.
  
  
• An amp with a lower impedance rating connected to a speaker won’t be harmed but may have trouble driving the speaker to a useful level.

These are more heuristics than rules, and a full understanding of why these things are true in general will help you understand the exceptions.

 

I could not find detailed audio specs for the module. One mono 8 ohm speaker is recommended then if its amplifier is bridged, the output power with a 5V supply will be less than only 1.5W which is not loud. Distortion and frequency response are not mentioned.

 

If the audio output rating of the MP3 player is not known, then look at the input power rating, which is probably in watts. If the electrical input (Mains power) rating is less than the power rating of the speakers, then certainly the output power to the speakers will also be less, and thus no damage from output power will happen. his does not mean that the operation will be satisfactory, but only that no damage will be done.

 

Welcome to AAC.

To understand the reason it is OK to use these speakers you need to know at least a little about what the specifications mean. It will help you make decisions like this in the future for yourself.

300W MAX is the absolute maximum rating. Ratings labeled this way by the manufacturer are the limits the device can experience without permanent damage or failure.

Sometimes this rating will include a time limit or temperature. Devices can often handle vey large peaks for short periods that will damage them if extended, this is about heating, so a temperature may also be included. Devices might be derated, that is, have reduced ratings for higher temperatures as they can tolerate less additional heating in such a case. Low temperatures can also affect ratings for other reasons.

You will find absolute maximum ratings for every component.

20W NOM is the nominal or ideal rating. It means the speaker will perform best, most closely meeting its other specifications like distortion and frequency response if used with this much power. This is a best case but doesn’t mean less or more won’t work well enough for any give use.

You will find something like a nominal rating for every component though some are rated by normal minimum, maximum, and typical. This maximum differs from the absolute maximum in that it is the top of the normal operating range. These numbers can also be affected by temperature and so often have a specified temperature (or range) at which they are valid.

Both of these are specified in Watts, which is a measure of power. Watts are the product of Volts and Amps. The formula is \( \mathsf{W=V \times A} \). Power is the amount of work that can be done, so all things being equal, delivering higher power would be louder in the case of speakers.

Be very clear that the speakers themselves are loads. That is, they use electrical energy and transduce it to acoustic energy. So, they will never add to a signal, they always represent a loss due to inevitable inefficiencies found in every component. The will have an efficiency rating though and a speaker with a higher efficiency will convert more electric energy to acoustic, being louder for a given input. This all about “wasting” less of the input as heat.

8Ω is the impedance of the speaker’s coil. Impedance is the tendency for the coil to resist the application of the signal. It is akin to DC resistance, but it is about AC instead. Impedance is complicated and changes with frequency. It’s worth learning about, but for our purposes here it can be understood as how hard the amplifier has to work to drive the voice coil. (This is a very simplified but functional version of the truth).

This means that an amplifier that has an 8Ω output impedance will perform closest to its specifications with a matching speaker, but also that if you were to connect it to a 4Ω speaker it would not be able to be turned up fully without additional distortion. Conversely, a 4Ω amp on an 8Ω speaker will not be able to drive it to the same volume as the expected one.

So the rules for specifications in general are like this:

• A supply that exceeds the voltage rating of the load is going to do damage because it is the supply that determines the voltage that will be present in the circuit.
  
  
• A supply that exceeds the current rating of a load is not a problem because it is the load’s resistance combined with the supply voltage that determine this the current that will flow.
  
  
• A supply with an insufficient voltage rating connected to a load will not power it, but also won’t be harmed or do any.
  
  
• A supply with an insufficient current rating (but sufficient voltage) connected to a load can be damaged by it since it is the resistance of the load that determines the current.

Translating these into corollaries for amps and speakers:

• An amp that exceeds the power rating of a speaker can damage it if it is made to deliver too much power.
  
  
• An amp that has a lower power output won’t harm a speaker but may not be able to drive it to a useful level.
  
  
• An amp with a higher impedance rating connected to a speaker can be damaged by if it is made to exceed its own maximum ratings by increasing the gain to the point of overheating the output stage.
  
  
• An amp with a lower impedance rating connected to a speaker won’t be harmed but may have trouble driving the speaker to a useful level.

These are more heuristics than rules, and a full understanding of why these things are true in general will help you understand the exceptions.

Thank you for the explanation. When I started testing the module was worried I could overpower something, but i'm glad there i'snt really a problem (just that the speaker won't performace won't be as good). Once again, thank you for your reply

 

Overpower? A car battery has gobs of power, 600 cold-cranking Amps so it can start the cold car engine when the cold oil is thick.
In the summer the car battery is warm and it can produce maybe 1000A for a few seconds.
But the little clock in the car runs fine using maybe only 5 thousands of an Amp.

The module's amplifier can produce less than 1.5W into an 8 ohm speaker. The amplifier still produces only less than 1.5W into a 8 ohm/300W speaker that can be driven with a much more powerful 300W amplifier.

I disconnected the little speaker in my clock radio and enlarged a few coupling capacitors to pass bass frequencies. It drives a 40W speaker fine and sounds great. The 0.5W output from the amplifier in the clock radio is loud enough in the better speaker but does not blast very loud 40W in my bedroom.