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Steve Browning

Loudspeakers - how?

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Posted (edited)

I have often wondered this but never asked.

A loudspeaker is, basically, a mechanical device. The current in the coil promotes the movement of the cone. My question is, how does a speaker 'do' tone? What happens when I turn up the treble control? How does the speaker translate that into an audible change?

Edited by Steve Browning

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The speaker doesn't translate a change in the treble control. It merely passes on the information supplied to it by the amp. When the treble control is turned up the pre-amp increases the high frequency content relative to the rest of the audio spectrum.

Speakers do influence tone to the extent that the audio signal they reproduce isn't exactly the same as the electrical signal they receive from the amp. This is called 'coloration'. The ideal hi-fi speaker has no coloration, while guitar speakers intentionally have very high coloration. Bass speakers lie in between those two extremes.

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That's my question really. How does it pass on that information? The speaker is the only thing that transmits the sound/tone to the listener so what is happening that makes the cone pass on the difference?

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A loudspeaker is a transducer. It converts the electrical waves coming from your amp into more--or-less* equivalent compression waves in the air.

 

*More = hi-fi, FRFR etc; less = 'coloured'; very much less = crap sound.

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5 hours ago, Bill Fitzmaurice said:

The electrical signal to the voice coil has changed.

I realise that but it is still the same cone moving and it can only go in and out. It's that in and out that I am trying to understand. I am possibly overthinking this!!

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Posted (edited)

The cone reproduces different frequencies by vibrating at different speeds. At low frequencies it moves in and out, say, 40 times a second. To reproduce high frequencies, it moves in and out at, say, 2,000 times a second. To reproduce a low frequency and a high frequency at the same time, it has to move in and out 40 times, while simultaneously moving in and out 2,000 times a second.

That's just to reproduce two frequencies. When a speaker is asked to reproduce a musical signal, it has to reproduce many different frequencies simultaneously.

Edited by stevie
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2 hours ago, Steve Browning said:

 

I realise that but it is still the same cone moving and it can only go in and out. It's that in and out that I am trying to understand. I am possibly overthinking this!!

Yes you are overthinking. Have a cup of tea and a biscuit and a nice sit down 😊

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28 minutes ago, stevie said:

The cone reproduces different frequencies by vibrating at different speeds. At low frequencies it moves in and out, say, 40 times a second. To reproduce high frequencies, it moves in and out at, say, 2,000 times a second. To reproduce a low frequency and a high frequency at the same time, it has to move in and out 40 times, while simultaneously moving in and out 2,000 times a second.

That's just to reproduce two frequencies. When a speaker is asked to reproduce a musical signal, it has to reproduce many different frequencies simultaneously.

But can it? It's a purely mechanical device and the cone is a single entity so the whole thing can surely only move all at the same time/frequency. 

Taking the example you give if the cone is moving at 40 times a second and simultaneously moving at 2000 times a second, it has to be moving at 2000 times a second. How could it do both (other than the fact that 2000 is divisible by 40).

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Posted (edited)

Speaker cones are very complex transducers, which are required to produce many frequencies simultaneously all the time. (as any hifi speaker maker will be only too happy to explain to you at length). Given the nature of the OP's question, how they do that is probably beyond the scope of this thread since it would involve an exercise in waveform analysis that would in all likelihood raise more questions than it would answer, but the simple fact is that they do. If anybody is interested, they might want to cast their eyes over this article, which will serve as an introduction to the topic. Fair warning though, it is highly mathematical in nature.

The picture of a loudspeaker producing a single frequency at any one time that appears to lie behind the OP's question is just plain wrong I'm afraid. With no offence intended, it simply doesn't work like that.

 

Edited by leftybassman392
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5 minutes ago, leftybassman392 said:

Speaker cones are very complex transducers, which are required to produce many frequencies simultaneously all the time. (as any hifi speaker maker will be only too happy to explain to you at length). Given the nature of the OP's question, how they do that is probably beyond the scope of this thread since it would involve an exercise in waveform analysis that would in all likelihood raise more questions than it would answer, but the simple fact is that they do. If anybody is interested though, they might want to cast their eyes over this article, which will serve as an introduction to the topic. Fair warning though, it is highly mathematical in nature.

The picture of a loudspeaker producing a single frequency at any one time that appears to lie behind the OP's question is just plain wrong I'm afraid. With no offence intended, it simply doesn't work like that.

 

Thank you. I have no problem accepting my knowledge limitations in this area (or any other). I wanted to understand the process by which a (seemingly) simple mechanical device was able to do such a complicated job. I'll see how far I get through the article to which you provided a link! Then I'll have a cup of tea and a biscuit. 🙂

 

 

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1 minute ago, Steve Browning said:

Thank you. I have no problem accepting my knowledge limitations in this area (or any other). I wanted to understand the process by which a (seemingly) simple mechanical device was able to do such a complicated job. I'll see how far I get through the article to which you provided a link! Then I'll have a cup of tea and a biscuit. 🙂

 

 

Might be an idea to have the tea and biscuit first. Just a thought... :)

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57 minutes ago, Steve Browning said:

if the cone is moving at 40 times a second and simultaneously moving at 2000 times a second, it has to be moving at 2000 times a second. How could it do both .

The same way that a microphone diaphragm does, which is a speaker in reverse. For that matter the same way that your eardrums do, as they are microphones.

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Here's a video that helped explain it for me. The guy talks / rambles a bit. It's worth watching from the beginning but its the visualisation of his hand movements just after 4 mins that helped me visualise what was happening.

 

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Posted (edited)

Update: in order to explain why speakers are required to be able to produce many frequencies simultaneously, it might also be of use to have a look at this article, which explains how musical notes consist of a series of pitches sounding at the same time in order to produce the character of the instrument being played. Also, it's a bit less technical than the Fourier Analysis article I referenced earlier.

Edited by leftybassman392
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Yes, I think you are probably making this too complicated for yourself!

I take it you are familiar with waveform 'graphs', as seen in audio editing programs, DAWs etc? These are displaying the way the voltage of the signal changes with time. A single simple continuous note is displayed as a nice neat sine-wave kind of graph, whereas a complicated sound (or an entire song) consisting of many frequencies simultaneously looks like a messy, scribbly kind of line.

These graphs showing the electrical signal rising and falling over time correspond directly to the in-and-out movements of the cone of a speaker reproducing these sounds - you can think of the graph as also representing forwards-and-backwards movement of the speaker cone over time. So a speaker reproducing a single continuous note is going in and out in a fairly simple and obvious manner, whereas a speaker reproducing complicated 'multi-frequency' sounds goes in and out in a much more complicated set of movements, like the 'scribbly' waveform graph.

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1 hour ago, Steve Browning said:

I wanted to understand the process by which a (seemingly) simple mechanical device was able to do such a complicated job.

Totally agree. I think it's a great question. 👍

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2 hours ago, paulbuzz said:

 So a speaker reproducing a single continuous note is going in and out in a fairly simple and obvious manner,

That's true of a sine wave, but even a single note isn't a sine wave. It consists of the fundamental plus all of the harmonics of the fundamental, so it too is a complex wave form. Where bass instruments are concerned in the lower registers the second and third harmonics tend to be louder than the fundamental. https://www.puremix.net/blog/musical-instruments.html

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7 hours ago, gjones said:

Yes you are overthinking. Have a cup of tea and a biscuit and a nice sit down 😊

Sage advice for most situations.

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It really is a great question. I'll bite.

It's not the speaker you need to think about really. Imagine two people standing very lose together on stage singing a simple song like Frere Jacques. (it could be any two things making any sounds but I want a simple example) Each singer as they sing sends a complex wave of sound into the air and once the sound leaves their mouths it starts to combine and the now doubly complex sounds spread together to your ear where the eardrum vibrates in time with the combined voices. Eventually this is converted into signals in your auditory nerve and is carried into your brain. The magic bit is what happens there. Your brain analyses the signals, works out that it's not one but two voices and then that it is singing, it is words, that they are in French and whilst one person is singing Frere Jacques the other is singing Dormez vous? It can only do this because you've learned to interpret the sounds. A new born baby won't be able to distinguish the two voices or understand the words because it's brain hasn't learned how yet, and if you don't know any French you might only hear the sounds phonetically. If you take the people away and replace them with a speaker playing a recording of the song you'll hear almost the same wave pattern made by the movement of the speaker and still be able to decode it. Even if it's digitised and a lot of the information stripped out by making it an MP3 your brain can still process the information and work out what we are listening to. Your brain is brilliant at this and even better if you are a musician. You could probably listen to a symphony orchestra and pick out one instrument at a time especially if they played a bum note. The same note played on a Rickenbacker or a Jazz, no problem.

All the speaker needs to do is transmit the data in a reasonably honest way, your brain will sort it all out when it gets there.

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8 hours ago, Phil Starr said:

It really is a great question. I'll bite.

It's not the speaker you need to think about really. Imagine two people standing very lose together on stage singing a simple song like Frere Jacques. (it could be any two things making any sounds but I want a simple example) Each singer as they sing sends a complex wave of sound into the air and once the sound leaves their mouths it starts to combine and the now doubly complex sounds spread together to your ear where the eardrum vibrates in time with the combined voices. Eventually this is converted into signals in your auditory nerve and is carried into your brain. The magic bit is what happens there. Your brain analyses the signals, works out that it's not one but two voices and then that it is singing, it is words, that they are in French and whilst one person is singing Frere Jacques the other is singing Dormez vous? It can only do this because you've learned to interpret the sounds. A new born baby won't be able to distinguish the two voices or understand the words because it's brain hasn't learned how yet, and if you don't know any French you might only hear the sounds phonetically. If you take the people away and replace them with a speaker playing a recording of the song you'll hear almost the same wave pattern made by the movement of the speaker and still be able to decode it. Even if it's digitised and a lot of the information stripped out by making it an MP3 your brain can still process the information and work out what we are listening to. Your brain is brilliant at this and even better if you are a musician. You could probably listen to a symphony orchestra and pick out one instrument at a time especially if they played a bum note. The same note played on a Rickenbacker or a Jazz, no problem.

All the speaker needs to do is transmit the data in a reasonably honest way, your brain will sort it all out when it gets there.

A fantastic answer Phil, thanks so much. There's generally quite low understanding among musicians of the fact that the 'sound' and 'tone' of instruments, amps and cabs is created, or more correctly processed and at times biased and/or predicted (subjectively interpreted) in the brain. That our brains acquire certain priorities over time also explains why our tastes differ, and why two people can sometimes hear two different things from the one source.  

And in this context, never underestimate the power of prediction in relation to, for example the sound quality of a £10,000 set of speakers verses that of a £100 set of speakers :)  

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On 22/07/2020 at 15:32, Bill Fitzmaurice said:

That's true of a sine wave, but even a single note isn't a sine wave. It consists of the fundamental plus all of the harmonics of the fundamental, so it too is a complex wave form. Where bass instruments are concerned in the lower registers the second and third harmonics tend to be louder than the fundamental. https://www.puremix.net/blog/musical-instruments.html

Except on a flute/penny whistle where it is, to all intents and purposes, a sine wave

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On 22/07/2020 at 12:40, Acebassmusic said:

Here's a video that helped explain it for me. The guy talks / rambles a bit. It's worth watching from the beginning but its the visualisation of his hand movements just after 4 mins that helped me visualise what was happening.

 

Acebassmusic understood the OP question and this video explains clearly how a speaker driver produces different frequencies simultaneously. Many thanks.  

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