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Old 21st January 2016, 05:46 AM   #1
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Default Understanding how speakers work and are tested - in simple terms

Understanding how speakers work and are tested - in simple terms

On the long road to building a better speaker, after some study (possible not enough) and some experimentation (again more is needed) I feel I need to get to the basics here and try to piece together how speakers, and in the broader context, how audio systems work, before I progress any further.

My starting point is the following animation.

How loudspeakers work - Explain that Stuff

The amplfier sends an alternating current to the speaker, the cone of the speaker vibrates at this frequency. Assume a sine wave signal. The vibration is transferred to the air, and reaches the ear. The eardrum vibrates in according to the changing sound pressure and the auditory signal is sensed by the brain.

I have used my own words for clarify and simplicity, and also as a basis for correction.

Sound is transmitted as a transverse wave, consisting of varying sound pressure as shown in this page:

The Nature of Sound

When a sound is created, it is actually a short series of comressions and rarefactions, spanning from a few milliseconds upwards. So there is no single 'sound' as it were, but a short duration sequence of pulses, which are of such short duration we refer to it as 'a sound'

Have I got it right so far?
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Old 21st January 2016, 11:30 AM   #2
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For a sine wave, it is easy to imagine the speaker cone vibrating at a single frequency. However for music, how does the speaker cone produce a sound which is a composite wave, which in the original live session consisted of sounds coming from multiple instruments, each vibrating independently of each other? Surely there must be a trade-off in reproducing which in effect is a summation of all the sounds that are produced. Since the microphone diaphram can only vibrate at one freqeuncy at a time, how can it pick up complex music without leaving something out? Then again our eardrums can vibrate at only one frequency within a certain number of milliseconds, so is it the same as a microphone diagram? It all comes down to the response rate of the eardrum? That is, there must be a minimum time in milliseconds that is needed for the eardrum to respond to certain sounds. For example if a 1 khz tone is followed after 5 ms by a 10 KHz tone and then again by a 400 hz tone will this be heard accurately? Will it be recorded accurately?
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Old 21st January 2016, 12:33 PM   #3
Scott L is offline Scott L  United States
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Location: Knoxville, TN
Default Start Reading Books

Forget the net.
Read a book.
And then read another book.
Repeat.


Designing, Building, and Testing Your Own Speaker System with Projects
(by David B. Weems)

https://www.google.com/?gws_rd=ssl#q...g+loudspeakers
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Old 21st January 2016, 01:47 PM   #4
TBTL is offline TBTL  Germany
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Speakers cannot be correctly explained in simple terms. It's one of the reasons why our hobby has such a steep learning curve. I doubt whether you would want to go the way of studying books until you understand the basics of all aspects of speaker building, as this will take several years. You would have to start with calculus which does not seem to be linked to speaker building, but which is necessary in order to understand the other books. Building with just enough knowledge to know what things to try is much more fun.

With respect to the subject of viewing sound as a sum of multiple frequencies, you could read books about Fourier transform, transfer function, bode plots. You will learn things like that a single frequency cannot have a finite duration and that any vibration (also non-sinusoidal) can be written as a sum of multiple frequencies.

Sorry for the discouraging post, do not let it stop you.

Last edited by TBTL; 21st January 2016 at 02:01 PM.
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Old 21st January 2016, 02:01 PM   #5
Scott L is offline Scott L  United States
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Default Never ending process

I have been at it for 43 years and still continue to learn.

But I started it all by reading a book. That's how I learned to learn.

But, of course, the internet was not invented yet.

Loudspeakers 101


Loudspeakers 101
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Old 21st January 2016, 02:11 PM   #6
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I think that BasicHifi got it right
it's YOU that don't make that little step to comprehend


Just a little note: the AC current is applied to the voice coil of the speaker which is attached to the membrane ( for dynamic speakers )
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Old 22nd January 2016, 04:26 AM   #7
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Default Look inside its' a good book

Quote:
Originally Posted by Scott L View Post
Forget the net.
Read a book.
And then read another book.
Repeat.


Designing, Building, and Testing Your Own Speaker System with Projects
(by David B. Weems)

https://www.google.com/?gws_rd=ssl#q...g+loudspeakers
Thanks for the recommendation. It's at Amazon, and using the look inside feature I have some of my questions answered already.

http://www.amazon.com/Designing-Buil.../dp/007069429X

Does not cover open-baffle systems - any book for that?
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Old 22nd January 2016, 07:32 AM   #8
Juhazi is offline Juhazi  Finland
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This is a good start
https://en.wikipedia.org/wiki/Loudspeaker

And going deeper
http://education.lenardaudio.com/en/05_speakers.html

Perhaps there are similar page in Spanish too
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AINOgradient speaker project
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Old 22nd January 2016, 09:47 AM   #9
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Reading...

Nice plot of directivity. https://en.wikipedia.org/wiki/Loudsp...ar_pattern.png

At high frequencies, apparently we have a problem. Dual tweeters then?
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Old 22nd January 2016, 10:09 AM   #10
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Nope. The shorter the WL, the higher the probability ( and it will !) to generate interference
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