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?
 
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?
 
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.
 
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Look inside its' a good book

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=DB+weems,+building+and+testing+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-Building-Testing-Speaker-Projects/dp/007069429X

Does not cover open-baffle systems - any book for that?
 
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Does not cover open-baffle systems,any book for that?

Thanks for the recommendation. It's at Amazon, and using the look inside feature I have some of my questions answered already.

Designing, Building, and Testing Your Own Speaker System with Projects: David Weems: 9780070694293: Amazon.com: Books

Does not cover open-baffle systems - any book for that?

It's not covered for a very good reason. Once you thoroughly learn how a loudspeaker works, you will realize just how preposterous the open baffle concept is. It can be, however, an okay thing for mid range. It just depends on many factors. There exists a lunatic fringe of the open baffle "cult" that absolutely swears by this concept and will all join in here and discount my belief in the facts. Similar to "Tulip Bulb Mania" and the "South Seas Bubble".
 
I started reading one of the Forum's "open baffle" Threads.
I asked what low frequency EQ was required.
He came back and said "none" and effectively told me I was being stupid.

A year or so later it has become clear that massive single pole EQ has been incorporated to allow the speaker to work at all.

They have not yet admitted to the massive LF power that will have to be used to drive that EQed LF speaker.
Or the opposite which is more likely:
how low the LF output needs to be to avoid overloading the LF speaker.
 
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@AndrewT, I've experienced moderately good levels from open 15"s EQed to 20Hz, driven to xmax by 50W (96dB/W/m).

I did that a few months back. Beyma 15P1200Nd drivers, so they could move some air. I saw 30mm p/p cone travel when the bass went low - kinda scary. That was at a couple of hundred watts per side.

The people that use Eminence Alpha/Beta-15 drivers are, I suspect, missing LF headroom.

Chris
 
Adding a few more might help...
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Source: http://www.diyaudio.com/forums/multi-way/142015-my-open-baffle-dipole-beyma-tpl-150-a.html
 

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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=DB+weems,+building+and+testing+loudspeakers

Majority of people now spend more time in front of some sort of monitor be it laptop or tablet than reading books, so I can guess safely that more people are getting info from the net. If there's a good source of learning from the net, why not taking it?
 
Majority of people now spend more time in front of some sort of monitor be it laptop or tablet than reading books, so I can guess safely that more people are getting info from the net. If there's a good source of learning from the net, why not taking it?

Even better than reading a book is to be able to discuss the subject with the author of such books online. Do come prepared though :D.
 
Majority of people now spend more time in front of some sort of monitor be it laptop or tablet than reading books, so I can guess safely that more people are getting info from the net. If there's a good source of learning from the net, why not taking it?

because of the great risk that you will read some alluring propaganda about open baffle speakers, and be sucked into the Dark Null of Destructive Interference. It's more dangerous than Scientology and ISIS together, and it's right there in your living room.