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Old 8th May 2004, 07:13 PM   #1
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Default Sound pressure, is that the same?

One ten watts, non distorted amplifier, reproducing a clean 100 hertz sine wave, into a 10 inches diameter speaker mounted in a very big panel (no phase cancellation). the cone movement will be 10 milimeters each half cicle..... 20 milimeters compliance.

Now, a hundred watts, non distorted amplifier, reproducing a clean 100 hertz sine wave into a 10 inches diameter speaker mounted in a very big panel (no phase cancellation). the cone movement will be 10 milimeters each half cicle... 20 milimeters compliance.

This way, speaker factory made new coil, better heat dissipation, more magnetic power and the same chassis with a bigger magnet on it.... suspension the same, also paper cone the same.

Same distance to metering..... can i suppose that i will have the same audio result.... same volume in music?.... in others words, 1 watt audio in a 1 watt full movement speaker will be same as 1000 watts audio in a 1000 watts full movement speaker?

Speaker can have more compliance...... but this have a limit, and this makes sinusoidal into square wave audio when over excited.

So, a bigger compliance speaker with 1 watt can be better than a 100 watt speaker that have lower compliance?

Can i understand that power do not matter..... and everyone making big amplifiers to have more power?.... maybe it will effective only if someone uses more speakers to have more "piston" area pulling air molecules.

Can i understand no need of power?.... that i need hi compliance speaker adequated to the amplifier characteristics to have the best we can have (related sound pressure, volume, decibels) in sound reproduction?

This is real a "stupid" question.... but maybe not so stupid.

Please, let me know what you think.

Carlos
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Old 8th May 2004, 07:41 PM   #2
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Hi,
I guess it's the 'sensitivity' of a speaker you're talking about? I suppose that is the result of variations in compliance and cone construction and materials etc.
So 1watt played through 82dB/W/m speakers will produce the same SPL as 2watts through 89dB/W/m or 4watts through 86dB/W/m. I think that's how it goes anyway, as a 3dB represents a halving/doubling of power.
I think that was what you were getting at
Steve
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Old 8th May 2004, 07:43 PM   #3
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Oh and as to the last bits of your post, that's why so many people these days are going for SE triode amps that only put out a few watts, but use very efficient speakers/horns etc.
Steve
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Old 8th May 2004, 11:10 PM   #4
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Default I think you get it, bagstevo82

My English is unclear, i know that...but you get it.

I am asking the people that, do not agree, to explain me some.

And i am trying to say that; if you have a very good an clean 10 watts amplifier, and some speakers very soft suspension.... the one you can move with your breath on it.... you will have a very good air compression.... good sound.... efficient system... adequate power from amplifier and speaker capacity do dissipate the energy, and transform a big amount of energy into mechanical movement to compress air particules, and also rarify, to produce what we capture, and understand, as "sound"

The opposite idea, is when we have a 100 watts amplifier, clean audio and a very hard to move speaker suspension....this way, you will have to spent 100 watts to move this speaker, making the same amount of air pressure than the first one!.... so.... spending power to nothing.

Of course i believe in high compliance units that needs hi power to move it.... but also believe in high compliance units that needs not hi power to move it too.

As i am not sure.... i am asking people....i have my own ideas and i want to check them, or modified them depending people's input.

Thank your kindness to answer my question...you get it!...my idea!

Carlos
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Old 8th May 2004, 11:19 PM   #5
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Hi,
I guess it depends on what kind of sound you're trying to achieve, for example i doubt you'll find many home theater subwoofers running on a single ended 2a3 amp. The system just has to be matched, if you have 100watts available you dont need efficient speakers, if you only have a few, then you do. Each can sound as good as the other potentially I guess, apart from lower power amps being able to use simpler nicer sounding topologies
Steve
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Old 8th May 2004, 11:31 PM   #6
Magura is offline Magura  Denmark
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Take a look at the rushmore article at www.passlabs.com
It might give you an explanation to why loads of power is not all good.

Magura
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Old 8th May 2004, 11:40 PM   #7
Svante is offline Svante  Sweden
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I think you are on the right track, but have the physics of loudspeakers slightly wrong.

The mechanical parameter that determines the cone excursion in the main frequency range is the moving mass, not the compliance. A high mass will lead to small excursions, a small mass to the opposite. This mass, in combination with the driving force and its frequency will determine the excursion.

But you are right in that the cone excursion, or rather its acceleration determines the sound pressure level. It does not matter if it is accomplished by a heavy cone and a strong driving force, or by a light cone and a weak force. At least that is the basics.
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Old 8th May 2004, 11:48 PM   #8
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Indeed Svante,

And to add to that the bare cone is not matched very well to the acoustic impedance of the air it has to move. So it will always be an inefficient system unless you use an impedance transformer like a good horn or use a cone as light as air

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Old 8th May 2004, 11:50 PM   #9
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It is not only the stiffness of the suspension, which brings down
the efficiency of some modern speakers.

The goal is to work with small cabinets.
They offer only small air volume inside. The smaller this
volume is, this air will behave.
In a closed box this acts like an additional spring which is directly paralleled to the suspension of the speaker.
f you gave a speaker with very soft suspension and low moving (that's the next point...), the resonance frequency of this system will become quite high.
The stiffness of the resulting suspension and the moving mass will determine the resonance frequency system.
In vented boxes it is more complicated (two coupled mass/spring systems), but also here you will need a high moving mass in order to work with small cabinets.

The stiffenss of the speakers suspension is reflected in the Vas value of the speaker. Soft suspensions give large Vas. Vas is simply the volume of air which would give the same suspension....

Back to the fundamentals.
If you increase the moving mass, you only get one advantage (lower resonance frequency), but immediately two drawbacks:
-damping gets poor
-efficiency drops

Both can be compensated by designing a very strong magnet and
coil (==> High BL product).
Typically they are designed so that you get again a good damping behaviour. Unfortunately the efficiency drops by the square of the moving mass! So still with a strong motor the efficiency is getting poor.

If we now consider that the resonance frequency does only move with a root function....

It is no fun to get low frequencies and high sound pressure from a small box.....
But with modern speaker designs and power amps you can get amazing results.

Cheers
Markus
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Old 8th May 2004, 11:58 PM   #10
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...wow, quite a poor description from my side...., I should go to bed....
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