question of theory

cominup · 6th May 2004, 12:41 AM

Dear all,

Please, could you explain something below:

First:
- I know that impedance of loudspeaker is not constant while they are being used. It rates to audio frequency. But I dont know it rates directly or inversely.

- Otherwise, power (Watt) inversely rates to impedance (ex: 8 Ohm ~ 100W; 4 Ohm ~ 200W).

=> So, I am asking the relationship between audio frequency and power.

Second:
- Wide audio frequency bandwidth causes wide loudspeaker impedance bandwidth. But speaker manufactors just tell us only one power (ex: 100W @ 8 Ohm).

So, how to know the loudspeaker impedance bandwidth. What is the marked power on the loudspeaker?

Third:
- The relationship of amplifier power (Watt), loudspeaker sensity (dB) and loudspeaker power (Watt). Are there some equation and/or formula of them? Or it is just only human feeling?

Thanks for your looking.
Regards,

Cominup

sreten · 6th May 2004, 06:37 AM

Speakers sensitivity is rated at dB/2.83V.

For an 8 ohm nominal driver / loudspeaker dB/2.83V = dB/W
For an 6 ohm nominal driver / loudspeaker dB/2.83V = dB/1.3W
For an 4 ohm nominal driver / loudspeaker dB/2.83V = dB/2W
For an 2 ohm nominal driver / loudspeaker dB/2.83V = dB/4W

The above are just approximations as real efficiency at each
point of the impedance curve is hardly ever considered.

sreten.

Ron E · 6th May 2004, 09:59 PM

1.
Ohms Law: Volts = Current * Impedance

Power = Current^2*Impedance
Power = Volts^2/Impedance

Power doubles into a halved impedance only if voltage is constant and source impedance = 0.

2.
Impedance bandwidth (whatever you mean by that) is unimportant. Impedance only matters in most cases if it is too low or too reactive.

The marked power on a speaker is rated by IEC or DIN specifications. THese are a band-limited noise signal that is used to find the thermal (not mechanical) limits of the speaker. Search for "IEC power" or DIN power" in your browser.

3.
efficiency = 9.6e-10*Fs^3*Vas/Qes [Vas in liters]
sensitivity = 112+10*log10(efficiency)

SPL in dB = 10*log10(power) +Sensitivity

cominup · 7th May 2004, 04:28 AM

Hi Ron E,

Many thanks for yr help,

Cominup

6th May 2004, 12:41 AM	#1
cominup diyAudio Member Join Date: Apr 2004 Location: hanoi	question of theory Dear all, Please, could you explain something below: First: - I know that impedance of loudspeaker is not constant while they are being used. It rates to audio frequency. But I dont know it rates directly or inversely. - Otherwise, power (Watt) inversely rates to impedance (ex: 8 Ohm ~ 100W; 4 Ohm ~ 200W). => So, I am asking the relationship between audio frequency and power. Second: - Wide audio frequency bandwidth causes wide loudspeaker impedance bandwidth. But speaker manufactors just tell us only one power (ex: 100W @ 8 Ohm). So, how to know the loudspeaker impedance bandwidth. What is the marked power on the loudspeaker? Third: - The relationship of amplifier power (Watt), loudspeaker sensity (dB) and loudspeaker power (Watt). Are there some equation and/or formula of them? Or it is just only human feeling? Thanks for your looking. Regards, Cominup __________________ Ill do it by myself

6th May 2004, 09:59 PM	#3
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	Re: question of theory 1. Ohms Law: Volts = Current * Impedance Power = Current^2Impedance Power = Volts^2/Impedance Power doubles into a halved impedance only if voltage is constant and source impedance = 0. 2. Impedance bandwidth (whatever you mean by that) is unimportant. Impedance only matters in most cases if it is too low or too reactive. The marked power on a speaker is rated by IEC or DIN specifications. THese are a band-limited noise signal that is used to find the thermal (not mechanical) limits of the speaker. Search for "IEC power" or DIN power" in your browser. 3. efficiency = 9.6e-10Fs^3Vas/Qes [Vas in liters] sensitivity = 112+10log10(efficiency) SPL in dB = 10log10(power) +Sensitivity __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan* Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley

7th May 2004, 04:28 AM	#4
cominup diyAudio Member Join Date: Apr 2004 Location: hanoi	Hi Ron E, Many thanks for yr help, Cominup __________________ Ill do it by myself

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6th May 2004, 06:37 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Speakers sensitivity is rated at dB/2.83V. For an 8 ohm nominal driver / loudspeaker dB/2.83V = dB/W For an 6 ohm nominal driver / loudspeaker dB/2.83V = dB/1.3W For an 4 ohm nominal driver / loudspeaker dB/2.83V = dB/2W For an 2 ohm nominal driver / loudspeaker dB/2.83V = dB/4W The above are just approximations as real efficiency at each point of the impedance curve is hardly ever considered. sreten.

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