Really? Are you serious? What do you think voltage is, my friend?
Voltage is "electro motive FORCE". Halving the voltage does not reduce
the force to 1/4. It reduces power to 1/4 since the formula for power
expressed simply with voltage and resistance is: The problem here is that voltage does not exist without current. The two together are power. Even though we refer to speakers as 'voltage driven' that is a bit of a charged term (referring to the fact that many amplifiers are designed to act as 'voltage sources' and many speakers are designed to expect a voltage source to be driving it); but in fact power is actually making the speaker move. If you can somehow make a speaker move with voltage but *without* current, you will have a new branch of physics :) A 3db reduction is halving amplifier power, which is what drives a loudspeaker. Its the 'force' that makes a speaker move and because of that if you reduce the voltage by half, the power to move the speaker is reduced to 1/4 of previous. |
I believe that the references to force in this discussion are unnecessary and are contributing to confusion, and I believe that Atmasphere is correct. A short while ago I posted as follows in the other thread I referenced above, in relation to this matter: Almarg 4-20-2018
Assuming that a speaker is operating in a reasonably linear manner, meaning for example that it is not being over-driven to the point that thermal compression becomes significant, it seems to me that the relation between acoustic power out and electrical power in will remain constant to a close approximation. And electrical power in will be proportional to the square of the applied voltage.
Therefore it would seem to me (and I believe also to Erik, Atmasphere, and Kijanki) that since a 50% reduction in applied voltage will result in a 75% reduction in electrical power in, which corresponds to a 6 db reduction in electrical power in, the result will be a 6 db reduction in acoustic power out. My comment was seconded in that thread by Erik_Squires, who is particularly knowledgeable and experienced in speaker design. An excerpt from his post: Erik_Squires 4-20-2018
... the SPL at a reference distance, measured in dB, changes
in proportion to the power OR voltage when either is expressed as dB
assuming there is no compression in the driver.
Said another way, for a single driver:
Delta V dB = Delta W dB = Delta SPL dB
That's what's so cool about dBs!
Regards, -- Al |
I believe that the references to force in this discussion are unnecessary and are contributing to confusion, and I believe that Atmasphere is correct. A short while ago I posted as follows in the other thread I referenced above, in relation to this matter: - almarg
Look up the formula for sound power. It is defined by a force exerted over an area and assigned a vector (dot product). The formula for electrical power consumed is entirely different and far simpler - based on measured voltage and current. Understanding the distinction between the two is what provides the necessary insight to explain why efficiency is increased when voltage is DIVIDED (series) among loudspeaker drivers and remains unchanged when SPREAD (parallel) across the same driver. This is trivial first year electrical engineering subject matter. I can’t help the fact that you don’t understand it - regardless of your so called "credentials", "qualifications", or number of posts on Audiogon. To pay adequate deference to the people who developed this body of knowledge, you have to pay attention to things like units. Mixing and matching units in these equations results in obvious error. Again, the formula for sound power is readily available on Wikipedia for all to see. It involves applied force and area which dramatically alters the net resulting analysis. Electrical power input is totally separate and distinct and you cannot ASSUME the two are equivalent. There’s a reason the graph shown in the web page for db conversion that Erik linked to has a value of -6db for voltage gain/loss and -3db for sound power. One look at the two formulae for sound power and electrical power will explain why if you care to devote the time to examine them closely. And with that, I’m done attempting to set the record straight. All I get are insults for my trouble. No good deed ever goes unpunished. |
CJ1965 4-20-2018
There’s a reason the graph shown in the web page for db conversion that
Erik linked to has a value of -6db for voltage gain/loss and -3db for
sound power. One look at the two formulae for sound power and electrical
power will explain why if you care to devote the time to examine them
closely.
I'm not sure what you are referring to. The only graph on the page addressing db conversion that Erik linked to is this one, and it just deals with voltage, not power. In any event, if (as it appears) you are saying that a 6 db reduction in electrical power into a speaker results in a 3 db reduction in SPL at a given distance, rather than resulting in a 6 db reduction in SPL at that distance, we'll have to agree to disagree. Regards, -- Al |
What is this sound power I keep hearing about this week on Audiogon? It seems new and interesting. Oh look, donuts ...
Best,
E |
