Another one for skeptic or anyone else. Amps, watts & volts ??? [Archive] - Audio & Video Forums

PDA

View Full Version : Another one for skeptic or anyone else. Amps, watts & volts ???



dontknownuttin
12-02-2003, 07:28 AM
Hello, My moniker says it all. I have a 60 wpc receiver & I would like to know what travels through my speaker cables. As I turn up the volume do more watts go through the cable? Is it AC or DC current? Also, how many volts travel through the cables or is that dependent on the volume level? I have alot of questions. Thanks in advance, d.

FLZapped
12-02-2003, 08:05 AM
Hello, My moniker says it all. I have a 60 wpc receiver & I would like to know what travels through my speaker cables. As I turn up the volume do more watts go through the cable? Is it AC or DC current? Also, how many volts travel through the cables or is that dependent on the volume level? I have alot of questions. Thanks in advance, d.

Yes, more watts, which is comprised of both voltage and current. (Power=Volts * Current)

Power varies with your volume control and it is an AC signal.

That's the Reader' Digest version. A google search can probably find you sites that explain and give examples of how this all works.

-Bruce

spacedeckman
12-02-2003, 02:51 PM
Volume control adjusts output voltage (imagine a steady state AC signal), impedance changes in moving speaker drivers change current draw, the amplifiers job is to maintain output voltage into the load as it changes. Now, if the impedance of the speaker drops in half, say 4 ohms from 8 ohms, the current demand will double for however long the speaker stays in the 4 ohm area. The amplifier will attempt to fill the need for additional current and maintain voltage, if it can't, the voltage will drop and become a power shortfall. Amplifiers that are good to excellent at dealing with this are often labeled as "high current" amplifiers.

Generalizing (and opening myself up for taking some shrapnel) here, but higher current amplifiers tend to have better bass response (tighter, better definition) and generally sound a lot more powerful than they really are. This happens because the amplifier is actually able to deal effectively with the demands of the speaker load. Better sound should be the goal, but advertising tarnishes that idea a bit.

Space

Mash
12-02-2003, 07:44 PM
What happens when you change the volume or when speaker inpedance changes (and I don't know a reason to consider speaker inpedance changes unless you are changing speakers) all depends.......

True,
1. Power = Current x Voltage
2. Power = Current x Current x Resistance
3. Power = Voltage x Voltage / Resistance

But if you use (2) you are assuming that Voltage is a constant. Most amps 'tend' to act like constant-voltage sources. A true constant-voltage-source amp will produce TWICE the power at 4 ohms as it will produce at 8 ohms. See (3).

Most amps that 'tend' to act like constant-voltage sources cannot produce TWICE the power at 4 ohms that they can produce at 8 ohms. My Musical Fidelity A2 will produce 25 wpc at 8 ohms and 50 wpc at 4 ohms. This means that the Musical Fidelity A2 will operate as a true constant-voltage-source amp.

Your wall plugs ARE for all practical purposes constant-voltage sources.

Futterman OTL amps 'tend' to operate as constant-current-sources. This meand my mono-100's will produce 100 wpc at 8 ohms and 160 wpc at 16 ohms. Of course, they also produce less distortion at 16 ohms w/r/t 8 ohms. A have-your-cake-and-eat-it-too deal.

Higher speaker volume is usually obtained by delivering more power to a loudspeaker. Electrostatics are the sole exception since a pure electrostatic does not dissipate power.

spacedeckman
12-03-2003, 07:27 PM
You seem to have a pretty sophisticated answer for someone who doesn't seem to know that speaker parameters vary by the millisecond. Impedance constantly fluctuates meaning the amplifier has to constantly adjust to a moving target. Add to that capacitance, inductance, back EMF from the woofer, and phase angles...you have a real mess you are dealing with even with an "easy" speaker load.

As far as an amp acting as a perfect voltage source...sorry. Circuit impedances in the amplifier preclude that from happening. What MF and a lot of other companies do (especially car audio) is downrate the 8 ohm rating to hit a doubling at 4, or in the case of Krell and the like, find the output into 1 or 2 ohms and figure back from that. It's fudging downward, not up, so you aren't ripping anyone off, understating power output is not illegal, overstating is...somewhat.

Space

Beckman
12-03-2003, 10:00 PM
Hello, My moniker says it all. I have a 60 wpc receiver & I would like to know what travels through my speaker cables. As I turn up the volume do more watts go through the cable? Is it AC or DC current? Also, how many volts travel through the cables or is that dependent on the volume level? I have alot of questions. Thanks in advance, d.

Starting from the wall outlet:
1. AC is converted to dc inside the amplifier.
2. Transistors or tubes are used in combination with other circuit elements to amplify the signal. That is transistors are biased properly to amplify the signal coming from the source(cd player, tuner, etc.).
3. As the volume is turned up the voltage used to bias the transistors is increased. In turn the signal is amplified more.
4. Volts don't travel through the speaker cables, current does. Voltage is the potential difference from one speaker to the other.