High Instantaneous Current Amp Spec

[MacManNM]

Want to try that on a typical driver used in a Home Theater Speaker? Not a 15" Subwoofer that was designed for sound reinforcement.
d.b.

Here are the results from a ratshack supertweeter, horn midrange and an eminence 8" woofer. Standard drivers.

 

[Dan Banquer]

High Current into tweeters

I don't believe your data. Period. I've blown tweeters on far less than that.
d.b.

 

[PENG]

I posted this on the all channels driven thread and then noticed this thread so I am going to post this here also. Hope it helps.

Let's take a look at what 75 amps peak current means mathematically when it comes to power: The following numbers are derived from the good old formula for power which is the square of the current times the resistance.
For 8 ohms that equals 45,000 peak watts. If we divide by 5 we get 9,000 peak watts per channel.
For 4 ohms that equals 22,500 peak watts. If we divide by 5 we get 4,500 peak watts per channel.
For 2 ohms that equals 11,250 peak watts. If we divide by 5 we get 2,250 peak watts per channel.
After looking at those numbers does anyone think their unit has the headroom in voltage to actually do that?
Does anyone here possibly think that the voice coils of their speakers can actually handle that?
After looking at these numbers does anyone here think that this is at all applicable to home theater especially when the impedance of Home Theater speakers drop only to 4 ohms?
After looking at these numbers does anyone still think that instantaneous peak current spec is at all relevant?
d.b.

Dan, I don't think the average amp can drive 75A into 8 ohms, peak or not. V=IZ (currentX impedance). Into 1 ohm, perhaps, if the impedance dips that low.......so I say forget about that 45,000W scenario.

 

[MacManNM]

Here a few pics of misc stuff from that test:

http://pg.photos.yahoo.com/ph/johnmbod/album?.dir=f516

 

[MacManNM]

I don't believe your data. Period. I've blown tweeters on far less than that.
d.b.

You have no idea what you are talking about. You have blown tweeters by clipping the amp and sending pure DC into them. That, melts the coils. Do you want me to e-mail you the complete database, and notes from the tests? pics above are of the pulser we built along with the 8" driver. The other is of the blown 15" EV

 

[Dan Banquer]

That high current thingy

"You have no idea what you are talking about. Do you want me to e-mail you the complete database, and notes from the tests? pics above are of the pulser we built along with the 8" driver. The other is of the blown 15" EV"

I think you need to go back and reabsorb the numbers I put up on amplifiers and the actual output of 75 amps. Amplifiers used for home theater just cannot put out that kind of power into the impedances used, so even if your data is plausible it's certainly not applicable. BTW: and the answer is I still don't believe your data.
d.b.

 

[Votrax]

You want to bet? This is a test of an electrovoice 15" driver I performed a few years ago. This woofer took 22.66 kW for more than 1ms. We tried to increase it but it blew up.

I believe Dan was referring to the available rail voltage in an AV receiver would make it impossible to draw 75A through an 8 or 4 ohm speaker. If you had a 300-600VDC rail voltage it wouldn't be a problem. You would also need output transistors rated for that high of voltage and current as well.

 

[Dan Banquer]

High Current thingy

"I believe Dan was referring to the available rail voltage in an AV receiver would make it impossible to draw 75A through an 8 or 4 ohm speaker. If you had a 300-600VDC rail voltage it wouldn't be a problem. You would also need output transistors rated for that high of voltage and current as well."

Thank you, that about sums it up.
d.b.

 

[MacManNM]

"You have no idea what you are talking about. Do you want me to e-mail you the complete database, and notes from the tests? pics above are of the pulser we built along with the 8" driver. The other is of the blown 15" EV"

I think you need to go back and reabsorb the numbers I put up on amplifiers and the actual output of 75 amps. Amplifiers used for home theater just cannot put out that kind of power into the impedances used, so even if your data is plausible it's certainly not applicable. BTW: and the answer is I still don't believe your data.
d.b.

The numbers you put forth are meaningless (HT amps and such). You stated that drivers can't take that power. I have data that says they can. Your (lack of) belief in my data shows how little you know about how things really work. Typically, components can handle impulses many orders of magnitude higher than their RMS rating.

 

[MacManNM]

I believe Dan was referring to the available rail voltage in an AV receiver would make it impossible to draw 75A through an 8 or 4 ohm speaker. If you had a 300-600VDC rail voltage it wouldn't be a problem. You would also need output transistors rated for that high of voltage and current as well.

That's fine. He shouldn't have stated that a speaker couldn't take that peak power.

 

[thxgoon]

I believe Dan was referring to the available rail voltage in an AV receiver would make it impossible to draw 75A through an 8 or 4 ohm speaker. If you had a 300-600VDC rail voltage it wouldn't be a problem. You would also need output transistors rated for that high of voltage and current as well.

Maybe somebody could sum up how an amplifier actually works. I was under the impression that based on the input signal strength, the amp outputs a voltage of a certain value, say 12volts. Then, depending on the load (impeadence) the amp would have to output enough current to sustain that voltage. (water in a hose theory, volt=pressue, current=current) The lower the impeadence, the more current becomes necessary and thus volts*amps=watts. More watts are required. So in an extreme case, you could be talking about 75amps at a realistic volume into an extrememly low impedence. Am I right here or is this the wrong way of thinking?

 

[MacManNM]

Maybe somebody could sum up how an amplifier actually works. I was under the impression that based on the input signal strength, the amp outputs a voltage of a certain value, say 12volts. Then, depending on the load (impeadence) the amp would have to output enough current to sustain that voltage. (water in a hose theory, volt=pressue, current=current) The lower the impeadence, the more current becomes necessary and thus volts*amps=watts. More watts are required. So in an extreme case, you could be talking about 75amps at a realistic volume into an extrememly low impedence. Am I right here or is this the wrong way of thinking?

You are right on the money on how an amp works. It would take a very low impedance to achieve that kind of current, and normally drivers (impedance)doesn't dip that low. So 75 amps would be a stretch. Using a mackie M1400i amp, I have measured output currents in excess of 17 amps. That is into one driver. So in theory if you paralled a few of them you could output a lot more current.

 

[PENG]

Maybe somebody could sum up how an amplifier actually works. I was under the impression that based on the input signal strength, the amp outputs a voltage of a certain value, say 12volts. Then, depending on the load (impeadence) the amp would have to output enough current to sustain that voltage. (water in a hose theory, volt=pressue, current=current) The lower the impeadence, the more current becomes necessary and thus volts*amps=watts. More watts are required. So in an extreme case, you could be talking about 75amps at a realistic volume into an extrememly low impedence. Am I right here or is this the wrong way of thinking?

You're right. That's why I have problem with people saying "its current that matters, not watts" and therefore 55 HK watts=100 Yamaha/Sony watts. As you mentioned, volts*amps=watts (assuming p.f.=1), or amps*amps*resistance=watts. Surely current matters, but a low power (watts) rated high current amplifier cannot deliver high currents into a speaker load unless the impedance is extremely low, like <1 ohm. Or, as Mac mentioned, parallel a few speakers, to get the equivalent super low impedance load.

 

[Dan Banquer]

Amplifer Power

Power is a function of three separate but related parts. They are as follows:
voltage, current, and resistance/impedance. The basic formulas are:
Power = voltage times the current
Power = the square of the current times the resistance
Power = the square of the voltage divided by resistance.

If you try a few of these formulas with some numbers from an amplifier data sheet it will help you understand that voltage, current and resistance/impedance are interrelated when it comes to power.

Hope this helps;
d.b.

 

[aarond]

Okay,
1) Not fact, not sure if its fiction or not.
2) 120WPC may be closer to fact, certainly not 120W all channel driven, but I don't think Yamaha has ever made that all channel driven claim.

Yamaha makes the claim when they call the rxv1600 a "7-Channel 840W Powerful Surround Sound " then they put a 500w power supply in the unit so its seems the 840w claim is an outright lie

 

[PENG]

Power is a function of three separate but related parts. They are as follows:
voltage, current, and resistance/impedance. The basic formulas are:
Power = voltage times the current
Power = the square of the current times the resistance
Power = the square of the voltage divided by resistance.

If you try a few of these formulas with some numbers from an amplifier data sheet it will help you understand that voltage, current and resistance/impedance are interrelated when it comes to power.

Hope this helps;
d.b.

The first one, Power=Voltage times the current times power factor. Power factor=1 for d.c., and less than 1 for a.c. with a complex load such as a loudspeaker that is not purely resisitve.

 

[thxgoon]

The first one, Power=Voltage times the current times power factor. Power factor=1 for d.c., and less than 1 for a.c. with a complex load such as a loudspeaker that is not purely resisitve.

Could you explain this? Thanks.

 

[PENG]

Yamaha makes the claim when they call the rxv1600 a "7-Channel 840W Powerful Surround Sound " then they put a 500w power supply in the unit so its seems the 840w claim is an outright lie

Let's take a look of the HKAVR335 as an example. Page 7 of the instruction manual show a picture of the back plane and it shows

"AC INPUT 120V/60 Hz 370W".

On page 54 under the technical specifications, it says

"Power Consumption 118W idle, 890W maximum (7 channel driven).

So even HK, well respected for being honest about their ratings, may have specified their all channel driven power output under "maximum" condition, not necessarily under continuous condition. Likewise, the Yammie's 500W number is a power consumption number. Unlike HK, Yammie did not tell us what their "maximum" consumption is, we have to guess. Please keep in mind that power transformers in general have excellent overload rating for say 10/30/60 minutes. A high quality unit should not have problem producing short term power that far exceed its continuous rating.

Regardless, if the RX-V1600 claims 840W, you have a valid point. Thanks!

 

[PENG]

Could you explain this? Thanks.

Sure, I can try. Power factor is defined as the Cosine of the phase angle between the voltage phasor (a.k.a. vector in the old days) and the current phasor.

For an inductive load, such as a voice coil, the current will be lagging behind the voltage. For a capacitive load, the current will be leading. You can see the phase relationship between the voltage and current phasors if you display their waveforms on an oscilloscope. For a purely inductive load (i.e. with negligible resistance), the current is 90 deg lagging the voltage. Cosine 90 deg is 0, so you can only develop reactive power (unit is VAR, not Watt) into a pure inductive load such as an inductive coil. The real power dissipation (watt), is 0. I believe a conventional loudspeaker circuit is a complex load that has all 3 components of resistance, inductance and capacitance. The overall impedance has the same unit as resistance, i.e. ohms. However, the amplifier that drives the loudspeaker will see a complex load, and the current driven into this complex load will generally be lagging the voltage by an angle, say 40 deg (just an example). That will give a power factor=Cosine 40 deg=approx 0.766. I suspect different speakers will have different power factors and the p.f. will likely varies with frequencies. In any case, it will be less than 1, may be in the range of 0.7 to 0.9 except at 0 (d.c.) frequency.

I mentioned the p.f. thing because like efficiency, it has to be in the equation for any a.c. power calculations, unless the load is purely resistive.

Sorry if I failed to explain it clearly. Hopefully others can do a better job.

 

[mtrycrafts]

One good thing about this thread is that people can debate the two somewhat related topics (high current/all channel driven) fully and freely without getting the original poster upset. I hope Gene won't really give up on us here.

And, the original poster might learn something he would have asked later, perhaps