Perceived volume vs. mathematical volume.

[KJung]

The bigger issue seems to be why anyone would design an amp to add a speaker in series Either make the thing 2ohm stable or make the internal speaker 8 ohms.

Looks like another stroke of Eden genius here

As most have pointed out, adding a speaker to a SS in parallel results in little or no volume gain... just more to carry.

 

[Lelander]

If indeed the power drops from 200W (4-ohm load) to 150W (8-ohm load) output, the voltage at 150W (8-ohm) setting will be higher.

The OP was extrapolating the 150W @ 8 ohm rating based on the published spec from a different amp. I wouldn't be surprised if it is really is more like 100W @ 8 ohms, which negates any increase in volume to to power output.

I agree that if that extension cab is an average of 3dB more efficent than the combo's cabinet (over a meaningful range of frequencies) then the pair will be noticeably louder. Of course, if that is really the case then the best case scenario for volume is to disconnect the drivers in the combo completely and power the extension cabinet with 200W @ 4 ohms

 

[DavePlaysBass]

The OP was extrapolating the 150W @ 8 ohm rating based on the published spec from a different amp. I wouldn't be surprised if it is really is more like 100W @ 8 ohms, which negates any increase in volume to to power output.

The existing EDEN technology is 200W into 8-ohm and 320W into 4-ohm. I have not seen too many power amp ratings that halve going from 4 to 8. But then you get into the whole conversation of how do they derive power ratings. I agree with Bill that it all comes down to how much voltage you apply.

 

[Bob Lee (QSC)]

If indeed the power drops from 200W (4-ohm load) to 150W (8-ohm load) output, the voltage at 150W (8-ohm) setting will be higher.

There is no 200W or 150W or 4- or 8-ohm setting on an amplifier. Keep in mind that even "power" amplifiers are voltage amplifiers.

Thus you get more than 1/2 the initial voltage on each speaker. This implies the 200W rating IS NOT based on power amp voltage limitation but rather power amp CURRENT limitation.

Keep in mind that amplifier power ratings are determined by the voltage at the amp's clipping point. Below clipping, doubling the load impedance will result in a halving of the power delivered into the load because the output voltage does not change with load (unless its output impedance is substantial), but current does.

Changing the load impedance does not change the amplifier voltage, but it does change what voltage the amp clips at (unless the output sections power supply rails are regulated). That's because higher current demand of lower load impedances cause more voltage drop in the power supply's internal impedances, so the supply rail voltages droop somewhat more.

 

[ashtray]

Even though it's outside this particular discussion, would it matter if I had replaced the 2 power caps with larger ones?

 

[Lelander]

The existing EDEN technology is 200W into 8-ohm and 320W into 4-ohm. I have not seen too many power amp ratings that halve going from 4 to 8. But then you get into the whole conversation of how do they derive power ratings. I agree with Bill that it all comes down to how much voltage you apply.

Yes.

I wonder, can anyone expound on this whole "wattage @ 8 ohms > 1/2 W @ 4 ohms" business. Granted, it's been a very long time since I took intro to circuit analysis, but it's my recollection that Ohm's law states that voltage is inversely proportional to resistance at constant current. That being the case shouln't twice the resistance always result in half the voltage, which (if I am understanding this correctly) means half the volume?

 

[Bob Lee (QSC)]

Why would the current be constant?

 

[Lelander]

Changing the load impedance does not change the amplifier voltage, but it does change what voltage the amp clips at (unless the output sections power supply rails are regulated). That's because higher current demand of lower load impedances cause more voltage drop in the power supply's internal impedances, so the supply rail voltages droop somewhat more.

Apologizing in advance for my ignorance, what your saying is that reactance of the amplifier electronics ultimately result in lower-than-calculated voltage at lower loading, thus the output doesn't truly double at half the resistance?

[edit] No, what you are saying is that at outputs below clipping the change in power is proportional as expected, I think. I will get my head around this someday.

 

[Bob Lee (QSC)]

Apologizing in advance for my ignorance, what your saying is that reactance of the amplifier electronics ultimately result in lower-than-calculated voltage at lower loading, thus the output doesn't truly double at half the resistance?

No, that's not what I am saying.

 

[Lelander]

The bigger issue seems to be why anyone would design an amp to add a speaker in series Either make the thing 2ohm stable or make the internal speaker 8 ohms.
QUOTE]

But then you have to market it as a 150W combo rather than a 200W combo!

 

[billfitzmaurice]

But what everyone seems to be saying, is that the volume should increase with the 2 cabinets going.

I'm not saying that, and neither is Bob. With two cabs and the amp set at the same level there will be no change in the output compared to one. You may get more output from two cabs if one cab alone is not adequate to handle the output of the amp, allowing it to be turned up louder with two cabs, but that's it.

OTOH, if the cabs were parallel wired sensitivity would go up by 6dB. You don't have that option, since apparantly the amp won't handle a 2 ohm load, which is the only reason why the extension jack would be series wired.

 

[KJung]

But then you have to market it as a 150W combo rather than a 200W combo!

Trust me, they would still market it as a 200 watt combo. There are a zillion examples of manufacturers naming their products based on the extreme 2ohm output... The MesaBB750, the Genz 750 and 600, the EBS650, etc., etc., etc. (or 8ohm combo's based on their 4ohm output with extension cab).

The sad thing is, given what I've learned from Bill and Bob and others on this site, is that the 8 ohm power output is probably plenty to drive those speakers to pretty much full output.

 

[Lelander]

Trust me, they would still market it as a 200 watt combo. There are a zillion examples of manufacturers naming their products based on the extreme 2ohm output... The MesaBB750, the Genz 750 and 600, the EBS650, etc., etc., etc.

The sad thing is, given what I've learned from Bill and Bob and others on this site, is that the 8 ohm power output is probably plenty to drive those speakers to pretty much full output.

Or at least as much output as you would need. I have a 100W combo for rehearsal and have never heard it distort or clip at any volume I use.

You know, I would really expect companies like Genz to market with a smaller BS factor. Damn my naiveté.

 

[billfitzmaurice]

Even though it's outside this particular discussion, would it matter if I had replaced the 2 power caps with larger ones?

No. The amp might have less 60 cycle hum, but that's about it.

 

[KJung]

Or at least as much output as you would need. I have a 100W combo for rehearsal and have never heard it distort or clip at any volume I use.

You know, I would really expect companies like Genz to market with a smaller BS factor. Damn my naiveté.

To be fair to the Genz guys, their large amps are among the few bass specific integrated heads that are really designed to run optimally at 2ohms, so I guess it's not that bad to do that.

 

[Lelander]

To be fair to the Genz guys, their large amps are among the few bass specific integrated heads that are really designed to run optimally at 2ohms, so I guess it's not that bad to do that.

Overly optimistic specs certainly wouldn't keep me from picking one up if I had the coin

 

[DavePlaysBass]

There is no 200W or 150W or 4- or 8-ohm setting on an amplifier. Keep in mind that even "power" amplifiers are voltage amplifiers.

At 8-ohm, many solid state amps may put more effective voltage at the output terminals than with a 4-ohm load. This could be cause of current limiting that protect an amplifier from over current conditions. Or it could simply be because of source impedance of the amplifier itself. If you look at the amp as a voltage source and a source impedance, you will get a higher percentage of the available voltage out to load at higher load impedances (8-ohm). We can argue over why and this and that. But at the end of the day, power amp 8-ohm ratings are higher than 50% of the 4-ohm rating. And that is because the EFFECTIVE voltage at the amp output is higher with the increase load impedance (and decrease current). That is the key point. FOR WHATEVER REASON.

Keep in mind that amplifier power ratings are determined by the voltage at the amp's clipping point. Below clipping, doubling the load impedance will result in a halving of the power delivered into the load because the output voltage does not change with load (unless its output impedance is substantial), but current does.

Changing the load impedance does not change the amplifier voltage, but it does change what voltage the amp clips at (unless the output sections power supply rails are regulated). That's because higher current demand of lower load impedances cause more voltage drop in the power supply's internal impedances, so the supply rail voltages droop somewhat more.

Your are supporting my statments that you get greater more EFFECTIVE voltage out of an amp when running an 8-ohm load versus a 4-ohm load. And as I stated, at 4-ohm it is the current that gets you. At 8-ohm you run into the voltage capability of the amplifier rails.

 

[Lia_G]

Overly optimistic specs certainly wouldn't keep me from picking one up if I had the coin

Apologies for going off topic, but ...

On the contrary, Genz specs are about the most conservative I've ever encountered. The GBE600, which is rated at 425 watts into 4 ohms, is louder than some amps I've played which are rated at nearly twice the power.

Sorry for the off topic blurb ...

Cheers

 

[Bob Lee (QSC)]

At 8-ohm, many solid state amps may put more effective voltage at the output terminals than with a 4-ohm load. This could be cause of current limiting that protect an amplifier from over current conditions. Or it could simply be because of source impedance of the amplifier itself. If you look at the amp as a voltage source and a source impedance, you will get a higher percentage of the available voltage out to load at higher load impedances (8-ohm). We can argue over why and this and that. But at the end of the day, power amp 8-ohm ratings are higher than 50% of the 4-ohm rating. And that is because the EFFECTIVE voltage at the amp output is higher with the increase load impedance (and decrease current). That is the key point. FOR WHATEVER REASON.





Your are supporting my statments that you get greater more EFFECTIVE voltage out of an amp when running an 8-ohm load versus a 4-ohm load. And as I stated, at 4-ohm it is the current that gets you. At 8-ohm you run into the voltage capability of the amplifier rails.

Below clipping, the difference between the voltage into an 8-ohm load and into a 4-ohm load is negligible, typically less than 0.05 dB. For all practical purposes, it is the same.

As I said, the increased current demand causes greater supply rail sag because of the losses in the power supply's internal impedances (unless the supply is regulated); that will affect the output voltage at which clipping starts. That is why an amp's 4-ohm power ratings are usually less than double its 8-ohm figure. The higher current draw does not change the gain of the amplifier, so again, the effective voltage does not change with the lower load impedance.

 

[DavePlaysBass]

Below clipping, the difference between the voltage into an 8-ohm load and into a 4-ohm load is negligible, typically less than 0.05 dB. For all practical purposes, it is the same.

As I said, the increased current demand causes greater supply rail sag because of the losses in the power supply's internal impedances (unless the supply is regulated); that will affect the output voltage at which clipping starts. That is why an amp's 4-ohm power ratings are usually less than double its 8-ohm figure. The higher current draw does not change the gain of the amplifier, so again, the effective voltage does not change with the lower load impedance.

I agree with your first statements. Before you go into saturation both sound the same. No surprise there. But that is not what this conversation seems to be about.

If the 8-ohm rating of an amplifier is greater than 50% of the 4-ohm rating (and you say this to be true), then there is greater voltage applied accross and 8-ohm load than a 4-ohm load. It is governored by P = V^2 / R.

If R doubles, P is cut in half if V stays the same. If when R doubles, V increase somewhat, the result is P greater than 50% of the 4-ohm rating.