3dB louder sounds like this

[Mark Reccord]

Originally Posted by mystic38

I simply am not seeing that you have any engineering point here...

a) "meeting spec"
not a single amp can meet a hard fixed spec. specs are "minimum" or toleranced for a reason...

I didn't say that. Of course everything has some tolerance. Though if an amp is spec'd to produce 500W @8Ohms, 0.1% THD, it damned well better come within 1% of that under the conditions the manufacturer measured it at. This is certainly the case for any pro-level power amp I've seen.

b) Supplying 2x power into 0.5x load
If i wish to design an amp that can produce the amp/voltage envelope for 2x power into 0.5x load..i can. period... there is no technical reason why i cannot.

Sure there is: Ohm's law. If you happen to have a lossless power supply design, I suggest you patent it post-haste!

Sure, A by product of that is that the transformer will be bigger with larger windings, the heatsink larger with more devices and the wiring will be upgraded.. but if that is my design objective it can be done.

No it can't. Not with real components with real impedances. This isn't debatable and I don't even know why anyone with any technical knowledge would even disagree. You can approach it with good design but you'll never actually reach it. Even a 0.01% loss is still a loss. Once again, I am talking about maximum output power at the load impedances, right at the knee where clipping comes on. No real world amp will actually be able to double full power between the 8 and 4 ohm loads. Not until the lossless power supply exists anyway.

c) spec fudging
if your argument is that the only way this can be engineered is by over-achieving at one specification simply to support the other spec is a requirement.. you are wrong.

note, I am making an engineering statement here, not a budget one.. the statement "an amp will only produce 1.5x power into 0.5x load" is wrong. period...most do, that i agree but its not a theory limitation, nor a practical one..more budgetary in nature

regards..

I didn't say ever say that an amp will only produce 1.5x power into 0.5x load. What I am saying is that you can design an amplifier to mitigate I^2R losses but you can't ever completely negate them. It's disingenuous to suggest otherwise.

[JHAz]

Originally Posted by mystic38

I dont understand what part of
250W min into 8R 0.1% THD max
500W min into 4R 0.1% THD max

are weasel words... ? those specs clearly and specifically state its twice the power into half the impedance.

A high quality amp can provide 2x power into 1/2 impedance. fact.

consider:

a) Running 250W into 8R. P=V2/R ergo this requires a PSU with voltage rails of 45V. P=VI therefore PSU amp supply is ~5.5A

b) Running 500W into 4R. P=V2/R therefore PSU rails required to be 45V. P=VI therefore PSU amp supply needs to be ~11A

Running an amp into 8 Ohms is limited by the PSU voltage, but running into 4 Ohms is limited by PSU current.

Design a solid and capable power supply and you will get 2x power into half the impedance... This is not new, not rocket science, and given even an 8 ohm speaker can have impedance (frequency dependent) varying from 3 to 16 ohms the ability to drive current is a MAJOR factor in a good amp

"minimum" is the unquoted waasle word (to me). If the amp really delivers 500 watts at 4 ohms, maybe it would normally test at 325 or 350 watts at 8 ohms with the same THD. Saying a "minimum" of 250 at 8 ohms lets the marketers say their amp doubles down, if that kind of thing is important to a buyer. FWIW, I'd rather see them spec the additional dB or so of 8 ohm power, but to each his or her own.

[Mark Reccord]

Originally Posted by JHAz

"minimum" is the unquoted waasle word (to me). If the amp really delivers 500 watts at 4 ohms, maybe it would normally test at 325 or 350 watts at 8 ohms with the same THD. Saying a "minimum" of 250 at 8 ohms lets the marketers say their amp doubles down, if that kind of thing is important to a buyer. FWIW, I'd rather see them spec the additional dB or so of 8 ohm power, but to each his or her own.

Which is exactly how that Krell behaves.

[RS66LB]

Originally Posted by mystic38

I simply am not seeing that you have any engineering point here...

a) "meeting spec"
not a single amp can meet a hard fixed spec. specs are "minimum" or toleranced for a reason...

b) Supplying 2x power into 0.5x load
If i wish to design an amp that can produce the amp/voltage envelope for 2x power into 0.5x load..i can. period... there is no technical reason why i cannot.

Sure, A by product of that is that the transformer will be bigger with larger windings, the heatsink larger with more devices and the wiring will be upgraded.. but if that is my design objective it can be done.

c) spec fudging
if your argument is that the only way this can be engineered is by over-achieving at one specification simply to support the other spec is a requirement.. you are wrong.

note, I am making an engineering statement here, not a budget one.. the statement "an amp will only produce 1.5x power into 0.5x load" is wrong. period...most do, that i agree but its not a theory limitation, nor a practical one..more budgetary in nature

regards..

oh, p.s. am aged 50, designs to 250A@150V with water cooled heatsinks of 200 transistors, bank voltage regulation, and size of a double wardrobe.. do i qualify for the "around the block award" too?

lol -great comment and have a wonderful day

[Downunderwonder]

Originally Posted by Foz

IMO the first step for someone looking to address the challenge of loud lows equivalent in scale in the mid-band - as represented in the original material - and yet not highly distorted [muddy] = embrace the point made by the OP.

This aint a teddy bear's picnic, per the OP's track, 3 dB is just enough to notice a difference - and further, a 3 dB increase is no more than a first small step toward the goal.

To me, the bottomline is:

Playing louder is much more of a challenge for the low frequency end of the band [a pun!] than the guitardist end of the band. And if you want to accurately reproduce the original material - then playing louder lows than traditional bass rigs can provide is necessary.

You're bucking:

1) the equal loudness curve [-20 dB difference from 60 Hz to 1k Hz for a 75 dB composite signal]

2) the 1/f distribution typical to music [generally - each octave lower you go requires 3 dB MORE loudness to accurately emulate the original material]

3) The electro-mechanical non-triviality of getting drivers and boxes to stand the weather when making sub 100 Hz sound [low frequency production is hard on the horses].

TB is always telling folks that if you need to be louder: you don't need a bigger amp / turn off the bass, play mids / get another cab just like the one that aint cutting it now.

And that's alright - if you are willing to stop playing bass and settle for playing mids - because getting louder in the lows is a BFD. But with modern drivers and cab designs you can do it without hiring a road crew or mortgaging the farm, or making a muddy mess of the low end. Drivers can be had that have enormously improved from a weight to spl ratio and amp watts have become cheap both in dollars and pounds [OMG another pun!]. But if you are gonna really make a difference you have to accept that one must quit f*cking around and make some big changes from the traditional methods and means.

What original material? Traditional methods work fine for trad. rock. Our lows have always been our low mids, always will be.

[mjac28]

[dincz]

Originally Posted by Bassamatic

+3dB (double) of AMP power gives less than 1 dB of acoustic power gain - most people can not even hear this.

Unless you're running into speaker compression, that makes no sense at all.

[Downunderwonder]

It's a gibberish statement made to confuse. Nobody else uses "dB acoustic power".

[mystic38]

are you actually a design engineer?.. lol

This is not a hard problem man... simply create an output transitor bank capable of cleanly delivering 11.2A max and 44.7V max into a load... then ohms law will tell you you are voltage limited to 250W into 8 Ohm and current limited to 500W into 4 Ohm

Lossless doesnt come into it.. math does

fyi i dont need any lectures on losses in a system... read the 30kW part of my last post

Originally Posted by Mark Reccord

Sure there is: Ohm's law. If you happen to have a lossless power supply design, I suggest you patent it post-haste!
.

[throbgod13]

the amp design, and class, will dictate if there is a doubling of output current from lowering the impedance..

very few amplifiers do this..

[bgavin]

Originally Posted by dincz

A lot of questions come up about the difference in volume between 4 and 8 ohm cabs, or about doubling amplifier power.

A 3dB change sounds like this:

Just curious: did you measure +3dB with an RTA, or is this just from a control console?
It would be an interesting experiment to measure the output of your MP3 to see if the 3dB delta is produced by my speakers.

[ThisBass]

Originally Posted by mystic38

are you actually a design engineer?.. lol

This is not a hard problem man... simply create an output transitor bank capable of cleanly delivering 11.2A max and 44.7V max into a load... then ohms law will tell you you are voltage limited to 250W into 8 Ohm and current limited to 500W into 4 Ohm

Lossless doesnt come into it.. math does

fyi i dont need any lectures on losses in a system... read the 30kW part of my last post

max Voltage means no load which means the output current is zero.
If the output current is >0 means the voltage drops down.
< Volt max

[atrapp]

Well for sh**'s n giggle's here is a link to Stereophiles testing of the Krell KSA250 - many folks around here call Voodoo with regard to a lot of audiophile accessories - these seem to be fairly sound numbers.
Looks like it does 325 into 8 and 635 into 4 or just a hair under doubling power (not 1.5x being suggested as the maximum) at half the impedance. The article goes onto suggest it would have doubled output had sufficient current been available from the standard wall outlet.
A caveat here - I like high end audio gear (into which I used to pour too much money) and trust the folks at Stereophile to be honest in their reporting of tech specs.

http://www.stereophile.com/content/k...r-measurements

[ThisBass]

Originally Posted by atrapp

Well for sh**'s n giggle's here is a link to Stereophiles testing of the Krell KSA250 - many folks around here call Voodoo with regard to a lot of audiophile accessories - these seem to be fairly sound numbers.
Looks like it does 325 into 8 and 635 into 4 or just a hair under doubling power (not 1.5x being suggested as the maximum) at half the impedance. The article goes onto suggest it would have doubled output had sufficient current been available from the standard wall outlet.
A caveat here - I like high end audio gear (into which I used to pour too much money) and trust the folks at Stereophile to be honest in their reporting of tech specs.

http://www.stereophile.com/content/k...r-measurements

Krell specifies a 4kW output rating in 0.5 ohms, I didn't have a half-ohm resistor that would handle such power.

Which means the Krell is designed to be a 0.5 Ohm amp.

Most musicians gear are designed to work at 4 Ohm.
That means a 2 Ohm load won't provide additional power.

[ThisBass]

Let's tell some words about 4 Ohm amps and different loads.

Sometimes people do forget that max. Voltage depends on the load.

max. Voltage at 8 Ohm is (in general) significant bigger then max. Voltage at 4 Ohm.

Lets say 45 Volt max. at 4 Ohm, Master pot at 14:00

but

appro 55 Volt max. at 8 Ohm, Master pot turned up to 14:30 .. 15:00

Most of folks do forget that max power at 8 Ohm is reached at higher master pot settings.

[Mark Reccord]

Originally Posted by mystic38

are you actually a design engineer?.. lol

This is not a hard problem man... simply create an output transitor bank capable of cleanly delivering 11.2A max and 44.7V max into a load... then ohms law will tell you you are voltage limited to 250W into 8 Ohm and current limited to 500W into 4 Ohm

Lossless doesnt come into it.. math does

fyi i dont need any lectures on losses in a system... read the 30kW part of my last post

Right, so show me an unregulated power supply that can meet the 4 Ohm 44.7V@11.2A spec that will stay at 44.7V when the current demand is halved. We both know that even the stiffest power supply will sag a little under load and conversely rise as load decreases and if said amplifier circuit meets the 4 Ohm design goal, it will inherently exceed the 8 Ohm one if even by a tiny amount. No?

Clearly a regulated or massively overspec'd power supply would mitigate this almost completely, but there will always be some I^2R loss in an amplifier between no load and maximum load.

I don't think you need a lecture on losses but you seem to be resistant to the idea that power supply losses will prevent the perfect theoretical doubling of power when the load impedance is halved.

[ThisBass]

Originally Posted by Arjank

Dincz did a good thing in showing how much 3dB (and 6dB) is. IMO the thread should have ended here.

Then there came others who added a few other things to consider (thermal/mechanical compression, loudness level, frequency range, tube vs SS). I can add anotherone myself, bafflestep. Stack two cabinets and the baffle size increase, which in turn lowers the bafflestep frequency and the ear percieves that as a beefier sound....

So, there are a lot of variables why adding a 2e identical cab sounds fuller(thermal/mechanical compression aside):
-doubling cone are +3dB
-8-->4ohms load approx +2dB (with SS amp)
-lower bafflestep frequency due to stacked cabs(works best with cabs in horizontal orientation, or, if you place two big cabs next to eachother)

Also, when stacking cabs, one cab can just stay on the floor which makes a huge difference in the amount of lowend. In most cases people put their (single) cab a bit higher to hear the mids which in turn decreases lowend output.

my 2 cents.

+1

[ThisBass]

Originally Posted by mystic38

imo the ability to drive current is more important in an audio amplifier given there is no such thing as a speaker of constant 8 ohm impedance... so the ability of the amp to provide equal power across the impedance/frequency spectrum where the impedance can vary by a 4-5x is a clear indicator of amplifier quality.

So, with all other things being equal, it is most certainly NOT erroneous to assume an amp with higher current driver capability is a better amp.. Those companies dont put huge toroids and cans and heavy wiring in their amps for poops and giggles.

Fortunately bass guitar frequencies don't produce critical amounts of power at the frequency area of Zmin.

IMO audiophile amplification is a different animal.
By the other hand audiophile amplification should work with headroom all along the line, which means the need of max potential current should never take place in real live.

[B-string]

This thread got pretty wild for what I found to be a demonstration of little practical use. Lossless power supplies, not in audio use, if you did manage it you still have an imperfect junction in what ever output device with whatever typology. If you COULD develop an amplifier that had no increase in heat loss from halving the load it would most likely sound really poor as you are now talking about a switch not audio reproduction.

[ThisBass]

Every amp concept should be designed with taking account of some worst case scenarios.
A design engineer can't predict the (specific) usage of an amp. But by the other hand it's a valid point to do some considerations on a specific usage.
IMO every specific usage (or specific scenario) needs it's specific consideration.