The Myth Lives On!! (Underpowering)

[walterw]

Originally Posted by megafiddle

The only interpretation that makes sense is that the amp's
rated power should not be significantly lower than the cab's rated
power.

not even that!

if the lower-rated amp gets the signal loud enough for the job without any clipping, then that amp is fine no matter how much lower it is.

the only "rule" i can see is "an amp rated just a little below the speaker (or higher) should not be driven into hard, continuous clip, because it will create too much power for too long, cooking the speaker."

[two fingers]

Originally Posted by Tractorr

True, it is just kind of shocking that a company that is known as a quality brand feels they need to stoop to using terminology that they know to be incorrect.

Um.... it's called marketing and every single company does it.

One 12AX7 stuck in the middle of a preamp circuit is almost always useless. It is for marketing purposes only.

But this thread is about to get interesting.............

[KJung]

Originally Posted by PlungerModerno

The source that inspired this thread said:

"If you already have an external amplifier and want to save some money, this may be a great option. Just be sure you provide the correct power range to the monitor. It's obvious that too much power can fry a monitor, but too little power can also cause permanent damage."

I interpret this as pretty unambiguously stating that too much or too little power can fry a monitor. Which is wrong. The tweeter can be blown easier than the woofer and mid (if there is one) but it's not blown by too little power - if that was the case muting an amp would cause the attached cabs to blow.

Again, this is such a tired old topic. What I assume they were saying is, again, pushing a low powered amp way too hard can blow a tweeter. This is a fact. The esoteric reason that 'pushing an amp' results in it putting out a lot of distorted power is meaningless to the typical player.

So, I guess they could have said that pushing a really low powered amp actually results in blowing a tweeter with too much distorted power that can happen when you have an amp and speaker combination that 'isn't up to the job', but how would that help anyone make a decision?

[KJung]

Originally Posted by two fingers

Um.... it's called marketing and every single company does it.

One 12AX7 stuck in the middle of a preamp circuit is almost always useless. It is for marketing purposes only.

But this thread is about to get interesting.............

Two of your three statements are false.

The first one is true. Every company uses marketing.

The second statement is, of course, rubbish. The impact of a preamp tube varies greatly across executions. Some preamps with single tubes (like the Alembic) and multiple tubes (like the Mesa Walkabout, the Streamliner, etc.) have a huge impact on the tone. Other executions like the Eden circuit, not so much.

Also, given this tired old topic has had multiple threads that always turn out the same way (resulting in those with just a little bit of technical knowledge being appalled and shocked (shocked I tell you) that some product descriptions are not totally technically correct, even though the vast majority are correct in spirit (i.e., the use of the term 'digital' to loosely describe a small, SMPS driven amp). So trust me, like all the others, this thread is not going to turn out interesting.

[KJung]

Originally Posted by walterw

if the lower-rated amp gets the signal loud enough for the job without any clipping, then that amp is fine no matter how much lower it is.

the only "rule" i can see is "an amp rated just a little below the speaker (or higher) should not be driven into hard, continuous clip, because it will create too much power for too long, cooking the speaker."

Your rule is not really correct. The 'rated power of a speaker' means nothing regarding this issue, and that is incorrect. The rated power of a speaker is based on the thermal limits of a driver. The only way to do harm regarding that spec is to apply too much absolute power, and the vast majority of cabs will let you know there is a problem by farting out or compressing LONG before you damage a woofer.

The only issue with using a low powered amp pushed very hard has to do with blowing tweeter, since the hard clipping from that abuse is mostly high frequency.

Again, very minor issue here, but the statement that is causing a few to be 'shocked' is basically true. On a list of 100 things to consider when buying a system, it would be around 95 on the list, but whatever.

This, to me, is similar to some companies that are selling mid driver loaded cabs saying it will have a massive impact on 'helping you spread the sound more evenly around the room'. The reality is, it will help spread a relatively narrow band of upper midrange versus one way cabs. Interestingly, if you don't have a tweeter in a typical 12/6 or 15/6 cab, it will actually spread the treble LESS effectively than a typical two way cab with a tweeter. Same thing, a bit of 'looseness' in the marketing description that is 'kind of true', but not really in the absolute sense that the information is provided.

Edit: To be fair to all these companies, given that I make most of my money as a marketing consultant/data miner, it is very difficult to walk the line between communicating relatively accurate information to a relatively uninterested consumer in a way that is 'correct in spirit' and relatively accurate in a technical sense but still get the point across in a word or phrase. Not an easy thing to do.

[ThisBass]

AES2-1984 (r2003)

4.5 Power-Handling

4.5.1 Test Conditions and Equipment.
The lf driver shall be mounted in free air so that the direction of motion of the diaphragm is in a horizontal
plane and so that there is no appreciable air loading from adjacent structures. The driver shall be excited with a
band of pink noise extending one decade upward from the manufacturer’s stated lf limit of the device. The
noise shall be bandpass filtered at 12dB per octave with Butterworth filter reponse characteristics, and the peakto-
rms voltage ratio of the noise signal supplied to the lf driver shall be 2:1 (6 dB). Refer to Appendix C for
recommended method. The manufacturer shall state the upper and lower cutoff frequencies (– 3 dB) of the
noise signal.

NOTE: The committee adopted this free-air power-handling test only after many hours of intense deliberation.
We recognize that such a test will not always produce results that reflect the intended use of the loudspeaker.
However, the free-air test is more practical than an “infinite battle” (5VAS) test. It avoids the issue of which
enclosure to use and has the same net effect on diaphragm excursions on an infinite baffle. The free-air test
requires a dramatically smaller test facility, produces much lower sound-pressure levels, and is easily
duplicated, with simple test equipment and in the field. This test method allows similar loudspeakers from
different manufacturers to be compared on an equal basis.

4.5.2 Test Procedure.
The device under test shall be subjected to successively higher powers and allowed to reach thermal equilibrium
at each increment (approximately 2 h). Power shall be determined as the square of applied rms voltage, as
measured with a “true rms” voltmeter, divided by Zmin. The rated power of the device shall be that power the
device can withstand for 2 h without permanent change in acoustical, mechanical, or electrical characteristics
greater than 10%.

[KJung]

Originally Posted by ThisBass

AES2-1984 (r2003)

4.5 Power-Handling

4.5.1 Test Conditions and Equipment.
The lf driver shall be mounted in free air so that the direction of motion of the diaphragm is in a horizontal
plane and so that there is no appreciable air loading from adjacent structures. The driver shall be excited with a
band of pink noise extending one decade upward from the manufacturer’s stated lf limit of the device. The
noise shall be bandpass filtered at 12dB per octave with Butterworth filter reponse characteristics, and the peakto-
rms voltage ratio of the noise signal supplied to the lf driver shall be 2:1 (6 dB). Refer to Appendix C for
recommended method. The manufacturer shall state the upper and lower cutoff frequencies (– 3 dB) of the
noise signal.

NOTE: The committee adopted this free-air power-handling test only after many hours of intense deliberation.
We recognize that such a test will not always produce results that reflect the intended use of the loudspeaker.
However, the free-air test is more practical than an “infinite battle” (5VAS) test. It avoids the issue of which
enclosure to use and has the same net effect on diaphragm excursions on an infinite baffle. The free-air test
requires a dramatically smaller test facility, produces much lower sound-pressure levels, and is easily
duplicated, with simple test equipment and in the field. This test method allows similar loudspeakers from
different manufacturers to be compared on an equal basis.

4.5.2 Test Procedure.
The device under test shall be subjected to successively higher powers and allowed to reach thermal equilibrium
at each increment (approximately 2 h). Power shall be determined as the square of applied rms voltage, as
measured with a “true rms” voltmeter, divided by Zmin. The rated power of the device shall be that power the
device can withstand for 2 h without permanent change in acoustical, mechanical, or electrical characteristics
greater than 10%.

Not sure what this has to do with anything. The accuracy of the thermal limit of drivers is not really an issue at all. What is an issue is players, over and over again, misinterpreting thermal limits as 'power requirements' (hence, all the misunderstanding and discussion about 'underpowering').

There is NO issue in using a 100 watt head with a cab that can potentially use much more power (i.e., rated 500watt thermal). That is a different issue, and the concept of 'underpowering' there is obviously completely wrong and misunderstood. That is NOT due to fudged thermal ratings IMO.

The issue of pushing an amp not up to the task into a cab of ANY thermal rating that has a tweeter (especially an unprotected tweeter) is a real issue, and again, while not actually a result of 'underpowering', it IS a result of pushing an amp way beyond its capability, which is a different definition of 'underpowering' (i.e., using an amp too small for the volume required, regardless of the thermal rating of the speaker or cabinet).

One definition is 'reasonable', the other is not.

[ThisBass]

Originally Posted by KJung

Not sure what this has to do with anything. The accuracy of the thermal limit of drivers is not really an issue at all.

I would doubt there is a thermal limit at all.

Because the limit is given by rms voltage and:

"...2 h without permanent change in acoustical, mechanical, or electrical characteristics
greater than 10%."



Power handling of lf-driver is then calculates by:

"square of applied rms voltage, as measured with a “true rms” voltmeter, divided by Zmin."


Consider that Zmin is used for Power Handling calculatin.
And calculation is only calculation.
Other methods use Znominal, then the result will be significant different to the AES results.

Consider that the test signal is pink noise with peak to rms ratio +6dB.

Consider that amp power is most of the time measured as 1kHz sine power at 1% THD.


Consider that the peak to rms ratio of a true bass signal is in general totally different to all of them.


Powering any cabs with its rms power rated value using a true bass signal will destroy the drivers very quickly (I'm sure).

[KJung]

Originally Posted by ThisBass

I would doubt there is a thermal limit at all.

Because the limit is given by rms voltage and:

"...2 h without permanent change in acoustical, mechanical, or electrical characteristics
greater than 10%."



Power handling of lf-driver is then calculates by:

"square of applied rms voltage, as measured with a “true rms” voltmeter, divided by Zmin."


Consider that Zmin is used for Power Handling calculatin.
And calculation is only calculation.
Other methods use Znominal, then the result will be significant different to the AES results.

Consider that the test signal is pink noise with peak to rms ratio +6dB.

Consider that amp power is most of the time measured as 1kHz sine power at 1% THD.


Consider that the peak to rms ratio of a true bass signal is in general totally different to all of them.


Powering any cabs with its rms power rated value using a true bass signal will destroy the drivers very quickly (I'm sure).

What makes the 'thermal rating' of a cab additionally useless is that most amps rarely reach their rated power, even in short bursts, so you have a 'loose number' on one side that people try to match with a 'loose number' on the other side.

The good news is, most speakers reach their mechanical limits, which is pretty easy to hear, long before any thermal damage is done, so again, the best thing for players to do is really ignore the thermal specs and not get caught up in the 'I have an '800 watt cab' or whatever.

edit: The other issue here is that a bass guitar signal, which has lots of 'rests' between the peaks, would seem to be much more forgiving than programmed music or a 'test lab constant input source of pink noise or whatever'. Thermal is, well, thermal, and can build up over time. Lots of 'cooling time' for drivers between the notes I believe.

So again, +1, in that none of these specs, even if accurate, tell you much about either an amplifier's performance or a speakers real capabilities.

[Tractorr]

Originally Posted by two fingers

Um.... it's called marketing and every single company does it.

There is a big difference between marketing/marketing speak and just false information.

For example, an auto manufacture could make the claim most powerful V-8 on the market, and as long as by some measurement that is true then they are not lying. This measurement may not mean anything in reality but they can point to that spec and say "no other V-8 is more powerful in that respect." They could not say most powerful V-8 on the market when in fact the engine is a V-6. As a matter of fact the GK example is kind of worse because they are making something up entirely (there is no such thing as a digital power amplifier). This would be like a car company claiming their car has a nuclear fusion engine. Now they could put "Fusion Powered" in ad copy, but I almost guarantee that their would be an asterisk and at the bottom the page vehicle power by blah blah blah. "Fusion Powered" in this case is a catchphrase not something that is listed as a feature.

GK on the other hand, has listed as a feature "Digital Power Amplifier." Again, big difference between marketing speak and a flat out lying.

[ThisBass]

Originally Posted by KJung

What makes the 'thermal rating' of a cab additionally useless is that most amps rarely reach their rated power, even in short bursts, so you have a 'loose number' on one side that people try to match with a 'loose number' on the other side.

That's right.

But the situation is very different for heavy distorted bass signals. That means for very audible distorted signals.

Consider the test signal for speakers is +6dB peak to rms ratio.
However distorted bass signals peak to rms can be anything.
There is no way to predict the peak to rms of a distorted signal unless you can measure the signal.

By the other hand a very extreme situation for an amp output power is the amount of twice the rated power by Zero Peak To RMS.

Originally Posted by KJung

The good news is, most speakers reach their mechanical limits, which is pretty easy to hear, long before any thermal damage is done, so again, the best thing for players to do is really ignore the thermal specs and not get caught up in the 'I have an '800 watt cab' or whatever.

Or keep your eye to the excursion. Extreme excursions are visible.
Most of the time the low frequency transients cause higher excursions.

Originally Posted by KJung

edit: The other issue here is that a bass guitar signal, which has lots of 'rests' between the peaks, would seem to be much more forgiving than programmed music or a 'test lab constant input source of pink noise or whatever'. Thermal is, well, thermal, and can build up over time. Lots of 'cooling time' for drivers between the notes I believe.

So again, +1, in that none of these specs, even if accurate, tell you much about either an amplifier's performance or a speakers real capabilities.

I agree.

IMO with some audible content of clipping it is not possible to reach more then 1/3 rms of the rated rms output power of an amp.

But the situation runs out of control with heavy distorted signals.

[KJung]

Originally Posted by Tractorr

There is a big difference between marketing/marketing speak and just false information.

For example, an auto manufacture could make the claim most powerful V-8 on the market, and as long as by some measurement that is true then they are not lying. This measurement may not mean anything in reality but they can point to that spec and say "no other V-8 is more powerful in that respect." They could not say most powerful V-8 on the market when in fact the engine is a V-6. As a matter of fact the GK example is kind of worse because they are making something up entirely (there is no such thing as a digital power amplifier). This would be like a car company claiming their car has a nuclear fusion engine. Now they could put "Fusion Powered" in ad copy, but I almost guarantee that their would be an asterisk and at the bottom the page vehicle power by blah blah blah. "Fusion Powered" in this case is a catchphrase not something that is listed as a feature.

GK on the other hand, has listed as a feature "Digital Power Amplifier." Again, big difference between marketing speak and a flat out lying.

Again, 'digital' as a short hand description for class D/SMPS amps, has been used for decades, and is pretty well understood as representing 'small and lightweight' (primarily in the power supply) versus 'bigger and heavier'.

Using commonly accepted jargon that is clearly understood is not lying at all. And, nowhere do the many companies who describe their class D/SMPS amps suggest that 'digital' is better than their own 'analog' amps (using analog as a short hand for larger amps with a traditional power supply).

Again, I guess we will all go round and round like every other thread on this topic (there is a massive thread from a couple of months ago discussing the 'digital' thing). I just don't get the issue in this case. That term has been used FOREVER, and does not connote any sort of 'superior claim' (i.e., lying to get market share from a competitor). EVERYONE knows what 'digital' means the way it has been used for decades..... basically SMPS (resulting in small and lightweight). Nowhere does any company (that I know of) suggest that their amp is 'better because it is digital'.... it is just a quick, shorthand way of saying 'small and lightweight'. This sort of 'redefinition of a technical term to become understood jargon' is quite common.

[two fingers]

Originally Posted by KJung

Two of your three statements are false.

The first one is true. Every company uses marketing.

The second statement is, of course, rubbish. The impact of a preamp tube varies greatly across executions. Some preamps with single tubes (like the Alembic) and multiple tubes (like the Mesa Walkabout, the Streamliner, etc.) have a huge impact on the tone. Other executions like the Eden circuit, not so much.

That's why I said ALMOST always. And the Walkabout and Streamer aren't exactly ONE tube now are they? But there are a great many amps with a single 12AX7 stuck in them for the purpose of calling it a "hybrid" only. I owned the Eden and a couple of SWR's and have a Shuttle 6.0 now. I also own the Walkabout and some old tube heads. I am also currently in school for electronics. While I don't know everything yet I am perfectly capable of using both a schematic and my ears to determine whether or not a tube is useful or marketing dribble. And quite often from a tone standpoint and an electronic one the tube does virtually nothing and was put there just so they could point it out in an ad. You could straight wire the socket (using no tube at all) and get almost same results.

But thanks for your input.

Sorry to derail.

[KJung]

Originally Posted by two fingers

That's why I said ALMOST always. And the Walkabout and Streamer aren't exactly ONE tube now are they? But there are a great many amps with a single 12AX7 stuck in them for the purpose of calling it a "hybrid" only. I owned the Eden and a couple of SWR's and have a Shuttle 6.0 now. I also own the Walkabout and some old tube heads. I am also currently in school for electronics. While I don't know everything yet I am perfectly capable of using both a schematic and my ears to determine whether or not a tube is useful or marketing dribble. And quite often from a tone standpoint and an electronic one the tube does virtually nothing and was put there just so they could point it out in an ad. You could straight wire the socket (using no tube at all) and get almost same results.

But thanks for your input.

Sorry to derail.

+1 I agree. The Eden thing was pure smoke and mirrors. That tube didn't impact voltage at all, and from what a number of EE's have posted, you could get identical sound by just bypassing with a hardwire.

The Shuttle tube can be pushed pretty nicely to break-up, and the single tube Alembic pre is about as close to an old Bassman amp as you can get. IMO.

Not really OT. This goes to the entire issue that is being discussed.... when is 'marketing info' dishonest versus just 'quick simplification of complex items in a way that will appeal to the consumer and generally communicate the product benefits'. That is a grey area for sure. IMO, Eden marketing that 'hybrid' thing years ago was MUCH worse than a number of companies describing SMPS as 'digital' or suggesting that matching optimum power to a system being better than not', etc.

Of course, those old Eden amps sounded killer, and did perform IMO as advertised, so even there, not much harm done IMO.

[Tractorr]

Originally Posted by KJung

Again, 'digital' as a short hand description for class D/SMPS amps, has been used for decades, and is pretty well understood as representing 'small and lightweight' (primarily in the power supply) versus 'bigger and heavier'.

Using commonly accepted jargon that is clearly understood is not lying at all. And, nowhere do the many companies who describe their class D/SMPS amps suggest that 'digital' is better than their own 'analog' amps (using analog as a short hand for larger amps with a traditional power supply).

Again, I guess we will all go round and round like every other thread on this topic (there is a massive thread from a couple of months ago discussing the 'digital' thing). I just don't get the issue in this case. That term has been used FOREVER, and does not connote any sort of 'superior claim' (i.e., lying to get market share from a competitor). EVERYONE knows what 'digital' means the way it has been used for decades..... basically SMPS (resulting in small and lightweight). Nowhere does any company (that I know of) suggest that their amp is 'better because it is digital'.... it is just a quick, shorthand way of saying 'small and lightweight'. This sort of 'redefinition of a technical term to become understood jargon' is quite common.

Well all of these companies refer to their amps as Class D:
Ampeg, SWR, Fender, Carvin, Aguilar, Genz Benz, Orange

These companies do not list anything it their marketing literature (I do not know if they are class D as we all know micros can be small and not Class D):
Eden, Markbass, TC Electronics

The only two that I could find that call them "digital" are:
GK, EBS

When all of the major manufactures except 2, who name their topology, use the correct term then I think that is generally accepted term. Plus, if Class D were some really long term then I could see coming up with a shorthand, but a term is not short hand if it is the exact same number of key strokes.

[Tractorr]

Oh, and the accepted term on TB for small light heads are "micros"

[KJung]

Originally Posted by Tractorr

Well all of these companies refer to their amps as Class D:
Ampeg, SWR, Fender, Carvin, Aguilar, Genz Benz, Orange

These companies do not list anything it their marketing literature (I do not know if they are class D as we all know micros can be small and not Class D):
Eden, Markbass, TC Electronics

The only two that I could find that call them "digital" are:
GK, EBS

When all of the major manufactures except 2, who name their topology, use the correct term then I think that is generally accepted term. Plus, if Class D were some really long term then I could see coming up with a shorthand, but a term is not short hand if it is the exact same number of key strokes.

Markbass also uses 'digital' as a descriptor now (in quotes on their material), and Walter Woods uses the term also when discussing his category-creating amp designs (although I'm sure he is similarly using it as a simple, loose descriptor to talk to layman players about his amp).

Again, the big question is 'so what'. Do you think, for some reason, some marketing genius is sitting in a dark back room saying 'yeah, if we call this 'digital' the kids will buy it. Remember, ALL these companies have non SMPS amps also. Never has anyone said (IMO) a 'digital' amp is somehow better, or that a 'digital amp' is better than another companies 'class D' amp or whatever. That would be lying and cheezy!

The only company who's ethics in this regard every really bothered me was Accugroove, who actually purposely used technical terms to mislead IMO. Of course, they were pretty much drummed out of business. (edit: Epifani is also in my 'marketing hall of shame' also, for increasing the weight of their UL cabs, which were marketed primarily as 'light weight' and then not updating their website or telling any of their retailers about the change. The market seems to have pretty much punished them also).

GK calling the MB line 'digital'.... wow, if that upsets you, you must REALLY be pissed about world hunger

[Tractorr]

Originally Posted by KJung

Markbass also uses 'digital' as a descriptor now, and Walter Woods uses the term also.

Again, the big question is 'so what'. Do you think, for some reason, some marketing genius is sitting in a dark back room saying 'yeah, if we call this 'digital' the kids will buy it. Remember, ALL these companies have non SMPS amps. Never has anyone said a 'digital' amp is somehow better, of that a 'digital amp' is better than another companies 'class D' amp or whatever. That would be lying and cheezy!

The only company who's ethics in this regard every really bothered me was Accugroove, who actually purposely used technical terms to mislead IMO. Of course, they were pretty much drummed out of business.

GK calling the MB line 'digital'.... wow, if that upsets you, you must REALLY be pissed about world hunger

Doesn't piss me off because I know better, but I have met people who swear that their amps are "digital."

I just find it annoying that they could use the correct term and they don't, and there is certainly someone who made that decision to call it a digital amp.

If they just picked a term that was unrelated entirely it would be better, but in the audio world digital usually refers to digital signal processing.

[KJung]

Originally Posted by Tractorr

Doesn't piss me off because I know better, but I have met people who swear that their amps are "digital."

I just find it annoying that they could use the correct term and they don't, and there is certainly someone who made that decision to call it a digital amp.

If they just picked a term that was unrelated entirely it would be better, but in the audio world digital usually refers to digital signal processing.

I guess being 'personally annoyed' is every person's right! I guess you can vote with your pocketbook and not buy their gear.

Doesn't bother me in the least, again, since there is IMO no 'intent to mislead' or take share from competitors due to mistating the actual performance of the product.

Anyway, interesting topic (the entire thread), and as one who has either worked in the marketing divisions of a few major companies and who now consults to quite a few marketing divisions of major companies (for the last 20 years or so), often involving creating, spec'ing, describing and marketing new products, this topic is near and dear to my heart. Getting the technical versus marketing balance 'correct' is not easy.

[Tractorr]

Originally Posted by KJung

I guess being 'personally annoyed' is every person's right! I guess you can vote with your pocketbook and not buy their gear.

Doesn't bother me in the least, again, since there is IMO no 'intent to mislead' or take share from competitors due to mistating the actual performance of the product.

Anyway, interesting topic (the entire thread), and as one who has either worked in the marketing divisions of a few major companies and who now consults to quite a few marketing divisions of major companies (for the last 20 years or so), often involving creating, spec'ing, describing and marketing new products, this topic is near and dear to my heart. Getting the technical versus marketing balance 'correct' is not easy.

It is not so egregious an offense that I wouldn't buy from GK.

I suppose more than anything I dread walking into a Guitarcenter and having one of their brain dead associates adamantly tell me that the GK has a digital power amplifier, because that is what it says in the marketing literature.