More on amps and cabs power balance

[HolmeBass]

Not mentioned indeed, it’s derived.The article says for not clipping use 1/4 of the RMS power (which equals 1/8 of the Program and 1/16 of the peak).

I am sorry I posted that article. The idea that you should run a bass rig only at 1/4 of its rated RMS power to avoid clipping is absurd.

Once again: I posted it to let you know that Program power does not equal RMS power, and that’s it.

 

[HolmeBass]

Ahah why? It’s been so informative thanks to great pieces of info generously given by expert TBrs, and I believe I can do my math now

Too many falsehoods and misleading questions posted. Altogether it is pretty confusing. I didn’t help by posting the Carvin article.

 

[agedhorse]

Not mentioned indeed, it’s derived.The article says for not clipping use 1/4 of the RMS power (which equals 1/8 of the Program and 1/16 of the peak).

Again, you have come to an incorrect conclusion.

 

[JeezyMcNuggles]

The power is only distributed evenly among the attached cabinets if they have the same impedance rating.

That's exactly what I said

 

[JustFunk]

https://www.talkbass.com/threads/amps-faq-info-on-ohms-allsize-rigs-overunderpowercabs-diy-techtalk-links.166225/

Fishheadjoe

I passed there already. Many links don’t work to me, dunno why

 

[JustFunk]

Again, you have come to an incorrect conclusion.

Agedhorse, I believe you once again are wrongly attributing to me information that I didn’t write personally. This comes from the article linked by HolmeBass. And my (primary school) math is correct based on that (maybe not wrong but misleading) information.

I wouldn’t make a case out this, I think that everybody got the idea behind (if I did, I believe all others did too).

The exercise I did a few posts ago was to understand if I understood. If correct, you should not repeat ad nauseam basic info that in such case I have evidently learned already. If not correct, I would appreciate your math by mine and understand where I am wrong still (and I would be really thankful to you, as to all others here to help me, for that ).

 

[agedhorse]

Agedhorse, I believe you once again are wrongly attributing to me information that I didn’t write personally. This comes from the article linked by HolmeBass. And my (primary school) math is correct based on that (maybe not wrong but misleading) information.

I wouldn’t make a case out this, I think that everybody got the idea behind (if I did, I believe all others did too).

The exercise I did a few posts ago was to understand if I understood. If correct, you should not repeat ad nauseam basic info that in such case I have evidently learned already. If not correct, I would appreciate your math by mine and understand where I am wrong still (and I would be really thankful to you, as to all others here to help me, for that ).

It's not the link (which is poorly written) but your conclusion based on the already discredited link.

For AMPLIFIERS, there is power based on RMS voltage (which is what quality manufacturers use) and there is peak power which is based on peak voltage. Peak voltage is 1.414X the RMS voltage (for a sine wave) and when squared in the power equation becomes 2X the power.

For SPEAKERS, there is power based on RMS voltage (colloquially called RMS power as shorthand) which generally refers to the thermal power handling of the speaker. There is also program power, which derives from a speaker's power handling under dynamic conditions WHERE THERE IS NO CLIPPING OR COMPRESSION/LIMITING, and this is generally accepted to be 2X the RMS power (where RMS here represents the shorthand thermal limits of the driver) and is still represented in RMS units. Then, there is peak power which is presumed and generally accepted to be 2X the program power which becomes 4X the RMS power. This is not RMS units but peak units based on peak voltage which is 1.414X the program power's RMS voltage and when squared in the power equation becomes 2X the RMS power.

Note the difference between the amplifier definition and the speaker definition, these are generally accepted conventions, though not all manufacturers follow this as some have even more creative and manipulative marketing departments. These are generally off-brand, or bottom feeder brands that are trying to show better numbers not by actual performance but by manipulation of the numbers to appear better to those who don't understand them and generate their own incorrect conclusions. That's exactly why it's done.

The reason program and peak power doesn't have merit in higher quality MUSICAL INSTRUMENT gear is because of the specific conditions of no clipping (including intentionally generated overdrive and distortion) and no compression/limiting which is NOT the case in MI gear applications.

Does this make any sense?

 

[Wasnex]

The idea that you should run a bass rig only at 1/4 of its rated RMS power to avoid clipping is absurd.

Interpret it the other way. The idea is to spec enough headroom in the rig, so it reaches your volume requirements before the average long term power level exceeds 1/4 of the RMS rating. The idea is if the average long-term power level is 100W RMS, the amp must be able to produce 400Wpeak, which is only 200W RMS (short term). As I mentioned, I believe the crest factor of bass is generally higher than 6dB, so AFAIK this advice is not conservative.

The rest is a bit above my head, so hopefully it is reasonably accurate.

AFAIK clean, uncompressed bass has more like a 12dB crest factor. So if the amp must produce transients at 800Wpeak/400W RMS (short term), the average long-term power will be down at about 50W RMS

AFAIK the crest factor from 800Wpeak to 50W RMS is [Log(800/50) x 10] = 12dB.

However if you use compression or push a tube amp to it's limit, the crest factor is reduced...so maybe you get back to the 6dB crest factor. It depends on the sound and feel you want.

 

[agedhorse]

Interpret it the other way. The idea is to spec enough headroom in the rig, so it reaches your volume requirements before the average long term power level exceeds 1/4 of the RMS rating. The idea is if the average long-term power level is 100W RMS, the amp must be able to produce 400Wpeak, which is only 200W RMS (short term). As I mentioned, I believe the crest factor of bass is generally higher than 6dB, so AFAIK this advice is not conservative.

The rest is a bit above my head, so hopefully it is reasonably accurate.

AFAIK clean, uncompressed bass has more like a 12dB crest factor. So if the amp must produce transients at 800Wpeak/400W RMS (short term), the average long-term power will be down at about 50W RMS

AFAIK the crest factor from 800Wpeak to 50W RMS is [Log(800/50) x 10] = 12dB.

However if you use compression or push a tube amp to it's limit, the crest factor is reduced...so maybe you get back to the 6dB crest factor. It depends on the sound and feel you want.

Unfortunately this is misleading because it usually quickly exceeds the mechanical power handling of a bass guitar speaker.

 

[HolmeBass]

That's exactly what I said

I must have missed it. It didn’t seem clear when I read it.

 

[Wasnex]

Unfortunately this is misleading because it usually quickly exceeds the mechanical power handling of a bass guitar speaker.

IMHO, Consideration of crest factor should not overrule the requirement for the speaker to safely handle whatever the amp can throw at it.

The response had two sections. Are they both wrong?

In the first section I assumed spec'ing the rig for a 6dB crest factor is generally insufficient. That's why I wrote:

this advice is not conservative.

I did not say it's wrong because I assumed a fuzzed out tube rig might be in the ballpark.

Are you saying spec'ing for a 12dB crest factor is also insufficient?

AFAIK clean, uncompressed bass has more like a 12dB crest factor. So if the amp must produce transients at 800Wpeak/400W RMS (short term), the average long-term power will be down at about 50W RMS

What crest factor should we expect from bass guitar? Also, is it reasonable the expect a rig to reproduce the full dynamic range of bass guitar at concert volume without any compression?

 

[agedhorse]

I’m addressing the powering with 4X average power.

 

[JimmyM]

Talk about making a relatively simple task monumental!

1. Never trust numbers to save you from a lack of common sense.

2. Don’t try to eke out every single little bit of volume out of a too small rig if you want to be puke loud.

3. If your rig sounds like it may blow, it will.

Done.

 

[RandomKaren]

+1 with jeff62!

This probably won't be well accepted from most of the T.B. community, but, case in point.

I've a bassplayer friend that plays in a moderately loud, country rock group, using a PV Mini Mega head (1,000 watts at 4 ohms, 750 at 8 ohms), into a single, 8 ohm, old, old, old, Hartke 115XL cabinet that's only rated at 200 watts power handling.

He's been doing this for years, (prior to the PV head he powered the 115XL with a Hartke LH1000 bass head.)

His sound/tone is, big, clean and clear with projection.
He's had absolutely no problems driving a low power handling cab with a high power head..."as long as he uses his physical head and the ears that are on it."

No overly high settings with the bass knob, no distortion pedals, and listening for anything sounding overdriven from the driver.

I myself gig with a G.K. MB800 Fusion head, (800 watts at 4 ohms, 560 at 8 ohms), into a 8 ohm, 500 watt capacity, 210 cabinet for small to medium sized jobs, a 4 ohm Berg CN212 rated at 700 watts for large stage, outdoor jobs.

I've had zero problems

If you play with a clean tone then it's easier to hear when the cab is being pushed too hard. If you're playing with overdrive sounds, no chance. Either way I wouldn't buy a cab off you guys

 

[JustFunk]

Unfortunately this is misleading because it usually quickly exceeds the mechanical power handling of a bass guitar speaker.

I know this differs from cab to cab, but in your experience, where does the mechanical power handling sit by the thermal one, on average? Like -20%, -40%? It may be too much but, do you also have (roughly) variance data among cabs? Or said differently, a percentual range of mechanical limit in relation to the thermal one?

 

[WRM]

I know this differs from cab to cab, but in your experience, where does the mechanical power handling sit by the thermal one, on average? Like -20%, -40%? It may be too much but, do you also have (roughly) variance data among cabs? Or said differently, a percentual range of mechanical limit in relation to the thermal one?

I have my popcorn handy, but in the meantime, I'll offer some thoughts....

Heat transfer is a complicated science, and one of the few instances that require 4th power equations to solve problems. There are three types of heat transfer - conductive, convective, and radiating. I'm not even going to begin to try to "calculate" the temperature of the voice coils vs. power input, but would guess the equation would have to include enough time to reach a steady-state temperature at a certain power (e.g. some factor of Max mechanical Watts for X minutes), and be a curve if plotted.

 

[JimmyM]

I know this differs from cab to cab, but in your experience, where does the mechanical power handling sit by the thermal one, on average? Like -20%, -40%? It may be too much but, do you also have (roughly) variance data among cabs? Or said differently, a percentual range of mechanical limit in relation to the thermal one?

On average, I’d say around the 50% mark. Some of the newer speakers with neos do a little better, and some designs may do worse.

 

[agedhorse]

I know this differs from cab to cab, but in your experience, where does the mechanical power handling sit by the thermal one, on average? Like -20%, -40%? It may be too much but, do you also have (roughly) variance data among cabs? Or said differently, a percentual range of mechanical limit in relation to the thermal one?

Varies from no derating to ~70% derating for mechanical power handling depending on the driver and the cabinet design.

 

[Wasnex]

I have my popcorn handy, but in the meantime, I'll offer some thoughts....

Heat transfer is a complicated science, and one of the few instances that require 4th power equations to solve problems. There are three types of heat transfer - conductive, convective, and radiating. I'm not even going to begin to try to "calculate" the temperature of the voice coils vs. power input, but would guess the equation would have to include enough time to reach a steady-state temperature at a certain power (e.g. some factor of Max mechanical Watts for X minutes), and be a curve if plotted.

Mechanical power handling is not directly correlated with the RMS power rating of voice coils.

Mechanical power handling relates to both the driver's characteristics and how the box is tuned. Put the same driver in boxes with different tunings and the resulting mechanical power handling will vary. AFAIK the mechanical power handling of most bass cabs is less than the driver's RMS power rating. Some of the Kappalite LF designs do not comply with this. For example with the appropriate HPF, this design is thermally limited rather than mechanically limited

Same driver in different cab design is mechanically limited to 400W

 

[JimmyM]

Varies from no derating to ~70% derating for mechanical power handling depending on the driver and the cabinet design.

I should point out that I was referring specifically to typical commercial bass cabs when I mentioned that on average they hit around the -50% mark mechanical.

It’s oversimplified, but I don’t think it’s far off