An XXcontroversial Way to Compare the Output of Class D Amps.

[dmccombe7]

21 minutes ago, Chienmortbb said:

 As you know human hearing, like so many things in nature is logarithmic, so we use Log or Audio scaling on pots or in DSP to mimic a linear increase in volume. I am unclear what people mean when they say Linear in relationship to Gain or Volume controls. However I fear we have gone way off topic, my apologies to all.

 

 

Not at all, i'm still finding this thread interesting. 

Dave

[itu]

dB(A)-meter is a good thing to have at hand while measuring loudness. It is probably one of the simplest piece of equipment to own. Cheap ones are not very accurate, but give a good hint where the level is at the moment.

 

I have used Brüel & Kjær and similar units earlier (prices were sky high). Now that I have changed company, I decided to buy a simple and cheap meter of my own. Saves ears, if the band starts a volume war.

[chyc]

1 hour ago, Chienmortbb said:

 As you know human hearing, like so many things in nature is logarithmic, so we use Log or Audio scaling on pots or in DSP to mimic a linear increase in volume.

To me it's one of those things where, when asked "what is natural?", the answer would be "I know what it isn't." I own a TV, of a brand that funnily enough has come up in this thread already. I cannot tell the difference in volume once the volume slider passes around 1/3 of the way up. There's nothing natural about that. Whether musical instrument manufacturers do anything quite as egregious as that I cannot say because I've never owned one that does.

[agedhorse]

18 hours ago, chyc said:

To me it's one of those things where, when asked "what is natural?", the answer would be "I know what it isn't." I own a TV, of a brand that funnily enough has come up in this thread already. I cannot tell the difference in volume once the volume slider passes around 1/3 of the way up. There's nothing natural about that. Whether musical instrument manufacturers do anything quite as egregious as that I cannot say because I've never owned one that does.

Some in fact do.

[Nebadon2000]

21 hours ago, chyc said:

To me it's one of those things where, when asked "what is natural?", the answer would be "I know what it isn't." I own a TV, of a brand that funnily enough has come up in this thread already. I cannot tell the difference in volume once the volume slider passes around 1/3 of the way up. There's nothing natural about that. Whether musical instrument manufacturers do anything quite as egregious as that I cannot say because I've never owned one that does.

Sometimes volume is limited by speaker and/or room; So after a certain point on Volume Control and power delivery Speaker and/or room is putting out their max volume so continuing to crank volume knob will do nothing for more volume except maybe blow something up😀 Want more volume Bigger/More Speaker and Room.

[paul_c2]

How does the room limit volume?

[TimR]

Look at the actual specifications of any amp. They should give the number of Watts and reference that to a frequency and the amount of total harmonic distortion. So 1000w at 1kHz with 1% THD.

 

It wouldn't be too difficult to supply a graph showing the amount of distortion it varying frequencies for each power output. It's done for component amplifiers. 

[Stub Mandrel]

4 hours ago, TimR said:

Look at the actual specifications of any amp. They should give the number of Watts and reference that to a frequency and the amount of total harmonic distortion. So 1000w at 1kHz with 1% THD.

 

It wouldn't be too difficult to supply a graph showing the amount of distortion it varying frequencies for each power output. It's done for component amplifiers. 

 

The fundamental problem is that most amps don't have that sort of data available. 

 

Even 'responsible' manufacturers don't give totally transparent information.

 

For example Marshall and Orange give reslistic ratings, but for two very similar designs Marshall rate 50W and Orange 30W, because they measure at different levels of THD. You won't find this in the manual.

[Nebadon2000]

9 hours ago, paul_c2 said:

How does the room limit volume?

I will just say this 'Have you ever noticed whether Bass[music in general] in a Vehicle or Room sounds extremely loud outside but if you enter vehicle or room it is not as loud.

Rooms can only hold so much sound pressure/Volume and it dissipates itself out sorta like water.

[LukeFRC]

On 21/07/2022 at 10:09, Chienmortbb said:

I well remember when at Panasonic that a certain company (Korean company beginning with S) claimed a huge brightness figure for their Plasma screens. How did they do it? By reducing the size of the white area measured. The power supply of plasma screens could not maintain full brightness over the whole screen so the smaller you could make the measured square, the brighter the picture. They reduced the square from 2.54 x 2.54cm  to 1 x 1 cm and hence the power supply could maintain a higher brightness.

 

Your calcs on the Bugera are about right.

That's true metric brightness rather than your old fashioned imperial brightness

[agedhorse]

2 hours ago, Stub Mandrel said:

 

The fundamental problem is that most amps don't have that sort of data available. 

 

Even 'responsible' manufacturers don't give totally transparent information.

 

For example Marshall and Orange give reslistic ratings, but for two very similar designs Marshall rate 50W and Orange 30W, because they measure at different levels of THD. You won't find this in the manual.

In a bass/guitar amp, depending on the player’s gain structure and intent, a great deal of design effort is placed on the non-line as aspects of the amplification. This means intentionally developing distortion components (spectrum of fundamental to the multiple harmonics), alterations to the dynamic response transfer function, and how entering into and out of these non-linear regions is handled by the design elements. 
 

This makes specifying power versus THD difficult because there are multiple curves overlapped that describe this behavior. 
 

Good designs sound good to players and delivers the required power under the conditions each player uses.

[Bill Fitzmaurice]

11 hours ago, paul_c2 said:

How does the room limit volume?

Boundary reflection sourced cancellation. It can boost it as well, via cabin gain.

Quote

Rooms can only hold so much sound pressure/Volume and it dissipates itself out sorta like water.

I'm afraid not. What is happening is that the cancellation modes that exist within the walls don't exist outside of them. It's the exact same reason why volume on or near the stage can be less than at the back of a room. That phenomenon gave rise to the myth of wave propagation.

Quote

Sometimes volume is limited by speaker and/or room; So after a certain point on Volume Control and power delivery Speaker and/or room is putting out their max volume so continuing to crank volume knob will do nothing

Running out of driver excursion will do that, but not the room. Continuing to crank the volume results in increased compression and THD. It won't hurt an amp, and may not hurt the speaker. It's how guitar amps get a sweet cranked sound. Guitar drivers are made with a short excursion, xmax, to make it happen with as little power as possible. Bass drivers have long excursion to prevent it from happening to the greatest extent possible.

[TimR]

4 hours ago, Stub Mandrel said:

 

The fundamental problem is that most amps don't have that sort of data available. 

 

Even 'responsible' manufacturers don't give totally transparent information.

 

For example Marshall and Orange give reslistic ratings, but for two very similar designs Marshall rate 50W and Orange 30W, because they measure at different levels of THD. You won't find this in the manual.

 

The 'problem' would be trying to convince the manufacturers that bass players would understand what they're looking at. 

 

The plots would be easy to produce. 

 

But as the two previous posters have explained. Add in cabs (which have different impedance at different frequencies) and all other aspects you're onto a loser to start with.

 

 

 

Edited July 24, 2022 by TimR

[TimR]

3 hours ago, Nebadon2000 said:

Rooms can only hold so much sound pressure/Volume and it dissipates itself out sorta like water.

 

Your ears can only deal with so much volume before they give up trying to make sense of what's assaulting them. 

Edited July 24, 2022 by TimR

[Nebadon2000]

1 hour ago, Bill Fitzmaurice said:

Boundary reflection sourced cancellation. It can boost it as well, via cabin gain.

I'm afraid not. What is happening is that the cancellation modes that exist within the walls don't exist outside of them. It's the exact same reason why volume on or near the stage can be less than at the back of a room. That phenomenon gave rise to the myth of wave propagation.

Running out of driver excursion will do that, but not the room. Continuing to crank the volume results in increased compression and THD. It won't hurt an amp, and may not hurt the speaker. It's how guitar amps get a sweet cranked sound. Guitar drivers are made with a short excursion, xmax, to make it happen with as little power as possible. Bass drivers have long excursion to prevent it from happening to the greatest extent possible.

 

Thanks for clarification; I was only conveying what I have experienced and my uneducated guess at what was happening. IE; My home stereo seemed[I perceived?] played louder in my Livingroom than in smaller bedroom where at a point it stopped increasing volume as compared.

 

I went to a friends house and Music was ear splitting outside but just loud inside. I asked a couple audio engineers about this both gave answer rooms have volume limits they didn't elaborate.

 

I worked in Home HI-FI Business and a few customers complained that bought Audiophile level power amps and large speakers that sound was not loud enough. Told them to put system in larger room and they were then happy.

[Downunderwonder]

16 hours ago, paul_c2 said:

How does the room limit volume?

By finishing their drinks and leaving when you are too f n loud

[Bill Fitzmaurice]

3 hours ago, Nebadon2000 said:

 

Thanks for clarification; I was only conveying what I have experienced and my uneducated guess at what was happening.

That's not only not unusual, it's common. How sound waves work isn't the least bit intuitive, so it's a field where you must be taught. Figuring it out on your own isn't impossible, somebody was the first to do so, but it's not easy.

[chyc]

22 hours ago, Nebadon2000 said:

Sometimes volume is limited by speaker and/or room; So after a certain point on Volume Control and power delivery Speaker and/or room is putting out their max volume so continuing to crank volume knob will do nothing for more volume except maybe blow something up😀 Want more volume Bigger/More Speaker and Room.

 

This may be true in an abstract sense, but my TV shares a room with my bass amp and my hifi, neither of which exhibit this phenomenon. Now it may be that it just so happens that the TV is situated in a spot such that it causes real-world volume to cap after a certain point on the dial, and this bad luck has followed the TV across house moves, but I ain't buying that. I'm calling marketing shenanigans, particularly when this brand has such a poor reputation already on such matters.

[Chienmortbb]

1 hour ago, chyc said:

 

This may be true in an abstract sense, but my TV shares a room with my bass amp and my hifi, neither of which exhibit this phenomenon. Now it may be that it just so happens that the TV is situated in a spot such that it causes real-world volume to cap after a certain point on the dial, and this bad luck has followed the TV across house moves, but I ain't buying that. I'm calling marketing shenanigans, particularly when this brand has such a poor reputation already on such matters.

TVs are so thin that they cannot hold decent sized speakers or decent sized amplifiers. So while the number in the screen may go up to 11, the sound will only reach 5 or 6. 

[chyc]

57 minutes ago, Chienmortbb said:

TVs are so thin that they cannot hold decent sized speakers or decent sized amplifiers. So while the number in the screen may go up to 11, the sound will only reach 5 or 6. 

Since we're venturing into Spinal Tap territory, "Why not make it go up to 5 or 6"?

[Franticsmurf]

18 minutes ago, chyc said:

Since we're venturing into Spinal Tap territory, "Why not make it go up to 5 or 6"?

Awkward pause.... "This one goes to 11". 😀

[Bill Fitzmaurice]

3 hours ago, chyc said:

 

This may be true in an abstract sense, but my TV shares a room with my bass amp and my hifi, neither of which exhibit this phenomenon.

All drivers exhibit this behavior if sufficient power is applied to push the cone past xmax. However, at higher frequencies the voice coil may burn out first. Even when present one might not be aware of it when it's not severe. The fact that speakers have a point beyond which more power applied only creates higher THD has been employed by Klippel GmbH in redefining how xmax is measured. It used to be calculated by comparing the voice coil length and magnet top plate thickness. It's now the excursion at which THD reaches 10%.

[Chienmortbb]

29 minutes ago, Bill Fitzmaurice said:

The fact that speakers have a point beyond which more power applied only creates higher THD has been employed by Klippel GmbH in redefining how xmax is measured. It used to be calculated by comparing the voice coil length and magnet top plate thickness. It's now the excursion at which THD reaches 10%.

This it bullshine. Just like amp manufacturers quoting THD + N at 10%

[agedhorse]

1 hour ago, Chienmortbb said:

This it bullshine. Just like amp manufacturers quoting THD + N at 10%

No, it’s real world performance definition specifications. The old way of defining Xmax would often result in THD numbers even greater.

 

There are also speakers designed for increased THD numbers (and specific ~ratios of the harmonics) for coloration or texture purposes. This is seen sometimes in the bass world (think older Ampeg SVT 10” drivers) but also very often in the guitar world). 
 

Regarding amps, you might be surprised at the THD numbers that are generated within the preamps of many popular bass amps, 5% is common, and when overdrive effects are used, that number can quickly jump to over 20%. How an amp is used should go hand in hand with how it’s specified.

[dmccombe7]

Thankfully i'm not a "Theorist" cause i'm lost in this techiness of the speaker world now. 

Its nice to know some of you out there understand all of this to keep us numpties on the right path to true bass nirvana. 

Dave