Can you explain the newer class "D" amps to me?

[agedhorse]

One think I found fascinating however was as I was researching this, I came upon a thread about damping materials. It was stated the damping materials in a speaker enclosure (sealed) served a two fold. First, it served to breakup standing waves. I understand this but the other reason was that it "absorbed" heat from the speakers themselves as the sealed enclosure and compression of the air caused heat which the material absorbed. Like a heat sink.

I did not know this.

You should continue not knowing this because it's hogwash, complete and utter crapola.

1. standing waves occur because of the dimensions of the box and the wavelengths being amplified.

2. Damping material does not break up anything.

3. Damping material has no effect on low frequency (say <250Hz) signals because the absorption coefficient is way too low.

4. Damping material begins to absorb energy starting at ~250 Hz and gradually increases absorbtion as frequency increases.

5. Damping material is used to absorb midrange frequencies that eminate from the back ofthe cone and reflect off of the back of the box then back through the paper causing alterantions to the midrange voicing of a cabinet.

6. Heavy application of damping can alter the low frequency response of the enclosure as it alters the functional air mass inside the enclosure.

7. Damping hinders the flow of heat to the surface of the box, it's a thermal insulator and is never used for any kind of heatsink properties.

8. The heating due to compression of the air is maybe in the 0.001% range... insignificant on virtually any practical scale.

 

[Bassamatic]

Mr. Foxen: YES - there are beat frequencies that can occur between the the 2 switching clocks from intereference carried on the power busses and also RFI just spraying around inside the case. You are switching huge amounts of voltage and current, and thereby creating powerful RF transmitters. It seems that it would be easy to keep the clocks synchronized, but it is not. There are only a couple of companies such as PowerSoft, that seem to have really solved the issues.

 

[Quickie]

You should continue not knowing this because it's hogwash, complete and utter crapola.

1. standing waves occur because of the dimensions of the box and the wavelengths being amplified.

2. Damping material does not break up anything.

3. Damping material has no effect on low frequency (say <250Hz) signals because the absorption coefficient is way too low.

4. Damping material begins to absorb energy starting at ~250 Hz and gradually increases absorbtion as frequency increases.

5. Damping material is used to absorb midrange frequencies that eminate from the back ofthe cone and reflect off of the back of the box then back through the paper causing alterantions to the midrange voicing of a cabinet.

6. Heavy application of damping can alter the low frequency response of the enclosure as it alters the functional air mass inside the enclosure.

7. Damping hinders the flow of heat to the surface of the box, it's a thermal insulator and is never used for any kind of heatsink properties.

8. The heating due to compression of the air is maybe in the 0.001% range... insignificant on virtually any practical scale.

Now I am lost again. The damping material heating was from a user on this board, Jerrold Tieres. I am going to find the post. He said it absorbed heat. I think he worked for Ampeg as an engineer.

OK....so I will continue to monitor this thread as it has gotten very interesting indeed. Thanks for the time you are spending here.

 

[agedhorse]

Mr. Foxen: YES - there are beat frequencies that can occur between the the 2 switching clocks from intereference carried on the power busses and also RFI just spraying around inside the case. You are switching huge amounts of voltage and current, and thereby creating powerful RF transmitters. It seems that it would be easy to keep the clocks synchronized, but it is not. There are only a couple of companies such as PowerSoft, that seem to have really solved the issues.

There are quite a few companies that have this solved, QSC, Crown, PowerSoft, Peavey, Crest, B&O, just to name a few.

It's one of the aspect of Class D and SMPS that seperate the men from the boys.

 

[agedhorse]

Now I am lost again. The damping material heating was from a user on this board, Jerrold Tieres. I am going to find the post. He said it absorbed heat. I think he worked for Ampeg as an engineer.

OK....so I will continue to monitor this thread as it has gotten very interesting indeed. Thanks for the time you are spending here.

I'm sure you just misunderstood something about Jerrold's explaination (OR, I am misunderstanding your comment). He is a capable and knowledgable engineer.

 

[Quickie]

I'm sure you just misunderstood something about Jerrold's explaination (OR, I am misunderstanding your comment). He is a capable and knowledgable engineer.

Actually, the filling in a sealed cabinet like that (or a ported cab for that matter) isn't to slow down the sound.

What it does is to absorb heat! Yes, heat.

When you compress air, even a little, it heats up. Has to.

Heated air expands. So the heating causes the air to "push back" harder than it would if it didn't heat up. The total heating in degrees is small, but it does occur.

The stuffing acts as a heatsink and keeps the air from heating as much by absorbing some heat. So the "push back" isn't quite as much as it would be.




http://www.talkbass.com/forum/f15/ampeg-8-x-10-speaker-cab-help-132659/#post1517542

Here you go, I found it.

 

[Fab Superlative]

This may be somewhat OT, but I'm wondering what effects (if any) the planned power-grid experiments will have on class D amps.?

 

[Mr. Foxen]

Again, none on class D amps, but switch mode power supplies maybe, but probably not, the input frequency isn't super relevant to them since it is rectified anyway, although maybe artifacts of it make their way further. My understanding is limited, but I'm learning, so open to correction from the knowledgeable sorts.

 

[PhiDeck]

Fooling around with the frequency of the AC power system will affect:
- Synchronous motors (as in some clocks and turntables)
- Electronics that count zero crossings of the input power-line to establish a time-base

A Class-D amplifier, with or without an SMPS, involves neither of the above, so should be OK.

 

[seamonkey]

Clocks aren't hard to sync.
Many Home Theater gear is all digital and ad AD converters even synced with the amp clocks if their in the same case.

Class-D is analog, the signal going to the speaker is the same as class-AB, Class-A, or any class. Except for inaudible high frequencies that leaks around the output filters. This is not a big deal except some test equipment can pick this up and read it, when it should ignore it. If we can't hear it, test gear should ignore it.

THD is lower than it has ever been with Class-D
Even at higher audio frequencies. It's the best it's ever been. Here too, we can't hear above 1% (if that) and any class amplifier can do that. Really, class-d doesn't sound any better because we reached the human hearing threshold years ago with other amps.

Every laptop and TV seems to be class-d. Battery power gear even more. Even hearing aids. It's everywhere and growing more.

 

[chadds]

May I say, I used Marshall and Hiwatts and SVTs back in the late '60s early '70s.
Loved the Hiwatts. Tried a Reeves recently on an SWR GIII. Freakish cone excursion even with bass eq off. It sounded terrible too. Put my SWR Bass 750 head back on and all was well. Please explain my experience. Damping factor by crushed Trolls?

 

[chadds]

Is there a bias here against, " very short under the bridge living " Sandinavian and European diminutives?
Like Smurfs and shite?

 

[agedhorse]

Actually, the filling in a sealed cabinet like that (or a ported cab for that matter) isn't to slow down the sound.

I never said this.

What it does is to absorb heat! Yes, heat.

This is inaccurate unless you look well to the right of the decimal point. Really far to the right.

When you compress air, even a little, it heats up. Has to.

Again way to the right of the decimal point, and then when it expands it cools down again in a perfectly linear system.

Heated air expands. So the heating causes the air to "push back" harder than it would if it didn't heat up. The total heating in degrees is small, but it does occur.

Again, so far to the right of the decimal point as to be immeasurable (ignoring long term heating due to VC heating). Again, getting away from "theoretical" to practical.

The stuffing acts as a heatsink and keeps the air from heating as much by absorbing some heat. So the "push back" isn't quite as much as it would be.

Incorrect and inaccurate except for minscule theoretical purposes. The thermal capacity of stuffing is very, very low and the thermal resistance is very high. This is precicely what makes it a good thermal insulator, not a heatsink of any practical, measureable value. By this token, the surface of the enclosure is a much better heatsink.

http://www.talkbass.com/forum/f15/ampeg-8-x-10-speaker-cab-help-132659/#post1517542

Here you go, I found it.

I stand by my comments.

1. Stuffing is used to reduce internal reflections and has a much greater impact at frequencies above 250-300Hz due to the absorbtion coefficient versus frequency plot of these materials. The result is improve midrange clarity and amplitude uniformity, though sometimes these characteristics are used in the voicing of some cabinets. These may be standing waves if the frequency is high enough (wavelength short enough) compared with box dimensions.

2. The mechanical losses as the sound travels through these fibers can make the cabinet's internal volume appear to be slightly larger than it really is. The difference is maybe 5-15%, but by the time you approach this the midrange tradeoff may start to work against you. It's often a compromise.

3. The reduction of midrange signal that is phase shifted due to the distance traveled from the back of the cone to the back of the enclosure and then through the paper summing acousticly with the original signal is probably the most common and appreciated benefit of all.

I recommend that you do some reading of engineering papers or articles that discuss this more in depth, and that you get a grasp of the quantitative values being discussed. You want to look at the cause and effect ofthe BIG things that affect the performance first, those that have a practical impact of performance rather than the really tiny stuff that is barely (if at all) measureable in the real world.

All of this is "in my opinion" of course.

 

[Eight_Stringer]

Many aspects to this venerable topic of class D type devices. Do feel for the people whom are eager to learn about the equipment they use, and how to best judge performance based on their understanding of complex technology. One of the more glaring anomalies in the modern age of communications, the very best efforts of the knowledgeable to impart the fundamentals, in order that all users can become better at evaluating a product or problem. Along the way some people misinterpret these first principles, propagate misunderstandings. Wifes tales not based on engineering fact, now become the banner of choice for anyone looking for words, that match their understandings at that point in time.

Rather than punch away at correcting these wifes tales handed down "mother to daughter", spend countless hours typing only to have the same wifes tale come again and wipe out all the progress. Game of snakes and ladders, many pack up their ladder and go home, done so myself many times, as it is just too depleting warding off the incorrect engineering dogma's. ( There are some beaut's in this topic ).

Damping, have absolutely no interest in it at all. From bass string/instrument to speaker cone, how many variables do you think there are? Then multiply those combinations by interactions. Sure if a problem or problems arise we need to identify that problem with sound based engineering ( pun intended ). The rig here is a mish mash of technologies. 6 string basses ( fretted and fretless ), hex pickup(s) into 3 dsp's running flat out ( VB-99 ), mixer ( keys part of the rig ), into a 200watt valve/tube "head" ie no tone stack. fEarful and TL606's as required. Forget subtle sound changes playing live, i want big changes on demand, modern "preset" tone control gives me that. So the speaker cone looks like its about to come out of the cabinet, even after i stop playing a note... it works for some sounds desired and not others.

Look forward to trying a class D amp one day, have the knowledge to design my own, yet to make it sound "proper" that is another thing all together, well people like Agedhorse know so into long hours on the R and D bench.

Down to the local musical instrument shop and you can try this amp and that cabinet, all down to personal choice as we all know. Yet the sounds produced changes and changes completely home to rehearse to venues.... all part of the game we play.... and for the most part this is because we care and strive to be the best we can be, guess being a bass player makes us a better person in life for the efforts expended.

Regards to all.

 

[agedhorse]

May I say, I used Marshall and Hiwatts and SVTs back in the late '60s early '70s.
Loved the Hiwatts. Tried a Reeves recently on an SWR GIII. Freakish cone excursion even with bass eq off. It sounded terrible too. Put my SWR Bass 750 head back on and all was well. Please explain my experience. Damping factor by crushed Trolls?

Quite likely that a combination of voicing and a lack of any high pass filtering, but have you ruled out that there wasn't a problem with the Reeves?

 

[agedhorse]

The first 2 paragraphs of Eight Stringer's last post justifies reading a couple of times. And may I add that once old wive's tales are propagated, some marketing departments exploit these myths or 1/2-truths further burying sound engineering principles.

 

[billfitzmaurice]

I stand by my comments.

Rightfully so. Jerrold may have fallen into the trap of believing that damping works via adiabiatic conversion. Many have, as until fairly recently even some of the best theorists didn't fully understand the damping process, especially with heavily damped enclosures, and looked to far more complicated reasons for what happened than was actually the case. Tom Nousaine would probably be the best example. It's now understood that major low frequency response alteration via heavy damping is simply a matter of lowering of the system Q due to the fibrous filling offering higher impedance than air alone. The heat factor is just as you mentioned, with increased heat measured within the enclosure versus an undamped box the result of the insulating properties of the damping material.
One disagreement I have is with the value of even moderate damping on standing waves. An inch or two of damping won't kill resonances below 250Hz, but it does have enough effect to make a difference. You're still better off to minimize internal dimensions, of course.

 

[JimmyM]

The quote from Jerrold that Quickie posted was from 7 years ago. Just thought that should be noted.

Listen, we've all been wrong about stuff like this on the internet before with guys who know way more about this stuff than us mere mortals. The thing to do is to accept that you're wrong, find out why, and move on. The thing not to do is tell people you're right and you don't want to argue about it, then get mad and say you're not going to participate any further when the inevitable arguments come in. That's being a poor sport.

 

[agedhorse]

Rightfully so. Jerrold may have fallen into the trap of believing that damping works via adiabiatic conversion. Many have, as until fairly recently even some of the best theorists didn't fully understand the damping process, especially with heavily damped enclosures, and looked to far more complicated reasons for what happened than was actually the case. Tom Nousaine would probably be the best example. It's now understood that major low frequency response alteration via heavy damping is simply a matter of lowering of the system Q due to the fibrous filling offering higher impedance than air alone. The heat factor is just as you mentioned, with increased heat measured within the enclosure versus an undamped box the result of the insulating properties of the damping material.
One disagreement I have is with the value of even moderate damping on standing waves. An inch or two of damping won't kill resonances below 250Hz, but it does have enough effect to make a difference. You're still better off to minimize internal dimensions, of course.

On this it appears that we agree pretty much 100%!!!

I also agree with your comment about damping below 250Hz, but for some of the same reasons and some different ones too perhaps.

While the fundamental may be say 250Hz, there exists significant energy in the 2nd and 3rd harmonics as to significantly alter the tonal profile of the amplified note through what is happening to the harmonics via damping also. I think this plays a big factor in the feel and texture of a more or less damped enclosure and may be part of a defined personal preference to many players (one way or the other).

 

[agedhorse]

The quote from Jerrold that Quickie posted was from 7 years ago. Just thought that should be noted.

Listen, we've all been wrong about stuff like this on the internet before with guys who know way more about this stuff than us mere mortals. The thing to do is to accept that you're wrong, find out why, and move on. The thing not to do is tell people you're right and you don't want to argue about it, then get mad and say you're not going to participate any further when the inevitable arguments come in. That's being a poor sport.

Good point Jimmy, and to clarify, I wasn't saying he was wrong. I was saying that the mechanisms that he mentioned, are not IMO the primary mechanisms responsible for the audio effects of adding damping in a speaker.

This is one of the problems with delving into some of the more esoteric engineering details on a fourm where there is a wide level of understanding amongst participants. It's easy for somebody to latch onto a minute detail and miss the big picture.

I also have a lot of respect for Jerrold, I am familiar with some of his work, and what he mentioned 7 years ago was in fact based in valid science but taken out of the context of the big picture IMO. There is no doubt that Jerrold is completely comfortable with the science of the big picture based on his years of work in this industry. There is a lot to learn from him.