[FrivolsListener]

  OK,I'll play.  In the interest of full disclosure I'm an electrical engineer and I've designed loudspeaker passive crossovers (professionally in a former life) for more than 40 years:
 
1) Even simple loudspeaker models account for all physical behavior that matters.  It's electricity and acoustics and physics, it's not magic.

 
Yes.  But speakers do things their designers don't want, like resonate.  Making the perfect speaker is like trying to find the perfect unicorn.
 
 

2) No audio amplifier should EVER go into oscillation, unless it is defective or there is an error in the design.  This has absolutely noting to do with the loudspeaker load.  Unless something has broken or you have designed an oscillator, an audio amp will never oscillate.  Now if you are talking about parasitic oscillation because of a high capacitance output in an amplifier, then what will happen is distortion and excess heat.  But again, a properly designed amplifier should never do this.  And at 40KHz you will never hear it.

 
Yes, parasitic oscillation, a problem with amplifiers.  Jason mentioned briefly a problem with one of the Vidar prototypes.  Perfect amplifiers don't exist, and they don't exist in a vacuum.  A good amplifier design can be wrecked with a underpowered power supply.
 
Anyway, I'm not doing this to get into a war of, er, genital waving, but rather to say that not everything plays nice together, and sometimes you have to design to take into account an unpleasant load.

 

[FrivolsListener]

   
I'm glad Schiit has a purist philosophy, and strives for no-compromises in the pursuit of quality audio.
 
There's a reason why a lot of the best audio gear uses vacuum tubes even though they aren't the most modern and efficient design.
 
Same thing for class A and AB, no matter how good class D gets it won't be the same:
 

 
Since I'm tilting at windmills....
 
No, no, no, I'm just saying that a bad implementation of a class A amp can be beat with a good implementation of a class AB amp.  What I want is an accoustically transparent amp for my listening needs.   I don't treat amp topology with a sort of reverence.

 

[Ableza]

A good loudspeaker designer always takes resonance into account.  Some even use it as part of the system's tonal signature.  Bottom line: you are worried about things that in general just don't matter after the design phase is complete.

 

[dmckean44]

  LOL.  The one 6SN7 tube that is virtually unobtainium, or $150 per tube if you can find it.
 
Come on Mike, what's your second favourite tube.  

They're worth it. I have Red Base 5691s in my phono preamp and they're so much better than the Tung Sol's that came stock it's ridiculous.

 

[AndreYew]

  2) No audio amplifier should EVER go into oscillation, unless it is defective or there is an error in the design.  This has absolutely noting to do with the loudspeaker load.  Unless something has broken or you have designed an oscillator, an audio amp will never oscillate.  Now if you are talking about parasitic oscillation because of a high capacitance output in an amplifier, then what will happen is distortion and excess heat.  But again, a properly designed amplifier should never do this.  And at 40KHz you will never hear it.

 
I agree when it's properly designed, but how often does that happen? The first time Sony demonstrated SACD in public at CES, they had to replace the Mark Levinson amps driving some B&W speakers at the last minute with Pass amps, because the Levinsons started oscillating when they saw all of the high-frequency noise that accompanies SACD. Now, one could have guessed that based on looking at the big resonant peak often seen in that generation of ML amps' frequency response.
 
Oscillation at 40kHz can be heard. If the amp suddenly loses all of its negative feedback because it's lost all of its gain, its nonlinearity is going to increase, and can modulate signal down into the audible region. It's complicated, and highly situation dependent, but when things go non-linear, all bets are off about what's audible and what's not. Oscillation can also destroy drivers, and sometimes you can hear the magic smoke being released.
 

4)  Again, a properly designed Xover will minimize the effects of the natural impedance swings across frequency of the overall system, no matter what might be happening in any specific driver.  Unless you are listening to large pipe organ music or some EDM, you will never experience a signal at 10Hz, but if you do and if a loudspeaker system hit 2-ohms at 10Hz (unlikely) than the only thing that will happen is this: if the amplifier can handle the load, the power output will increase over what it was putting out at higher impedances.  If the amplifier cannot handle the load, it will go into protection.
 

 
Woofers also have two regions of operation: amp-limited and excursion-limited, and where one transitions into the other depends on the speaker design, driver impedance, etc. Lower frequencies tend to be excursion-limited and higher frequencies are amp-limited, so lots of different things can happen when you ask a system to play loud bass. BTW, lots of LF out there due to footfalls (eg. live recording of an opera with people walking around on stage) or recordings in concert halls that were built on top of subway lines.

 

[FrivolsListener]

I swore I wasn't going to swipe at strawmen, but having recordings with subsonic frequencies on it isn't that unusual.  I can even give a listing of one from the disc jacket.

 

[ScottFree]

I swore I wasn't going to swipe at strawmen, but having recordings with subsonic frequencies on it isn't that unusual.  I can even give a listing of one from the disc jacket.

Please.

 

[Ableza]

   
I agree when it's properly designed, but how often does that happen? The first time Sony demonstrated SACD in public at CES, they had to replace the Mark Levinson amps driving some B&W speakers at the last minute with Pass amps, because the Levinsons started oscillating when they saw all of the high-frequency noise that accompanies SACD. Now, one could have guessed that based on looking at the big resonant peak often seen in that generation of ML amps' frequency response.
 
Oscillation at 40kHz can be heard. If the amp suddenly loses all of its negative feedback because it's lost all of its gain, its nonlinearity is going to increase, and can modulate signal down into the audible region. It's complicated, and highly situation dependent, but when things go non-linear, all bets are off about what's audible and what's not. Oscillation can also destroy drivers, and sometimes you can hear the magic smoke being released.
 
 
Woofers also have two regions of operation: amp-limited and excursion-limited, and where one transitions into the other depends on the speaker design, driver impedance, etc. Lower frequencies tend to be excursion-limited and higher frequencies are amp-limited, so lots of different things can happen when you ask a system to play loud bass. BTW, lots of LF out there due to footfalls (eg. live recording of an opera with people walking around on stage) or recordings in concert halls that were built on top of subway lines.

​Interesting story about the Levinson amp.  What an embarrassment.  There are always outliers I suppose.  I suggest not living there.  Also interesting that Sony, who I worked for in the late 80's, would use anything other than their own gear at a demo.
 
As far as how subwoofer systems are designed, we can get into that if you like.  It is one of my areas of experience, actually.    As far as I know most film soundtracks strive to not include subsonics in normal sound effects tracks, well except maybe horror or dinosaur films, but they are often used in some genre for mood effects.  But again, amplifiers and subwoofers don't really care.  They can either produce them at sufficient dbSPL or they cannot.  And if they are driven to a point where they cannot handle the signal, then they either protect themselves (good amplifier design) or they break.

 

[FrivolsListener]

Please.

 
Michael Murray
Bach
The Great Organ at Methuen
Toccata in F, BWV540
Telarc CD-80049
DIDZ-10031
Recorded June 22, 23 1979.

 

[johnjen]

snip  
Woofers also have two regions of operation: amp-limited and excursion-limited, and where one transitions into the other depends on the speaker design, driver impedance, etc. Lower frequencies tend to be excursion-limited and higher frequencies are amp-limited, so lots of different things can happen when you ask a system to play loud bass. BTW, lots of LF out there due to footfalls (eg. live recording of an opera with people walking around on stage) or recordings in concert halls that were built on top of subway lines.

Eric Clapton's Unplugged album, the Walkin' Blues track is an excellent example of foot falls on a resonant stage.
 
Not to mention air handling system rumble and duct harmonics as additional sources of low frequencies…
 
JJ

 

[earnmyturns]

  That all said, class D isn't necessarily terrible. Old/cheap class D is meh, newer stuff is much better (but also heavier as they beef up all the supporting circuitry) and quite frankly most people would be very hard pressed to tell the difference as long as you're not comparing crap. Every tech/topology has it's place.

The Bel Canto C7R (class D) integrated I'm listening to is definitely not crap, but there's a reason a Hegel H360 (class AB with its own proprietary circuitry) is on its way to replace it. There may be many factors why I fell for the H360 when I auditioned it, but even its little brother the H160, which is just a bit more expensive than the C7R, is more convincing. The funny part is that what sent me looking to replace the C7R was listening to a lot of the same music on my mid-range Schiit headphone chain (Bimby>Jodie) and finding that the C7R's mid-to-upper frequencies feel overly smooth in comparison. There are complications in these comparisons, especially different DACs, and the C7R still sounds pretty good overall, but the reference that the mid-price Schiit headphone stack provide is pretty demanding. I need an integrated for my living room speaker system (long story), so I went with the Hegel, but I'll be complementing it with an Yggy just in case 

 

[belgiangenius]

They're worth it. I have Red Base 5691s in my phono preamp and they're so much better than the Tung Sol's that came stock it's ridiculous.

Perhaps so, but there are lots of really good tubes out there.

I dont think too many people are going to spend $700 on a preamp and another $700 on tubes, so it would be great to have feasible suggestions. Anyone can point to the most expensive NOS tubes and say they are the best. That's not terribly useful information for most people.

I would agree that new production tubes suck, though. I have never heard new production tubes that didn't suck compared to NOS.

 

[MWSVette]

Perhaps so, but there are lots of really good tubes out there.

I dont think too many people are going to spend $700 on a preamp and another $700 on tubes, so it would be great to have feasible suggestions. Anyone can point to the most expensive NOS tubes and say they are the best. That's not terribly useful information for most people.

I would agree that new production tubes suck, though. I have never heard new production tubes that didn't suck compared to NOS.

 
 
You would think that...   
 
I originally thought that.  I now have several times the cost of my Lyr in vintage NOS tubes.  Fortunately there are not as many tube variants for the new Schiit preamps.
 
I have also found that the most expensive is not always the best.  Most of the newer production tubes are subpar when compared to vintage NOS tubes.
 
IMHO, YMMV, yada yada yada...

 

[madwolfa]

  Yes, parasitic oscillation, a problem with amplifiers.  Jason mentioned briefly a problem with one of the Vidar prototypes.

 
Key word here is prototypes.

 

[US Blues]

 

  Yes, parasitic oscillation, a problem with amplifiers.  Jason mentioned briefly a problem with one of the Vidar prototypes.

 
Key word here is prototypes.

Tis true, I was in on that conversation with Jason and @FrivolsListener (an erudite fellow who is keen of Ear) at RMAF. Jason was recounting a number of interesting stories regarding the development of the Vidar, which I hope he shares in a forthcoming chapter when the time is right. For me this conversation provided an interesting insight into the product development process, and gave me an appreciation for the dedication the Schiitheads have for building us really cool toys.