[Split]Technical split from: Pear Cable CEO Calls James Randi's $1 Million Offer a Ho

[sol invictus]

Sol, your prejudices are only too obvious. You are not challenging his technical claims, you are just resorting to some form of fallacious arguments to protect your belief that your amp can handle all power requirements in the world for realistic playback.

I've already explained in detail precisely how and why your technical claims were wrong. You never responded. The article you linked to contains many distortions as well as some technical falsehoods (for example that SPL falls by 6dB when you double the distance - that's true only in anechoic circumstances, and way off in most living/listening rooms).

As I said before, the correct procedure is to identify how much power you need based on the sensitivity of your speakers, the driver's maximum power handling capability, and the maximum SPL you want to acheive. Having done so you can choose an amp.

I chose mine according to that procedure - any more power and I would risk damaging my speaker drivers at high levels. My amp clips (at around 80W/channel, very audibly) a bit before the woofers are driven non-linear. The level at that point is painful and would cause hearing loss with sustained listening.

 

[rsaavedra]

Sol open another thread and let's discuss power amplifier requirement and realistic playback in its own thread if you want. If you'd like, please start that thread by indicating how many "way-off" dB SPL does decrease with distance in a decently sized room, with references supporting your claim.

Not only this is all off topic here, you keep nagging with your own amp choice, something that definitely can cloud your impartiality.

The fact that you mention "Driver's maximum power handling capability" already puts us under rather different assumptions. Of course, you have to take that into account. If you only have PC speakers certainly it's a waste of money to consider a high quality powerful amp. I was speaking under the context and assumptions of aiming at the most realistic possible playback, a context from which you are obviously not speaking from. Fitting the restrictions of some (possibly highly limited) equipment someone already has is a completely different purchase-related decision making scenario. That still won't change the physics of amplifier power requirements, and how sound propagates with distance, and how our hearing identifies and enjoys undistorted realistic sound pressure levels and proper dynamic range though.

Your idea of "contradiction", your self proclaimed "detailed and precise explanations", and your liberal use of the words "many", "most", and "typical" are really funny.

 

[sol invictus]

The fact that you mention "Driver's maximum power handling capability" already puts us under rather different assumptions. Of course, you have to take that into account. If you only have PC speakers certainly it's a waste of money to consider a high quality powerful amp. I was speaking under the context and assumptions of aiming at the most realistic possible playback, a context from which you are obviously not speaking from.

What are you talking about? Do you have speakers with drivers with infinite power handling capability? If so I suggest you do start a new thread: on the $1M challenge you're going to propose with your magic speakers. There - back on topic!

Over here in the real world, speakers are damaged if you feed them too high a voltage. Mine are particularly vulnerable to that (being open-baffle). An amplifier with higher capability than that is a detriment and a danger, not a benefit.

If you only have PC speakers certainly it's a waste of money to consider a high quality powerful amp.

After auditioning a very wide variety of speakers over a period of years, some in the $50K range and up (including Wilson, MBL, ATC, Thiel, B&W, and many more) I found the pair I consider to be the best in the world. I'm listening to them as I type this, and I can assure you they are not "PC speakers".

 

[sol invictus]

Heard, yes, a very poor design and concept.

I don't agree at all that the concept is "poor". It's actually rather innovative, or was when it was first introduced. In the case of the 901's (at least the pair I heard, which were not the most recent version) I agree it's not particularly well-executed.

In my opinion one of the biggest obstacles to advancing speaker design is the insistence on conventional boxes. That design has some major problems which simply can't be solved, the worst of which is that the radiation pattern depends on frequency very strongly, and in a way that's extremely unnatural compared to any ordinary sound source.

As a result they all tend to sound a lot like, well... box speakers.

 

[rsaavedra]

Sol open another thread and let's discuss power amplifier requirement and realistic playback in its own thread if you want. If you'd like, please start that thread by indicating how many "way-off" dB SPL does decrease with distance in a decently sized room, with references supporting your claim.

Apparently noone took interest in this suggestion I made. The way volume decreases with distance in a non-anechoic room should be a worthwhile technical topic to further exchange posts on here. In particular the notion of "critical distance", when reverberating sound equals the direct sound from the speakers, and how sound is much less accurate the more reverberations you have. (And that's precisely why audio monitoring is done with near field monitoring, particularly when the monitoring room is small.) Will post some links and info about all this myself.

 

[sol invictus]

First of all, there's no such thing as an anechoic room. Trying making a wall that fully absorbs sound at 20Hz.

In a real room, SPL as a function of position depends on the room and the spectrum of the sound. As an example, if you take some average-sized listening room (say 20x20x8 feet or so) and play a sound at a low resonant frequency (say around 55 Hz), the SPL will not depend on distance to the speakers, to a good approximation.

Don't believe me? Try it yourself. You won't be able to tell where the sound is coming from. As you walk around the room you'll hear nulls and maxima, but their locations don't depend much on the positions of the speakers. So at low frequency, SPL does not depend on the distance to the speakers (it depends on position of course, but position relative to the walls, floor, and ceiling, not the speakers).

At high frequency SPL does depend on the distance to the speakers, but in a complicated way: it depends on the distance to speaker 1, the distance to speaker 2, the distance to every reflecting surface, and the HF damping and diffraction characteristics of the walls, ceiling, and floor - AND on the location of the speakers in the room.

So the total SPL for music will depend on all of those factors and the spectrum of the music. If the SPL is dominated by bass it essentially won't fall off at all. If it's dominated by HF it depends very much on damping. There's no one answer, but 6dB when you double distance is close to correct only for speakers with a LF cutoff at 20Hz suspended in space with at least, say, 50 feet of emptiness around them in all six directions. Not exactly your typical listening room (although I've read that that is how ATC tests their speakers at their factory).

 

[alfaniner]

!!! The addition of the [Split] tag in the title could take this thread in a whole new direction. After all, didn't Don Imus get in big trouble for doing something similar?

 

[rsaavedra]

Here's the definition of critical distance, a very important notion if you care about good sound:

http://en.wikipedia.org/wiki/Critical_distance
http://www.tonmeister.ca/main/textbook/node287.html


And in this excelent manual that I highly recommend to anyone interested in audio, you can see diagrams and definitions of critical distance, as well as explanations of direct vs. reverberant sound fields, from page 5-12 on:

Sound System Design Reference Manual - JBL Professional
http://www.jblpro.com/pub/manuals/pssdm_1.pdf


Page 5-13 has a graph showing how the directionality of the speakers affects the critical distance. Page 5-15 has a graph that shows what I inquired about quite a few days ago now: how SPL decreases with distance in a non-anechoic room.

And page 5-16 has a graph indicating direct sound field vs reverberant sound field ratio depending on distance. Effective transition zone between reverberant sound field and direct sound field is somewhere between half and twice the critical distance.

All in all, the fact is, if you are listening to your system beyond the critical distance, you are mostly immersed in the reverberant sound field, and indeed in that region SPL doesn't decrease 6 dB with every doubling of distance; in fact, that far SPL doesn't decrease any more within the room (see how the lines eventually get horizontal on graph at 5-15.) But it also means, you are listening to a crappy representation of the music all equalized by the reverberations of your room. Quite a poor setup to begin with for critical audio listening.

In ideal conditions, you want to have a sufficiently absorbing/large room and speaker directionality to yield a critical distance so that you sit within that distance from your speakers; so that direct sound field is sufficiently stronger than the reverberant sound field at your listening position. Within the critical distance, the slope of decreasing SPL over distance is in fact quite close to 6 dB per doubling the distance, as shown in that graph on all lines in the regions to the left of the little circles.

Provided a sufficiently large/absorbing room and directionality of speakers, the critical distance can be a relatively long distance, so SPL still does decrease quite fast with every doubling of distance, as shown in the graph on page 5-15. And once again, depending on that distance, and to preserve proper dynamic range with realistic playback, you need quite a lot of power capacity in your amplifier, as properly explained in article by Alan Lofft, link posted earlier in this thread.

 

[sol invictus]

All in all, the fact is, if you are listening to your system beyond the critical distance, you are mostly immersed in the reverberant sound field, and indeed in that region SPL doesn't decrease 6 dB with every doubling of distance; in fact, that far SPL doesn't decrease any more within the room (see how the lines eventually get horizontal on graph at 5-15.) But it also means, you are listening to a crappy representation of the music all equalized by the reverberations of your room. Quite a poor setup to begin with for critical audio listening.

You've got a great sense of humor.

What do you think the "critical distance" is for low audio frequencies?

 

[rsaavedra]

You've got a great sense of humor.

Thanks, though my previous post was absolutely humorless.

What do you think the "critical distance" is for low audio frequencies?

Glad you start using the right terminology. But please let's switch turns since my post was already quite long. Indulge yourself in explaining whatever you'd like answering your own question.

PS. But how about you post not just your opinion or empirical "discoveries" in audio, but you could back up your statements with credible/solid references. After all, most things audio have been well studied for many many years.

 

[sol invictus]

Glad you start using the right terminology. But please let's switch turns since my post was already quite long. Indulge yourself in explaining whatever you'd like answering your own question.

It's not very good terminology, actually. The reference you gave treats sound as if it were composed of particles - which is completely wrong when the wavelength is of order the size of the room (as is the case for low frequencies in typical rooms). One can roughly capture that by saying the critical distance depends strongly on frequency, but it's really just the wrong terminology. Sound isn't made of little particles.

That may not matter too much when you're trying to decide where to set up some speakers, but if you want to know how total SPL varies in the room it cannot be ignored.

PS. But how about you post not just your opinion or empirical "discoveries" in audio, but you could back up your statements with credible/solid references. After all, most things audio have been well studied for many many years.

If you don't believe what I say, that's not my problem. I'm not going to give a course on audio here. You're correct this stuff has been understood for a long time... an excellent reference is Lord Rayleigh's Theory of Sound, published in 1896. You can read it online for free using google books.

Reading and understanding Chapter 13 would be a good start if you want to learn more.

 

[rsaavedra]

Hahaha you do have a sense of humor Sol.

So you think a drawing with dots suggest the author thought sound was made or particles, hahahahaha

 

[Paulhoff]

Sound isn't made of little particles.

So, right there we can throw out the atom theory.

Paul

 

[sol invictus]

So you think a drawing with dots suggest the author thought sound was made or particles, hahahahaha

So, right there we can throw out the atom theory.

Nice contradictory responses, you two. One thinks it's ridiculous to model sound as particles, and the other that it's ridiculous not to.

Paul, a sound wave is a collective motion of air molecules. The energy and momentum of the wave is not carried by any individual molecule, or even by any finite collection of them - in fact none of the molecules move any significant distance as the wave passes, any more than water molecules are carried along by water waves.

Rs, The analysis in the reference you posted treats sound in what would be called the geometric optics approximation if we were discussing light. That is, light (or sound) travels along straight lines and reflects off boundaries with angle of incidence equal to angle of refraction. It is equivalent to treating the wave as being composed of little particles traveling along geodesics, and it works only when the wavelength of the sound is quite short.

So yes, the author does think sound can be modeled as little particles, and that is what the diagram indicates. I'd be entertained to know what you thought it meant.

 

[rsaavedra]

Come on, you had promised you wouldn't give us any lecture. I don't think anyone really asked for any lecture from you.

But I would ask you to read. For instance, read pages 5-12 and 5-13 of that document, which obviously you didn't read. The dots are perfectly explained there as indications of relative energy density.

There is a wise saying in Spanish which more or less says (in my poor translation): "There isn't a blindness worse than the blindness of he who doesn't want to see."

 

[sol invictus]

Come on, you had promised you wouldn't give us any lecture. I don't think anyone really asked for any lecture from you.

Really?

But please let's switch turns since my post was already quite long. Indulge yourself in explaining whatever you'd like answering your own question.

But I would ask you to read. For instance, read pages 5-12 and 5-13 of that document, which obviously you didn't read. The dots are perfectly explained there as indications of relative energy density.

Yes, in a particle model like that each particle carries some energy, and so the density of dots is proportional to the SPL. Again, this is totally inapplicable when the wavelength is long.

I'm sure the author would agree with me - the method in that manual is intended to be as simple as possible and to help someone without much knowledge set up some speakers. It probably works well for that. It's NOT intended as a method for calculating the total SPL in a room.

There is a wise saying in Spanish which more or less says (in my poor translation): "There isn't a blindness worse than the blindness of he who doesn't want to see."

When someone in an internet forum starts making vaguely mystical pronouncements about how the other is blind and just doesn't want to see the light, it's usually time to end the discussion. If you want to have a conversation, respond substantively. As I said earlier, I couldn't care less if you don't believe what I say - and I'm not interested in a pissing match.

 

[rsaavedra]

Really?

Yes, really. Giving you the token for your turn in a conversation isn't an invitation to give any lecture.

the method in that manual is intended to be as simple as possible and to help someone without much knowledge set up some speakers.

This is one of the few things you've said that I agree with. The reference is simple and clear enough (as well as the article by Alan Lofft.) That simplicity is the exact reason why I chose to post those references, precisely because extra simplicity and clarity apparently was required for you to understand some basics.

 

[sol invictus]

That simplicity is the exact reason why I chose to post those references, precisely because simplicity and clarity apparently was required for you to understand some basics.

Again, rather than respond to anything substantive you say something like this.
That's the third or fourth time, and it's pretty obvious why.

Why don't you answer this simple question: for a 50Hz tone played in a normal sized (let's say 20x20x9 in feet) listening room, do you think those diagrams are a good representation of the sound field?

 

[rsaavedra]

Why don't you answer this simple question: for a 50Hz tone played in a normal sized (let's say 20x20x9 in feet) listening room, do you think those diagrams are a good representation of the sound field?

Why don't you spend some time learning a bit more about acoustics before arguing wildly. Look up room acoustics, room modes and cancellations etc. And not just look up. Read.

 

[sol invictus]

Again, rather than respond to anything substantive you say something like this.
That's the third or fourth time, and it's pretty obvious why.

Why don't you spend some time learning a bit more about acoustics before arguing wildly. Look up room acoustics, room modes and cancellations etc. And not just look up. Read.

What a surprise - you did it again.

Anyway, I'll take that as a "no".

So then why did you post a link to something with little or no relevance to the question at hand?