Head-Fi.org › Forums › Equipment Forums › Sound Science › Testing audiophile claims and myths
New Posts  All Forums:Forum Nav:

Testing audiophile claims and myths - Page 129

post #1921 of 3125
Quote:
Originally Posted by Steve Eddy View Post

 

That has been on my bookshelf since the Second Edition.

 

And I can't recall any instance where it was ever recommended to manage reflections by using REFLECTORS. Diffusion and absorption, yes. And even varying degrees of absorption to suit one's tastes. But not reflectors.

 

Keep in mind that this is what you wrote that I was responding to:

 

 

Well, you question the use of the phrase "reflective panels". Well in my brief description I use this word to describe how you are managing reflections. I go on to say that these are to be managed by using different materials (meaning of course, for absorption or diffusion).

 

Here is what I wrote:

 

To manage those reflections you can use reflective panels in the centre of the walls and in the centre of the ceiling. These are ideally replaceable with panels of different materials and also these panels are to be adjustable for angle.

 

As you can see I was writing in the context of reflection, so the use of the term "reflective panels" is really reasonable and sensible in that context.

 

Steve, you go on to write:

 

Can't think of any instance where it would be required it be reflected rather than diffused or absorbed.

 

This is referring to these reflections of course.

 

Unfortunately this is a repetition of a myth concerning creating an ideal acoustic in a listening room.

 

If you do not plan and manage reflections in your listening room but absorb and diffuse them all, you will end up with a very small soundstage. Trust me, I have done this myself.

 

Every acoustic engineer who you might wish to speak to would tell you this is their experience and they would follow that up with a discussion about the importance of managing reflections.

 

You can of course manage reflections with different levels of diffuser/reflector, and of course this is what I pointed at in my initial posting.

 

I would like you to have a look at the following diagram:

 

 

This is from a website for a company that creates a product called a "Tube Trap". When I created the acoustic treatments for my listening room I would have loved it if I could have had these.

 

With considerable simplification I will write that each Tube Trap is a column with an absorbing side and a reflecting side.

 

Tube traps can be used for the three basic categories available to the acoustic engineer, diffusion, reflection and absorption.

 

In the above diagram you can see that the Tube Traps are not simply all used to maximise diffusion and absorption, instead they are deployed carefully to managing diffusion, absorption and reflections.

 

In the simpler system I described for my own room I actually describe managing the minimum of reflections, merely those from the side walls, and in fact one from the ceiling.

 

Today an acoustic engineer in creating a listening room will work with many more reflections than this, and they will be using reflectors for that purpose. Now those reflectors might well be diffusors and absorbers for different frequencies or to create different levels of reflection, but they will also be reflectors. And when the engineer is talking about them in the context of reflection he or she will describe them very likely as reflectors.

 

I'm delighted to see that jaddie has included a quote from the Fifth edition of F. Alton Everest's Master Handbook of Acoustics

 

Lateral Reflections and Control of Spaciousness
 
The lateral reflections from the side walls have been essentially eliminated by the absorbing material placed on the wall. A critical listening test should be performed with the sidewall absorbers temporarily removed, but with the floor, ceiling, and diffraction absorbers still in place. The recommendations of Fig. 18-7 can now be tested. Does the strong lateral reflection give the desired amount of spaciousness, or does it cause unwanted image spreading? The adjustment of the magnitude of the lateral reflections can be explored by using sound absorbers of varying absorbance (light cloth, heavy cloth, velour, acoustical tile, glass fiber panel) on the side-wall reflection points. For example, the lateral reflections can be reduced somewhat by hanging a light cloth instead of velour.
 
Techniques such as these provide the ability to adjust the lateral reflections to achieve the desired spaciousness and stereo and surround imaging effect to suit the individual listener or to optimize conditions for different types of music. The discussion of the acoustical design techniques for small rooms is continued in the following chapters.
 
This is excellent and totally in line with my own actions based on a much earlier edition of this book. I currently have the fourth edition and this text is in that edition as well.
 
jaddie tells us:
 
In no case was it suggested that a deliberate reflector be added.
 
Steve Eddy also writes:
 
And I can't recall any instance where it was ever recommended to manage reflections by using REFLECTORS. Diffusion and absorption, yes. And even varying degrees of absorption to suit one's tastes. But not reflectors.
 
So, it is, apparently my use of the word "Reflectors", which is the cause of all the problems for Steve Eddy and jaddie.
 
Well acoustic engineers talk in terms of "Reflectors", "Diffusors" and "Absorbers" however all acoustic treatments have some level of each of these properties.
 
In F. Alton Everest's description he tells how he uses different levels of absorption and diffusion on the side walls to manage reflections. Well, if, for example you are using light cloth then there will be a great deal of reflection of most frequencies. And those reflections are "deliberate" :)
 
jaddie writes about me:
 
He must have the terminology messed up.
 
Apparently I have the terminology messed up because I wrote "reflector" :)
 
Well I was writing about reflections so I think my terminology was appropriate.
 
In my original post I could, of course, equally have written that to manage the reflections use absorbers/diffusers and reduce absorption/diffusion to increase reflection. However it is very wordy, given that I was, in fact, writing about managing reflections.
 
But this still wouldn't have kept Steve Eddy happy unfortunately, remember he writes:
 
Can't think of any instance where it would be required it be reflected rather than diffused or absorbed.
 
Okay, so in summary:
 
When creating a listening room you will be in the business of managing reflections as well as diffusion and absorption.
 
The idea that creating a listening room is about absorbing all reflections is false.
 
When I am using devices to manage reflections I am perfectly entitled to describe them as reflectors (and this is true of professional acoustic engineers who will talk about reflectors, trust me!) or absorbers or diffusors depending on context.
 
And finally:
 
If Steve and jaddie are ever in London I would love it if they could join me in a trip to a concert at the Royal Festival Hall.
 
This concert hall had a massive acoustic redesign in 2000 and today it is possibly the finest concert hall in the world, although I have not heard them all so, I will tell you that it is at least one of the finest at least.
 
You will find the quality of the sound reproduction to be superb.
 
Here is a pic:
 

700

 

The internal treatments consists of the deployment of diffusors, absorbers and (whisper) reflectors. Some massive ones actually.

 

 
 
 
 
 
 
 
post #1922 of 3125
Quote:
Originally Posted by p a t r i c k View Post

 

Well, you question the use of the phrase "reflective panels". Well in my brief description I use this word to describe how you are managing reflections. I go on to say that these are to be managed by using different materials (meaning of course, for absorption or diffusion).

 

Here is what I wrote:

 

To manage those reflections you can use reflective panels in the centre of the walls and in the centre of the ceiling. These are ideally replaceable with panels of different materials and also these panels are to be adjustable for angle.

 

As you can see I was writing in the context of reflection, so the use of the term "reflective panels" is really reasonable and sensible in that context.

 
 
 
 
 
 

 

It's not "reasonable and sensible" by any definition of the adjective "reflective" that I'm aware of. And according to my Oxford English Dictionary, in this context it means "That throws back something striking or falling upon the surface." Or if we defer to Webster's, "capable of reflecting light, images, or sound waves."

 

So when you say "To manage those reflections you can use reflective panels..." you're essentially saying that the way to deal with a reflectION is to use something that's reflectIVE. Which simply makes no sense at all. In other words, what you said was the equivalent of saying that the way to deal with a reflection from a mirror is to put a second mirror over the first mirror, the second mirror being the "reflective panel" that you referred to.

 

Quote:

Steve, you go on to write:

 

Can't think of any instance where it would be required it be reflected rather than diffused or absorbed.

 

This is referring to these reflections of course.

 

Unfortunately this is a repetition of a myth concerning creating an ideal acoustic in a listening room.

 

And neither I nor anyone else stated any such "myth." This is a straw man.

 

Quote:
You can of course manage reflections with different levels of diffuser/reflector, and of course this is what I pointed at in my initial posting.

 

But you pointed to it in such a way that made absolutely no sense.

 

Quote:
jaddie tells us:
 
In no case was it suggested that a deliberate reflector be added.
 
Steve Eddy also writes:
 
And I can't recall any instance where it was ever recommended to manage reflections by using REFLECTORS. Diffusion and absorption, yes. And even varying degrees of absorption to suit one's tastes. But not reflectors.
 
So, it is, apparently my use of the word "Reflectors", which is the cause of all the problems for Steve Eddy and jaddie.

 

It was your use of the phrase "reflective panels" in the context of dealing with reflections.

 

Quote:
jaddie writes about me:
 
He must have the terminology messed up.
 
Apparently I have the terminology messed up because I wrote "reflector" :)
 
Well I was writing about reflections so I think my terminology was appropriate.

 

No, your terminology was not appropriate as your terminology made no sense.

 

Quote:
But this still wouldn't have kept Steve Eddy happy unfortunately, remember he writes:
 
Can't think of any instance where it would be required it be reflected rather than diffused or absorbed.
 
Okay, so in summary:
 
When creating a listening room you will be in the business of managing reflections as well as diffusion and absorption.
 
The idea that creating a listening room is about absorbing all reflections is false.

 

I'm sorry, but NO ONE here said that creating a listening room is about absorbing all reflections. This is another straw man.

 

Your post related to dealing with first reflections from the floor, ceiling and sidewalls. And you said that the way to deal with those reflections was to use reflective panels. And in doing so, you were essentially saying to put mirrors on top of mirrors, which makes absolutely no sense.

 

se

post #1923 of 3125
Quote:
Originally Posted by p a t r i c k View Post

You will find the quality of the sound reproduction to be superb.
 
Here is a pic:
 

700

 

The internal treatments consists of the deployment of diffusors, absorbers and (whisper) reflectors. Some massive ones actually.

Excellent hall.  Not used for sound reproduction.  Ever.  It's used for sound production, performance.  The purpose is completely different, and the room is built specifically for that.  If it were a room that size used for  sound reproduction, as in a movie theater, the acoustic treatment would be completely different.  

 

We were talking about listening rooms used for sound reproduction.  The comparison of a home listening room to Royal Albert Hall makes no sense whatsoever.

 

Read the Toole book, it will clear this all up for you.

 

You say, "When I am using devices to manage reflections I am perfectly entitled to describe them as reflectors (and this is true of professional acoustic engineers who will talk about reflectors, trust me!) or absorbers or diffusors depending on context."

 

Actually, as evidenced by this thread, if you intend exercise your right to use the wrong terminology, you must also be prepared to be misunderstood. 

 

You're hanging onto and defending your use of the terms "reflector" and "reflection", despite some rather painstaking replies and excerpts from authoritative reference works.  If you were to say to an acoustic engineer, "I have a lot of reflections in my listening room.  Please add some reflectors to control them", he would probably decline the job, or at least make a large effort to explain why that wouldn't work.  

 

If you were to say to an acoustic engineer, "I have a lot of reflections in my listening room.  Please add some something to control them", he would add a combination of absorbers and diffusors, and you'd be happy.

 

It's apparent you have the basic concept, this is really a terminology issue.  But if you do decide to use the right terminology, life will be easier, you'll be understood the first time, and you (and we) won't have to spend all this time trying to clear up the misuse of words.

 

Steve has just explained it very well. +1.  

post #1924 of 3125

Having a DAC discussion with a DAC designer and he is claiming that different filter technologies can affect the presentation of sound. Is this true?

post #1925 of 3125
Quote:
Originally Posted by Yahzi View Post

Having a DAC discussion with a DAC designer and he is claiming that different filter technologies can affect the presentation of sound. Is this true?

It depends on what he means by "the presentation of sound".  Sounds pretty ambiguous. Could mean anything, in which case, he could be right...or not. 

post #1926 of 3125

In what way could he be right? Please explain.

post #1927 of 3125

Are there any positive results from DBT's involving DAC's? I just need to have my facts in order. I haven't seen one on the net yet, but maybe I missed one or two.

post #1928 of 3125

"The presentation of sound" is completely ambiguous, could mean anything from an obviously audible effect to a nebulous and elusive character that can't be measured or reliably heard (and is probably imaginary).  Since I have no idea what he means by "the presentation of sound", I've given him room to be right and wrong, until we know more.  

 

The general idea of the filters in a DAC is reconstruction and removal of the sampling frequency.  There are now several different ways to do that, which is I'm sure what we're talking about.  In the early days of digital audio the filters were multi-pole analog filters that were rather difficult to make, and didn't always perform well.  There were three main issues: making the response in the audio band flat (complex filter tuning often introduced response wobbles), presenting the highest audio frequency possible while deeply cutting off above the Nyquist frequency (this required a complex filter of many poles and zeros), and doing all of that with the least amount of in-band phase shift as possible.  The three goals are actually pulling the design in completely different directions, which made for a lot of wild filters and some necessary compromises.  Usually they moved towards less sampling frequency in the output and more phase shift in the audio band.  The audibility of that phase shift was, at the time, a concern, particularly since each recording channel had a filter, and each play channel had a filter, and if there was analog mixing in production, add a few more.  All those cascaded filters added a lot of phase shift into the signal.  

 

Today we have high sample frequency recording, so the filters are bumped way up, and we have digital mixing, so no D>A and A>D round-trips with more filters to worry about. 

 

Today the reconstruction filter is mostly done with oversampling, moving the final sampling frequency way up so that the filter itself doesn't have to be so severe, and taking advantage of some digital filter techniques.  Once you have flat audio band response with minimal phase shift and have removed the sampling frequency, the job is pretty much done.  

 

That's my simplistic view on it.  I have no doubt a DAC designer would have at least some arguments to support his design.

post #1929 of 3125
Quote:
Originally Posted by Yahzi View Post

Are there any positive results from DBT's involving DAC's? I just need to have my facts in order. I haven't seen one on the net yet, but maybe I missed one or two.

Don't know, but a DBT of a DAC isn't as easy to do as some other gear.  You really need two complete systems running simultaneously, and in sync, then hit a hardware ABX comparator, which isn't something everybody has access to.  The source of the digital stream needs to be identical two, so that's two computers identically configured, also kind of expensive.  It would be a project, to say the least.  These things take a budget of time and money.  

 

Now, if somebody has the money....I have the ABX comparator, and would make the time.  smily_headphones1.gif

post #1930 of 3125

Very good reply jaddie.

 

Quote:
Originally Posted by Yahzi View Post

Having a DAC discussion with a DAC designer and he is claiming that different filter technologies can affect the presentation of sound. Is this true?

 

If you mean digital filters, for a real-world example have a look at the "Tech Highlights" page of the gamma2 website (a high quality DIY DAC). The main difference between the three filters is in the roll-off in the FR, and the pre/post ringing in the impulse response. I've done some very casual comparisons listening out for pre-ringing and couldn't tell the difference, but I would not be surprised to find a trained ear which could detect it. The point though is the differences between digital filters are very small as they have all pretty much converged to a compromise between the things jaddie mentioned (FR, phase shift, impulse response).

post #1931 of 3125
Quote:
Originally Posted by joeyjojo View Post

Very good reply jaddie.

 

 

If you mean digital filters, for a real-world example have a look at the "Tech Highlights" page of the gamma2 website (a high quality DIY DAC). The main difference between the three filters is in the roll-off in the FR, and the pre/post ringing in the impulse response. I've done some very casual comparisons listening out for pre-ringing and couldn't tell the difference, but I would not be surprised to find a trained ear which could detect it. The point though is the differences between digital filters are very small as they have all pretty much converged to a compromise between the things jaddie mentioned (FR, phase shift, impulse response).

The reason you won't clearly detect the "sound" of pre or post ringing of a given impulse response is that the ringing is not just a defect of a filter, but rather the result of the attenuation and removal of high order harmonics from a perfect impulse or square wave.  Even in a theoretically perfect filter, you'd have pre and post rings because of the filter action.  Ringing can be made to look worse by changing the filter type or cut-off frequency, but they will all ring at least somewhat except for something like a first order 6dB/octave, which isn't really useful for this purpose.  The application that shows less ringing is mostly the result of a higher cutoff or lower order, which is the point of oversampling.  But rings themselves aren't audible.  In fact, you can mess up a square wave beyond recognition with an all-pass filter and it will still sound the same.  Nor are rings an indication of any audible difference in SQ.  

post #1932 of 3125

Is it possible to measure the level of graininess in music ?

post #1933 of 3125

Maybe, once the term graininess is better defined. 

post #1934 of 3125

Another blind test using amplifiers (I did not conduct this test) :

 

 

Quote:
With stereo, this is relatively easy. Same source, same speakers, tone defeat on all, loudness etc off, level matched with a accurate volt meter. Not sure what you mean by time-synchronised.

We've done this very test with the 3 brands of amp I mentioned (model is irrelevant), with a source switch and a speaker switch, so no need to change cables, and the cables were exactly the same between all. Some might argue that the switches introduce distortion - maybe so, but again it's the same distortion introduced in all the signal paths. The same goes for the source and speakers - nothing changed between amps.

A luddite friend controlled the test, from behind a sheet - we couldn't see him, nor the equipment.

I'm not sure how more controlled we could make this test, being the amateurs we are. Yet, the differences were easily discernible by most attendees.

As an aside - we've done the same with high-end car amps, not to long ago, although there were added complication of cables having to be swapped, which admittedly could cloud the sonic memory due to the delays involved. Yet, even there, with a group of about 30, the differences were noticeable and repeatable. Even my girlfriend, a complete audio luddite, picked up some of the more obvious differences...

Both of these were done completely blind - we could not see the equipment nor the operators, everybody sat in the same seats every time, and outputs were level matched according to voltage.

I'm willing to redo the test - I have a cheapy Pioneer, and a higher-end Yamaha at my disposal. Unfortunately I no longer have the speaker switch

I have to stress - these test were not done to find a "better" amp - merely a test to find out whether there are discernible differences between brands. And there are. Proven.

 

What do you think of these results? Any issues with the tests, questionable results based on improper testing .... ??

post #1935 of 3125
Quote:
Originally Posted by Yahzi View Post

 

What do you think of these results? Any issues with the tests, questionable results based on improper testing .... ??

They're not very detailed results. Were there fake switches? Did they correctly identify whether it was amp A, B, or C?

 

If they just said there was a difference every time a switch was made, then that isn't really worth much.

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Sound Science
Head-Fi.org › Forums › Equipment Forums › Sound Science › Testing audiophile claims and myths