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Testing audiophile claims and myths - Page 122

post #1816 of 2956
Quote:
Originally Posted by p a t r i c k View Post
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.

 

I think I'd recommend diffusors over reflectors.

 

se

post #1817 of 2956
Quote:
Originally Posted by Steve Eddy View Post

 

I think I'd recommend diffusors over reflectors.

 

se

 

In my brief description I pointed out that you need to manage reflections using what I described as "reflectors". These are placed on the walls on each side of the speakers and on the ceiling positioned between the listener and the speakers. You can actually work out the positioning using a mirror. You get a friend to hold the mirror in place. You sit in the listening position and you will ask your friend to move the mirror around until you see the speaker drivers in the mirror. Your friend marks the position. Now you know where the primary reflections are coming from.

 

You can then manage those reflections. It might well be, and indeed often is the case, that a reflector is what is required, in other words, a panel with no diffusion. It might be that a bit of diffusion is required. In practice you will need to experiment, but for those panels you are in the business of managing reflections which are essential to good sound.

 

Edited by p a t r i c k - 2/4/13 at 9:47am
post #1818 of 2956
Quote:
Originally Posted by p a t r i c k View Post


You can then manage those reflections. It might well be, and indeed often is the case, that a reflector is what is required, in other words, a panel with no diffusion. It might be that a bit of diffusion is required. In practice you will need to experiment, but for those panels you are in the business of managing reflections which are essential to good sound.

 

 

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

 

se

post #1819 of 2956
Quote:
Originally Posted by Steve Eddy View Post

 

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

 

se

 

If the room is part of the computation for a reflex horn, or back loaded horn is the only thing I can think of. Unless you are talking about designing a concert hall where you are concerned with un-amplified projection from stage to the nose-bleeds. 

post #1820 of 2956
Quote:
Originally Posted by Steve Eddy View Post

 

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

 

se

 

I recommend you get hold of F Alton Everest's Master Handbook of Acoustics.

 

There are many excellent resources on the Internet as well for you to consider.

 

You will find that in designing an acoustic treatment for a room for listening to music from a Hi Fi you will be creating management for key reflections in the room.


Edited by p a t r i c k - 2/5/13 at 8:57am
post #1821 of 2956
Quote:
Originally Posted by liamstrain View Post

 

If the room is part of the computation for a reflex horn, or back loaded horn is the only thing I can think of. Unless you are talking about designing a concert hall where you are concerned with un-amplified projection from stage to the nose-bleeds. 

 

Well I have treated one room for use for listening to a Hi Fi in my time and I recommend you read F. Alton Everests Master Handbook of Acoustics.

 

You will find that in creating such a room you will wish to manage some key reflections rather than simply diffuse or absorb all sound.

post #1822 of 2956
I brought up the subject in this thread of my past experience of treating a room acoustically for listening to music from a Hi Fi.
 
I since moved house so I have that room no more and my new house is too small to have a dedicated listening room. This is because I now live in a very expensive part of the UK whereas I used to live in a very cheap part of the UK.
 
My treatments were based primarily on my reading F. Alton Everest's book Master Handbook of Acoustics. I recommend anyone to read this book, it is if you like a "bible" for anyone wishing to get into acoustics, however it is well written and easily comprehended.
 
I have read the book cover to cover and some!
 
I've seen a couple of posts now in the thread which repeat one of the many myths about acoustic treatments, this myth being that acoustic treatment is about removing all possible reflections. This is not true.
 
In fact the vast majority of reflections are removed however there are some essential key reflections which are to be managed, as I described earlier.
 
I will now quote from page 410 of the fourth edition if the Master Handbook of Acoustics in chapter 19 Acoustics of the Listening Room.
 
Allowing a single lateral reflection of adjustable level would place control of the spaciousness and image effects in the hands of the experimenter/listener! The potential of this concept is staggering. Therefore, the next step in improving the listening conditions in this listening room will be the effective elimination of all of the early reflections, except for those of the lateral reflections off the left and right side walls that will be adjusted for optimum sound quality.
 
F. Alton Everest then goes into considerable detail about how to manage these reflections.
 
As I say I used this book (in fact an earlier edition) as the primary guide to my creation of my listening room and the results were excellent.
 
So I recommend anyone interested in getting good sound reproduction to read this book.

Edited by p a t r i c k - 2/5/13 at 9:30am
post #1823 of 2956

Personally, I think the sound of the room can be an important part of good sound. When you achieve a soundstage that has the subtle natural room ambience wrapped around it, it can add an extra level of realism. I also think that it isn't important, or even desireable to have the sound exactly the same at every seat in the room. A little natural variation is a good thing. It adds a perspective to the sound.

 

Sometimes home theater guys (the ones who really work room acoustics) go overboard in trying to squeeze the last drop of theoretical sound quality out, and they end up with sound that is technically perfect, but acoustically sterile. Wen I was setting up my listening room, I was limited as to what I could do. The room is panelled floor to ceiling in beautiful golden knotty pine from the 50s. I wasn't about to junk it up with a bunch of giant dark brown acoustic panels. So I focused on the arrangement of the room. I tried putting furniture and rugs in different places and carefully adjusted the placement of the speakers. Even though I didn't go balls out on acoustic treatment, it still got me to where I wanted to go.

 

it was a lot harder to balance the relative volume and EQ of the six channels than it was to set up the room. A little adjustment one direction or the other can have a big impact.

post #1824 of 2956
Quote:
Originally Posted by p a t r i c k View Post

I brought up the subject in this thread of my past experience of treating a room acoustically for listening to music from a Hi Fi.
 
I since moved house so I have that room no more and my new house is too small to have a dedicated listening room. This is because I now live in a very expensive part of the UK whereas I used to live in a very cheap part of the UK.
 
My treatments were based primarily on my reading F. Alton Everest's book Master Handbook of Acoustics. I recommend anyone to read this book, it is if you like a "bible" for anyone wishing to get into acoustics, however it is well written and easily comprehended.
 
I have read the book cover to cover and some!
 
I've seen a couple of posts now in the thread which repeat one of the many myths about acoustic treatments, this myth being that acoustic treatment is about removing all possible reflections. This is not true.
 
In fact the vast majority of reflections are removed however there are some essential key reflections which are to be managed, as I described earlier.
 
I will now quote from page 410 of the fourth edition if the Master Handbook of Acoustics in chapter 19 Acoustics of the Listening Room.
 
Allowing a single lateral reflection of adjustable level would place control of the spaciousness and image effects in the hands of the experimenter/listener! The potential of this concept is staggering. Therefore, the next step in improving the listening conditions in this listening room will be the effective elimination of all of the early reflections, except for those of the lateral reflections off the left and right side walls that will be adjusted for optimum sound quality.
 
F. Alton Everest then goes into considerable detail about how to manage these reflections.
 
As I say I used this book (in fact an earlier edition) as the primary guide to my creation of my listening room and the results were excellent.
 
So I recommend anyone interested in getting good sound reproduction to read this book.

In the fifth edition at least some of that chapter has been re-written.  It is suggested that reflections be treated by absorption with the possible desirability of lateral reflections, and that's in relation to the possible improvement of "spaciousness".  The degree of lateral reflection is to be determined experimentally:

 

Excerpt: -----

 

 

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.
-----
 
In no case was it suggested that a deliberate reflector be added.
 
The chapter doesn't discuss the use of a diffusor to control reflections, though diffusion is discussed in the following chapter on small studio acoustics.
 
I don't have my copy of the fourth edition to compare to, sorry.
 
edit: indicated book excerpt

Edited by jaddie - 2/5/13 at 11:54am
post #1825 of 2956

This might be my understatement of the week, but the book "Sound Reproduction - Loudspeakers And Rooms" by Floyd Toole covers the subject of reflections and their positive and negative effects in greater detail, a discussion spanning several chapters.

post #1826 of 2956

Can someone please explain, what is the best way to level match speakers when using a stereo amp for evaluation purposes?

post #1827 of 2956

Use a preamp to balance the level.

post #1828 of 2956
Quote:
Originally Posted by Yahzi View Post

Can someone please explain, what is the best way to level match speakers when using a stereo amp for evaluation purposes?

 

Are you talking about level matching for the purposes of ABXor DBT testing, to eliminate volume differences as a biasing factor? Or something else? 

post #1829 of 2956
Quote:
Are you talking about level matching for the purposes of ABXor DBT testing, to eliminate volume differences as a biasing factor? Or something else?

 

Well if you are comparing two speakers in an apples to apples way ... in a sighted test, the best you can do is try to level match the volume between both. With a stereo set up, how would one go about doing this?

post #1830 of 2956

Comparing two speakers is easy. Just put one pair as the A speakers and the second set as B. Switch between them. If there is a volume difference, you'll need two amps.

 

Usually when I'm comparing speakers, I compare at a volume that is the loudest that is comfortable.


Edited by bigshot - 2/5/13 at 10:30pm
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