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Topic: Most sound reflective surface? (Read 19744 times) previous topic - next topic
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Most sound reflective surface?

Hey new poster, long time lurker here!


I have speakers that are connected, the sound isn't wide enough so im thinking of putting something between the speakers like this

___/\______
i_________i            ^Front of speakers              /\ = reflector things between speakers.


I was wondering what material I should use, I looked but couldn't find any solid recommendations. Also is this the right formation for reflecting sound. Also how much would it alter the sound. Like let's take some random frequency like 250 hz, obviously it'd lower it a little since some of the sound would get absorbed, would it alter it by a decibel or a tenth or less then a tenth of a decibel or what?

Most sound reflective surface?

Reply #1 –
Pretty much any 'hard' material would do, but I think something like plywood would be the easiest way. The lowest frequency it can reflect hasn't got anything to do with the thickness or specific material (as long as it's reflective) but the size of the panel has.

I really can't say what it would do to the sound, that depends on quite a lot more, like the room acoustics, speaker radiation pattern etc. I'd just try it.
Music: sounds arranged such that they construct feelings.

Most sound reflective surface?

Reply #2 –
Why isn't it letting me edit my post? Those are supposed to be question marks instead of periods.

I might try using marble, anyone have an idea of how that would effect the sound before I buy some?

Most sound reflective surface?

Reply #3 –
Quote from: peterh on
Why isn't it letting me edit my post?

There is a time limit (one hour I believe) within which to edit a post.

Edit: I would expect marble to be an excellent reflector, but a piece large enough to reflect low frequencies would be very large/heavy/expensive.

Most sound reflective surface?

Reply #4 –
In a recent post, I recommended experimenting with a pair of books before building anything.  I was thinking hard-cover books, but I didn't specifically say it.

I think the ideal reflector would be flat, smooth, hard, and stiff.    Maybe a piece of plywood with Formica on it, or a piece of Masonite Hardboard.  A mirror or a piece of glass would make a great sound-reflecting surface, but it might need some backing to keep it from resonating/vibrating.    If it's small and stiff enough, just a piece of glass might be fine.    If you search the Internet, you can find charts showing the sound absorbing properties of various materials at various frequencies.

I'm not quite visualizing your diagram, but you'll need a separate deflector (reflector?) for each speaker unless the speakers are so close together that the deflectors come together and form a 'V". 

Visualize the speakers as a lamp and the defectors as a white surface, and imagine the path the light will take from the speakers to your ears.    (Light isn't a perfect analogy, but it shoud help you to visualize the reflections.)

In order to get the sound to your ears, it also needs to bounce off the walls.  This is where you'll tend to loose high frequencies.  In my other post, I suggested experimenting with not blocking/deflecting the sounds from the tweeter.


Different frequencies will behave differently because of their different wavelengths.  A 10kHz sound  has a wavelength around 1.5 inches and is more "focused" or directional like a laser or flashlight.  Higher frequencies are also more easly absorbed.  A 50Hz signal has a wavelength of around 20 feet.  Low freqencies are not directional and they will tend to just "wash around" the deflector like a big water-wave.  Low frequencies tend to be reflected off of walls, rather than being absorbed.    Mid frequences should be reflected "nicely" off the deflectors and the walls.



Quote
Also how much would it alter the sound.
The effect should be dramatic, but you'll just have to experiment to see if you like it.    As the sounds bounce around, the various soundwaves will mix in-phase at some frequencies and out-of-phase other frequencies (depending on room size,  room acoustics, and your listening position).    This always happens, but it will be exaggerated when you deflect the direct sound from the speakers.  The "random" comb-filtering effects are something like adjusting the sliders on a grahic equalizer randomly and then moving the sliders as you move around the room.  This will be most noticable at mid-frequencies.  Your brain probably won't "hear" it as EQ...  It be more of a spacial effect making, the the sound non-directional.   

Comb filtering effects also tend to be very bad at bass frequencies (unless you have an acoustically treated room with bass traps), but the "acoustically small" deflectors will make no difference.

This not something I'd recommend for a recording/mixing studio or a "proper" listening room.  But, if you like it and you feel it makes an improvement to your existing setup, go for it!  It'll be fun, and you'll learn something about acoustics.

Most sound reflective surface?

Reply #5 –
Thank you very much! So if my speakers are facing towards the bottom of this post, should I put the reflectors in between them like this V or like this /\?

Most sound reflective surface?

Reply #6 –
like this /\


Or,
[Right Speaker]

\
.\        Deflector
..\
...\
....\
.....\

Right Wall
|
|
|
|
|
|
|
|

[Listener]


This is a simple concept, but kinda' hard to explain in words...  Maybe I can make a better sketch when I get some time later...

Another analogy/visualization...  Do you ever play pool?  The ball shoots straight out of the right speaker...  It hits the deflector at an angle and bounces toward the right-wall...  It bounces off the wall at an angle...    So, the ball comes at you from the direction of the wall instead of directly from the speaker.  (I believe that would be called a "double bank shot".)

Most sound reflective surface?

Reply #7 –
Quote from: DVDdoug on
like this /\


Or,
[Right Speaker]

\
.\        Deflector
..\
...\
....\
.....\

Right Wall
|
|
|
|
|
|
|
|

[Listener]


This is a simple concept, but kinda' hard to explain in words...  Maybe I can make a better sketch when I get some time later...

Another analogy/visualization...  Do you ever play pool?  The ball shoots straight out of the right speaker...  It hits the deflector at an angle and bounces toward the right-wall...  It bounces off the wall at an angle...    So, the ball comes at you from the direction of the wall instead of directly from the speaker.  (I believe that would be called a "double bank shot".)


A great post I perfectly understand what you mean with your sketch.

Just one more thing, if i have two pieces of marble like this /\, as you can see there is an open space between them. According to this chart http://realtraps.com/art_surfaces.htm some of the sound is absorbed. So for instance 2000 hz is lowered by about .1 db because that much sound is absorbed. My question is, will it be altered less then that because when the sound is absorbed it "passes through" the surface?

Most sound reflective surface?

Reply #8 –
If your sound source is a PC have you considered a stereo "widening" plugin?  Unfortunately, none is available for the current foobar2000 but it appears there is one for Winamp:
http://uploadgeneration.info/Winamp/www.wi...namix/3973.html

Another option worth a try is to "toe out" your speakers; that is angle them so they are aiming a bit out toward the side walls.

Most sound reflective surface?

Reply #9 –
Quote from: Apesbrain on
If your sound source is a PC have you considered a stereo "widening" plugin?  Unfortunately, none is available for the current foobar2000 but it appears there is one for Winamp:
http://uploadgeneration.info/Winamp/www.wi...namix/3973.html

Another option worth a try is to "toe out" your speakers; that is angle them so they are aiming a bit out toward the side walls.


Thanks, but I don't like stereo wideners, and my speakers are connected so that's not an option otherwise i'd definitely do that.

Most sound reflective surface?

Reply #10 –
Quote
So for instance 2000 hz is lowered by about .1 db because that much sound is absorbed. My question is, will it be altered less then that because when the sound is absorbed it "passes through" the surface?
You can't hear a 0.1dB loss.  Sound will "go around" more than "pass through".  The bigger loss will be from the walls, and if you had marble walls it would sound terrible because you'd have way too much "small room reverb".

The biggest effect will be due to the way the indirect sound is reflected around, and the way all of the soundwaves mis together summing & canceling.  Plus the possible loss of high frequencies, absorbed by the walls.  You always have a lot reflected sound, but you are eliminating the direct sound and increasing the reflected sound.

Most sound reflective surface?

Reply #11 –
Quote from: DVDdoug on
Quote
So for instance 2000 hz is lowered by about .1 db because that much sound is absorbed. My question is, will it be altered less then that because when the sound is absorbed it "passes through" the surface?
You can't hear a 0.1dB loss.  Sound will "go around" more than "pass through".  The bigger loss will be from the walls, and if you had marble walls it would sound terrible because you'd have way too much "small room reverb".

The biggest effect will be due to the way the indirect sound is reflected around, and the way all of the soundwaves mis together summing & canceling.  Plus the possible loss of high frequencies, absorbed by the walls.  You always have a lot reflected sound, but you are eliminating the direct sound and increasing the reflected sound.


Ok but i'm saying lets say there was a larger loss, would 100% of the "absorbed" sound be turned into heat, or would some of the absorbed sound mean it doesn't get reflected but just goes through the surface/goes around the surface? Is any sound that's not reflected considered absorbed?

This question doesn't really have to do with the speaker question, i'm just wondering.

Most sound reflective surface?

Reply #12 –
I heard a demonstration at an audio show of a different approach that worked quite well. Instead of reflective barrier, use an absorptive barrier that blocks the direct sound from each speaker to your opposite ear. This also keeps the comb filtering and excessive reflections down and it sounded very separated indeed. They used expensive acoustic panels but I'm guessing a mattress would also do the trick. Kinda extreme, but it looks like you're not bothered by that.
Was that a 1 or a 0?

Most sound reflective surface?

Reply #13 –
Quote from: peterh on
I have speakers that are connected
How are they connected ? IMO the only good way to get better channel separation is to put the speakers further apart (apparently not possible?) or move them closer to your head.
The recommended listening angle is +/-30° from centre. What's your current angle ?

Most sound reflective surface?

Reply #14 –
Quote from: Kees de Visser on
Quote from: peterh on
I have speakers that are connected
How are they connected ? IMO the only good way to get better channel separation is to put the speakers further apart (apparently not possible?) or move them closer to your head.
The recommended listening angle is +/-30° from centre. What's your current angle ?



As in its a big rectangle with front mounted speakers.

Most sound reflective surface?

Reply #15 –
Quote from: peterh on
...  Thanks, but I don't like stereo wideners, and my speakers are connected so that's not an option otherwise i'd definitely do that.


What 'bout spatial enchancer?

http://www.hydrogenaudio.org/forums/index....st&p=864119

You could try SHEPPi mentioned there ... it can be found through KVR - http://www.kvraudio.com/product/sheppi_spa...mbience_project

Most sound reflective surface?

Reply #16 –
Quote from: Juha on
Quote from: peterh on
...  Thanks, but I don't like stereo wideners, and my speakers are connected so that's not an option otherwise i'd definitely do that.


What 'bout spatial enchancer?

http://www.hydrogenaudio.org/forums/index....st&p=864119

You could try SHEPPi mentioned there ... it can be found through KVR - http://www.kvraudio.com/product/sheppi_spa...mbience_project


Is there any way to use it on mac in iTunes?

Btw so are people saying sound absorbing or reflecting would be better? If I had a panel that had .35 absorption for x frequency, then would having a 6 inch panel absorb 100%? Thus not changing the EQ at all when the sound comes out of my speaker? Also one thing is I don't understand when in a chart when it says it has absorption of 1.07 or something? How can something have 107% absorption?

Most sound reflective surface?

Reply #17 –
Quote
Ok but i'm saying lets say there was a larger loss, would 100% of the "absorbed" sound be turned into heat, or would some of the absorbed sound mean it doesn't get reflected but just goes through the surface/goes around the surface? Is any sound that's not reflected considered absorbed?
That's a darn-good question!    (I'm pretty sure they aren't talking about sound going-around.)  Obviously, sound passes through a sheet of regular window glass more easily than super-thick bulletproof glass.    From inside the room you wouldn't care, but if you are soundproofing a room it's very important.  Maybe you can find a chart for soundproofing???

In your application, far more sound will go-around.    Imagine the difference between putting a piece of plywood a few inches in front of your speaker compared to putting the speaker inside a sealed plywood box. 

Quote
Btw so are people saying sound absorbing or reflecting would be better? If I had a panel that had .35 absorption for x frequency, then would having a 6 inch panel absorb 100%?
What?? No.  You are never going to get 100% absorption.    You're talking about thickness, right?  I think it's something like a percentage-of-a-precentage...  You know...  If you cut something in half, and then cut the remaining part in half again,  etc., you never get to zero. 

Quote
Thus not changing the EQ at all when the sound comes out of my speaker?
Right! Speakers (and microphones) are sometimes tested in an anechoic chamber which has (nearly) zero reflected sound.    That way, you only get the direct sound from the speaker and you can test the frequency response of the speaker without the room messing-up the measurements.  It also allows you to change the angle and measure the off-axis response. 

Of course, you need to reflect the sound if you want to change the perceived location of the speakers.   

Quote
Also one thing is I don't understand when in a chart when it says it has absorption of 1.07 or something? How can something have 107% absorption?
Maybe its a typo.  The chart linked to from RealTraps says, "Remember that full absorption is 1 whilst full reflection is 0".

Most sound reflective surface?

Reply #18 –
Quote from: peterh on
Hey new poster, long time lurker here!


I have speakers that are connected, the sound isn't wide enough so im thinking of putting something between the speakers like this

___/\______
i_________i            ^Front of speakers              /\ = reflector things between speakers.


I was wondering what material I should use, I looked but couldn't find any solid recommendations. Also is this the right formation for reflecting sound. Also how much would it alter the sound. Like let's take some random frequency like 250 hz, obviously it'd lower it a little since some of the sound would get absorbed, would it alter it by a decibel or a tenth or less then a tenth of a decibel or what?



The best broadband sound reflector I know of is thick plate glass.  The reflective surface should be smooth and hard. Marble might be about as good.

Most sound reflective surface?

Reply #19 –
OK, I did a little experiment with my sound level meter:

The setup/enviroment -
My home office is a small bedroom.
My computer's small 2.1 speakers are setup on either side of the video monitor, close togeher but I can hear the stereo separation fine sitting at the desk.  The walls are wood paneling.  The wall on the right has a tall bookcase.
I set up the SPL meter in about the middle of the room, pointed at the video monitor.

I started some music, and then I propped a DVD case in front of each speaker as a deflector.  (Not the best deflector, but I had two of them sitting on the desk.*) The most noticeable thing was that the sound was slightly muffled.  The highest frequencies were rolled-off, but there wasn't much overall drop in volume.  The sound quality wasn't "terrible".  The stereo image was only slightly wider, maybe a litte more than the width of the DVD case deflector.  The bookcase didn't seem to make any difference, as the left & right "image" moved about the same.    I think a lot of sound may have been bouncing off the back wall (only a few inches back from the speakers) and a lot of it was leaking-around my defelectors.  The "width" didn't change much when I moved back toward the center of the room.

Next, I generated a 500Hz test tone (with GoldWave).  With the deflectors in place, there was about a 1dB loss.  Just moving my body around around behind the SPL meter, I was getting variations of more than 6dB, so I tried to stand in the same spot for both readings.  And, I could hear changes in the volume as I moved around too (standing wave nodes & antinodes).   

Then, I generateed a 10kHz tone.  This time, the deflectors caused about a 6dB drop.  At this higher frequency, moving around behind the meter had very little effect.  But every time I moved a few inches, the sound level in my ear changed drastically.  After taking the above measurements, I tried moving the SPL meter and a movement of about 1/2 inch caused a drop more than 6dB.  I guess I was accidently/randomly at a peak (antinode) in the standing wave.





* The last thing I did was push the DVD covers against my ear to get an idea of how much sound was passing through.  I'd guess I was only getting 10-12dB of loss (listening to music).    Covering my ears with my hands works better.  Maybe -30 dB or so.  I haven't had my ears calibrated recently, so those are just guestimates!

Most sound reflective surface?

Reply #20 –
OK, here's a thought. What is the cost difference between adding reflectors to widen the separation of your present speakers (with unknown results), vs. buying new speakers?

Most sound reflective surface?

Reply #21 –
Quote from: pdq on
OK, here's a thought. What is the cost difference between adding reflectors to widen the separation of your present speakers (with unknown results), vs. buying new speakers?


Lots and lots of money.

Also doug you're experiment was very informative and cool, thanks for taking the time!

Although don't worry I literally only have 1 question left then i'll be done, if I where to put sound absorbing panels in between my speakers in order to make them seem more separated, wouldn't that change the EQ a lot because the sound is getting absorbed?

Most sound reflective surface?

Reply #22 –
You've said little about your room or system setup. What are the speakers and what electronics are driving them? Are they on stands? How close to the front wall are they? How close to the side walls? What is the size and the material makeup of the room?

I honestly don't think this idea will work very well. At a minimum, your sound stage will collapse. Reflective surfaces, in general, do bad things to stereo imaging. You may be able to fiddle something that artificially makes the sound stage appear wider, but it will likely be at the cost of other qualities.

Have you experimented yet with different speaker placements and the angling of the speakers relative to your listening position?  Have you tried listening in the nearfield to minimize sidewall reflections?

Most sound reflective surface?

Reply #23 –
Quote from: peterh on
the sound isn't wide enough so im thinking of putting something between the speakers


Could this really be feasible in practice?

And are you trying to solve the right problem? Are you sure that, for example, the stereo image is not distorted by reflections where you hear either speaker both directly and by way of a wall or three? If you happen to have a couple of foam mattresses available, then try to put one up your left wall (such that, if it were a mirror, you would see the speakers) and another on the right. How does the sound change?

Most sound reflective surface?

Reply #24 –
Quote from: DigitalMan on
I heard a demonstration at an audio show of a different approach that worked quite well. Instead of reflective barrier, use an absorptive barrier that blocks the direct sound from each speaker to your opposite ear. This also keeps the comb filtering and excessive reflections down and it sounded very separated indeed. They used expensive acoustic panels but I'm guessing a mattress would also do the trick. Kinda extreme, but it looks like you're not bothered by that.


It works with two immediately adjacent speakers (each speaker placed on opposite sides of the barrier, in contact with it) as long as the barrier extends almost all the way from the speaker location to your listening location.  Your head needs to be placed about a foot or so from the barrier (listener looking directly at the two speakers in front, edgewise at the barrier, as if the barrier were an extension of her nose).  A simple sheet of plywood or cardboard works well as a test barrier.  A hard, sonically reflective barrier works better than an absorptive one if the speakers are placed directly against it so that the sound propagates along it in a boundary layer condition.

The barrier eliminates most of the significant crosstalk between channels.  In that sense it's somewhat analogous to wearing the entire room as a giant pair of headphones.  There are some significant advantages to listening this way over typical equilateral triangle speaker placement or headphones.  Perhaps the most significant is that it places the physical sound reproducing sources directly in front of the listener at the center of the reproduced soundstage.  The stereo imaging extends as phantom images out towards either side, to the extent that the program material contains suitable stereo difference information, rather than the standard scenario which is the reverse- phantom imaging towards the center between two widely spaced physical speaker locations.  In that imaging sense it "turns the stereo paradigm inside-out".  That makes mores sense in many ways- monophonic material is firmly anchored to the center, stereo imaging appears as wide as the program material rather than being dictated by speaker placement, HRTF interactions are more correct and simplified, reduced comb-filtering between channels, etc.  The technique works very well to render a wide and very even soundstage with a solid center. 

I recommend experimenting with this as an excellent demonstration to help understand how stereo listening works.  Unfortunately is not a very practical setup for most people for obvious reasons.  Electronic cross-talk cancellation techniques attempt to replace the unwieldy physical barrier with clever cancellation schemes (usually requiring slightly wider speaker spacings of about 10 degrees or so).  The electronic methods have improved, but are still artifact prone and typically don’t work as well as a simple physical barrier.