Just moved a pair of speakers into a new room. Did the slap test to listen for any ringing and realized I could use some absorption. Purchased a 6 pack of 2" 2x4 703 panels. Built some frames and covered with tapestries. Did a placement experiment before I built the frames so I had general idea about placement.
So down to the basic question. The norm is first reflection using a mirror from the listening position for cones and domes. I have a horn set-up 70x70. Do you ignore the directivity and stick with the mirror or use the speaker directivity to determine placement?
The panels did a good job of decreasing the slap echo my imaging is good and overall I am happy with the results. Curious about how others using horns have set-up their panels or if they use them at all.
Rob 🙂
So down to the basic question. The norm is first reflection using a mirror from the listening position for cones and domes. I have a horn set-up 70x70. Do you ignore the directivity and stick with the mirror or use the speaker directivity to determine placement?
The panels did a good job of decreasing the slap echo my imaging is good and overall I am happy with the results. Curious about how others using horns have set-up their panels or if they use them at all.
Rob 🙂
Naturally beyond 70 degrees moves toward diminishing returns but it's not that simple. A close wall can be louder. A horn can vary in directivity.
Ideally you will use the measurement at that angle to assist in making this determination.
I'd start by working out the angle from the speaker through the reflection.
Ideally you will use the measurement at that angle to assist in making this determination.
I'd start by working out the angle from the speaker through the reflection.
Yes first reflection zone rule of thumb still apply even if 'high' directivity loudspeakers.
The idea is to define an RFZ and despite being more controlled by design the first reflection area doesn't change.
Slap test is interesting to define the 'character' of a room but it doesn't take into account the loudspeaker location and how they interact with the said room.
In fact it's interesting for a recording space less for a listening space. That doesn't stop me to look like a psycho when i run into a room and perform it in presence of other people... 😉
Just be aware of the limitation.
The idea is to define an RFZ and despite being more controlled by design the first reflection area doesn't change.
Slap test is interesting to define the 'character' of a room but it doesn't take into account the loudspeaker location and how they interact with the said room.
In fact it's interesting for a recording space less for a listening space. That doesn't stop me to look like a psycho when i run into a room and perform it in presence of other people... 😉
Just be aware of the limitation.
Yes I agree and that doesn't account for Toe-in which will pull the first reflection further down the wall using -6db as the line. You would be looking at aprox. 90 degree's on the polar if you were using 20 degree's of toe in as an example. I tried a protractor on top set to 70 degrees and used sight lines to get an idea of where the stronger reflection point might be.
Rob 🙂
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OK but you would you not have a stronger reflection down the wall? The way I am set-up now I meet the original mirror test it just catches the panel. If I sight down the protractor I almost completely miss the panel. It seems to be working just found it paradoxical looking at it from a Directivity aspect.
Slap test is crude but you can clearly hear the echo/reverb from the crack. Just use it for overall which lead me to build the panels irrespective of speaker placement. Room seemed to lively for lack of a better word.
Rob 🙂
It's not unusual designing the reflections to shoot over the listening position, but I see you've brought these into a room they weren't designed for. If you have a stronger reflection down the wall, it's going to affect room power more than your early reflection. That may be OK but will take some measurement to be sure.
Have you measured the optimum listening angle for these?
Yes. A 'laser' pointer on top of protactor help define the area on wall too.
But... in fact it's a bit more complicated as you have to take into account many parameters:
_ the effective frequency range at which your panel are effective
_ the level of attenuation you 'target' at listening point @ the frequency of interest (and up)
_ the angles of your walls/directivity of loudspeaker/toe in...
When i implemented RFZ i started with an 'above view' sketch of room including loudspeakers location, toe in and main listening point.
From there i choose a side ( L or R) and draw expected directivity angles of loudspeakers @ -6db and where it crosses walls on both side of room.
it'll give the 2 main areas where early reflections will occurs ( if room is mirored through longitudinal axys... iow a rectangle, 'regular' room).
Now we can estimate the early reflection behaviour ( where they are going to be redirected) and the approximate level they'll have at main listening point.
To define the behaviour i take some approximation: when wavefront hit a wall at an angle we can approximate how it'll be redirected by using something similar to what we observe when playing billard pool/8 pool: when balls hit the wall, if you take the impact point, draw a perpendicular line and measure the angle the ball have to this line, you can predict where it'll be going by transfering this angle in mirror to the perpendicular line.
Wavefront behave more or less the same. Except than following a straigth path like the ball they are redirected through a corner portion.
To approximate it, i take the straigth billard path as main redirection and add +/-15* each side to define the corner portion. It's very conservative but works well in practice.
In fact this is how crude 'ray tracing' is performed by an acoustician i've worked with... 😉
From there you can see how the first reflection is 'sprayed' into the room and how it'll affect main listening position from both side of the room.
It helps to define the length of travel ( distance) the Early Reflection will experience too ( as well as the initial 'time of flight' from loudspeaker to wall) and so the aproximate attenuation from this distance only ( we assume your walls are 100% reflective which is a worst case scenario).
So from here we can works with the panels by themself: if their range of effectiveness is from 1khz and up ( aritrary choice for sake of explanation) then we have to approximate their behaviour.
1khz equal 30cm ( 1foot) wavelength. We assume that for an obstacle to have significance regarding acoustic it must be 3 time the wavelength ( it's here again very crude but this is what is observed with redirection (reflector/diffusor) in practice..) so for your panel to have an effect they should be 1meter ( 3 feet) wide. If it goes to 500hz then the width should be 2m (4feet) and so on...
Know we know where to locate them from previous sketch, the width they should have (we assume the middle of panel located/centered at the defined first Early Reflection) and if you have datasheet with sabine coefficient the attenuation they'll give ( as well as the attenuation given by 'the time of flight' himself) so what you can expect...
If it's not clear i'll post picture example tomorow...
But... in fact it's a bit more complicated as you have to take into account many parameters:
_ the effective frequency range at which your panel are effective
_ the level of attenuation you 'target' at listening point @ the frequency of interest (and up)
_ the angles of your walls/directivity of loudspeaker/toe in...
When i implemented RFZ i started with an 'above view' sketch of room including loudspeakers location, toe in and main listening point.
From there i choose a side ( L or R) and draw expected directivity angles of loudspeakers @ -6db and where it crosses walls on both side of room.
it'll give the 2 main areas where early reflections will occurs ( if room is mirored through longitudinal axys... iow a rectangle, 'regular' room).
Now we can estimate the early reflection behaviour ( where they are going to be redirected) and the approximate level they'll have at main listening point.
To define the behaviour i take some approximation: when wavefront hit a wall at an angle we can approximate how it'll be redirected by using something similar to what we observe when playing billard pool/8 pool: when balls hit the wall, if you take the impact point, draw a perpendicular line and measure the angle the ball have to this line, you can predict where it'll be going by transfering this angle in mirror to the perpendicular line.
Wavefront behave more or less the same. Except than following a straigth path like the ball they are redirected through a corner portion.
To approximate it, i take the straigth billard path as main redirection and add +/-15* each side to define the corner portion. It's very conservative but works well in practice.
In fact this is how crude 'ray tracing' is performed by an acoustician i've worked with... 😉
From there you can see how the first reflection is 'sprayed' into the room and how it'll affect main listening position from both side of the room.
It helps to define the length of travel ( distance) the Early Reflection will experience too ( as well as the initial 'time of flight' from loudspeaker to wall) and so the aproximate attenuation from this distance only ( we assume your walls are 100% reflective which is a worst case scenario).
So from here we can works with the panels by themself: if their range of effectiveness is from 1khz and up ( aritrary choice for sake of explanation) then we have to approximate their behaviour.
1khz equal 30cm ( 1foot) wavelength. We assume that for an obstacle to have significance regarding acoustic it must be 3 time the wavelength ( it's here again very crude but this is what is observed with redirection (reflector/diffusor) in practice..) so for your panel to have an effect they should be 1meter ( 3 feet) wide. If it goes to 500hz then the width should be 2m (4feet) and so on...
Know we know where to locate them from previous sketch, the width they should have (we assume the middle of panel located/centered at the defined first Early Reflection) and if you have datasheet with sabine coefficient the attenuation they'll give ( as well as the attenuation given by 'the time of flight' himself) so what you can expect...
If it's not clear i'll post picture example tomorow...
Not sure what you are asking? Are you talking degrees off axis? Kind of like Earl G. has his Summa's at 15-20 degrees for flattest response? I am essentially on axis in a close to equilateral triangle gives me the best imaging, Are you suggesting less toe in? None of the rooms in this house had anything other than living space in mind so the room is what it is, have to do the best with what I have.
Rob 🙂
The optimum angle of the speaker, as you say like Earl. Not the flattest angle. What you want is the most representative angle. After this you can rotate and position the speakers and yourself, adding absorption especially where the plan doesn't fit the room, otherwise a well fitted domestic speaker wouldn't need much absorption.
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