[gravy]

Hi all,

I've done lots of reading of the great FAQs, but I couldn't figure out if I should be factoring in the amount of speaker toe-in when attempting to identify my first reflection point using mirror-along-the-wall method?

 

Thanks for the insights,
Scott

[ctviggen]

I had a hard time doing this, too.  I simply moved the mirror until I could see barely see the front of the speaker.  I'm still not sure I placed my treatments in the right spot.

[Ethan Winer]

Scott,

> should be factoring in the amount of speaker toe-in when attempting to identify my first reflection point using mirror-along-the-wall method? <

No. Just look for places where you can see either speaker, regardless of the speaker cabinet's angle.

--Ethan

[gravy]

Scott,

> should be factoring in the amount of speaker toe-in when attempting to identify my first reflection point using mirror-along-the-wall method? <

No. Just look for places where you can see either speaker, regardless of the speaker cabinet's angle.

--Ethan

Thanks Ethan!

[John Casler]

A mathemetician, I am not, but I think if you measure a line between the front of the speaker and the listening position, and divide it in half, you will have the spot on the wall where first reflection might take place.

Does this look right?




I think if you run a line perpendicualr to the wall from the half-way point it should give you the exact angle.

[PLMONROE]

John, move your speaker positions so that they almost touch the side walls (not that one would really want to do this) and retest your hypothesis.

Paul

[ted_b]

John,
No, the actual way you do it is like a pool shot.  If the speakers are 2 feet from the wall, draw a 2 foot line extending outside the wall, then draw a line from you to that point out in space.  That's the reflection point (where it intersects with the wall).   It also has a formula (paraphrased from Realtraps site).

Let's say the speaker is 2 feet from the side wall (x1), and you're 6 feet from that same wall (x2), and the loudspeaker's tweeter is 5 feet in front of you (y). The distance to the center of the panel is solved as follows:
distance from you on side wall = (y * x2)/(x1 + x2) or 3'9"

Ted

[John Casler]

Thank Goodness I threw in that disclaimer

[John Ashman]

By nature, that point will be always closer to the speaker than to the listener, but usually about 1/4-1/3 of the distance from the speaker to you along the wall (it could be as little as 1/10th), to get you started.  Only if the speaker were directly in front of you would the half way point be valid.  Someone skipped geometry!

[gravy]

By nature, that point will be always closer to the speaker than to the listener, but usually about 1/4-1/3 of the distance from the speaker to you along the wall (it could be as little as 1/10th), to get you started.  Only if the speaker were directly in front of you would the half way point be valid.  Someone skipped geometry!

Lol this is why i grabbed a mirror... good stuff guys.

[John Casler]

By nature, that point will be always closer to the speaker than to the listener, but usually about 1/4-1/3 of the distance from the speaker to you along the wall (it could be as little as 1/10th), to get you started.  Only if the speaker were directly in front of you would the half way point be valid.  Someone skipped geometry!

Many years ago somone told me that was the way to figure "ceiling" reflections (since it is hard to get a mirror up there) and I assumed it true in all cases.

Anyone know if it is accurate in ceiling reflections?

[ted_b]

John,
Just turn this on it's side for ceiling math.  Same deal.



Ted

P.S.  Thanks to Ethan and his RealTraps website for this pic, and the subsequent explanations.

[Ethan Winer]

John,

Ted beat me to it and posted the drawing I would have.

> Anyone know if it is accurate in ceiling reflections? <

For ceiling RFZ panels the center is halfway between your ears and the tweeter. This assumes the tweeters are at ear level, which they should be.

--Ethan

[ctviggen]

What I've also done is looked past the front (parallel to the front) of the speaker and ensured that I saw the trap at that location.  The only thing I wonder about the posted diagram is that it doesn't take into account the dispersion characterictics of the speaker.  Nor does it take into account toe in.  For instance, with the RM40s, I would assume there's a relatively narrow dispersion.  One would think that if I toe in my speakers a lot (which I do), that I would not put the realtrap at the same location as if I had the speaker pointed directly into the room, but that figure does not appear to take toe in into account (or does it?).  Perhaps there's a spot that's better for the first reflection point and that's not dictated by the drawing.  It would be nice if you could simply walk along the wall and put the trap where you hear the highest level.

[John Casler]

What I've also done is looked past the front (parallel to the front) of the speaker and ensured that I saw the trap at that location.  The only thing I wonder about the posted diagram is that it doesn't take into account the dispersion characterictics of the speaker.  Nor does it take into account toe in.  For instance, with the RM40s, I would assume there's a relatively narrow dispersion.  One would think that if I toe in my speakers a lot (which I do), that I would not put the realtrap at the same locatio ...

Good points and ones I consider relevant, yet difficult to compute.

While  the average room is rectangular and many set their speakers up on the "short wall", I don't.  This reduces the concern of sidewall first reflections (Maybe why I am such a numbscull at finding the points)

The convergence angle and dispersion characteristics "will" affect the side reflections, but won't change the basic physics.

Additionally, the dispersion of the various frequencies, is on a sliding scale, with low frequencies energizing in more of an omnidirectional pattern and extreme high frequencies acting more like a beam.

I have developed and particularly like addressing the frequencies with a type of frequency specific filtration "at the speaker" before the frequency reaches a room boundary.

That way, it takes the room out of the equation to a much greater degree.

Then you don't worry about side wall reflections because for practical purposes, there aren't any.

[ted_b]

John,

Ted beat me to it and posted the drawing I would have.

> Anyone know if it is accurate in ceiling reflections? <

For ceiling RFZ panels the center is halfway between your ears and the tweeter. This assumes the tweeters are at ear level, which they should be.

--Ethan

The exception to this is if the tweeter is aimed at the ears, but not ear height.  My RM/X's, for instance.  The tweeter pod is considerably higher than my ears-at-sweetspot-height, aimed down.  You can get around all this craziness by making sure the Sonex, whatever, is wide enough to cover the differences and the math errors.

Ted

[Russtafarian]

At what frequency range do you have to be concerned with the first reflection point?  

The reason I ask is that I control the dispersion of my Gallo Nucleus Reference tweeters by wrapping damping material (a cut to size mouse pad) around the back and side of each cylinder.  This effectively blocks side and rear dispersion from 2 kHz on up, but doesn't affect the midbass drivers that cover the rest of the spectrum.

The first reflection point on one side of the room is a bookcase-ish cabinet loaded with records (not CDs), so I'm not too worried about that.  The reflection point on the other side of the room is my front door.  I'm not sure I can talk my wife into letting me mount an acoustic panel to that.

[woodsyi]

Wasn't Gallo's cylinderical design chosen to elimiate boxy baffle diffraction?  By putting up side and rear shields, aren't you creating some defraction?  I don't know what is worse:  reflected sound arriving late or interference created by baffle diffraction?  Anybody know?

[ted_b]

First reflections are broadband, but primarily affect higher frequencies.  At least those are the ones you want damped.   However, to block them at the speaker like you are doing is not what I'd do.  I'd think you're losing a lot of air and hf info that's critical to good imaging and soundstage cues.

I'd let the speakers breathe, and then at least take your record cabinet and try to create an uneven (diffusion) effect with some records out an inch or two.  With the door on the other side is there a way you can place a large plant or something between you and the door (i.e on that line)?

And don't forget about the other dimension (ceiling and floor).  Heck, I had my side walls treated and though the imaging was MUCH better until I realized that the marble coffee table in front of me was as big, if not bigger, culprit.  A soft thick blanket or tablecloth does the trick.  Wow, huge improvements, really.  Same idea with an unobstructed floor.

Ted

[Ethan Winer]

Bob,

> the posted diagram is that it doesn't take into account the dispersion characterictics of the speaker.  Nor does it take into account toe in. <

Those don't matter unless the speakers are so directional the sound doesn't hit the walls (or ceiling) at all. Most speakers are designed to be as wide-reaching as possible horizontally, to make the "sweet spot" wide.

--Ethan