"First reflection"...what it means, why it's important, how to find it

[tomlinmgt]

I can see how that would change the amplitude, but to assuage my own curiosity, the actual reflection point would remain the same, correct? Do you forgo the mirror technique with different dispersion types and have to figure out a different 1st reflection point location in a different way?

I should have stipulated it's more the ceiling and floor primary reflections that become a non-issue with line source dipoles. They have a null zone as you move off axis in the vertical plane above and below the driver. Because of this, primary reflections are not as critical on the horizontal boundary layers (since very little content gets dispersed to the primary reflection points there). Many in the line source dipole camp claim sidewall interaction is less of an issue, as well. I think there is some validity to this statement, but don't believe it to be absolute. With a dipole as you move from on axis to 90 degrees off axis the strength of the sound wave weakens until ultimately you reach a null zone at the sides of the speaker. Since the content dispersed to the side walls is weaker than what is typical of a monopole there will be less interaction with the side walls......but still some and, though the sound wave that reaches side wall primary reflection will be weaker, it's still content that will reflect back into the room. Personally, I still want (and have) absorption at side wall and ceiling first reflection points with my line source dipoles....but it is widely agreed upon that dipoles do not suffer the same room interaction issues that monopoles experience. Linkwitz has gobs of info regarding this....it's the fundamental concept from which he bases his designs.

So, replying to your question with a more direct answer I'd say no, different designs don't change the primary reflection locations but some designs, as I've pointed out, aren't as influenced by them as much as others. Which, after reading over Wavetouch's post/infomercial again, see that he touched on that in his sales pitch.

 

[Wavetouch]

I don't understand what you mean by "2nd reflection." That's not a term I've encountered before.

"2nd reflection" is 2nd time bounced sound. The sound travels appx. 1000ft./sec. The length of our room is 15ft~30ft. So, the sound bounces back and force for few times (10 ~ 15 times) between walls to every direction before the sound loses acoustic energy.

For regular speakers (no horn), 1st reflection points are walls, floor, and ceiling. For horn speakers, 1st reflection point will be the soundwave guide of speaker. 2nd reflection points are walls, floor, and ceiling.

2nd time reflected sound is only half strong than 1st time reflected sound because the acoustic energy becomes half every time it bounces. The weaker sound is easy to control and less influence to the music.

So, well designed horn speaker’s sound is more focused and easier to control in a "live room" because walls and ceiling are weak 2nd reflection points and sounds which have little influence to the music. It’s much easier to control soundwaves right at the source of sound which is a speaker. Once the sound is shoot off from the speaker, there is only passive ways to regain the control of sound. Unless the room will be totally covered with sound treatments like a movie theater and recording studio, the soundwave guide is the right idea if designed right almost all situations. Of course, this applies only for well designed horn speakers.
.

 

[RevMen]

2nd time reflected sound is only half strong than 1st time reflected sound because the acoustic energy becomes half every time it bounces. The weaker sound is easy to control and less influence to the music.

No, that's not how it works.

The reflected energy of a sound wave depends entirely on the absorptivity of the reflecting surface. If the surface has absorption coefficients of 0 in all frequencies, then all sound energy will be reflected.

But remember that there will be geometric spreading from the reflection, continuing the spreading that originated with the sound source. So the strength of a reflection at the receiver depends on the total distance traveled as well as the absorptivity of the reflecting surface.

Since a wave guide is a very hard surface, there is very little absorption and almost 100% of the sound energy from the driver makes it out of the guide.

The reflections inside a wave guide do not count as "first reflections." First reflection refers mainly to the timing with which reflected waves arrive at the listener. The first reflections are the first reflected sounds arriving at the listener after the direct sound (which always gets there first, due to traveling the shortest distance).

There's no point in specifying a "second reflection", as any of the many "second" reflections arrive too late to be considered anything other than just reverberation.

First reflections are special because (in small enough spaces) they arrive in time to reinforce the direct sound. In other words, the lag between the arrival of the direct sound and the first reflections is small enough that your brain can't tell that they're separate sounds.

In live, acoustic music, first reflections are desirable, and are referred to as "early reflections." There's a cutoff in milliseconds discovered by Baranek that separates early reflections (which reinforce) from reverberation. Auditoriums (auditoria?) are designed to maximize early reflections to the audience so that everyone can hear the singer or acoustic instruments on stage better. That is why you see things like oddly-shaped clouds hanging from the ceiling and stepped side-walls. The idea is to deliver as many early reflections to each audience member as possible.

In a listening room or other space where sound is generated electronically, being loud is no longer an issue, so there's no point in encouraging early reflections. So we discourage them because they confuse our perception of where the sound is coming from. In a stereo system we're working hard to fool our very intelligent sense of hearing into believing we're hearing something that's not there, so we strive for complete control of the pathway the sound takes arriving at our ears. That is why we absorb or scatter first reflections in listening rooms.

 

[Wavetouch]

Directionality is still very frequency dependent. Music spans a frequency range that includes both highly directional frequencies and almost completely non-directional frequencies.

There is no non-directional freq. Less-directional freq. is correct. You can hear where a sound comes from. Human brain perceives every little sounds even very low freq. I have a powered sub-woofer, and I know where they are playing in 2 ch stereo even if I set them at 40hz. When the sub is left side corner, I hear the balance of right and left speakers is not even. I move around the sub to different locations, I perceive the sub every time I move it, and the balance of 2ch setup changes. Less-directional freq. is correct.

Many speakers offer horn type soundwave guides for tweeters only without soundwave guides for woofers because lower freq (actually more mid-range is included) is less-directional. That’s mistake. Many of them are usually off balanced between low and high freq. which makes un-natural sound and loosing control over low freq. Those speakers may be OK for rocking music which the true quality of sound is not important. They can’t produce delicate high quality sounds of vocals, piano, and violin sound.

Low freq. is even harder to control than high freq. Controlling low freq at the sound source (speaker) is much effective and easier than doing that at walls, floor, and ceiling. The woofer horn is a very effective way to control low and mid freq. There are only very few speakers which offer soundwave guides for woofers and tweeter.
.

 

[Wavetouch]

The reflected energy of a sound wave depends entirely on the absorptivity of the reflecting surface. If the surface has absorption coefficients of 0 in all frequencies, then all sound energy will be reflected.

But remember that there will be geometric spreading from the reflection, continuing the spreading that originated with the sound source. So the strength of a reflection at the receiver depends on the total distance traveled as well as the absorptivity of the reflecting surface.

You are right! I totally agree with you. The absorptivity of the reflecting surface depends on the sound treatment.

 

[RevMen]

You are right! I totally agree with you. The absorptivity of the reflecting surface depends on the sound treatment.

So why are you telling people a reflected sound has half the energy as the incident sound?

 

[Wavetouch]

The reflections inside a wave guide do not count as "first reflections." First reflection refers mainly to the timing with which reflected waves arrive at the listener. The first reflections are the first reflected sounds arriving at the listener after the direct sound (which always gets there first, due to traveling the shortest distance)
You are right about timing. What I wanted say in “acoustic energy” is the quality of the sound. The sound emitted from a diaphragm is full of physical energy which makes the movement of sound zigzag and slow motion. After the sound bounces off from the soundwave guide, the sound becomes smoother, faster, and natural. It’s like a bullet fired from a pistol moves in rotating motion (more destructive power but slow), and same bullet moves straighter and faster after it bounces from a wall.

There's no point in specifying a "second reflection", as any of the many "second" reflections arrive too late to be considered anything other than just reverberation.
My point is these reverberations (2nd & 3rd) are a problem for many people who want to hear music in live room.

First reflections are special because (in small enough spaces) they arrive in time to reinforce the direct sound. In other words, the lag between the arrival of the direct sound and the first reflections is small enough that your brain can't tell that they're separate sounds.
Yes. First reflections are special. And my brain can perceive these separate sounds. So, let's make 1st reflection point where the control is possible. It’s easy to control the soundwave at the source of the sound to reduce reverberations.
Too many people are struggling with room acoustics. Even if the room is totally covered like recording studios, there is no control of booming bass and low mid range from big woofers. Almost recording studios use small monitors.

In live, acoustic music, first reflections are desirable, and are referred to as "early reflections." There's a cutoff in milliseconds discovered by Baranek that separates early reflections (which reinforce) from reverberation. Auditoriums (auditoria?) are designed to maximize early reflections to the audience so that everyone can hear the singer or acoustic instruments on stage better. That is why you see things like oddly-shaped clouds hanging from the ceiling and stepped side-walls. The idea is to deliver as many early reflections to each audience member as possible.
However, we are not listening live music. The recording we have already contains 1st reflections and reverberations. We don’t need any more reflections sound from walls. More we let the sound bounces from walls (reverberation), we are listening our room rather than what is in recording, the singer and the concert hall.

In a listening room or other space where sound is generated electronically, being loud is no longer an issue, so there's no point in encouraging early reflections. So we discourage them because they confuse our perception of where the sound is coming from. In a stereo system we're working hard to fool our very intelligent sense of hearing into believing we're hearing something that's not there, so we strive for complete control of the pathway the sound takes arriving at our ears. That is why we absorb or scatter first reflections in listening rooms.
I am with you! We don’t need reflection sound from walls. The sound reflected from dry walls sound like dry wall. We don’t want to hear dry and tasteless wall sound. To reduce unwanted reflection sound from a room, it's easier to control soundwave at the throat of speakers.

 

[dumptruck]

Many speakers offer horn type soundwave guides for tweeters only without soundwave guides for woofers because lower freq (actually more mid-range is included) is less-directional. That’s mistake.

It's not a mistake, it's a deliberate compromise like any speaker, and that's not why it's done. It's done that way because in order to have a pattern-matched waveguide for the LF driver, you need a far larger speaker that won't fit in most situations, and even if you can fit it, a new (large) problem of acoustic center spacing arises.

 

[dumptruck]

Many directional speakers offer only high freq soundwave guide. This will make unbalance between high, mid, and low freq. Those bring a headache, tiredness, and “listener fatigue" quickly. Be sure to find perfect balanced directional speakers such as Wavetouch GT speaker. Wavetouch GT spkr INFO

Wavetouch / AK vendor

Ohhhh I see what's going on here. Please come back with a good resolution polar response measurement of your speaker, and we'll see how much LF pattern control you've got there.

 

[RevMen]

You are right about timing. What I wanted say in “acoustic energy” is the quality of the sound. The sound emitted from a diaphragm is full of physical energy which makes the movement of sound zigzag and slow motion. After the sound bounces off from the soundwave guide, the sound becomes smoother, faster, and natural. It’s like a bullet fired from a pistol moves in rotating motion (more destructive power but slow), and same bullet moves straighter and faster after it bounces from a wall.

This is gibberish. Sound always moves at the same velocity through a given medium. There is no slow or fast about it. And how does this relate to you saying that a reflection causes a sound to lose half its energy?

My point is these reverberations (2nd & 3rd) are a problem for many people who want to hear music in live room.

Your point is poorly developed. There can certainly be too much reverberation, but isolating the individual reflections and calling them 2nd or 3rd or 50th is just silly.

Yes. First reflections are special. And my brain can perceive these separate sounds.

No, it can't. Unless you're a cyborg. Are you a cyborg?

So, let's make 1st reflection point where the control is possible. It’s easy to control the soundwave at the source of the sound to reduce reverberations.

What? Please explain how it is possible to control reverberation at the source.

Too many people are struggling with room acoustics.

I'll say.

Even if the room is totally covered like recording studios, there is no control of booming bass and low mid range from big woofers. Almost recording studios use small monitors.

They also, often, use subs in control rooms. And recording studios are not usually covered completely in treatment.

However, we are not listening live music. The recording we have already contains 1st reflections and reverberations. We don’t need any more reflections sound from walls. More we let the sound bounces from walls (reverberation), we are listening our room rather than what is in recording, the singer and the concert hall.

You don't say?

I am with you! We don’t need reflection sound from walls. The sound reflected from dry walls sound like dry wall. We don’t want to hear dry and tasteless wall sound. To reduce unwanted reflection sound from a room, it's easier to control soundwave at the throat of speakers.

I'm getting the sense that English is not your first language. That might explain some of the disconnect we have here.

 

[RevMen]

OK, now I see what's going on. All this talk about wave guides is marketing.

http://wavetouchaudio.com/products.html

 

[Wavetouch]

My name is in the review of Wavetouch GT speaker.
All I said were from my experience. May be you want to see only what you want to see. And I want same. But the speaker and technology I have are real.

I am trying to help people who want music in their life. We know how many people got the perfect sound system after trying for all their lives. I just want to help people to get that dream possible.

 

[tomlinmgt]

OK, now I see what's going on. All this talk about wave guides is marketing.

http://wavetouchaudio.com/products.html

Yep. Like I said...it's all been an infomercial.

 

[RevMen]

I am trying to help people who want music in their life. We know how many people got the perfect sound system after trying for all their lives. I just want to help people to get that dream possible.

It's an admirable goal but your first step should be to learn some basic physics.

With YoonTone technology the sound is pressurized at the most effective area of sound source. The speed of sound increases and the physical energy is reduced.

That is nonsense. You cannot change the speed of sound by changing the cross-sectional area of the medium. Just about everything on your "Technology" page is nonsense.

You're free to peddle your snake-oil where you like, but please don't come to forums like this where people are trying to learn and pollute our threads with false information.

 

[Rob41]

Great tutorial. Seems like this would be a valuable sticky.

 

[tomlinmgt]

Thanks Rob. I've offered people the link to this thread more times than I can possibly remember. I'm just glad folks are using the info to their benefit.

 

[armyslowrdr]

Maybe because I sit practically near field and in a very small room that was meant as a 4th bedroom, and there is a mix of "hard" (computer desk, Ikea Kallaxes-etc) and soft (large exec style chair, an Ikea chair, a padded foot stool, carpeting, drapes), the sound is very stellar to me, and although I briefly explored where I could put bass traps, sound absorbers and what not, I have decided it would be a very big waste of money. I simply don't want them.

 

[davidro]

Your system is highly likely incapable of achieving its full potential without proper room treatment. Hell, probably about 60% of such at best.

YMMV yes, but you're really inviting criticisms on a thread like this.

Sent from my X10a using Tapatalk 2

 

[Rob41]

Thanks Rob. I've offered people the link to this thread more times than I can possibly remember. I'm just glad folks are using the info to their benefit.

I think I'm focused on threads like this, distributed bass etc. because it's either new territory or neglected territory for me. I'll be using it as a reference for sure.

 

[tomlinmgt]

Maybe because I sit practically near field and in a very small room that was meant as a 4th bedroom, and there is a mix of "hard" (computer desk, Ikea Kallaxes-etc) and soft (large exec style chair, an Ikea chair, a padded foot stool, carpeting, drapes), the sound is very stellar to me, and although I briefly explored where I could put bass traps, sound absorbers and what not, I have decided it would be a very big waste of money. I simply don't want them.

A near field arrangement and certain furnishings can remove some of the detrimental acoustic influences created by the room, but even that arrangement can be improved (and considerably so) when that space has been given proper attention to its acoustic response. Go over to gearslutz where the true acoustic gurus hang out and the primary listening environment they're discussing on that site is recording and playback studios (near field). Those guys are extremely determined to create a room free of acoustic anomalies because they're mixing, engineering and producing and they go to great lengths to achieve it. Bottom line...there is simply no free pass from the physics of acoustics just because the listening arrangement is near field and the room has a few furnishings.

If you don't feel you have a problem and can enjoy the reproduction you're currently getting then I'm not going to suggest you change a thing. And no doubt what you do in your listening space is your business and no one here is going to try to force anything upon you or tell you you're wrong to not want acoustic devices in your room. But let's be very clear about one thing...your observation regarding not being able to benefit from acoustic treatments and that they'd be a waste of money is premature and without merit since you haven't actually implemented any acoustic treatment devices to see what effect they'd have on the quality of the reproduction you're getting without them. I wouldn't make that statement if you were in a very large room and listening near field, but you and anyone else reading this should know that small spaces are notoriously bad acoustic environments and no amount of "wishing it away" will correct one.

And if you ever find yourself in or near Arlington/Mansfield (I-20/287) then I'd be thrilled to have you come over to hear my system and a demonstration of what acoustic treatments can do. The treatments I'm using are easy to remove from the room, so in a matter of seconds (well, a few minutes) you could hear a before and after comparison.