|   Question for Terrence or anyone interested | bigwally
May 5, 2002 4:46 PM | | What's your opinion on our ability to hear the height of a sound source? The Haas effect nicely explains why we can pinpoint direction so well, but it doesn't seem to address height issues. I'm just curious because I've been experimenting with center channel height and surround height, and it seems I can't "hear" different heights nearly as well as I can hear direction. Maybe I need another ear on the top of my head for my brain to make that kind of triangulation?
Thanks in advance. |
| Here's a test for you..... | karl k
May 5, 2002 5:19 PM | | How long does it take for you to find a plane when your near an airport? Or a bird in your back yard? The same applies to your sound system but IMO it's much harder in the home as the changes in height are much less and the reflections are greater.
It does bring an interesting question...
In HT, will there ever be a center channel for altitude?
HMMMM.
Providing cheap entertainment for all,
Karl K.
The shortest distance between two points is a straight line in the opposite direction. |
| A follow-up experiment | bigwally
May 5, 2002 6:03 PM | | "How long does it take for you to find a plane when your near an airport? Or a bird in your back yard?"
Not long, but I think that's because our brain tells us the direction and we know to look high.
I just conducted an experiment with my roomate (who's shaking his head in a condescending fashion) that was quite interesting. (To me, not him.) I asked him to stand about 8-9 feet away from me and while I closed my eyes he flicked a lighter with his arm held alternately down and then up, a height difference of about 4-5 feet. I found that I couldn't tell him if the lighter was high or low better than random guessing. |
| Exactly! | karl k
May 5, 2002 6:42 PM | | Thats the point, nature teaches us that most of the danger is low on the ground and when we here a sound that is unique to above, the first thing you do is to look up and usually pretty high because it's those sounds that are the most dangerous(right on top of us) and allow the least time to react to. Once you look up, your 2D hearing more accurately locates the sound, since your ears are more sensitive to sounds in front of your face, till you see the cause. Those sounds of altitude have to be fairly loud and occurr a long time for us to place in a 3D setting without changing the position of our ears. I'd be willing to bet that the higher your friend flicks the lighter, the easier you will be able to tell. Try a sound that is continuous and have him move around the room in 2D first and then go vertical. You might want to try it outside also as room reflections will also cloud perception.
There's no science that I will refer to for this, it's just my perception of how things are.
Karl K.
The shortest distance between two points is a straight line in the opposite direction. |
| Interesting, thanks for your input. | bigwally
May 5, 2002 7:20 PM | | My experiment was very limited by time, but I am going to try some other tests.
Here's how I got on this: I had my center channel speaker on top of the TV and have done this since I got my first HT rig. I've recently come to the conclusion that it's too heavy for the TV and it's really up too high anyway. My concern was if I moved it to below the screen, my center image would suffer because in 2ch stereo, the center image tends to focus at the height of the center speaker anyway although it's not playing. Someone mentioned that if I tried moving the speaker to below the screen my 2ch image focus would move with it as it's simply a mind trick. Your brain sees that speaker and wants to stick the image on it. After moving the speaker below the screen I found that this was indeed the case, the 2ch stereo image has shifted downward although the speaker still was not playing. This led me to realize that we aren't able to truly discern height of sound nearly as well as direction, hence this topic.
I didn't formulate a good question here: I'm wondering if others have noticed the same thing and/or if anyone knows of a link or article somewhere that addresses this. |
| My center ch sets on the floor... | karl k
May 5, 2002 7:47 PM | | I'm so concentrated on the picture, as long as the center IS centered, I don't notice if it low or high as the volume adj. of the center accounts for off axis response.
As far as music, I do play in ProLogic but use the Phantom center mode which takes the center and adds it to the LF and RF equally.
It's been fun,
Karl K. |
| re: Question for Terrence or anyone interested | DaveHK
May 5, 2002 5:23 PM | | I'm not sure about what you really mean, the Haas Effect ( precedence effect) is preceiving two sound sources as one provided they arrive with 20-30 ms of each other. Its possible to generate a sound from a speaker or headphones but make it sound as if its nowhere near the speaker. As far as adressing height issues, how big is the differences in height you are listening to? |
| re: Question for Terrence or anyone interested | bigwally
May 5, 2002 5:57 PM | | I was thinking along the lines of the time-gate effect that uses the first .62 milliseconds of an impulse to determine the direction of the sound source, and then largely ignores directional cues from anything arriving after that first .62 milliseconds. The height differences are within a four foot range from the top of the TV to the bottom, or from ear level to the ceiling with surrounds. |
| 128.48.5.31 | Terrible Terrence
May 6, 2002 8:13 AM | | Height is very difficult to localize...... |
| Height is very difficult to localize...... | Terrible Terrence
May 6, 2002 8:16 AM | | BW,
Localizing direction when sources are high over head is very difficult. We humans are used to a phenomina called floor bounce. Because floor bounce is a part of daily life, our ears use it to help determine direction. As long as the bounce comes relatively soon after the first arrival of a signal to the ears, direction can easily be determined. As the floor bounce arrives farther and farther after the direct arrival, it becomes more difficult to determine the direction of the source. Airplanes flying overhead not only has a late floor bounce, but is also affected by reflections off of buildings, hills, and various other sources before reflecting off the head and reaching our ears. That what makes airplanes difficult to locate overhead.
As sounds hit our heads, the shorter paths(more direct)head straight for the inner ear canal after several relfections off the pinna. For instance, a signal coming from the left side of the head will pretty much have a direct path to the left ear. However, it must travel completely around the head before it reaches the right ears. This is called interaural crosstalk. As long as a signal sources is coming to the ears from a single direction close to our height, this is not a problem. When multiple signals coming from different directions hits the head, thats when interaural crosstalk becomes a problem. Signals coming from over our heads have to reflect off the head first(after many previous reflections) and then find a path to the inner ear. Because this introduces many delays and reflections, it makes localization very difficult.
Height channels can be very effective when emphasized within a mix. When IMAX theaters do their channel calls before playing their feature, you can clearly ascertain height in the absence of signals from other channels. When other channels play simultaneously with the height channel, it will be perceived as adding spaciousness, not direction.
"Maybe I need another ear on the top of my head for my brain to make that kind of triangulation?"
That would certainly help.
Terrence |
| Thanks. One more question. | bigwally
May 6, 2002 12:05 PM | | If you had a choice between these two placements of a CC speaker for solo or occasional dual listening, which would you choose and why?
1. Below the screen on a 12" stand, tilted slightly upward, tweeter 13" from that of the mains and approx 12" below the ears when seated. L,C,R speakers all 8 feet from listener.
2. Above the screen, aimed downward, tweeters 26" from those of the mains and approx two feet above the ears. L,C,R, speakers all 9 feet from listener.
And could you factor this theory in as well?
"Those of you who are familiar with some of posts, will know I am death on placing center channel speakers below the screen rather than behind an acoustic screen or above the screen. Here's why:
Look at someone's ear (be careful who!). The outside edge of the ear has a feature called the Helix. From the top of the Helix to almost level with the Concha (the place all the wax comes from), you'll notice the Helix is bent over forming sort of a cup. This is the Scapha.
When sound comes from below the ear, some of that sound enters the ear directly. Some of the sound is reflected off the scapha and then into the ear. This causes a notch and comb filter effect. The lower the source (with respect to the height of the ear), you'll see that more and more of the scapha will be "catching" the sound and reflecting into the ear. From about 90 degrees, and as the source is raised, the scapha's effect is sigificantly reduced...hence a reduction of the notch and comb filter effect. Further, due to the geometry of the Helix, you're more sensitive to every 6" of downward displacement than you are to every six inches of upward displacement.
While this is over simplified and by no means all the factors that come into play, it is the reason why that center channel belongs behind the screen or above the screen and certainly never below the screen.
------------------
Dennis Erskine "
Thanks for your time, T-Man. |
| Dennis is very knowledgeable but..... | Terrible Terrence
May 6, 2002 1:23 PM | | BW,
Not all ears are shaped the same way. The thresholds of the notch and combfiltering you get from placement below the screen is variable with each person. Also keep in mind as you raise the source 6" as he ascerts, then you also bring your entire head into play as a reflective source.
In spite of what Dennis says(and he is right) I still would pick the first setup(#1) because it places the center more on the same plane as the L/R mains, and there is no evidence that this position will interact negatively with your ears.
While raising the center over the screen MAY(and thats a big may) control or minimize these reflections, side to side pans will definately suffer from a discontinuity of placement from the tweeters of the center speaker, and the L/R mains. It just takes 6-7 inches of disparity before pans will change height as it moves through the center speaker.
Also above television placement introduces ceiling reflections because the source is close to the ceiling. Ceiling reflections are very distructive to imaging and frequency response. Floor bounces are as part of life(in terms of hearing) as breathing is. Dennis is right in one area, the center should be located behind the screen ideally. The next good position would be vertically sitting under the screen, and the last would be over the screen itself.
Terrence |
| Thank you, Terrence. | bigwally
May 6, 2002 1:34 PM | | Since I ordered a CC stand yesterday, I'm glad you confirmed my thoughts on this! |
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