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post #2011 of 10465 Old 02-22-2007, 11:48 AM
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Quote:
Originally Posted by Ethan Winer View Post

Terry,

> Ethan, to better understand dipole speakers in familiar recording studio terms, think "ribbon microphone" <

Indeed, and I already mentioned that in my post #1983 above.

Also, to be completely accurate, what you're talking about is a Figure 8 pattern. This is not unique to ribbon microphones.

--Ethan

Sure, I never meant to imply the a ribbon microphone is the only type which can exhibit a figure eight pattern. Two cardioid capsules facing in opposite directions will do the same. I mentioned a ribbon microphone because it was the first of this type, and has had a long history in professional recording and broadcasting.

As far as I know, figure eight pattern == dipole. I don't think that it is possible to achieve this directivity pattern in any other way.

- Terry

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post #2012 of 10465 Old 02-22-2007, 01:25 PM
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Aren't the "teeth" on a comb filter close together and usually thought of as being at higher frequencies (than 250Hz)? Of are you referring to peaks and nulls in the bass region as being part of the comb?


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post #2013 of 10465 Old 02-22-2007, 04:22 PM
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I don't have 4 solid corners in my room. In a couple I have windows. I won't really need to access these.

Wll bass traps still work well if I have it straddling a room corner and some of it is covering the window?

There are more corners than just vertical room corners. Ceiling to Wall. I want to maximize with the space I have though.
LL

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post #2014 of 10465 Old 02-22-2007, 11:44 PM
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Quote:
Originally Posted by pepar View Post

Aren't the "teeth" on a comb filter close together and usually thought of as being at higher frequencies (than 250Hz)? Of are you referring to peaks and nulls in the bass region as being part of the comb?

The higher frequencies are certainly what I had in mind discussing the inaudibility or even positive effects of room comb filtering.

I suppose the "teeth" can show up elsewhere, like the SBIR distortion in bass when a loudspeaker playing full range without a sub is placed a few feet away from the wall behind.
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post #2015 of 10465 Old 02-23-2007, 11:49 AM
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Quote:
Originally Posted by Terry Montlick View Post

As far as I know, figure eight pattern == dipole. I don't think that it is possible to achieve this directivity pattern in any other way.

A regular cone driver not mounted inside a box?

--Ethan

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post #2016 of 10465 Old 02-23-2007, 11:53 AM
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Quote:
Originally Posted by pepar View Post

Aren't the "teeth" on a comb filter close together and usually thought of as being at higher frequencies (than 250Hz)?

Yes, "usually thought of" is the case, but it's not really correct. As TB pointed out, SBIR is also comb filtering. Whatever the cause, comb filtering starts at some low frequency and repeats indefinitely at regular intervals. With acoustic comb filtering caused by reflections, the pattern repeats only at frequencies that are reflected. So for a wall covered with one inch thick 703 the peaks and nulls start low but stop when the 703 kicks in.

--Ethan

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post #2017 of 10465 Old 02-23-2007, 01:14 PM
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Quote:
Originally Posted by Ethan Winer View Post

A regular cone driver not mounted inside a box?

--Ethan

Correct. That's most easily understood as an acoustic doublet == dipole. There is sound radiating from the front and back with opposite phase.

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post #2018 of 10465 Old 02-26-2007, 03:03 AM
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Here are my completed Bass Traps and Acoustic Panels. I built 2 2'x2'x2" panels for my early reflection points and 2 2'x4'x4" bass traps for my corners. Also I built 1'x2'x2" panels and placed them behind my Left and Right front speakers, those the panels are not covered with fabric yet. Now the traps and the early reflection panels and consist of owens corning 703 fiberglass framed in pine lumber. The back of the panels are covered in black gardening fabric, which does let air pass but very ugly although it was free from my father. The front of the panel and sides are covered in Guilford of Maine fabric. The difference in audio clarity is dramatic. High freq's are tamer. Bass is tighter. And surround affects are more pinpoint. So here are the photos:

Also, you can click my signature for more photos.
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post #2019 of 10465 Old 02-26-2007, 05:00 AM
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Quote:
Originally Posted by longfellowfan View Post

Here are my completed Bass Traps and Acoustic Panels. I built 2 2'x2'x2" panels for my early reflection points and 2 2'x4'x4" bass traps for my corners. Also I built 1'x2'x2" panels and placed them behind my Left and Right front speakers, those the panels are not covered with fabric yet. Now the traps and the early reflection panels and consist of owens corning 703 fiberglass framed in pine lumber. The back of the panels are covered in black gardening fabric, which does let air pass but very ugly although it was free from my father. The front of the panel and sides are covered in Guilford of Maine fabric. The difference in audio clarity is dramatic. High freq's are tamer. Bass is tighter. And surround affects are more pinpoint. So here are the photos:

Also, you can click my signature for more photos.

It is kind of hard to see and maybe you did, but are you sure you have the thinner panels in the first reflections? Did you use a mirror to find those spots? The one side panel looks kind if high on the wall.



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post #2020 of 10465 Old 02-26-2007, 05:06 AM
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Quote:
Originally Posted by myfipie View Post

It is kind of hard to see and maybe you did, but are you sure you have the thinner panels in the first reflections? Did you use a mirror to find those spots? The one side panel looks kind if high on the wall.



Glenn

Yes my fronts are high and I did use the mirror trick before and after placing the panels.
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post #2021 of 10465 Old 02-26-2007, 05:11 AM
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Quote:
Originally Posted by myfipie View Post

It is kind of hard to see and maybe you did, but are you sure you have the thinner panels in the first reflections?

Thinner? I probably missed something along the way here, but isn't thicker better so that first reflection absorption extends as low as possible?


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post #2022 of 10465 Old 02-26-2007, 05:22 AM
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Quote:
Originally Posted by pepar View Post

Thinner? I probably missed something along the way here, but isn't thicker better so that first reflection absorption extends as low as possible?

For early lateral reflections which create image shift problems, there is no need to go below 1 kHz. Perceptually, this is a high frequency phenomenon.

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post #2023 of 10465 Old 02-26-2007, 08:15 AM
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Quote:
Originally Posted by Terry Montlick View Post

For early lateral reflections which create image shift problems, there is no need to go below 1 kHz. Perceptually, this is a high frequency phenomenon.

- Terry

Thanks, that makes sense. What about skewing the decay unfavorably toward the upper bass by not using the "opportunity" - no additional HF would be removed - to trap some upper bass?


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post #2024 of 10465 Old 02-26-2007, 08:25 AM
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Quote:
Originally Posted by pepar View Post

Thanks, that makes sense. What about skewing the decay unfavorably toward the upper bass by not using the "opportunity" - no additional HF would be removed - to trap some upper bass?

Sure, I never pass up an opportunity to absorb lower frequencies if a room needs it (which a room typically does). Side wall absorbers can do double-duty here. Note that effective treatment of decay times typically requires many square feet of absorption, not just the "spot" absorption necessary to handle early reflections.

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post #2025 of 10465 Old 02-27-2007, 12:44 AM
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Quote:
Originally Posted by Terry Montlick View Post

For early lateral reflections which create image shift problems, there is no need to go below 1 kHz. Perceptually, this is a high frequency phenomenon.

- Terry

Surely there's more to it than just an effect on image shift. Also affected (adversely by absorption) is image size. The thickness would also determine the tonality of what's heard (affected adversely by thinner panels). There may also be reason to believe that absorption smothers important spatial cues.

It increasingly seems to me that absorption seems to have a benefit only when listening to mediocre speakers. The Holy Grail of top performance probably lies in attaining perfection in polar response. What's called for is not only a respectable off-axis performance (and a subsequent absence of absorption for this prowess to be realized), but a darn good robust showing in a loudspeaker's extreme off-axis performance. Very few loudspeakers could pull this off well.

A must reading should be the highly regarded Siegfried Linkwitz' ebullient 2007 update of his pet project:
http://www.linkwitzlab.com/orion++.htm
Also very informative is an older Mix Magazine article summarizing the work of Professor David Moulton at Sausalito Audio Works.
http://www.sawonline.com/wp_mix_article1.shtml

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post #2026 of 10465 Old 02-27-2007, 03:49 AM
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Quote:
Originally Posted by pepar View Post

Thanks, that makes sense. What about skewing the decay unfavorably toward the upper bass by not using the "opportunity" - no additional HF would be removed - to trap some upper bass?

Sure if you can fit them and afford them, then thicker panels are better. But someone should never think that using thicker panels in the early reflections is going to give enough bass control. I always assume people have plenty of bass trapping in the corners.

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post #2027 of 10465 Old 02-27-2007, 04:25 AM
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Quote:
Originally Posted by TumaraBaap View Post

Surely there's more to it than just an effect on image shift. Also affected (adversely by absorption) is image size. The thickness would also determine the tonality of what's heard (affected adversely by thinner panels). There may also be reason to believe that absorption smothers important spatial cues.

It increasingly seems to me that absorption seems to have a benefit only when listening to mediocre speakers. The Holy Grail of top performance probably lies in attaining perfection in polar response. What's called for is not only a respectable off-axis performance (and a subsequent absence of absorption for this prowess to be realized), but a darn good robust showing in a loudspeaker's extreme off-axis performance. Very few loudspeakers could pull this off well.

A must reading should be the highly regarded Siegfried Linkwitz' ebullient 2007 update of his pet project:
http://www.linkwitzlab.com/orion++.htm
Also very informative is an older Mix Magazine article summarizing the work of Professor David Moulton at Sausalito Audio Works.
http://www.sawonline.com/wp_mix_article1.shtml

Tumara Baap

This is the Dedicated Theater Design and Construction area, so we should take a cue from that. It is important to remember that any Holy Grail is for a specific ideal listening purpose: 2 channel music, for example. Choose another purpose, and you get a different Grail, and potentially, a completely different engineering solution.

Another must read, and a good example of this, is everything at the ambiophonics site:
http://www.ambiophonics.org

It comes to a very different conclusion regarding speaker polar response and the use of room treatments. Its rooms are deader than home theaters, and its speakers directional criteria are not the polar response, at least in the normal sense. Compared to other approaches to sound reproduction (high-end two channel music, livish room; high-end movie surround sound, deadish room), it is completely sideways. But its purpose is to create an extremely realistic spacial music experience for a single listener only. And it only needs two channels of source material (old stereo recordings) to do this!

- Terry

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post #2028 of 10465 Old 02-27-2007, 06:57 AM
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I need advice:

As you can see in this picture, I have three cabinet cavities across the planned screen wall and one on the front of the right wall. The right front corner (where the TV hole is now) is going to be squared off. The cabinets are going away. The screen will be flush with that wall.



Options:

a) remove the cabinets completely and drywall the wall.

b) remove the cabinet fronts and leave them flush to the wall. Fill them with cotton or 703. They'll be covered by GOM or equivalent when I treat my front wall. Essentially free bass traps in non-ideal positions. No implication that they would be the only bass traps (I'm still looking at soffit and corner possibilities).

General plan for now is dead front wall, first reflections left and right, carpet. I'm using CARA to model how much further absorption/diffusion I'll need.

Thoughts?

Paul Meyer
Bee Cave, TX

(see MeyerHT for more pictures and details of my project)

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post #2029 of 10465 Old 02-27-2007, 07:52 AM
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I am thoroughly enjoying the discourse between TumaraBaap and Terry Montlick. Having waded through the Toole paper so graciously provided by the former, I know from where he comes.

Absolutely not to take anything away from Dr Toole, but I still need to reconcile his direction - he didn't present it as a conclusion - on absorption with my own senses. And my senses tell me that reducing/eliminating the first (and strongest) reflections will improve imaging. I know that when I added my absorbers (2" OC SelectSound Black) to the first reflection points, I achieved nearfield listening vis-a-vis the LCR speakers at my main seating positions. How can anything be better than nearfield listening? How can letting the room affect what the artist/engineer/producer mixed be better?


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post #2030 of 10465 Old 02-27-2007, 08:50 AM
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pepar,

Again, I think the consequences of side reflections with regard to imaging are dependent upon the specific purpose of the reproduction. Is it for multichannel home theater, for which there are reference theaters which one would like to match? Or is it for conventional stereophonic playback, which has no such reference environments?

Indeed, for the latter, side reflections can be beneficial if done properly, as they can widen the front sound stage (which was Tumara Baap's point). This sense of widening can be accomplished without image shifting or smearing if you play by the correct psychoacoustic rules. This means that the reflections should be below the threshold for such shifting or smearing, but still be audible. Side wall diffusers -- rather than absorbers -- can work very well for this purpose.

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post #2031 of 10465 Old 02-27-2007, 09:24 AM
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...although, Floyd Toole's recent work suggests that the choice of diffusion and absorption (quantity and type) should be dependent upon the quality of the off axis response of the speakers.

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post #2032 of 10465 Old 02-27-2007, 12:34 PM
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Quote:
Originally Posted by Terry Montlick View Post

pepar,

Again, I think the consequences of side reflections with regard to imaging are dependent upon the specific purpose of the reproduction. Is it for multichannel home theater, for which there are reference theaters which one would like to match? Or is it for conventional stereophonic playback, which has no such reference environments?

My multi-channel home theater match a reference theater? Nah, that's not my goal. I think a good home theater goes way beyond any "movie theater." If I'm in the nearfield of "proper" speakers - I'm basically using what a lot of studios use (M&K 150s) - then I'm hearing exactly what the mixdown team did. Am I missing something? How is this not As Good As It Gets?


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post #2033 of 10465 Old 02-27-2007, 12:40 PM
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Quote:
Originally Posted by pepar View Post

I am thoroughly enjoying the discourse between TumaraBaap and Terry Montlick.

Of course, I'm merely a health professional. Terry is an acoustician. I seek concepts and answers from other audio professionals, and largely base my own beliefs on their credibility. I listen to a 7.1 channel system with wide dispersion active loudspeakers myself but otherwise have very limited exposure to the best systems. Frankly, I doubt I'll have the time to fully peruse through extensive links as the one provided by Terry (gracias by the way...will check it out). I don't always have an answer for the ever inquisitive Honcho of this thread either ;-) So take what I have to say with a grain of salt.

However, my thoughts on this: If a Theater/Music enthusiast wants to choose seven wide dispersion loudspeakers such as the NHT Xd over the ample competition, design a room with broadband absorption on the center portion of the backwall and ceiling, go with extensive bass trapping, and otherwise eschew the thin panel absorption elsewhere that seems to be the acoustic norm, it would indeed be a stride taken with the grail in mind. I concede that with multi channel systems, one can get away with directional loudspeakers or poor loudspeakers plus lots of early reflection absorption. The more the channels, the more the leeway with that approach. But that doesn't amount to respective stereo and muli-channel speaker/room systems being at an absolute tangent in their quest for perfection. In that vein proprietary 10 channel surround formats such as by Audyssey try to make up for the dearth of reflection cues in a 5.1 or 7.1 channel formats, especially the front soundstage. Linkwitz' system, already enriched with sonic energy from the front soundstage thanks to its inherent dipole design with excellent polar radiation raises the bar with four wide dispersion omnipoles utilizing a surround format similar to Chesky's six speaker setup. Granted the role of reflections in a multi channel system are far from established. But there seems nothing incompatible with an *accurate* wide dispersion loudspeaker system/lively room combo and multi channel formats either. The NHT Xd owner just might as well be making a precocious move to reference systems of the future based on such central ideas...
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post #2034 of 10465 Old 02-27-2007, 01:26 PM
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Am I missing something? How is this not As Good As It Gets?

Yup. Room size.

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post #2035 of 10465 Old 02-27-2007, 01:44 PM
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Quote:
Originally Posted by TumaraBaap View Post

Of course, I'm merely a health professional. Terry is an acoustician. I seek concepts and answers from other audio professionals, and largely base my own beliefs on their credibility. I listen to a 7.1 channel system with wide dispersion active loudspeakers myself but otherwise have very limited exposure to the best systems. Frankly, I doubt I'll have the time to fully peruse through extensive links as the one provided by Terry (gracias by the way...will check it out). I don't always have an answer for the ever inquisitive Honcho of this thread either ;-) So take what I have to say with a grain of salt.

However, my thoughts on this: If a Theater/Music enthusiast wants to choose seven wide dispersion loudspeakers such as the NHT Xd over the ample competition, design a room with broadband absorption on the center portion of the backwall and ceiling, go with extensive bass trapping, and otherwise eschew the thin panel absorption elsewhere that seems to be the acoustic norm, it would indeed be a stride taken with the grail in mind. I concede that with multi channel systems, one can get away with directional loudspeakers or poor loudspeakers plus lots of early reflection absorption. The more the channels, the more the leeway with that approach. But that doesn't amount to respective stereo and muli-channel speaker/room systems being at an absolute tangent in their quest for perfection. In that vein proprietary 10 channel surround formats such as by Audyssey try to make up for the dearth of reflection cues in a 5.1 or 7.1 channel formats, especially the front soundstage. Linkwitz' system, already enriched with sonic energy from the front soundstage thanks to its inherent dipole design with excellent polar radiation raises the bar with four wide dispersion omnipoles utilizing a surround format similar to Chesky's six speaker setup. Granted the role of reflections in a multi channel system are far from established. But there seems nothing incompatible with an *accurate* wide dispersion loudspeaker system/lively room combo and multi channel formats either. The NHT Xd owner just might as well be making a precocious move to reference systems of the future based on such central ideas...
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Wow, you've obviously given this a lot of thought, so who besides you would be best suited to execute it? I'll gladly provide you with server storage space for the blog of your new project!


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post #2036 of 10465 Old 02-27-2007, 01:45 PM
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Originally Posted by Dennis Erskine View Post

Yup. Room size.

In the nearfield (of a room with smooth bass response), there is no spoon, er . . room.


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post #2037 of 10465 Old 02-27-2007, 05:38 PM
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But, if you're in the nearfield to the extent the room effects are not audible, then you don't really care about the room, reverberent field, surround channels, etc. Equally to the point, the more in the nearfield you are, the more critical that you have exactly the same speakers as the engineer used during the mix...the closer to the speaker the greater the impact of speaker differences on the mix and what you hear.

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post #2038 of 10465 Old 02-27-2007, 07:01 PM
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Originally Posted by Dennis Erskine View Post

But, if you're in the nearfield to the extent the room effects are not audible, then you don't really care about the room, reverberent field, surround channels, etc.

That's exactly my point. It's in fourth place in having one-to-one control of our eardrums, just behind in-ear monitors, and high quality on- and around-ear headphones. You are there.

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Equally to the point, the more in the nearfield you are, the more critical that you have exactly the same speakers as the engineer used during the mix...the closer to the speaker the greater the impact of speaker differences on the mix and what you hear.

Exactly the same speakers or very good and very close? I would think it more comes down to the skills of the artist, producer and engineer in creating a believable environment (in their mix). If it's a hackneyed mix, it will be (painfully) obvious to the listener.


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post #2039 of 10465 Old 02-28-2007, 11:41 AM
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If I'm in the nearfield of "proper" speakers - I'm basically using what a lot of studios use (M&K 150s) - then I'm hearing exactly what the mixdown team did.

Not necessarily. You'd have to put your ears literally next to the loudspeakers to be close enough to overcome the room effects. Now that would be nearfield!

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post #2040 of 10465 Old 02-28-2007, 12:12 PM
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Not necessarily. You'd have to put your ears literally next to the loudspeakers to be close enough to overcome the room effects. Now that would be nearfield!

--Ethan

Or we could just wait for the HeaDMI interface.


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