Should the center be as capable as the mains? - Page 2 - AVS Forum | Home Theater Discussions And Reviews
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post #31 of 33 Old 02-07-2012, 07:08 PM
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I also vote for the three identical WMTMWs but make sure they are either tilted down to face the listening area directly (they look high in the drawing???) or place the speakers closer to the floor so the tweeter is at listening height. IOW, make sure the tweeter-ear axis is perpendicular to the baffle and ensure M & W pairs are equidistant from the primary listening position. That should help facilitate the rock-solid L>C>R soundstage the WMTMW driver configuration can provide.
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post #32 of 33 Old 02-07-2012, 07:12 PM
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Originally Posted by SilentJ20 View Post

It did get a bit OT, and unfortunately that is some stuff that I would like to learn about. But in the spirit of the forum, I suppose we should stay somewhat on topic.

Here's a question about frequently response at the listening position that was mentioned. With the larger center that matches the fronts, would I measure each channel seperate or would all 3 (or 7.1) play at the same time for an overall system? It seems it would be beneficial to know how each channel was doing, but I'm still learning this stuff.

I guess that's not completely on topic, but its useful to me and it relates to having a more full range center. And it's my thread, lol.

Good question.
In the room you are not really concerned with the frequency response of the speaker itself.

In fact, you are not really interested in the frequency response at all. I know, this will shock some and seem anathema. After all, everything revolves around he frequency response,right?


In terms of he speaker-room interaction, the frequency domain is derivative, not causal. And except for a very limited ability to perform LIMITED EQ merely to mitigate peaks below about 80 Hz where energy is still predominately minimum phase, the frequency domain provides no insight except that the superposition of direct and indirect energies result in polar lobing and a "pattern" that only exists as a pattern in a frequency response plot, but which not an actual 'thing'!

Thus, all the frequency response confirms is that which I, or anyone aware, could easily tell you before the measurement.

So.....what re we actually dealing with, and what should one do about it...

First, the causal domain of the aberrations is the Time domain.
Both modal and specular issues are a result of indirect and indirect signals combining (properly termed "superposing" or "superposition").

How do we look at this and obtain information about the various energy signals sufficient to be able to affect modification or a solution?

For modes, and only because of their large size, we typically view them in terms of a modified frequency response and waterfall resolved into time slices that indicate the resonance or persistence and decay of such locally variable sound fields.

For energy above the Schroeder critical frequency, fc, where energy behavior changes from modal standing waves to focused specular waves, we use the impulse response convolved into the Energy time curve or ETC response.

We perform the ETC measurement for each individual source, as we are concerned with the time of energy arrival and its gain. For all practical intents and purposes, forget frequency. that is simply an alternative perspective on the same behavior that is not actionable with regard to solving problems.

We isolate each source in measurements as we are able to determine the arrival times, gain, and to derive the specific vector paths and points of boundary incidence of the energy wavelets as well as to determine qualitative information such as how sparse or semi-diffuse the energy is. We can also determine the degree of liveness or spaciousness that the room imposes.

In conjunction to overall acoustic room response models and a knowledge of the psycho-acoustical principles at play, we can both precisely and surgically determine both the actual existing behavior in a bounded space and to then determine the proper treatments sufficient to effect the changes necessary in order to predictably modify and correct aberrant results within the room relative to specific listening position(s).

In other words, we can control and modify the causal factors that contribute to the perception of sound in the complex bounded space that results from the complex interaction of speaker and room.

The largest challenge here? That's simple to identify, and a bit harder to affect...

The largest challenge is the required paradigm shift in thinking that is a radical departure from what most are familiar and used to. For some this is a real threat. For others an exciting but slightly confusing change in perspective. But ultimately is is a very productive POV that can enable one to make very real improvements, even when give less than ideal components, speakers or spaces. of course, there may be limits created by the combination of such factors, but those limits are also able to be precisely determined so that one works with the space and limits actions to those factors that can be productively modified.

Thus, one can continue to debate the utterly fascinating and less productive issues that so often have come to dominate audio; or, one can choose to move into the new acoustics - an advancement equivalent to a quantum leap in acoustics made possible largely by advanced time domain measurement tools initialed by Richard Heyser.

This leap is now about 40 years old, and while much of the professional world lives in this domain daily and routinely, MUCH of the world of consumer and audiophile ('phool') audio remains mired in the old view still debating OLD long since resolved topics such as 'what can or cannot be EQ'd... It is this inertia that has the realm of consumer audio lagging far behind much of the world of 'Pro' audio and most definitely 'pro acoustics'.

(I mean, where else will you find the majority of esoteric $40,000 speaker systems consisting of large format line arrays that folks will listen to in the near field and then claim that they sound GOOD!?!?!?!?!? That in itself should be more than sufficient to demonstrate that money (can have) an amazingly detrimental affect on perception and reasoning abilities!) And I would hope that the response from all here would be a universal 'of course'!
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post #33 of 33 Old 02-07-2012, 08:28 PM
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But doesn't all available software (to amateurs, at least) use a measured frequency response to derive an impulse repsonse, which shows clearly first arrivals, reflections, etc?

How would such an impulse response (and subsequently, ETC), be measured if not by freq sweeps, white/pink noise? With an impulse like the 'clicks' in the old Avia test discs? MLS could do it as well, but would the results between MLS Impulse response vs swept sine or RTA of enough resolution differ enough to be significant?

I am uneducated on this topic. Most of my knowledge comes from deriving impulse from freq response, such as what REW and HolmImpulse do, and EQ in the freq domain can fix issues in the time domain, shown in Toole's book. I may be stuck in the modal region, so to speak.....

If Freq response and Impulse response are just a Fourier/Inverse Fourier away from each other, why is freq response not as important?

Care to explain further?

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