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post #1 of 871 Old 05-31-2012, 10:39 AM - Thread Starter
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Does sound and bass sound better in a small room (4.3 x 4.6m) full of furniture or it sound better in the same room but without alot of furniture and stuff ?

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post #2 of 871 Old 05-31-2012, 10:48 AM
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Depends on what type of furniture and what it is made out of.

Any hard or reflective surfaces too close to the listeners head, can have destructive comb-filtering issues. But some diffractive and absorptive materials can be beneficial.

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post #3 of 871 Old 05-31-2012, 11:00 AM - Thread Starter
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Quote:
Originally Posted by Rutgar View Post

Depends on what type of furniture and what it is made out of.

Any hard or reflective surfaces too close to the listeners head, can have destructive comb-filtering issues. But some diffractive and absorptive materials can be beneficial.

I sit on the couch @ the listening positon . I got a piano on the right of the room and a double curtain behind it , my computer desk and the computer near the piano , and the unit that i got my tv on.

the room is 4.3 m x 4.6 m
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post #4 of 871 Old 05-31-2012, 11:08 AM
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Quote:
Originally Posted by dazkyl View Post

Does sound and bass sound better in a small room (4.3 x 4.6m) full of furniture or it sound better in the same room but without alot of furniture and stuff ?

This will answer a lot of your questions:

Acoustic Basics

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post #5 of 871 Old 05-31-2012, 12:13 PM
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^Linking to your own site to sell stuff?

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post #6 of 871 Old 05-31-2012, 12:29 PM
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Quote:
Originally Posted by beaveav View Post

^Linking to your own site to sell stuff?

Have you ever been to Ethan's site. Yes he sales acoustic products. But there is also useful information on basic room acoustics, as well as some DIY articles.

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post #7 of 871 Old 05-31-2012, 02:19 PM
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Yes, I've been to his site. So what? I also clicked on the link he provided. It was, IMO, not very helpful to the original poster, but helpful to EW instead, if you know what I mean.

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post #8 of 871 Old 05-31-2012, 02:43 PM
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If you have couple of sofa/couch, it will be very good for the sound.
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post #9 of 871 Old 06-01-2012, 04:32 AM
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Quote:
Originally Posted by beaveav View Post

Yes, I've been to his site. So what? I also clicked on the link he provided. It was, IMO, not very helpful to the original poster, but helpful to EW instead, if you know what I mean.

At the very least it provided some information pertaining to the OP's question. I don't see where you have provided anything.

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post #10 of 871 Old 06-01-2012, 10:16 AM
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Furniture does help. If you've ever moved, you may recall that an empty room echoes horribly. So furniture does help to some extent. Bookshelves with books can also help to disperse sound. Furniture which is fabric covered is best since it will absorb sound. Leather furniture will not absorb sound nearly as well.

So yes, furniture will help, but it's merely a start. Acoustic treatments are the next step, and Ethan's page will help if you wish to pursue that route.
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post #11 of 871 Old 06-02-2012, 09:53 AM
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Quote:
Originally Posted by Rutgar View Post

I don't see where you have provided anything.

I noticed that too.

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post #12 of 871 Old 06-02-2012, 10:21 AM
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Quote:
Originally Posted by Rutgar View Post

At the very least it provided some information pertaining to the OP's question. I don't see where you have provided anything.

I have been to Ethan's site many times and unless something has changed, I don't see how it has contributed to OP's question regarding impact of furniture in a room. Unless you define "furniture" as fiberglass panels put on the wall . I don't recall Ethan advocating use of furniture instead of acoustic products.

Answering OP's question, yes, furniture helps and can help create a good listening environment. It won't help with low frequencies below transition frequency of 200 to 400 Hz (nor will most acoustic products) but can be very useful in making sure the room is not too reflective. An empty room is not a good space for audio.

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post #13 of 871 Old 06-02-2012, 11:27 AM
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Quote:
Originally Posted by amirm View Post

I have been to Ethan's site many times and unless something has changed, I don't see how it has contributed to OP's question regarding impact of furniture in a room. Unless you define "furniture" as fiberglass panels put on the wall . I don't recall Ethan advocating use of furniture instead of acoustic products.

Yes, exactly. Furniture is not proper acoustic treatment, and furniture is rarely placed symmetrically which is also needed, at least in the front of the room. So in fact my Acoustics Basics article does explain a lot to help the OP.

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post #14 of 871 Old 06-02-2012, 11:40 AM
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Quote:
Originally Posted by Ethan Winer View Post

Yes, exactly. Furniture is not proper acoustic treatment....

Well, there are top experts in this field who dispute that. From Dr. Floyd Toole's presentation:

"The amount of reflected sound will alter impressions of spaciousness and
reverberation (sounds that persist after the source has gone quiet). There is an optimum amount of reflected sound in small listening rooms - not too live, and not too dead. Normally-furnished rooms (carpet, drapes, chairs and tables) tend to be close to optimum, but custom home theaters need to be treated.
[...]
This is one of the main reasons why a normal well-furnished room can sound so good. Combined with carpet/underlay, drapes, and seating the combination can work superbly with little tweaking."


Here is a nice graph from his book on how furnishing helps reduce reverbration time in the room:



Seems quite different than your advice.

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post #15 of 871 Old 06-02-2012, 12:47 PM
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Nice selective quoting of your expert. This is the problem when one is not an expert himself - all he can do is quote others, often getting it wrong.

The goal of all listening rooms is a relatively uniform reverb decay time versus frequency. Most of the data on Floyd's graphs cover a range narrower than 200 Hz to 5 KHz. Do you understand why his graphs are limited to that range? Here's another quote from Floyd's book:

Quote:


The corners of the room are available for low-frequency absorbers.

It seems Floyd understands that bass traps are necessary and why. Now look at this Before / After graph showing a properly treated small room, and you'll see that the decay times are far more uniform versus frequency than a room containing only "furniture." Look especially at how low in frequency the uniformity extends to:



What I don't understand (I honestly don't) is why you have such strong opinions, and feel the need to challenge me at every opportunity. Do you really believe that acoustic treatment is not useful or necessary?

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post #16 of 871 Old 06-02-2012, 01:25 PM
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Quote:
Originally Posted by Ethan Winer View Post

Nice selective quoting of your expert. This is the problem when one is not an expert himself - all he can do is quote others, often getting it wrong.

Selective quoting? Have you ever talked to Dr. Toole? If you have, you would know that I am expressing his point of view precisely. Happy to quote tons more.

Quote:


The goal of all listening rooms is a relatively uniform reverb decay time versus frequency.

There is no such goal for small home listening rooms. In the context of figuring out if the room is too live or too dead, what we care about is the reverb time around 500 Hz. The rest is not of importance since small rooms are not reverbrant spaces.

Quote:


Most of the data on Floyd's graphs cover a range narrower than 200 Hz to 5 KHz. Do you understand why his graphs are limited to that range?

I do. It was right on the graph. He is trying to contrast the room's measurement against he survey of large number of home living rooms by Bradley which also covered the same range.

Quote:


Here's another quote from Floyd's book: "The corners of the room are available for low-frequency absorbers."

It seems Floyd understands that bass traps are necessary and why.

Did you read what I wrote? I said: "It won't help with low frequencies below transition frequency of 200 to 400 Hz." So yes, furniture is of no help in taming low frequencies. And this is the full quote:

"The corners of the room are available for low-frequency absorbers.
These are preferably of the membrane/diaphragmatic/panel type, because
they are located in high-pressure regions of the low-frequency standingwave
patterns."


So no, he doesn't say all bass traps are good. Here is what he says about bass traps:

"Sometimes these (modular bass absorbers) are called "bass traps." The problem with the name is that some of them don't "trap" much of anything excpet cash from unwiiting purchasers."

That doesn't seem to be the endorsement you just attributed to him.

Quote:


Now look at this Before / After graph showing a properly treated small room, and you'll see that the decay times are far more uniform versus frequency than a room containing only "furniture." Look especially at how low in frequency the uniformity extends to:



What I don't understand (I honestly don't) is why you have such strong opinions, and feel the need to challenge me at every opportunity. Do you really believe that acoustic treatment is not useful or necessary?

--Ethan

I was not even talking to you Ethan. This thread is about the effect of furniture in a room vs it being empty. It asked nothing about buying bass traps. Your answer was this prior to linking to your web site: "This will answer a lot of your questions:" beaveav correctly pointed out that you seemed to just be advertising your wares instead of answering OP. Someone disagreed and I chimed in to give my opinion and confirmed that your web site does nothing to answer OP's question.
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post #17 of 871 Old 06-02-2012, 01:27 PM
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post #18 of 871 Old 06-02-2012, 03:16 PM
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A room without furniture is very uncomfortable, essentially inhospitable to either HT or stereo, regardless if furniture helps the sound.
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post #19 of 871 Old 06-02-2012, 03:19 PM
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Quote:
Originally Posted by swampfox View Post

a room without furniture is very uncomfortable, essentially inhospitable to either ht or stereo, regardless if furniture helps the sound.


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post #20 of 871 Old 06-02-2012, 08:39 PM
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Quote:
Originally Posted by Rutgar View Post

At the very least it provided some information pertaining to the OP's question. I don't see where you have provided anything.

Fair enough. I am an EE but no expert in acoustics. I was hoping the info in the link would be relevant and educational but was disappointed with what it was. So I voiced my disappointment.

And I would like to point out that you, too, have now joined my group of people providing nothing constructive. Welcome, come on in, have a drink.

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post #21 of 871 Old 06-03-2012, 04:34 AM
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Quote:
Originally Posted by beaveav View Post

^Linking to your own site to sell stuff?

I find that the article seems to be relevant and doesn't seem to mention any particular products.

Why did it disappoint you?

What do you think was missing?
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post #22 of 871 Old 06-03-2012, 05:14 AM
 
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The more it changes the more it stays the same. …So much talk and so little understanding of acoustics. But I guess that is due to the loopy assumption that acoustics is just too complex a behavior for science to understand – or maybe it’s just, in fact, forum participants who exhibit that characteristic.

Talking in such generalizations is near meaningless. Simply adding furniture may or may not have a beneficial or a deleterious effect – especially as the nature of such furniture is not specified! Thus the effect is as similarly amorphously specious for someone to suggest that adding unspecified “treatment”, be it absorptive (at ‘some frequency’), diffusive (at ‘some frequency’), or simply reflective (at ‘some frequency’) would be “beneficial”!

At best it MIGHT serendipitously be beneficial, as considering that most furniture will not function effectively as a sub 100 Hz absorber limiting its use as an arbiter of modal behavior, at worst you have effectively frequency selective ‘treatments’ that function as non-broadband treatments upsetting the frequency response of the ambient energy effectively creating an effective treatment that simply EQs the various specular energies in a manner that Toole correctly decries.

And then we have the erroneous overly generalized use of statistical reverberant methods used to describe a space that by definition is defined as NOT being reverberant and which is characterized instead ONLY by the localized distribution of various modal and specular energies that vary dramatically from one spot to another – rendering even the reference to ‘reverberant' behavior as absolutely nonsensical in a space where ANY semblance of reverberant behavior not only is far too high in frequency to care about, but which whose level is so low as to exist only below the ambient noise floor! But it’s amazing how many in stating that such spaces are NOT reverberant, still cling to such a specious and meaningless metric. But any derivative calculation in a storm, I guess, regardless of how meaningless it is in a given environment, right?

Bottom-line, furniture MIGHT be beneficial or it MIGHT even be harmful: depending solely upon its functional nature acoustically. And to the degree that it is functional, it depends specifically upon how it interacts with the various actual modal and specular behaviors in the specific room.

Anything more than that is an unsubstantiated assumption. So if you want to determine each piece of furniture's specific effect, measure the before and after modal and specular behavior in the room, and address it just as you would any other treatment.
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post #23 of 871 Old 06-03-2012, 09:46 AM
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^^^ I agree with much of this, but don't discount RT60 as a useless measurement in small rooms, even if true reverb doesn't usually exist there. RT60 is a standard metric used by professional acousticians even in small rooms. In this case it shows how the individual reflections decay over time. Further, an empty small room does indeed have true reverb. Flutter echoes might drown out the reverb to varying degrees, but it's still reverb. Of course, an equally useful metric in small rooms is ETC which shows each reflection separately.

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post #24 of 871 Old 06-03-2012, 09:57 AM
 
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The reverberant field, specifically the low frequency limit, in a space is determined by the volume (and topology) of the space.

Thus, as was noted, in a small space the low frequency limit of any actual reverberant behavior is prohibitively high, below which NO statistically reverberant behavior exists. Rather all that exists is the various regionally variant modal and specular behavior.

And as we generally do not care about behavior lower than 10 kHz, and a small room's lower frequency reverberant field limit is often in the realm of 19-20 kHz, the concept is specious - as has been conclusively presented and discussed by prominent acousticians, significant among them Dr.Ted Schultz of Bolt, Beranek and Newman.

If one wants to persist in squinting and believing that a derived calculation (as RTxx are NOT a direct "measurement" of any "thing") has value applied to a space in which no such appropriate behavior actually exists - enjoy the hallucination. (And such an assertion is WORTHLESS for the "room" exhibiting ONLY specifically regionally variable behavior!) One can just as easily assert a convenient imagined correlation with barometric pressure, astrological signs and fung shui.
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post #25 of 871 Old 06-03-2012, 10:35 AM
 
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I am not going to try to get into this issue in too much depth, (especially as this issue has been beaten to death and exploded within the formal acoustics realm - as opposed to the colloquial realm of folks who casually are want to 'use' acoustics without a formal understanding of the concepts - 30+ years ago! )... but a few observations...

Two optional criterion more useful in a space than the RTxx calculations are the T30 and EDT. STILL, and it is is critical to understand this, both are properly applied ONLY to situations where a factual and statistically homogeneous reverberant field exists (i.e. medium to large rooms with low absorption).

Their use in small spaces (i.e. control rooms, home theaters, and other rooms with high absorption relative to room volume) is questionable at best.

A further irony and caveat exists in that while the determination of T30 and EDT according to ISO3382 may SEEM straightforward, such that one might expect to get the same result from any measurement program, the FACT is that this is simply NOT the case!

So much for Standards!

So even if we were to want to use the standard as a measure of the behavior of a system placed in a room, it is not consistent with the standard nor the proper measurement procedure!

Rather, the intended use of the standard was NOT created nor intended to measure the behavior of a sound system in a bounded space as is done here, but rather it was created specifically to be used for room acoustics testing.

Such testing is independent of a particular speaker system and speaker placement.

And as such, a specifically low-directivity sound source is required. Traditionally this was supplied in the form of a Dirac impulse (a balloon or starter's pistol shoot). But if a loudspeaker is used, it MUST exhibit low directivity (i.e. a dodecahedron).

Paraphrased from another source:

When measured in this way, the -5 dB point on the Schroeder curve is typically beyond the direct arrival and early-reflection contributions and on a straight segment of the decay. When typical highly directional loudspeakers are used, the steeper slope of the early Schroeder curve extends further into the RIR.

In such cases the -5dB start of the T30 calculation may be too early, producing a shorter T30 (steeper slope) than the actual RT. While strong early energy is a good thing for sound systems, it can fool the algorithm used to determine the actual RT.

Long before the existence of a standard, reverb times were determined from the manual placement of cursors on the Schroeder curve. A left and right cursor were used to segment a straight portion of the curve and the RT
(RT60 in those days) was determined from these placements.

The left cursor was moved beyond the slope change caused by the early reflections and direct field (typically >300 ms for most rooms). Since ISO3382 defines the slope to be from -5 dB to -35 dB on the Schroeder curve, this can result in the "start point" being on a different slope of the curve than the "end point."

The result is incorrect determinations of the RT time.

Additionally, the ISO Standard is defined for 30 dB of room decay, and extrapolated to 60 dB. The reason is that actual impulsive testing tends to produce RIRs with poor signal-to-noise ratio, so one can rarely get the required 45 dB of decay before running into the noise floor. The presence of noise causes a reduction in the slope of the late part of the Schroeder curve
(Fig. 6). It can be impractical to expect a quiet environment when testing real spaces (Sabine did his testing in the middle of the night), where Murphy's Law assures that a vacuum cleaner is likely running somewhere in the vicinity.

In fact, it can be difficult to achieve 45 dB of decay!

The standard provides a T20 (-5..-25) and T10 (-5..-15) that can be used in lieu of T30 for noisy data, both extrapolated to 60 dB of decay.

Measurement systems used for testing sound systems can easily yield 60 dB or more of SNR, so it is not necessary to base the RT on only 30 dB of decay. The slope-change at the end of the Schroeder curve is most often due to noise being integrated along with reverberation.

Most measurement programs provide automatic or manual methods for excluding this part of the curve from the calculation. But, what if it's not noise?

Some rooms can actually have a triple-sloped Schroeder curve. This can happen in "coupled spaces" where two different sized rooms are joined. The first 10 dB (the basis for EDT) is steep due to a strong direct field and/or strong early reflections. A lower-slope straight-line section is next (for one space) and a lower-yet slope segment is next for the more reverberant of the two coupled spaces. These slope changes can cause problems for automatic T30 algorithms that are programmed according to the Standard. Again, manual cursors are often provided to handle these special cases.
And how does one know if a late slope change is due to noise or a multi-sloped room? A good noise compensation algorithm can often make the distinction, but no standard exists so this is left up to the ingenuity of the programmer.

Another source of differences between measurement platforms lies in how the standard is interpreted. The standard is based on a "best fit linear regression line" to the Schroeder curve and should be "free" at both ends. A line connecting the relevant levels (0 to -10 dB for EDT, -5 to =35 dB for T30) is not the Standard but is sometimes used.

Thus, before one blindly assumes a "standard" is even applicable, let alone valid:

- One must remain cognizant that they were NOT written consistent with the many assumptions that are not necessarily true in the specific scenarios in which many are actively trying to employ them.

- "One number" specifications are rarely useful. Practitioners should gather a complete, low-noise RIR at any seat that is worth investigating.
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post #26 of 871 Old 06-03-2012, 10:46 AM
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^^^ Way too much to comment on so I won't even try to address it all.

Yes, at low frequencies modal ringing dominates and reverb per se doesn't exist. This is why programs like Room EQ Wizard that I use don't even extend the reverb display to the lowest frequencies. But above 300 Hz or whatever, depending on room size, there can be true reverb. Or at least something close enough to reverb that an RT60 display is not useless. Again, I'm not the only professional acoustician to use RT60 as a metric in small rooms.

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post #27 of 871 Old 06-03-2012, 12:20 PM
 
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Manfred Schroeder defined the large room frequency, and derivatively, the volume of a room necessary to support a reverberant field at the large room frequency and above.

There is NO reverberant sound field below that frequency.

Since we are concerned with volume, and using a generally accepted breakpoint value for RT of 1.6 seconds:


Volume = K^2 (RT60/(Lg Room freq^2))


K in SI (metric) is 2000 and 11,885 in imperial/US terms

Thus,
for 300 Hz and above, the room must be a MINIMUM of :

(11,885)^2 (1.6/(300^2)) = 2511.168 or

2511 ft^2

When someone has a room larger than 2511 ft^2 and is ONLY concerned with reverberant times ABOVE 300 Hz, determined properly - NOT with a directional home speaker but with a true omni-directional source stimulus - call me.

In a space less than that volume, you are necessarily dealing instead with non-homogenous locally variable combinations of modal and specular distributions. Any single generalized number value one tries to use to characterize the space is inaccurate at almost every single point in the room. And any point at which it might coincide is purely serendipitous.

Until then, believe whatever you like - seeing as how the root of the word "belief" is appropriately "to wish it so"...
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post #28 of 871 Old 06-03-2012, 06:52 PM
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Originally Posted by dazkyl View Post

Does sound and bass sound better in a small room (4.3 x 4.6m) full of furniture or it sound better in the same room but without alot of furniture and stuff ?

Generally with, although a coffee table between you and the speakers is detrimental.
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post #29 of 871 Old 06-04-2012, 12:28 PM
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Manfred Schroeder defined the large room frequency ... There is NO reverberant sound field below that frequency.

The Schroeder frequency is not a sudden hard cutoff. Whatever. You tell people what you want, and I'll do the same. I don't need prove I'm right, and I certainly don't have an attitude about this stuff. The key point is that real acoustic treatment, and proper placement and symmetrical layout, gives better sound than random furniture.

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post #30 of 871 Old 06-04-2012, 12:56 PM
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But above 300 Hz or whatever, depending on room size, there can be true reverb. Or at least something close enough to reverb that an RT60 display is not useless.

rt60 is to be measured well past Dc and with a Dodec/omni-source (something typical home loudspeakers do not exhibit) - as rt60 is a characteristic of the acoustical space.

can someone show me measurements past Dc for a given frequency in a small acoustical space (home residential room)??

and if there does exist statistical reverb sound-field in SAS then why do we need the large labs to do random-incidence absorption testing for porous absorbers?

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Originally Posted by Ethan Winer View Post

The Schroeder frequency is not a sudden hard cutoff. Whatever. You tell people what you want, and I'll do the same. I don't need prove I'm right, and I certainly don't have an attitude about this stuff. The key point is that real acoustic treatment, and proper placement and symmetrical layout, gives better sound than random furniture.

i hope this isn't an attempt to discredit Schroeder's work? it's all quite clearly defined. FsubL is frequency-dependent, and a transition just like that of modal to specular in SAS.

in SAS we deal with local areas of variable pressure - and isolate focused specular reflections with the ETC (*not statistically). this is why placement of broadband absorbers for specular energy absorption (attenuation) are not randomly distributed throughout the room like that of a large acoustical space where the energy is statistical. instead, in SAS, we place the absorbers (or other treatment) at areas incident of a particular isolated indirect reflection based on source/receiver position(s) - and with a known angle of incidence (vs random-incidence/diffuse-field).
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