Do bass traps produce noticeable audible difference? - Page 2

I started off measuring like that. It's quite labour intensive and takes a long time if you want to write things down and graph it. Okay if you just want to take one measurement now and then. The beauty of using a computer program to do it I found, is that it is so quick and simple that you can make small changes in the room or AVR configurations and then instantly remeasure and see what effect it had. Much more user friendly in terms of getting a flatter frequency response in your room... not just seeing your room's FR.

Well absolutely, I agree.



Thanks

BTW, with OmniMic, real time changes can be seen and changed easily by merely a twist of the knob.

I have a RS meter. It is not trustworthy. Besides, even if you manage a stable correction curve (the meters vary), you can only measure spl with them. No ETC, no Waterfalls, no impulse data, no decay curves.

I agree, I down with the time domain, .... we were discussing the vast majority seeking simplicity, ... many of whom can't spell ETC This is the group that doesn't even wish to bother with something as easy as OmniMic. Hell, ... it'd be tough talking them into a Rives Test disc and a Rat Shack meter!

Jim, I'm with you. It's all about the room, the room is all about the time domain.

I didnt mean to sound like I was putting YOU in that group

But I did mean to point out that in this case, something a bit simpler subtracts about 90% of the data needed to make a worthwhile interpretation of the room (i.e. RS meter). I would even argue that Omnimic is simpler than the RS meter method in that it graphs the data for you and with the RS treatment, you have to take the time to write down the data

I will add that for a long, long time, I resisted getting proper measurement tools because I was intimidated by what all the data meant and over estimated the procedure to get things set up right. I also underestimated the effect of treating a room properly. Looking back at all the equipment upgrades ive made over more than 30 years, treating my room was by FAR a bigger improvement than ANY of them. By FAR!!!!!! You just dont realize the detrimental effect of unmitigated reflections until you hear a well treated room. And unfortunately, many will go to their grave having never done so.

Said another way, I would MUCH rather have a $2000 stereo system in a properly treated room than a $10,000 one in the average untreated one. Really!!!!!!!

fbov, after our discussion, i'm once again re-iterating my response regarding small rooms.

post #17:
you've stated that "Waterfall is an RT measurement." and that you can "hear the reverb" in your living room. this is not accurate.

the waterfall plot is NOT related to reverberation time (RTxx) - of which is a calculation, NOT a measurement.

again, to limit confusion to other novices on this forum, there is no appreciable reverberant sound-field at any frequency us humans are concerned with in small acoustical spaces (residential rooms, living rooms, etc). RTxx is not a relevant calculation here because the pre-requisites are NOT satisfied.

discussing Sabine's equation or a "room whose RT(frequency) is a straight line with a slight downward slope in the 0.3 sec range" is completely erroneous to the small rooms being discussed here.

if you are challenging this notion then you are challenging the entire careers of Leo Berenek, Manfred Schroeder, Ted Schultz, Peter D'Antonio, Don Davis, etc...
Edited by localhost127 - 2/14/13 at 3:31pm

I used to accept that too until I actually tested the theory. Now, if you add "typically furnished" to "small acoustical spaces" then I'd agree. But an empty room can be highly reverberant, even if it's relatively small. My two-car garage is no larger than many living rooms, but when it's empty it produces a very nice sounding reverb that extends for at least several seconds! The reverb decay time is also fairly uniform versus frequency. If anyone doesn't believe me I'll make a recording and post an MP3 file here.

--Ethan

unfortunately, you're merely using the term "reverb" as slang for any form of specular room decay. you are free to modify the acoustical definitions to your heart's content, but it does not change physics! surely you do not refer to ice, rivers, lakes, waterfalls, mist, etc as simply water.

you do not have an exponentially rising, exponentially decaying statistically random-incidence reverberant sound-field in your garage.
edit: unless you have the pleasure of owning a garage the size of an auditorium.


no recording is necessary; simply provide a measurement past Dc (critical-distance) of which you will then be in the reverberant sound-field. then you will be "testing the theory".

i'll wait.

no. a small acoustical space is distinctly defined by the lack of an appreciable reverberant sound-field above the ambient noise floor!!

there is NO NEED to "add" any descriptive commentary to that of a Small Acoustical Space!!! it is implied by definition!

your agree-ance is not required. this is physics and has been well understood for many decades.

someone in your position should understand these basic fundamentals of acoustics.

That's in line with international standards for small (less than 3500 cu ft) control rooms and studios. ITU recommends a RT60 of .25s and BBC recommends a RT60 of .3s, both allowing for deviations of ±0.05s from 200Hz to 4kHz; EBU recommends a RT60 of .2s to .4s. In an old post on these forums, theatre designed Dennis Erskine said "I try to keep it in the range of .35 to .40".

http://www.avsforum.com/t/1443066/oc703-on-bottom-of-soffits/0_60#post_22668729

No, it really is reverb. Versus flutter echo that favors one frequency strongly. You're welcome to visit and hear it for yourself.

--Ethan

since we are now apparently ignoring the well established acoustical definitions and understanding of the physics involved, may you at least present your specific definition of "reverberant sound-field" of which is the slang you are using here?

long specular room decay times does not imply a statistically random-incidence reverberant sound-field!!
or maybe dr. manfred schroeder's entire career is wrong!


save me the trouble of travels: just inform me whether i am going to "hear" a point within your garage where the reverberant sound-field becomes higher in gain than the direct signal. does this exist in your garage or no? is there a point (in 3space) in your garage where i will thus be in the "reverberant sound-field"?

Sure.

you simply cannot admit that there is no critical-distance in your garage. hilarious. nor can you provide me with your definition of "reverb" (since we apparently are just modifying the definitions on the fly, per-person).

for being an "acoustics specialist" here on AVS, i find this conversation all very entertaining. what i find even more comical is your blatant disregard for the physics involved as you use such acoustical terms as slang.

"Physics" is the wrong branch of science to determine if a reflection in a room will be heard as a distinct/second event (i.e. echo) or not. The relevant science is psychoacoustics which is driven by how we hear. To wit, listening tests going back decades show that whether we hear a reflection as an echo is a function of how loud it is, and how much delay it has until it arrives at our ear:



As we see there, you can hear an echo when the delay gets to be greater than 30 milliseconds for reflections that are less strong than our direct sound. 30 milliseconds is about 33 feet. In a large enough garage that condition can exist and hence what Ethan is hearing may very well be true. It will be especially true of him because he lives in the recording music side of the population and those people tend to develop more sensitivity to reflections and hence for Ethan, the curve may be pushed more to the left than the rest of us.

Speaking of the rest of us, the black dots show where the first 6 reflections occur in typical home listening spaces so outside of Ethan's example, we are firmly in the area where we don't hear echoes. Instead, the cognitive (thinking) portion of the brain uses those reflections to accumulate more energy and amount of information that it uses to determine what is being heard. But we digress .

Likewise, references to Schroeder and conditions for reverberant field are inappropriate in this context. Those terms come up when discussing the characteristics of large acoustic spaces. They do not read on whether you will or will not hear an echo. The listening tests and our brain function explain that per above.

echos??? lol.

i know you're constantly in a rush to copy-paste a host of information from sources to make yourself appear knowledgeable on the subject ... but at least read the discussion taking place before responding. what you've presented is entirely irrelevant to the discussion at hand. you are the first person in this thread to mention these types of "echos".


but alas, when all one has is a hammer, every conversation must look like a nail.



by all means, why don't you list the "conditions for reverberant field" for ethan?



i like your new choice of vocabulary in some of your most recent postings. i guess as they say, imitation is the sincerest form of flattery.

I'm so glad you chose to sample the forum for its point of view; my PM inbox thanks you for no longer soiling it.

Anyone else feel as if localhost only has a hammer?

Have fun,
Frank

LOL, ya think?

I forgot this thread was in this forum, so I started a new thread to discuss this exactly issue over at Gearslutz where Local is also a member. Since I already made the files to post there, I'll repeat it here:

After a recent discussion here about what constitutes "real" reverb, I decided to record an audio snippet in my 2-car garage and attach it here (in a Zip file). To my ears this garage gives real reverb, even though it's nowhere near the size of an auditorium. The T30 decay is about half a second as viewed in Sound Forge, so that equates to an RT60 of 1 second. It's cold out so I didn't bother to remove my car.

When the garage is totally empty the reverb is even longer and more pronounced. I recorded myself whistling (poorly) at several pitches and also three different types of hand claps. This is to show that the garage does not have a pronounced flutter echo, and the reverb is more or less uniform at midrange frequencies. The attached photo shows my little Zoom H2 on top of my car. I stood right next to the H2 as I whistled and clapped. The H2 was facing me, though I was facing the other way. If I rotated the H2 toward the wall behind me, I'm sure the ratio of direct sound to reverb would have been even greater.

So - ignoring official definitions - does this sound like reverb to you?

--Ethan



Garage Reverb.zip 299k .zip file

and yet it was you that initiated the conversation. and you state the "Waterfall shows RT". i beg to differ.

ignoring official definitions?!? what is the point of this exercise if you are "ignoring official definitions" - this just proves that you are indeed using the term as slang!

you still have yet to provide your "official" or "non official" (!) definition of reverb.

are you able to reference (read: google) these "conditions" for ethan ?

Going back this original question, I am completely persuaded that listening in an unfurnished room would be greatly improved by traps and diffusors. But my room is furnished. As I look around, I see lots of things that probably produce acoustic complexities -- open windows and doors, curtains, rugs, sofa, cushioned easy chairs, bookcases, wall hangings, fiberglass panels on ceiling, wood paneling on walls, a Christmas tree. So a more interesting question is: Would additional treatments be likely to improve the sound in a room of the sort people actually live in?
Edited by GregLee - 2/19/13 at 7:36am

In the bass, absolutely, IMO. curtains, rugs etc just won't absorb bass (you need 1/4 wavelength to fully absorb, according to what I've read, so you need just under 3 feet of absorptionto capture the 100 Hz wave striking the absorber). Whether a chair happens to absorb some bass is irrelevant if it's not capturing a wave/"reflection" that contributes to a problematical peak or dip in the listening area (ie not positioned or tuned correctly).

but the real bottom line is, given what our rooms really are, we cannot likely trap all the bass porblems away. While using some trapping may clear things up, especially in the (relatively critical) mid and upper bass frequencies, probably the easiest way to get more-even bass is to add another sub, and place the multiple subs apporpriately in the room.

Localhost may only have a hammer, but at least he knows how to use his hammer well. He does not provide any contradictory statements in this thread at all - these are all very standard, agreed upon, well tested, and well documented facts.

Reverb in this discussion has nothing to do with psychoacoustics. RT60 is a calculation, not an effect - and reverb is the physical effect not one that is generated in our heads. Therefore, it is physics, and physics does describe it.

As usual, this argument doesn't need to exist. Obviously localhost, you understand what Ethan means when he says "reverb" - the decay of sound after the initial sound, ringing out for a substantially long time compared to a bedroom, and not fixated on a particular frequency. And Ethan, you obviously understand what localhost means when he's giving the technical definition of reverb, and why you persist to argue that what you hear is reverb against his definition, though you are both using two different definitions is beyond me. I think it is really unnecessary to comment further on each other's posts about the subject. My stance is on the actual physical definition, though I clearly understand what Ethan means.

I still see absolutely no use for an RT60 calculation at all for a bedroom, even if it were valid. A waterfall simply has much more relevant information present.

This actually is a common misunderstanding of text! It doesn't simply drop off right there, it rolls off (rather slowly). I've seen over 1/16 wavelengths get absorbed graciously - testing confirms this. You can check any of the tests that we've had conducted by Riverbank - they're available on our website - none of our products are 36" thick, yet all absorb under 100 Hz.

This really is on a per room basis, but I do agree a second sub can really help level things out in a wildly unbalanced room.

Recognizing the acoustic "complexities" of normal room contents is what got me interested in acoustics - why didn't my room have the bass mode issues everyone else reported? Why was 1 large sub enough to make everyone uncomfortable?

Room construction: stick walls / floor / ceiling, paneling on standoffs, ~45 sq ft of glass, a full height fireplace and double doorway all affect bass, mostly to absorb or transmit it. All are hard to retrofit to existing construction.
Easiest, perhaps, but not most effective.
Here here!

I see no need to banish English just because we're talking acoustics.
Reverberate: 1) to re-echo, resound. 2) to be repeatedly reflected
Time: 1a) a nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. (the first of 10 for the noun will suffice...)

Not

Reverbreration time only exists when the relation (RT60 = constant x V / S) is true
where S = alpha A,
V is room volume,
alpha is acoustic absorption coefficient and
A is room surface area covered with coefficient alpha.

While the latter may be techinically correct under certain well defined conditions (localhost's hammer), it makes for poor conversation, and tends to drive folks away who would benefit from a general discussion of the topic.

Put another way, the mathematical rigor is mandatory if you want the equations to make accurate predictions. This is general conversation, not university, so anything more than basic awareness is overkill.

HAve fun,
Frank

You say they are agreed upon yet I can cite peer reviewed paper after peer reviewed paper, industry luminary after industry luminary who will not only challenge what he says with science but also with listening tests. You give me the count of how many you want me to cite, and I will cite them . Sure, there are a group of people who agree with that point of view and he repeats those statements over and over again but that doesn't make them the consensus of the industry.
I said nothing about RT60 but see more below. I explained why in a space as large as that garage, one can hear secondary events. And if you can hear secondary events, then it is a form of reverb or echo. What tells us that is psychoacoustics and listening tests. But by all means, post a physics formula that gives the curve I posted. I am pretty sure you cannot.

While you are at it, do you want to explain why such things as speech intelligibility actually improve with more reflections than the other way around? What in physics tells why that happens?
Using waterfalls correctly requires considerable skill and knowing its limitations just the same. Knowing that requires another field of science called signal processing.

RT60 is a usable shortcut and can easily be demonstrated to track (more or less) how much late reflections one has. Fact that the room reflections are not fully diffused in small spaces does not invalidate its use.

Here is a case study as preformed by Dr. Toole:



Before you say you don't agree with that, let me remind you that you said everyone agrees with you all's point of view.

The demonstration shows that late reflections can be reduced and that effect shows up in RT60 calculations. Do we care if the relationship is 1:1? No. This is a rough measure with wide latitude of 0.2 to 0.5. We are not after precision.

Note how Ethan remarked that if he removed the car from his garage, the amount of lingering reflections will be higher. Same observation as the above graph. Indeed, that is why furnishings in the home help keep the room from being overly live, or to use Ethan's term, overly reverberant. Again, the fact that the reverberations are not diffused is not important.

sorry, but a statistically random-incidence reverberant sound-field is not characterized by "listening tests". this is physics.


im sorry but this is utterly incorrect. again, someone who is clueless as to the definitions of the acoustical terms exhibits a formal lack of understanding for public display.

in a reverberant sound-field, the energy is so "well-mixed" that one cannot resolve a discrete reflection's gain, time-arrival, or vector/direction. an echo, by nature of being a specular return (with sufficient delay), contradicts this very definition.

and the rest of your commentary is irrelevant. we are discussing reverberant sound-field. you joined the conversation out of the blue attempting to discuss echo's. the two terms are not interchangable as you mistakenly believe.


incorrect again. but why shouldn't we expect this - you have no formal training in physics nor acoustics. the extent of your knowledge is what you are able to copy/paste word-search from toole or google.

as a google user myself, i have no difficulty searching for the well-defined acoustical definitions.




still waiting for you to reference these "conditions". this is very fundamental, you should be able to google this in no time.
Edited by localhost127 - 2/19/13 at 4:33pm

sorry, but the disagreement was most certainly NOT with the casual use of the term "reverb" as slang. it was the factual evidence that RT60 is not valid if the pre-requisites are not satisfied.
just because you refer to the room decay in your living room as "reverb", does not automatically imply the energy flows are sufficient for the calculations to be valid.