Rod is much more diplomatic than I am. I hope to be as good as he is someday.
Rod Gervais wrote:
camsr wrote:
To treat the bass, how do I tune the basstraps? I want them tuned to the frequency where the sound phase cancels at the listening spot?
camsr,
refer to chapter 9 of the Master Handbook of Acoustics - the section dealing wihth Diaphragmatic Absorbers......... there's a great chart there that lays it all out........Figure 9-21 (and be sure to check out Fig. 9-34).
Chapter 19 of MHoA deals with listening room acoustics. At on point in it it is written
Quote:
It is not practical to acoustically treat each mode separately. A general low-frequency treatment is usually sufficient to control "room boom" and other resonance anomolies
Andre
Rod Gervais Moderator
Joined: Jun 8, 2003
Posts: 3188
Location: Central Village, CT
He's already read the entire book and learned everything he needs to know - so I assume he is only looking to treat the couple of specific frequencies that are going to be left after he does whatever else he intends to do.......... It was for that reason I pointed him in the direction I did.
I think he must have forgotten what Alton called that specific treatment - and was just trying to help him out (because I DID remember what he called it from when I read his entire book cover to cover and learned everything I needed to know so I could write a book).
Perhaps he should do just that - write a book - by the time he was finished he would probably remember pretty much everything he had learned........ it worked for me.......
That is (of course) if he can get a publisher to sign a contract before hand with him - otherwise the year it takes to write the book might be wasted if he doesn't do that in advance - trust me - I certainly would not have written it without the contract and advance money.....
Just trying to be helpful am I..........
Sincerely,
Rod.
_________________ Rod Gervais
Acoustics Moderator Sometimes - late at night..... when the wind whips
through the trees........ and the moon shines bright in my
face......... I think deep thoughts.......... and my head hurts.
Codemonkey Recording Org Pro Audio Group
Joined: Dec 11, 2007
Posts: 1169
Location: Scotland, UK
I might know a dentist can fix you up good with that.
Bass traps, I thought the purpose was to absorb the bass, not reflect it and cause phase cancellation (which wouldn't work anyway, and would be too much of a notch filter).
_________________ Curious button pushing Church sound guy.
In Soviet Russia, Phase Cancels You!
camsr Recording Org Pro Audio Group
Joined: Jul 19, 2006
Posts: 48
Location: Sonoma County, California
I say treat the frequencies that phase cancel at the listening spot because we hear the bass waves pressure and not its velocity, correct? And the pressure builds against the walls and must be absorbed. If that pressure is absorbed at the wall then it won't reflect and phase cancel at the listening spot?
Let's say I had a phase cancellation because of the vertical axial mode at the listening spot. Since the corner doesn't come into play, I would treat that notch with a trap tuned for that specific mode? And for treating the tangent and oblique modes use corner traps?
You guys are experienced, why am I asking all these questions!?
Rod Gervais Moderator
Joined: Jun 8, 2003
Posts: 3188
Location: Central Village, CT
I say treat the frequencies that phase cancel at the listening spot because we hear the bass waves pressure and not its velocity, correct? And the pressure builds against the walls and must be absorbed. If that pressure is absorbed at the wall then it won't reflect and phase cancel at the listening spot?
you don't have a clue - and should re-read that book you have again - because as to how modes work you don't know anything - never mind a lot.
ALL modes result in the greatest pressure buildup in the corners...... they permeate the room........
and you speak only of phase cancellation - what bout anti-nodes? what are you going to do with them?
Do you think for a moment that you can have 10 or 12 panel traps tuned to different frequencies and that they will get the job done?
Tuned Panel traps are a last resort - for whatever might remain after all other treatments have been applied - and even then - they are generally less han desirable.
Quote:
Let's say I had a phase cancellation because of the vertical axial mode at the listening spot. Since the corner doesn't come into play, I would treat that notch with a trap tuned for that specific mode? And for treating the tangent and oblique modes use corner traps?
Like I said - not a clue..........
Quote:
You guys are experienced, why am I asking all these questions!?
You claim to have learned all you need to know from the book you have - so that is actually my question to you - Why are you asking all these questions?
Reading a book and learning some pretty terms is a long way from understanding anything - to anyone who is a newbie you might sound smart and knowledgable - but to anyone who knows even a wee little bit about this - your lack of knowledge screams out to them........... but your arrogant statement screams out even more
Rod
_________________ Rod Gervais
Acoustics Moderator Sometimes - late at night..... when the wind whips
through the trees........ and the moon shines bright in my
face......... I think deep thoughts.......... and my head hurts.
andrebrito Recording Org Pro Audio Group
Joined: Jun 28, 2004
Posts: 80
Location: Almada (near Lisbon), Portugal
Just me personally, I heard the arrogance before I heard the ignorance.
Now I'm getting a stereo image with a short delay: ignorance, arrogance, ignorance, arrogance...
"You guys are experienced, why am I asking all these questions!?" /quote
If I had to guess, it is because the information was so overwhelming you made a snap decision to try out your learning. Having painted yourself into a corner you are now trying to isolate a broadband method to achieve a different goal.
camsr Recording Org Pro Audio Group
Joined: Jul 19, 2006
Posts: 48
Location: Sonoma County, California
You guys have me wrong. I didn't come here to be arrogant and say I know a lot. My main point of confusion is how to use so many acoustic devices to treat my room. I understand how treatment for specular reflections work, but the low room modes I just don't understand. I looked up nodes and antinodes and I know why it causes problems but I can't SEE it in my 3D third eye view.
For antinodes, since it's wave velocity it should be treated with just open absorber like cotton balls or something soft. Treatments like corner traps work by changing that pressure to velocity inside the trap and forcing it through an absorber. At least that's what I got from reading around.
And I'm taking from Rod's response that corners matter even with axial modes. Stupid of me not to realize that earlier. I just don't see how all the modes make the bass disappear in the middle of the room. If someone could explain that I would be satisfied. Thanks.
Maybe simplifying the physics of mathematics down to a video will make sense to someone who's read Everest?
Take note of what happens in the corners. It's a pretty graphic example of what the pressure gradient action looks like in a room... oh and the harmonic nodes really stand out too.
For someone who's attempting to come across as a knowledgeable well read, you seem to be the only one who thinks that a single source of information can possibly give you all the insight into the acoustics and the science of building a good room out of a marginally decent existing structure.
I'm sorry, but while I think Everest's MHofA is an essential primer, it's not the complete authority. Not because Everest is wrong, but because there are others who are improving on his work and working with newer construction methods and materials.
Beranek's work is also an interesting read, but try Newell and Gervais as well... You might just be surprised to find out that there are indeed some construction methods that pseudo counter Everest's initial findings... and work better... again, because of materials such as Green Glue and updates to construction codes.
You should also spend some time rooting through the archive's of Studio Tips and Sayer's sites.
_________________ The insanity can be seen in bigger pix and greater detail at: http://www.dmmobile.com
"A committee is a cul-de-sac down which ideas are lured and then quietly strangled." -- Sir Barnett Cocks (1907 - 1989)
Rod Gervais Moderator
Joined: Jun 8, 2003
Posts: 3188
Location: Central Village, CT
For antinodes, since it's wave velocity it should be treated with just open absorber like cotton balls or something soft.
Wrong - completely wrong......
Listen - you are looking at the outcome and not the cause...........
To heck with what's happening in the middle of the room - and focus on what's happening at the edges and corners.......
The node and antinodes are caused by exactly the same thing - at exactly the same time - and for a single tone they both exist in the room at exactly the same time.
Play one steady tone in your room, walk around and listen to the whole series of peaks and dips that exist..........
all caused by one tone - in one room.
Quote:
And I'm taking from Rod's response that corners matter even with axial modes. Stupid of me not to realize that earlier. I just don't see how all the modes make the bass disappear in the middle of the room. If someone could explain that I would be satisfied. Thanks.
Not just the middle........ 1/4 wavelength, etc.
It's simple - wherever a wave is in sync with itself there is constructive interference and a peak appears......... wherever it is out of sync there is destructive interference and a dip appears.........
It occurs with all modes - regardless of what the cause is - and IS WHAT A MODE IS.
All mode behave exactly the same - with the only difference being the amount of interference,
Axial modes are the most powerful........
Tangential modes require 2 times the power of an axial mode to produce the same change in amplitude (pressure level),
Oblique modes require 4 times the power of an axial mode to produce the same change in amplitude (pressure level).
But they are all the same animal in the end - they are all modes.......
Can you see it now?
Rod
_________________ Rod Gervais
Acoustics Moderator Sometimes - late at night..... when the wind whips
through the trees........ and the moon shines bright in my
face......... I think deep thoughts.......... and my head hurts.
BobRogers Recording Org Pro Audio Group
Joined: Apr 04, 2006
Posts: 1257
Location: Blacksburg, VA
Here's a bit of perspective from someone who has been teaching undergraduates for almost 30 years. camsr is in a classic "sophomore slump" phase of learning acoustics. He has learned a whole bunch of things about half way and has them all mixed up. He thinks he has learned a lot (and he has) but it's so scrambled that he comes off as if he knows less than when he started. He's hoping that a few quick ideas will get it all straightened out and he's impatient for it to come together. Frustrating time for a student and (unless you are used to it) a teacher. There is a long road ahead if you really want to understand this. Be patient. (For those answering questions - remember he's trying to learn stuff that it took you months or years to master.)
Rod Gervais Moderator
Joined: Jun 8, 2003
Posts: 3188
Location: Central Village, CT
I have the Master Handbook Of Acoustics already and have read it from front to back. What is Build It Like A Pro going to tell me besides what I already know?
Now I could care less if he buys my book or not - it could be any other book that he was recommended - it's the attitude that ticks people off - it's arrogant and condesending - and actually says that he needs no help (anyone who read Everest and got it all would hardly need any help from anyone on this board - they would be able to teach us a thing or 2).
Now - I have nothing but respect for the teaching profession - and can appreaciate what it entails - but when someone rejects good advice by stating that they know it all - it makes it difficult for anyone to want to assist them to any great degree.
And until a student accepts that he/she really doesn't know it all - they are beyond help - and become simply adversarial in their nature.
You cannot help anyone like that.
Perhaps he is begining to come around - perhaps not = only time will tell.......... but at the very least I offered an honest response to the past post- - and not sarcasm.....
Thanks for your take on this - it always helps to get a clean objective analysis on the conditions when the waters become muddied.
Sincerely,
Rod
_________________ Rod Gervais
Acoustics Moderator Sometimes - late at night..... when the wind whips
through the trees........ and the moon shines bright in my
face......... I think deep thoughts.......... and my head hurts.
BobRogers Recording Org Pro Audio Group
Joined: Apr 04, 2006
Posts: 1257
Location: Blacksburg, VA
I saw the statement and it is a classic symptom. The classic student going through this kind of thing has read one book, it's a good book, and he balks at the fact that to learn the stuff in it he's going to have to read several more on exactly the same material. He's never had to learn a subject this complicated. Before he's had to read one book, learn the answers, become an expert. It's not necessarily arrogance - just that in the past all he has had to do was read one book, ask a few questions to clear up a few details, work a few examples, and ace the test. He keeps looking for a quick fix. He hasn't figured out that it is a very different game and what worked in the past isn't going to work now.
Now, I have no idea how much of this applies to camsr, a few message board posts don't usually tell the whole story. But I've seen this with a lot of students (hes and shes) and I'm guessing that is what is going on.
camsr Recording Org Pro Audio Group
Joined: Jul 19, 2006
Posts: 48
Location: Sonoma County, California
When I said "What is Build It Like A Pro going to tell me besides what I already know?" what I really meant was "What is Build It Like A Pro going to tell me besides what I can find in MHoA?". Don't take it personally Rod, I am on a budget and you don't save money by spending a lot of it.
What I am trying to understand is how to build a basstrap for my particular needs here in my studio. I would like to build my own because I can save space by integrating them into the wall. But I am also hesitant to buy any premade traps because I don't know how well they will work for me. I still have to do some measurements in the empty room and am waiting on a friend with the mic and amp.
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