Yes Glenn, this is exactly what I'm asking. However, I envision the panels are fully free to flex, unrestrained by the practical matter of the edge joints that might skew things. --Ethancan we compute the absorption characteristics of these 2 panels?
Panel Absorbers
Originally posted at johnlsayers.com, topic 9538.
i wonder if Eric's MSM spreadsheets have any practical value in computing this? I would prefer to have practical calculations rather than just pure theory since then I can, er, use that information for other purposes... :twisted:
Ethan:
I thought of a good example. A Florence Flask. You scale linearly, but the volume changes by the cube.
Andre
That seems too far away from a panel trap to apply here. --EthanA Florence Flask. You scale linearly, but the volume changes by the cube.
Yes. Back in the threa it waqs brought up as a correction for the person who thought volume was the wrong word. Little application for us. AndreThat seems too far away from a panel trap to apply here. --EthanA Florence Flask. You scale linearly, but the volume changes by the cube.
I agree with you here, it's a good point.I can't tell you the best ratio of mass versus spring, but I can say for sure that there is an ideal to aim for. In electrical circuits you can tune an inductor and capacitor to the same center frequency using many different values. But the efficiency of the tuned circuit falls off as you get away from the ideal balance of values. A tiny capacitor and huge inductor is inefficient, and vice versa. In an electrical circuit the ideal balance is achieved when both components have the same impedance at the center frequency.Another assumption I hope you guys an approve, is that it's more efficient to create a panel trap for a certain center frequency from lighter material and greater depth then a heavier material and lesser depth? I think it would start to vibrate faster, therefor improving the "attack" of the panel.
But I do disagree with you here. Suppose you have the same amount of energy that suppose to move a very light membrane vs. a very heavy membrane. Of coarse the "motor" will not be able to move them exactly as fast, nor the same suspension system will act the same once the input is interrupted. This is one very important reason why you don't see 12" tweeters! If you have an array of panels in the rear wall, you sure want them to start working quick before significant phasing will occour."Attack" is the wrong concept, and is wrong in the same way that some people believe one subwoofer can be "faster" than another. I see people argue about subwoofer "speed" all the time in audiophile forums, but it's not the right concept for subs or panel traps.
I would be really glad if someone can aswer these questions.I have a question. Suppose you measure your listening position and some boundry point in the room, let's say, the middle of the side wall. If you see a peak in the boundry and a corresponding peak/null in the listening position then you know that you can choose which trap (low bass/high bass) to put in there. So far so good, right? But what if you see a null in the boundry that is a peak/null in the listening position? Should you look for the place in the room which this problem frequency peaks? I'm looking at the room mode application in here: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2441 In that simulation, you can only see the frequencies that are peaking at the boundries. I suppose it makes sense in regard to resonators, which respond to maximum pressure and not velocity. So, should I ignore nulls in the boundry measurements, in regard to bass trapping? How will I decide what IS best to put in that spot?
But a tweeter is not trying to reproduce bass frequencies, and a 12 inch speaker is not trying to generate 10 KHz. The key point is to match the mass of the panel with the frequency of interest. If you're targeting 70 Hz with a panel absorber, the panel does not need to move quickly. This may seem to defy common sense, but it's correct.But I do disagree with you here. Suppose you have the same amount of energy that suppose to move a very light membrane vs. a very heavy membrane. Of coarse the "motor" will not be able to move them exactly as fast, nor the same suspension system will act the same once the input is interrupted. This is one very important reason why you don't see 12" tweeters!
Again, as long as the panel can vibrate easily at the frequency of interest, that's all that matters. --EthanIf you have an array of panels in the rear wall, you sure want them to start working quick before significant phasing will occour.
All frequencies "peak" at the boundaries because that's where the pressure is greatest. Our ears respond to pressure, as do SPL meters.But what if you see a null in the boundry that is a peak/null in the listening position? Should you look for the place in the room which this problem frequency peaks?
There are two types of absorbers - those that work on velocity (fiberglass and foam) and those that respond to pressure (panel traps). Bass traps of either type work best at locations where the bass is loudest. This short article might help: http://www.realtraps.com/lf-noise.htm --EthanHow will I decide what IS best to put in that spot?
Well I measured the boundries and there sure are nulls as well as peaks.All frequencies "peak" at the boundaries because that's where the pressure is greatest. Our ears respond to pressure, as do SPL meters.But what if you see a null in the boundry that is a peak/null in the listening position? Should you look for the place in the room which this problem frequency peaks?
I know about velocity vs. pressure absorption - and anyway panel traps are better- otherwize I wouldn't bother to build them- what i was asking is if nulls should be visually ignored from the measurements in order to decide whether to put a high or low panel trap.There are two types of absorbers - those that work on velocity (fiberglass and foam) and those that respond to pressure (panel traps). Bass traps of either type work best at locations where the bass is loudest. This short article might help: http://www.realtraps.com/lf-noise.htm --Ethan
Suppose you got a 1.0 NRC panel. A bass signal hits it. if the panel will not respont immediatly, then it will reflect the sound, am I correct? By that logic (and excuse me if I'm mistaken), your claim should be interpreted as if the panel peaks to full capacity immediatly...?But a tweeter is not trying to reproduce bass frequencies, and a 12 inch speaker is not trying to generate 10 KHz. The key point is to match the mass of the panel with the frequency of interest. If you're targeting 70 Hz with a panel absorber, the panel does not need to move quickly. This may seem to defy common sense, but it's correct.But I do disagree with you here. Suppose you have the same amount of energy that suppose to move a very light membrane vs. a very heavy membrane. Of coarse the "motor" will not be able to move them exactly as fast, nor the same suspension system will act the same once the input is interrupted. This is one very important reason why you don't see 12" tweeters!
Adam, you're correct. Analyzing modes, even the simplest Axials shows you these nuls at the alongside walls, and with complete sound field analyzes you will encounter them too. I even wonder in how far the efficiency of porous corner absorption is related to that. You have plus and minus pressure fields. Between them you must have nuls are there shouldn't be plus and minus either. EricWell I measured the boundries and there sure are nulls as well as peaks.All frequencies "peak" at the boundaries because that's where the pressure is greatest. Our ears respond to pressure, as do SPL meters.
Sorry I didn't understand that one...Between them you must have nuls are there shouldn't be plus and minus either. Eric
Check the animations on this page:
http://web.archive.org/web/200108092000 ... terOne.asp
Do you understand what's happening there?
You have plus (over-pressure) and minus (under-pressure) areas oscillating around 0 points. These 0 points are what you refer as dips or nulls. They are as well at the boundaries as free in space.
A real sound field can be a complex thing, but will also show such phenomena.
You can probably find more via this thread as well:
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=6210
Why would it not "respond" immediately? Also, Eric (and you) are correct about nulls at boundaries. I wasn't considering the side walls for length modes or vice versa. --Ethanyour claim should be interpreted as if the panel peaks to full capacity immediatly...?
And lots of other stuff.I wasn't considering the side walls for length modes or vice versa. --Ethan
As Jeff reminded both of us recently, give it a friggin' break, okay? Sheesh...And lots of other stuff.
Ah yes, here it is:
You're both uniquely incorrigible. :evil: :P Eric, ignore Ethan. Ethan, stop poking Eric. Geez. :roll:
As Jeff reminded both of us recently, give it a friggin' break, okay? Sheesh...And lots of other stuff.
1) You activate things which are not needed here, and spread over 2 posts to make sure it jumps out enough, while you easily could integrate it in your first post even without "edit" notion at the bottom. Aren't you the guy stating you stick to the physics and content? I only replied related to physics and content. 2) You do NOT need to use Jeff when you assume it serves you. I can't very well imagine Jeff does appreciate this as well (but I agree, knowing you, he asked here to be used, giving you a pseudo useful tool). Further if you like to USE Jeff, then read also that Jeff wrote: Ethan stop poking Eric. Be a man and speak for yourself, I never use others to hide behind. And stay on topic, if you have to say something. And don't play the eternal victim, within some days a complete and ugly thread is trashed at Recording Org, caused by you. Playing this roll does poke me, because I know it's a roll for public use, in NO way meant to tell me whatever. Further Jeff tells me to ignore you, which I do try, unless I react to incorrect information you give to others. For me that's not about you but these others. I stayed on topic. You did/do NOT. 3) I gave very to the point physical correct information here.Ah yes, here it is:You're both uniquely incorrigible. Evil or Very Mad Razz Eric, ignore Ethan. Ethan, stop poking Eric. Geez.
- You started with a wrong comment (same you wrongly tells for years already).
- I explain short, referring to related animations proving my point.
- For one or the other reason you see that your long lasting typical 1/4 wave argument doesn't seem to fit.
- In stead of leaving it as is, you humbly admit (in function of others) not considering the side walls for length (read axial) modes, as some accidental oversight, while we both know this is based on a wrong basic principle, which we discussed for ages already. I think it's the first time that you very, very, very hesitating accept, that your, always as proof referred, stylized 1/4 wave 2D picture is only part of acoustics.
- I correct this again with a very short sentence and as correct as can be.
- You choose again not to let this be and go in your victim role, activating something which shouldn't be activated and drawing someone in this who did not asked to be drawn in this.
- Maybe it even has the positive effect now that something in your mind starts comprehending this in relation to this over simplified 1/4 wave topic.
Ethan: Ignore Eric.
Eric: Stop poking Ethan.
Also, in his defense, Ethan made a mistake and owned up to it. No reason to bring old garbage into this thread. ;)
IMO, at least.
Jeff:
Stop poking Eric. And that's without smiley.
And no he didn't. We're only still at the axial mode stage.Ethan made a mistake and owned up to it. No reason to bring old garbage into this thread.
Not poking anyone; just trying to help keep things calm around here. And that's with :). Peace,Jeff: Stop poking Eric. And that's without smiley.
Jeff, how the hell is life treating you? It's been a coons age......... RodNot poking anyone; just trying to help keep things calm around here. And that's with :). Peace,Jeff: Stop poking Eric. And that's without smiley.
The minute Eric wrote "and other stuff" I felt a flame war coming...
Gentlemen, cut the crap and stay of each other's back okay.
We're all adults here, right!
(I'll buy if that helps...)
Peachy, Rod. How've you been? :)Jeff, how the hell is life treating you? It's been a coons age......... Rod