MJL21193 said:
Add damping to the panels walls. Adds mass with no increase in stiffness... pushes panels resonant frequency down.... bracing needs to be closer to counter this .... hence more bracing...
If the panel resonances are high and not excited then there is no resonance to damp so why try to cure a problem that doesn't exist?
dave
planet10 said:
Make a large bell - it rings at a low frequency, difficult to halt the ringing (damp) once started. Melt this bell down and make smaller bells - they ring at a higher frequency, easy to damp the ringing.
Damping is not adding mass for nothing, it's a system for absorbing vibration. No extra bracing needed.
How is that when you drive up the panels resonant frequency, that it won't be excited? What resonances are you trying to damp in a 4" driver? How is it that the driver basket can have its resonance excited when the box panel does not?
Going back to the bell analogy, how much damping material would it take to critcally damp the large bell? If we made 100 smaller bells from it, would thedamping material for each be 1/100 of what is needed for the large bell? Most likely not, as the frequency to be damped is higher, therfore easier to damp.
MJL21193 said:
You must have missed the part where i stated, and Svante showed a chart, that the exciting energy decreases as the square of the frequency. A panel will not resonate unless a critical quantity of energy at the panel resonance is input into the panel. And if the panel is made of an inherently well damped material like plywood, it have to reach that energy threshold while the panel is draining the energy. If you get the panel resonance high enuff, there is never enuff (close to) instantaneous energy to overload the inherent damping in the panel. It is like trying to fill a container to the top when there is a big leak at the bottom and your delivery tool is a straw. Not being excited, it as if the panel has no resonance at all... so again, why would i complicate things to fix a problem that doesn't exist, especially when that fix will actually make things worse?
John, after extensive discussion in theother thread, one could get the feeling that most of it went over your head...
A basket/motor is a very different beast than a wall panel. It is not inherently well damped like a plywood panel... and a small resonance has a much more profound affect on the sound then a small panel resonance since it is directly connected to the speaker (actually it is part of the speaker)...
... and did you also miss the part where you got 2 fixes for the price of 1 -- just as important, in some cases more important, is the shaping of the basket exit. Even if you have a basket that doesn't need any damping, it can benefit from careful shaping.
dave
planet10 said:
Yes, right over my head.
I found it interesting that you would advocate basket damping but not panel damping. I already agreed that basket damping has some value, and as for the shaping to streamline airflow? Could have some merit.
You have finally put into clear words how it is that the system of speaker building that you have adopted works. Sounds good to hear it explained like that.
I (as usual) have a problem though. We have been refering to resonance a lot, and it seems to be a kind of benchmark for noise. What about in frequency spectrum above it, and below it? You yourself said it's the noise 40dB down that will ruin the way a speaker sounds.
I know that there >might< not be enough enery to excite the panels resonant frequency, but it will vibrate none-the-less. This I know from my own speakers built from BB plywood with no damping.
Using your own analogy, the container doesn't overflow, but we can still hear the water running.
hey, dave.
I've read a number of threads and comments you've posted here, and I think I'm forming an idea of your design philosophy, but now I've got a question.
I understand you to prefer plywood (BB) to MDF for speaker cabinet making. There have been a number of discussions about the practical aspects of building with one or the other, but I thought your primary reason was sonic. However much damping plywood has, I thought MDF was more damped. So I had figured your designs to push primary resonances out of the passband, but to use some level of vibration in the cabinet constructively. The double horn designs you've been involved with (which I find super neato, from my cursory inspection) don't seem to damp out much high frequency from the horn mouth - at least not compared to the venting styles I'm more used to seeing. So anyway, I've taken you to be a "controlled resonance" type of guy, where I figured folks like MJL to be more "eliminated/damped resonance" school of thought. (Not to put words in either of your mouths...)
But now you say "I use finese to keep my boxes from being a sound source, not brute force."
If your box isn't a sound source, then why do you prefer the sonic properties of plywood to MDF? Preference of one over the other seems to be an acceptance of the proposition that they emit sound (have sonic properties), though I suppose your position could be that the MDF becomes an acoustic source but that the plywood does not.
- Adam
I've read a number of threads and comments you've posted here, and I think I'm forming an idea of your design philosophy, but now I've got a question.
I understand you to prefer plywood (BB) to MDF for speaker cabinet making. There have been a number of discussions about the practical aspects of building with one or the other, but I thought your primary reason was sonic. However much damping plywood has, I thought MDF was more damped. So I had figured your designs to push primary resonances out of the passband, but to use some level of vibration in the cabinet constructively. The double horn designs you've been involved with (which I find super neato, from my cursory inspection) don't seem to damp out much high frequency from the horn mouth - at least not compared to the venting styles I'm more used to seeing. So anyway, I've taken you to be a "controlled resonance" type of guy, where I figured folks like MJL to be more "eliminated/damped resonance" school of thought. (Not to put words in either of your mouths...)
But now you say "I use finese to keep my boxes from being a sound source, not brute force."
If your box isn't a sound source, then why do you prefer the sonic properties of plywood to MDF? Preference of one over the other seems to be an acceptance of the proposition that they emit sound (have sonic properties), though I suppose your position could be that the MDF becomes an acoustic source but that the plywood does not.
- Adam
planet10 said:
A panel can vibrate at any frequency without resonating. By your own admission the driver will transfer energy to the box (in the form of vibrations). Vibrations from any source, at any frequency will be a source of sound (noise).
Not much finese involved in my construction projects? Too much brute force utilised? I don't think so.
AdamThorne said:
I'm the "let the drivers do the talking" type. For the most part I'm not looking for any contribution from the box at all, not reinforcement, not noise.
I use bracing, I use damping, I use CLD - I use what works for what I'm trying to do.
I have built a pair of speakers using Dave's method. I can't say they sound bad. In order to assess thier quality, I'd have to build a second pair the way I normally would. It's my contention, that there probably would not be a great difference, if any at all.
Think for a moment of a driver's cone like you are sitting on a magnet pushing an air by hands. The heavier is the driver + wall against an air, the lower will be amplitude of your oscillations seating on a magnet. Also, on lower frequencies will be the same amplitude of your oscillations (thanks to Sir Isaac Newton, we know that!)
Now consider, that wall the speaker you are seating on is mounted on is flexible. And every time you push the air the wall with you sitting on a speaker mounted on the wall goes back. Do you feel that oscillations?
You will definitely feell them, even without any resonances. Now, suppose the wall is heavier... According to Sir Newton, will be amplitude of it's oscillations lower on the same frequencies? Yes! It will be lower! But on some low frequencies it will still resonate...
Now, suppose the wall is buried into a sand. The sand accepts a mechanical energy turning it into a heat... Resulting Q will be lower... Amplitude of oscillations will be lower (both because of higher mass against moved air and loss of energy in the sand).
Do you understand now how damping of walls work?
I was born in Siberia where people build stoves from bricks. Stoves are good and usable appliances, right?
Are speakers good and usable?
Why nobody build speakers of bricks?
Now consider, that wall the speaker you are seating on is mounted on is flexible. And every time you push the air the wall with you sitting on a speaker mounted on the wall goes back. Do you feel that oscillations?
You will definitely feell them, even without any resonances. Now, suppose the wall is heavier... According to Sir Newton, will be amplitude of it's oscillations lower on the same frequencies? Yes! It will be lower! But on some low frequencies it will still resonate...
Now, suppose the wall is buried into a sand. The sand accepts a mechanical energy turning it into a heat... Resulting Q will be lower... Amplitude of oscillations will be lower (both because of higher mass against moved air and loss of energy in the sand).
Do you understand now how damping of walls work?
I was born in Siberia where people build stoves from bricks. Stoves are good and usable appliances, right?
Are speakers good and usable?
Why nobody build speakers of bricks?
I get that for sure... that is why you will usually find my speakers have a magnet brace to couple that reactive force to as much of the enclosure as possible (instead of just concentrating it into the weakest panel in the box, the one with all the big holes cut into it) and why i will rarely build a woofer that is not push-push (active cancelation of the Newtonian force)
dave
AdamThorne said:
I had a nice post in reply much earlier in the day but it got eaten by a database glitch.
Until recent comments by a couple people i had no reason to dispute that "common knowledge" Now i'm not so sure... BB is essentially a pre-built constrained layer panel.
Controlled resonance only in the sense that i want to control where the resonances are so that i can avoid having them excited. We both have the same goal, to not have the cabinet panels contribute to the sound of the box. From years of experience -- including a phase where i built boxes in a similar manner to John -- i have developed my current technique which is much more about finesse than brute force, works better than brute force, and you can still lift the cabinet without a helper.
This unsolicited comment from someone just recently exposed to a set of Fonkens pretty much tells me i am achieving my goals BTW, I think I've finally put my finger on exactly what it is I like about them so much. They don't sound ANYTHING like a box speaker whatsoever. All box speakers I've ever heard sound like box speakers, but these don't. I still haven't figured out exactly what it is they sound like, but whatever it is, it ain't a box speaker.
Plywood is better suited to helping me achieve my goals in a cabinet. And in the end it sounds better. MDF has a problem with energy storage... It leaks time delayed energy that wipes out the subtle detail in the music that are required to make it sound more real.
I started out with K3 particle board, graduated to HDF (often laminated with formica inside & out to increase the stiffness), had a short fling with MDF (it was free but those cabs were not very pleasing sonically) and then plywood. I keep looking for ways of improving things, but given standard made from flat panel speaker building technology i've not found anything yet that ptovides the combination of sonic performance and cost effectiveness of multi-ply.
dave
MJL21193 said:
OK lets get anal about the definition of vibrating. Everything is vibrating. The definition of heat is how much the substance is vibrating. But that is uncorrelated vibration and most of it cancels out before it can have any sonic affect. Correlated vibration -- the kind that affects the gross sonic radiation of a speaker panel -- is always associated with a panel resonance.
dave
planet10 said:
Resorting to name calling you are, anal I am? First an ignorant, dim witted brute, now this??
Your panel doesn't resonate, just vibrates along, producing low level noise.
I need to complete my research into panel properties, to see how bracing and damping compare, before we can continue this discussion.
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