A resonance with a broad Q can accept frequencies over a broader range to excite it (so it is easier to excite) and it dissipates any resonance over a longer period giving more time smear. It cannot be considered on its own thou, and i would not put a hi Q resonance anywhere where it is likely to get excited.
dave
dave
planet10 said:
Sorry Dave, I'm not getting it either. Nothing in these recent posts seems really clear, except that we went from speaker frames to cabinet walls.
My understanding of your technique is to use intelligent, well designed bracing instead of the brute force methods such as tar, lead and sand.
What I don't understand is the technique. How does one figure out where and what to brace so that it kills the audible vibrations in the cabinet or baffle? And does it really work better than other methods, or is it just more practical?
planet10 said:
Apparently I'm not the only one who's not getting it.
I'm going to continue shortly with the practical tests that I started in the other thread, should shed some light on what is real, and what is assumed to be real.
It is a good discussion. I know you're not used to someone doggedly questioning your methods, and I'm not trying to make you change your method of speaker building. I'd just like to point out to anyone reading these discussions that there is absolutely nothing wrong with using other materials beside BB plywood to build speakers with. Also that damping is a crucial part of a speaker, and is not counterproductive.
Pretty straightforward. As the Q of a resonant system decreases the peak amplitude drops but the affected frequency range increases. Viewed amplitude vs. frequency, tall sharp spike vs. low broad bump. The ear reacts differently to each case, the question of which is audibly most objectionable I'ld imagine is as much related to program material as cabinet material.
"As the Q of a resonant system decreases the peak amplitude drops but the affected frequency range increases"
true, but if damping is used properly, most of this wideband vibration will translate to heat, instead or re-transmitted acoustically.
if misapplied (no translated to heat), it will re-transmitted(acoustically).
so it depends on the application.
Hartono
true, but if damping is used properly, most of this wideband vibration will translate to heat, instead or re-transmitted acoustically.
if misapplied (no translated to heat), it will re-transmitted(acoustically).
so it depends on the application.
Hartono
planet10 said:
I don't believe BB plywood acts as a constrained layer - it's laminations are solidly glued, there is no movement within the panel.
A true constrained layer damps vibrations by the inner layer absorbing the energy and flexing via a "lossy" medium against the outer layer. This act of flexing burns off the energy in the form of heat from friction. This requires the layers to move (in a limited sense - thus "constrained") independently of one another.
Plywood does not do this.
planet10 said:
Hi Dave,
What is it about MDF that makes you believe it stores energy? And how is it that plywood doesn't? Which material has the higher Q?
A swinging pendulum is storing energy, just as an oscillating panel is. When the pendulum stops swinging, all of the energy has been lost (usually through friction with the surrounding air).
Same for a panel.
If a panel is critically damped, it will not oscillate, and will not store energy. A panel that is not damped will oscillate and will store energy, be it wood, MDF, metal, plastic or even BB plywood.
panomaniac said:Nothing in these recent posts seems really clear, except that we went from speaker frames to cabinet walls.
Yea, i'm going to merge the most recent stuff with the discussion where it got started.
Exactly. Move the panel resonances to where they are unlikely to get excited and so that the inherent damping in the panels is sufficient to kill everything else.
Experience no doubt helps, as you get a feel for how far to go. Being able to easily build it also plays a role on how far to go (ie trapezoidal subpanels would be better than rectangular panels but are harder to execute), The premise is that you create light, stiff panels that have high Q non-coincedent resonances at high frequencies where there is little energy to excite them. You have to then have high frequency energy in a very narrow bandwidth that injects energy at a high enuff level over a short enuff period of time to excite the resonance. If that threshold is not reached the energy is converted to heat (uncorrelated vibration). If the resonance is not excited then as far as audio is concerned the panel has remained rigid/unmoving (ie it has done its job). An artificial stimulus at high enuff level (ie a sine wave) might be able to exite them (so they could be objectively explored), but the dynamic transitorry nature of music is very unlikely too.
Yes it really works. And in my experience works better than anything else i have tried.
dave
Hartono said:
Undoubtedly correct but it also partially begs the question. The ear may be so much more sensitive to the broad/low bump case that a great deal more energy loss is required to make it less objectionable than the sharp spike. Not saying this is correct or proven, only suggesting that how the ear weighs stimuli is potentially a trumping factor over a straight energy dissipation/release analysis. Harman or Wilson have probably examined this in depth.
"The ear may be so much more sensitive to the broad/low bump case that a great deal more energy loss is required to make it less objectionable than the sharp spike. Not saying this is correct or proven, only suggesting that how the ear weighs stimuli is potentially a trumping factor over a straight energy dissipation/release analysis."
I think the problem in properly damped enclosure is not the panel sound itself. it's the reflection inside, coming back to the driver, and the stuffing/damping material non-linearity. and energy storage.
In modeling /making analogy of something it's sometimes good to go to the extreme to see what happen in the larger scale.
Infinitely stiff and heavy wall will vibrate very little, but the reflection inside the box still happen and there's no perfect absorbing material exist, the damping material non linear characteristic combined with lots of reflection inside the enclosure form energy storage, release with long decay. this will affect the sound coming out from the driver and the port.
the damping material will translate the vibration to heat, but it also affect the compliance of the air inside the box in non-linear way as well , disturbing the driver/port behaviour. all this happen while the panel itself vibrate very little.
Hartono
I think the problem in properly damped enclosure is not the panel sound itself. it's the reflection inside, coming back to the driver, and the stuffing/damping material non-linearity. and energy storage.
In modeling /making analogy of something it's sometimes good to go to the extreme to see what happen in the larger scale.
Infinitely stiff and heavy wall will vibrate very little, but the reflection inside the box still happen and there's no perfect absorbing material exist, the damping material non linear characteristic combined with lots of reflection inside the enclosure form energy storage, release with long decay. this will affect the sound coming out from the driver and the port.
the damping material will translate the vibration to heat, but it also affect the compliance of the air inside the box in non-linear way as well , disturbing the driver/port behaviour. all this happen while the panel itself vibrate very little.
Hartono
OK, Dave - now I understand. Your goal is to change the resonance of the panels so that they will not matter in the audio band. You do this rather than massive damping to save weight and expense, right?
For example, if you wanted to span the Golden Gate in S.F. you could build a massive mountain of stone and concrete, or you could take an engineering approach and build an elegant suspension bridge. Both would get the job done, but at what weight and expense?
Taking the bridge idea further, a well designed bridge will be stronger than a somewhat more massive bridge that is not well designed.
This is where I have trouble. A panel may not resonate, because its resonant frequency is not being excited, but it can still vibrate at other frequencies because of the air pressure inside the box - or can it? That vibration may not be as large as a panel resonating at it's peak, but it could be heard, none the less.
Are you saying that with proper bracing you can move all vibrations out of the audio band, or far enough down in level so as not to be heard?
For example, if you wanted to span the Golden Gate in S.F. you could build a massive mountain of stone and concrete, or you could take an engineering approach and build an elegant suspension bridge. Both would get the job done, but at what weight and expense?
Taking the bridge idea further, a well designed bridge will be stronger than a somewhat more massive bridge that is not well designed.
planet10 said:
This is where I have trouble. A panel may not resonate, because its resonant frequency is not being excited, but it can still vibrate at other frequencies because of the air pressure inside the box - or can it? That vibration may not be as large as a panel resonating at it's peak, but it could be heard, none the less.
Are you saying that with proper bracing you can move all vibrations out of the audio band, or far enough down in level so as not to be heard?
panomaniac said:
Yes... i like the analogy
If the panel is moving in any corelated manner it is because it is resonating. The energy in the box from air pressure is a lot less than directly transmitted into the box by the driver (unless we are talking about a push-push woofer with good coupling where most of the direct energy transfer can be actively cancelled). In a single driver system the maximum energy that can be transmitted by air pressure is a 1/3 of the total energy and that in a sealed box. In practise it is a lot less because air is squishy, you are using airspace damping, and in many cases energy is being used for bass augmentation (any box with a hole in it)
That is certainly the goal.
dave
OK I have read the complete posting and while not able to follow all of the arguments presented think I'll straddle the fence for a while.
I do not think any0one here in melbourne has affordable stocks of BalticBirch so I want to ask peoples opinion of the combination of chip(particle)board and MDF glued together??
It was my thinking that the stiffness of the chipboard would help stiffen the MDF and experience has told me that the glue acts as a damping factor.
I have no experience with other box building materials.
I do not think any0one here in melbourne has affordable stocks of BalticBirch so I want to ask peoples opinion of the combination of chip(particle)board and MDF glued together??
It was my thinking that the stiffness of the chipboard would help stiffen the MDF and experience has told me that the glue acts as a damping factor.
I have no experience with other box building materials.
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