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Multi-Way Conventional loudspeakers with crossovers

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Old 27th April 2008, 03:53 AM   #271
gedlee is offline gedlee  United States
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Default Re: Re: Re: Re: Re: Re: Re: Re: and???

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Originally posted by MJL21193
My lack of confidence in it (MDF) as a brace material hasn't changed.

I still don't believe there is an audible difference between these materials.
Aren't these a contradiction?
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Old 27th April 2008, 04:05 AM   #272
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Default Re: Re: Re: Re: Re: Re: Re: Re: Re: and???

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Originally posted by gedlee


Aren't these a contradiction?
In the wonderful world of audio everything and nothing is a contradiction it would seem.
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Old 27th April 2008, 04:15 AM   #273
dlr is offline dlr  United States
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Originally posted by planet10


Which -- barring a bit of arithmetic qymnastics is exactl what i said.
And I believe is essentially not meaningful. That was my point.

Quote:

It is not the only thing. Raising the panel resonance frequency also means that the resonance is less likely to get excited in the 1st place. Push it high enuff and the natural damping in the panel material is suffiicent.
Please explain why is it less likely. Facts and details, please, especially for the case of full-range drivers (your preference, no?) where it's highly unlikely that resonances will be pushed outside of that driver's passband.

For your latter statement the suggestion of using a light material that has less internal damping is contradictory to your belief that MDF is not a good material. If you want natural damping to be effective, you need a material that has getter damping properties. BB is not better compared to MDF from what the links presented earlier.

Quote:

Earl's 2 points that brought this part of the discussion up, where that the vertical brace in the Fonkon was oriented incorrectly and that a preferred bracing was a set of point braces, both points which are incorrect based on the research done all that time ago, and information that has been readily available for a looonnnggg time.
I don't accept that as factual at all at this point, especially when one gets into what counts, audibility. You have no data to counter Gedlee who does, unless you are going to challenge the veracity of what he says on that.

The final determinant is audibility as far as effectiveness is concerned. I haven't seen anything presented so far, yours included, that is in any way a reputable, factual analysis of audibility with respect to the various methods of bracing and at what point bracing, any kind, is of diminishing returns. Given Gedlees background I, for one, will accept his comments with regard to tests made on audibility. My own experience is as I said before, boxes are overrated. But it may be that full range drivers have this as an additional drawback in comparison to good 3-way, true full range systems since it's impossible to separate anything when using "full range" drivers alone.

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Old 27th April 2008, 04:25 AM   #274
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Default Re: Re: Re: Re: Re: Re: Re: Re: Re: and???

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Originally posted by gedlee


Aren't these a contradiction?

Hi again Earl,

No, how do you see contradiction? When I talk about bracing, I'm talking about structure again. MDF will not make as strong a brace as plywood.
The point is to effectively brace the box, then there shouldn't be an audible difference.
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Old 27th April 2008, 04:50 AM   #275
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Default Re: Re: Re: Re: Re: Re: Re: Re: and???

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Originally posted by MJL21193
I can be a bit daft about some things at times.
John, are you saying you just realised the reason why you've been bracing your cabinets?

What did you think it was doing before?
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Old 27th April 2008, 04:57 AM   #276
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Originally posted by dlr


Please explain why is it less likely. Facts and details, please, especially for the case of full-range drivers (your preference, no?) where it's highly unlikely that resonances will be pushed outside of that driver's passband.


I'm not Dave but...if I understand it correctly:
50% of the acoustic energy that the box has to deal with is from 350Hz down. If the resonant frequency of any panel in the box is in that region, the panel will (obviously) resonate.
The higher you go in frequency, the less energy there is to excite resonances. Less energy to excite plus minimal damping will stop it before it starts. Dave says that the plywoods damping properties are adequate at this frequency.


Dave: Feel free to correct me if I am getting any of this wrong.
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Old 27th April 2008, 05:11 AM   #277
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Originally posted by ShinOBIWAN


John, are you saying you just realised the reason why you've been bracing your cabinets?

What did you think it was doing before?

Hi Ant,
It's not that simple. It's been long established that to build a box that doesn't vibrate, you brace. Not only do you brace, you damp as well. Also, it helps if the walls are massive and thick.
This is all absolutely correct, of course and works very well (I know from doing it).
What I was daft about, what I was told repeatedly and ignored, was that there is a more efficient way of reaching this same end. There isn't any reason to make the walls thick. There isn't any reason to line the box with roofing membrane, or lead sheets or carpet. CLD is unnecessary.
All you need to do is effectively brace the box so that no panel will resonate below 1KHz.
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Old 27th April 2008, 05:32 AM   #278
soongsc is offline soongsc  Taiwan
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Default Re: Re: Re: Re: Re: Re: and???

Quote:
Originally posted by MJL21193



I'm not Dave but...if I understand it correctly:
50% of the acoustic energy that the box has to deal with is from 350Hz down. If the resonant frequency of any panel in the box is in that region, the panel will (obviously) resonate.
The higher you go in frequency, the less energy there is to excite resonances. Less energy to excite plus minimal damping will stop it before it starts. Dave says that the plywoods damping properties are adequate at this frequency.


Dave: Feel free to correct me if I am getting any of this wrong.
Long time ago I've used some closed cell foam stuck to the panels which seem to damp the acoustic forces quite well. But I do wonder whether the panel resonances are excited by the dirver vibration or the acoustic energy.
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Old 27th April 2008, 07:15 AM   #279
GM is offline GM  United States
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Both if you don't completely isolate the driver from the cab, so if it vibrates from acoustic compression, rarefaction and/or standing waves, then we have the complex interaction of the 'dog wagging the tail' and vice versa, ergo at minimum there's a loss of acoustical-mechanical efficiency since the driver doesn't have a rigid work platform.

GM
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Old 27th April 2008, 12:12 PM   #280
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Quote:
Originally posted by soongsc

But I do wonder whether the panel resonances are excited by the dirver vibration or the acoustic energy.

Kinetic energy from the driver falls off with frequency also - at 1KHz it's nearly zero. As you know, a resonance can not be excited unless there is enough energy at that frequency to do so. Think of the opera singer who shatters the wine glass.

Kinetic energy from the drivers motion wants to push the baffle in opposition to the cones outward movement, therefore to resist this, the front baffle and the driver itself needs to be well braced to transfer this energy to the rest of the box.

A good question is "what happens to all of this energy?" If the box panels are not allowed to vibrate, they will not burn off any of this, where does it go?
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