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post #181 of 337 Old 02-27-2016, 03:30 PM
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Nevertheless, quoting from p15 in "On the Design of Loudspeakers for Broadcast Monitoring",

" The approach adopted by H.D. Harwood and now an established BBC tradition is to contruct cabinets of thin plywood backed by a layer of highly damped bituminous sheet"

download the doc at:
http://www.bbc.co.uk/rd/publications/rdreport_1988_14
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post #182 of 337 Old 02-27-2016, 05:35 PM
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How do you test to see if you have too much vibration? If I put my hand on my 4cuft flatpack SI HT18 sealed sub that I have 4 lbs of r13 fiberglass insulation inside, I feel something when the sub is pumping, but I have no idea if it's bad or good. Do you put a quarter on top and if you can see it bounce it's bad? A glass of heavy cream and if it turns to whip cream your in trouble?
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post #183 of 337 Old 02-27-2016, 07:09 PM
 
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Originally Posted by corradizo View Post
How do you test to see if you have too much vibration?
You measure it. Audible vibrations will show up on the response chart. Of course you'd measure at expected listening levels, not just 1 or 2 watts.
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post #184 of 337 Old 02-27-2016, 07:11 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
You measure it. Audible vibrations will show up on the response chart. Of course you'd measure at expected listening levels, not just 1 or 2 watts.
Thanks Bill, I have REW and a umm6 mic. Would I take reference sweeps nearfield? At the mlp? What would I look for in the measurements?
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post #185 of 337 Old 02-27-2016, 07:15 PM
 
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You have to measure outdoors, otherwise anything in the room that vibrates will show up. With a sub measuring at 4 meters with at least 100 watts input will reveal box vibrations as narrow spikes above the pass band.

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post #186 of 337 Old 02-27-2016, 08:34 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
You have to measure outdoors, otherwise anything in the room that vibrates will show up. With a sub measuring at 4 meters with at least 100 watts input will reveal box vibrations as narrow spikes above the pass band.
Got it. Thank you. If any subs leave my house, I'm afraid my wife would not allow them back in.
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post #187 of 337 Old 02-27-2016, 11:17 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post
It's not. The only place where mass damping is the better option is when bracing isn't an option. Sheet metal car doors, for example.
Hope I am getting this, the damping is mostly there for distortion (Harmonic) in the back wave so it does not come out through the cone? The fundamental we want to hit the back of the cone so it brings the cone back to zero when the signal changes?
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post #188 of 337 Old 02-28-2016, 06:48 AM
 
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Originally Posted by bob_m10 View Post
Hope I am getting this, the damping is mostly there for distortion (Harmonic) in the back wave so it does not come out through the cone?
That's something different. Mass damping is intended to reduce panel vibrations. Acoustical damping, using open cell foam, cotton or polyester batting or Type 700 rigid fiberglass, is intended to reduce internal reflections. Stuffing a sealed cab with acoustical damping lowers system Qtc.
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post #189 of 337 Old 02-28-2016, 07:38 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post
That's something different. Mass damping is intended to reduce panel vibrations. Acoustical damping, using open cell foam, cotton or polyester batting or Type 700 rigid fiberglass, is intended to reduce internal reflections. Stuffing a sealed cab with acoustical damping lowers system Qtc.
so we are talking about three items,

1) There is damping that can be applied to a panel to reduce panel vibration
2) Then we have damping for integral waves which uses soft material like foam, this is generally a inch or so on the inside panels.
3) Then we have "stuffing" which is when we add even more soft material and is used to lower Qtc if required by design.
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post #190 of 337 Old 02-28-2016, 01:47 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
That's something different. Mass damping is intended to reduce panel vibrations. Acoustical damping, using open cell foam, cotton or polyester batting or Type 700 rigid fiberglass, is intended to reduce internal reflections. Stuffing a sealed cab with acoustical damping lowers system Qtc.
http://home.earthlink.net/~ralphmeister/subbox.htm

I'm going to put 4.26lbs if r13 into a 2.8cuft box per the link above. That's 1.5lbs/cuft. I need to get a dats kit or figure out how to measure impedance with REW to figure out the actual QTC.

And from the cookbk:


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post #191 of 337 Old 02-28-2016, 05:48 PM
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Do you guys think this is good enough with bracing? The two rear panel braces are 1 3/4 inch wide 3/4 MDF.
The enclosure is for HST-18 with 2200 watts @4ohm pushing them. I was thinking about adding a brace to go from the rear panel to the center brace on the top and bottom but don't know if I need it or not. Let me know what you think.


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post #192 of 337 Old 02-29-2016, 05:10 PM
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I added 4 braces that goes from the rear panel to the center brace. Do I still need to add the same to the front part of the enclosure even though it has a double front baffle? Here is a current picture.

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post #193 of 337 Old 03-04-2016, 10:30 AM
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Hello @Bill Fitzmaurice and @bitmap42 :
I wish I had read this thread before I glued the top panel of my cabinet (now its fairly hard to add more bracing). I am building a dual opposed 3.5 CF cabinet for a pair of Infinity 1260s. I have depicted the existing bracing in the attached picture. It’s basically 3 lengths of 1” x 0.75” mdf (2 horizontal and 1 vertical) ; the internal box dimensions are 16.5 x 16.5 x 23.25 (height). The speaker hole on the front baffle is actually closer to the top of the box (such that the cut is ~5” from the top and ~8” from the bottom). The MDF I used is 0.75” throughout.
When I glued the front and side walls to the base panel the cabinet seemed very sturdy so I was lazy to add more bracing. How bad is my situation? Can I get away with this or do I absolutely need more bracing?
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Speakers: Boston Acoustics VS260, VS325C
Subwoofers (sealed): Dayton UM18, 2x Infinity 1260 dual opposed + iNuke6000DSP
AVR: Yamaha RX-A2000
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post #194 of 337 Old 03-04-2016, 11:20 AM
 
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Even with that minimal bracing it increases the stiffness to close to that of 1.5" unbraced, so it maybe fine. I'd use at least double that amount, but I also use 1/2" plywood for my cabs.
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post #195 of 337 Old 03-06-2016, 09:41 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
Resonance is moot. I thought I already covered that point.

It's not moot; it's the crux of the problem.

If a box "sings", it's at a panel resonant frequency.

This has been shown many times in speaker tests where they put accelerometers on the panels and link observed response issues to these resonances.

Quote:
Originally Posted by Bill Fitzmaurice View Post
Vibration, which isn't the same thing, will detract from the performance of any speaker. If the speaker panels don't vibrate you're good to go. If they do then it's back to the old drawing board time.

By definition, resonance is vibration; it's the frequency at which mass and stiffness produce the highest vibration amplitude.

Wood-product panels that aren't heavily damped will have many times the vibration amplitude at resonance than any other freq.

Noah

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post #196 of 337 Old 07-15-2016, 01:13 AM
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Great Idea for Bracing

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Originally Posted by Bill Fitzmaurice View Post
That does happen, but it's a by-product of what bracing really does, which is to make the cab stiffer.
Pretty much, although you'll also hear any resonances inside the box unless it's well damped.
You're using at least three times the necessary material. This scheme gives as good a result as you can get but with the minimum of material:


It shows round dowels, but square or rectangular are OK as well.
Seems pretty sturdy to me, not exactly the same as the example. Didn't take much effort to do. Thanks Bill.
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post #197 of 337 Old 07-21-2016, 01:23 AM
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Originally Posted by Ferroll Givens View Post
Seems pretty sturdy to me, not exactly the same as the example. Didn't take much effort to do. Thanks Bill.
You could still have had twice as many reinforcement points if you simply hacked the sticks in 45 degree angles and applied them such:

But people will stick to what they have already done, or already think is right. Just human nature.

cms, aka driver diaphragm suspension mechanical compliance: 0.000065 meter/Newton or in standard form 6.5e-05 m/N. (smaller number is better)
rms, aka driver diaphragm suspension mechanical resistance: 6.41 Newton.sec/meter. (higher number is better)
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post #198 of 337 Old 07-21-2016, 05:30 AM
 
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Originally Posted by ronny31 View Post
You could still have had twice as many reinforcement points if you simply hacked the sticks in 45 degree angles and applied them such:
The reason why that scheme is less than optimal is clear: the braces themselves will flex. When the braces are perpendicular to the panels they can't flex.
Quote:
But people will stick to what they have already done, or already think is right.
Or what experience has proven to work.
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post #199 of 337 Old 07-21-2016, 11:34 AM
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There's always concrete enclosures
http://www.concrete-audio.com/en/

I'm not talking about the kind of speakers you just listen to, I'm talking about the kind of sound you can feel.
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post #200 of 337 Old 07-22-2016, 01:01 AM
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Heavy Concrete Enclosures

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Originally Posted by 16hz lover View Post
There's always concrete enclosures
http://www.concrete-audio.com/en/
Might work very well, but not practical in home audio, especially DIY.
They might as will be made out of lead.
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post #201 of 337 Old 07-22-2016, 02:53 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
The reason why that scheme is less than optimal is clear: the braces themselves will flex. When the braces are perpendicular to the panels they can't flex.
Or what experience has proven to work.


The flexing of the bracing is insignificant in either case, because the difference in panel flex is very small with the two schemes. Only one scheme uses HALF the amount of material, so you can brace twice as many points on the sheets with the same amount of wood pole material. Furthermore, the bracing can be applied when the enclosure is completed, because all the parts fit through the driver hole.

Math tells us what is correct. The math says you are twice as well off by bracing diagonally, unless you wish to dispute the math then you are simply just disagreeing for the privilege to continue bracing in a less effective way. Why would you do that? I did the work because someone said to prove it and then the proof isn't enough to change existing opinion? Why do I even bother trying to improve your future?

PS: If you aren't familiar with models, the flex is exaggerated in the images or else you wouldn't be able to tell what flexed in what direction at all. its the numbers that matters.

cms, aka driver diaphragm suspension mechanical compliance: 0.000065 meter/Newton or in standard form 6.5e-05 m/N. (smaller number is better)
rms, aka driver diaphragm suspension mechanical resistance: 6.41 Newton.sec/meter. (higher number is better)

Last edited by ronny31; 07-22-2016 at 02:58 AM.
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post #202 of 337 Old 07-22-2016, 05:07 AM
 
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Originally Posted by ronny31 View Post
Math tells us what is correct.
Experience tells me what works.
After you have designed, built and tested your first hundred speakers we can compare notes.
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post #203 of 337 Old 07-22-2016, 05:53 AM
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Math tells us what is correct. The math says you are twice as well off by bracing diagonally, '


I don't know the answer as to the optimal bracing configuration (though I expect it includes some sort of damping rather than rigid attachment) but your models only brace in 2D. How would you expand it to 3D?

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post #204 of 337 Old 07-22-2016, 10:39 AM
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I don't know the answer as to the optimal bracing configuration (though I expect it includes some sort of damping rather than rigid attachment) but your models only brace in 2D. How would you expand it to 3D?
What do you mean? You don't have to brace a point twice. If the cross-section is looking through the longest dimension of the enclosure (height, lets say), it should be easy to tell how you brace it. The left side of the model would then be the double thickness baffle.
Of course, if you have a very large diameter driver in your baffle, the bracing to the baffle may need to be slightly different in spots. It would be rather cool to see someone use the driver basket for its strength.

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Experience tells me what works.
After you have designed, built and tested your first hundred speakers we can compare notes.
I am perfectly willing to take your experience as argument enough on things I do not understand, if I do not want to take the time to learn about it for myself. But in this case argument from authority does not make me tip my hat. You can argue that your experience is the reason you do things the way you do them, but you can't make the argument that you are correct because you have experience.

cms, aka driver diaphragm suspension mechanical compliance: 0.000065 meter/Newton or in standard form 6.5e-05 m/N. (smaller number is better)
rms, aka driver diaphragm suspension mechanical resistance: 6.41 Newton.sec/meter. (higher number is better)
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post #205 of 337 Old 07-22-2016, 11:18 AM
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What do you mean?


I mean a box is not a ring. Your scheme only accounts for four of the six sides. I'm having trouble seeing how it would work in a real box, where all six sides should be connected with bracing.

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post #206 of 337 Old 07-22-2016, 11:57 AM
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I mean a box is not a ring. Your scheme only accounts for four of the six sides. I'm having trouble seeing how it would work in a real box, where all six sides should be connected with bracing.
Well you should install google sketchup. Its free.

The bracing scheme depends on how many points you want to brace on each face (or rather, the max distance that can be unbraced). Draw up those points and begin planning your diagonal bracing. Remember to brace to your bracing instead of another side, if you already placed a brace nearby.

You can't really go wrong because however wrong you do, it still ends up being far stronger for less material (and only scrap material at that) than if you do window bracing or bracing between opposite sides.

cms, aka driver diaphragm suspension mechanical compliance: 0.000065 meter/Newton or in standard form 6.5e-05 m/N. (smaller number is better)
rms, aka driver diaphragm suspension mechanical resistance: 6.41 Newton.sec/meter. (higher number is better)
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post #207 of 337 Old 07-22-2016, 12:06 PM
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My buddy used some fancy software to model the bracing for my 24's (He is a structural engineer and designs sky rise buildings)..





they are dead.... drivers moving full tilt - I can put a glass of water on top with few ripples across the surface......




Guess the science is there (obviously or else there would be a lot of buildings fall down during seismic events)


Please note: There is a COMBINATION of Braces..... One style only was not efficient according to the computer... and connection points are varied... Notice the lengths and placement of each brace point are not all the same...
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post #208 of 337 Old 07-22-2016, 01:55 PM
 
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I am perfectly willing to take your experience as argument enough on things I do not understand, if I do not want to take the time to learn about it for myself. But in this case argument from authority does not make me tip my hat.
And yet only a few months ago you stated that this was the best way to brace a cab:

Has your understanding of how speakers work and how to build them expanded all that much since you wrote post #51 in this thread?
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post #209 of 337 Old 07-22-2016, 05:03 PM
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Originally Posted by uniquepattern View Post
My buddy used some fancy software to model the bracing for my 24's (He is a structural engineer and designs sky rise buildings)..





they are dead.... drivers moving full tilt - I can put a glass of water on top with few ripples across the surface......




Guess the science is there (obviously or else there would be a lot of buildings fall down during seismic events)


Please note: There is a COMBINATION of Braces..... One style only was not efficient according to the computer... and connection points are varied... Notice the lengths and placement of each brace point are not all the same...
Looks like you have both "styles" Going on there. Cross opposing panels and the angled approach.
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post #210 of 337 Old 07-22-2016, 07:08 PM
 
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Originally Posted by corradizo View Post
Looks like you have both "styles" Going on there. Cross opposing panels and the angled approach.
I use angle braces where you can't use panel to panel braces, like where the driver would get in the way. I also use them where they can do double duty, as corner located ports. In a structural engineering situation they do have an advantage over panel to panel, as they will reduce the effects of rotational forces on the structure, whereas panel to panel won't. That tends not to be an issue with speakers, as they're not subject to rotational forces. This cutaway shows a Simplexx 18 sub that uses corner ports that double as braces, angle braces where there's no opposite panel to connect to, and panel to panel braces where they can be used:
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