Adding Dampening to a Cab?

[Dave Tipping]

... In my typical manly way of having to take everything I own apart , I discovered tonight that my Laney Nx115 Cab has NO dampening at all .. and also no internal bracing . It really doesn't sound bad with my Orange head .. but I have been dialling a fair bit of bass out the eq to get it sounding how I want.

Questions :

1. What would be the best method of bracing it? Metal threaded rod? Timber dwangs spanning from one side to another? Timber/ ply fins glued internally?

2. What would be the best material and fixation method for the dampening? How much would I need? (read something from Bill Fitz suggesting 2"?)

... I reckon it's worth a shot .. if it makes no difference then hey ho .. if it makes a negative difference then i'll take it out!

[Lfalex v1.1]

Y'know, I tried putting some spare Spectraflex Deflex panels in my Trace 2x10. All it did was make it even heavier.

From experience, I'm beginning to form the opinion that, given the levels at which we commonly use our equipment, any benefits are so marginal as to be completely eclipsed by other factors.

I always thought that threaded rods through the driver mounting holes and right through the back panel of the cab might be good.
You'd need to drill out the back panel, and probably use washers either side of the panel, then have washers/nuts behind the baffle. Slide the driver over the rods and secure with nuts. Best part is you can [i]really[/i] tighten the nuts securing the driver, without fear of stripping them like woodscrews do.

Just an idea I had. Once.

[icastle]

The idea of bracing was to be able to make efficient cabs (acoustically and mechanicale) out of lighter materials - if your Laney hasn't got bracing then it probably doesn't need it and the same is probably true for the dampening material.

[Lozz196]

There are some similar threads on Talkbass, specifically re the Gallien Krueger MBE Series speaker cabs, where some people have added their own dampening to the cabs to stop excessive boom. One of the threads showed exactly what had been done, in photos and explanations. May be wrth a search over the water.

Edited March 20, 2012 by Lozz196

[Bill Fitzmaurice]

[quote name='Dave Tipping' timestamp='1332274032' post='1586003']
... In my typical manly way of having to take everything I own apart , I discovered tonight that my Laney Nx115 Cab has NO dampening at all .. and also no internal bracing . It really doesn't sound bad with my Orange head .. but I have been dialling a fair bit of bass out the eq to get it sounding how I want.

Questions :

1. What would be the best method of bracing it? [/quote]This, using 25mm dowels glued in place.



Line it with either open cell urethane foam or polyester batting, as used in uphostery. One average 25-50mm thick, secure it with spray adhesive.

[quote]tried putting some spare Spectraflex Deflex panels in my Trace 2x10. All it did was make it even heavier.[/quote]cabinet damping weighs next to nothing, so whatever you used was the wrong stuff.

[quote]The idea of bracing was to be able to make efficient cabs (acoustically and mechanicale) out of lighter materials - if your Laney hasn't got bracing then it probably doesn't need it and the same is probably true for the dampening material.[/quote]All cabs should be braced and damped. Those that aren't are defective. The only reason for not doing so is to save on build costs, pure and simple.

Edited March 20, 2012 by Bill Fitzmaurice

[Dave Tipping]

Fantastic info bill and nice sketch up model! It was a cheap cab so I figured it was missing both purely down to costs. With regards to the dampening does it matter if it partially blocks the vent? Also would there be any need to surround the dowels with anything?
Thanks again for the clear info.

[Mr. Foxen]

I'd guess the dowels being round is enough to mean they aren't a source of interfering reflections. Dampening should be acoustically transparent to the low frequencies for the port, but keep it a bit clear of the port because the airflow will be a bit disturbed and tend towards sucking the stuff out the port and move about distractingly if you can see it.

[LawrenceH]

Depending on the types of vibrations/resonance seen I'm not sure the rods method will be as effective as stiffening the cabinet with conventional parallel braces running along the open faces of the panels. The rods will mainly act to prevent flexure in opposite directions - in phase flexure won't be nearly as effectively prevented, while glued-in parallel braces would seem to have a greater impact on raising primary panel resonance frequencies as they're providing stiffening along more of the panel's surface. Raise the resonances and you can kill them more effectively with damping material.
Re damping, the keen-eared on the fEarful pages have expressed a preference for 1" or so acoustic panel-type pyramidal open cell foam of the type sold by aurelex, studiospares etc. The published absorption coefficients suggest they'd make a good choice, it's hard to find materials that absorb effectively into the low-mids. With bass guitar in a well-braced tweeterless cab I've found it surprisingly hard to tell much of a difference using generous amounts of wool/poly 'acoustic fibre' type stuff compared to the bare cab (yet damping makes a really noticeable difference on hi-fi).
As Mr F says keep damping well away from the ports.

[Mr. Foxen]

I've definitely heard the difference before and after sticking knobbly foam in a cab, it was an acoustic 2x15 so shallow front to back and had an ugly bit high up, possibly the shallowness front to back meant it was quite high and thus greatly affected by lining?

[Bill Fitzmaurice]

[quote name='LawrenceH' timestamp='1332282640' post='1586220']
Depending on the types of vibrations/resonance seen I'm not sure the rods method will be as effective as stiffening the cabinet with conventional parallel braces running along the open faces of the panels. [/quote]They're more effective. [quote] glued-in parallel braces would seem to have a greater impact on raising primary panel resonance frequencies as they're providing stiffening along more of the panel's surface. [/quote]It's not the raising of the resonance that makes the cab better, it's the stiffening of the structure. The raising of the panel resonant frequency is a side effect of that stiffening. Cross bracing is no less than twice as effective as spline bracing in so doing.

[LawrenceH]

[quote name='Bill Fitzmaurice' timestamp='1332285765' post='1586276']
They're more effective. It's not the raising of the resonance that makes the cab better, it's the stiffening of the structure. The raising of the panel resonant frequency is a side effect of that stiffening. Cross bracing is no less than twice as effective as spline bracing in so doing.
[/quote]

Hmm...so your rods method raises the resonance further due to stiffening in that design? I must say that directly contradicts my experience.
If an engineer wants to stiffen an internal structure like this they typically use i-beams, not point contacts which still allow flexure around the point, so if your method works better there must be more to it than overall wall stiffness

[chris_b]

It seems there is more than one way to effectively brace a cab....

[url="http://greenboy.us/fEARful/bracing.htm"]http://greenboy.us/fEARful/bracing.htm[/url]

[Bill Fitzmaurice]

[quote name='LawrenceH' timestamp='1332325212' post='1586547']
Hmm...so your rods method raises the resonance further due to stiffening in that design? I must say that directly contradicts my experience.
If an engineer wants to stiffen an internal structure like this they typically use i-beams, not point contacts which still allow flexure around the point, so if your method works better there must be more to it than overall wall stiffness
[/quote]Raising resonance in and of itself does nothing; what's the resonance of a six inch thick concrete cab? If a panel is not stiff enough to withstand the pressure generated within the cabinet it will vibrate. If it's too stiff it won't. Your I-beam comparison is correct, but the most effective i-beam configuration is with the i connecting the 'beams' of opposing panels, so that the opposing vector forces against those panels cancel each other out. There are no opposing vector forces with a spline brace.

[quote]It seems there is more than one way to effectively brace a cab.[/quote]I once used those methods, but stopped after I actually built two versions of the same cab, one using spline, one using cross bracing, measured the results, and found cross bracing to be far superior.
...

Edited March 21, 2012 by Bill Fitzmaurice

[Phil Starr]

You will wish you had never asked. the problem is that there isn't a single mathematical model that will predict the total effects of either damping or bracing. The way any panel resonates will depend upon it's dimensions, its density and how flexible it is. Much of this is frequency dependent and so something which will reduce some resonances will actually make others worse.

Cross bracing will stiffen panels and will effectively double the mass of the panel. At most frequencies the pressure changes in the cab will tend to move the panels in the opposite directions so the damping will be excellent. At some frequencies two identical panels will resonate and you could conceivably get some coupling between them, you would avoid just sticking a brace straight across the middle of two panels. The practical problem of cross bracing is that in some cabs finding convenient points to fix braces can be problematic.

Vaned ribbing will also increase the stiffness of a panel and to an extent its mass. I wouldn't fix them parallel to each other though as although it looks neat it can create a new resonant panel between the vanes.

I don't think anyone giving you categorical advice is helping much, after all using cross braces doesn't stop you also adding some stiffening ribs to other panels. Both will help.

Your original speakers will have been built to a budget. Stiffening the panels will help reduce resonances and tighten up the sound. You don't have a lot to lose if you fix them so they can be moved/removed whilst you play around. Of course some of the resonances may be what gives your speaker it's 'character' and removing this distortion may not be something you like.the sound of. These are instrument speakers not hi-fi or PA cabs.

Now stuffing and damping panels, that's really controversial.

[Bill Fitzmaurice]

[quote]the problem is that there isn't a single mathematical model that will predict the total effects of either damping or bracing. [/quote] There are. A civil engineer would be quite comfortable with the bracing aspect, while advanced speaker modeling software can accurately predict the effects of various thicknesses of damping materials based on their index of resistivity.

[charic]

42

[Phil Starr]

[quote name='Bill Fitzmaurice' timestamp='1332340791' post='1586926']
There are. A civil engineer would be quite comfortable with the bracing aspect, while advanced speaker modeling software can accurately predict the effects of various thicknesses of damping materials based on their index of resistivity.
[/quote]

You didn't read this. "There isn't a single model" "There are" which is plural.

My point is that whilst there are good models for calculating the frequency response of a speaker box there isn't a simple model for feeding all the complex parameters to do with sound transmission across the boundaries of the box which is available to automatically do the sort of optimisation that is routinely done with box design. If you know of one then I'd be glad to hear of it.

Whilst it is quite possible to calculate the effects of single braces on the forces acting on and movements of individual panels to calculate the overall effects of multiple bracing on all six panels would be beyond any practical utility. I very much doubt that you have performed these calculations on the bracing of your own designs. I expect you do what most of us do and use your experience to position your braces where you believe they will probably be most effective.

[Phil Starr]

[quote name='chris_b' timestamp='1332326856' post='1586579']
It seems there is more than one way to effectively brace a cab....

[url="http://greenboy.us/fEARful/bracing.htm"]http://greenboy.us/fEARful/bracing.htm[/url]
[/quote]
[quote name='Bill Fitzmaurice' timestamp='1332334930' post='1586784']
I once used those methods, but stopped after I actually built two versions of the same cab, one using spline, one using cross bracing, measured the results, and found cross bracing to be far superior.
...
[/quote]
Hardly a scientific test. We don't know what the problems were that you were trying to ameliorate with the bracing. You'd need a lot more evidence than this to say (as you have) that in all cases cross bracing is more appropriate than spline bracing. It may be better in many cases and it is often simple to install and lighter in weight than extensive splines. Chris-b is more accurate and more helpful. The OP can try either or both forms of bracing.

Your statement that rigidity is more important then raising the resonance is also false because again it is absolute. You apply it by implication to every cab ever built. If you had simply said that in your opinion rigidity is usually more important I don't think I'd disagree.

[Dave Tipping]

No. It's light as hell thanks to (neo speaker ..and minimal bracing ), sounds good, goes more than loud enough and was cheap. Cheers for all the comments above .. I'm def. gonna stick some internal bracing in and line it with dampening .. as I said if it doesn't make a difference I've wasted a couple of hours and very little dosh, if it does then great!

[Phil Starr]

[quote name='Dave Tipping' timestamp='1332425286' post='1588147']
No. It's light as hell thanks to (neo speaker ..and minimal bracing ), sounds good, goes more than loud enough and was cheap. Cheers for all the comments above .. I'm def. gonna stick some internal bracing in and line it with dampening .. as I said if it doesn't make a difference I've wasted a couple of hours and very little dosh, if it does then great!
[/quote]That's great, I think you'll definitely hear a difference in the sound with some bracing and it will probably be an improvement. look to brace the biggest panels first and don't put anything in the middle of the panels as it will simply shift the resonance up an octave. Anything off centre is better.

If you pump music through the speaker at a decent volume then you can usually feel where the resonance is greatest with your finger tips, aim to damp those points first.

I'm not a fan of wadding in a reflex/ported cab if I do anything at all it is usually just behind the speaker to cut reflections off the rear panel and dampen any standing waves.

good luck.

[Bill Fitzmaurice]

The center of the panel is the most important bracing point, as it's where the panel is subject to the greatest flexion. The cabinet should be fully lined to absorb all internal reflections. BTW, greenboys text is very well done, and I might add that it reads better than my Omni cab plans that was the original source. That would be the same cab that I built in both spline and cross braced versions to confirm by measurement which bracing scheme worked better, and by how great a margin.

[LawrenceH]

[quote name='Bill Fitzmaurice' timestamp='1332505729' post='1589245']
The center of the panel is the most important bracing point, as it's where the panel is subject to the greatest flexion. The cabinet should be fully lined to absorb all internal reflections. BTW, greenboys text is very well done, and I might add that it reads better than my Omni cab plans that was the original source. That would be the same cab that I built in both spline and cross braced versions to confirm by measurement which bracing scheme worked better, and by how great a margin.
[/quote]

On the flip side the Omni is a structurally unusual cab, it's much more asymmetric and the design is already inherently heavily braced thanks to the horn and internal baffle compared to a typical nasty box, not necessarily the most relevant comparison. In a more typical scenario a cross brace right into the centre of a panel would presumably damp the lowest mode but set up a symmetric pattern of vibrations above this, which can reinforce thanks to the symmetry.
In the real world though any bracing at all is a lot better than none and I think a law of diminishing returns applies quite quickly - plus, shift the resonance higher and it's easier to absorb anyway. I was actually surprised how little subjective difference damping appeared to make in a braced, tweeterless cab I built recently - much more important for full-range and hi-fi use I think where the HF (although unaffected directly) gives 'context' to what you're hearing lower down. But perhaps that was also partly due to all the bracing which made the inside highly asymmetric anyway!

[Bill Fitzmaurice]

[quote name='LawrenceH' timestamp='1332509605' post='1589358']
On the flip side the Omni is a structurally unusual cab, it's much more asymmetric and the design is already inherently heavily braced thanks to the horn and internal baffle compared to a typical nasty box, not necessarily the most relevant comparison. In a more typical scenario a cross brace right into the centre of a panel would presumably damp the lowest mode but set up a symmetric pattern of vibrations above this, which can reinforce thanks to the symmetry.
In the real world though any bracing at all is a lot better than none and I think a law of diminishing returns applies quite quickly - plus, shift the resonance higher and it's easier to absorb anyway. I was actually surprised how little subjective difference damping appeared to make in a braced, tweeterless cab I built recently - much more important for full-range and hi-fi use I think where the HF (although unaffected directly) gives 'context' to what you're hearing lower down. But perhaps that was also partly due to all the bracing which made the inside highly asymmetric anyway!
[/quote]That's all logical if one accepts that the purpose of bracing is to shift the resonant frequency of the panel upward. It isn't. The purpose of bracing is to reduce the flexing of panels in response to the air pressure inside the cab alternately pushing and pulling against the panels. If that is not done energy that otherwise would be useful acoustical output is lost. That's best accomplished by minimizing the size of the unbraced areas between braces. A side effect of so doing is that the resonant frequency of the panel is raised, but that's a side effect which in and of itself does not impact the response of the speaker.

[stevie]

I needed a laugh:-)

[Phil Starr]

[quote name='Bill Fitzmaurice' timestamp='1332505729' post='1589245']
The center of the panel is the most important bracing point, as it's where the panel is subject to the greatest flexion. The cabinet should be fully lined to absorb all internal reflections. BTW, greenboys text is very well done, and I might add that it reads better than my Omni cab plans that was the original source. That would be the same cab that I built in both spline and cross braced versions to confirm by measurement which bracing scheme worked better, and by how great a margin.
[/quote]

Do you still have the data? It would be genuinely interesting to see what you came up with.

Actually I agree with you about cross bracing being the way to go. Its not that vanes won't work but they work best if critically applied and the big minus, you need an awful lot of vanes to really stiffen up a cab and that can add a lot of weight. On the other hand we don't know the dimensions of this cab or the dimensions of the speakers themselves, there may not be convenient places to place cross bracing.

You are wrong about the placing of the brace in the geometric centre of two panels of equal size and mass. We are talking about resonance and not simple mechanical strength here. the aim is to stop unwanted sound being radiated by the panel and a brace in the centre is going to be as effective as trying to damp a bass string with a finger directly over the twelfth fret.