Head keeps rolling off my cab?

[joelb79]

Originally Posted by B-string

beat frequency interference going on?

I dunno why the bassline from "Beat It" just popped in my head.

[BogeyBass]

its very simple

krapload of pressure coming off the back of the speaker.

the deeper you make the cabinet less chance of the pressure pounding and flexing the rear baffle. Also gives more area and time for the damping material to absorb some of the energy. Before it bounces right back to the speaker

EV has shown that cabinet depth has the largest effect on cabinet Q in a few of their patents

[creis2]

Originally Posted by BogeyBass

its very simple

krapload of pressure coming off the back of the speaker.

the deeper you make the cabinet less chance of the pressure pounding and flexing the rear baffle. Also gives more area and time for the damping material to absorb some of the energy. Before it bounces right back to the speaker

EV has shown that cabinet depth has the largest effect on cabinet Q in a few of their patents

Did not know this. Would a front to back brace help the problem?

[joelb79]

Oh man those EV patents are full of nuggets of information. Check this out:

Ideally, a loudspeaker system should not color the sound in transforming electrical energy into acoustical energy. In order to avoid accentuating one frequency over another, resonances within the audible range must be avoided, whether thoseresonances are in the loudspeaker diaphragm or the enclosure. The walls of the loudspeaker enclosure are resonant at some frequency determined by the effective mass and stiffness of the wall. Even though the resonance may be damped, it is preferablethat the mechanical resonance of the enclosure wall fall outside of the response range of the loudspeaker. The resonant frequency of the enclosure wall will be increased by descreasing the mass or increasing the effective stiffness of the wall. Hence,a wall with sufficiently low mass and sufficiently high stiffness can be made to have a resonant frequency above the response range of the loudspeaker. For those enclosure walls having a mechanical resonance in the response range of the loudspeaker,high stiffness and low mass will reduce the magnitude of the resonance.

A loudspeaker enclosure can also color the audio energy produced by generating sounds in the walls of the enclosure. A void in the wall of the enclosure will have at least one resonant frequency, and at that frequency, the void will cause theadjacent portions of the wall of the enclosure to vibrate excessively, thus creating a buzz or whistle which colors the acoustical energy produced. Hence, voids should be avoided in the walls of the enclosure.

Historically, wood has been the most popular material for loudspeaker enclosures. Wood is readily available, and in the past has been a relatively cheap construction material. Wood however is subject to nonuniformity, that is, the acousticalcharacteristics of wood vary with the type of wood and even with the particular piece of wood within a given category. Wood tends to have knots, and the knots tend to come loose. A loose knot will vibrate, and other sounds can be generated by voids. The stiffness and mass of wood will vary between different pieces of wood of the same general characteristics. Wood also has become costly in recent years.

Plywood has also been used in loudspeaker enclosures, often augmented by a vinyl wrap to improve the appearance of the enclosure. Plywood generally has at least three layers of wood, each layer having a grain which is oriented perpendicular tothe adjacent layers. Plywood aften has voids, and often has an irregular outer surface making it more difficult to produce a loudspeaker enclosure which is attractive, either by treating the plywood itself, or cementing a vinyl wrap on the plywood. Voids in plywood are particularly objectionable in that they produce coloring sounds. Additionally, plywood tends to delaminate when subjected to moisture or temperature change.

More recently, particle board has been used for loudspeaker enclosures. Particle board comprises small generally uniform particles of wood or other fibrous materials in a plastic binder. Particle board generally has a high ratio of binder towood particles, and the stiffness to weight ratio of particle board is lower than that of plywood. Accordingly, particle board results in an enclosure which is heavier than that of plywood, assuming the same wall stiffness.

continued here: http://www.patentgenius.com/patent/4624338.html
List of EV patents: http://www.patentgenius.com/assignee...orporated.html

Thank you BogeyBass. Some of this stuff right here was what I was talking about.

[BogeyBass]

Originally Posted by creis2

Did not know this. Would a front to back brace help the problem?

Yes most likely

as mentioned the longest length or largest panel is the weak point
especially with thin plywood. Its just gonna flex more and eventually resonate.



I have not seen what this cabinet looks like but from how described. Sounds like the front baffle is tall and wide most likely the largest longest piece. cut some holes in it now weaker mount some weight to it even weaker.

so the longest taller piece needs some reinforment so it does not flex any more. add some dowels front to back might help.

might be impossible to brace it correctly since the longest lengths need to be braced like I showed in post #203

Just imagine the longest length of plywood strung between 2 points as a bridge, how would you strengthen it so you could walk across it so it would not flex and just break.

[1n3]

Originally Posted by BogeyBass

... Sounds like the front baffle is tall and wide most likely the largest longest piece. cut some holes in it now weaker mount some weight to it even weaker. ...

If securely fastened to the baffle, the speaker frame will contribute some stiffness to the panel. The weight shouldn't weaken the panel, though the mass would have an effect on panel resonance.

creis2 - none of us have enough information to understand the mode of vibration that moves heavy amps around on its top when C# is played (though it's interesting to speculate). Without that understanding, bracing recommendations here will be guesswork.

[BogeyBass]

Originally Posted by 1n3

The weight shouldn't weaken the panel, though the mass would have an effect on panel resonance.

its another argument yes, either its seen as to reduce cabinet vibration you need to raise the resonant frequency of the cabinet.

and it has been found that adding mass can lower the resonant frequency.

others argue it has nothing to do with changing resonant frequency it really just is the panel flexing. and to reduce cabinet vibration you simple need to reduce panel flexing.

easy to mend the 2 together when you think of the plywood as a bridge. If its not strong enough to walk across the plywood wood simply bend or flex. then if you added more weight to it then it would just flex even more.

likewise if it was strong enough to walk over and it didnt flex.
even if you added more weight and it was still strong enough to hold .It would have no effect on it because its strong enough and the extra weight has no effect and would not cause flexing.

same could be argued about adding more mass would increase vibration/ lower resonate frequency. add it to a weak panel yes. more vibration/lower resonant frequency. Add more weight to a already strong panel
no effect, weight does not lower resonate frequency/increase vibration.

either way testing could support both theorys wrong and right , just depends if the panel is already flexing or not. So again the real problem is not the resonant frequency...its panel flexing.

and again testing could prove that raising/lowering resonant frequency does does not reduce vibration.
Its the same dam thing it either flexes or not, how much or how little it flexes could or could not change resonant frequency.

but again the problem is panel flexing, causing the cabinet to vibrate making the head fall off.

how do you stop the flexing, add braces across the longest lengths, just like a bridge.
no flex no vibrate no head fall off.

there is no guess work it is simple just brace the longest lengths. with the correct brace in the correct direction

[Downunderwonder]

What's your take on my supposition that adjoining panels effectively brace each other along their edges making all edges into nodes?

[B-string]

I am wondering if it may have turbulence trouble as well. The narrow chamber at the top may be creating a "separate" (acoustic) chamber causing a beat frequency disturbance.
I still agree bracing is needed, some creative treatment may be needed as well.

[joelb79]

I still argue there could be voids and areas where the cellular mass of the wood is compromised causing this. It's extremely more likely that a void in the wood would effect the tone and vibration of the cabinet when you only have 1/2" of wood there in the first place.

Wood's cellular structure will vary enough in a cabinet that it could be something of that sort. Nothing like this is happening with my LDS 15/6/1; But I cannot set a drink on top of it without the drink falling off the cabinet (when played at any serious volume). I think the 1/2 wood has something to do with that.

[hover]

Yes, but if the wood is spec'd "void free" that isn't an issue as it's continuous rotary cut veneers, and most all plywood is cross-grained (directionally opposed 90 degrees) per laminate during production to strengthen (and deaden) to begin with...

[smeet]

Originally Posted by joelb79

I still argue there could be voids and areas where the cellular mass of the wood is compromised causing this. It's extremely more likely that a void in the wood would effect the tone and vibration of the cabinet when you only have 1/2" of wood there in the first place.

Wood's cellular structure will vary enough in a cabinet that it could be something of that sort. Nothing like this is happening with my LDS 15/6/1; But I cannot set a drink on top of it without the drink falling off the cabinet (when played at any serious volume). I think the 1/2 wood has something to do with that.

I don't get this with my DIY 15/6/1 (1/2" baltic birch). I can play at window-rattling volume (cranking the ShuttleMax 9.2) and the sides and top of the cabinet barely vibrate. I put in all the recommended bracing, plus a bit extra on every face, so maybe that's why.

[CL400Peavey]

Originally Posted by joelb79

I still argue there could be voids and areas where the cellular mass of the wood is compromised causing this. It's extremely more likely that a void in the wood would effect the tone and vibration of the cabinet when you only have 1/2" of wood there in the first place.

If there are voids, then the materials used are not up to snuff. Void free wood should have been used.

Originally Posted by joelb79

Wood's cellular structure will vary enough in a cabinet that it could be something of that sort. Nothing like this is happening with my LDS 15/6/1; But I cannot set a drink on top of it without the drink falling off the cabinet (when played at any serious volume). I think the 1/2 wood has something to do with that.

All my cabs are 1/2" baltic birch. I have no such issues.

Originally Posted by smeet

I don't get this with my DIY 15/6/1 (1/2" baltic birch). I can play at window-rattling volume (cranking the ShuttleMax 9.2) and the sides and top of the cabinet barely vibrate. I put in all the recommended bracing, plus a bit extra on every face, so maybe that's why.

+1

I have had zero vibrational issues with the 15/1, 1515/66/1, or 12/6/1's I have owned. I hit them with huge power too. A drink rattling off? Thats way too much vibration IMHO.

[joelb79]

Originally Posted by smeet

I don't get this with my DIY 15/6/1 (1/2" baltic birch). I can play at window-rattling volume (cranking the ShuttleMax 9.2) and the sides and top of the cabinet barely vibrate. I put in all the recommended bracing, plus a bit extra on every face, so maybe that's why.

Its more like things vibrate OFF the amplifier, not the head though. Drinks are a no no now, I've seen a full pint glass of pepsi on the floor thanks to my fearful thingy.. something my UL410 couldn't do. I bet you the rat fur holds drinks better; and it has nothing to do with the wood thickness at all.

I know Don uses void-free woods. But every now and then a lemon has to make it off the line. I'm sure "void free" also has tolerance levels for variances, much like capacitors and resistors.

[Chef]

I agree with all of this.

It's pretty easy to pull a driver and look at bracing.
It's pretty easy to get with Don and fix this.

Originally Posted by CL400Peavey

If there are voids, then the materials used are not up to snuff. Void free wood should have been used.



All my cabs are 1/2" baltic birch. I have no such issues.



+1

I have had zero vibrational issues with the 15/1, 1515/66/1, or 12/6/1's I have owned. I hit them with huge power too. A drink rattling off? Thats way too much vibration IMHO.

[hover]

And, if you pull the driver(s), take a walk around the cab with a rubber hammer , mildly rappin it on each panel in different areas to check for "distortion" sounds which would denote a loose dado / joint / brace. Not very scientific with charts and graphs, but it'll do the job well.

[dukeorock]

I've had a few drinks and whatnot slide off the amp, but it's from the hollow stage floor under the cab...no quick fix for that

[CL400Peavey]

Originally Posted by Chef

I agree with all of this.

It's pretty easy to pull a driver and look at bracing.
It's pretty easy to get with Don and fix this.

+1

I think the purposed front to back brace would be among his suggestions as well.

[joelb79]

Originally Posted by dukeorock

I've had a few drinks and whatnot slide off the amp, but it's from the hollow stage floor under the cab...no quick fix for that

Uh-huh! There it is. That's my problem too at this place (and just about every place).

[wcriley]

Originally Posted by dukeorock

I've had a few drinks and whatnot slide off the amp, but it's from the hollow stage floor under the cab...no quick fix for that

Hmmm........
Something no one has thought of:
Is it possible that the resonance isn't coming from the cab, but from the floor structure under it?