pete.young Posted October 23, 2012 Share Posted October 23, 2012 [quote name='alexclaber' timestamp='1350996617' post='1845973'] I've never seen much sense in buying a lightweight rig and then carting an amp stand around with you. [/quote] The solution that Tecamp provide for the small Puma combos is light and effective: a 1/4" diameter hollow rod which slots into a socket on the back of the combo and allows it to be tilted backwards, and is stowed in a couple of clips when not required. Can't find a picture. FWIW, even if the maths say that a Gramma pad can't work, it does have a noticeable effect on boomy stages. I have no explanation. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted October 23, 2012 Share Posted October 23, 2012 [quote name='pete.young' timestamp='1351010857' post='1846211'] FWIW, even if the maths say that a Gramma pad can't work, it does have a noticeable effect on boomy stages. I have no explanation. [/quote]Read my posts again. I never said that a Gramma can't have an effect, just that it doesn't work via the methodology that they claim. As for Alex's device, I'd lean towards foam as a material as well, because it's so easy to cart, and any isolating of the cab from stage vibrations that it might offer can't hurt. Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted October 23, 2012 Share Posted October 23, 2012 I usualy swipe a stool from the pub's counter and place my cab on top of it. It's efective, i don't need to tilt it, i get my sound at ear level and i don't need to cart a stand along with me! Quote Link to comment Share on other sites More sharing options...
Protium Posted October 23, 2012 Share Posted October 23, 2012 I find that a piece of carpet (which I might add was free out of one of them carpet "books" they have in showrooms) works fine. Quote Link to comment Share on other sites More sharing options...
LawrenceH Posted October 23, 2012 Share Posted October 23, 2012 Sorry Bill but you're still wrong about this. Count Bassy understands and has said much the same thing as me but expanded on the role of mass. A speaker cone vibrates, that creates the pressure waves in the first place. Now, third law of motion. It's not '95% acoustic 5% mechanical' it's 95+% heat, the rest mechanical. That mechanical energy will be distributed between the cone and the magnet/frame/whatever that's attached to. Quote Link to comment Share on other sites More sharing options...
Kiwi Posted October 23, 2012 Share Posted October 23, 2012 Quote Link to comment Share on other sites More sharing options...
Musicman20 Posted October 23, 2012 Share Posted October 23, 2012 [quote name='Kiwi' timestamp='1351016809' post='1846306'] [/quote] Lol. Quote Link to comment Share on other sites More sharing options...
Count Bassy Posted October 23, 2012 Share Posted October 23, 2012 (edited) [quote name='Bill Fitzmaurice' timestamp='1351010302' post='1846197'] Sir Isaac and myself are in complete agreement. When the cone moves back and forth it alternately pressurizes and de-pressurizes the surrounding air. Said pressurization and de-pressurization causes your eardrums to move back and forth in reaction; that's how we hear. [b]Said pressurization and de-pressurization also causes the floor to move,[/b] [b]how much being a property of the stiffness and mass of the floor[/b]. If the floor was vibrating in reaction to the walls of the speaker vibrating said cabinet walls would have to be moving as far as the cone does. [/quote] I agree with the bit I've put in bold. The bit before that is correct, but a bit patronizing, and the bit after that is wrong. Also, I did say that I wasn't sure how significant the direct inertia affect was, but to deny its existence dismisses three centuries of conventional physics. What I am describing has nothing to do with acoustic energy, other than the fact that any physical vibration is acoustic. If you put a speaker in a completely sealed and completely rigid, effectively sound proof, box, suspended on long strings (or floating on air), Then if you vibrate the speaker within the box the box itself will move. Indeed, remove the cone and replace with a weight of the same mass, so that the acoustic energy output is negligible, and the box will still move by the same amount. This is basic physics at a level far more fundamental than acoustic engineering. Some basic calcs - say the cone assembly weighs 0.5 Kg and moves at 10 M/S, and the rest of the assembly weighs 25 Kg, then that will move at 0.2 M/S in the opposite direction i.e. 0.5 x 10 = 25 * 0.2. In terms of energy distribution between the two: Energy in the cone would be 0.5 x 0.5 x 10 x 10 = 25 Joules Energy in the box would be 0.5 x 25 x 0.2 x 0.2 = 0.5 Joules It's been several decades since I did my physics degree. I've forgotten lots, and much has changed, but I believe that Newtons laws still hold for everyday life. Edited to say "I hope I've got the maths right - otherwise could be very embarrassing" Edited October 23, 2012 by Count Bassy Quote Link to comment Share on other sites More sharing options...
funky8884 Posted October 23, 2012 Author Share Posted October 23, 2012 Wow, I didn't know a Foam Wedge could cause all this ! Some great reading here Quote Link to comment Share on other sites More sharing options...
alexclaber Posted October 24, 2012 Share Posted October 24, 2012 If you want to update the maths with more useful values, you're looking at ~50g moving mass on a typical single 12", ~80g moving mass on a typical single 15". Action and reaction being equal and opposite, there is indeed a reaction to the action. But they are both vector quantities and as such perpendicular to the floor, so shouldn't excite it that much. But something is definitely happening, you can hear it when you add or remove inter cab/floor damping! Quote Link to comment Share on other sites More sharing options...
Happy Jack Posted October 24, 2012 Share Posted October 24, 2012 [quote name='alexclaber' timestamp='1351066008' post='1846747'] If you want to update the maths with more useful values, you're looking at ~50g moving mass on a typical single 12", ~80g moving mass on a typical single 15". [/quote] And the angle of the dangle? Quote Link to comment Share on other sites More sharing options...
alexclaber Posted October 24, 2012 Share Posted October 24, 2012 [quote name='Happy Jack' timestamp='1351066576' post='1846756'] And the angle of the dangle? [/quote] Well obviously that depends on the heat of the meat! Quote Link to comment Share on other sites More sharing options...
EBS_freak Posted October 24, 2012 Share Posted October 24, 2012 I find this really bizarre. Out of all the years of the professional gigs that I have been to, I never ever seen anybody use any sort of Auralex contraption... I'm not saying that the physics doesn't sing true, I'm just not sure how much of an impact in the real world that all this has. Quote Link to comment Share on other sites More sharing options...
fatback Posted October 24, 2012 Share Posted October 24, 2012 [quote name='EBS_freak' timestamp='1351070746' post='1846826'] I find this really bizarre. Out of all the years of the professional gigs that I have been to, I never ever seen anybody use any sort of Auralex contraption... I'm not saying that the physics doesn't sing true, I'm just not sure how much of an impact in the real world that all this has. [/quote] Honestly, a strip or two of auralex foam cures stage boom. Not at a subtle change either, a dramatic improvement. As for the er... debate above, I have no idea. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted October 24, 2012 Share Posted October 24, 2012 [quote name='alexclaber' timestamp='1351066008' post='1846747'] But something is definitely happening, you can hear it when you add or remove inter cab/floor damping! [/quote]It is happening, just not in the frequencies where one expects it. When you measure in room with and without isolation the difference is seen in the lower mids, not the lows. That's on a bare wood floor. On a carpeted floor there's no difference. What's really telling is when you measure in the room below where the speaker is placed. Frequencies capable of exciting floor vibration to the extent that it's audible also pass through the floor. When you measure in the room below there's no difference between isolated and not. Quote Link to comment Share on other sites More sharing options...
WinterMute Posted October 24, 2012 Share Posted October 24, 2012 [quote name='fatback' timestamp='1351081598' post='1847027'] Honestly, a strip or two of auralex foam cures stage boom. Not at a subtle change either, a dramatic improvement. As for the er... debate above, I have no idea. [/quote] Many people report significant improvement for boomy stage and rooms by using such devices, wether they be the overpriced Auralex offerings or a couple of bits of packing foam, so there is, demonstrably, an effect that players like. The Auralex GRAMMA is rated for 300lb I believe, so is good for an 8x10, I'm not sure I'd want to put an 8x10 on bits of foam that weren't up to the job. Several people have made their own versions, Auralex foam isn't cheap, so I reckon the discounts that are out there make it worthwhile. I'm certainly going to be looking at either the GRAMMA or the Iso-tilt once it arrive. Quote Link to comment Share on other sites More sharing options...
TimR Posted October 24, 2012 Share Posted October 24, 2012 You don't need huge amounts of vibration to get something to vibrate at its resonant frequency. You don't even need to vibrate it at the resonant frequency. Any sub-harmonic will do it. The stage doesn't even need to vibrate that much as it's the chamber underneath that amplifies the boom. Sit on your cab next time you play and tell me it's not vibrating! Quote Link to comment Share on other sites More sharing options...
Happy Jack Posted October 24, 2012 Share Posted October 24, 2012 (edited) As a completely non-technical, non-scientific person, I'd just like to add that you get very rich if you could have £5 for every time someone on Basschat advises you to "[i][b]use your ears[/b][/i]" in one context or another. I've tried playing without a Gramma Pad on wooden stages, and with one. [u][b]I use my ears[/b][/u]. The difference is obvious. Like, I mean, like, really [i][b]really [/b][/i]obvious. Everyone I know who has tried the same simple experiment has reached the same conclusion. This solution works. Game over. I wonder how many of those arguing against Gramma Pads on this thread have actually tried using them, and in an appropriate setting, rather than arguing from some sort of principle. If you use a Gramma Pad on an earth floor or on flagstones then it will do you no good at all. Use one on concrete and the effect is limited depending (I presume) on the density and thickness of the concrete. Most stages aren't made of earth or flagstones or concrete. Edited October 24, 2012 by Happy Jack Quote Link to comment Share on other sites More sharing options...
deanovw Posted October 24, 2012 Share Posted October 24, 2012 This /\ I was having massive issues on a hollow stage we used to rehearse on. Gramma pad solved all those issues. I dont use it everywhere but I have it at my disposal now. Quote Link to comment Share on other sites More sharing options...
Lfalex v1.1 Posted October 24, 2012 Share Posted October 24, 2012 So if all these bits of foam are so good, why do 99.9% of cabinets have RUBBER feet? Quote Link to comment Share on other sites More sharing options...
Paul S Posted October 24, 2012 Share Posted October 24, 2012 [quote name='deanovw' timestamp='1351088900' post='1847180'] This /\ I was having massive issues on a hollow stage we used to rehearse on. Gramma pad solved all those issues. I dont use it everywhere but I have it at my disposal now. [/quote] And again. For the miniscule amount of effort and cost involved I use it every time. Although mine is the slightly cheaper Studiospares version, it has cured the boom I experienced in raised wooden stages. Maybe it uses the same laws of physics that allow bumblebees to fly? Quote Link to comment Share on other sites More sharing options...
LawrenceH Posted October 24, 2012 Share Posted October 24, 2012 I have also found that it's typically in the lower mids, and that it's easily audible - I've used foam under monitors on numerous occasions and a couple of times I've had the time to experiment with and without. On a particularly resonant wooden stage (with a microphone that's not directly mounted on the stage on a rigid stand, removing that from the equation) I've gained greater than 6dB before feedback when ringing out, centred around 315Hz. The audible effect is consistent with what the 31-band graphic suggests; a 'tighter', more coherent sound. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted October 25, 2012 Share Posted October 25, 2012 [quote name='Paul S' timestamp='1351094271' post='1847284'] Maybe it uses the same laws of physics that allow bumblebees to fly? [/quote] Flapping. The famous calculation was done on fixed wing bees. Quote Link to comment Share on other sites More sharing options...
RandomBass Posted October 25, 2012 Share Posted October 25, 2012 How on earth do fixed-wing bees fly? That, I must see.... Quote Link to comment Share on other sites More sharing options...
TimR Posted October 25, 2012 Share Posted October 25, 2012 [quote name='RandomBass' timestamp='1351153422' post='1847879'] How on earth do fixed-wing bees fly? That, I must see.... [/quote] The same way as a fixed wing helicopter. Downwards, quickly. Quote Link to comment Share on other sites More sharing options...
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