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.

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]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.

[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. ...

[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.

[quote name='xgsjx' timestamp='1332269890' post='1585905'] & the 4Ω cab would probably only put out 3 db more than the 8Ω equivalent. [/quote]It may have 3dB higher sensitivity, but not 3dB higher output. Output is limited by displacement, displacement is not altered by impedance.

[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.

[quote name='sixdegrees' timestamp='1332267960' post='1585872'] Surely if you went for a 4 ohm cab in the first place, and got full power from the head, you would be less likely to want to add an extra cab to get more volume/presence? And the 4 ohm option would be kinder to the head in the long run. [/quote]No, and don't call me Shirley. Getting full power from the head is moot, driver displacement is what limits output. Nor will a 4 ohm load be kinder, the lower the impedance load the higher the current draw, the higher the current draw the more heat produced, more heat shortens component life.

[quote name='Pete Turton' timestamp='1332178077' post='1584390'] [size=5]I have a great little Marshall MB4210 combo that I love and am going to add a 15" cab for a little more bottom-end.[/size] [size=5]As it is, its pushing out 300 watts @ 4ohms and with extention cab will go to 450 watts @ 2ohms. Marshall have a MBC 15" cab that is rated at around 300 watts, but I have the chance of buying a Peavey 15" cab, 4ohms, but pushing out 150 watts. Would this be suitable as it takes the total wattage to the amps needs?[/size] [/quote]Watts are immaterial. You want a fifteen with the same impedance as the two tens combined and at least as much displacement. The trick will lie in finding out the displacement of the tens you have and the fifteens you're considering. As for what displacement is all about, and why it matters while watts don't, have a look here: http://barefacedbass.com/technical-information.htm

Not as sick as I am of seeing blokes proclaim "I WON!!!" When you win something your cost is nothing. When you 'win' on ebay you're the one who was left paying the highest price after all the rest decided it wasn't worth it.

[quote name='bertbass' timestamp='1331570421' post='1575027'] I'd take both ratings with a pinch of salt myself. [/quote] A truckload is more like it. What consumers are most interested in is how loud they go, be it PA or bass cabs. Wattage doesn't tell you that. SPL charted frequency response, sensitivity, and driver displacement do. Many PA manfacturers provide all of that data, as opposed to the electric bass cab industry, where none do. Of course it's the higher end goods that are best documented.

[quote name='Beedster' timestamp='1330350638' post='1555988'] Thanks Bill, and I would guess that, to a certain extent, a 1x15 topped by a 2x10 forms two diagonal pairs? [/quote]Absolutely. When drivers aren't vertical dispersion is lost. That's one of the reasons why the 4x10 configuration makes no sense. Ostensibly tens are used due to the generally higher frequency response they're capable of. But when placed side by side the dispersion of those highs, and of the mids as well, is halved.

[quote name='Beedster' timestamp='1330338567' post='1555767'] but for whatever reason have always been a little suspicious of diagonally orientated cabs? [/quote]Justifiably. That's not the best way to make a cab, vertical drivers is, and if they don't know how drivers should be placed you must wonder what else they don't know. Not that they're alone in faulty engineering practice by any means, the guys who get it right are distinctly in the minority. But that shortens the list to choose from.

[quote name='Beedster' timestamp='1330122759' post='1553216'] , I've had mixed/unpredictable results with mixed cabs. [/quote]That's because different cabs have different reponses, which don't always play well togther. But if you're running separate pickups into separate amps having speakers with different responses isn't a concern. I suggested a twelve on top with the bridge pickup as that pickup has more highs, less lows, and a twelve or even perhaps a ten may work better with it than a fifteen where you already have the fifteen on the neck pickup to handle the lows.

[quote name='Beedster' timestamp='1330027054' post='1551759'] OK, looks like I'n not bi-amping then. Not really stereo I'm after either. Bridge cab on top is what I've done in the past (the Mesa 1516 didn't give me a whole lot of options in that respect), and I loved it. FWIW Bill, I could certainly hear a substantial difference between the same instrument (Ric 4003 FL) going through one channel and then into the 1516, and the same bass going through two channels and then each into the two separate inputs of the 1516. While I'll admit that part of this was the different EQ on each channel, even flat there was a significant and pleasing difference. Assuming then that it's stereo and not bi-amping I'm after, what combination would you recommend? Chris [/quote]Normally you use identical cabs with stacking, but as you have two sources there's no need for that. Trial and error is your best bet, until you find what you like the best, I'd start with a 15 on the bottom 12 on the top.

[quote name='Beedster' timestamp='1330018732' post='1551580'] Thanks Bill Not sure I agree with Point 1 (having tried it a few times). Point 2, not after a stereo bass effect for sure, but it would be fun to try the HiFi thing, if only to scare the neighbours, Point 3, I agree entirely Just to reiterate, I think a lot of this comes down to taste, and most Ric players I know prefer a certain tone which is perhaps different to mine. I play heavy flats and prefer both PUPs wide open, with a pronounced 'click' and punchy attack from the bridge PUP with a full on rumble underneath from the neck PUP (I don't use a pick but have enough nail on my first two plucking fingers to go for a soft flesh only finger style to using nail and getting quite a fast pick-like attack). No doubt I can get this without bi-amping, but the few experiments I've tried so far allow for far more control over the tone when I do by amp then when i don't. And like I said, it's a slow day at work 's [/quote]I don't believe you know what bi-amping is. It's running a single source into a two-way speaker system with an active crossover and two amps, one for each passband, rather than a single amp with a passive crossover. What you're describing is simple stereo, two full range cabs with independent sources independently powered. 'Stereo effect' is what happens if you have the two speakers horizontally separated by six feet or more, When placed vertically there is no stereo effect. The preferred setup would have the bridge pickup cab on top.

[quote name='umph' timestamp='1330002401' post='1551128'] get a guitar amp for the bridge, put it on full [/quote]+1. Bi-amping with two bass cabs accomplishes zilch. [quote]I've tried the guitar amp thing and it wasn't quite what i was after,[/quote]That suggest that bi-amping is not what you want to do. Perhaps you mean stereo. . [quote]it looked crap [/quote]Only guitar'd players should care more about how their rig looks than how it sounds.

Back in the day Fenders had a piece of neoprene under the bridge cover. The first thing everyone did after buying one was to remove it. I suppose you could use some urethane foam, but my advise is to learn how to mute the strings with your hands.

[quote name='xgsjx' timestamp='1329072456' post='1536813'] I dare say that 10 or so boost pedals in a row should do the job. [/quote]No need to experiment, the maximum clean output of ten pedals would be the same as one. Power amps are not optional. They are a necessity. [quote]I dare say that 10 or so boost pedals in a row should do the job[/quote]For the cost you could buy a micro amp, and it would actually work.

[quote name='EBS_freak' timestamp='1328885200' post='1534360'] What the hell is ohmage? [/quote]It's what you pay to Ent or Sir Paul. Perhaps Sting.

[quote name='Clarky' timestamp='1328793097' post='1532685'] Sorry but £45 for a device that improves your sound quality live is hardly a fortune. [/quote]No argument there. However, a great deal of the justification for that price is the claim that [i]'This riser yields nearly total acoustic isolation, resulting in a purity of tone that has to be heard to be believed![/i]' is pure unadulterated baloney, a fact that should be pointed out to those considering purchasing one. One of the purposes of a forum such as this is to point out whether a product delivers on it's promises, and if there are alternatives that work just as well at a far lower cost.

[quote name='LawrenceH' timestamp='1328740333' post='1532100'] I have not found camping mats as effective as strips of thicker structural foam. [/quote]I use a single thickness to isolate a rattling head from the cab and it works very well. If you need more isolation you may use more than one layer, and there's a lot of material in one mat to cut up and stack. The only application where I've found thick structural foam to be necessary is for isolating a drum riser from a flimsy floor or stage.

[quote name='Oldman' timestamp='1328736330' post='1532029'] It's all very well being "Techy" with Vested interest, I'm just a punter happy with a product. It might suit, it might not, no big deal . I'm sure a trial would clarify this.... Snake Oil ...shame on you are you not selling enough "Voice of the Theatre" design concepts? Oooooer . [/quote]There are uses for isolation pads, decoupling isn't one of them. Sorry that you accepted their advertising claims at face value and paid ten times what you needed to. But there's no need to recommend that others follow suit.

[quote name='Oldman' timestamp='1328724387' post='1531762'] [url="http://www.bassdirect.co.uk/bass_guitar_specialists/Auralex_Isolation_Risers.html"]http://www.bassdirec...ion_Risers.html[/url] This item might alleviate any feedback and give you all the ooomph you amp and cab can provide. I use one, it de-couples the cab from the floor and thereby removes unwanted resonance as well. [/quote]Most of the claims made by that are snake-oil. Alex covers it well on the Barefaced Bass site. If you do need to do what the Auralex does one of these does it just as well: http://www.walmart.com/ip/Ozark-Trial-Camping-Pad-Blue/16783660 [quote]As for the problems resulting from raising the cab, I've posted about that before and it seems the loss of low and low mid isn't from lack of contact but from boundary cancellation. Basically, i'm raising the cab too high. [/quote]+1, there are no losses from lack of mechanical coupling because there's no such thing as mechanical coupling, other than in advertising copy. Raise it too high and you lose some acoustical coupling in the midbass, when that's the case don't lift it so high to hear the mids, just til it back.

[quote name='fatback' timestamp='1328713624' post='1531541'] So i was idly wondering whether a lower impedence cab would free up some headroom. [/quote]Not enough to bother with. If your amp has adequate voltage swing to drive the speaker to full output at 8 ohms then you gain nothing by going to four. If it doesn't the most additional output you can get is 2dB, because an amp doesn't deliver twice the power into a halved impedance load at full power, it does so only at small signal levels.