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.

[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.

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.

[quote name='paddy109' timestamp='1332085148' post='1582935'] We all played like complete muppets mind you - hey it's only rock n roll! Paddy [/quote] especially the drummer?

There's something slightly odd about the specs here. That really is quite a heavy cone and likely to be quite stiff as a result so you would expect the frequency range to be more restricted than 5.8k. You'd also expect fs to be lower. I don't think efficiency is particularly low, we don't know how it was measured and a lot of the higher figures other manufacturers publish are generated by 'favourable' testing procedures. (It may be OK, we just don't know.) A lot of Eminence figures are bumped up by quite big mid-range frequency humps for example. You'll get an extra 6dB by having a 2x10 and 100dB per watt is good. On the plus side excursion (Xmax) looks good and Q of 0.34 is pretty near perfect for engineering a flat response in the bottom octaves without too sharp a roll off. I quite like using PA drivers in bass cabs as I prefer the more 'polite' sound you get. You aren't happy with your current PA monitor though so maybe your taste is for something less accurate but more lively sounding. The big problem with building your own is that you can't test the sound until after you have built.

Having just 'upgraded' from a Cort to a Fender Highway I'm curious over this. The Cort is very generic but shows excellent quality control. It is clearly CNC routed to great accuracy. It is so easy to set up, remains very stable in every way, it'll stay in tune for weeks and the action once set just sits there. Even the timbers in the neck look like someone took care selecting them. It plays like a dream. The Fender has poor finish, things like frets not properly filed and so on the machine heads and bridge lack quality, the nut had to be re-formed. The neck has been made out of some less decent maple than the Cort. It is tricky to set up and drifts out of setting easily, at gigs I have to re-tune if I move into another room and again at half time. Even then it can be slightly out after an hours playing. The only plus is the sound, it is so much nicer than the Cort. Given that the Cort has superior tuners,neck and bridge I'm wondering how much better it would sound with a decent pickup. The body is basswood I think. The Fender is ash. What else is there that contributes to the tone (given that I use the tone controls on the amp not the guitar? I guess the OP has to look for something well made, some of the really cheap stuff isn't well put together but some of them are surprisingly good.

The problem with the studio monitors and the ex hi-fi speakers is efficiency. They often only produce 88dB/W or thereabouts. The Wharfedale titans will give you an extra 6dB to play with which will be noticeably louder. At a pinch they will do as PA speakers for an acoustic set in a small bar and as floor monitors in a band so you might get extra uses out of them.

Problem solved except now my car has broken down so I can't get the spare part I need! The plastic socket had disintegrated. Many thanks for all your help. Cheers.

I don't know if this will help, [url="http://www.ultimate-guitar.com/columns/gear_maintenance/choosing_speakers_to_drive_your_cabs.html"]http://www.ultimate-guitar.com/columns/gear_maintenance/choosing_speakers_to_drive_your_cabs.html[/url] I tried to write something to help with this. The Eminence website stuff is useful too. Using WinISD will mean you can see what the bass response is like without having to buy and build the speakers first but it could be confusing if you don't understand the models it uses. If you can get hold of the Loudspeaker Design Cookbook by Vance Dickerson that will help but there is loads on the internet. If you ask specific questions here there are loads of bright people here who will try and help. Good luck

thanks again, the connections are standard jacks, a mono 2.5 and a stereo 3.5. the problem seems to be with the 2,5 socket which is the input for the pups. It all works perfectly with an outboard Tanglewood pre that I have borrowed so I'm optimistic I can fix it even if I have to bodge in a lead and a line socket. I'm just about to remove the pre and have a proper look. Wish me luck

Thanks guys, this gives me a bit more confidence that a good solution is possible.

Not strictly bass related but you are a knowledgeable lot and I am a regular BCer and not on any guitar forums. My old Takamine has a broken pre amp and i don't think they keep any this size any more. Fishman make one similar in size and I am wondering whether they will work as good as the originals with the Takamine pup's ??

I wouldn't advise anyone to build a one off speaker purely to save money. The cost of parts has gone up since so much manufacture moved overseas and 'cheap' manufactured units have fallen in price and improved in quality over the years. Good second hand stuff is usually cheaper and retains more value than a home build if you ever want to sell it on. However quality stuff can be built with a saving and you can make speakers to match your needs exactly if you know enough. The problem is that you need a lot of experience (and knowledge) to design anything which will be as good as a top end unit and the only way of gaining this is by doing it. Having said that for little money you can build something quite respectable and you learn quickly. Speaker design is technical but it isn't rocket science. Computer modelling and Thiele/Small's work means you can design something competent without an engineering degree or advanced maths which means it is probably easier now than in the past.

The majority of cabs like these have an active crossover and two amps, one each for the bass unit and horn. You aren't going to be able to use a slave with these. The LD units have looked like great value for money for some time so definitely worth checking out.

Welcome to BC. You know the answer to this, if the pot is scratchy and you are going on tour then it has to be replaced, you can sometimes clean them up with some Servisol (switch cleaner) but it is often a sign of wear and only a temporary fix. It will of course fail mid gig in the middle of nowhere at a weekend if you don't sort it first. Sorry

Good Luck, I started playing bass from scratch at 55 and was playing in public within months. I'm now in two gigging bands. The only thing you can do to keep the nerves under control is practice,boring but it helps. Once you get to the end of the first song you'll find it easier. Make sure you enjoy it, it is over so quickly.

[quote name='jonunders' timestamp='1330297222' post='1555489'] I'm sooooo glad i read the wiki article, everything is now as clear as mud! [/quote]It is pretty hard to explain something as technical as this in simple terms. One day I'll have a proper go. Mr Foxens analogy is as good as anything. I'll attempt something in between this and the wiki article. You need to understand the way the amp works just a little The sound from a speaker is made as the speaker moves forward and back in time with your strings vibration. To make it do this the amp increases the voltage to push speaker cone forward and reduces it to let it back, at some point the voltage then reverses and the speaker moves further backwards behind its starting/resting position. The simplest way to do this is to have a single output transistor or valve doing the whole process. This is class A. The problem with this is that when the speaker is in the halfway position the voltage and current in the amp are also halfway so the amp is working pretty hard when the speaker is in the resting position doing nothing. This means class A amps get very hot even with low signals as all that energy has to go somewhere. As a result class A amps tend to be low powered and inefficient as it is the heat that kills transistors and valves. The next trick is to split the signal so one device does the positive side of the cycle and another does the negative side. This is class B. Now when the speaker isn't moving neither transistor or valve needs to do anything and there is no energy to disperse as heat. This makes class B amps more efficient and more reliable. The problem now is the point where you switch from one transistor/valve to another. The output devices aren't very linear at the bottom end of their range, there's always a bit of a gap and you end up with distortion when they change over, This is really noticeable in the quiet bits of music or whatever. The solution which worked for years was to have both output devices working at the crossover point, meaning you had a class A amp at this point filling in the gap and class B for the loud stuff. This is class AB. This is still the most common way of doing things though it is changing rapidly. The next way is to control the sound by switching the output devices on and off very quickly. This is class D. By switching them on more than off you get more current and therefore more power and less by having them off more than on. Because transistors make really efficient switches this means less energy and so the manufacturer saves on expensive heatsinking and supermassive transformers. this means class D is cheaper for really powerful amps. so your PA amp or anything over 200W is likely to be class D. Class H (orG) is using a different trick of varying the power supply voltage in the amp to make it more efficient again saving on heat problems and expensive power supplies. The reality is that you don't need to know any of this. You won't find a class B amp. Guitarists might have a class A amp or even one they can switch from A to AB. Some people think a class A amp sounds sweeter. Typically switching from class A to AB means the amp will go from 7W to 15-20W. Bass amps won't be class A unless they are nutty 'boutique amps'. (discuss). You'll get class AB, D or H. It won't matter because you'll be playing and not designing the thing. They do have different distortion characteristics but you aren't intending to distort by overloading the amp anyway. It is more important that they are well engineered rather than what class they are. Hope this helps

Hi Tom, I hope you are going ahead with this project. If you haven't already chosen your drivers then I'd like to add a bit. For any given driver there is an optimum solution both in terms of cab size and tuning frequency. For example you really want your port output to be tuned to the speakers resonance so that you get maximally flat responses and the cabinet size needs to be adjusted to achieve the optimum damping of the speaker. Any of the speaker design programs will recommend the optimum cabs and tuning and the better ones like WinISD will allow you to see what happens with a less than optimum alignment. Generally speaking if you wanted a flat response down to bottom E then you would start with a driver with a resonance below that point. This means a heavier cone or a softer suspension and usually means lower efficiency. It also means your speaker will have to be designed with a longer excursion to cope with these low frequencies. If you want a smaller box then you look for a driver with a bigger magnet for better electromagnetic damping to compensate for less damping from your box. Also look for low Vas. I wouldn't get hung up on deep bass, speaker designers talk about cut off frequencies but the speaker doesn't just stop here, there will still be some sound but at lower levels right down below 41Hz and the bass is often reinforced by boundary reflections from floors and walls in real life situations indoors so a lot of deep bass can be difficult to manage. The character of your speaker is going to be more determined by any hump in frequency response above 100Hz and the midrange peaks which both the Eminence drivers show. I haven't modelled these speakers but it looks as if the deltalite is better than the basslite by a small amount probably proportionate to the price difference. If you decide that you are going ahead and it isn't too late I will run them through winisd and give you more detail. Cheers

[quote name='Mr. Foxen' timestamp='1329860810' post='1548819'] Speaker could have died, shorted and taken out the power section. [/quote] That's right too, but it is more usual nowadays for speakers to go open and not short circuit and the protection circuitry should protect the amp. It may well be that a speaker short will have blown an internal fuse. It is pretty hard to say without the amp in front of me

Just to second JTUK,, It's possible the amp and speaker are both blown but unlikely. The problem is, and I know nothing about this particular amp, that separating amp and speaker for testing might need breaking into the case and an hours labour, only to tell you its bust and can I have £30 please. With a low value combo they probably didn't think it was worth spending your money on it. You could either try another tech or go back and ask them if they tested amp and speaker separately and if they didn't then how much would it cost. Then you can decide if it is worth the risk. Recieved wisdom is that Behringers are hard to source parts for though I've no direct experience.

Try recording the sets and playing it back to them the gaps are pretty shocking. It's pretty disrespectful to the audience to constantly retune on stage and I don't think they realise quite how much time they take up. Are they playing drop D or DADGAD or something, then get a second guitar or run the set so the retuning only has to be done once or twice. In the end I run an extra mic for me and we banter whilst the guitarist sorts himself out. Not perfect but better than ignoring the audience. Sometimes it seems like Ken Dodd could do his whole routine in the gaps.

[quote name='crez5150' timestamp='1329690270' post='1546103'] [/quote]lol

It's an amusing idea. This is how it works. Your guitar gives out about 1/1000 of a volt from the pups. Your effects pedals may boost this a little but the most they will boost the voltage up to will be about 1V (most won't go anywhere near this) The maximum they could possible create by chaining them together (a la Bart Simpson) would be about 2.8V if you are running off a 9V battery or supply. Above this the battery runs out of volts. The battery won't let you have very much current either. You won't run 100W out of a PP3! The amplifier takes the signal of around a volt and boosts it to 30V for a 100W output. It also will do this with all the current needed to provide this power. You've got slightly mixed up between gain and power.

Most of us operate with one or two monitor mixes if we are lucky. Learning to pick what you need from the jumbled onstage sound is a skill you have to develop early for the average pub band. In the days before monitor mixes I used to split the bass and guitar stacks so the guitarist would have one of your 4x10's and you would have one of his 4x12's in your stack, That would enable you to hear each other. The other thing would be to buy a little powered monitor which you could feed from one of the other mixes, the guitarist's as has been suggested or even the FOH mix

There really should be no more problem with this than doing exactly the same with an electric bass. You wouldn't put an electric bass through a vocal PA with 8" speakers and yes, you can run out of headroom much more quickly with bass frequencies so a decent amp and speakers are required but bottom E is still the same frequency. The only difference I can see as an engineer is getting a clean feed of your sound and a double bass is much more prone to feedback so you need to keep stage volumes down.