Phil Starr

I think people are being a bit pessimistic about the inverter. The guy who did the calculations is probably pretty close ( i can't fault his reasoning) but remember you are not playing full volume continuously, there are loud and quiet bits. My 20W Peavey practice amp almost matches a drumkit when we practice in an enclosed practice space and even, say, 5W will be louder than an acoustic bass and more than match an acoustic guitar. If you turn it down it should give you a lot more battery life and are you really going to play longer than a two hour set. I'd try it and if it runs flat too quickly you can always connect it to a car battery for more life.

I've used these a lot and being lazy and usually prototyping/fiddling tend to just solder direct. the resistors don't usually get that hot and I've even got away with 1W resistors. It is unlikely that there will be any inbuilt protection or internal resistor. As far as I know Motorola and CTS have stopped making piezo's and all I've been able to find recently are the cheap clones. Having said that I've had a lot of success with this one [url="http://www.bluearan.co.uk/index.php?id=SKT902490&seeimage=YES&img_name=902490_CO1"]http://www.bluearan.co.uk/index.php?id=SKT...name=902490_CO1[/url] which is unbelievably cheap for the sound it makes. If anyone out there finds a supplier of better quality piezos I'd be pleased to find out. I'd recommend using silicone to fix the resistor down to the back of the tweeter.

The termination between the cone and the surround takes an awful lot of energy and eventually like all moving parts it fails. Often you find that the paper fibres under the glue are what has actually failed. The joint has to be flexible so the only really practical glue to use is a latex based one like copydex. Ive successfully repaired small tears with toilet tissue replacing the broken fibres laminated in place with Copydex but I don't think You'll be successful with such an extensive repair.

I love Basschat the answers are always so sensible. It looks like the BBC's description of bassists as the responsible organised ones in the band was pretty close. The other possibility is that the protection circuits in your amp were cutting in. Some amps have a circuit in the power supply that cuts the power in adverse conditions to protect the amp. Again it would be the generators at fault. It does mean that your amp won't suffer any long term harm though.

I use a little 4 channel mixer with some decent headphones for most of my practice. (it was actually designed for dubbing sound into videos and cost £10) You get the cleanest sound you will ever hear so it is great for highlighting any technical problems and you can mix in an iPod or a drum machine. It isn't like playing live but it is like studio work and you can practice for hours whilst the family watch the TV if you need to. Headphones.

The easiest way to do this would be to buy a lead with a muting plug. Pull it out 1/4" and it will automatically ground the signal.

If you are picking up only when you are near the other instruments it is less likely to be the hearing loop than radio pickup. Shielding may help a lot and there is nothing to be lost by checking this. If there is radio pickup then one little trick is to short it out before it reaches the amp. A very small capacitor will be a straight short to rf but not to audio frequencies. If you have a jack lead where the cover will unscrew then try touching a 4.7pF capacitor across the two terminals (sleeve and pin). If it works then you can solder it permanently to the jack socket inside the guitar. A capacitor this size only costs pence.

Of course that is true though if you are running high levels of distortion then you can get to within a significant %age of these figures. Nevertheless heat remains one of the main reasons for failure of drive units and magnets do regularly reach temps of well over 100C in normal use. I know from the days when I manufactured speakers that their reliability and longevity was better without stuffing. Modern coils are much better than older ones at resisting thermal breakdown but why create a problem? In addition some manufacturers do publish figures showing the loss of power due to rising temperatures when operated at continuous high levels.

[quote name='Mr. Foxen' post='866195' date='Jun 13 2010, 05:35 PM']I know this one has been disproven, BFM has pointed this out a few times, apparently it lowers the box Q but not the other benefits of increased size, although I still don't know what that means, aside from it cleans up midrange, rather than adding bottom like a larger box would.[/quote] If you get a look at the Loudspeaker Design Cookbook there are a collection of Graphs which represent data from experiments with different levels of stuffing and differing materials. They show both the lowering of Q directly from the impedance curves and the changes in frequency response created by stuffing. At low frequencies they tie in fairly with the idea of a 10%'ish increase in volume. I don't have the data in front of me but the concept of the transmission of sound being slower in dense stuffing comes from work on transmission line cabs and the phase inversions at the exit ports. Certainly the speed of sound is different in different materials and this is something you can look up in books of constants. I'm not keen on stuffing high power cabs for an entirely different reason. All of the stuffings are also good heat insulators. Speakers only convert between 2 and 5% of the energy into sound the rest is dissipated as heat in the cab. A 500W speaker is radiating the same heat as 4or 5 large incandescent lights or a 500W electric bar fire. All this inside a tiny enclosed space. The back of a speaker magnet at full power will be hot enough to burn without any insulation. All this heat changes the resistance of the voice coil dramatically and the tolerances of every part of the system and the air inside the cab will have very different properties too. None of the thiele/Small figures will continue to hold true and the sound of the cab does demonstrably change if you push it hard over a long evening. Adding the weight of stuffing needed to change the characteristics of a cab will make these problems a lot worse and will also increase the chance of failure of the speaker quite dramatically. I'd need to be able to hear a great deal of sonic benefit to take this on. I suppose I just wanted to alert you to the controversies about stuffing which theoreticians will pursue never mind the more practical people you will come across here. You won't get definitive answers to this one.

Stuffing is quite a complex matter as there are at least three ways in which it affects the internal environment of the cab. Heavy felts and rubbers mass load the panels and reduce resonances and the bits behind the cone reduce reflection of sound out through the thin paper of the cone itself especially if it is thick and its surface is uneven. (The felt that is, not the cone) Fibrous stuffing in the air space behind the speaker helps to break up standing wave resonances especially if placed at the nodal points of such resonances. Finally filling the air space slows the transmission of sound which increases the effective volume of the cab by about 10%. If you get hold of the 'loudspeaker design cookbook' by Vance Dickason there is some extensive information on this. Having said this opinion is really quite divided as to the advantages of 'stuffing' and what the best materials are and how much to use. I guess the difference between bass and guitar usage is that bassist like their speakers to be more accurate than guitarists who depend upon reaonances to give a characteristic cab sound.

You've probably guessed that getting the old stuff off is the tricky bit. I'd just use a scraper and some judicious heat as the adhesive will just clog up sandpaper. I use white PVA adhesive to stick the vinyl on. Sticking it on the flat surfaces is easy and you can use a seam roller to remove air bubbles if you have to. Getting it to fold round the edges is much trickier; I use the adhesive on both surfaces and let it almost dry. then I heat the vinyl/tolex with a hot air stripper (take care) which makes it quite floppy and then I smooth it over whatever the problem bit is. If the PVA dries on both surfaces it can be melted with an iron and your tolex becomes iron on but be careful as a hot as opposed to warm iron will melt your covering. Where did you get the coloured tolex from? It is hard to track down.

[quote name='Bill Fitzmaurice' post='857879' date='Jun 5 2010, 12:46 AM']Not if they do it the right way, by reducing the number of windings on the same former. But your point is valid, not every driver manufacturer does things the right way, and you must pay attention to all the driver specs, not just impedance.[/quote] You're right Bill, there is no reason for this to be a problem other than keeping the cost of manufacture down by a few pence/cents but all the drivers I have looked at by Celestion/Eminence/Fane have gone down this route, more exotic manufacturers may have done this properly. I simply don't have the data to know if the 4/16 ohm units in commercially made cabs have been properly engineered. It is something I can get very grumpy about, the manufacturers must know they are selling these speakers which are sometimes not fit for purpose and usually to someone who thinks they are getting the same speaker but just in 4ohms.

There's a problem with most 4ohm drivers as well. they are usually made by just changing the voice coil for a shorter one which makes them less than optimum. typically the low level efficiency goes up at the expense of a much reduces excursion (Xmax) which means running out of grunt at higher sound levels. Another reason for not doing it.

You really need to try your speaker with another amp or another speaker with your amp to be certain of where the fault is. The speaker is the leading suspect but some failing capacitors could give you crackling at high levels. It is not unusual for one speaker to move more than another even if they are all working perfectly though if they do it probably means this speaker should not be in this cab for other reasons. Good luck

Actually I think a lot of this has to do with technology. When I started amplifier watts were really expensive and transistors which ran above 70V were unreliable and almost non existent. 100W was a big amp. Speakers were therefore made to squeeze as much sound out as possible with lots of big but lightweight cones which were loud but lacked bass extension. Now with FET's and class D amps watts cost pennies and we have more flexibility. Unfortunately guitarists watts are equally cheap and they can all afford to buy amps which make your ears bleed so we have to compete. The other thing is the improvement in PA's and monitors. We can be quieter on stage if we want and let the PA do the work. Hence all the metallists discussing 2x4x10's versus 8x10 whilst others pursue the ultimate lightweight solution. We are in the great situation of having choice so long as the rest of the band let us.

It also sometimes happens that an amp will start to oscillate without a load which could cause problems. It is one of those things that will probably be OK but isn't really good practice.

[quote name='stevie' post='848913' date='May 26 2010, 08:58 PM']It was a budget brand. I knew their PA speakers but I didn't even know they made a bass amp. They were well built though, with decent parts, but they were aimed at the lower end of the market. Your best bet might be to keep your eyes peeled for a secondhand unit. The current budget speaker best buys in the UK come from Fane and Celestion, both designed in the UK and built in China. I believe Phil has some recent experience of these.[/quote] It is the 10" Fanes that I have been using recently so no direct experience of the 15's. Very happy with the 10's so far and they are well made and meet their specs pretty well. If you go for Fane use the sovereign 15-500, the 15-300 is discontinued, the 15-400 would work in your cab and is cheaper but would compress the bass slightly more than the 500 at high volumes. Blue Aran have a single Eminence Kappa on offer at the moment which would just work for you.

[quote name='Mr. Foxen' post='847483' date='May 25 2010, 01:38 PM']The by all accounts very good Eminence Kappalite 3015 looks to be ok in this box, not gonna go really low, but it is the first thing I modeled, and it looks happy, I am supposing the port is a round one? If you can get another driver much cheaper, might be better with one of those, you'd be wasting a bunch of the potential of the kappalite.[/quote] Yep the kappalite looks good for this cab and it does have a nice little peak. If you can put up with a bit less presence and a bit of boom at the bottom end then the Fane Soveriegn 500 would just about do the job. Blue Aran are good suppliers.

Just to save anyone else needing to do the calculation the cab is 52litres. this is fairly modest for a 15" speaker so you are probably looking for something with a fairly decent magnet if you want a tight non boomy bass. Try reading this as a start [url="http://www.ultimate-guitar.com/columns/gear_maintenance/choosing_speakers_to_drive_your_cabs.html"]http://www.ultimate-guitar.com/columns/gea..._your_cabs.html[/url] You sound as if you quite like the tone of the speaker you have so why don't you stick with it whilst it is reliable the only speakers I can find quickly that would be happy in a cab this size would be the Celestion BN15-400S or one of the Peavey Black Widows though I am sure that there are others. Of course it is not unusual for manufacturers to compromise the cabinet volume for convenience and for people to be happy with the sound. It would be interesting to see a pic of the current speaker to see if the magnet looks adequate for the cab it is operating in.

[quote name='Bo Millward' post='845843' date='May 23 2010, 04:21 PM']Cheers for the advice man, if I partition the cab inside so each speaker is loaded in its own sealed enclosure would that help to prevent this? (Oh, and add ports to each section)[/quote] I quite like partitioned cabs because they stiffen up the structure and reduce the interaction between two speakers however this won't solve the problem of the cabinet volume. I have done this by removing the back of a speaker and then putting a new back in place a few inches in front of the old back which I then put back to cover up what I had done. this makes the cab quite heavy but since the outermost 'back' is just cosmetic you could use a very thin panel. Sorry I was a bit negative about your speakers but if you like the sound then they are good and if it is the sound you want then you should trust your ears and not some techie advice. Thinking about what you are trying to achieve though it would be quite interesting to use just one of the Celestions with a partition inside the cab and then another 15 with a better midrange/top end in the larger top half of the cab. I don't know how you are getting on with WinIsd but if you are having problems I'll try and give you a hand with design.

your finished speakers are going to be overdamped which means that the bass, whilst going deep, will be somewhat squashed. With a Qts of 0.24 damping is very high and the speakers are designed to be used in a smaller box than the one you are going to put them in. Although the bass promises to be clean and have good transient response I suspect they wont be the bass monsters you are hoping for. In addition the lack of response above 2500Hz will mean that they will lack articulation and the ability to cut through the mix

[quote name='Ruck' post='840163' date='May 17 2010, 08:38 PM']Thanks for the suggestion, Im currently getting a second opinion from another techy but if he says the same about needing a replacement driver I might try fully removing the dustcap. Whats the best method for this please?[/quote] There's no magic method just work it loose a little at a time work round gently from the loose bit.

If it is any help I've found that when a dust cap comes loose the only way to fix it is to take it right off and re glue it all round. Just tackiing back the loose bit never seems to work. However pressing on the dust cap doesn't just move the dust cap so it may be a coil scratching which does mean a new speaker. You may be able to get it re-coned though which may only cost £40-50 if you can find someone to do it. I use copydex to re stick loudspeaker parts.

I used a Black Widow in my 1x15 and it does sound good. Clean bass and great top end for a 15.

[quote name='Bill Fitzmaurice' post='828743' date='May 5 2010, 06:05 PM']60l is adequate for twelves with Qts of .4 or less. As for the perception of low end response, the human ear is very inaccurate; most people are about an octave low in their estimates of the frequency they're hearing. Low 'B' players who swear they're knocking down walls with 32Hz output are actually hearing the 2nd harmonic at 64Hz. Good thing, as otherwise even a Fridge wouldn't be up to 5 stringer needs.[/quote] so true,try to get the chance to listen to a 32Hz sine wave through your speakers . If you hear it at all then you'll be amazed at how low it sounds. [quote name='Mr.T' post='828812' date='May 5 2010, 06:55 PM']Does that mean it's Ok for me to think that my new cabs sound good? [/quote] theory is great but if it sounds good; then it sounds good!