Phil Starr

[quote name='gilmour' post='902509' date='Jul 22 2010, 11:08 PM']Found time to glue the arrays today. I'm pleased they look pretty smart. They still feel a little brittle but hopefully once the glues had a coupe of days to go off this will change, otherwise I'm not sure what to do. Anyone got any suggestions? Peace'n'hair grease R[/quote] You've left the flanges on the sides so run a batten along the back and fix the horns to the battens which will stiffen them up

You might find this useful [url="http://www.ultimate-guitar.com/columns/gear_maintenance/a_guide_to_fixing_intermittent_faults.html"]http://www.ultimate-guitar.com/columns/gea...ent_faults.html[/url]

[quote name='algmusic' post='899855' date='Jul 20 2010, 11:48 AM']I love this kind of bravery.. I just can't afford the risk of blowing my amp.. I've only done this once at rehearsal an played very quietly, but I always have the rule of getting a cab that can handle at least about 20% more than the amp, then you can drive the beast how you want... I'm sure you get a better sound.. well IMHP[/quote] I'm not that brave. I make my own speakers so the cost of a replacement drive unit is a lot less, plus I use meters on the output of amps and sound level meters to monitor whilst testing. In the end though the physics is pretty reliable. I suppose the point I am making is that you don't need to do anything other than take a lot of ratings with a pinch of salt. A 250W amp shouldn't be capable of blowing a 200W speaker in a month of Sundays unless there is tremendous abuse. The only exception to this is tweeters. When driven into distortion the bulk of the extra power will go into the speaker as high frequency energy and blow the tweeter if fitted. I haven't blown a speaker in nearly 40 years. [quote name='Mr. Foxen' post='899903' date='Jul 20 2010, 12:37 PM']Depends on what you mean by 'handle', and at what rating. Plenty of cabs won't handle 80% of their rated RMS power due to excursion limit at the frequency where cone excursion is at maximum. Exceeding the excursion limit is the bit that will break most bass guitar speakers, because you don't need to do it for a length of time, push the speaker past that limit and its gone.[/quote] Exceeding the excursion limit is a theoretical cause of failure but one that doesn't occur in properly designed musical instrument drivers. Remember that at high levels the coil moves out of the gap to the fringes of the magnetic field so the force moving the cone is reduced (causing distortion and loss of power.) At the same time the suspension will exert a much greater restoring force to the cone holding it in place. I can't think of a single example of a designer failing to allow for this and have never seen a speaker fail in this way. However reflex/sealed and open cabs require different levels of protection against this so I would avoid using a speaker in the wrong cab. you are qute right about speakers not handling their RMS power due to excursion limits though There are very few if any bass speakers that are not excursion limited at low frequencies and full power.

[quote name='270degrees' post='897331' date='Jul 17 2010, 03:03 PM']You're more likely to blow a cone using an underpowered amp. Just use common sense when operating the volume control. Also note that the speaker can probably handle more power than stated and the figure quoted includes a safety buffer of some sort.[/quote] This is one of the old chestnuts and like most it has a grain of truth in it. Assuming we are talking RMS or EIA watts or something similar the amp is rated on the undistorted sine wave it can produce for a few hours continuously into a stated load. usually nowadays it is rated on sine waves in the form of filtered noise called pink noise which is meant to be like music in its energy content. When an amp distorts the sound waves rise to a peak much more quickly, clip at the amps full power and then drop quickly. This means that on every wave there is more time at full power and the amp has more energy to handle and so does the speaker. The absolute maximum is a Square wave which contains 1.414 (root 2) times the power of a sine wave with the same voltage peak. So a 100W amp with total distortion will give 14oW in the speaker. It won't outpower a 200Wamp though. Speakers are rated differently. What destroys speakers is heat, 100W through a speaker means the coil gets as hot as an old fashioned light bulb. in the old days this melted the glue and the coil unwound, sometimes you even saw charring and smoke from a paper former. The EIA rating of a speaker is the heat it can dissipate for a few hours. It even assumes that the air can circulate freely in the test room and is at 20degrees. There is usually a peak or music figure 2-4 times the EIA rating, if this is done properly this should be the figure where the distortion reaches 10% and becomes audible. If you are playing normally then you have loud bits and quiet bits. The quiet bits let the coil cool down so the speaker can handle a lot more than its rating so long as it isn't distorting. If you play with a 40dB range (no compression) your 500w amp is only putting an average of 5W into the speakers. If you use lots of compression and bass boost/distortion you probably still have a 20dB dynamic range and are only putting an average 50W into the speakers so don't worry about a minor mismatch unless you get lots of distortion. The physics is on your side.

Ashdowns only give half there rated power through the internal 8ohm speaker so adding another 8 ohm cab will give you roughly an extra 6dB. If you buy a cab you want to keep then this could be the start of a new rig and in the meantime you have something gigable. If you buy a top quality cab then you can add a head when you can afford it. If the state of the Ashdown is troubling you then they can usually be cleaned up. Stick any loose covering back down (sometimes it can be ironed back down as the heat melts the adhesive) Clean carpet with carpet shampoo and a suede brush for stubborn stains. Any vinyl comes up a treat with a wipe with a clean cloth and WD40. Replace any damaged corners with a new set.

Go for the polyester or poly propylene, Don't use ceramics

You've probably got more than enough leads now but Mansons in Exeter is always a joy to visit if you are into guitar/bass ,and does a good job and there is a guitar tech at Westside music in Taunton (who actually showed me how to set my neck up)

Enjoying this thread, keep up the good work!

Its worth looking at something that runs off batteries if your like me and just want to set up anywhere to practice.

I do most of my practice with headphones. The most important thing is the quality of the headphones. Good over-ear headphones are needed, I use Sennheisers though my daughter's £30 Sony are nearly as good. Any cheap mixer will do the job as a headphone amp and a mixer gives you the possibility of playing along with backing tracks/drum machines. I use a very cheap 4 channel mixer designed for dubbing sound onto Video but have used a DJ mixer. Even my cheap mixer sounds much cleaner than any stage amp or even DI into the PA. The headphones go deeper than any currently available speaker (20Hz) and are clean all the way down, they also go up to 20,000Hz. The result is that you hear yourself very clearly and every little fault shows up. I think this is just what you want for a practice but it takes a little while to get used to the sound. I can remember seeing an amp modelling unit which had a built in drum machine and a headphone amp. I think it was a Boss. I didn't buy it because I didn't like the sound of the amp modelling but it would be ideal for headphone practice.

Why not get another Hartke if it suited you perfectly?

I'm not sure what you mean by depth of sound. If you mean more power then I'm not sure adding to your speakers in this way will help. You can't have a lower impedance and still match your amp and a higher impedance will lose power though it may increase efficiency, the best you can hope for is to stay the same as far as volume is concerned unless you change your speakers entirely. If it is the limitation of your 2x10 and you want deeper bass then the best way of doing it would be to convert your cab to 16 ohms (probably not difficult) and add another 16 ohm speaker. You could also take up the suggestion of an extra amp. It need only be a cheap PA power amp driven by your existing amp. Better still get the extra volume off stage and DI through the PA which avoids all the problems of the bass being pcked up by the vocal mics.

+1 for Ashdown being helpful. Have you tried another Speakon lead? It sounds like an intermittent connection and could be the socket but is more likely to be the lead. If you are my end of Dorset then Axe music in Axminster does repairs

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.