Phil Starr

When you pluck your strings they move backwards and forwards over the pickup. Just like a pendulum they are moving fastest as they cross the centre and slow down just before they reverse tracing out a pattern called a sine wave. This is turned into a voltage in the PU and then amplified to a bigger voltage by your amp. The speaker turns this into forward and backward movements tracing out the pattern of movement of your strings. The bigger the voltage your amp can swing the bigger the movement the speaker will make until it reaches its own limits. Because the movement is peaks and troughs there isn't a constant power so we don't measure the peak it only reaches for a tiny fraction of a second, especially since the amp can be designed to produce these peaks momentarily on a test but not in real life use. Since the speaker and also the voltage go backwards and forwards in equal amounts the average position and voltage is always zero so that isn't a useful measure of power either. Instead we use a mathematical trick to calculate the average displacement of the voltage called the Root Mean Square. This corresponds also to the heating effect you would get if you passed a maximum signal from the amp through a heating element instead of a speaker. There are international standards and national ones about how you should carry out these tests. Peak means nothing as there are hundreds of ways of cheating the system and no standards to protect you. There are 5W amps claiming to be 120W PMPO out there. Any amp manufacturer who publishes peak ratings is trying to cheat you and you should become suspicious of their RMS ratings too. These won't be lies (advertising laws in your country protect you) but they are just advertising. The truth will probably be in their manuals. The most common trick is to quote the RMS power into a speaker with low impedance which you would never use and which would overheat the amp if you did. For example my PA amp claims to be 2400W RMS but the manual states quite clearly that it gives 400W per channel continuously into the 8ohm speakers I actually use and 650W into 4ohms. Wikipedia is pretty good on this if you want more.

Can't really find any details on the combo. What sort of cab are the speakers in? If it is sealed there are likely to be a number of alternatives to look at. If it is ported then what are the ports like? If they are cardboard or plastic tubes then it might be possible to re-tune the cab to match new speakers.

Good advice, the port is the problem, it means you have to have an exact match. If the T/S parameters are difference the cab won't be tuned and the bass will suffer and the midrange response will determine most of the character of the speaker. Contact Trace for recommendations, you may also be able to get a re-cone, contact Wembley speakers.

[quote name='chaypup' post='1115864' date='Feb 4 2011, 08:31 PM']Thanks, thanks & thanks! Lots of good advice - this is why I love Basschat![/quote] There seems to be something about bass players! If this thread is around long you'll get Stevie, Lawrence, Alex and BFM joining in. What do you want the 8" speaker for? Are you building an alternative to your 15 or wanting something to complement it? This could affect your choice of speaker.

[quote name='bumnote' post='1115801' date='Feb 4 2011, 07:29 PM']I know from previous posts you are quite clued up on this sort of thing, I have been using an ashdown 4x8 for a while now, as does a mate of mine, and we get a really nice sound out of it, and the SWR Henry the 8x8 is pretty well regarded so its surely just a matter of finding the right speaker. As I mentioned in a previous post you can get the Sica/Ashdown spec in Neo from Hotrox but they are dear. What about the 5" speakers in Phil Jones?[/quote] You're right, there is nothing magic about speaker size and there is no reason why the right 8" speaker shouldn't sound lovely. There is no reason why a tiny speaker shouldn't go way down below bottom E or even B. All you have to do is make the cone heavier and the suspension floppier. There are loads of fairly successful hi-fi speakers that go deeper than most bass cabs with a 4" bass driver! The truth is though that all speakers are a compromise. Adding weight and reducing cone size both reduce efficiency, how much sound you get per watt. The ultimate volume you can produce depends upon the amount of air the speaker moves which is cone area times Xmax, the excursion. You can increase Xmax by increasing the coil length but this again reduces efficiency. You can also increase the efficiency by increasing the magnet size and the overall maximum volume by making a higher power handling speaker but these both increase the cost and big magnets increase the weight. An 8 might well weigh more than a 12" speaker with the same bass response and maximum output. On the plus side an eight will have a better radiation pattern than a bigger speaker. All speakers beam the sound forwards when the frequency they are producing has a wavelength less than the diameter of the speaker. Roughly 2kHz for an 8 and 1kHz for a 15. This is important for a backline speaker as it is the upper frequencies we need as musicians to cut through the mix. Alex Claber has written extensively on this. You lose this advantage if you put speakers side by side, so Chaypup should consider putting his speakers vertically in line. It is a good idea to copy/adapt successful commercial designs so I'd definitely look at the speakers you recommend. It was looking at the Phil Jones speakers in Mansons in Exeter that started me looking at small speaker designs.

Hi, PA speakers will be OK in the sense they will work ok. The sound is going to be 'neutral' though in most cases as they should be designed to have a flat response. If you can read the Thiele/small parameters look for something with a decent Xmax which is the distance the coil moves before it leaves the magnetic field. Anything over 3mm is good less than that and it will struggle to produce any real bass at high levels. I looked at the Fane sovereign 8-225 and 8-125's as possible candidates as well as the Eminence beta 8. The 8-225 looked favourite to me but I bottled it and went for 10's. All these are available from Blue Aran. Obviously you are not going to get deep bass at high efficiency out of small speakers but I love the sound of my practice amp and wondered if I could achieve this sound at gig levels. What sort of sound are you trying to get and what sort of designs are you considering?

One of the big problems for bassists is that room acoustics vary so much. Generally we practice in small rooms and I tend to be well away from my amp and facing it. Then in gigs I'm in a larger room often facing the longest room dimension and due to lack of space I'm leaning almost against my stack with the sounding passing me at knee level. In the small room at home the lowest frequencies won't propagate because there wavelength is too long, in a long thin room the lowest frequencies resonate. Surrounding walls and low ceilings reflect the sound, reinforcing bass frequencies especially and also cause comb filter effects which suck out certain frequencies. I also hear a very different sound from the audience because higher frequencies are very directional and low frequencies are not. So it often sounds woollier to me than it does for the audience. Alex has written a lot about the directional qualities of speakers including an article in a recent Bass Player magazine, and LawrenceH is spot on about trying to separate instruments in their tone spectrum. I always expect to reset my EQ every time I set up in a new room and it is more about matching the room than about my tone per se. Almost always this is about trimming bass and boosting mids compared with my practice settings. If we don't have a sound engineer then I try to use a long lead to see what it sounds like out where the audience are. The other reason for mud is the vocal mikes picking everything up. If you can get sound levels on stage down even a little and put more through the pa it really helps clean up the sound.

Fortunately this is a simple repair not least because you know exactly what needs doing. getting to the pot is time consuming, it could take over an hour to take the case apart and put it back together but replacing the pot is a five minute job. Two hours labour and a few pence for the pot should cover it but messing around with glue won't do it. Good luck!

You have 4 2x15's? I recently bought some carpet covered PA speakers. filthy but they cleaned up OK with a stiff brush and a vacuum cleaner. Getting carpet off is awful, I doubt whether it would be economic to do this unless you really love those cabs.

When you say shabby do you mean that they won't clean up well or are they torn. You can do wonders with vinyl with a can of WD40. Spray it on like a generous squirt of furniture polish and buff off with a clean cloth. repeat until clean and shiny. You can stick down little tears with PVA glue. If it curls then use a hair dryer to warm the vinyl and it will soften. You can actually iron down the vinyl if you coat both cab and vinyl with PVA and let it dry, but be warned the temperature at which the vinyl melts and the glue goes tacky are quite close. Don't melt the vinyl. Finally you end up with a few join lines where the restuck viny joins the other side of the tear. Disguise this with a black marker pen. Have fun.

I'd also recommend you get a quote for a recone, just forgot to add it.

I got my stand from Lidl, Sturdy and it folds. I am such a cheapskate.

The short answer is that it is more complex than that. If the cab is sealed then there is a good chance that the speaker will work ok in your cab. Too small a cab will raise the resonant frequency,cut deeps and create a frequency hump at the bottom end. Too big and the cab will start to roll off earlier with a weakened but extended bass but a fairly wide range of volumes will work. Big and small depend upon the speaker you choose. If the cab is a reflex(ported) cab then the speaker is tuned to the cab and just plonking a speaker in is a bit like fitting new strings and not adjusting the tuning pegs. People here will tell you what to do if you need to re tune though. If the tuning ports are round tubes it is often a relatively easy mod if the port is just a hole in the cab or worse a deep wooden channel it could be tricky. I don't know of a specialised 18" bass speaker but if you don't like the sound of an 18 then what are you doing with this cab. Fane also do 18's, Check out Blue Aran or the Fane website.

I think we are coming to the end of an era. No-one builds a computer at home in the sense of soldering components onto a circuit board and computer repair is a matter of unplugging a card and plugging a new one in. I doubt that a digital amp will be any different from a computer or an iPod in this. The other problem is that with nearly all electronics manufacture moving overseas it is getting harder to locate components. On the plus side I think that eventually digital amps are going to be a lot more reliable than the analogue stuff we are used to and these amps are going to offer ever more facilities and power at lower prices. If the copper in the transformer is worth more than the cost of a new amp then no-one is going to opt to repair. That won't stop me from trying to repair the first digital amp I break however. I must get up into the loft and start to repair those Betamax's.....

I find Behringer the most frustrating company in music. They almost get it right and somehow end up missing the point. The EP1500 is a little gem. We've had one for years, does what it says on the tin and looks to be well made. They haven't spent a lot on designing the Nuke. It is just one of their PA amps in a case with their bass pre-amp. They've just combined two products they already make into a single case. Some of their design are quite good, when they work but they are let down with stupid cost cutting, crappy connectors a handful of cheap components in an otherwise good product combined with the same couldn't care less attitude to after sales that Apple show to their customers. Don't their people read the press they get on the internet. It would cost them pence to improve the quality of their critical components and they would still have huge economies of scale. 5% on their production costs would probably improve their reliability fourfold and their sales by 50%. If their stuff was 20% more expensive but was reliable and repairable we would all be looking at it seriously, it would still be cheap. I'd love it if there was someone making cheap reliable exotic gear. I can't afford the real thing. Behringer could potentially solve all my problems, but it doesn't.

I've used an EP1500 for PA for years without problems. I've gone on to buy an EP2500 because of my so far good experience. Their PA stuff seems a lot better than their instrument amps. The EPX range are newish and use a digital power supply (which should be better) but some of their digital stuff has had reliability problems. I've no idea whether or not it applies to these amps. Don't forget though that if you are using this as a bass amp you will still need a decent pre-amp and speakers so the saving may be less than you expect. The pursuit of kilowatts isn't the best way of getting the best sound. If you want this amp for PA then it is worth considering.

The problem we all have is that we don't really have a great vocabulary for describing sounds. To me flat means that the output is the same across the frequency range but to another it could mean 'neutral sounding'. I doubt very much whether the output of the guitar is flat in a technical sense of equal output across the frequency range especially as the inductance of the coil kicks in at higher frequencies.with reinforcement from floors walls and ceilings The bottom end won't be flat in a real room either. A truly flat speaker would sound rather boomy in most rooms. The best way to hear what your bass really sounds like 'flat' is to plug it straight into a mixing desk and out to a decent pair of headphones and the next best is to listen to it DI'd. If this is the sound you like then why not go for a couple of lightweight active PA speakers?

[quote name='bassman2790' post='1084654' date='Jan 10 2011, 07:10 PM']I originally started out with one 4x10 which was more than adequate then added the second one to give me more headroom (never had the master above 2). Now, as I'm DI'd into the desk, I only need my backline to be heard primarily by me. The drummer and guitarist get a feed through their monitors. I'm thinking a 2x10 on a stand, bringing it to ear level will probably do the trick.[/quote] sounds like a plan.

[quote name='TimR' post='1083564' date='Jan 9 2011, 08:38 PM']The sensitivity of the 4x10 is 97dB the 2x10 is 95dB.[/quote] If these figures are correct then in your position I would play a gig with just one 4x10, which won't cost you anything to try. You will be 7dB (ish) down overall. I think what you will notice more is that with a lower stack you will no longer have speakers at ear level. I predict it will be loud enough, but that will depend on many things including your personal preferences. If you are worried then keep the other 4x10 in the car ready for the second half. If it does turn out to be OK then you can follow the 2x10 option. There are more sensitive 2x10's than the Peaveys out there.

Don't forget that the impedance and DC resistance are not the same. As well as the resistance of the wire itself there is the inductance of the coil to add on. Inductance is frequency dependent and so the impedance of the coil is a 'nominal' figure anyway.

the drop from 450 to 170 is 2.5dB and from 300 to 170 is 1.76dB. you will also lose some efficiency when you reduce the number of cones you are using. Using multiple cones causes all sorts of problems as the cones both reinforce and cancel the sounds each creates depending upon the phase of the sound. Ignore that last bit if it is gobbledegook. It means that the sound is beamed and what you hear depends upon where you stand. 1dB is just noticeable, 3dB is noticeable but not dramatic, 10dB is what you need to be twice as loud. I'd guess that you'll be about 6dB down. Noticeable but not half the volume. 170W through a decent 2x10 ought to be enough for most situations but it does depend upon the tone you use. If you use a mid balanced tone it will be fine, if you use a lot of deep bass then it won't and you'll need more headroom. The audience will probably hear you but you may have trouble hearing yourself. Place the 2x10 on its side so one speaker is on top, which gives the best dispersion, and point it at your ears if you can.

There are amps which more or less give double the power into 4ohms and even ones which nearly double again into 2ohms but the only amps I've seen that pull this trick off are hi fi amps. All of the designs I have seen that achieve this trick have regulated power supplies. The biggest problem is that there are several impedances in the chain, power supply, amplifier and speaker leads. Under high power all the components heat up and their resistance/impedance will rise. You'll burn your fingers on a mains transformer that has been running flat out for any time. I would think that the main restriction is the size of the mains transformer and of course, its cost. To reduce its impedance you'd have to increase the size of the windings considerably and you'd have to do something about the heat dissipation as the surface area/volume ratio decreases with size. In the end you reach a point where the cost of the power supply is exceeding the rest of the amp by a considerable amount and the supply starts to get too heavy to lift so as a designer you start to compromise. In any case if you are using the amp to amplify music rather than test signals you are more interested in the amps short term output than its continuous power. so, yes looking to see how an amp handles into 4 or 2ohms is an indication of how well it handles high currents and the quality of its power supply only giving 70% extra into 4 ohms doesn't mean the amplifier is somehow crap. I can't imagine there are these sorts of discussions on the guitar forums somehow.

I too think it is the speaker protection. You shouldn't see it round the speaker though as it should be airtight and hence light tight, probably. Anyway one thing that will cause the tweeter to overload is distortion, particularly clipping. Distortion is mainly high frequency energy and your tweeter may be getting a lot more power than it is designed for. The bulb is protecting it but you might like to think about turning down any treble boost or any distortion effects.

Behringer stuff doesn't have a good reputation but we have been using an EP1500 for years without problems and as a result I've just bought an EP2500. Their digital stuff seems to have problems because of poor connectors and their instrument amps don't sound too good but some of their PA seems ok. the biggest problem is their after sales which is on a par with Apple.

Your amp should be safe enough but I too don't really understand the thinking behind running silently. On-stage you need to hear yourself and when recording you need a good clean feed which you can more easily shape after you've recorded, unless you want the sound coming from the amp, in which case you need to mic' up the speakers. One problem with dummy loads is you can't hear if anything goes wrong, normally if you get any strange noises or high levels of overload distortion from an amp you turn it off/down pronto to save damage. you won't be able to do this if you can't hear.