Phil Starr

[quote name='dincz' post='1123066' date='Feb 10 2011, 07:28 PM']Is there any way to widen the high frequency dispersion of large drivers by adding some kind of magic reflector (effectively a kind of "audio lens") in front of the cone?[/quote] this used to be quite common with high frequency horns sporting multi finned diffraction gratings and bullet tweeters with diffracting slots. The other pathway is to use a horn to control directivity, though the horn itself will act as a high pass filter and boost the efficiency within its pass band but not below leaving you with a shelved response. Bass horns are too big to be practical. A far better option for bassists is to use a midrange cone in the 4-6" range with a proper crossover to handle the upper octaves. Alex already does this as do several other manufacturers and this is a lot less gimmicky than adding a HF horn.

Maybe it is because I used to teach science but I worry about over-simplification intended to clarify explanations for non-technical people because it leads to the spreading of ideas which are false, particularly since the salesmen and advertisers are only too willing to exploit any such myths. There aren't any truths about all 15's or all 10's, even the beaming isn't true because as Alex has explained the cone is flexing at higher frequencies so the radiation is effectively from a reduced area. (That in itself is a simplification) However there are things that are easier to do with big speakers and small ones and if you go through, say, the Eminence catalogue you will see that on average their 15's are more efficient go deeper and have poorer hi frequencies than their 10's. Both this and the fact that there are exceptions to this general tendency are easily explicable with the physics that a lot of us know. A lot of modern designs are concentrating on the holy grail of deep bass with portability. Smaller cabs are easier to carry for musicians and easier for shops and distributors. Smaller cabs ultimately need to use smaller speakers (although not all small speakers need smaller cabs). Smaller speakers are also generally lighter. It has never been true that there is a sound of a 15 or a 10 and small speakers can be made to go low by simply adding weight to the cone and using a softer suspension, no different to a bass string really. Adding weight to the cone will generally make it more rigid and this will increase the area in which the speaker acts as a piston and will subdue the midrange. Making it heavier will make it harder to accelerate reducing the top end further and will also reduce its efficiency. That is why this happens [quote name='alexclaber' post='1121592' date='Feb 9 2011, 05:19 PM']A more consistent thing is that any conventional cab (i.e. woofer only or woofer plus tweeter) which has particularly deep fat lows is likely to be subdued in the midrange.[/quote] Designers make trade offs and then look at ways of compensating for the effects. Better magnets, more power handling, longer excursion limits, shaped frequency responses can all be used to restore some of what has been lost by using a smaller speaker and you can also use multiple units, but that comes at its own costs. Equally someone using a single 15 in a design can compensate for the shortcomings inherent in this pathway to squeeze extra mids and reduce beaming. This is pretty much what the Barefaced Compact represents for example, a good set of compromises using modern speaker technology to achieve a particular design aim. I suppose what I want is for people to be aware of the idea of speaker designs all being compromises, and that they can't have everything in a single solution. If someone promises everything in a simple tiny box they aren't being honest. There isn't any magic either, good engineering and the laws of physics can explain what a design does and how it does it. In the end musicians have to trust their ears and if a design works for you that is good, the designer has made the compromises that suit you. Don't close your mind to new designs without hearing them but don't believe all the hype either.

I'm going to back up Lawrence here. The information on beaming is spot on with Mr Foxen's figures but with Alex's proviso that this refers only to the theoretical piston region and that all practical drivers operate under cone break-up which both extends their frequency response and affects their dispersion characteristics. Diameter also affects the weight of the cone which affects its resonant frequency, big cones can and do go lower. Diameter affects the area of a cone which affects efficiency and maximum volume. It also affects the amount of air that can be moved needing lower excursion for the same volume. Excursion limiting is a big factor in bass speakers design and something both Bill and Alex pay a lot of attention to. In fact most of the T/S parameters are affected by the diaphragm mass so to say that all the rest is Theile/Small is missing something. On top of all this are all the practical considerations like changing the suspension to accommodate a bigger heavier cone and probable changes to coil diameter, diaphragm thickness etc. etc. The problem is that all speakers are compromises, change one thing and you gain in one area but lose elsewhere. A thick heavy cone will lower your resonant frequency but has all sorts of other implications for the sound of a speaker. It is easier to get certain things out of a big speaker and easier to get other things out of a small speaker but the world of speakers is a Venn diagram where there can be a lot of overlap. Saying Usain Bolt can run faster than me because he is so tall is missing an awful lot of other differences but a good big un cvan do things that a good little un can't

What is the volume of a bass uke like unamplified?

Ported cabs are tricky beasts, both the volume of the cab and the size of the ports have to be matched to the speakers you use in them. If the cab is too big then it squashes all the bass out, too small and it cuts out early and gives you a bass hump. The port has to tune to the resonance of the speaker, too high and the speaker is uncontrolled at the low end, too low and it will do nothing worthwhile. Putting any old speaker, even good ones in a cab is just like putting new strings on your bass but not bothering to tune them. Unlikely to sound good! If you can give us the internal dimensions of the cab and the size and shape of the port(s) we might be able to suggest some mods which will tune the cab.

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.