Phil Starr

[quote name='LawrenceH' post='1177372' date='Mar 26 2011, 05:12 PM']Also, incidentally that graph is very revealing about axial rotation on the string movement. I assume that the rise-dip-rise response on the 1st harmonic (or 2nd, depending on preferred nomenclature!) is because the plane of string vibration shifts from horizontal to vertical back to horizontal in relation to the pickup poles. Makes me realise that there's another potential source of audible 'beats' to a note, on top of any pitch-based phase interference (as in when tuning by harmonics). It also makes me think that a volume drop in low frequency harmonics in my slap playing v fingerstyle is probably because I'm hitting the string too vertically, and I should aim for a different angle of string attack to better excite the pickup. Who'd have thought that a frequency response graph could teach you something about playing technique? [/quote] It's an interesting graph the even harmonics are showing a very different decay to the odd numbered harmonics, I wonder why. I'll bet there's some sort of series in the maths. Back when i taught science we used to stretch a long steel wire over a bench and watch the vibration with a strobe light. You could clearly see the nodes moving as the vibration decayed.

I can think of several good reasons why effects should change with volume. One is the equal loudness effect which Alex Claber has recently written on. Basically (no pun) as volume increases you hear bass and treble better so it sounds the same as if you had adjusted your EQ. At high sound levels there can be an audible doppler effect if one speaker is trying to reproduce all the frequencies. Also at high frequencies the speaker will become less linear as the voice coil moves out of the magnet gap. Fuzz involves extra high frequency energy and this can overload a tweeter or kick in the protection circuit. None of this helps though as you would have to experiment to find the best settings at any given volume for any given speaker. At least you know you aren't imagining this effect,

The HK Lucas speakers are also highly rated and though I can't find specs for your system which seems to be discontinued I cetainly wouldn't expect the Proels to be any louder, However there does seem to be something wrong here, it probably is time to get back to the dealer.

It doesn't sound right for it to buzz/hum with nothing connected. Is the hum coming out of the speaker or is it coming from something inside the cab. I've had poorly made transformers be really quite noisy especially when you first switch them on. It is fine for your mic to be able to overload the system. You'd want to be able to get the full wattage out of even a low output mic so the 'hotter' mic's would be able to overload the amp. you just have to turn down.

[quote name='yorks5stringer' post='1170112' date='Mar 20 2011, 09:53 PM']No, it's not a perception thing...if I plug via the Mixer into the Mic In on the Speakers then there is plenty of power but the clip light comes on with the gain on at 9 oclock (zero is at 6 oclock) If I plug into the Line In, they are about half the volume and no louder than my Hi Fi even on full gain. Both with an MP3 track which rattles the other PA This is coupled with a buzz when first switched on which does not go by pressing ground loop switches or swapping to different mains circuits. Gigged with them last night, plenty of power when into Mic In but clip light on as above. Have tried fiddling with EQ's but surely I should be going into the Line In and getting adequate volume: the Mic In is really too sensitive( hence the early clipping)? Could'nt get to the back of the pub to listen last night as the cordless bass thing was on the blink![/quote] OK I think we may be confusing gain with power. The position of the volume control is irrelevant, it doesn't matter if the volume control is at 9 o'clock or 3.30. You may just be dealing with a mismatch between your mixer and your new speakers. Let's say your mixer gives out 100mV, the mic input is expecting 1mV and the line input 1000mV. This means your mixer is swamping the mic input unless it is turned right down. When you transfer the output to the line input the 100mV aren't enough to drive the amp to its full capacity. You can't get full output. The hum and noise the mixer put out will have a fixed component which is unaffected by the position of the volume controls on the mixer, especially the hum. Let us say it is 1/10th of a mV. When you were driving your old amp the hum wasn't noticeable as it was only a thousandth of the signal. Into the much more sensitive mic input it is now a 1/10th of the signal and you hear it all the time. A little test you can do is to set it up for maximum hum and then turn off the mains to the mixer, but not to the amp. It should keep going for a second or two but the hum will magically disappear. Another problem is that the mic input is probably 300ohms or low impedance and the mixer may be designed to match a high impedance input. Alex Claber has an article on this site [url="http://basschat.co.uk/index.php?showtopic=3730"]http://basschat.co.uk/index.php?showtopic=3730[/url] which might be worth reading. There's a number of things you could do, borrow another mixer with a higher output and see if the problem goes away. You can buy booster pre amps which will give you a little extra gain so you can match the line input. One cheap way of doing that might be to buy a simple little stereo mixer or even a graphic with a bit of gain to go between mixer and amp. If the Behringer is like the one I used to use then you might find one of the other line outputs or the control room output is a better match for your speakers. Let us know how you get on

The Proels ought to be OK, as you say they have reviewed extremely well. They use well rated Celestion drivers and claim a peak output of 128dB. The cdx1-1731 compression driver gives 110dB @ 1W and handles 75W giving 128dB which matches the Proel claim well enough. Proel say the amp is 400+100W 'continuous' and I'd use a 100W with this horn driver so the ratings probably are 'RMS' The bass driver looks like the TN1230 which will 'only' give 124dB at 400W however. The Celestion drivers don't have particularly good excursion so low frequencies might be limited at very high power. The HK's aren't bad speakers but the Proels ought to be louder. The only possible explanation I could guess at is that the lack of a bass bin is leaving you a little short here or that the flat response of the Proels is making them subjectively quieter. Alternatively the limit Leds may be coming in too soon. I've just re read your post. The noise when you switch on shouldn't happen. It may indicate some instability in the system which is eating up power. If they are under warranty get it checked out. Good Luck

This brought back memories, I designed something similar back in 1974. Bill is being a little harsh, though he is spot on with his date. It was around this time that the work of Thiele and Small was beginning to circulate which put the design of bass reflex/ported cabs on a firm theoretical basis. Before this the design of ported cabs was down to experience and inspired guesswork. We knew well enough how to tune the cabs as the physics of Helmholtz resonators was well enough known. Practical cabs were developed by measuring impedance plots. My theory was that by using a wedge shaped port I could produce a broader and flatter impedance peak for the 'horn' to better match the impedance peak at resonance of the speaker. It sounds a little far fetched to me now and I would explain it all in terms of Q but it was an honest attempt at the time, blown away now by better theoretical understanding and much better drivers. The speaker itself sounded quite good by the standard of the day and I sold quite a few. Enjoy your speaker as it is but don't waste money trying to upgrade it.

Those are PA speakers, I have some Yamaha monitors which are slightly older than these and they are awful! I also have some S112's and they are great. At some stage Yamaha started manufacturng in the USA using eminence speakers and as far as I can see the 15's could be eminences. If the S prefix indicated they are part of the club series then they are likely to be quite good speakers

firstly I don't believe this to be a universal truth, I am sure a lot of valve amps work perfectly happily with a lot of ported speakers. If there is a grain of truth in this I would suspect the interaction between the amp and speaker at low frequencies. The underlying reason for the impedance changes in the post above is that the speaker creates electrical currents as it moves in the magnetic field, these are in the opposite direction to the original signal. The biggest back EMF is created in a sealed cab at the bottom resonance but the sealed air in the cab controls the movement of the cone and hence the back EMF below resonance, in a ported cab the resonance peak is reduced but there is very little to control the movement of the cone below resonance and the back EMF can be quite large. Solid state amps differ from valve amps in three ways which would interact with this back emf. They usually have much larger amounts of negative feedback designed into the circuits which (sort of) compares the output of the amp with the input and corrects for any distortions. Secondly they usually have lower output impedances than valve amps and hence better damping factors. Thirdly the output transformers of valve amps are going to react in a fairly complex way with the back emf which will already be out of phase with the signal. A lot of this can be got rid of by filtering subsonic signals and most amps do this either by accident or design anyway. At a practical level this is not something I would worry about. Your ears will tell you if a particular amp and speaker work well together.

[quote name='stingrayPete1977' post='1149127' date='Mar 4 2011, 12:35 AM']I had a 115 with a black widow and was easily a better sound than my top of the range Ashdown rig that blew up 18 months ago! I only changed rig because as someone said earlier it won't match a Marshall 4x12 which is exactly what our guitarist bought. Heavy and awkward but great sound and good volume for £2-300 I wouldn't hesitate if that was my budget [/quote] You're going to have to show your guitarist the volume control. It might take a lot of explanation but they get there in the end.

[quote name='challxyz' post='1142135' date='Feb 26 2011, 10:22 AM']I'm toying with the idea of modifying my mesa 1x15 8ohm cab, I want it be a 4ohm cab, now this might sound like a really dumb question but is it just a case of swapping the 8ohm for a 4ohm and that's that? does the tweeter make any difference to the impedance and if so would I need to change that too? any advice greatly appreciated :-) Cheers[/quote] I guess you've decided not to do it but there is one more reason not to. Making a 4ohm speaker is often done by just changing the voice coil and this changes all the T/S parameters meaning you need to change the cab. The most common change is to simply use a shorter voice coil and this reduces the excursion limit and hence your bass at power. Both Celestion and Eminence do just this. There's no reason why you can't engineer a 4 but it is rarely anything other than a bodged 8.

[quote name='VxR Rusty' post='1140512' date='Feb 24 2011, 09:47 PM']Just curious really, ive had a laney 2x15 cab for 5-6 years now, its pretty good, but ive used a few other 2x15s and some single 15s with my head at gigs and, well they seem to drive better. just wondering what your opinions are really[/quote] I think you've found out that 15's don't have a'sound', they are all different. The size of a speaker is only one factor in the way they sound. It's nice to have a speaker and your amp at head level and a 'fridge' looks good but why carry two speakers when one will do?

the question is not whether the sound will be better than using 'proper' subs, it won't, but will it be better than just your PA on its own. Without knowing all about the band ,the venues and the PA none of us mcan say. icastle is right, without a crossover all the signal can go through the PA speakers, so the speaker won't be acting as a sub. If you drive the amp off the mixer everything will go through it and the PA speakers so vocals will be distorted by the bass speaker. At the same time the kick will either overload the PA and cause problems or it won't and you didn't need the 4x10 anyway. The alternative is to use the 4x10 as a kind of drum monitor/backline. We tried putting kick through my bass amp just once, funnily enough it made timing an issue because it was hard for me to hear my 'leading edges' over the kick. If you run the 4x10 as just a drum speaker it won't affect the bass amp or the PA though so that isn't an issue. It might sound OK or not. Try it out at practice though first.

[quote name='Marvin' post='1132565' date='Feb 18 2011, 06:35 PM']Band I'm with are currently working on Roxanne and Every Breath. I was considering suggesting Spirits in a material world. We did Roxanne for the first time last night at practice. The most difficult part seems to be just timing that first note on the verses. The drummer isn't too sure about the song so everything is a little hesitant.[/quote] We do Roxanne. It became part of our set when we had to play it to accompany a dancer. The timing problem is a quarter beat pause on the bass at the beginning of the verse, not to tricky to coordinate with the vocals if your bass player and singer can synchronise! Once it clicks it's fun to mess about with the rhythm.

There are loads of threads on this. Something is loose and it is a resonance effect, ie it is loose all the time but only sounds when it resonates. It could be anything up to a damaged voice coil but it is probably something trivial. Most buzzes are loose bits of speaker. Mainly things become un glued. Number one suspect is the dust cover, the dome in the middle of the speaker. Give it a very gentle poke all round then look all around where the cone joins the corrugated surround and finally where the surround joins the metal frame. Stick anything loose back with Copydex adhesive which is rubber based and flexible. If not check nothing is touching the back of the speaker including any cables inside the cab. then work systematically round the cab itself looking for loose bits. A stethoscope even a child's one helps here. Good luck

Bands have a choice here surely. Form a tribute band if you want to make money and pick up bookings, because everyone knows what they are getting. Play all the old favourite covers if you want regular work and an instant audience reaction and become a genre band if you want something in between. At the other end of the scale you can keep your integrity, be creative and play originals but there is no ready made market or audience and you risk struggling for gigs money and audience reaction. We've decided as a band to play covers but to choose the songs we like playing and do best and take the hit in terms of pay. We don't do weddings/parties unless someone particularly wants us because we aren't a dance band. My worry is that with a limited range of instant recognition songs and a lack of imagination from promoters and bands we are going down a blind alleyway. Pub band down here means mainly 70's/80's rock covers with a bit of more modern guitar music chucked in. If you don't like this or the genre band (blues,punk/ska etc.) then you don't go to the pub when there is a band on. Pubs are closing down or stopping music due to a lack of punters but no-one is offering the range of music which might draw in new audiences. It's as if every restaurant in the country decided that as Chicken Tikka (Mustang Sally)is our favourite food and they were all only serving curry from now on. We need to be more outward looking if we want a vibrant live music scene. There's nothing wrong with Mustang Sally, it is the folk music of our times, nostalgic and comfortable but it is a bit sad to see a bunch of musicians born in the 80's only playing songs written before they were born.

I'd say go for it. It makes a lot of sense if you don't go for bargain basement. You can't really compete with the cheapest speakers on the market but they use the cheapest materials and speakers to produce fantastic value for money with inevitable limitations imposed by the need to keep the cost down. If you go to the mid=range products then spending a little more on the drive units and a little more time on construction will give you real benefits in sound and if you get it right you can outdo commercial products at the same price. At the top end design becomes a serious issue and you wouldn't expect to beat someone who has spent a lifetime studying and working in the area, though this expertise comes at a serious price. Think about what your needs are. You could simply buy drive unit(s) use one of the excellent computer programs to design an optimum cab for your units. Someone here may even run the program for you. If you are less confident then you can buy plans and have someone guide you through the process or copy the plans that someone else on here has used. Either way you are going to learn loads and so long as you don't do anything too stupid you should end up with something which works, and may work well. Celestion isn't a bad choice but it is a particular one. The Celestions are designed to give your instrument a 'sound' they tend to have mid-range peaks (neither bad nor good, just a question of taste) they are not the most efficient speakers and excursion tends to be low even allowing for the fact that they do use the strictest methods in measuring this. Some of their dedicated bass speakers have quite high resonant frequencies meaning they cut the bass from a higher point than many others. All of this depends upon the particular model you choose though so do double check what you are getting before you buy. Fane, Eminence and Celestion have the mid price range covered and i wouldn't go for anything cheaper, ignore the cheap Chinese stuff and anything not designed for instruments or PA. B&C, Precision Devices, Beyma, Ciare do more exotic high end stuff. Good luck

Just a thought and it isn't a neo though at 4.6 kg it isn't the heaviest either but the Beyma SM212 is a good buy. Nicely made with a cast chassis. Fs is 40Hz Xmax a brilliant 7mm and Qts 0.38. Response is quoted up to 6kHz though 5kHz is probably closer. Sounds good with bass in a 40l cab

[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.