Phil Starr

[quote name='Bill Fitzmaurice' post='1303817' date='Jul 14 2011, 05:41 PM']You may still be hearing a lot of harmonics, as your speakers create them. If you play a pristine 40 Hz or lower sine wave through a capable speaker with very low THD you can't even discern pitch.[/quote] Fair comment, I should have said there is little point in doing this with your computer speakers. Even with decent hi-fi speakers you will get some audible harmonics but it does give you an idea of just how low the fundamental of bottom E is and it's usually a shock to people who hear it for the first time.

Bill is right. Funnily enough I was driving home today listening to Lou Reed's 'Walk on the Wild Side' and I thought If anyone asks this question they should listen to this. The Bass sounds amazingly deep because it is played on an upright, even though the bottom frequencies are no lower than a four string the different mix of harmonics gives it a rich deep sound. There are loads of signal generators online and if you are deeply boring (like me)it is quite interesting to listen to a 40Hz (roughly bottom E) pure tone and realise just how low that is. If your speakers can go that low of course.

the easiest way to test your tweeter/horn is to put some recorded music through it. You should be able to rig up a lead to feed your iPod into it or even connect it to your hi-fi in place of one of the speakers. Cymbals have a lot of high frequencies so if you can't hear them then you know they aren't working. Check fuses and trace the leads back to the socket via the crossover to check there are no broken connections, then get on to Ashdown who are very helpful. Good luck

[quote name='Mr. Foxen' post='1293074' date='Jul 5 2011, 09:16 AM']All that is wrong. Watts don't mean anything, and ohms mean not much, the bit that matches drivers to cabs are another set of specifications entirely. Predicting how speakers work in a box without actually trying is quite difficult, but if you throw up the box dimensions (ideally internal, it is the amount of air in the box that is important), and where the box has a port/vent/hole in it and how big that hole is, some people can make some more informed decisions.[/quote] [quote name='brensabre79' post='1293209' date='Jul 5 2011, 11:36 AM']I beg to differ. Its not just about matching cabs to drivers... put a 100w 4 ohm speaker into a 200w 8 ohm amp and you will soon see, the power will be too much for the speaker and the amp will be underloaded. result, blown speaker, blown amp. Having said that, there is more to speaker/cabinet matching than just chucking in any old speaker. If your cab is an ashdown (don't get me started) then the best replacement would be an ashdown speaker - the cabinet is designed for this. Although in a 2x10" most are quite similar in size. Yes you may need to adjust the port length for the particular speaker to get optimum results but the end result of using a mis-matched cab/speaker combo is purely the frequency response which you can compensate for with EQ to some degree. The result of using a mis-matched amp/speaker combo is you could either underload or overload the amp and speakers and lose both![/quote] Mr Foxen is right and up to a point so is brensabre. A replacement needs to match the amp in watts and impedance but only in the sense that it needs to be able to handle the power. You can use 250W of speakers with a 200W amp or even 1000W of speakers with a 5W amp but not the other way round. Anything with an impedance of 4-16 ohms is fine with a solid state amp though you may lose a little volume/power. If the amp is a valve amp then you need to match the impedance and if you use this cab with another it needs to match that in impedance ideally. The speaker also needs to match the cab though. If the cab mismatches then you might need more than eq. and you might lose a bit more than just the sound. If the cab is tuned to the wrong frequency then the speaker may effectively be unloaded by the cab and may suffer excessive excursion and an early grave. This is especially true for a ported cab. Check the amp and everything else first, if it is definitely the speakers then ideally contact Ashdown and replace like with like. They are really helpful and reasonably priced. If for some reason you decide you want to replace the drivers with something different someone here will help you re-tune the cab, but there is a better than even chance the original speakers will sound nicer.

Well Done!

OK I think your problems are becoming clearer. I guess you don't have a lively used market in Greece and the same access to cabs to try out, something we take for granted in the UK. This makes building relatively more attractive. It's not as hard to design your own cab and come up with a successful design as some of the experts will tell you (they have a position to protect after all) but neither is it something you can do without considerable effort and the risk of an expensive failure. In fact it is fairly unlikely that you'll get the tone you want with a first attempt. If you want to learn speaker design you have to start somewhere so learn as much as you can and go ahead. It looks however that you actually just want a good all round cab to play through without spending a fortune. Correct me if I'm wrong but I don't think you really want to spend months learning how to engineer speakers. You really need to use an established design where someone else has done the work, designed the box and chosen the drive units. Eminence have designs on their website and you have the fearful designs, there are loads of designs if you care to trawl the web and plenty of build diaries on this site. You could also copy a speaker you like so long as you stick to exactly the same drive units. I hope you understand that the box and the speaker work together and that you just can't put any speaker in a box and expect it to sound good. Your builder needs to have exact dimensions if they are to do a good job so you are more likely to be successful if you use one of the designs which gives a lot of detail. You also need the details for any crossover I think it would be sensible to look at using a fEarful design. Price up what it would cost and then what a commercial speaker would cost including shipping (Thomann don't charge for shipping to Greece over 300euro). Then make your decision.

there's nothing much wrong with either of the speakers you suggest at the price, I'd go for the 15-400 by the way. Going neo won't change your sound per-se but there are some well regarded speakers out there that happen to be neo. You have to decide if you want to save your back and lighten your wallet! My 15 has a Peavey Black Widow in it which I picked up cheap. Nice sound but pricey, Peavey's box was all wrong by the way. Another 15 I've used is the Fane 15-500 which is great value. It's probably aimed at PA rather than bass as it behaves pretty well at cone break up, basically it has a more even response at the top end than the speakers you mention, but if you are going to use a 6 as well then that might not be a problem. It should have a more accurate bottom end than the other two speakers.

Now you have to tell us how you got on. I'm thinking of taking the plunge myself but the possibility of total humiliation is a bit daunting. The experience of someone in the same position would be great. (the lessons not the humiliation)

[quote name='Monckyman' post='1282252' date='Jun 25 2011, 04:37 PM']Thanks for the reply, yes I understand how it may be the context that`s emphasising certain freqs, and I can cut them reasonably well on the amp eq. I`ve asked a P.A firm friend to see if he has something knocking about that I can try out. I`m fully expecting to be proven wrong but it`s just an idea I want to try. MM[/quote] a good quality LPF isn't going to be cheap and without some way of measuring you could end up trying at the 'wrong' frequency to get the result you want. If your PA friend can lend you a stereo amp and an active crossover you can try different frequencies and different roll off slopes really quickly, then you can decide what frequency you want to crossover at and whether you want to use a high pass filter on one cab a low pass on the other or a full crossover. Use your bass amp as a pre amp if you have the right output (but use a dummy load if it is a valve amp). Have fun

assuming your cabs are all 8ohms you have it right. There will be no problems with power handling with what you suggest. The easiest way to rig up speakers in series is to wire up a special lead or adaptor box. Any competent repair shop should be able to do this. I don't know of any commercially available leads.

basically if you have four speakers in a square then the sound will be beamed in a cone which narrows with increasing frequency whilst placing them in a line will radiate sound in a broad flatter beam. This is going to be better in most auditoria because more of the audience will hear a better balanced sound with more mids and highs. Also having a speaker close to a hard floor will increase bass output by 3dB which could be good or bad depending upon what you are trying to achieve. It is also good to have a speaker at ear height as then you will hear more mids and highs which you need to hear what you are playing. You also hear a sound which is closer to that which the audience hear. Alex Clabers article is really worth a read. If it is possible I'd always stack vertically

Good to hear you are getting the sounds you want, I hope we helped a little. Careful about fiddling with vents though, it can get addictive.

[quote name='Nostromo' post='1274087' date='Jun 18 2011, 08:28 PM']Thanks for all the input so far guys . . . . I guess it gives me a lot to think about ? . . . . Must say, I haven’t got access to, or the knowledge of, WinISD Alpha Pro so not sure I'm likely to be able to employ anything like a computer program to any advantage, but I do take the point that it could produce a more optomised cab design/environment for the speakers . . . having said that I wouldn't know what effect that would have on the sound/tone/character of the cab ? . . I guess we all sort of know that basic sound that 2 x 15"cabs tend to have . . . and I sort of like that old vintage sound . . . and that’s definitely what I'm after here ? Obviously I'd like to create a cab that presents a good environment for those drivers to sit in . . one that would let them sound their best and operate properly ? . . I hadn't realised that the 70's cabs were developed with so little technical input . . sounds like it was more luck than judgement if they sounded good ? . . . I do like the picture posted up by Mr Foxen . . . thats the sort of thing I had in mind I think ? So, what gives that 70’s tone ? . . . is it the speakers themselves or the (sometimes badly designed) cabinetry ! . . . I’d definitely like to get a 70’s sound from this cab, thats the whole point of the exercise, but if a seventy’s design can be tweaked a bit to allow the speakers to perform even better without loosing the 70’s character then that would be worth doing I think ? . . . Not sure where to go next now ! . . . Further comments much appreciated ! [/quote] WinISD is a free program which google will find straight away. You probably need to know a bit about speakers to drive it though. AJ systems offer a simpler though less flexible box caculator which will offer optimum box sizes. The basic theories of box design were first published in the early 70's and many designers didn't pick them up until later so almost no cabs sold then were designed using the Thiele/Small models. In addition materials technology was developing so drivers got better. At the beginning of the decade most amps were valve amps with a very high price per watt. Speakers were usually general purpose designs with paper voice coils and low power handling. Magnets were small and often lost a lot of there power over time. There were very few horn tweeters around and these were expensive and unreliable. Most speakers tried to cover the whole audio range and tended to have thin flexible cones often with a second 'whizzer cone ' in the middle of the main cone to boost the higher frequencies. To get the most out of the low powered amps the voice coils tended to be short to boost efficiency and suspensions were often soft to lower the resonant frequencies. All this meant that most speakers were in boxes that were often too small and that the designs were often under damped meaning that you got a nice warm bass frequency hump at the expense of deep bass. Distortion set in early because of the lack of excursion and the only way of getting deep bass was using big speakers (2x15) or lots of them (8x10). By the end of the 70's glass fibre coil formers were creeping in and large ceramic magnets were common and designers were starting to use maths to design cabs though remember computers still used punched cards in the early 70's and pocket calculators were just being introduced. I was still using a slide rule and mechanical caculators at University. Bill is right, you'll get a better sound and more quickly without the error part of trial and error if you use a computer modeller. the seventies procedure was to listen to a lot of speakers so you knew the basic sound of each driver and then to keep building cabs untill you'd home in on the sound you wanted. Sometimes you had a lucky accident. Your best bet is to copy an earlier design where someone has done all this for you. Most of the 'character' apart from deep bass will come from the drivers. Good luck, let us know how it turns out.

Duvets and pillows are stuffed with polyester wadding which is the same as most of that sold for speakers I use it sometimes. Mostly I use higher density materials for PA/instrument cabs, Glassfibre or Rockwool. the disadvantage is that you rally have to keep the dust out of the voice coil gap. Even the commercial wadding does 'bugger all' unless you really pack it in though it works better for hifi designs.. I don't usually stuff reflex cabs, restricting myself to just trying to prevent internal reflections off the back panel. the advantage of a wedge is that the rear panel doesn't run parallel to the speaker so the primary reflection doesn't go straight forwards back through the cone. I'm agnostic about the benefits of stuffing, people get very nerdy about it wanting the long hair wool from mountain sheep sheared on a full moon in July. Having done a lot of A/B testing of my own designs I'm not convinced it adds a lot and I miss it out except for dealing with specific resonances or standing waves. Others will disagree. Gio for whatever sounds best unless you have acces to a lot of testing equipment,

If both cabs are the same size then replace the corners with ones that interlock, which most of the plastic ones do. Available from Maplin or Blue Aran amongst others.

Stuffing a cab is an interesting one, there are loads of theories around and you probably need to distinguish between damping the panels and stuffing the air space. On the panels it can reduce the internal reflections and mass load the panels reducing their resonance. In the air space it will affect the propagation of the sound, dampening standing waves and changing the effective volume of the cabinet, If you can get hold of a copy of the Loudspeaker Design Cookbook by Vance Dickason their are some nice measurements of the effects of differing stuffings upon the performance of cabs. One of the less well advertised effects of stuffing is that the speaker doesn't cool down so well if it is surrounded by a load of wadding/fibreglass.

[quote name='LawrenceH' post='1266138' date='Jun 12 2011, 02:58 PM']To match your point of order, accepted acoustic engineering practice for musical instrument cabinets has different design goals and acceptable compromises to hi-fi style cabinets designed for accurate reproduction. In the context of a budget alteration to a bass cabinet Phil's comment was a fair enough reality check, from his other posts it's clear he understands why there are limitations to mixing drivers - the physics behind it is something a child could understand (and yes, I have demo'd wave cancellation/reinforcement at a science festival for children). But from a practical perspective I've certainly never had serious problems mixing different bass cabs that were caused purely by phase compatibility, that weren't dwarfed by the usual limitations of playing in enclosed spaces or the inherent voicings of the speakers themselves. It's typically not nearly as a big a problem as having crap drivers or a poorly tuned cabinet and certainly not the deal-breaker it's sometimes made out to be when considering straightforward upgrades. In fact, mixing drivers often has the subjective effect of smoothing out the mid-range which can be beneficial. I don't understand the need to be so combative about these things. Your own cab designs contain many compromises from the point of view of convenience/cost some of which go directly against 'accepted acoustic engineering practice'. Not least arrayed tweeters spaced greater than 1/2 wavelength for much of their operating range. Yet you count yourself an acoustic engineer, understand the compromises and for you and the majority of your builders they're acceptable. Oh btw Phil was saying he is both 'old' and 'an acoustic engineer'. Hence 'both' in response to your 'neither'[/quote] Thanks Lawrence. I'm tempted to say 'leave him, he's not worth it'. The only reason I raised this is that advice from 'technical experts' is sometimes not that helpful and if it is too categorical it is often incorrect. Ultimately speaker design is about compromises even when you are designing for hi-fi and PA. When you are designing for musical instruments there are many more compromises which can give results some people will like. the idea that everyone who has ever used a 15 with a 4x10 was wrong or that all your speakers should be from the same manufacturer is a little odd. To claim that this is due to the laws of the universe and that anyone who disagrees can't possibly know any engineering principles is stretching things a little too far. Oh well. For anyone following this I'd say that mixing speakers is a bit like blending drinks. If you mix Cabernet and Merlot then you will lose some of the character of each. You get some mid range smoothing, but some people like Cabernet/Merlot. Cheers

I'm now feeling a bit guilty about not answering your original question and let some of the other posts distract me. The cab size will suit quite a range of drivers though you will need to adapt the ports. I gather you are just trying to fill out the bass a little so top end is less important. Do you have a budget in mind? If you find other drivers in your local shops tell us what they are and if the TS specs are available someone will advise you how to modify the ports. I'll look at drivers when I get more time. Gigging tonight.

[quote name='Bill Fitzmaurice' post='1263395' date='Jun 9 2011, 10:43 PM']And old acoustical engineers. From your response I gather you're neither. The advantage to identical drivers is that you always know what you'll get. With mixed drivers you never know what you'll get until you've got it, and that can turn out to be an expensive experiment.[/quote] How rude. and I'm both.

All this stuff about not mixing drivers is just an old wives tale. The 'character' of a speaker is largely about frequency irregularities asnd if you mix drivers these are not likely to coincide so you might lose some character, but some characters do need a little turning down at times. There are problems with any multi driver set up too but this is as true of identical drvers as differing ones. Some combinations work and some don't and some of us like a coloured sound and some don't. You have to listen to judge whether a particular combination will work for you.

Its not very helpful is it, the way speakers are rated. The trouble is that there are two limits to a speaker the first is how many electrical watts it takes to break the speaker and the second is how far the cone can move before it leaves the magnet behind. The ratings you see are all related to electric watts. The 'RMS' rating is simply a measire of how much heat it can dissipate. Put 300W through a mumber of speakers and if none of them fry after several hours then they are 300W speakers. This is easy to measure and check so RMS is what we see. The problem is we put music not test signals through our speakers. When you pluck a string the note starts loud and decays then there will be a gap and then you play more notes, some loud some quiet. You may be playing with your 500W amp flat out on the loud bits but your average power will be only 20W or so depending upon what you are playing. Your 300W speaker will handle this for years. Manufacturers can easily claim silly 600W program and 1200W max because of this but it is still a 300W speaker. A 5W speaker could handle 1000W for a fraction of a second! You play bass however and the lower the note the further the cone has to travel to reproduce it. there's examples out there of speakers that only have a couple of mm movement before the coil starts to move out of the magnet. For bottom E this means that they can only handle a few watts. Under these conditions your 300W speaker might be only a 30W speaker, Finally there is the question of longevity. Constant movement of any material will lead to its eventual breakdown and the harder you drive a spaeker the faster this happens. Your speaker may well be safe with an overpowered amp but it won't last as long, though it may be years before you find out. There isn't really an easy answer to all this. By and large I use amps and speakers that 'match' I currently run a 600W amp into a 550W speaker and i don't expect a failure. Then again I'm only running it at a fraction of its power and the rest of the band all complain about the volume being too high. the advice that you should just be aware of any distortion and turn down is just perfect. People agonise about this a little too much.

four 8ohm speakers will give you what you want, 2 ohms overall but I'd seriously consider the other options first. A dummy resistor will take half the power and will have to be a fairly impressive resistor to dissipate 150W, not a good option. A second cab will work and give you potentially a bit more sound but will change the tone. Changing the speakers will also change the tone and it won't be an ampeg any more. It might be better of course. Unless you have years of experience it won't be a predictable change of tone, there are so many variables. If you are going to spend £200 on speakers then what would you get for the cab second hand? Add the two together and that is what you could spend on a new cab which you could try before spending your money. Qts of 0.38 is perfect for a reflex (ported) cab but a bit low for a sealed cab, it might work but could well be a little overdamped. You'd want to model it with WinIsd or something similar as there are plenty of other things which would affect the outcome. If it was your cab then it would be up to you to take the risk of an unpredictable outcome but if it is for someone else I'd recommend they look at getting a more appropriate cab and selling this one to pay for it.

I'm still using my Dr Duck's which is lasting forever. I use a lot of Danish oil on my joinery and would use it on a wood body but not the fretboard, its got a lot of tung oil in but I think at least some brands contain alkyd resins which I'm not happy with putting on my neck. I just bought a 500ml bottle of lemon oil from TK Max of all places (for a fiver) so that should do me for the next thirty years or so.

3dB louder noticeable but not by much. Try this [url="http://www.ultimate-guitar.com/columns/gear_maintenance/making_it_loud.html"]http://www.ultimate-guitar.com/columns/gea...ng_it_loud.html[/url] Cheers

The most common cause of buzzes if it isn't something loose are the dust cover (dome in the middle ) coming loose or the corrugated surround coming loose. both can be re glued with copydex latex adhesive. Alternatively it could be a small tear in the cone which can be 'layered up' with copydex and tissue paper. I assume youve checked that nothing is touching the cone and it isn't the rattle of something loose in the cab. Good luck, I hope it isn't something too serious.