Phil Starr

Just covered a cab today. Use ordinary PVA woodwork glue, the flat bits are easy, to stick round the tricky bits use a hair dryer to soften the Tolex slightly and it won't try to uncurl so much.

[quote name='JTUK' timestamp='1399633092' post='2446059'] Wouldn't mind a punchy lightweight 12 or 15 sub... [/quote] My original idea was to pump out some simple designs that people could build themselves. Stevie and Lawrence have persuaded me that we need to build and test our designs extensively before publishing them. If you want a sub, or anyone wants a specific design and is prepared to share their build with other people them i'm sure we could give dimensions easily enough. For example building this speaker into a box twice the size (110l) and with a 4.6cm long 10.2cm dia port would give you a sub which would deliver 120db dropping to 116 db at 40Hz. That took me 5 mins to calculate and you could build a cab with that information. I'm sure there are plenty of people here who would help you, or anyone else design a cab, it just wouldn't be one we had built and tested. If not we should be able to come up with 2-3 tested and developed designs a year.

I'm fairly sceptical about wadding. First of all, to answer the earlier question it doesn't alter the effective volume. There's a lot of air in the wadding and it moves inside the cab. I've seen the argument that lots of wadding increases the effective volume of sealed and transmission line cabs and seen some measuremnts that would seem to support this. However the data I've seen implies that only high density wadding has a significant effect on damping inside the cab. Vance Dickason talks about 50% of the cab being stuffed with 4lbsfibreglass/cu ft. The wadding you have is almost certainly too light to be very effective. I've also seen arguments that wadding inside a ported cab is generally a bad idea, certainly it needs to be kept away from the ports, I've tried packing a cab and completely removing the wadding from its pair, ending up with little difference in sound between them. the exception to this is the wadding directly behind the speaker which aims to stop sound bouncing off the rear panel being reflected straight back through the thin paper cone. I like to put some fairly heavy wadding on the back panel and leave the rest of the cab unfilled. This does make an audible difference and I'd move your wadding to the back panel immediately behind the speakers.

I suspect it is 100mm outside diameter if so this is esily available though not so easy in black. Wickes/Screwfix all do it in white http://www.screwfix.com/p/round-pipe-350-x-100mm/15872?kpid=15872&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&gclid=CODQz6OvnL4CFbDJtAodpgcABg

You don't need maths to understand what is going on with speaker sizes until you start to design the cabs yourself. So, in Alex's absence... Thicker bass strings go lower not because they are thick but because they have more mass. The note they make doesn't depend just upon their mass but upon how they are tuned and how flexible they are. It's the same with speaker cones. Heavy cones go lower so a thick 10" and a thin 15 could weigh the same and resonate at the same frequency. Tuning speaker cones depends upon the suspension, the magnetic circuit and the cabinet design, with the rider that you mainly can't get them to do much below their resonant frequency in free air. Interestingly thin cones flex and this means thin cones are often better at high frequencies, though this may be distorted. thin coned 15's may end up with more top end than thick coned 10's. Just depends upon the specific design and where the designer puts the extra paper pulp. The Eminence 3015HO is a good example of this. The other thing is that efficiency depends upon surface area and a lot of cheap large cones can end up making a loud noise, as in the 8x10's around. If you want super small lightweight cabs to do the same they generally need a lot of power. The final consideration is excursion, to make loud bass you need to move a lot of air and small speakers need to move a long way to create say 120dB of 40Hz fundamental. Too far for any single 10, and for most 12's. So, you can get the frequency response from a small speaker but at a cost, one way or another.

I was going to recommend the zoom! I have an Olympus, basically a dictaphone though with fairly good quality. One of our band has the Zoom H4 and it is so much better! The problem is that the standard recorders have automatic level controls and roll off the bass to make voices clearer. That's great for their intended purpose but not what you want for recording your band or bass generally. Try a new memory card if it's just a standard card.

you could try bolting some finned heat sink to the aluminium chassis as close to possible to the amp to increase the cooling. Smear it with a heat conductive paste first. This is the sort of thing http://www.rapidonline.com/Electronic-Components/Heatsink-159-X-200-50-0159/?source=googleps&utm_source=googleps&gclid=CIeHpe2wjb4CFQcTwwodgzoAKg though you will need to look for something that is as good a physical fit as possible. look for the lowest thermal resistance you can find. It won' be as good as mounting the amp directly onto the heatsink but it should help a little without too much surgery on the amp.

Great, that's the deal. free advice for telling us how it comes out.

Oh of course you might be able to improve the cab with some judicious stuffing and adding some bracing to the panels, the betas aren't great speakers but they aren't the worst either.

You don't say what your 2x10 is, if it is a home brew then it isn't going to sell for anything much, the drivers would sell for more on their own. If it is a reasonably well known brand then you would probably get enough by selling it for that to be the cheaper route as everyone has said, there are some real bargains to be had used. If it is a reasonably well made home brew and you are determined to tinker anyway then there are better speakers. For £50ea the Beyma SM110 is a bargain, well made, good excursion though you'll have to wait for delivery at the moment as they are imported specially from Spain. For £60ea there are the Fane 10-300 pro's which i've used. Very strong controlled bass but very neutral top end so they lack sparkle. The eminence deltas are £65 here and are a bit better than the Betas but not as good IMO as the Beymas. For £95 you have the Celestion BN10's (neo speakers) and the Eminence basslites are £90. I'd go for the Beymas or the Celestions. So for £100 you can improve your cab and for £200 you could have quite a good cab with modern lightweight drivers. Hmmm I feel a purchase coming on, rather like those Celestions. You'd probably need to re-tune the ports and check the size of the cut out holes. Look to see what you could trade up to used and then decide

There's a lot of compromise in any speaker design and where you end up depends upon opting for a design philosophy as well as doing all the tests and calculations. We haven't debated this in public yet but one of the issues we are looking at is tuning. I want to tune the cab for the lowest excursion at low frequencies, something that will handle low B fundamental at a couple of hundred watts. Stevie wants it tuned higher for maximum power handling. For most people neither of these would be the issue you might expect, I doubt you'd be pushing these speakers to the extremes they would get in testing or be able to hear a difference. The same is true of cab rigidity past a certain point. Bracing of whatever sort follows a decay curve, a little bracing will dramatically improve the sound of a cab, adding an extra brace to an already well braced cab, hardly at all. Sooner or later you will reach a point of diminishing sonic returns at a cost in time, effort and weight. The philosophy behind this cab is to make it easy to build, whilst sounding as good as possible. I'm thinking of a first time builder who wants a practical cab at a better price than an equivalent commercial cab. At the same time there will be no secrets so it is open to anyone to go for a 'better' driver or better bracing if they have the inclination. I hope a lot of you will be very happy with the sound of the basic cab.

I deliberately built the prototype out of thin panel to investigate the panel resonances and then to investigate optimum bracing. the result is truly awesome at the moment. The cabs sound great at low volumes and dreadful once the volume gets high enough to excite the panels, The final versions will probably be 3/4 and I'll then do some comparisons between 1/2" extensively braced and 3/4 with little bracing. Remember this is just a test bed.

[quote name='JTUK' timestamp='1398434635' post='2434098'] Good... proper ports and not those horrible shelve things.. and 18mm Ply and the additional 3.5kgs weight wouldn't worry me either. Just sayin' [/quote] the whole beauty of a project like this is that you are building it and you are in charge. If you want round ports not a shelf then it's an easy substitution, in all probability we will use the same port area so the lengths will be the same. My intention for this design is to make it as easy as possible to build so people will be encouraged to have a go and will then almost certainly be successful. The big advantage of a shelf port is that you can get B&Q to cut everything and all you need to do then is stick it together. We'll give enough details to do round ports too. My cabs will almost certainly be 3/4 ply. we'll also give enough details to adapt cabs for other drivers and to design your own kickback.

OK thanks, misread GK's website. It's probably still worth the OP trying to find out if it is the pre amp or the amp. If it is the pre amp then check the valve, if it is the amp it's probably beyond home fixes. The 550 will have large storage capacitors in it which could make it dangerous to poke around in, even when unplugged. I doubt there is anything user serviceable in the class D power amp which would cause this sound. I've never worked on a GK but no-one else answered so I thought I'd give my penny's worth.

you are probably in the wrong part of the forum, repairs and technical would be better. Which Fusion is it, one with a valve or one without? Really hard to tell but if it was a conventional amp I'd look at biasing or at something overloading. You could try putting a signal into the effects in channel and seeing if the buzz disappears. If it does the power amp is OK. Alternatively you could take a line out into another amp, if the buzz remains it is before the line out and I'd be looking at a valve swap if yours has a valve. In the end you are probably looking at taking it to a tech I'm afraid.

Speaker ready for its first run out. [attachment=161129:1x12 prototypes 006.jpg]

ports cut (from standard downpipe) to try assorted tunings. [attachment=161128:1x12 prototypes 005.jpg]

I think we might have one to try, though I don't have one here. This cab is meant to be full range for bass and the LF has very restricted top end so it wasn't a top choice for this though it models Ok in this box.

Ok they are up and working, though I want to test them extensively before giving out detailed designs. To me they just run down to bottom E with no change in timbre, just an even open sound. The top is pretty neutral sounding too, no obvious sound added by the cab. this is just a 10 min workout though. More to come

[attachment=161098:Beyma SM212.jpg] Speakers about to go in. Spec Sheet http://www.lautsprechershop.de/pdf/beyma/beyma_sm212.pdf chosen because of excellent excursion figures, good damping and good cone break up performance giving useful upper frequencies. Also because they sound good and are cheapish for a quality speaker. Without more testing though we're not ready to recommend them as the final design, that's why we have two cabs, we can swap ports and drivers and do A/B comparisons.

[attachment=161064:1x12 prototypes 001.jpg] Cutting a long story short I've a new band, a list of 30 songs to learn, and fell so far behind with the diary that I decided time was better spent building a speaker. I'll revisit the discussions we had when I get time, for those of you who find it useful. Anyway if I've done this right it should be a pic of the prototype. Four ports because we intend experimenting to see if port noise is an issue and we want to try tunings for maximum power and maximum output down to low B. The final version will probably have a shelf port for ease of construction. As ordered it is proportioned to take a rack amp on one of its sides. The cab is 50 litres plus enough for the ports, bracing and the speaker. The cab is made out of flimsy 12mm ply because we want to investigate panel resonances. This cab is 6.9kg and the speaker is 4.6kg so with bracing and fittings the cab will weigh in at about 12.5 kg. a one handed lift. I'm off to fit the drive units; Beyma SM212's

I'm assuming he will use the same output he feeds into his current amp or that he intends feeding into his class D amp.

Why do you need an amp? All the eq is done and the monitoring is through in ears, so you only need to be louder and only need something with a flat output. Go straight into the PA and the audience should hear what you do through the in ears. If you or the rest of the band need some on-stage bass then use an active PA speaker, possibly a wedge, possibly not, with the flat class D amp you want already built in. Why carry a box, which for the way you are set up is not needed. Decent PA speakers should handle bass as well as a bass speaker and if you have DSP built in then there should be no way of blowing the speaker.

Just to expand upon the complexity that Stevie mentioned. there are several ways in which you can 'blow' a speaker. The wattage is based on the speakers ability to withstand the heating effect of lots of watts, The cab isn't part of this so putting in two 500W speakers would give you a 1000W thermal rating for example. But speakers also blow because they try and move too far and leave the safety of the magnetic gap and/or bang against the back of the magnet. People talk about Xmax or excursion limits. Since the cab alters and damps the movement of the cone and each speaker is different the cone will move more in the 'wrong' cab than one designed specifically for it and will blow at a much lower power than its rated power. You wouldn't just drop a different engine with more horsepower into a car and expect the gearbox etc to work properly without modification and sometimes it just wouldn't fit, or be a sensible mod.

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