stevie

If anyone reading this thread is going to the South West Bass Bash next month, you'll be able to try out the system I've been building here. I've also been promised a CNC kit of parts in time for the Bash. Fingers crossed that it happens.

Luke and Richard have more or less answered this question. My answer is: not much. You could reduce the volume by no more than 10 litres if you wanted to. You would lose a bit of bottom end but not a huge amount. Drop the size by any more and you'll lose the bottom end solidity. The Beyma SM212 will work in a slightly smaller box than the Faital - so you could in theory make that even smaller. The problem is, of course, where can you shrink the cab? If you were to use a box pan grille, you could reduce the width of the cab marginally, as the baffle has been sized to accept a picture frame grille. You could also take about 30mm off the height (but no more) and still keep the horn. But as Luke has pointed out, you can't reduce the front-to-back depth because of the port. Personally, if I wanted a smaller cab than this one, I'd be looking at using a 10" driver. If you try to cram a 12" driver into too small a box it's easy to end up with a thin sounding cabinet. You then need to use two of them to get a decent sound.

It was me, Mike. As there's little likelihood of me ever getting over to Taunton to have my bass set up, I'd like to contribute it to the next raffle. What are the chances of me winning it again, I wonder?

At last, someone who understands what Basschat is all about.😀

Jack, the HyDrive HD112 manual says "The HyDrive HD112 has an innovative dual voice coil design that allows the cabinet to operate at either 4 or 8 ohms impedance." So it looks like dual-coil drivers.

I don't think it's one of his brightest ideas, BigRed, although to be fair, he is one of the few people around who does bring new thinking to bass cab design. He's just responding to demand and I'm sure he's engineered it sensibly.

I think it was Duke le Jeune. He offers the option of switching in a high power resistor on his 4-ohm cabs to turn them into 8 ohms. I think it just takes a one- or two-ohm resistor to take his cab from nominal 4 to nominal 8 ohms because the impedance of his 4-ohm cab is already on the high side.

Dual voice coils are particularly popular with the car audio people, but even they would never suggest using just one coil of a dual coil driver. Sure, it's physically possible, but nobody does it because it halves the driver's power handling, halves its xmax, reduces its efficiency, increases its distortion and alters its TS parameters so much that it drastically changes the sound of the cab. Dual voice coil drivers are normally wired either in series of parallel. They give you a choice of, for example, 8 or 2 ohms. If I had to choose, I'd take the Accugroove solution.

I don't disagree, fleabag, but I suspect the OP just wants to make use of the bits he has in his possession.

Sorry to disagree with the general consensus that this is so complicated, but you really don't need the driver parameters to port your cabinet. Don't use 2" ports - they are too small. Use either 2 x 70mm ports (standard drainpipe size) or preferably 1 x 100mm port. The length in both cases should be about 180mm. The Eminence Megoliath is described as a bass guitar speaker. So you have a good chance that it will work, as 30 litres is a reasonable size of cab for a typical 10" bass guitar driver. Without the TS parameters you won't be able to predict the driver's performance in the cab, but as you have never used speaker modelling software, you are unlikely to have a clue what to look for anyway. Just port the cab and see what it sounds like. I wouldn't expect the driver to handle its rated output and I would expect the solid pine cabinet walls to resonate at volume. Just suck it and see. Good luck!

The latest version of the PDF drawing is now up on page 18 of this thread along with the revised cutting list. Thanks Richard!

Oh, and another (even more important) reason why an adjustable attenuator is not a good idea is that our crossover rolls the bass unit off fairly steeply at 2kHz. On almost every other bass cab (with very few exceptions), the bass unit is not connected to the crossover; it just carries on happily as high as it can. If there is a tweeter, it is added at a relatively high frequency - usually about 5kHz, which is too high to be much use - and protected by a cap and a coil. So when you attenuate the tweeter, you get the sound of the bass/mid driver on its own.

Yes, that is certainly possible. There will probably be a fixed-value L-pad on the crossover (2 resistors connected to the HF unit). You could replace those with an 8-ohm L-pad attenuator. If you wish, I can provide more precise instructions once the finished crossover is ready. However, I don't like L-pads on speakers. And I'll tell you why. - First, it's one more thing to go wrong - and L-pads aren't nearly as reliable as wirewound resistors. - When you rely on an L-pad for attentuation, you have no idea what is flat. The 12 o'clock setting means absolutely nothing. If the frequency response is not flat, the phase of the crossover will be out. That means dips (and peaks) in the response, especially off-axis. - This particular design measures as flat as a very expensive studio monitor. Why would you want to compromise that when you can roll the top off with the tone controls on your amp or bass? When was the last time you saw an L-pad attenuator on a studio monitor, or a hi-fi speaker? About 50 years ago. - Finally, from what I can gather, most people attenuate the HF unit on their cabs because it doesn't sound very good. I can understand that, but that's certainly not the case with this cab. The HF is not strident, edgy or honky. Your P-Bass with flats will sound like a P-Bass with flats, and if you want a more old-school sound turn the treble down on your amp or use the tone control knob on your bass. You are entitled to disagree with all of this, and if you'd really like to fit an HF attenuator, I'm happy to provide the details. It's not a difficult job.

Err, yes, you're right, although I don't think that would bother most saw operators.

You could try Duchy Timber: <http://www.duchytimber.co.uk/our-products/sustainable-sheet-material/> They're part of the Premier Forest Group: <http://www.premierforest.co.uk/premier_forest_products_products.htm> who definitely sell poplar plywood. So if Duchy haven't got it in stock, they should be able to order you a sheet. Try to get Italian or Spanish rather than Chinese. Your local wood merchant should be able to order you a sheet too. A lot of wood merchants will cut the sheet up for you for a small fee. Not only will that save you a lot of time and effort, it'll make the wood easier to transport home. Just give them the cutting list in the PDF with the drawings.

Thanks for your kind words, rc. The cabinet design is finished - so you can start cutting as soon as you like from the plans in the thread. The crossover is still being tweaked, however. Once I've finished the crossover to my satisfaction, I'll post a list of parts and components you'll need to complete your cab. I'm struggling to find a company that will supply small quantities of badges for the front grille at a reasonable cost - say a fiver or less. Can anyone help?

And your design goals were?

Exactly. I think the bass guitar has suffered for many years from being confused with the electric guitar, where the speaker plays an important role in creating the sound. A bass guitar isn't like that. It's more like an electric piano or a double bass.

No, I'm afraid not.

During the past few years of messing about with bass cabs, I've come to the conclusion that a flat response, low colouration, constant directivity cab is the best solution for bass - certainly for me - and not just for use with modellers.

You might as well run your bass through the earbuds on your phone.

Yes. When they are positioned close to one another, multiple speakers couple at low frequencies (they act as a single driver) and sensitivity increases. This is fine at very low frequencies where wavelengths are long, but at higher frequencies the sound produced by the individual drivers will start to cancel (be out of phase) as a result of the inter-driver spacing. It's the same principle that causes a single driver to roll off off-axis. To avoid this when multiple bass drivers are used, they should be crossed over to a midrange driver before the phase cancellation takes place.

Basically, yes. There's very little actual design input in these cabs. The basic principle is - keep sticking drivers in a box until it's loud enough. With multiple drivers you get lots of midrange cancellation, which results in peaks and dips in the frequency response. The off-axis response is hopeless and there is usually no HF. When a tweeter is fitted, it usually operates too high to make any real difference.

The only bass guitar cab I know that has half a chance of being neutral is the Greenboy F-series. Apart from that, your best bet at the moment is a PA cab. It's impossible for your usual 2 x 10 and 4 x 10 bass cabs to be neutral.