stevie

Definitely. The more quality speaker cab makers around, the better for us all.

Thanks Funkle. Much appreciated. I thought I'd go and re-measure from above the cab, as it really is quite impressive now. Remember this is from nearly six feet above the cab. Here you are: It's possible that one of the Audiokinesis models could do something similar, I agree. I saw that Duke has used a 90 x 90 horn on one of his models. The reason the response of this cab doesn't collapse at higher frequencies is because I've turned the horn round so that the 90-degree dispersion is directed towards the player's ears - and because the crossover point is relatively low. The Barefaced model can't do this because its crossover point is much higher (and it doesn't have a constant directivity horn). The ideal crossover point for our system would actually be around 1.5kHz, but that would take a more expensive compression driver and a larger horn. The measurement below shows what happens when you listen to a 12" driver with no tweeter from the same position. The Basschat cab is in green and a 12" bass guitar driver (with an on-axis response beyond 3kHz) is in red. It shows why you cannot hear your bass clearly when you stand close to a normal bass cab on the floor. That 1 to 3kHz region is really important for intelligibility.

Finally, here is the RTA measurement of the cab standing on the floor in my garage. It is the average of about 12 points in space and gives a good idea of how the cab will sound in a room. The rolloff at high frequencies is normal for this type of measurement.

Achieving a smooth response from above the cabinet was one of the design goals. However, I was surprised at the following measurement, which was taken from 4 feet in front of the cabinet with the mic at ear level, or about 5 ft. 7 inches. What this means in practice is that you will be able to clearly hear the pitch of what you are playing even when standing close to the cab. I'm fairly sure there isn't any other bass cab capable of doing this without being raised or tilted. This is actually an older measurement, taken before the last modification to the crossover, which improved the phase tracking and filled in the slight dip you see here between 2 and 3kHz.

Here's the 60-degree curve (30 degrees off axis). And the 90 degree curve (45 degrees off axis).

It looks like the prototypes of our CNC kit will be ready tomorrow. I'll therefore be bringing them to the South West Bass Bash on Sunday. The crossover is now finished and I'll post a photo shortly along with the circuit diagram. Here are some measurements of the final system. This is on axis:

I seem to remember that little cab sounding particularly good last year.

Is that the Thunderchild TC112?

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.