stevie

I don’t think anyone has said that slot or triangular ports haven’t been used or that they are unusable. John was explaining the reasoning behind our choice of single round port for this cab. There are some practical benefits to using alternative shapes but, if your aim is to minimise port chuffing/distortion/compression, a round port performs better than any other shape because it allows for the most uniform flow of air through the port. On small, high power cabinets, a carefully optimised port can make a big difference.

It'll be interesting to find out what two sound like.

Dunno so much about the bass sound but the playing was absolute quality. It doesn't get any tighter than that. Loved it.

I'm not sure I'd put it quite like that, but yes. 😄 That's the beauty of it.

Yes, with the BC12MkIII. However, that was a much more complex design with extensive bracing that benefited from being CNC'd (and encouraged quite a few forum members to build one who probably wouldn't have bothered). I'm not sure that CNC is the way to go with this cab though, because the assembly technique Phil developed simplifies the way the cab is put together. You just need to get the panels cut accurately, which many wood merchants will do for you at nominal cost. And then it almost assembles itself.

Yes, there are pluses and minuses for front and rear porting and we agree about the fallibility of making subjective judgements. Chienmortbb makes a good port about the physical attack of a well designed front port (in a well-braced cabinet). A lot of that is going to be dissipated if the port is vented to the rear.

I agree that front-mounted ports sound better on bass guitar cabs - not so much on hi-fi cabs though. Theoretically they shouldn't, and even acknowledged experts in the field can't agree on this one. If the cabinet is large, you could make a case for a reduction in port volume from the port in the nearfield due to distance. Bill's first point is a good one but I suspect you might not get a completely satisfactory answer to this question.

Respectfully, agedhorse, you barged onto this thread, which was proceeding in a nice, friendly, positive manner, and claimed that the porting of the cabinet was flawed. The professional thing to do, as a member representing a commercial entity on here, would have been to send me a pm saying ‘I think there might be a problem with the porting of the box’. But no, you post on the thread that the “port area is too large for the driver”. So I had to spend time that I can ill afford explaining why this is not the case. The professional thing for you to do then would be to say simply, ‘it looks like I might have been wrong here’. That’s obviously not your style. No, you then double down and post in a really aggressive manner, implying that you can’t be wrong because ‘look who I am’ – really not impressive (a technique honed to perfection by Donald Trump if you don’t mind my saying). You don’t even acknowledge that you might have been a bit hasty and proceed to repeat your assertions about port aspect ratios, which you haven’t made any effort to substantiate and, frankly, I don’t think anyone has the slightest interest in. They’re certainly not pertinent to this thread. The only reason I responded to your first post was to explain for the benefit of the people already building the cab that the design was fine. I have already explained why I don’t agree with some of your ideas (which you have ignored) and I’m not in the slightest bit interested in arguing about them now. I was enjoying seeing the builds come together and hope we can dispense with this nonsense, call a halt here and resume the constructive spirit of the thread.

Adding to the previous comments, although the Beyma would probably work quite well in this cabinet, I can't see any real benefit in using it. The xmax is about the same. I'd be suspicious about the 250W power handling, as the driver only has a 1.5" coil (compared with the 2" coil in the Celestion). It does seem to be slightly more extended in the HF, due I expect to the smaller coil, and its main breakup point is higher, which is a plus point. Unfortunately, this means that the crossover won't work as well as with the Pulse 10 and you'll get a peak at around 3.5kHz. Probably not a biggie in a budget cab. If you already owned the Beyma, I'd say - sure, try it. But otherwise, I'd stick with the Celestion personally. It's up to you: if you feel like experimenting, there's nothing to stop you and I certainly wouldn't expect it to be a disaster.

As I explained to Jon in an earlier post, there isn’t a problem with the port length. Also, a 4-inch port isn’t too large for a 10-inch driver – that’s just a completely weird assertion. As far as port nonlinearity is concerned, the number one priority (by far) is maximising the size (and optimising the shape) of the port. The maximum vent air velocity in the cab at its rated output is currently about 14m/sec/Hz, which is very good and I dare say better than virtually any commercially built small bass guitar cabinet. Reducing the area of the port would mean going to a 3-inch port, which would nearly double the vent speed. In fact, 80W through the 3” port will take the vent air velocity to the same level that the 4” port experiences at 200W. Although most bass guitar cabinet designs would actually meet the two-to-one ratio requirement, it is purely arbitrary with no real basis. Try designing a compact subwoofer with those constraints in place and you won’t get very far. In fact, you can make a port as long as you like as long as you know how to deal with the trade-offs. We’re using a 100mm diameter port 170mm long. So that’s all right then. 🙂

You're making some good points. The gap between the end of the port and the back panel certainly matters but the rule you mention applies to slot ports. If you have a full-width slot port, you should leave a gap equivalent to at least the height of the slot port between the end of the port and the rear panel of the cabinet. Otherwise, you’re constraining the air flow into the port, which will speed it up and cause turbulence. Designers have been trying for decades to find ways of reducing turbulence in ports – so this is the last thing you need. Round ports are different. You can go closer than the diameter of the port. The main thing is that the flow of air into the port isn’t constricted. You need to visualise it and use a bit of basic geometry. On your speaker you should have about 40mm of space behind the port. That’s fine. You could actually go closer than that without restricting the air flow. Nice work, by the way.😊

Tickets £5.98 incl tax? I can't believe it. Get touring!

Or south west England?

Scarily good!

I think Phil designed this box to be 30 litres net - or about 34 litres gross. WINisd probably deducts the volume of the driver and port from the total - my software does this. Also, and without checking, it's quite possible that the internal diameter of the 100mm port is something like 97 or 98mm internally. I only used modelling software to prove the concept and did the tuning on the box itself. You'll find the impedance curve showing the tuning frequency a few pages back in this thread. As others have pointed out, you have to be very careful with xmax, as there are different ways of calculating it. I tend to use coil length and xlim as my yardsticks nowadays. The three power-limiting factors - thermal power handling, excursion and vent speed - are nicely balanced in this design, which should work well with a 200W amp.

German Schlager of the 1970s probably represented the nadir of Western popular music.

Lol. He also recorded this. If you can listen to more than 10 seconds, you're a better man them me. It's a youthful version of Heino's ditty you posted earlier.

It's worth repeating that the on-axis frequency response of the bass driver, whether it's a 12 or an 8, is less relevant than you might think because you hardly ever listen to a bass cab directly on-axis. When you're standing above or to the side of a cab, the midrange and HF frequencies are greatly attenuated. The horn in this design crosses over at 2kHz (more than an octave lower than most commercial designs) to compensate for this and allow you to hear those mid and high frequencies clearly - even when you're above and to the side of the cab. Also, if you're playing without PA support, what your audience hears is not the on-axis sound from your cab but the 'power response' or the sum total of the speaker's radiated output. This is why live bass often sounds dark and murky with no energy even if a cab has a tweeter.

The Pulse 15 is probably the best Celestion bass guitar 15. The BN-400X is underdamped. This will boost the frequency response around 80Hz in a normal sized bass cab, making the cab appear to have oodles of bottom end. In practice it's not conducive to a great bass sound IMO. Put the Pulse 15 in a cabinet with an internal volume of 100 litres. Fit two 100mm ports, 112mm long or (better) a 150mm port of the same length. That will tune the cab to 45Hz, which should be fine for 5-string bass.

The PDF plans are attached to the first post in the thread. Unfortunately, we lost all the photos of the initial builds but I reposted all the later ones showing the cabinet build process in detail. Also, check out funkle's build thread, which also contains useful info.

The 12FH500 is a very nice driver - I've got some 12FH520s in my workshop. It sounds a bit leaner in the bass than the 12PR320 but it's very well defined. Unfortunately, its midrange response is different, which means it would need a crossover redesign to get the best out of it. It's a shame there's such a delay with the horns. If I'd known, I'd have specified something that's more readily available. The horn's integral to the design, I'm afraid. Fitting another horn is possible but would also require a different crossover.

That's an excellent idea, @Stub Mandrel. At £3 a pop, it's hard to go wrong. The stuffing is made from recycled plastic bottles and is used in a number of acoustic products - so eco-friendly too. The only question is whether the material is self-supporting, like sheets of BAF wadding, or whether it's loose fill, which would be difficult to fix down inside a cab. I'll buy one next time I pass Morrisons and report back.

The easiest way to do this is to build a second cab without an HF unit or crossover. Then link it to the full-range cab in the normal way. A second HF unit isn't helpful because you'll get phase-induced constructive and destructive interference between the two units (comb filtering).