stevie

The large polepieces that work well on the Duncan Strat and Tele pickups have never really done it for me on the Precision Bass. They're louder than stock pickups but you lose the unmistakable character of a normal output P-Bass pickup like the SPB-1. The same applies to the Duncan Hot P-Bass pickup, incidentally, which sacrifices too much top end and tends to be muddy and characterless.

Wasn't this amp voted the worst amp in the 'What's the worst bass amp you've ever used?' thread?

For comparison, here's an Eminence Basslite.

I doubt very much whether they'd do that, but it wouldn't account for the differences. Apart from the 1dB difference in sensitivity, which could be down to my mic placement and is neither here nor there, the main differences are in the size of the peaks and dip between 2 and 3kHz and the fact that my curve shows a dip at 6kHz. Other than that, they are remarkably close. Peaks and dips can be minimised by using smoothing, a technique that's commonly used to make frequency response curves look a bit better. It looks like Celestion has made some effort to tame the peak at 2.5kH and have turned it from one large peak into a less worrying twin peaks and a dip. Bear in mind that this is an inexpensive chassis and that virtually all bass guitar cabs have resonances at around this frequency, most of them much worse than what we're seeing here.

I've just come across Celestion's own published measurement of the Pulse 10 chassis. It's interesting to compare it with the one I took, as it looks like it's been smoothed slightly. I also measured 1dB more sensitivity.

I decided to do a quick crossover hookup yesterday evening and managed to sort it out in an hour. You'll need three, cheap components, which is just what we wanted. The cab sounds surprisingly good too. More info and measurements to follow.

Sorry for the confusion with the graphs. It's not exactly easy to delete and replace images (although I finally managed to figure it out).

Here are a few more measurements. The first is the Pulse 10 at one metre. Unfortunately, I didn't calibrate the measurement, but from 200Hz to 1,7kHz it's 96dB. Between those frequencies it's really smooth - better than much more expensive drivers in fact. You can see the effect of the cone breakup between 2 and 3kHz. Not brilliant, but not as bad as your average Eminence. The compression driver (second graph) works well with the horn - thank goodness. Celestion say it can be used down to 2.5kHz, which is really good for such an inexpensive HF unit, but our crossover frequency here will be dictated by the bass unit rolloff, which is higher than that. Crossing over at 2.5kHz would also require a more complex crossover than I'm aiming for here.

Phil's working on the cabinet assembly instructions at the moment and will post them as soon as he's sorted. Once I've retuned the cab, located the cause of the 60Hz resonance and measured the bottom end response, I should be able to sign off the tweeterless cab design. Then you can build to your heart's content. The two-way version will obviously take longer.

I've been a bit busy with work recently, which is slowing the project up, but I managed to fit the drivers to Phil's cab and measure the in-cab impedance of the bass driver this morning. The tuning frequency with our 100mm diameter x 120mm port is around 58Hz. We need to get it lower and I've already planned for that. Those of you familiar with WinISD might like to enter the parameters of the Celestion Pulse 10 to see what's happening. The impedance curve is a useful troubleshooting tool, which tells you a lot more than just the load the driver is placing on the amp. Notice the bump just above 2kHz, which was there when I measured the impedance in free air. That's the main breakup point of the cone. There's likely to be some irregularity in the response here, depending on how well the manufacturer has managed to damp the resonance - if at all. There's also a faint bump at about 350Hz. That's caused by the vertical standing wave inside the cab. It looks better than I'm used to. The most interesting - and unusual - bump is at 60Hz. I have a good idea what that is but will have to troubleshoot it. Any suggestions?

That question opens up a big can of worms, @martyy. Yes, at a pinch, you could use it as a PA speaker. However, cabs used for bass guitar normally take into account the extra bass response you get from using the cab on the ground. So it will sound bass-light when used on a pole in the air and you'd need to eq it accordingly. The design goals of this project are not the same as a PA speaker, where the midrange is the focus of your attention. Remember also that this is a budget project. The Basschat Mk III cab was designed with no compromises in the midrange (expensive compression driver, low crossover frequency, good system power response) and works really well as a floor monitor or a PA speaker (in the latter case with the necessary LF eq). In fact, before lockdown, a group of us compared it with an active RCF cab and agreed that its reproduction of voice was superior. I'll be testing the finished design using all kinds of material, including full range audio - and I'll report back.

Sounds like an interesting project. You could probably keep the cab the same size, as the few litres that the amp would take up won't be a problem. You'd just have to alter the port length slightly.

You'd have to watch for vibration and air leaks. Otherwise, it might be worth a try.

One of those grilles would work fine. It's a cheap solution and protects the cone, but does look a bit home made. The round grilles made from punched metal, i.e. with small, round holes, look a lot better (if you can find them) but are more expensive. There's enough space on the baffle to fit a picture frame for a cloth grille. Then there are the metal grilles from Ebay mentioned above. I had real problems getting the etch primer to stick on the aluminium one - I tried two different brands. Although heavier, steel grilles are easier to finish with the type of spray paint that goes straight onto metal (Hammerite, Platikote and the German discounters' specials when they're available).

That's interesting. What I haven't mentioned is that builders have the option of making a tweeterless version, or building in two stages and adding the compression driver later. So a cab built from this plywood with just the 10-inch driver should weigh between 8 and 9kg, depending largely on the weight of the grille.

Thiele Small parameters of the Pulse 10 checked and they're in line with the manufacturer's published data, bearing in mind the temperatures and the fact that the driver's still not fully run in. I also ran a free-air impedance curve and there are no nasty surprises. First main resonance is at just over 2kHz, which isn't unusual. When I have the cabinet, I'll be able to compare the modelled LF response with the actual measured response.

6 minutes ago, Happy Jack said: Any recommendation as to who to buy these from? I'd get the Pulse 10 and Celestion comp from Lean Business and take advantage of their free delivery. Blue Aran don't stock Celestion but they're selling the B&C horn for under a tenner. Both companies are good to deal with. https://www.lean-business.co.uk/eshop/ http://www.bluearan.co.uk/

I've got a Celestion CDX1-1070 and a B&C ME10 horn waiting to be installed. That makes the cost of the drivers and horn under £90 in total. Total weight comes in at under 4kg. The benefit of using these drivers is that they're readily available worldwide. In the UK, the Celestions are available from a number of outlets, but Lean Business are currently offering free shipping on Celestion. The horn's available from Blue Arran. No free shipping, but you can pick up any bits and pieces (like cabinet corners and feet) when you order the horn.

The back is normally a single separate piece. It might make sense just to replace the back piece. Or you could just paint the bare wood black and ignore it.

Soldering is obviously preferable, but there's a good chance the crossover and wiring could be configured to be solderless - using spade connectors and a terminal strip, for which you'd just need pliars and a small flat screwdriver. It depends on how the crossover turns out. Keep watching.

I believe Phil is making good progress with the cabinet, which will be our starting point, and I'm expecting to see the cab assembly details on here before too long. The 10" driver we'll be using is the Celestion Pulse 10. I gave it an hour of 30Hz sine wave in open air to soften the suspension, but my first efforts at measuring the Thiele Small parameters were thwarted by the cold weather. I've had the driver warming up in the house for a day and will try again later.

Well somebody was bound to comment. You were just the first past the post.😊

😊 Yes, he would.

Thomas Eich says those drivers were engineered to work together.

I have in mind something with more excursion - like the 12CL76, but neither of those B&C drivers will have much bottom end in a 30-litre cab. If you model them, you'll see that they have less than the two Beymas - and Phil was specifically going for a bass-light cab. It depends what your goals are (price, weight, size, output , bass extension), but a 10" system might make more sense in a 30-litre cab. There's also a wider choice of bass guitar drivers available in that size.