stevie

That's not Every Time you Say Goodbye. Good though.

Nik bought some speakers from me. I stupidly mis-spelled my Paypal address, which cause some complications, but Nik stayed with it and made sure that the funds eventually arrived chez moi. A good old boy!

I had an MB115. It had a thin, cheap cabinet whose build quality was dire. The speaker was the cheapest possible Chinese dross. The amplifier section had some nice features but the cabinet started vibrating at anything more than room volume. It's light because it's insubstantial and it's cheap because it's built down to a price. There's no doubt a market for that kind of thing, but I'd be very reluctant to buy Gallen Krueger again after seeing how they cut corners on that series of amps. Mine was Chinese-built, by the way.

Aluminium is not stiffer than steel and was used for loudspeaker chassis long before neo came along.

It's a Celestion neodymium compression driver. QSC have lots of info on their website, including a parts breakdown of their cabs. Here's the K10: http://www.sesystems.com/Assets/QSCPartsSheets/QSC_K10_exploded_drawing_with_parts_list.pdf QSC spares are normally quite reasonable but if you can't find one at a reasonable price, do a bit of digging (or open up the cab) to find out what model it is. You can buy a replacement diaphragm for about £30 and easily fit it yourself. I think Celestion even have an instruction video on YouTube showing you how.

It's now finished and this is what it looks like. I took a lot of measurements when I was designing the crossover but didn't save any that I can post. So, I'll do another set and then try to explain what this setup does that most others can't (IMO). [IMG]http://i57.tinypic.com/2meaa1g.jpg[/IMG]

Hi Phil, yes, it is indeed a heavy duty crossover - the system is 500 watts. To give you an idea of scale, those resistors are 30W jobbies - not the usual 9/11 watt wirewounds. The crossover frequency was dictated by the midrange driver, which has a large peak and a nasty delayed resonance at around 500Hz that needs to be suppressed. This is therefore a 24dB Linkwitz Reilly filter at 800Hz - roughly where the 15" starts to beam, which works out OK. So there is very little overlap and no comb filtering. With a better behaved midrange unit I could have used a 12dB per octave x-over. The bright box idea is OK, but I'm trying to minimise compromises here, as this system is for my own personal use.

[quote name='IBWT' timestamp='1402138173' post='2470329'] Why bother? [/quote] Good question! The Ashdown cab spotted by the eagle-eyed bassman bears as much resemblance to the original Ashdown cabinet as this one does to the original Celestion cabinet. The only things that have not been swapped out or altered are the grille and the metal corners. As far as appearance is concerned, I’ll let you judge for yourselves when I take some photos of the complete rig. It’s not a one-brand look, that’s for sure, but it looks OK to me. I’m more interested in how it sounds than how it looks. I suppose it would be possible to construct a wooden cab to match the Ashdown, but that would have been a lot more work. Here’s a picture of the prototype crossover, which answers xgsjx’s question. For the cost of those components, you could easily buy yourself an electronic crossover, which is the option I'd recommend for most people. The passive crossover has the benefit of convenience - once it's installed it doesn't need any tweaking and you don't need a second amp. [IMG]http://i58.tinypic.com/2rm8fnc.jpg[/IMG]

I'm surprised nobody has asked any questions, like 'why bother'? I hope to answer that particular one when I post the measurements in a few days' time.

The only bit of woodworking needed is to cut out a spacer for the Eminence - the cutout in the cabinet is just a tad large. There's no need for precision here and my jigsaw was adequate. I apply layer of foam strip before screwing the spacer in and trying the driver for size. It fits, and is starting to look like a proper cab. We're still missing the most important part, the crossover, but as that's where all the real work is, it will have to wait for another day.

Just had a look at the price of the Eminence - they're not so cheap after all. They do appear on eBay for only a few pounds, but I think I'd probably use the Celestion equivalent (TF0818MR) if I were buying new (I got mine from eBay for a few pounds ). It looks like a more advanced driver all round with a slightly lower resonance frequency, a less pronounced peak at fundamental resonance, a smoother response and more controlled breakup at the top end. And it's almost half the price of the Eminence too! I have some TF0615MRs in my workshop but they are not loud enough for this system (which uses a 4 ohm bass driver). The next version of this system (should I ever do one) will cross lower, probably to a 6.5" midrange chassis. But that's another story. Here, I’m going to fit the passive crossover inside the mid cabinet with two Speakon sockets on the back – one will be the main input from my amp and the second will be the filtered output to the bass cab. This means that I won’t need to carry out any modifications to the bass cab whatsoever. Oh well. Now to drill a couple of holes in the back of the box for the Speakons. Wire them up and screw them in. Time for a beer after all that hard work. Edit for a missing indefinite article.

In this case, however, I’m going to fit a sealed midrange driver, an Eminence Alpha 8MRA. Although it is quite an old design, it performs surprisingly well, particularly for the money. The sealed back means that it comes with its own enclosure, so to speak. If you install it in an existing cabinet all you have to do is cut a hole the right size. The downside of this arrangement is that it pushes the driver’s resonant frequency up to around 500Hz. 800Hz is therefore the lowest crossover point that’s realistically possible with this driver, and only if you use steep slopes. As the BMS 15” I’m partnering it with performs beautifully well beyond this point, that’s something I can live with. The midrange driver. A bit dusty but it works OK.

Here are a few photos of my midrange cabinet project. It uses the cabinet from a non-working Celestion KRi2 that I picked up on eBay for not very much money. The first task was to remove everything from the Celestion so that I had an empty shell to work with. [IMG]http://i59.tinypic.com/25asqp0.jpg[/IMG] Despite all the internal bracing, the box itself rings like a bell and I’d want to apply lots of bitumen damping to the walls before I even considered using it as a midrange enclosure, never mind bass. [IMG]http://i60.tinypic.com/153uslv.jpg[/IMG]

A 15" Trace Elliot 1153 cab for £59 Buy-it-Now. Not bad. http://www.ebay.co.uk/itm/TRACE-ELLIOT-1X15-BASS-CAB-/121350485828?&_trksid=p2056016.l4276

The (original) Trace cabs I've owned were MDF and I think most of them were. Ashdown ABM cabs have always been advertised as plywood but they made more than a few in MDF without telling anyone.

It's not that long ago you would pay two grand for a monitor like that. Progress.

Would somebody please point me to the forensic examination of the Markbass business? I must have missed it.

I think Yorks is referring to the non-linear nature of sound pressure. In other words, doubling the size of your amp won't make the sound subjectively twice as loud. In theory you'll get a 6dB increase at lower frequencies by adding a second cab. To make a sound appear to be twice as loud you need an increase of 10dB. So they say.

Well if it works, fair enough. I suspect that judicious use of the bass control could have the same result, but DB and hollow wooden stages complicate matters.

[quote name='Ghost_Bass' timestamp='1400155408' post='2451245'] I lift my cab off the floor to prevent this coupling from happening. I have subs up front on the PA, i don't need any more sub-bass up on stage to muddy things up and mess with the drum mics. I also prefer to hear my sound tight and defined, any trouser flapping bass is EQ'ed at taste. Different views on the same subject [/quote] Can't your eq deal with the excess bass? Having a cab on the floor shouldn't produce excess sub bass or stop you getting a tight and defined sound. Virtually all bass cabs have been designed to be used on the floor.

That depends on what inputs and outputs you have, but the best way in theory is to use two separate Speakon to Speakon cables from your amp. Unfortunately the LMIII only has one Speakon output. The Hydrive (sensibly) has two Speakons available, doesn't it? If so, connect a Speakon to Speakon from your amp to your first cab and then connect your two cabs together using another Speakon to Speakon cable.

If your current Hydrive 410 is 8 ohms, that's absolutely right.

[quote name='Conan' timestamp='1400077990' post='2450520'] Whatever floats your boat... [/quote] Conan, I've just taken you off my Christmas list. No more bottles of best malt for you, laddie!