stevie

[quote name='6v6' timestamp='1412242726' post='2567012'] Interesting update! FWIW in my build I made the fixed shelf tuned to ~50Hz, and later I added a removable extension which moves it down to ~42Hz tuning. It's fair to say the difference is subtle, but audible, and since I fitted the shelf extension I'm getting occasional ugly sounds on hitting the low notes (only a 4 string but I'm running a 300w LM3 into one speaker) - it's interesting that you note port noise, I've not checked my plots but perhaps that explains it. [/quote] My guess is that your'e hitting xmax at 70/80Hz. If you look at Phil's excursion diagrams above you'll see that dropping the tuning to 40Hz reduces the power handling of the system quite a lot between 50 and 80Hz. If the problem didn't occur when your system was tuned to 50Hz, it's not likely to be noise, because lowering the tuning to 40Hz will move the turbulent noise from the ports down out of harm's way.

If I weren't expecting the builders to come in and demolish our internal chimneys tomorrow, I would have a go, but I'm going to be a bit tied up for the next few days. Apart from that, I don't have a 5-string. I don't think it would be that complicated to do. You'd have to play pink noise through a hi-fi system or a bass amp and use a RATA to equalise it until it's flat between 30Hz and 200Hz. Then play your B and measure what you get on your RATA. That should represent the input the speaker receives for each frequency band. Perhaps somebody on here could give it a go...... It's well known that the energy of the bass guitar is concentrated in the first two harmonics rather than in the fundamental, and that applies to plenty of other instruments too. The second graph tks.se posted shows that the fundamental accounts for just 2% of the total energy of the note, which strikes me as rather low, unless an unequalised speaker system was used for the measurements.

I think most people will assume that it's straight from the bass because that's the only data that makes any sense, but the measurements shown are of SPL. So we need a bit more information on what was measured.

Why don't you try it and see?

[quote name='tks.se' timestamp='1412160565' post='2566219'] When playing a low B, most of the tone consists of harmonics to the fundamental. Here's the result of playing a low B and running the signal through a spectrum analyser: [/quote] What exactly was being measured here? Was the loudspeaker eq'd to be flat to 30Hz?

[quote name='LukeFRC' timestamp='1411939880' post='2564215'] I'm willing to bet that the average ABS PA cab will be better engineered than the average Bass cab (note the second average there ) properly done I don't see how it would be worse. if you look at this they take a RCF HD12a apart.... not that ABS stuff has a fair bit of bracing there.... also a cab I would love to try sticking electric bass through [/quote] Just to agree with Discreet here, check out this video at around 1 minute in. It tells you all you need to know about that speaker, and plastic cabs in general. If you don't know what I'm talking about, google 'knuckle rap test'. The ideal way to use this kind of cab for bass guitar is to put it on top of a 'proper' bass cab with an electronic crossover. Like a normal PA, in fact. On its own it will sound like bass in a plastic bucket. IMO, of course.

That's not too far from Dorch - so I'll try to come too.

If you're going to continue to use these as monitors, your only solution is to replace the damaged driver with an identical one. Anything else will change the sound. Unless you can find out who makes the driver (it's unlikely to be M-Audio) you are stuck and an original spare part is your only answer. I'd guess it's a Chinese special, but you'll need to examine it to find out more.

Funkle, it seems I missed your post. in answer to your question, I use the RTA section of Liberty Instrument's Praxis measurement software. It used to be available separately as a download but I now see that you have to download the whole program. I expect it's still available on the web somewhere. However, there are plenty of other free RTAs. I use a Creative EMU (0202, I think) connected to a netbook. I happen to have a very expensive calibrated mic but a cheapo would do nearly as well, as most of the benefits of expensive measurement mics are at the HF end. I try to measure about 4 or 5 metres from the cab, as less than that fails to capture what the room is doing. You have to be quick though - people don't particularly like the sound of pink noise. Apart from that, mic position doesn't seem to be critical for this particular purpose, although you do need to move it about a bit to make sure you're not stuck in a null. I currently have two Behringer parametric eqs and they make superb bass preamps. Because they have balanced/unbalanced ins and outs, you can plug directly into your bass amp, although they have enough output to drive a power amp on its own. I bought the second one for backup but have never needed it - so I will be selling it soon. As the measurement process is a bit of a faff - not to mention having to tote the extra equipment - I only do it nowadays when I know I'll have plenty of time to spare.

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