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Phil Starr

1x12" Cab Design Diary

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[quote name='LukeFRC' timestamp='1391723481' post='2360715']
Regional High End Cab Hoarders - N Wales branch captain. (as awarded by the Scottish Captain Funkle)
[/quote]

Ha!

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Damn, so good I said it twice....

I'm down to my Acme B1, the Berg IP112ER, and the Berg CN112. Not too bad, really...

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[quote name='funkle' timestamp='1391724757' post='2360739']
Damn, so good I said it twice....

I'm down to my Acme B1, the Berg IP112ER, and the Berg CN112. Not too bad, really...
[/quote] you should keep thinning them down! ;)

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[quote name='Musky' timestamp='1391723201' post='2360711']


That's a little odd as bass is perceived as more prominent as volume increases
[/quote]

Purely hypothetically, if port area were too small for the power levels being used then a relative loss of bass as volume increases is exactly what you'd expect. Port compression should start to kick in as airflow resistance increases, before onset of more obviously objectionable chuffing. This is something we have talked about a lot and would like to address empirically with the prototype. Simulations and anecdotal reports on air speed suggest that with long throw woofers, port size is usually inadequate and this is as much or more of a limiting factor than xmax.

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Incidentally, that same issue of port flow means designing a compact box around the high excursion 8 and 10" drivers is difficult, if you want to make use of their full capability. You struggle to fit a long enough port in the box! Long ports are not without problems of their own either beyond mere size

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[quote name='LawrenceH' timestamp='1391729126' post='2360814']
Purely hypothetically, if port area were too small for the power levels being used then a relative loss of bass as volume increases is exactly what you'd expect. Port compression should start to kick in as airflow resistance increases, before onset of more obviously objectionable chuffing. This is something we have talked about a lot and would like to address empirically with the prototype. Simulations and anecdotal reports on air speed suggest that with long throw woofers, port size is usually inadequate and this is as much or more of a limiting factor than xmax.
[/quote]
Cheers for clearing that up Lawrence. Every day is a school day. :)

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[quote name='LawrenceH' timestamp='1391729126' post='2360814']
Purely hypothetically, if port area were too small for the power levels being used then a relative loss of bass as volume increases is exactly what you'd expect. Port compression should start to kick in as airflow resistance increases, before onset of more obviously objectionable chuffing. This is something we have talked about a lot and would like to address empirically with the prototype. Simulations and anecdotal reports on air speed suggest that with long throw woofers, port size is usually inadequate and this is as much or more of a limiting factor than xmax.
[/quote] which is what I found with my old "less than adequately engineered" cab - not only did it seem to be tuned daftly high but what bass there was would drop out when you turned up leaving lots and lots of slightly grating mids.

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I would love a cab engineered for the increased LF extension (fully accepting the efficiency trade-off) that my ACME offers. Would that be an option?

I am also a huge fan of DSP as evidenced in all the grownup PA systems as well as the Berg IP series. There was a thread on TB looking at DIY DSP http://www.talkbass.com/forum/f36/diy-line-mixer-crossover-eq-high-pass-filter-749884/ which would be great to slot into a nice 12" cab.

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I have Owen's Acme 12 on loan and it is the best single 12" cab I've ever heard, solid as a rock and still reasonably light weight.
Surprisingly loud with my LM11, (it's the 4 ohm version) and deeper sounding than than my 3015LF loaded 15, it's great to hear[b] all[/b] the bass [b]all[/b] the way down with no nasty peaks or bumps across the tonal range.

Here's a look inside:

[media]http://youtu.be/uJy3TscsL-U[/media]

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[quote name='owen' timestamp='1391880854' post='2362286']
I would love a cab engineered for the increased LF extension (fully accepting the efficiency trade-off) that my ACME offers. Would that be an option?

I am also a huge fan of DSP as evidenced in all the grownup PA systems as well as the Berg IP series. There was a thread on TB looking at DIY DSP http://www.talkbass.com/forum/f36/diy-line-mixer-crossover-eq-high-pass-filter-749884/ which would be great to slot into a nice 12" cab.
[/quote]

+1 to all the above. The minidsp stuff is really interesting, though the software is more geared at the moment to fixed installations (home hifi setups and the like). http://www.minidsp.com

I have started to wonder why we bother to use passive crossover elements (heavy, expensive) when a DSP crossover mated to the correct power supply could so the same for less weight (and be re programmable). Extra cost of course....and you need a laptop or PC to edit the software in the MiniDSP modules.

I was considering trying out a fearless F112 build, but I'm stoked to see what the three musketeers here come up with. Happy to support this project in any way I can.

Edited by funkle

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[quote name='owen' timestamp='1391880854' post='2362286']
I would love a cab engineered for the increased LF extension (fully accepting the efficiency trade-off) that my ACME offers. Would that be an option?

I am also a huge fan of DSP as evidenced in all the grownup PA systems as well as the Berg IP series. There was a thread on TB looking at DIY DSP [url="http://www.talkbass.com/forum/f36/diy-line-mixer-crossover-eq-high-pass-filter-749884/"]http://www.talkbass....-filter-749884/[/url] which would be great to slot into a nice 12" cab.
[/quote]

A cab engineered for LF extension (with the trade-offs that entails) is certainly on the cards but it will have to be based on drivers that are easily available to the DIY'er.

DSP is a fascinating field (and I'm discovering that the eq available from the current crop of bass amplifiers is not capable of properly equalising compact cabinets) but is beyond the scope of this project.

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[quote name='stevie' timestamp='1391955181' post='2362926']
DSP is a fascinating field but is beyond the scope of this project.
[/quote]

:(

So, in the spirit of this thread, who can do the DSP for us tech-numpties?

:)

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[quote name='owen' timestamp='1391955626' post='2362935']
:(

So, in the spirit of this thread, who can do the DSP for us tech-numpties?

:)
[/quote] some power amps have DSP built in with handy visual interfaces for the PC - it wouldn't surprise me if given the plans for a cab and the graphs of what it will do you could work it out yourself...

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[quote name='LukeFRC' timestamp='1391960892' post='2362993']
some power amps have DSP built in with handy visual interfaces for the PC - it wouldn't surprise me if given the plans for a cab and the graphs of what it will do you could work it out yourself...
[/quote]

There are many things in life that I [i]could[/i] do for myself, but I have learnt that there are lots of things that I never actually get around to doing, so if it is already done by someone who knows what they are doing then the magic happens that bit easier! I would also like a little DSP box to put before the power section of my AI so that I could avoid carrying a rack around with me :)

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Tiltback/monitor form factor as well? If this sounds like a shopping list, it is because it is a shopping list.

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[quote name='owen' timestamp='1392647245' post='2371012']
Tiltback/monitor form factor as well? If this sounds like a shopping list, it is because it is a shopping list.
[/quote]

+1 to this feature request!

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Has there been any progress? It all seems to have gone a little quiet...

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Big apology to all those following this, I've joined a new band and have new set list to learn and bass playing is what it is all about. My aim was to summarise about a weeks worth of discussion per post but I'll have to condense that a little to catch up.

When I left it we were starting to look for a good driver (the actual speaker) for our cab. I won't pretend it was an unbiased search. Stevie was keen we look outside the usual suspect (Eminence) I had previously done the search and bought a couple of Beymas. Celestion and Faital were mentioned early on.

Technically we had some design specs to meet. We decided it was practical to make a single 12 capable of matching a drummer which meant achieving 120dB @ 1m within its maximum power. Most 12" speakers handle around 300W so that means something like 95dB/W efficiency. We also decided a practical 1x12" needed to be pretty portable so a speaker capable of working in a box no bigger than around the 60l mark was needed. We also had a bias for something which would handle low frequencies without overloading too easily, this means looking at the excursion or Xmax and anything with an excursion below 4mm was out.

Then we considered frequency response. We discussed the bass characteristics a little. The choice is really between an under damped speaker which characteristically gives a bass peak at around 100-120Hz of a few dB and rolls off quickly below that or a well damped speaker with a bigger magnet and more control which would give a smoother response and a respectable output down to 40Hz ish. We didn't consider an over damped speaker which roll off gently from above 100Hz but can give good tight bass and acceptable responses if you apply a little eq. Damping is measured in the Q of a speaker and overall Q or Qts needs to be about 0.4, anything above 0.5 is underdamped and likely to give a bass hump in a practical cab anything below 0.3 is likely to be very tight and lack bass output. We decided to go for a modern controlled bass response so we looked for speakers with a Q between 0.3 and 0.5. if we wanted to look for an 'old school' sound we would have looked for something with a Q somewhat higher 0.5-0.6.

It's too easy to get a bit anal about bass response. It's the only bit you can really control as a cab designer and we are all bass players, but most of what we hear from a bass is actually mids and the higher frequencies are much more important in defining the 'sound' of a cab. We wanted a single speaker to cover the whole range for our first cab it would need to go up to at least 3500Hz and preferably higher. 12" speakers naturally cut off at about 1100Hz and response above this is down to the cone flexing so the sound comes mainly from the middle of the cone. A lot of speakers actually give a big increase in output at breakup so you get a peak in output from 1-3000Hz another contributor to the 'old school' sound. More about this later, probably.

So the 'ideal' driver would specify

Fs 40Hz
Qts 0.3-0.5
Xmax >4mm
96dB/W
frequency response 40-4000Hz +/- 6dB

We modelled all of these and probably some more Beyma SM212, Celestion BL12-200x and BN300X, Faital PR300,Fane Soveriegn 12-300, Eminence Deltalite 2512, 3012HO, 3012LF, Beta12-II.

more soon, I have to practice

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[attachment=161064:1x12 prototypes 001.jpg]

Cutting a long story short I've a new band, a list of 30 songs to learn, and fell so far behind with the diary that I decided time was better spent building a speaker. I'll revisit the discussions we had when I get time, for those of you who find it useful.

Anyway if I've done this right it should be a pic of the prototype. Four ports because we intend experimenting to see if port noise is an issue and we want to try tunings for maximum power and maximum output down to low B. The final version will probably have a shelf port for ease of construction. As ordered it is proportioned to take a rack amp on one of its sides.

The cab is 50 litres plus enough for the ports, bracing and the speaker. The cab is made out of flimsy 12mm ply because we want to investigate panel resonances. This cab is 6.9kg and the speaker is 4.6kg so with bracing and fittings the cab will weigh in at about 12.5 kg. a one handed lift.

I'm off to fit the drive units; Beyma SM212's

Edited by Phil Starr

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I really should be working, can you stop this nonsense now please - it's just too interesting!

Great thread, [i]really[/i] great thread. :D

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[attachment=161098:Beyma SM212.jpg]

Speakers about to go in.

Spec Sheet http://www.lautsprechershop.de/pdf/beyma/beyma_sm212.pdf

chosen because of excellent excursion figures, good damping and good cone break up performance giving useful upper frequencies. Also because they sound good and are cheapish for a quality speaker.

Without more testing though we're not ready to recommend them as the final design, that's why we have two cabs, we can swap ports and drivers and do A/B comparisons.

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[quote name='funkle' timestamp='1392661166' post='2371269']
[quote name='owen' timestamp='1392647245' post='2371012']
Tiltback/monitor form factor as well? If this sounds like a shopping list, it is because it is a shopping list.
[/quote]

+1 to this feature request!
[/quote]

Plus two(s)

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Ok they are up and working, though I want to test them extensively before giving out detailed designs. To me they just run down to bottom E with no change in timbre, just an even open sound. The top is pretty neutral sounding too, no obvious sound added by the cab. this is just a 10 min workout though. More to come

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Looking good Phil and well done for keeping the weight down.
Do you have an Eminence kappalite 3012LF driver to try in there?
I am particularly interested in it's low end capacity for dub reggae.

Steve.

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I think we might have one to try, though I don't have one here. This cab is meant to be full range for bass and the LF has very restricted top end so it wasn't a top choice for this though it models Ok in this box.

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