1x12" Cab Design Diary

[6v6]

[quote name='dincz' timestamp='1418932618' post='2635035']
Interesting. I just took a look and apparently they aren't airtight

[url="http://www.neutrik.com/en/speakon/speakon-chassis-connectors/nl4md-v-s"]http://www.neutrik.c...ctors/nl4md-v-s[/url]
[/quote]

You could just build a little box for the jack panel to fit into inside the box (obviously tweaking the rest of the dimensions slightly to maintain the same overall volume).

[Chienmortbb]

I would not use jacks for speaker fans for the following reasons:

1. Most sockets and plugs are rated for 3 amps or fewer. That is about 90 watts into 8 ohms.

2, There are 5 and 10 amp plugs and those are non switched types.

3. Because Jack plugs have exposed contacts, they are prone to short circuiting the amp output. One One power amp manufacturer told me that in MI, shorted jacks were the largest single cause of power amp failures.

4. As the cables can be used for either instrument or speakers, the two types of cable are quite different. A speaker cable is not good for instruments as there is no screening and an instrument cable will not be able to take the current and may cause a badly designed amp to oscillate.

If you feel you must use Jacks, switchcraft and nuetrik both make square bodied jacks withe the terminals at the end that are sealed. Cliff make a more traditional Jack with a dust seal that should be fairly airtight.

Of course the Soeakon was designed for high current use and the contacts are hidden on both plug and socket so it is really hard to cause an external short circuit.

Edited December 20, 2014 by Chienmortbb

[Beer of the Bass]

Those are reasonable points. I think in my case of wanting to connect two 4-ohm cabs in series, the simplest and least mishap prone solution would be a single speakon on each cab and a specially made series Y-cable with labelled ends. Switching jacks seem to be one of the most common failure points on line-level equipment, so I'd be a little wary of using them with a speaker signal.
This is a bit of a digression from the design diary, but I guess Speakon vs Jack is a relevant consideration for anyone building their own.

[LukeFRC]

So....

[Phil Starr]

Fair Question.

The position I'm in is that I've been successfully gigging the prototypes for several months but so far have failed to get anyone else to try the speakers. I'd prefer to give other bassists the chance to try them out and comment before I release the design, in case they need a bit of tweaking.

I'm down on the Somerset/Devon/Dorset border and ideally I'd like to set up an evening in a local pub, set up and let people come along and have a try. I'd even provide the basses! (American Deluxe P, Highway One J, Japanese T'Bird) If anyone is up for that let me know.

[Chienmortbb]

Phil, I live in Poole and I would love to meet to checkout the Cabs especially with the amp I am building. Unfortunately I can't get out much due to my wife's illness. Perhaps we could arrange a Somerset/Devon/Dorset get together at the same time around June.

[Phil Starr]

Hi Chienmortbb I'm keen to meet up with anyone who can tryout the cabs and indeed others i have already built or planned. I'm off to Japan for a fortnight but will get my head round it as soon as I get back. I'm hoping to get some technical measurements made as soon as I get back from Japan.

Like so many people who don't do this for a living life keeps getting in the way.

[Thunderpaws]

Hi Phil. You we're going to email me cab dimensions and component dimensions so I could make a CAD model. Are you still looking for that? Cheers, garry

[Phil Starr]

Hi Garry, yes I was going to just send some drawings but Stevie has offered to run some tests on the cab asap so I'm holding back until I know there are no further mods to be made. I'm hoping that will be as soon as I get back from Japan.

I'll pm you now.

[Phil Starr]

Hope this doesn't count as a necropost, but I'm a little embarrassed at how long it has been. Sorry people, especially those who have offered to help. Anyway there's some news.

I spent one of the most enjoyable afternoons I've had for years in Stevie's Garage running tests on the prototypes followed up by a session with a bass or two listening to the speakers, family commitments meant it was too short a time actually playing.

Basically we ran two tests, one was a simple frequency sweep and we then removed a driver and ran a check on the t/s parameters to see if the provided figures were accurate. The two prototypes were set up slightly differently, one tuned to 40Hz and one to 50Hz. Stevie will be along later to put up the actual data but the headlines are:

Beyma's published data is pretty accurate, Qts was slightly lower than spec and Bl correspondingly higher, Vas was lower than spec. All this means is that the speaker is better suited to an smaller cab and a better match for the 50l cab we designed. Of course we only tested one unit so there may/will be a manufacturing spread but Beyma clearly aren't puffing up their figures. It's also a nicely made unit.

Frequency response was pretty much exactly as expected, possibly less of a bass hump than expected due to the low Q of the driver. The speaker was substantially flat over most of the response with a noticeable but minor peak around 2kHz and the -10dB points were at roughly 40Hz and 5kHz..

There was a measurable difference in the bass between the 50Hz and 40Hz tuning with about 2dB more bass between 40 and 100Hz with the 50Hz tuning. If you remember we discussed this during the design process. I preferred the lower excursion at 30Hz of the lower tuning and Stevie preferred the extra bass and power handling of the 50Hz tuning. Well it showed up in the tests.

Into the listening room and we tried out two very different basses through the cabs. Fender American Deluxe with Elixirs and Highly modified Yamaha with Flats) I won't say too much about the sound as I'm hoping Stevie will pull no punches but they produce some nice clean deep bass with a pleasant 'flutiness' due probably to the 2kHz peak. You could hear the difference in the two tunings with the controls flat but it was very easy to dial out with a touch of eq on Stevie's Little Mark III. I marginally preferred the sound of the 50Hz tuning and I think stevie had a small preference for the 40Hz tuning but I'd suspect this would change depending upon the bass you use and the room acoustics.

Anyway, Stevie has the data and our conclusion is; the design does what it says on the tin, and the sound is something we'd be happy to share with other people, It's a better cab than most mid priced commercial offerings. I'm going to build the final cab and photograph the process and release the design.

[funkle]

Nice work. Really great job, and for free, I don't think anyone can complain re: time spent design/prototyping/testing.

Do you feel the only cabs 'better' than your design would be Fearless, Baer, Barefaced, TKS full range cabs, etc? Those are of course all, to one degree or another, 'full range', and have prices to match...

I'd be interested to know if you plan a version with a crossover to a 6" driver or tweeter.

Great job, once again.

[Chienmortbb]

Phil, you have no need to apologise. Life gets in the way sometimes and you are offering your collective expertise free to the community,

Having started on an amp build I have had the same problems and it always takes longer than you think to get it right. However it is no cheaper to build your own amp but it is possible to get a self build speaker at close to half the price of a commercial offering. Arguably time better spent than my amp build.

[Phil Starr]

[quote name='funkle' timestamp='1435389651' post='2808277']

Do you feel the only cabs 'better' than your design would be Fearless, Baer, Barefaced, TKS full range cabs, etc? Those are of course all, to one degree or another, 'full range', and have prices to match...

I'd be interested to know if you plan a version with a crossover to a 6" driver or tweeter.

Great job, once again.
[/quote]

Interestingly enough we went off piste a little yesterday and tested it and a couple of other speakers with Stevie's 6" midrange driver, which he is going to build into a cab with a 15" Ciare driver, I think this will be shared at a later date. It did sound a little better with the midrange driver.

It's not for me to compare cabs. First of all without a good collection of cabs to actually run tests on it wouldn't be fair or unbiased. Secondly a 'good' cab is one that creates the sound you want, so one person's good cab is another person's dog. What i'm trying to do is give an impression of the capabilities of the cab for someone who might want to build one, I suppose objectively I can say it's 40-5000Hz,(-10dB) 350W thermal, fairly neutral sounding with a more extended bass than many commercial cabs due to high Xmax.
[quote name='Chienmortbb' timestamp='1435392793' post='2808298']

Having started on an amp build I have had the same problems and it always takes longer than you think to get it right. However it is no cheaper to build your own amp but it is possible to get a self build speaker at close to half the price of a commercial offering. Arguably time better spent than my amp build.
[/quote]

But you learn so much doing these projects.

[stevie]

It's a busy weekend so far at Stevie Cuttings, but I'll be chiming in with some comments and posting some of the measurements we did shortly. But it's looking very promising!

[Passinwind]

[quote name='Chienmortbb' timestamp='1435392793' post='2808298']
Phil, you have no need to apologise. Life gets in the way sometimes and you are offering your collective expertise free to the community,

Having started on an amp build I have had the same problems and it always takes longer than you think to get it right. However it is no cheaper to build your own amp but it is possible to get a self build speaker at close to half the price of a commercial offering. Arguably time better spent than my amp build.
[/quote]

I've only built amps with unique feature sets not found in commercial offerings, so what it cost was sort of moot. But even with cabs, if you mentally pay yourself a reasonable labor wage DIY building is pretty much always a losing proposition monetarily, in my experience. Since I don't enjoy woodworking particularly, using a proven design such as the one in this thread will eventually be is a pretty nice hedge against huge budget bloat, and the design efforts are much appreciated.

[stevie]

After months of trying to arrange a meet up, Phil finally managed to come over with a pair of the Basschat cabs so that we could subject them to some proper measurements and find out what we were dealing with. As these were prototypes, Phil had just slapped a coat of black paint over them and fixed a round grille over the drivers. With a proper grille, however, a few appropriate fittings and a coat of speaker paint or some carpet/tolex covering, there’s no doubt that these could look very smart.

Using the single strap handle, they were quite a comfortable weight. I’d certainly put them in the ‘lightweight’ class - carrying one in each hand ought to be fairly easy for most people. (Phil, could you stick them on your bathroom scales and tell us how much they weigh?) Even though he’d used ½” ply of a not-very-wonderful quality, the very clever bracing design, which uses wood left over from the main cuts, meant that the cab did much better than I had expected on the knuckle-rap test.

The next positive result came when we ran an impedance test to measure the cab tuning. Phil had got it absolutely spot-on – which is good news for everyone using WinISD. As Phil has already explained, one cab was tuned to 40Hz and one to 50Hz. The measurements of the low end response of the two cabs showed that 50 Hz was probably optimum (for a 4-stringer at least) because of the extra output below 100Hz, whilst the lower tuning would probably be more appropriate for a 5-string. Builders will, of course, be able to try different tunings if they wish, and settle on the one they prefer. The ports are standard plastic drainpipe, the advantage of which is that it’s cheap and can be cut to any length.

The next measurement was LF extension. I took a measurement for each cab to show the difference the tuning made. The lower curve is 40Hz tuning and the upper curve is 50Hz. The mic was slightly further away when I did the 40Hz measurement (all of this was done in a bit of a rush) and the curve should therefore be about 1dB louder. Because the SPL was calibrated for 1m and I measured much closer than that, the absolute levels shown on the left of the graph are not valid.
[IMG]http://i59.tinypic.com/2rzqn0p.jpg[/IMG]

There was a lot more output below 100Hz than I had expected from modelling the driver, but there was a good reason for that, as were to discover later. (to be continued)

[LukeFRC]

Worse than a soap opera! Cannae take the suspense

[stevie]

It will be worth it in the end, Luke, I promise you. I'll be posting some more info later today and I believe Phil is now getting the drawings sorted.

[Ghost_Bass]

[quote name='stevie' timestamp='1435580461' post='2810170']
It will be worth it in the end, Luke, I promise you. I'll be posting some more info later today and I believe Phil is now getting the drawings sorted.
[/quote]

Will it be an option for adding a tweeter to the design and a suggested x-over (or at least a suggested x-over point)? Looking forward to this. I think i'll have a go at building one for the rehearsall space.

[stevie]

The next thing we did was examine and measure the driver. The Beyma certainly looks the business, with a very high build quality, sturdy cast chassis, and generous cooling via a large polepiece vent and a vented spider. This is definitely a cut above most of the drivers found in today’s commercial bass cabs.

I wasn’t too keen on this driver at first for a number of reasons, despite its obvious benefits. First, there was a dip in the published frequency response at around 500Hz which indicated a bad resonance. Second, when I modelled it using the published parameters, I saw that it started rolling off at around 100Hz in our box and that 40Hz would be -15dB down. Like this:


When I measured the Thiele-Small parameters it quickly became clear that this was not the same driver that we had been modelling. Beyma had changed the cone for a heavier one, tightened the suspension (reducing the VAS figure by two thirds, maintaining fs whilst reducing sensitivity), and added a Faraday ring (cutting Le in half). In fact, the parameters we measured were a perfect fit for our 50 litre box (QB3 alignment). The driver with the new parameters now models like this:


Which is close to the actual measurement in my previous post – with 40Hz about 10dB down – much better!

I had a look online for a spec sheet for the chassis, and discovered that there is in fact a new one on Beyma’s website: [url="http://www.beyma.com/getpdf.php?pid=SM-212."]http://www.beyma.com...php?pid=SM-212.[/url] It doesn’t completely match what I measured, but is close enough not to matter. Most of the information on the web contains the old parameters, including the info on the UK distributor’s website: ([url="http://www.lmcaudio.co.uk/assets/pdf/beyma/SM-212E.pdf"]http://www.lmcaudio....yma/SM-212E.pdf[/url]).

(Edit: one more post to come)

Edited June 29, 2015 by stevie

[stevie]

The final measurement taken was the upper frequency response of the cab:



Perhaps unsurprisingly, this matches Beyma’s latest published curve quite closely. Midrange sensitivity is around 96dB. The main cone resonance occurs at 2kHz, which is par for the course for a good quality driver. Most bass/midrange speakers break up like this at the top end. There are a few that don’t, but they are very much the exception. The resonance is mild and fairly well damped but the waterfall plot (which I did not bother saving) shows that the cone is definitely breaking up here. The highest you would want to use this driver in a PA cab is 1.5kHz but cone breakup at this frequency is not such a serious problem with bass as it is with voice, for obvious reasons. Anyway, flat to 3.5-4kHz and 12dB down at 5kHz is a result – and Beyma had fixed the 500Hz dip in the previous version, which was another piece of good news.

We spent the final part of the afternoon (hurriedly) trying the cabs out with a Mark Bass LMIII. I have a 1980s Yamaha BB with a Duncan SPB-1 pickup and TI flats. My initial impression with the amp set at flat was that I would prefer a bit more bottom end and a bit more top because that’s what I have with my own system. A tiny bit of adjustment of the tone controls was enough. I would be happy to gig it like that.

The real eye-opener came when we plugged in Phil’s Precision with roundwounds. With the amp flat, it was perfectly balanced. Every note sounded even playing up and down the fretboard from top to bottom. The bottom end was perfect, although this time I thought there was too much top end, as string noise was a bit excessive. It was the kind of clean, uncoloured type of sound from which you could easily dial in whatever tone you wanted because it was all there.

I thought the cab sounded much better with Phil’s bass than with mine, although I’m really not sure why.

The difference between the two cab tunings was not as great as I had expected from the measurements. Also, when we connected a couple of midrange drivers with crossovers at 800/900Hz (designed for another bass cab, so therefore not optimum), I thought there was a marked improvement in clarity, despite the fact that the Beyma is no slouch in the midrange (but I’ve always been a fan of a separate midrange driver anyway). Phil heard a difference, but from what he has posted, I don’t think he considered is as much of an improvement as I did.

We really could have done with a commercial 1 x 12” cabinet as a reference - and someone who is used to evaluating bass guitar cabinets to assist. Both Phil and I are used to testing fullrange speakers, but evaluating a bass guitar cab subjectively is a completely different kettle of fish.

Edited June 29, 2015 by stevie

[stevie]

[quote name='Ghost_Bass' timestamp='1435583892' post='2810239']
Will it be an option for adding a tweeter to the design and a suggested x-over (or at least a suggested x-over point)? Looking forward to this. I think i'll have a go at building one for the rehearsall space.
[/quote]

It shouldn't be too difficult to do, although I'm not convinced it would add much. The cheap option would be to cross over where the bass driver is 6dB down, which is about 4.5kHz. You could use something like a P. Audio PHT-407 (under a tenner, and a really nice HF unit) or the neo version, which I think is about £20. A more worthwhile alternative would be to cross over at 1.8 - 2kHz, which those drivers can cope with, but then you need a proper two-way custom-designed crossover, which would cost more.

[JTUK]

Good to see this thread back.
Hopefully this will help make 'Cabs' worth visiting again.

[Phil Starr]

I'd confirm everything Stevie has said about how they sounded. It was so good to have a second opinion after gigging them for so long. I had to check back to see what I said about the midrange, it does clean up the midrange and that made a difference using the roundwounds. It isn't a slap you round the face difference just a good cleaning up of the midrange sound, more detail. Since I suffer from vertigo above the fifth fret it wouldn't be as important to me. I'd describe it as being like the difference you get through a PA when you swap a decent dynamic mic for a condenser, like moving from a beta58 to a beta87. It kind of unveils everything.

I have one final dilemma which people can help me with. The prototypes worked so well and were so easy to build that I'm tempted to call it a day and release the design. I was going to go for an even simpler to build design with a slot port and less elaborate bracing in 18mm 3/4" ply. The current prototypes are heavily braced 12mm ply with four tubular ports (plastic drainpipe). It's a simple job to cut the port holes with a hole saw costing less than £10 and once that is done it is an easy build,
The slot port would be equally simple to build but could be done without any specialist tools. I don't think there would be a huge difference in sound or in weight as the mass of the braces would be similar to the mass of the thicker ply.

So? Any feelings about thin wall/bracing or committing to a cheap hole saw?

[Thunderpaws]

I'd go for thinner ply with a bit more bracing and circular ports. Depends on how you planned to build the slot port, but I would say it's easier to measure and mark the centre point for a circle than it is to line up measurements on three or four pieces of ply for the slot. Also, more bracing might give more long term stability than less bracing on a slightly thicker piece of ply. If you still want a 3d model and working drawing produced just let me know.