stevie

This is where we need some feedback, Thunder. The mids definitely help the cab cut through, and it's good to know that they are there if you need them. If I were building the cab for myself, I'd probably fit a notch filter to take away some of the mids. If there is a general consensus that the box is too mid-prominent, we could do that to provide the option of a more even sound balance.

[quote name='Phil Starr' timestamp='1436697862' post='2819967'] The overall impression I'm getting with now three bassists is of a really clean open sound from these speakers. On the minus side they really show up any untidiness in your technique ..... [/quote] I'm happy that I was able to highlight that particular feature for you, Phil.

Well - I finally gigged the 1x12 last Friday. Phil drove over to one of our gigs and I swapped from my 15" + 8" to the Basschat 12 during the break. I didn't really have enought time to adjust the sound to what I wanted. The cab seemed quite forward in the midrange - so I backed off the mids using the active EQ on my bass and that seemed to do the trick. The sound seemed clearer but not as full as my own cab, but because of the circumstances, I really can't say much more about the sound quality. A tweak on the bass control of my LMIII, or more mid-cut, would probably have given me the fatness I was missing - and if I'd had more time I would have done some more tweaking. (For reference I had the LMIII tone controls flat with just a touch of HF boost). Anyway, Phil was able to have a good listen from the audience (in fact he made up most of the audience!). I can say a few things about the cab, however. It is fairly sensitive: you don't need a 1,000W amp to get it loud. The top end is detailed. Dispersion is not bad - better than your average 12, I'd venture. I had the cab on the floor and I could hear myself when I was standing a couple of feet in front of it with the band playing. I would have preferred a bit more top end in my ears, but it was acceptable. I play with a reasonably loud drummer who puts the kick through the PA. You could say we're a loud pub band. The cab had no problem keeping up - it didn't even break into a sweat. (For those who use the Markbass LM III, my master volume was on 10-11 o'clock.) I think a lot of players would never need more than just a single one of these, especially if they were able to angle it up slightly. I really like this driver a lot. We're going to try some alternatives, but the Beyma seems to offer tremendous bang for the buck and is only a couple of kgs heavier than neo alternatives at twice the price. We could do with some other players gigging these now.

Good to see at least one person on this forum has his priorities sorted!

It doesn't seem possible that anyone could manufacture an electronic device, ship it half way round the world, advertise, pack and deliver it to you for the price of a pint. I've no idea how they do it.

An ohmmeter is a valuable tool to have around the house for testing batteries, cables, etc. You can get one for under £3 delivered from eBay: http://www.ebay.co.uk/itm/Professional-Digital-LCD-AC-DC-OHM-Volt-Meter-Ammeter-Multimeter-Tester-Checker-/400923875646?pt=LH_DefaultDomain_3&hash=item5d58ecd93e Everyone should have one (and a soldering iron).

I thought we were using a 30cm speaker......

It's interesting (well at least I think it is) that our European neighbours still refer to loudspeaker sizes in inches as well as cms.

I'd estimate the weight of the 18mm birch ply option at around 18kg, or slightly less than the Bergantino HD112 (at 20kg but with a tweeter), which is manageable but not what I would call lightweight. The poplar ply version would probably be around 12-13kg.

[quote name='Thunderpaws' timestamp='1435788036' post='2812552'] An 18mm ply cab with less bracing will not behave the same way as a 12mm ply can with more bracing. But can we hear the difference? Some clever person on here might know. [/quote] This is true - and it's one of the topics we discussed in PM but were never able to resolve. We probably need to do some calculations for weight and stiffness. My personal observations are these. An unbraced 12mm cabinet of this size is unacceptable for bass, as it rings too much. Phil's bracing method was very effective in damping this ringing (unlike some commercial offerings I've tried), but his 12mm cab was not as inert as my 18mm cabinet on the knuckle-rap test. I'd say it was an acceptable compromise in view of the weight savings, but it does make the build more complicated. The big unknown is 18mm poplar ply, which would be even lighter than the 12mm birch, have better internal damping and probably require less bracing - but would cost more. It does seem to be the material of choice of the mainstream makers of high-end lightweight bass cabinets. I'd also mention that there are some pro PA cabinet manufacturers using 18mm poplar for their bass cabs (although the overwhelming majority use 18mm birch) but nobody is using 12mm birch. [quote name='Thunderpaws' timestamp='1435788036' post='2812552'] I would still go for a slightly trickier 12mm braced design. A project is a project after all. [/quote] The bracing looked tricky, but Phil is saying that in practice it isn't. So perhaps it is not really an issue.

[quote name='Phil Starr' timestamp='1435666808' post='2811125'] It was very simple, though I do have a bench saw which made it easier. [/quote] It looked very neat when I saw it. Perhaps a photo would be helpful.

[quote name='Beer of the Bass' timestamp='1435665361' post='2811099'] There's one a bit closer to me who say on their website they have a range of speciality plywoods, so I could give them a ring too. Is the Chinese poplar core ply worth a look, or should it be the European stuff? [/quote] I've no personal experience but I've heard that the Chinese stuff is to be avoided as it delaminates and is full of voids.

Poplar is a bit specialist - that's a good point. It's not something you'll find at B&Q, although I think most major cities have an outlet. There's a supplier near you in Grangemouth. My experience with wood merchants is that they will get hold of whatever you ask them for from their suppliers. It's not usually a stock item though.

Like Passinwind, I don't enjoy woodworking. I find getting a straight cut with a perfect right angle nigh on impossible. If I were to build one of these I'd want to take a cutting list to the woodmerchant and get him to cut the pieces to size which I could then take home and assemble using simple tools. I'd therefore prefer an easy build with a shelf port and perhaps one semi-circular brace or a back brace. I'd go for 18mm birch ply for ultimate quality - or 18mm poplar ply if light weight is important. 18mm chipboard would be another option for someone who wants to try out the design without investing too much initially.

[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.

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.

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)

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.

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)

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!

[quote name='jonnythenotes' timestamp='1432066271' post='2777886'] I must be missing something here.... How can you have a bass cab that picks up no vibration from the speaker it contains. Unless you float the speaker, and completely isolate it from contacting the cab, you will transfer vibration to the speaker enclosure. Every cab I have ever owned has vibrated.... How else would you explain the 'boomy stage' we have all experienced, or the reasoning behind a Gramma Pad. Give me an example of a speaker cab that I could put my hand on top of, when it is being driven at gigging volume, and not feel any vibration, and I will eat my hat.... There is no such thing.... [/quote] You might like to look at Chris's earlier post. I have a (modified) Ashdown ABM Mini 15 that hardly vibrates at all even with a 500-watt driver fitted. You're right that you can't completely get rid of vibration, but you can get it down to negligible levels.

The problem really is with the cab. A properly designed cab shouldn't vibrate that much. It's definitely not good for the sound.

Search Google for :[size=3][font=arial,helvetica,sans-serif] [size=4]"GK MB500 (MB2-500) Supply Voltage Change"[/size][/font][/size] and you'll get the information you need. Please use a tech if in any doubt, but it does look like it's doable (although old man Krueger jumps into the Talkbass thread and is obviously not happy). [Edit] - and there's a Basschat thread too. Here: http://basschat.co.uk/topic/31330-gk-mb2-500/page__st__20

When you do build your cabinet, I'd strongly advise you to have a look at JBL's own plans for these drivers. The 2 cu. ft. or 55 litres that Bill suggested will work, but will be a bit bass light - around 80 litres would be better. Also, you need to tune the box to between 45 and 50Hz, preferably using 4-inch ports. If you tune it to 30Hz you will most likely blow your drivers. JBL suggests a volume of 3.75 cu. ft. for a single driver and 5.75 cu. ft. for two - that's 105 and 162 litres. I personally would stay at the lower end of that range because a smaller box will help power handling a bit and going any larger doesn't really get you any extra bass. There is plenty of discussion on the web about the K140 (lots of positive comments from bass players) and if you search you'll find quite a few plans. The JBL ones are here: <http://www.lansingheritage.org/html/jbl/plans/1970s-kit.htm>. Good luck! [Edited to fix the link.]

[quote name='funkle' timestamp='1431892239' post='2776021'] Responding to the OP: Having owned the BF BB2 and the Berg CN112 x 2, I will offer some thoughts. I have owned other flat cabs like the Acme B1 and B2, as well as the 'flat' powered Berg IP112ER. [/quote] That was an outstandingly well considered and even-handed review. Thanks.