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)

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.

I've not noticed any relentness sniping about "issues", Chris. I have noticed the flurry of aggressive posting seems to takes place whenever anyone says something less than flattering about Barefaced.

I'm now waiting for MoonBassAlpha to ask us what this has to do with the discussion. I must get some work done.......

[quote name='Merton' timestamp='1431880103' post='2775831'] Arsenal are losing, it's upsetting people [/quote] Well they're playing a proper team, what do they expect?

It was an innocuous lighthearted remark for goodness sakes!!! Merton took it in the spirit in which it was intended. What's up with everyone today? By the way, that was probably the politest trolling accusation I've ever heard......

McNach, your subsequent post was a rant in which you told me (I assume it was me, though you didn't actually say so) to piss off. I'm not going to dignify that with a response. If you missed the relevance of Talkbass to my ealier post – the one that you commented on – then I also give up, as I haven't a clue what you're getting at. I would just mention that I have always found your posts on here interesting and informative. Are you sure you are the real McNach?

That's a fair point. I've been lucky enought to hear some pro studio players playing live in small venues, and I have to say, some of them get a bass sound to die for from simple gear. We amateurs need a lot more help, which is probably why we spend money on our gear and fuss about it a lot more. We should be practicing instead.

I hear Merton gently waking from his snooze.........

[quote name='mcnach' timestamp='1431816762' post='2775341'] are you serious??? [/quote] Why wouldn't I be serious? That's one of the non-acceptable posting behaviours that will get you banned on Talkbass. As Alex is banned, it's not unreasonable to assume that might be why. Don't you agree? [quote name='mcnach' timestamp='1431816762' post='2775341'] if someone posts about a product of brand X, and the head of brand X joins the discussion, isn't that something good? well, except for those who dislike brand X. [/quote] Well that depends on what the head of brand X says. The Talkbass commercial user policy also prohibits: "comments on the products/services/character of competition (unless it is praise or recommendation)." So I don't think the head of brand X joining the discussion and slagging off the competition is something good, no. [quote name='mcnach' timestamp='1431816762' post='2775341'] Here's a thought, how about you leave those who like brand X in peace and not try to piss off the guy (head of brand X) whose contributions are appreciated by others? [/quote] Here's another thought. Why don't you have another scotch and let the mods decide what is permissible or not? (By the way, telling somebody to piss off will also get you banned from Talkbass and I trust it has caused one of the mods here to have a gentle word in your ear). Why should the head of brand X be pissed off? He doesn't even take the ban seriously. And by the way, I didn't bring this subject up, I just asked the head of brand X (do we have to play this game?) why he was banned. [quote name='mcnach' timestamp='1431816762' post='2775341'] Stop trying to sabotage other people's enjoyment and let them be, ffs. [/quote] Are you serious???

[quote name='alexclaber' timestamp='1431692789' post='2774026'] Seeing as I've been posting on talkbass since 2001 and two weeks ago was banned for a month according to the CUP, what do you think? [/quote] Well seeing as you asked Alex, I think that saying you were married for ten years before you shot your wife isn't much of a defence. Nor is the fact that other people have shot their wives. Not that I'm suggesting you have ever shot your wife, of course. By the way, what did they get you for? Spamming the discussion threads?

The B115D. Have you heard the Barefaced active speaker by the way?

But the Behringer is much louder.

I had one up to a year or so ago. It's a great-sounding speaker. However, it does not have the extended HF that you might expect from the aluminium dome. You won't find any frequency response measurements for the K140 anywhere, but I measured mine (which was brand new) and it rolled off around 2kHz (from memory), which surprised me. It also won't handle as much power as a modern top-or-the-range driver, but if you're using two it will be plenty loud enough for almost anything.

[quote name='Bill Fitzmaurice' timestamp='1431607112' post='2773102'] The interpretation of what the two 'sides' stand for depends on which you're on. Those on the purely subjective side who deny the benefits of objectivity make the assumption that engineers wear white coats, work in laboratories, and wouldn't know an E string from a pickup. I don't own a white coat, and I don't have a laboratory. My work clothes are well imbedded with sawdust, as is my 'office'. [/quote] Sometimes you're such a patronising old fart. [quote name='Bill Fitzmaurice' timestamp='1431607112' post='2773102'] I don't know how long Alex has been a bassplayer, but I have been since 1965, and not immodestly would put my chops and ears up against [i]anyone[/i] elses. [/quote] Post the YouTube link then!

[quote name='alexclaber' timestamp='1431617839' post='2773288'] Most bass knobs on amps are pretty broad shelving controls so you'd have to have a pretty extreme peak in response for the bass knob to fail to help. [/quote] That's exactly my point. Shelving filters are not much good for peaks. They will get rid of a100Hz boom but will also cut the frequencies below that. [quote name='alexclaber' timestamp='1431617839' post='2773288'] Then again, if you had a sharp boom at 100Hz you could just pull your cab away from the nearest wall until it's 2-3' from it, which will cause a notch in response at about 100Hz (due to the boundary reflection being out of phase with the direct sound). [/quote] Well in theory if you pulled your cab 2-3' away from the wall you'd still have a peak at 100Hz but you'd add a dip at 150Hz. So that approach, while it can be effective, is a bit hit and miss and not always possible anyway.

Unlike their competitors HH, Carlsbro never made their own drivers. It could be 200 watts, yes, but I'd play safe and treat it like a 150-watt driver. It looks in good condition from the photographs - so I would expect it to provide many years of good service yet.

Agreed - but you probably have the only properly built plastic bass cabs ever made. I have an old JBL Monitor 12, which is a lot more solid that what they make nowadays, but it still vibrates too much to be any good with bass guitar.