Bill Fitzmaurice

[quote name='Gwilym' post='82878' date='Nov 2 2007, 03:00 PM']as long as it handles a low B adequately, then I'm happy[/quote] That's quite at odds with a true 'vintage' tone; my 65 Fender Bassman wouldn't go below G before going apoplectic. But todays drivers aren't so anemic. An OTop 12 will handle a low B, the question is whether you'd need a 1x12 or 2x12 to get the levels you want.

[quote name='Gwilym' post='81947' date='Oct 31 2007, 05:06 PM']hi Bill, thanks for your thoughts - pretty much exactly what Steve explained to me too . Now I do like the idea of this cab, and if I can get up to Northampton and Steve has one built, I would love to try it. But! I'd still like to keep the bottom end if possible. Which of your cab designs would you recommend on that basis? thanks! [/quote] That depends on what your definition of a good bottom end is.

[quote name='Gwilym' post='80991' date='Oct 29 2007, 04:17 PM']BFM Omni 12 Top (maybe without the tweeters) as recommended by Thumper[/quote] If he has one I'd give it a try. 'Vintage' translates to weak bottom, strong midbass and midrange, and a weak high end. That's the way cabs of the 60's sounded because that's what the drivers and cabs of the day were capable of. The OTop 12 and 15 are PA tops by design, meant to be used with subs, and that means a weak bottom, strong midbass and midrange, and, when built sans tweeters, a weak high end. The result is very much a vintage tone, but between using modern drivers and cabinet technology a lot louder than their 1965 counterparts. Very different animals from the more hi-fi Omni models.

[quote name='ZPQ' post='80224' date='Oct 27 2007, 03:02 PM']If you only have one monitor mix you could have the subs from an aux and the tops in stereo.[/quote]True, but never buy to suit only your current needs, always plan for future system expansion.

[quote name='fusionbassist1' post='80147' date='Oct 27 2007, 10:48 AM']If anyone has absolutely any muses about 18" speakers to share pelase do as i'd much appreciate all the info I can get. I haven't had much response in other topics so i'm still a bit overwelmed. Anything at all...honestly....Thanx a lot everyone, FB1[/quote]My main advice with respect to an 18 is don't use one. Modern drivers don't have to be so large to deliver what you need, and as far as electric bass is concerned there's no need for an 18 whatsoever. Beyond that, response, sensitivity and usable output are determined by the combination of the cabinet and driver, and they must be precisely matched to work correctly. You can't separate the function of the one from the other, so if you're thinking about loading a new driver into an old box you'll have to use a speaker design program to find out what will work best in that box.

[quote name='Boy Thunder' post='80195' date='Oct 27 2007, 01:18 PM']My band has the same stage snake setup... 16/4 I have the crossover on the stage with the effects so I run 2 sends for that.. my other 2 sends run the monitors..ope thats a help...[/quote] With the crossover on the stage you can't run an aux feed to the subs, which is far more versatile. Get the 6 returns or get a few extra mic sends, all you need to convert them to returns is an XLR gender adaptor.

[quote name='BassBalls' post='77749' date='Oct 22 2007, 10:38 AM']Im not sure i totally understand what your saying. :wacko: So basically, i need to have a separate lead coming out of my speaker outputs on my head, put these both into an active frequency crossover "box," then have two outputs going into the separate cabs?[/quote] That is what you would do with a passive crossover. An active crossover takes the output of a pre-amp, splits it to high and low outputs, each feeding a separate power amp to drive the cabs individually.

[quote name='BassBalls' post='77371' date='Oct 21 2007, 11:51 AM']My question is... would an active frequency crossover solve my problem? Does anyone have experience with them? Do they work? Which ones are particularly good? Any help will be appreciated. Cheers[/quote] Yes and no. You're talking about bi-amping. First off you need a second amp channel, so if you're not already running a stereo power amp you'd need to add another power section somehow. Second, while bi-amping works very well with cabinets specifically designed to work over narrow bandwidths, the results with full range cabs is usually less than spectacular. With full range cabs a passive crossover works better, and a 6dB/1st order slope is adequate. You also don't need a second amp. Finding a passive crossover is the problem, you probably would have to build your own.

[quote name='alexclaber' post='77269' date='Oct 21 2007, 07:51 AM']Last words: [url="http://www.acmebass.com/forum/andy_lewis_on_horns.htm"]http://www.acmebass.com/forum/andy_lewis_on_horns.htm[/url] Alex[/quote]Mere coincidence that this was added to his site in the last 48 hours? A man who is as confident in the superiority of his products as Mr Lewis claims to be should have nothing to fear from a mere pinhead with a website who provides plans to do-it-yourselfers. Or should he? Methinks he doth protest too much. And that is my last word.

[quote name='alexclaber' post='77119' date='Oct 20 2007, 02:42 PM']The designs have evolved subtly over the years but the woofer has remained unchanged. But so has Hoffmann's law so I wonder why you're suggesting the woofer should have changed? Would you be being caught in the middle if you hadn't posted such speculative plots without any solid evidence? Hubris indeed... Alex[/quote] Alex, I expected better of you. In the course of this thread you've gone from [i]"Those plots tell quite an interesting story which is certainly not that far from reality. The plot in the Acme manual shows the Low-B4 at 96dB @ 100Hz dropping to 93dB @ 41Hz and 90dB @ 31Hz, so slightly greater bass extension than your plot. "[/i] to the above comment. You as much as anyone are perfectly aware of what those charts represent, which is a reasonable representation of what is possible from a bass reflex cabinet of similar size as those made by Acme, and that any claims made by Acme or anyone else of using drivers with unduplicatable specs are just so much tommyrot. You also are well aware that Andy's admission that the only testing he did on the cabs was done with a 10 band RTA means that he himself has no idea of the actual response of his own product. He obviously has no problem with that as [i]"I didn't have the capability of printing out a curve of any type then, and I don't give a damn now."[/i] Why you don't have a problem with that is most curious. Let me refresh your memory: "[i]My question is, unless they are flat out lying, there must be some aspect of truth to the "published specs" of the major cab makers. Does anyone know how they can legally get away with these specs?"[/i]-Kramer- [b] [i]"...they are flat out lying... "[/i] This is indeed the case. Alex[/b] __________________ [url="http://www.talkbass.com/forum/showthread.php?t=371215"]http://www.talkbass.com/forum/showthread.php?t=371215[/url] How incongruous.

[quote name='alexclaber' post='76922' date='Oct 20 2007, 06:30 AM']And some more from Andy: I designed the original B-2 using an Apple IIGS, Appleworks software, and a handheld 10-band real time analyzer in 1992 and 1993." Alex[/quote] The one thing I'll credit Andy for is he's not lacking in the hubris department. I for one would not be bragging on the fact that I hadn't made any advances in my designs since 1993, or that the only measurements ever made of them had only one octave resolution. But at least we now know why Acme doesn't post SPL charts. As for the rest, it's not worth dignifying with a response, nor is it appropriate for this arena, and I apologize to Basschat for getting caught in the middle.

[quote name='alexclaber' post='76306' date='Oct 19 2007, 02:41 AM']why you're claiming that you can throw some BP102s into an Omni 10 - which works far better with 2510s - and suddenly have a magic cab that beats an Acme hands down is baffling.[/quote] That's not exactly what I said, and to remove any doubt I posted a measured response chart of a BP102 loaded O10, which does have lower extension than a 2510 loaded O10. Comparisons to Acme remain academic and speculative until and unless measured charts of Acme are made available.

[quote name='alexclaber' post='76201' date='Oct 18 2007, 04:16 PM']Just to add a little more information to this discussion, apparently the Acme woofer is not based on the BP102 as it has not only a different cone but also a different magnet structure. Alex[/quote] Certainly that's possible, you should open yours up and see. But even if that's the case there's only so much leeway with what's possible from a box of a certain size, irrespective of what's inside. Hoffman's Iron Law applies to everyone. BTW, this is a measured chart of an O10 loaded with BP102s, no tweeter, 1m/1w.

[quote name='alexclaber' post='76012' date='Oct 18 2007, 09:36 AM']Also if you're just using the one cab and are comparing a Low-B2 to an Omni 10, the latter is significantly larger and although more sensitive cannot put out that big deep bottom. Alex[/quote] Unless you load it with BP102s. Not that I'd recommend it, as you'd have less midrange sensitivity, and the Omni doesn't need to use a long throw woofer to achieve adequate LF output. But the option exists.

[quote name='fede162162' post='75909' date='Oct 18 2007, 04:44 AM']i explain to you the matter: there's a guy who's offering me a beautiful cab built by delta 12 specs. and i want to know if a delta 12 speaker is a good speaker for bass guitar. the seller told me that if i want he can also put an other delta 12 speaker like the 12LF and hold the delta12, but i told him not,because i believe that a delta 12 speaker needs different cab specs. so you are saying me that a 1x12 cab with delta12 speaker isn't a good cab?[/quote]Why don't you just try it?

[quote name='alexclaber' post='75941' date='Oct 18 2007, 06:45 AM']The view from Andy: "I was wondering where he got one of my drivers, and assuming he had the right driver, what he used for parameters, and how he might have arrived at a box volume for running any type of simulation. (I discussed with you the notion of a "virtual volume," which can be vastly different that that measured with a ruler.) I hope this curve isn't flying around the internet as any kind of a true representation of my work. Clearly it's not. Or to put it differently: 1. different woofer 2. different midrange 3. different tweeter 4. different crossover 5. different tuning 6. different enclosure Same result?" Alex[/quote]The charts I provided clearly state what they represent. Posting actual measured reponse charts, or not doing so, is Andy's perogative, but if he's all that concerned about how his work is being represented then he should remove all possible doubt. With the proliferation of free response measuring software some one will sooner or later anyway.

[quote name='Stewart' post='75475' date='Oct 17 2007, 04:54 AM']Ported (reflex) cabs need to be matched to drivers, so if you already have a cab, you need to figure out (at least) the resonant frequency of the port....[/quote]At the very least, to say the least. A proper driver match requires using a comprehensive box program, like WinISD Alpha Pro, to determine not only box/driver compatablility but also to predict SPL and, perhaps most important for electric bass, displacement limited low frequency power/SPL. And that's just below 200 Hz. Above 200 Hz you must use the SPL charts on the driver manufacturer data sheets to see if the midrange/HF response is adequate. The Delta 12 has insufficient xmax/displacement limited power for electric bass, the D12LF must be used with a midrange driver for a good result. The Delta Pro 12 is a good bass driver, but like every driver must be matched to a cabinet with proper specs to function well. The fact that the original poster is asking what he's asking to begin with would indicate that he isn't familiar with speaker enclosure modeling software, so he would be better off building a tested design with appropriate drivers rather than using the dartboard approach.

[quote name='Merton' post='74936' date='Oct 16 2007, 03:57 AM']So I get to the rehearsal room early to set up and have a play but notice at any useable level (i.e. above about 1.5) there's a really nasty farty/rattly sound coming out. It lasts about 4 or 5 seconds or so before dying away (if playing a long note).[/quote] Usually that's a piece of schmutz that's got itself wedged between the cone and frame. When you initially hit the note the cone hits the junk, but as the note fades and excursion diminishes it no longer hits and the rattling stops. You can usually find the source quite easily by taking the driver out of the cab and running a low level signal through it.

[quote name='alexclaber' post='73746' date='Oct 13 2007, 08:13 AM']The Acme's midrange speaker is crossed over with a second order high pass at 1kHz. The Acme woofer is specifically designed to roll off smoothly at around the same frequency, so bearing those two points in mind the curve is probably a little flatter than the one you've plotted.[/quote] Could be, but it's academic once you put it in a real room.[quote]It would be nice to see an accurately measured curve on their website as it's one of the few commercial bass cabs that does what it claims.[/quote] Considering Andy's candor the lack of charts is a curious omission.

[quote name='alexclaber' post='73519' date='Oct 12 2007, 01:55 PM']Those plots tell quite an interesting story which is certainly not that far from reality. The plot in the Acme manual shows the Low-B4 at 96dB @ 100Hz dropping to 93dB @ 41Hz and 90dB @ 31Hz, so slightly greater bass extension than your plot. How did you ascertain the curve for the midrange and treble? Alex[/quote] I ran a sim in WinISD for BP102s, which rumor has it the Acme OEM is a variant of, and used that up to 200 Hz. 200 Hz to 2kHz comes from the BP102 data sheet. Above 2kHz is a generic midrange and tweeter. If the Acme driver is capable of going lower than the BP102 it would do so at the expense of midrange sensitivity and extension, but there's no point in further splitting of hairs, the results wouldn't be hugely different.

[quote name='The Funk' post='72711' date='Oct 11 2007, 06:36 AM']I'm looking to invest in some new cabs and I'm trying to decide between a pair of ACME B2s and a BFM Omni15 Tallboy for my main gig rig. (For small gigs I'm looking to get a BFM Omni10.5 Crossfire.) The criteria so far seem to be transportability, price, perceived loudness and evenness of response (including how low the low frequencies go). Any advice on this one?[/quote] This chart compares the O15 to the estimated response of a cabinet similar to a Low B4. I wish the Low B4 chart was measured, but like every manfacturer save Phil Jones Acme doesn't publish measured charts. I'd be more inclined to go with a pair of Omni 10s. This chart compares an O10 to the estimated response of a cabinet similar to the Acme Low B2

For the most part Mil Spec applies to the operating conditions that the parts are certified to operate in, mainly ambient temperature. High altitude cold and desert heat is the main concern. Actual performance usually isn't much different, though specified tolerance from measured values may be tighter than with so-called consumer grade.

[quote name='Alien' post='57245' date='Sep 7 2007, 06:36 PM']It's quite a short horn, around 950mm or so.[/quote]The last thing I would do is discourage experimentation, but I would be remiss not to point some things out. While it undoubtably works very well compared to commercial cabs, the path length is half that of a T39, which means the cutoff is a full octave higher. That takes it out of the realm of being a subwoofer and makes it just a woofer. Nothing wrong with that, it's still better than a 4x10, but if you're going to build a folded horn with such a high cutoff do so with a geometry that allows the woofer to work all the way up to 2.5kHz or so. Then a separate top cab wouldn't be necessary. In other words, a DR250 or DR280.

[quote name='dlloyd' post='63253' date='Sep 20 2007, 01:48 PM']Is that what a healthy fuse looks like?[/quote] C'est morte.

[quote name='dlloyd' post='62057' date='Sep 18 2007, 05:02 AM']The warning on the back of the amp specifies a 12 A 250V fuse. I've taken the amp to the local guitar shop, where there's a good tech, to be looked at. I think I'm going to start considering weight as a factor when I buy amps. Ouch.[/quote] I just double checked my schematics file to be sure, the fuse for the Twin 1968-1982 was 2.5 amp/110v. That would make a UK version 1.25 amp at 220v. Reissue versions woudn't be siginificantly larger. A 12 amp/220v fuse is large enough for arc welding, and your shop should know that. Since they don't, and they can't fix it either, that would serve as notice that they should be avoided in the future. BTW, the hum is probably from power supply caps that are in need of replacement.