Bill Fitzmaurice

[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.

[quote name='dlloyd' post='61516' date='Sep 17 2007, 04:30 AM']The fuse that blew was a 12 amp glass bodied fuse.[/quote]
That doesn't seem right. The US version runs no more than a 6 ampere fuse at 110v. so a UK transformer version shouldn't use more than 3 amps at 220v. Blowing a 12 amp fuse at 220v indicates a dead short inside there somewhere. Powering it up again with that large a fuse could compound the damage.

Carvin makes very good gear and sells it at very reasonable prices. But they keep their prices low by selling factory direct only, so they are generally not an option outside North America.

[quote name='lowhand_mike' post='59214' date='Sep 12 2007, 07:35 AM']i tried this with one cab from a pair that our guitarist picked up on ebay, they looked home made with 15" drivers full range, yeah they sounded loud but really struggled with the low end as they farted a bit, .[/quote]Which only goes to show you that a big driver does not a bass capable cab make.

[quote name='DrGonzo' post='59015' date='Sep 11 2007, 05:43 PM']I'm still not too sure why people are always going on about a flat frequescy response as being an "uncoloured" sound.[/quote]
Perhaps not in absolute terms, but if the response chart of the average PA resembles the view of the horizon in Cornwall then that of the average bass cab looks like St. Moritz.

[quote name='Chopthebass' post='58952' date='Sep 11 2007, 03:27 PM']But Mackie in the UK told me that won't be suitable for bass guitar, but they couldn't back it up with a technical reason![/quote]That's because they're clueless pencil pushers, not engineers. Assuming it's properly constructed it should work very well, I can't think of a commercial electric bass cab that would work as well. But it will sound quite different than what you're used to, and that may or may not be to your liking, so try one before you buy one.

[quote name='Russ' post='57273' date='Sep 7 2007, 09:45 PM']I've been toying with the idea of putting together a more "hi-fi" kind of bass amp, using either one or two PA speakers, a power amp and a preamp of some description. Basically, a system that will have a wide, full frequency response, without the colouring that bass-specific cabs add to the sound.[/quote]
IMO the best bass cabs and the best PA cabs are interchangeable, because they share the same requirements: wide bandwidth, high output uncolored response. The vast majority of bass cabs don't fit that description, being in reality modified guitar cabs. For that matter, until the '70s most bass cabs [i]were [/i]guitar cabs, sharing the same drivers and design. Bass players just used more of them to get the same output levels. With the advent of bass specific drivers and T/S cab tuning in the '70s bass cabs became more bass friendly, but the basic design has remained in the mold of guitar cabs, as has the sound, with restricted bandwidth and a lot of coloration. For all intents and purposes mainstream bass cab technology has not advanced in the last 30 years. If one looks at a 1970s bass cab and the current crop they look the same, and for the most part sound the same, the only improvements being those resulting from better drivers.

The PA industry never stagnated, with improvements coming at a regular rate. Today's concert bass sound is defined by the PA, not the backline, and the bassplayer who wants that same tone on stage has to look to PA gear or bass gear designed according to PA standards to get it.

[quote name='BOD2' post='57775' date='Sep 9 2007, 10:52 AM']To that end, as mr gig suggests, try to get the monitors as close to the ears of those using them as is practical as this means you can turn them down more.[/quote]Which brings up another point: each player needs their own monitor. One can't place them adequately close when they must be shared.