Bill Fitzmaurice

[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.

[quote name='BOD2' post='57738' date='Sep 9 2007, 09:39 AM']A feedback destroyer shouldn't be necessary if you follow the above steps but is there as a last resort.[/quote] Even if you have a 31 band graphic EQ it does you little good taming feedback if you don't know which frequencies are the offenders. Also, 31 band EQs have wide bandwidth 1/3 octave filters, so they remove too much information. Feedback destroyers use narrow bandwidth filters that kill the feedback without destroying intelligibility, and they find the offending frequencies on their own. [quote]Is there anything else I should be doing? EQ'ing?[/quote]Absolutely, you can't run monitors without their own dedicated EQ. If you don't have one you should purchase an EQ that has a feedback destroyer built in.

[quote name='Sibob' post='52094' date='Aug 28 2007, 08:16 PM']RSH, you're the first guy i know who has said they can't get a decent sounding E from a 350watt 2x10 Ampeg combo Si[/quote] That's very much a matter of how loud one plays. Most of the power requirement of an open E will fall at the second harmonic, about 82 Hz, and that's right in the range where the Ampeg cab is displacement limited to only about 60 watts before exceeding xmax and distorting heavily. I can see how anyone playing at even moderately high levels would be wanting for more.

[quote name='alexclaber' post='50179' date='Aug 24 2007, 09:51 AM']You'd be far better served by learning about pro sound and audio engineering. A huge amount of the audiophile market is driven by snake oil sellers and psychoacoustics, supported by the magazines whose revenue stream is driven by the advertisers of said snake oil.[/quote] Quite right. If the esteemed Mr P.T. Barnum were alive today ("[i]No one ever lost a buck overestimating the intelligence of the average person."[/i]) he would be selling $1,000 per foot cables and $200 power conditioners. Most power conditioners offer no more protection or 'conditioning' than is already present within your amp and other gear.

[quote name='OutToPlayJazz' post='47298' date='Aug 19 2007, 05:32 AM']You all know the routine - Leave your Fender plugged in & without touching it, the bad earth demons hit until you touch the strings & it all goes quiet![/quote] That's as it's supposed to be, and is the reason why the bridge/strings are grounded. It's an unavoidable consequence of high impedance pickups. Some are better/worse than others, but none are immune.

[quote name='d-basser' post='47955' date='Aug 20 2007, 03:58 PM']think this is the wrong section mate anyhoo I am 5'8''/9'' ish Look for something smallish body (ie not fender) I like Peavey. Shorter scale may also help though I play 34" and 35". Adjust strap/ posture, the positioning could bet he problem rather than the bass. I found raising the bass quite high helped (so when i stood it was the same as sitting) hope this helps, you need to specify the discomfort really[/quote]I'm 6 foot 250 pounds and I prefer a 30" scale. Both Fender and Gibson make some with 30 inch scale boards.

[quote name='ShergoldSnickers' post='46545' date='Aug 16 2007, 01:05 PM']On their own, wattage values are almost meaningless. It depends which speakers the amp is driving. Then there is the question of how efficiently the speakers convert the amp output into sound. This is probably a bit of a neglected area. Most look at the amp first and the speakers second. But, buy some really efficient speakers and you can then afford to look at a less powerful amp. You'll get the same sound power level (SWL) with fewer watts, lighter weight and less cost.[/quote] +1. I personally am now running one channel of a Superfly and find it's more than adequate, but I have high sensitivity speakers. It makes a difference with tubes too, as the natural compression of a tube amp can easily make it sound as loud as an uncompressed signal with 200 watts SS. While I'd not say that 50 watts tube is enough with off the shelf speakers, in the case of high sensitivity speakers it can even be more than enough.

[quote name='stanton119' post='44626' date='Aug 12 2007, 05:25 PM']Even when I used to have bass direct to amp. If I touched the strings and the radiator I would get a small shock as you have described.[/quote] This is where a GFCI outlet protects you. Your strings are grounded, but not perfectly so, as there is resistance in all of that wire that connects your bass to your amp, and then your amp to the outlet, and finally the outlet to the street mains panel. There can be quite a bit of resistance in that wire, while alternate paths to ground, such as heating systems and water pipes, or God forbid standing on damp earth or concrete floors with no shoes on, may have considerably less resistance. Electricity always takes the path of least resistance, and in cases such as described that path is you. GFCI outlets sense when current is flowing through pathways other than those intended and shut it off.

[quote name='stanton119' post='43891' date='Aug 10 2007, 12:50 PM']I think I may have sorted it out: Using a ground loop isolator i tried connecting item by item every configuration possible, measure the PD each time. The best solution I have found is by placing the ground loop isolator between the mixer and the laptop. There was then not shocks between the laptop case and the cable. However, know there are now sparks between the cable for the bass and the laptop case. Would it help to place ground loop isolators between everything?[/quote] Isolators aren't fixing the problem, they're just hiding the symptoms. All of your devices should be grounded together at one single ground point, say a power strip, while any peripherals such as cable or internet connections that are remotely grounded should be transformer isolated.

[quote name='stanton119' post='43506' date='Aug 9 2007, 05:07 PM']What can I do to eliminate this???[/quote] Is your TV also connected to cable? The voltage you're reading indicates more than one ground path is present. Read this: [url="http://www.rane.com/note110.html"]http://www.rane.com/note110.html[/url]

This is required reading for anyone using electric instruments and sound gear: [url="http://www.rane.com/note110.html"]http://www.rane.com/note110.html[/url]