Bill Fitzmaurice

[quote name='Balcro' timestamp='1361103782' post='1981030'] Enter the basic data as per the help file. Perhaps the first 5 paramenters, Qes, Qms, Vas, Mms and Cms [/quote]Even that is too much. The issue is that WinISD will calculate the parameters to a higher degree of accuracy than the spec sheets do, and when the results don't agree it results in error messages. The only specs you should enter are Qes, Qms, Vas, Fs, Re, Sd, Xmax, Le and Pe.

[quote name='zapp' timestamp='1360664766' post='1974085'] Has the price just shot up? [/quote]Two years ago. They peaked about one year ago, have come back down somewhat since then.

[quote name='Currrls' timestamp='1360572923' post='1972342'] If I soldered some jack plugs onto the end of the speaker wire and plugged them into the amp would this work? [/quote]Possibly, but hi-fi speakers are not made to withstand the stresses of pro-sound use, so if they do work it may not be for long.

It appears to be a ported cab, which probably indicates it's for bass.

[quote name='discreet' timestamp='1360520614' post='1971681'] Not necessarily. You could use an 8 ohm speaker - you just won't get the full 150 watts from the amp. [/quote]Not that it matters, as few speakers can make use of more than half their rated power anyway. It's always prudent to use a speaker twice the amp's rated impedance, should you need to add another down the road.

[quote name='Musky' timestamp='1360395397' post='1969712'] I'm certainly no expert, but doesn't stuffing a speaker into a smaller than ideal box create a hump in the low mids[/quote]In the midbass, actually, and that's what's responsible for boom. If you've got a cab that booms chances are the box is too small for the drivers. But the box size doesn't depend on the driver size alone, it depends on all the spces.[quote]- which seems to be what the OP is looking for? [/quote]One can't say. If the intent is to sound like a Berg one first has to quantify what that means. Since Berg doesn't post frequency response charts you'd have to measure one yourself, or find someone else who has done so. Then you can use modeling to match up the low frequency response and driver data sheets to match up the midrange and high frequency response. But without doing all that attempts to get a Berg tone, or any specic result, via sticking a random driver into a box will be as effective as tossing darts...blindfolded.

[quote name='discreet' timestamp='1360346593' post='1969131'] What Bill is hinting at but not said outright is that you should buy some of his excellent plans and build yourself a spiffy BFM cab! [/quote]Not if sounding like a Berg is the intent.

What Mr. Foxen has hinted at but not said outright is that you need to either learn how to use speaker modeling software to find the driver with T/S specs that will give the desired result, along with the cabinet volume and tuning, or you have to find someone who does have that skill to design it for you. Inches and watts are only a very small part of the overall picture. [quote]I noticed the vas was similar so they should both work in a similar sized box right?[/quote]No. Drivers may work well in a similar sized box if all the specs are similar, [i]or if they're totally different. [/i]The only way to know is with modeling.

The main issue is the size of the stand footprint, which is substantial. Amp stands take up less room.

[quote name='fatback' timestamp='1360163333' post='1965932'] Some acoustic foam under the cab or even the front bottom edge of the cab will probably sort the boom if it's to do with the floor resonating. Whether it's a gramma or something else doesn't matter. Honest, it works.[/quote]The boom is caused by the output of the speaker, not contact with the stage, so isolating the cab won't stop boom. It can only reduce the cabinet vibrating atop the stage. As for "I know what I'm hearing", if you did you could draw a response chart with and without the pad. I know I can't, but that's why they invented gear to measure response. If there was a measurable difference in the lows sellers of pads would show those measured results. They don't. Auralex does show a chart for the Subdude that shows reduction of 'Sound Transmission Loss', whatever that is, in the midrange. Why that matters with a subwoofer one can only guess, while their chart stops at 100Hz, when the output of a sub is all below 100Hz. Worse, read the fine print about their results: [i]This test was estimated. [/i] [quote] Losing reinforcement from the floor reflection can cost a fair bit of oomph in my experience. [/quote]Where controlling boom is concerned that's the point. The only issue is getting the height correct to reduce the correct frequency, or not raising at all when not required, but still tilting it back so that the highs are aimed at your ears.

Meh. Two years after the neo price crunch Jim Bergantino wakes up, realizes that the sky hasn't fallen after all, and resumes using neo drivers. It's not a bad thing, but hardly a stop the presses moment.

[quote name='kennyrodg' timestamp='1359931519' post='1962339'] I can't see much point in adding frequencies if you're struggling with boomyness. Surely it makes sense to cut the troublesome frequencies then add what you want....No ?? [/quote]Yes. Boom is too much midbass. To address it electronically the best tool is a parametric, set to a narrow width, perhaps 10dB cut, sweeping the frequency knob untll the offending frequency is found and attenuated.

[quote name='guntherbuffalo' timestamp='1359707392' post='1958975'] Replacing a speaker in a Mag 300 combo, I have decided to either go for the Emi Beta 15 or the Beta 15a [/quote]It's the same driver. The 'A' suffix denotes 8 ohms. The 600w rating is peak, which is meaningless. In any event inches and watts aren't how you choose a driver, you do so based on all the other T/S specs, using a modeling program like WinISD to match the driver and cab.

[quote name='nottswarwick' timestamp='1359664158' post='1958559'] Really?. I use one and have never A B tested n the same stage....so I just always assumed it must work [/quote]It does work, but not the way they claim. The cab contacting a stage does not cause it to vibrate; that would be the tail wagging the dog. The sound coming from the cab can cause a resonant stage to vibrate, which in turn can cause the cab to vibrate atop it. You may want to isolate the cab to stop it from vibrating. You can use a fifty quid gizmo, but rubber feet are all you need. Isolating the cab won't stop boom because the cab contacting the stage doesn't cause boom. It's the resonance of the stage and/or other reflection issues in the room.

[quote name='deepbass5' timestamp='1359587622' post='1957314'] too high could play havock with the vocal mics and piss band mates off [/quote]Why? It's no higher than an 8x10, let alone a stack. [quote]Would the Auralex help?[/quote]Not unless it's 30 inches or so high. The claims that Auralex makes for what it can do are as phony as a three dollar bill, or your equivalent thereof. Stages don't boom because the cab is touching them.

[quote name='bertbass' timestamp='1359584474' post='1957226'] Flight case. Protect your cab in transit and stand the cab on top off it to gig. [/quote]+1, though anything that will lift it 30 odd inches will do. Lifting it that high introduces a floor bounce reflection that counteracts boom in the midbass.

You're not considering the most important charts, maximum power and maximum SPL.

[quote name='flyfisher' timestamp='1358029850' post='1932209'] My school physics lessons included wave theory demonstrated using called ripple tanks like this: [/quote]There are a few nice tools found along with this one, from your side of the pond,www.acoustics.salford.ac.uk : [media]http://www.acoustics.salford.ac.uk/feschools/waves/flash/diffractionslider.swf[/media]

[quote name='TimR' timestamp='1358011860' post='1931859'] At secondary school we do the double slit experiment with light. Anyone who has seen that will instantly understand about 4x10s. [/quote]I guess most bassplayers nod off during that demonstration.

[quote name='Mr. Foxen' timestamp='1358008915' post='1931799'] The bit your brain makes up is a bit harder [/quote]A bit, but people have been studying this stuff since circa 1876, so at this point there isn't anything in the realm of audio that hasn't been scientifically explained. But it's not the sort of stuff they teach in secondary schools, nor even at the university undergraduate level at most institutions, not even those with EE programs.

[quote name='chris_b' timestamp='1357915228' post='1930537'] How much of the science doe we hear in the sound? [/quote]Everything you hear can be explained by the science. If you don't think that's the case it's your understanding of the science that's incomplete. The good news is that you can learn the science, should you be so inclined. Or you can ignore it, even deny it. No matter, the science is always right, whether you believe in it or not.

[quote name='chilievans' timestamp='1357850263' post='1929598'] Evening all I'm thinking of making a bass cab but as its my first one I have a few questions that need answering first [/quote]More than a few, I'd venture. First off, you need to understand what this is all about: [url="http://www.eminence.com/support/understanding-loudspeaker-data/"]http://www.eminence....udspeaker-data/[/url] And then how to use that data in this: [url="http://www.linearteam.dk/default.aspx?pageid=winisd"]http://www.lineartea...x?pageid=winisd[/url] And then how to use the results from that to construct a box, with help from sources like this: [url="http://techtalk.parts-express.com/showthread.php?219617-The-Speaker-Building-Bible"]http://techtalk.part...-Building-Bible[/url] If it seems like that's a lot to have to go through just to build a speaker, it is. But building a speaker is a lot more involved than just sticking a driver into a box.

[quote name='aende' timestamp='1357656959' post='1926103'] Ah - I see where you are now. Okay the amp has 2 x 250w outputs (it has dual power amps) @ 4 ohm each. [/quote]In that case run a 4 ohm cab off each channel IF you never anticipate needing more than two cabs. If you do make the cabs 8 ohms, allowing you to use four cabs should you ever have the need.

[quote name='aende' timestamp='1357650829' post='1925944'] Special cables? The amp is designed around 4 ohm cabs! [/quote]Are you aware that when you run two 4 ohm cabs the load is 2 ohms ? The amp impedance rating applies to when you're using the maximum number of cabs that you ever intend to. If you intend to run two cabs they should be 8 ohm, so that the combined load is 4 ohms. It's true that you could series wire two four ohm cabs for an 8 ohm load, but that means the output of the amp will be less with two cabs than with one, which is the exact opposite of what you want.

[quote name='Ghost_Bass' timestamp='1357655710' post='1926071'] [/quote] Really. Isn't there a search function here?