Bill Fitzmaurice

[quote name='voxpop' timestamp='1353316061' post='1873435'] I have a cab the contains a Celestion BL15-400X driver. The cab has two 7cm holes cut into the front of the cab. To my ears it sounds better with the holes blocked with foam. It gets tighter and more dynamic. Why cut the holes into the front as it is clearly not tuned to any frequency as there is no tubes behind them. Seems to me it's a crazy design, or maybe there is no design or thought put into it. [/quote]That porting would tune a typical 1x15 sized cab to 70-80Hz, making it a one-note boom machine. I once ported a sealed cab in that fashion. I was 15 years old, hadn't the slightest notion of how speakers worked, never having even seen a ported cab, so the error of my ways could be forgiven. That forgiveness shouldn't be granted to a company that should know better.

[quote name='Protium' timestamp='1353272527' post='1873177'] Let's be honest, there's not a great deal of designing involved in making a rectangular box is there. [/quote]It's still beyond the skill set of marketing departments and executives. And even a seemingly simple box on the outside if well designed is anything but simple on the inside. Then there's the matter of crossovers, which are not the least bit easy to design properly. If it was as easy as it seems you wouldn't find so many cabs with inadequate or non-existent bracing and damping, nor any with horizontally arrayed drivers.

[quote name='RandomBass' timestamp='1353047389' post='1870872'] Yes I've always considered BFB to be a bargain, considering what you get. Expensive compared to mainstream? perhaps. But still a bargain. [/quote]Expensive? Not at all. BFB uses premium drivers, none of the 'mainstream' manufacturers do. For that matter neither do most boutique brands.

[quote name='Bassman62' timestamp='1352996423' post='1870320'] Many loudspeaker cab manufacurers use the least expensive speakers that they can get away with whilst charging phenominaly high prices for the finished product. Some few short years ago two of the most popular cabs from a leading UK manufacturer retailed at £499 each, these being a 4x10 and a 1x15, the 10" & 15" speakers left the actual speaker manufacturer for approx £9.50 (10") & £32 (15") each which equated £461 £467 for the empty cabinets which were basic tuned cabinets, nothing complex. [/quote]Look at what Orange charges for their 410, then see what retailers get for four Eminence Beta 10s. For the price one would expect the 410 to contain premium drivers, especially as Orange doesn't pay the retail price. [quote]All loudspeaker cabinet manufacturers do: Barefaced for example charge ~£525 for a compact. A £125 speaker, equating to £400 for a bit of plywood [/quote]OTOH that bit of plywood doesn't assemble itself. Rule of thumb for any manufacturer to stay in business they must make no less than the cost of all materials, labor, marketing and distribution plus 40%. Since BFB has lower marketing and distribution by selling direct they're a bargain.

[quote name='Beer of the Bass' timestamp='1352916677' post='1869382'] Although it'd be unwise to substitute in other drivers blindly, the Peavey cabinets are a fairly standard size and tuning, so chances are good that you can find another speaker that works in that box. If you measure the box and port dimensions, you can model the performance of different drivers using a piece of free software called WinISD, until you find something that performs similarly or better than the original driver. [/quote]Too much work. Just go to the Peavey site, get the T/S specs, find a similar driver. Similar, but not the same, as the 2.8mm xmax of the 1502 is marginal at best. The CA 154 is not compatable, and xmax is no better. As for replacing the basket, the 1505 is a much better choice, specs are compatable, but I don't know if the 1505 basket will work with the 1502 magnet. It's worth checking it out.

[quote name='Protium' timestamp='1352674208' post='1866064'] By the way, their amps/cabs are present on almost every major festival stage in this country. By that standard I reckon they know [i]exactly[/i] what they're doing [/quote]Perhaps. That doesn't mean they don't cheap out on drivers, just that they're no worse than most other companies in that respect. And you're assuming that they design their own cabs. Most companies do not, farming that job out to independent speaker designers, like me. That gives me the unique opportunity to know exactly what manufacturers do to maintain the highest possible profit margins, and that seldom includes using the best drivers available.

[quote name='LITTLEWING' timestamp='1352643566' post='1865467'] I can't help thinking the cab could be upgraded with a couple of ports in the front of the sealed cab. [/quote]In order to vent the cab you must have the driver T/S specs and use speaker modeling software to see if it will work, and if so determine the required vent configuration, if the drivers have specs compatible with a vented cab to begin with. [quote]Ashdown must know what they're doing![/quote]Don't be so sure. As often as not drivers are chosen based on their price, not how well they function.

[quote name='andyjingram' timestamp='1352215142' post='1860224'] A larger body of air behind the speakers will of course affect the depth of the lows [/quote]What matters is the volume of air per driver. When considering two 1x versus one 2x that's what you look at.

With respect to the OEM Sica, the Qts of 1.16 means it's only suitable for a sealed enclosure, and will have a boomy response with weak lows, while the 2mm xmax limits actual low frequency power handling to perhaps 25 watts. In short, it's a really crap driver. The neo driver specs are much better, but the 3mm xmax is still marginal. IMO 4mm is the minimum acceptable.

[quote name='andyjingram' timestamp='1352199258' post='1859880'] So would anyone notice the difference between 300 and 500 watts through identical cabs? With the way the human ear works, the answer remains, probably not. [/quote]If the cabs are actually capable of handling 500 watts without exceeding the driver displacement limit the 2dB difference would be audible, though just. But what remains is the question as to whether the drivers can handle 250w each before exceeding xmax, and most twelves cannot. The displacement limited power handling of a speaker is one of the most important specs, if not the most important for bass cabs, yet one universally ignored by manufacuturers.

With 73Hz Fs the Celestion isn't well suited to electric bass. I wouldn't use a driver with higher than 55Hz Fs.

[quote name='xgsjx' timestamp='1352145207' post='1859397'] But would anyone really notice the difference in volume between an 8 ohm & a 4 ohm 2x12 (both of the same brand, etc)? [/quote]Probably not.

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[quote name='jonunders' timestamp='1352111589' post='1858717'] Hi Are there any advantages or disadvantages in having two 1x12 over one 2x12 or vice versa. Jonathan [/quote]You can't leave half of a 212 at home when you don't need it.

[quote name='gilmour' timestamp='1351611049' post='1853238'] specifically above I'm worried about Line level/instrument level thing. [/quote]That's key. Pedals are made to operate at 100mV or so, effects loops are at line level that runs around 1v, so most pedals won't work in a loop. If yours do you're in luck.

[quote name='alexclaber' timestamp='1351066008' post='1846747'] But something is definitely happening, you can hear it when you add or remove inter cab/floor damping! [/quote]It is happening, just not in the frequencies where one expects it. When you measure in room with and without isolation the difference is seen in the lower mids, not the lows. That's on a bare wood floor. On a carpeted floor there's no difference. What's really telling is when you measure in the room below where the speaker is placed. Frequencies capable of exciting floor vibration to the extent that it's audible also pass through the floor. When you measure in the room below there's no difference between isolated and not.

[quote name='pete.young' timestamp='1351010857' post='1846211'] FWIW, even if the maths say that a Gramma pad can't work, it does have a noticeable effect on boomy stages. I have no explanation. [/quote]Read my posts again. I never said that a Gramma can't have an effect, just that it doesn't work via the methodology that they claim. As for Alex's device, I'd lean towards foam as a material as well, because it's so easy to cart, and any isolating of the cab from stage vibrations that it might offer can't hurt.

[quote name='LawrenceH' timestamp='1351006496' post='1846113'] Efficient transfer of energy by a lightweight but rigid cab (without damping) will give greater vibration transfer to a resonant body like the floor. Mass greatly increases the force required to produce a noticeable reaction. This is secondary school physics in action! [/quote]One does not need a post graduate degree to know that if over 95% of the energy being output by the speaker is acoustical, not mechanical, then isolating that 5% is not going to stop the floor from vibrating, nor will the reduction accomplished have an audible result. But at the least one needs to have taken undergraduate courses in acousttcal engineering to know that over 95% of the output of a speaker is acoustical, not mechanical. The schlockmeisters who claim that their products will prevent a speaker from causing the floor to vibrate are well aware that the vast majority of consumers have no formal education in acoustical engineering, and that being the case many of them will accept their advertised claims at face value. At least enough of them to keep them in business. Alex at present doesn't fall into this category, having only stated so far that isolation does have an effect, but not the effect that Auralex for one erroneously claims. [quote]I (and I believe Sir Isaac Newton) disagree Irrespective of the stiffness of the cabinet or whether the sides are vibrating, Newton's laws/conservation of momentum means that if you are moving the speaker cone forward then the rest of the cabinet will to move backwards by an amount inversely proportional to their relative weight of the two parts (i.e. the cone/coil and the rest of the cabinet), so that the net momentum change is zero. This would occur even if it were in a vacuum.[/quote]Sir Isaac and myself are in complete agreement. When the cone moves back and forth it alternately pressurizes and de-pressurizes the surrounding air. Said pressurization and de-pressurization causes your eardrums to move back and forth in reaction; that's how we hear. Said pressurization and de-pressurization also causes the floor to move, how much being a property of the stiffness and mass of the floor. If the floor was vibrating in reaction to the walls of the speaker vibrating said cabinet walls would have to be moving as far as the cone does.

[quote name='alexclaber' timestamp='1350996617' post='1845973'] I was sceptical of cabs physically transferring vibrations to the floor directly but as bits of foam make a difference then something is clearly happening! Maybe what actually happens is that the cab is acoustically exciting the floor but by raising the cab on some suitable foam you damp the vibrations, as you now have a damped mass on the vibrating membrane - like the difference between fretting a string and muting a string? [/quote]It's closer to the difference between playing your bass with its body touching or not touching the cab. If the floor is vibrating and those vibrations are being transferred to the cab you've set up a feedback loop. Since the cone is isolated from the cabinet by the driver suspension the effect of the feedback loop isn't severe, but it's there.

Point of fact: Unless the cab is defectively constructed there's no such thing as mechanical coupling. That phenomenon can only occur if the cab walls flex, and the walls of good cabs don't flex. Even relatively flimsy cabs don't vibrate in the lows, they vibrate in the mids. If they vibrated in the lows they'd be unusable. All low frequency vibration of the floor is caused by the acoustic output of the cab. Therefore so-called isolation devices have absolutely no effect on floor or other room surface vibrations. However, if the floor is vibrating said vibrations can then be transferred back to the cab, and the head atop it, and stopping those vibrations can be worthwhile. But doing so doesn't require a high level of sophistication, let alone high cost. A bit of carpet will do the trick.

[quote name='davehux' timestamp='1350652037' post='1841799'] They say they want a single big speaker to share. [/quote]Bad idea. Hearing the monitors means hearing the mids and highs. Mids and highs are very directional, so each player needs their own to be in the 'sweet spot'. Hearing them also means a good EQ dedicated to the monitors is mandatory.

[quote name='bremen' timestamp='1350462921' post='1839075'] I modelled a 2by10 using Eminence Beta 10A in WinISD and however big or small I made the cab, however I tuned it, the power handling dropped to 20-40W between resonance and 100Hz. Should I have doubled their stated Xmax figure, or are they really this crap? Or is WinISD very pessimistic? [/quote]They really are this crap. Makes you wonder why Orange uses them, and charges what they do for them. The bad news is that the Beta 10 not only isn't unusual in its lack of output capacity, it's actually better than many OEM drivers.

[quote name='Rammsteinbrit' timestamp='1350404574' post='1838373'] Low is nearly on full [/quote]Doing that can cause both the speakers and the amp to reach their limits. Don't.

Most sources quote xmax one way, Eminence among them. One would think that it would be stated as a +/- figure, but it isn't.

+/-4mm is the same as 8mm peak to peak.