Bill Fitzmaurice

[quote name='billyapple' post='1054707' date='Dec 11 2010, 04:35 AM']So would having two 410's (or indeed an 810) on top of each other be like having two vertically stacked 410's next to each other?[/quote]I think you meant to say two pair of vertically stacked 2x10s next to each other, to which the answer would be yes if the horizontal driver spread is the same. IMO there's no reason to need more output than what three 2x10s will give, and they could all be vertically stacked. If the form factor allows it the amp could be placed beneath the uppermost cab for ease of access.

[quote name='Big Mick' post='1051078' date='Dec 7 2010, 04:45 PM']Although Bill's plans are pretty comprehensive with regard to cutting lists, component selection and assembly drawings, they don't provide some of the useful little tips, like what order to assemble the spacer and tee nuts in.[/quote]That's because I recommend using screws. A 4kg driver doesn't need the strength of bolts, and screws into 24mm of material have all the holding power one could need and more. [quote]It's Evo-Stick Serious Stuff ultimate strength adhesive, £7.95 at B+Q. Not sure it it's the same as the PU stuff that Bill uses[/quote]It doesn't appear at all the same. PL Premium expands to triple volume.

[quote name='fretmeister' post='1053960' date='Dec 10 2010, 07:55 AM']So - does it actually work, or is it another DFA thing like on the Accugrooves?[/quote] It will work if the driver has dual voice coils.

[quote name='jonthebass' post='1053221' date='Dec 9 2010, 02:07 PM']Am I right in thinking this is why the two 2x10" cabs stacked vertically is pretty much the ideal setup?[/quote]Yes, that way you don't reduce horizontal dispersion, you do reduce vertical dispersion to limit the output wasted going to the floor and ceiling, and you can hear your mids better as they pass closer to your ears rather than below the waist. Maybe not ideal per se, but for sure the best way to employ 2x10s. This explains why many players prefer a vertical 2x15 to a 4x10. Even though the individual tens have wider dispersion than the individual fifteens the 4x10 configuration squanders the potential offered by the tens.

[quote name='jonthebass' post='1053099' date='Dec 9 2010, 12:32 PM']I use two modern 1x15" cabs and the sound is all there up to 4kHz.[/quote]Not if you move over a few feet. At 4kHz the average fifteen is down 20dB at 45 degrees off-axis, compared to 10dB for the average ten. Of course if you put two tens side by side their dispersion is halved, so with that configuration they work no better off-axis than one fifteen anyway. [quote]Really, none of these generalisations apply to modern cabs. But a lot of old cabs are still being made[/quote]They didn't apply to vintage cabs either. If they did then all cabs loaded with tens would sound the same, as would all cabs loaded with twelves, fifteens, etc., and we could weed out 98% of the cabs out there as unnecessary duplication.

The only factor purely attributable to cone size is dispersion. Everything else is based on driver specs. Well explained here: [url="http://www.eminence.com/resources/data.asp"]http://www.eminence.com/resources/data.asp[/url]

[quote name='Musky' post='1051102' date='Dec 7 2010, 05:24 PM']Ampeg moved most of their production to Vietnam over two years ago now. I've not noted any negative comments about reliability with the new stuff, but then again I can't say I've really been looking for them.[/quote] Word is the gear is OK, but mismanagement by LOUD may result in their bankruptcy, and Ampeg is currently on the block.

[quote name='Mr. Foxen' post='1045155' date='Dec 2 2010, 09:51 AM']Basically, the box probably doesn't suit the blue driver that well, it will probably suit a neo even less[/quote]Not necessarily. What specs I've seen of Blues show them to have such high Qts and Vas that they can't possibly work well in a smaller box. Or even a large one, for that matter. Many neos have far lower Qts, and more significant lower Vas, than even good drivers of prior generations, allowing them to work very well in smaller cabs. You'd want to model a few to see what works best in the cab in question, of course.

[quote name='Phil Starr' post='1044858' date='Dec 2 2010, 06:37 AM']Have a look in Dickason or a look at Gunther J Krauss, AES Mar1990. "Low frequency Transient Response Problems in Vented boxes".[/quote] We've gotten a fair bit along since 1990. The very notion of different alignments (second order Bessel, second order Butterworth assorted Chebychev, QB3, BB4 etc) has been rendered obsolete. They date to the days of hand calculation; with modern software an infinite number of 'alignments' are easily realized, including vented which virtually duplicate sealed within a desired passband. [quote]I am hoping that you can add to the debate with your experience of how these theoretical problems work out in practical situations.[/quote] I have no time for debating, I'm too busy designing speakers. I offer the benefit of my professional expertise. Accept it or reject it as you see fit.

[quote name='wotnwhy' post='1044990' date='Dec 2 2010, 08:07 AM']are the eminence gamma 15's one of the recommended drivers?[/quote] It would work, but with only 3mm xmax the Gamma 15 is marginal for electric bass usage.

[quote name='4 Strings' post='1044469' date='Dec 1 2010, 06:07 PM']The Thumpinator sounds great but for that price I could buy a pretty good speaker. Is there a cheaper way to hit the rumble? If I wanted to put a cap in line I could solder something to the crossover board. Any ideas on values etc? Also, would it be in parallel across the speaker?[/quote] A cap alone won't work, you need at least cap and coil, and the price would be far more than a Thumpinator.

[quote name='Phil Starr' post='1043367' date='Dec 1 2010, 04:27 AM']Clearly sealed cabs offer better transient response and ... with a given driver, smaller size. The ports create problems of wind noise and manufacturing spreads in drive units mean that unless each driver is tested individually the tuning is a bit hit and miss.[/quote]That's the conventional wisdom, but it's not true. For every driver where that scenario does apply you'll find six where it doesn't. IME the only drawback to a vented box in general is the potential for driver over-excursion below the intended passband, and that's cured with a couple of capacitors in the signal chain to limit the LF bandwidth of the amp. [i]"would that be where sfx's Thumpinator would come in handy?"[/i] Or that. Not mentioned yet is that, while a sealed cab naturally controls below bandwidth excursion, it does nothing to relieve the amp of the load that amplifying below bandwidth content creates. Even with a sealed cab the sound will be cleaner and the amp will have more headroom when below bandwidth content is filtered. [quote]why shouldn't another designer exploit the same things in developing a sealed design?[/quote]The main obstacle is the lack of suitable drivers.

[quote name='Phil Starr' post='1037460' date='Nov 26 2010, 04:50 AM']I've found that spurious sounds from sources other than the strings (such as banging the guitar) can creep into the signal chain and cause some alarming excursions with some set ups.[/quote] The downside of a vented cab is that excursion rises below the tuning frequency, and below bandwidth string thump noise can be a major problem. That's usually compensated for by a high pass filter in the amp, most have them, but not all. This thread explains: [url="http://www.talkbass.com/forum/showthread.php?t=714170"]http://www.talkbass.com/forum/showthread.php?t=714170[/url] With sealed cabs excursion decreases as frequency decreases, so high passing is seldom required. But sensitivity and therefore output also decreases, so it's not the best route to eliminating below bandwidth noise and driver over-excursion.

[quote name='LukeFRC' post='1041797' date='Nov 29 2010, 06:11 PM']ashdown heads.... how were the speaker cables plugged in? I found this too. Plug both cabs into a socket on the amp..... and the volume drops. Plug one speaker into the amp, then daisy chain the other cab in, and it will be louder.[/quote] The amp outputs were either series wired or mis-wired with inverted polarity. The new G-K MBE210 combos came from the factory with the extension speaker jack reverse-polarity, so it does happen.

[quote name='Ghost_Bass' post='1041262' date='Nov 29 2010, 10:21 AM'][u]With two identical cabs, stacked, with the same setting on the amp (this includes the volume knob being untouched) we have[/u]: - Two cabs running at the same time will have more volume than each of them soloed; - The bottom cab running solo will have more than half of the the volume of two cabs; - The top cab running solo will have less than half of the the volume of two cabs; My main variable is floor coupling. If anybody with knowledge could do the math with a simple example to try and find if i'm very far from the truth i'll appreciate. Cheers[/quote]The volume of a cab is not related to watts, it's related to voltage. At a given gain setting the amp output voltage is constant, irrespective of the load impedance. Two cabs parallel wired both receive the same voltage as one, so if identical they will each run at the same volume. Floor 'coupling' in terms of a mechanical connection does not exist. Boundary loading from the floor does exist, and will be the same with two cabs stacked as with one on the floor, as the two cabs are acoustically coupled in the low frequencies where boundary loading occurs, acting essentially as one.

[quote name='Wil' post='1040946' date='Nov 29 2010, 06:25 AM']Probably a case of the head not being powerful enough to give any real volume increase when its output was split between the two cabs.[/quote] Adding the second cab halves the load impedance, doubling the current flow and therefore power. Another 3dB of sensitivity comes from the mutual coupling of the two cabs, so with the same amp the total volume increase is 6dB, which is the equivalent of four times the power. Then figuring in the greatly increased intelligibility of the mids and highs from the top cab versus the bottom and there would have been a huge difference between both cabs and the bottom cab alone if everything was working correctly. Conclusion: something was AFU, perhaps a blown driver or two in the upper cab.

[quote name='Lemming16' post='1040063' date='Nov 28 2010, 11:24 AM']Whoa, thanks for your answers, so, do you think i should get a speaker with 200 Watts? (8 ohms) or one with 300 watts? (8 ohms too).[/quote]Watts are the least significant factor. What matters is frequency response, sensitivity and driver displacement. Don't even think about trying to design your own speaker. Find an existing tested design that meets your needs, use the drivers recommended for use with it.

[quote name='Phil Starr' post='1035927' date='Nov 25 2010, 04:27 AM']For me the middle graph is significant. It shows extreme excursion below 50Hz at high power which I think may be part of the problem.[/quote]Loaded in 50L tuned to 50Hz excursion is at a minimum at 50Hz, and with 200w input only exceeds xmax below 43 Hz, so save for extreme drop tuning excursion is no concern. However, where excursion is at a minimum port output is at a maximum, seen in a port velocity chart, and that's what attention must be paid to where chuffing is concerned. [quote]I also question the extent to which you will hear the differences at these frequencies. I've been experimenting with just this at the moment with a low Q driver in an optimum box a high Q driver in a smaller than optimum box and running A/B comparisons with and without ports. Playing recorded music through them you get to hear all the things you'd expect. Earlier roll off and slightly reduced but cleaner bass from the sealed cab and warm woolly bass from the undersized cab, but you have to choose the source carefully to hear this. With bass guitar I can hear a difference but my guitarist can't and with the full band playing I'd be dishonest to say it makes a whole lot of difference. We just aren't very good at hearing deep bass and if you can't hear it it doesn't matter.[/quote]All true from the standpoint of what you're hearing on stage, where more often than not boundary effects severely limit audibility below 60 Hz or so. Combined with the masking effects of the other instruments you can eliminate much, if not all, content below 60Hz and not notice the difference when the band's playing. But in the audience the situation can be very different. You can be totally unaware of high output in the lows where you're standing, whilst 40 feet away patrons are contending with drinks falling off their tables. It's the 40 to 60Hz bandwidth that large PAs pound out with authority that can define good concert sound, or for that matter ruin it when there's a ham-fisted idiot at the FOH console.

[quote name='jonthebass' post='1035087' date='Nov 24 2010, 09:02 AM']Blimey, my heads spinning from this thread![/quote] Science does have a tendency to win out over dogma, though sometimes it takes a while. Ask Galileo. [i]'In 1979 Pope John Paul II asked that the 1633 conviction be annulled. However, since teaching the Copernican theory had been banned in 1616, it was technically possible that a new trial could find Galileo guilty; thus it was suggested that the 1616 prohibition be reversed, and this happened in 1992. The pope concluded that while 17th-century theologians based their decision on the knowledge available to them at the time, they had wronged Galileo by [b]not recognizing the difference between a question relating to scientific investigation and one falling into the realm of doctrine of the faith[/b].'[/i]

[quote name='Phil Starr' post='1034915' date='Nov 24 2010, 06:40 AM']Sealed cabs have better power handling and much better transient response than reflex cabs. For a given speaker the cab will be smaller. The trade off is that the ported cab gives an extra 3dB of bass around the resonant frequency and the f3 roll off point will be raised in a sealed cab. Having said that there is often more deep bass from a sealed cab ie deeper but not so loud.[/quote]Those observations do apply in a few cases, depending on the driver specs, but only a few. For the vast majority of drivers, no. In this case, a very low Qts driver, a sealed cab is totally inappropriate. It models very well in 50 liters net vented.

[quote name='Moos3h' post='1034209' date='Nov 23 2010, 01:48 PM']I'm SURE there must be a reason why this can't be done?[/quote] The same reason one doesn't fill the boot of their auto with concrete so that they might get all of the horsepower out of their engine. You'll use a lot more gas but you won't go any faster. I believe the subject is addressed in the FAQ.

[quote name='LawrenceH' post='1034111' date='Nov 23 2010, 12:15 PM']I honestly can't see what's at all controversial about the idea that porting is used to boost low-end output of speakers but comes with its own set of compromises and complications, and if it wasn't necessary to boost LF volume output we wouldn't use it.[/quote]There's nothing controversial about it, it just isn't true. One doesn't properly use a sealed versus ported alignment for any reason other than the specs of the drivers employed and the results desired. [quote]With sealed cabs you get a nice gentle drop in frequency response that is much more easily matched with a simple shelving filter than the more complex rapid drop (with small hump or shelf) associated with ported cabs[/quote]One can obtain the same results with either topology. And one can obtain totally different results with either topology. One just has to know what one's doing.

[quote name='4 Strings' post='1033517' date='Nov 23 2010, 03:48 AM']So, it seems I'm not going to improve things too much by changing the driver but might do so with adjustments to the port. Bit difficult to tell if the port is 'chuffing' or the speaker complaining. Assuming we do have 'chuff', what to do? There's not really space to make the port larger in diameter, what if I made the tube longer? How long would be best? What if I made another 3" port (say, in the back). What length tubes would be best?[/quote]Catch-22. A 3" port is too small in diameter to not chuff. A 4" would probably relieve the chuffing, 5" is better, but both require far longer ducts. The larger duct volume subtracts from the net cabinet volume, which raises the cabinet tuning and leads to boomy response. IMO you have a nice driver deserving of a new home. I wouldn't invest any more in the old one.

[quote name='LawrenceH' post='1033133' date='Nov 22 2010, 03:06 PM']hence the 'loudness function'[/quote] That is intended to address the issue of equal loudness. To do so it boosts both the lower and upper end of the spectrum when the volume pot is set at low levels, with the effect diminished as volume is increased.

[quote name='LawrenceH' post='1033098' date='Nov 22 2010, 02:35 PM']Bill has again decided to obscure my point entirely by saying that if 'sealed was superior then that's what would dominate the market'.[/quote] By the market I meant speakers in general, not just electric bass. In home use output isn't the concern that it is with pro-sound, and yet ported still dominates every segment of the hi-fi market save one, HT subwoofers. There sealed is well represented for two reasons: cabin gain and high driver Qts.