Bill Fitzmaurice

[quote name='alexclaber' post='275673' date='Sep 2 2008, 01:10 PM']I don't know of a difference between ported and vented, they're synonymous nowadays. Alex[/quote] The officlally recognized term for a direct radiator which is not sealed is VB, for Vented Box. Precisely how it's vented is another matter entirely.

[quote name='Zerofret' post='275502' date='Sep 2 2008, 10:20 AM']I think if I was in your shoes, I would build a substantial plywood cabinet and fit something like an Eminence 15" Legend 1518 which has an SPL of 102.2dB Steve[/quote] The sensitivity ratings for raw drivers apply to above 100Hz, so that in and of itself says nothing about sensitivity where demands are highest, from 40 to 100 Hz. As for the Legend 1518, it's a guitar driver. In a typical cab sensitivity below 100 Hz averages only 92dB, and its 0.8mm xmax limits its average power handling in the bass range to only 20 watts. Sensitivity ratings given by speaker manufacturers are outright piffel and are useless for comparison purposes. But the more drivers one uses the higher the system sensitivity, as there are more driver motors utilizing the power. For that reason a lot of tens will give a better result compared to a smaller number of twelves or fifteens in the same overall pack space. With the same input two 2x10 cabs will have 6dB more output than one, and that 6dB is the equivalent of going from 50 to 200 watts. With the price of watts as low as they are today using a small amp with lots of cabs isn't the most size efficient route, but it can work if you so desire.

[quote name='tom skool' post='274979' date='Sep 1 2008, 04:41 PM']yeah perhaps but i hadnt even got halfway. I had the volume, it just didnt sound that great more farty than nice overdrive. Being all valve i should be able to drive the hell out of it without any worries right?[/quote] The main difficulty with so little power is that it takes a lot of speaker sensitivity to get a lot of clean output. In the simplest terms getting high sensitivity meann using lots of drivers, so a pair of 2x10 at the least is in order. The speaker's power rating is almost meaningless.

[quote name='alexclaber' post='274718' date='Sep 1 2008, 11:37 AM']That doesn't make sense - you are overlooking that as sensitivity goes up displacement limited power handling diminishes proportionally. Alex[/quote] Model a typical MI driver in WinISD Alpha Pro using two box sizes, same tuning, then look at the Maximum SPL chart. If the box is already at optimum size then going larger won't be of any benefit, but the number of commercial electric bass cabs which are optimum size can probably be counted on the fingers of one hand, and then after one has lost three of them in an accident. With the typical undersized alignments used going larger or smaller can make a significant difference in the low end.

[quote name='alexclaber' post='274643' date='Sep 1 2008, 10:37 AM']Also note that although the HF cabs will produce more bottom with equal power they still have the same maximum low frequency output as the HR cabs because the limiting factor is the speaker displacement[/quote]-1. Maximum low frequency output is the product of sensitivity x displacement limited power. The larger cab will go louder in the low end, assuming they use the same drivers.

[quote name='doctorbass' post='264123' date='Aug 17 2008, 02:46 PM']Has anyone played the 410 or 115 and able to give an opinion on either?? I know they have a pretty huge power handling!![/quote] Power handling is the most quoted spec to imply performance, but it's also the least significant. Those specs which are significant are not available from any manufacturer, so it still boils down to trying before buying to be sure of a happy result.

[quote name='Sean.Robinson' post='264142' date='Aug 17 2008, 03:10 PM']how much would the work you previously stated cost then to have done[/quote]More than the value of the amp. That's why if you aren't happy with the amp's inherent signal to noise performance you're better off to find a better one. BTW, I had a Hartke 3500 that was rated for S/N at 78dB. While about average for a bass amp, that would be considered unusable for PA or hi-fi. In those genres 90dB is considered the minimum acceptable, 100dB being a really good figure.

[quote name='Sean.Robinson' post='264067' date='Aug 17 2008, 01:37 PM']having looked through the forums on hiss and hum is there any chance the old tubes (16 years old) could be causing the hum/hiss, i was considering some mullards or telefunks anyhow so will be replacing them at some point but would like this clarified first please[/quote] Tubes are seldom the source of hiss. In a tube amp it's primarily the resistors, in SS the SS devices themselves, which is why tubes tend to have less hiss than SS. Tubes that aren't biased correctly can contribute to hum. Old Fender designs had what they called a hum control. The only tools required were a screwdriver and your ears, you simply turned the control until the hum was at a minimum.

[quote name='Marcus' post='263920' date='Aug 17 2008, 07:43 AM']Hi Guys, I think one of my 10' drivers is on it's way (centre is detatched from the paper cone) I need some advice on a possible repair..... (is it possible to glue it ? if so what type of glue)[/quote] Superglue. Put a bead around the joint, then spray it with cure accelerator.

[quote name='Sean.Robinson' post='263962' date='Aug 17 2008, 09:43 AM']Ok thanks for all your help, i have shifted the topic onto eden as you've advised ([url="http://www.eden-electronics.com/forum/topic.asp?TOPIC_ID=13332"]http://www.eden-electronics.com/forum/topi...?TOPIC_ID=13332[/url])[/quote] Changing to a toroid power transformer alone would have an imperceptable effect on hum level. A complete refurbishing of the power supply, incuding major upgrading of the filter caps, would be required. Basically what you want to do is to take a Ford and bring it up to Mercedes specs. While not impossible to achieve, you'd find it a far simpler matter to sell the Ford and buy a Mercedes.

[quote name='Sean.Robinson' post='263790' date='Aug 16 2008, 06:15 PM']Hi, not something ive really thought about correcting until now as im sure its normal, but my amp hums/hisses a little when nothing is plugged in and it is just turned on though nothing is plugged in or been played. Ive heard it on all amps so im sure its normal, but is there any way to reduce or even get rid of it all together, such as using balanced cables, or by some mods to the amp head?[/quote] Cables can't very well be the issue if the amp behaves badly when none are plugged into it. All amps make noise, how much is a matter of how well engineered they are, or are not, as the case may be. Reducing noise is possible, but not easy, a usual prerequisite to doing so being a EE degree.

[quote name='Protium' post='256462' date='Aug 6 2008, 11:50 AM']the shape of the waveform does not matter.[/quote] Not a whit. BTW, what happens when you push a driver past xmax? It creates clipped waveforms, in exactly the same fashion as do over-driven amps, or stomp-boxes.

[quote name='Protium' post='256141' date='Aug 6 2008, 07:05 AM']I am still going by the argument that the speaker does not care what shape the waveform is, as long as the mechanical limit (Xmax) of the speaker is not exceeded.[/quote] Exceeding xmax doesn't bother anything, it just makes for a dirty/compressed tone. Guitar players get their tone by exceeding xmax, and being able to do so in the midrange is why guitar drivers have small xmax values. Exceeding xlim OTOH has disastrous consequences.

[quote name='Welshbassist' post='253794' date='Aug 3 2008, 12:11 PM']So if it's okay, what was the point of the whole incredibly long BS explanation then? That just made things too complicated and hard to understand. I love my Epi UL, but they just went a little crazy there.[/quote]What it came down to is that they were trying to make it seem that if one wanted the best result from their cabs, which sell well, one needed to use one their amps, which don't. They got called out on it and tried to retract their statement without admitting that it was a load of BS to begin with. The resulting 'clarification' contained even more BS than the original statement. The incident left a very sour taste, rightfully so IMO.

[quote name='molan' post='253445' date='Aug 2 2008, 01:53 PM']Sounds like fun, might make a great reggae cab [/quote] Perhaps, if reloaded with modern drivers. Those used in the original weren't much, but in 1968 what was? Also, their first generation SS circuits were powerful but unusably noisy if you set the treble knob above 12:00, and even full off the hiss was still quite obvious.

[quote name='alexclaber' post='252092' date='Jul 31 2008, 10:10 AM']Though with modern technology it would only take two 10" speakers voice coils to dissipate that heat[/quote]It wasn't the heat, it was the excursion. The original 1969 SVT drivers were guitar drivers, with perhaps 1mm xmax. It took two of the 8x10 cabs to handle the 300 watt head clean. Longer xmax drivers were introduced in the early 70s and since then only one cab was required. [quote]On alt.guitar.amps there was recently mention of "hang time" in relation to driving speakers, the idea being that with a square wave into a woofer it would be possible to have the voice coil stationary for most of each half cycle, and that excessive power would be dissipated in the relatively low resistive load (?) of the stationary voice coil.[/quote]Complete utter total piffel. That never happens. Said post was not made by a competant transducer engineer. Railroad engineer, maybe.

[quote name='Fraktal' post='252047' date='Jul 31 2008, 09:06 AM']Thanks a lot for your insight, Alex, always good to learn new things. Unfortunately I think Im having a hard time to understand your response, do you have any graphics? Maybe it would be easier with a picture or 2...[/quote] Graphics in this case is a culprit. The 'underpowering' nuts show a picture of a square wave as it appears on an oscilloscope to bolster their case. Musical waveforms of that sort do not exist. A clipped musical waveform consists of a normal sine wave at the fundamental to which has been added an abnormally high level of harmonics. Those harmonics can result in overpowering of tweeters, and in extreme cases midranges. They have absolutely no effect upon woofers.

[quote name='Mr. Foxen' post='251309' date='Jul 30 2008, 08:28 AM']run your amp into clipping and put a square wave dc current into your speakers[/quote]Said 'square wave DC current' falls into the same category as Medusa, Chimera, Unicorns, Hercules and Fiscal Responsibility in Government.

[quote name='waynepunkdude' post='248875' date='Jul 27 2008, 07:50 AM']I played with a band a few weeks back, the bass player had the same cab as me (Ashdown 4x10) so we decided instead of stacking them we set one up on each side of the stage and it sounded amazing, not much help but I'm never much help.[/quote] There probably were some places where it sounded amazing, but they would have been exceeded by those where it sounded worse than if stacked. A visual representation of why using spread low frequency sources is a bad idea found here: [url="http://www.falstad.com/wavebox/"]http://www.falstad.com/wavebox/[/url] BTW, the same destructive interference that occurs at low frequencies with cabs placed more than a few feet apart occurs in the mids and highs when drivers within a cab are horizontally mounted.

[quote name='bass_ferret' post='248504' date='Jul 26 2008, 12:03 PM']But is wide dispersion always desirable?[/quote]Dispersion is not a constant, it varies with frequency. No matter how a cab is oriented low frequency dispersion (roughly 400 Hz and below) is 360 degrees. Going higher in frequency the dispersion angle narrows as frequency goes up, so the cab sounds different depending where you're standing. The wider the dispersion angle is maintained with increasing frequency the more uniform it sounds within the listening area.

[quote name='bass_ferret' post='248346' date='Jul 26 2008, 06:55 AM'] Your'e a glutton for punishment The fallacy that the "bass" cab goes on the bottom and the "treble" cab goes on the top when they are both reproducing the same signal (unless they are actually being bi-amped) is an extension of the fallacy that a stack has to have 15's and 10's.[/quote] It's not a matter of both reproducing the same signal, it's a matter of dispersion. Even if the 15s and 10s have exactly the same frequency response chances are the tens will have wider dispersion in the midrange, so better to have them on top where that dispersion can be put to good use. [quote]The cabs on their side bit arranges the drivers vertically. This is because of another bit of science that may or not affect the sound (in your opinion) etc etc. Horizontal arrangement of drivers causes something called comb filtering or lobe filtering, where phase cancellation causes peaks and troughs in SPL depending on your position relative to the cabs.[/quote]The existence of comb-filtering isn't a matter for debate, it's a phenomena well known for at least 75 years. Those who deny its effect should also consider memberships in the Flat Earth Society. OTOH elimination of combing is not the overriding reason for vertically aligning drivers. Expanding the width of the horizontal plane of dispersion, as Alex explains above, is. Second to that is the narrowing of the vertical dispersion pattern, placing more sound in the audience, unless you're playing to dust mites on the floor and bats in the belfry. As a benefit of vertical alignment the elimination of combing comes in third.

[quote name='labougie' post='247261' date='Jul 24 2008, 03:47 PM']I'm coming back to bass-playing after many years away from it. I've got a pair of 1225e Celestions (300w, fs 61Hz, Xmax 3.3mm, XMech 12mm). Would I be banging my head against a brick wall trying to build two 1x12 cabs with these, driving them with maybe 250 watts of Peavey and expecting to get enough bottom end to do small pub gigs with?[/quote]You won't knock walls down but they'll do for a small club. 3.3mm xmax is about average for OEM drivers. Do the cabs right and you'll likely be better of than with commercial 1x12s.

[quote name='stevie' post='245674' date='Jul 22 2008, 03:52 PM']The SRX series is shown using the 2226H on the current JBL Pro website. [url="http://www.jblpro.com/pages/mi/srx/srx.htm"]http://www.jblpro.com/pages/mi/srx/srx.htm[/url][/quote] Check the publication date on that obsolete link. As opposed to this one: [url="http://www2.jblpro.com/catalog/general/ProductFamily.aspx?FId=10&MID=3"]http://www2.jblpro.com/catalog/general/Pro...Id=10&MID=3[/url] Also consider getting a life.

[quote name='alexclaber' post='245200' date='Jul 22 2008, 06:09 AM']curved sided cone, and concentric ribbing around the cone, all of which allow the cone to flex Alex[/quote]Those refinements are intended to make the cone stiffer, to reduce flex and along with it break-up. So doing allows a lighter cone material, and the benefits of same, which includes a higher response. The ribbing is similar in look, but not function, to Altec bi-flex drivers, which incorporated a surround in the cone that allowed more independance between a stiffer/lighter inner cone and softer/heavier outer cone.

[quote name='redstriper' post='244949' date='Jul 21 2008, 06:44 PM']would like to hear from people who have actually heard all 3 in the flesh[/quote] I've heard those and perhaps 100 more fifteens over a 40 year span. IMO for a single driver cab the 3015 is unexcelled. The 3015LF is even better in extension and power handling but should be used along with a midrange driver, although for raggae and dub one might get along without it.