Bill Fitzmaurice

[quote name='Finbar' post='396560' date='Jan 31 2009, 07:07 PM']I find they mess with my distortion sounds horribly, and I find my tone has more balls with it turned off. I just don't like the things.[/quote] Distortion and tweeters don't mix. That's why guitar amps don't have them.

[quote name='EBS_freak' post='396474' date='Jan 31 2009, 04:49 PM']if I have an 8 ohm cab, play, then switch over the cab to 4 ohm without touching any of the controls, the 4 ohm is louder... but thats presumably because the amp is putting more out at those same settings...?[/quote] At average settings, twice the power. Which requires drawing twice the current from the amp, which contributes to additional heating of the amp components. A free lunch there is no such thing as.

[quote name='EBS_freak' post='396477' date='Jan 31 2009, 04:52 PM']I dont like playing without tweeters... given what you've just said, perhaps I just like the artificial sound?[/quote]There is something to be said for having response above 4kHz. The problem lies with the 2kHz to 4kHz octave where neither woofers nor tweeters will go, and it's the lack of that octave that's artificial. A good midrange will deliver better response and dispersion than a woofer can from 1kHz with highs to at least 6kHz, which most will find quite adequate.

[quote name='bass_ferret' post='396293' date='Jan 31 2009, 01:00 PM']Are we paying extra for our cabs for a solution to a problem that does not really exist?[/quote] +1,000. Tweeters are to bass cabs as tits are to bulls. What's required are midrange drivers, which actually give useful response and dispersion that woofers cannot. They're generally not employed because they cost more than tweeters. Tweeters capable of working down to 2kHz are effective, but to make another animal based analogy they are as common as teeth on hens.

[quote name='EBS_freak' post='396071' date='Jan 31 2009, 07:15 AM']The speakers are identical apart from the impedance -[/quote] In that case the difference at small signal will be precisely 3dB, and the difference at full output, assuming the amp is able to drive both to full output, will be precisely 0dB. Again, the only advantage to the 4 ohm is if the amp has the ability to drive the 4 ohm cab to full output and not the 8 ohm, and if your amp can't driver an 8 ohm 2x10 to full output you really need a larger amp, because you've got no dynamic headroom.

[quote name='alexclaber' post='395732' date='Jan 30 2009, 03:57 PM']Here's an interesting question for y'all to consider - what impedance is the cab whose impedance curve is shown below? Alex[/quote] 6 ohms. Nominal impedance is generally considered to be within the range of 1.2 to 1.5 x DCR. DCR usually shows up as the lowest reading on a chart, in this case 4 ohms. The minimum impedance below 100 Hz, which is cabinet derived, makes it look more like an 8 ohm cab, but what the amp cares about is that minimum load area above 100 Hz, and in this case to be safe I'd call it 6 ohms. Of course, Alex's point here is that impedance is neither constant nor obvious. [quote]I've compared EBS 2x10 8 ohms with EBS 2x10 4 ohms. 4 ohm appears considerably louder.[/quote] With otherwise identical drivers the most difference that could exist is 3dB, and then only if the amp used was particularly anemic. If the difference is more than 3dB that would indicate the drivers are different in more than just impedance.

[quote name='alexclaber' post='395601' date='Jan 30 2009, 01:05 PM']I don't believe I've ever insisted that is is always a bad idea. Alex[/quote] +1. It can work reasonably well. The problem with doing so is that the results are totally unpredictable, so if you don't have the opportunity to try before you buy you're taking a big chance on the result. With identical cabs there's no question that they will work together well.

[quote name='fleabag' post='395105' date='Jan 29 2009, 07:56 PM']Does that also work in reverse , Like a 50w/4ohm amp into an 8 ohm speaker would only lose 1.5db, The difference being Still barely audible ?[/quote] At low power where the amp isn't stressed you'll get 3dB, with a halving of impedance, though 3dB isn't all that much either. But at full power there's not a lot of advantage, so if your amp is inadequate into an 8 ohm load it will likely be inadequate into a 4 ohm load. Conversely if you have plenty of output into 4 ohms you'll have plenty in to 8 as well. All things considered 8 ohm cabs are better because if you ever need to use two you can.

[quote name='ironside1966' post='394571' date='Jan 29 2009, 09:10 AM']As a rough guide most amps rate there power at 4 ohms, a 100w amp will deliver 100w into 4 ohms. 50w into 8 ohms. 25w into 16ohms[/quote] With SS amps output current delivery versus impedance load at full power isn't linear. A 50w/8 ohm amp can be expected to deliver 70 watts into 4 ohms, 35 watts into 16 ohms. As for the notion of running as low a load as possible to 'get all the watts out of my amp', in most cases that's not a good idea. Most cabs can't make use of more than half their rated power before the drivers run out of excursion, and running any amp at minimum load impedance significantly raises the amount of heat generated in the amp, significantly lessening component life. As in all things, moderation.

[quote name='alexclaber' post='391552' date='Jan 26 2009, 06:31 AM']Bear in mind the dustcap output of many 12"s goes higher than that.[/quote] Measure any twelve and you'll find the off-axis response starts drops around 1kHz. Where the dome output is concerned there's a transition zone between where the output of the cone starts to roll off and that of the dome kicks in, giving a hole in the off-axis. This doesn't show up in an on-axis plot. Using a mid at 1kHz-1.2kHz fills that hole. [quote]there are a surprising number that like the scooped out off-axis response of a woofer plus tweeter cab. Also, if you're going without a tweeter you may find many players that want to keep the on-axis clarity for themselves and just let the midrange punch and lowdown fatness be what the band and audience hears. Horses for courses.[/quote] IMO it's not so much a matter of preference as it is not ever having played through a cab with either flat response or uniform dispersion. One tends not to miss what one has never experienced.

[quote name='bremen' post='391096' date='Jan 25 2009, 12:59 PM']I understand that Vd is the volume of air the speaker can move, but why does this matter if the Winisd model shows such close frequency response, power handling and efficiency betwen the two drivers?[/quote] Look at the maximum power and maximum SPL charts and you'll see why.

[quote name='bremen' post='389950' date='Jan 23 2009, 03:04 PM']It's incredible isn't it (on paper at least). It's almost exactly the same response and power handling as the 3015LF, just a couple of dB quieter, in a box literally half the size. 110dB of bottom B from a 50 litre box![/quote] Don't get too carried away, the 3012LF Vd is 496cc, compared to 846cc for the 3015LF, so the price/performance award still goes to the 15. I'm recommending the 3012LF only when the cab size requirement is too small for the 3015LF to fit.

[quote name='bremen' post='389750' date='Jan 23 2009, 11:21 AM'][url="http://www.eminence.com/pdf/kappalite-3012lf.pdf"]http://www.eminence.com/pdf/kappalite-3012lf.pdf[/url] Modelled this in WinISD and it looks like it can make 114dB down to 40Hz in a 50 litre box! What do you think, Alex? Bill? I've emailed Eminence UK to see if they'll sell me one. Bluearan and Thomann don't list them yet.[/quote] I've had both the 3012LF and HO and a couple of OEM versions for about 6 months. They've been added to my plans where applicable. IMO the best twelves made. [quote]but like the 3015LF it'll need a midrange driver for the vast majority of players[/quote] Assuming one desires useful off-axis response above 1.2kHz or so every twelve does.

[quote name='sifi2112' post='389240' date='Jan 23 2009, 01:49 AM']Thanks for all the advice .. but just how does Bergantino do it with his NV series ?[/quote] Eminence OEM special makeup drivers that you can't get unless you open a factory and buy them in minimum lots of 50. If there was sufficient demand for a similar product at retail Eminence would offer it, but there isn't, so they don't.

[quote name='RIM Basses' post='389020' date='Jan 22 2009, 04:06 PM'][url="http://cgi.ebay.co.uk/Eminence-Beta-12-250W-12-Mid-Bass-Driver-8-ohm_W0QQitemZ140292857505QQcmdZViewItemQQptZUK_ConElec_SpeakersPASystems_RL?hash=item140292857505&_trksid=p3286.c0.m14&_trkparms=72%3A1301%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318"]http://cgi.ebay.co.uk/Eminence-Beta-12-250...A1%7C240%3A1318[/url] Any good alex?[/quote] Not gosh awful, but not great. You need to be looking at driver spec sheets for an EBP rating of between 50 and 75 for best results. This happens to generally equate with cheaper drivers that more than likely will have other performance issues and limitations. The demand for high quality drivers for sealed cabs is zilch, ergo there are very few to be found.

[quote name='Mr. Foxen' post='381501' date='Jan 15 2009, 12:02 PM']It's a clone af the Acoustic 36x: much like: Jaco got plenty of mid in his sound, something special about those?[/quote] That's a variation of the 1970s JBL Keele W bin, which is described by inventor Don Keele as [i][b]A medium-throw "W” folded horn providing uniform response from 55 Hz to 400 Hz [/b][/i]Just like a modern subwoofer It never should have been used alone, but should have been be paired with a 1x10 atop it. Jaco's tone was mainly the product of his fretless, and he boosted his treble to full and pulled the bass EQ down to make the best of the response shortcomings of his Acoustics.

[quote name='Mr. Foxen' post='380910' date='Jan 14 2009, 08:06 PM']For the purposes of those charts, is the speaker at the mouth of the horn, or is their fun with horn length as the speaker is inside? And for micing, is cramming a mic inside it going to give me a poor representation of the sound of the cab, but a less coloured one? Micing it has been a the main pain with it, mostly due to sound engineer unfamiliarity with it, been using sansamp DI instead. The sticking your head inside it to see what the mic will hear didn't give a spectacular result.[/quote] The horn mouth is the radiating plane. I can't comment further without seeing the cab.

[quote name='Mr. Foxen' post='380864' date='Jan 14 2009, 06:57 PM']So why does it take a distance before it makes sound instead of blows air[/quote] It doesn't. The reason you can't hear low frequencies close to the cab is !00% the result of boundary cancellation, mainly off the ceiling, that doesn't exist further away. That's explained here: [url="http://www.padrick.net/LiveSound/CancellationMode.htm"]http://www.padrick.net/LiveSound/CancellationMode.htm[/url] You can't hear midrange anywhere because the geometry of the cab filters midrange out. Very few folded horns are capable of being used alone with a good result. It would seem yours is not one of them. [quote]Some dude is trying to tell me the easily observable phenomena of this throw is scientifically impossible, I figure he is clueless.[/quote]He's quite correct. The phenomena is easily observable, or audible to be more exact. The explanation, for the layman at least, not so much.

[quote name='Brother Jones' post='376193' date='Jan 10 2009, 10:06 AM']Hi-fi speaker reviewers used to have an agreed standard fequency for sensitivity measurements. I think it was 1 kHz, but I could be misremembering.[/quote] There are standards, having to do with where the driver is operating in purely pistonic mode, which is roughly from 100-200 Hz as far as MI woofers is concerned. This specifically removes midrange and high-frequency breakup mode peaks from the equation. It is those same peaks that manufacturers like SWR and Eden quote, while Ampeg, for one, is pretty honest. In other words, any manufacturer who makes claims far off from what Ampeg does for the same driver configuration and box size is probably lying.

[quote name='Musky' post='374945' date='Jan 9 2009, 06:48 AM']Yeah - I noted the specs on the 1x15 as 102dB -3dB at 45Hz & 15kHz. Besides the fact that giving an SPL at just two frequencies is pretty pointless, I'm highly dubious that it can achieve that kind of volume at 45hz anyway.[/quote]It can't. If it's down 3dB at 45 Hz then the average sensitivity will be at best in the 95-97dB range. The 102dB quoted undoubtably is a midrange peak up around 2kHz. Contrary to advertising claims there are no magic drivers or mystical methods by which one company has any advantage over any other company.

[quote name='TimR' post='370459' date='Jan 4 2009, 05:44 PM']All this talk of 15" and 10" and power into each driver is all very well. These are 'nominal' impedances and power ratings. Using ohms law and DC is OK but in reality the impedance of each speaker varies at different frequencies.[/quote] SS amps are constant voltage devices, no matter what impedance they see the voltage output is a constant. Current, and therefore power, does fluctuate with the load, but drivers are also voltage dependent devices, and will put out a constant dB level with a given voltage input, irrespective of current/power. Things aren't so cut and dried with valve amps, but for all intents and purposes impedance versus frequency is still for the most part a non-issue. And a good thing that is, otherwise no dynamic driver would be usable, what with every note coming forth at a different volume level.

[quote name='bass_ferret' post='366578' date='Dec 30 2008, 03:26 PM']My Brain Hurts and I am not explaining myself very well !!!!!!!!!!!!!!!! On the drawing each pair of 10's is shown as a separate parallel connection to the 15. But its not. The two pairs of 10's are wired in parallel, and then the whole 2 x parallel 10's are in parallel with the 15. Thats why Protium thinks the 15 and each pair of 10's gets a third of the amps beans.[/quote] Electrically the diagram is correct. Electrons pay no mind to whether the 10s are in one box and the 15 in another. Since each paired set of tens is series wired those pairs each offer a 16 ohm impedance to the amp, so those pairs will each receive only half the current that the 15 does.

[quote name='Protium' post='366534' date='Dec 30 2008, 02:36 PM']How does the amp know which is the 410 and which is the 115 and thus where to split the power?[/quote] It doesn't know, and it doesn't split the power. Each cab will receive the same voltage. How much current each cab will receive is decided by each cab's impedance; with equal impedance the amount of current into, and therefore the power dissipated by each cab, with be the same. [quote]the lines from the sides to the 10's are wrong[/quote]If they are four 8 ohm drivers wired series/parallel for a total 8 ohm load the drawing is correct.

[quote name='ritch' post='365548' date='Dec 29 2008, 11:09 AM']Cheers Chris, Here it is, in all its glory. The covers are going to go back on though. Rich[/quote] As you have the cabs the highly directional high frequency output of the tweeter is passing you by around mid-calf. Barring your having a very odd genetic defect the 4x10 should be on top, so that you might hear those high frequencies.

[quote name='crez5150' post='360466' date='Dec 21 2008, 03:44 PM']Forget Bose L1..... it sucks for band use..... acoustic musicians can get away with it just about...... Have a look at this little beauty...... just done our first gig with it at the weekend.... 4k rig that fits into the boot area in my Audi A4 - [url="http://www.k-array.com/download/KR200S_data_07.pdf"]K-Array Redline System[/url] Full band through this and we hardly had to drive it.....[/quote] Probably better than the Bose, at least the sub driver is large enough, though the design appears to not allow multiple subs to be clustered, which is very poor practice. As with the Bose the 2" midbasses are too small to run down to the 100Hz that they need to, and too large to run to 12kHz with adequate off-axis dispersion. The main technical shortcoming of both this and the Bose is that no 2 way system can effectively function across the full 40Hz-12kHz bandwidth required for live sound reinforcement. But in the lower price ranges most PA systems suffer from a myriad of technical shortcomings, so they still might sound pretty good comparatively speaking.