Bill Fitzmaurice

[quote name='skidder652003' timestamp='1347709860' post='1804198'] . Im sure this has been asked before but has anyone run this config - one x 8 ohm and one x 4 ohm cabs into an amp with a 4 ohm minimum impedance? [/quote]Minimum load means just that, the minimum load you may safely use. 8 ohms plus 4 ohms is 2.7 ohms.

[quote name='Bassman Steve' timestamp='1347171389' post='1797569'] Did I not read somewhere that Hendrix actually used Marshall bass 4x12's? Maybe you need to turn your idea on its head and look at bass 4x12 territory. [/quote]The original stack was intended for bassists so that they could keep up with 2x12 guitar amps. That notion lasted perhaps a week before guitar players started using them. There was no real bass 4x12 versus guitar version early on though, as the drivers were the same. True electric bass drivers were still a decade away.

[quote name='shibby2407' timestamp='1347137098' post='1797398'] I have my eye on a cornford 4x12 with celestion v30's. [/quote]Their lack of bass output is why one had to use two of them back in the day, or today for that matter. Why guitar'd players think they need two when an AC30 with two v30s can kill small animals at 50 meters one can one only wonder.

If you'd read this you'd have known last night: http://basschat.co.uk/topic/135-impedance-etc/

[quote name='Lozz196' timestamp='1345586589' post='1779269'] 2nd time it`s happened to me as well with the PFs. The amp has a selector on the back for both 110, and 230, same as my last one. Just can`t remember which lead I bought last time, doh! [/quote]The jack on the amp should be the same in either case, the same style as used on computers.

If it's 2 pin, which is odd in itself, chances are it's for 110v.

Bridging should almost never be employed into a low impedance load. There's nothing to be gained except damaging the head by driving too low an impedance load or blowing the drivers with too much voltage swing, or both. Bridging should only be used into a high impedance load, say 16 ohms, which the amp would otherwise not be capable of driving to full output. The mechanics of what bridging does isn't about watts, it's about voltage swing. An instructive paragraph in the owner's manual about when to bridge, and more important when not to, should be SOP, but IME it's a topic that's seldom, if ever, addressed.

[quote name='VTypeV4' timestamp='1344893326' post='1770874'] Thats what I thought although I have seen versions with the fan mounted vertically blowing/sucking(?) at the valves in a Trace Elliot V-Type kinda way.. [/quote]Where valves are concerned keeping them cool isn't of any benefit, keeping the heat they create out of the other components is.

[quote name='warwickhunt' timestamp='1344844620' post='1769851'] it didn't seem to be 'that' hot at the end of the gig, certainly not enough to worry me! [/quote]Not worrysome perhaps, but that's not the purpose of a fan. Passive sinking keeps component temperatures down to a given differential above ambient. Fans can keep that differential smaller. The cooler components run the longer they last. And if you can hear the fan over your playing you're not playing loud enough.

[quote name='LiamPodmore' timestamp='1344780561' post='1769016'] would it not be easier for companies to use silent/low noise fans in the first place? [/quote]They cost more.

[quote name='scalpy' timestamp='1344768846' post='1768849'] The sticky point on Friday was that the guitarist has let me rag his Les Paul through his all original 58 Tweed Bassman, something it wasn't originally designed for either! [/quote]But at least it works well with guitar, never really did with bass.

AFAIK the Big Cat was an autosound driver. Hard to say for sure, as there are no references to it on the Eminence site. It appears to have been an OEM made for Maplins.

[quote name='Big_Stu' timestamp='1344531622' post='1766123'] That used to be a hanging offence in "What Hi-fi" magazine. [/quote]I guess that would have made Paul Klipsch public enemy #1?

Unless you have a valve head that can't run at 8 ohms there's nothing to be gained by using a 4 ohm cab. That's not the case with the 400+.

[quote name='Jimelliottbassist' timestamp='1344526968' post='1766006'] Have you had any experience with eminence speakers beta or delta? [/quote]What matters is matching them to the cab and amp, using their T/S specs and a speaker modeling program to determine suitability.

[quote name='Jimelliottbassist' timestamp='1344380315' post='1763828'] Hi I'm thinking about changing the speakers in a mesa 4x10 cab from 8 to 4 ohm. [/quote]Don't bother. Unless your amp is seriously underpowered it won't go any louder, which I assume is the reason for wanting to change.

[quote name='jezzaboy' timestamp='1344164132' post='1760509'] Why don`t they just fit a speaker capable of running at 300w at 4 ohms? I guess there must be a sound reason for it? [/quote]If they used a 4 ohm driver you couldn't add an extension. As for the power issue, few fifteens are capable of making use of even 150w, irrespective of the thermal power rating, so you'd need at least two to make use of 300w anyway.

[quote name='xgsjx' timestamp='1344118987' post='1760188'] Anyone know if it works & if so, why don't more cab manufacturers do this? [/quote]It does work, on tweeters, and many manufacturers use bulb protection. It does not work with woofers, the current flow being far too high. The only sure protection for woofers is an active limiter.

[quote name='Lozz196' timestamp='1344107438' post='1759979'] No doubts about that. But it sounds ideal to me. The same sound coming from either side of the stage. [/quote]Above 100Hz or so that's perfectly OK, be it on stage or with the PA. Below 100Hz not so much, as explained here: http://www.prosoundweb.com/article/in_search_of_the_power_alley/

[quote name='vintage_ben' timestamp='1344029780' post='1759074'] And just to nit pick, I did specifiaclly say equivalent (I realise this wasn't original comparison). I.e if an established company decided to develop an SVT style 8x10 in 2012 - so not a Neo superlight thing, clearly quality comes at a price. So I'll stand by that one I think. [/quote]The design process for the original SVT was to build a box large enough to contain the drivers on the baffle and to adjust the depth to give a decent result without being overly large. A week, tops. To do so today using modeling software perhaps an hour to come up with the basic design, using CAD a few more hours to create the cut sheets. Things get complex when you use vented cabs and/or multiple drivers with a crossover, and then it's the crossover that takes all the time and effort. One of my commercial designs went through literally months of B testing until the manufacturer arrived at the combination of cab tuning frequency and crossover component choices that gave him the best result according to the testers. That does not occur with a simple one-way sealed box. Alex's 69er seems to be taking a long time to come to market, I suspect partly due to the complexity involved with his 2.5 alignment, which would take a lot of B testing to get it right. I expect it to be worth the wait. If I was going to do a cab of that sort that's how I'd do it, which I've mentioned more than a few times on various forums.

[quote name='Protium' timestamp='1344026748' post='1759012'] If you tip a 4x10 45 degrees the speakers will be even further apart horizontally [/quote]Quite right. Pardon my brain-fart. The reason they'll work better that way is that rather than having two vertical line sources there will be three, with the center to center distance between each less than that of the two in a normal position. But it still won't work nearly as well as a single vertical line.

[quote name='vintage_ben' timestamp='1344023180' post='1758944'] My hunch is that the Ampeg 8x10 was much more expensive to develop than a modern day equivalent. [/quote]The 'engineering' required to develop the SVT cab took perhaps a week. It's a sealed box, how difficult is that? Theile modeling was not being used at that point, having been developed only a few years before and was only known of in Australia until 1971. Drivers using Theile parameters didn't come along until a few years after that. The SVT drivers already existed, guitar drivers BTW, which were also used in some Fender guitar combos. They were chosen based solely on their 32 ohm impedance, allowing a simple parallel wiring harness that the assemblers would be less likely to screw up than a complicated series/parallel scheme. If some 32 ohm twelves had been readily available they likely would have been used instead and quite possibly tens would never have become the standard for electric bass. The SVT driver has changed over the years, but it remains an inexpensive stamped frame unit that costs Ampeg about $30 each. The neo drivers used by Barefaced, for instance, come in at least four times that.

[quote name='Mog' timestamp='1343905577' post='1757057'] This confuses me. Is the only thing that can cause this proximity to the stage floor or is it some new fangled physics I haven't heard about. [/quote]The physics of dispersion by a sound source were quantified in the 1930s. [quote]The thing is you don't want the bass to go everywhere on a controlled stage as it is a bugger to get rid off if it bleeds into other signals.[/quote]The low frequencies [i]always [/i]go everywhere. Below roughly 250Hz the radiation pattern of a typical bass cab is 360 degrees. Above that dispersion progressively narrows as the wavelengths become shorter. The wider the source the greater the disparity between low frequency and high frequency dispersion. That disparity is minimized by keeping the source as narrow as possible. Contrary to popular belief this is why midrange drivers are smaller than woofers, and tweeters are smaller than midranges. As the operating range of drivers goes higher in frequency the size of the drivers is reduced not for the purpose of extending the operating range of the driver higher in frequency but rather to counteract the narrowing of the system angle of radiation with increasing frequency. [quote]True - but Jacks don't produce a real arse-shattering sub-type bass, though.[/quote]Jacks produce at least as much low end as direct radiating cabs using the same drivers. Where they differ is that they produce stronger mids. And they're not rear-loaded horns, they're front loaded horns. [quote]Isn't it strange that if the sound man does manage to get a reasonable sound out front during a sound check how it suddenly changes to rubbish during the gig.[/quote]The room acoustics are totally different when the room is empty versus full with an audience. [quote]For instrument monitoring we just hear each other on stage as normal.[/quote]That's even more of a challenge than having uniform sound in the audience, as the cone shaped midrange and high frequency dispersion pattern is much smaller close to the amps. With a typical stage setup the mids and highs from amps can only be heard directly in front of them. Only by running the instuments through the monitors may what's heard on stage be as close as possible to what's heard out front. Since the low frequencies as noted are omni-directional there's no need to have them in the monitors, so the instrument feeds to the monitors should be high-passed.

[quote name='KingBollock' timestamp='1343857819' post='1756572'] Would tipping the cab up, so that it was in a more diamond style configuration, so one speaker above another and then one either side at middle height, help? [/quote]It would be better. Horizontal dispersion is inversely proportional to the width of the source. By making it narrower dispersion is widened. Of course this makes the head placement a bit of a task. BTW, the entire reason why drivers were placed horizontally in the first place was to accomodate a wide amp, first in combos, then in separates. No consideration was ever given to the dispersion issue because the amp designers weren't aware of it.

[quote name='BluRay' timestamp='1343847483' post='1756345'] This thread's taken a turn for the better [/quote]It should have ended at post #3. That's when the answer to the original question was given, most of what has been posted since has been silly catterwallering. Little wonder Alex seldom comes here any more. If one doesn't want the opinion of an expert in the field one should not ask the question to begin with. Unless they be trolling, of course.