http://billfitzmaurice.info/forum/viewt ... =6&t=20250
I think this amplifier ‘specified impedance rating VERSUS applied impedance load’ safety margin needs some investigating, for the following reasons: The amp I have bought (Synq digit 1K0) and it’s bigger brother previously referred, only have 8ohm and 4ohm ratings. Pulseman (José?) uses these, and I’m pretty sure he uses them in 4 ohm nominal load configuration. I think it is probably implicit that one could take this 4ohm rating to the bank without needing a 2 ohm rating for margin of safety.Grant Bunter wrote:That's a great point Bas, and not one I ever consideredBas Gooiker wrote:I would advise noone to run all their cabs of one amp or amp channel. If one of your drivers dies in a series parralel configuration you will screw up the whole line.
Umm isn't a pair/channel 4 ohms? Lab 12 is nominally 6ohms, + 2 ohms for the cab = 8 for one cab, halved is 4.Bas Gooiker wrote:My advise would be to get 2 smaller amps and run 2 cabs parallel per channel. With Lab 12's this would already give you a nominal 3ohm load.
Charles,
Technically speaking, you should be able to run 4 x 8ohm cabs in parallel per channel if the amp is rated to 2ohms, as that would be a 2 ohm load overall.
Running an amp to 2 ohms when it's 2 ohms capable though is taking the amp to the bleeding edge, and while it may be designed to do that, eventually something will give.
Ideally then, the thing to do is use 2 amps with 2 cabs/channel (4ohms/channel), with an amp
that is 2 ohms capable.
The only reason to get overly powered amps is because they are unbelievably priced in comparison to anything else in the market.
Since we brick wall limit, that eliminates head room, or the residual power capability above the voltage limit.
The Crown XLS 2500 is about bang on the money output wise for running lab12/3012lf loaded cabs. That should give you an idea of the output required...
Where it gets cloudy therefore is in our example, the Crown XLS2500, which has the 3 different ratings, per channel: 440W (8Ω), 775W (4 Ω), 1550W (2Ω), and the reason this is important is not simply because one has to buy a second amp (approx. £500+), but because a reputable manufacturer has specified a rating. I would imagine the same aspects of margin of safety apply in design of electrical component assemblies as they do in mechanical, the case being that the amp should be designed to reliably run at 2 ohm if it is specified to be able to run at 2 ohm. Since it is a complex assembly, if the potential discrete & local failure modes are known they could be modelled or evaluated for say 10% failure rate at a 1.5 Ω load, such that there is reliability you can hang your hat on at 2 ohms. If the failure rate is only evaluated in the whole (i.e. discrete components are not considered individually) then there should have been a reasonable sample of amplifiers run to the maximum specified ratings on the bench (or perhaps in the rack) with the results being an acceptable & demonstrable statistical failure rate. I will accept that that failure rate may be higher at 2 Ω load and full power rather than breezing along at 50% power and the standard 8 or 4 ohm loading, so in essence your point still stands. But, if 2 Ω reliability is in doubt there should be reliability data available from a manufacturer, so the customer knows what he’s getting into. That, I would like to see. Of course, this partly only applies to customers who would care to appreciate it, and in most cases the supplier will just say your warranty covers it. FWIW that’s my mechy’s treatise on ‘the bleeding edge’. Having researched a little, I believe speaker impedance ratings are ‘nominal’ so some caution has to be exercised in that they can dip below the nominal values when running. I’ve looked in the Crown XLS2500 manual and there’s no caution about 2 ohm loads.
This part stumped me a bit: ‘The only reason to get overly powered amps is because they are unbelievably priced in comparison to anything else in the market.’…? And do you mean ‘Since we brick wall limit, that eliminates the need for head room, or the residual power capability above the voltage limit.’?
I’d like a bit more quantitative evidence, but overall I’m happy to accept a 2-ohm-higher-failure-rate-argument as true and valid for 2-ohm amps since no responsible person wants unreliable gear; but for stating the technical sufficiency, I’m interpreting that the Crown XLS2500 would run up to 4 LAB12’s (8 Ω cab!) at 50v per channel, because the power would be 1250W (2Ω), i.e. 80% of max power. I don’t know why I hadn’t seen it, but there is of course a 3 cab per channel option for a 2-ohm capable amp, if you’re wanting “that bit more”, where the nominal impedance would be 2.67Ω. Is that bleeding edge, sweaty palms, or there to be done, in the bang for budget stakes?
Which after all the amp loading theory, leads me to my specific issue: Being half-committed to starting building 1 or 2 (probably T30) subwoofers shortly; What voltage could I reliably run up to 2x T30’s (LAB12, 8ohm) wired in parallel, with my synq digit 1K0 amp, if I run them on one channel and my J12’s in parallel on the other channel? The amp is 540W (at 4ohm) per channel capable. I’m thinking; 540W at 4 ohm is about 46v, but I’d be better running limiter at say 35v (75%) for margin of safety.