2-ohm amps - reliability & bang for buck

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Charles Jenkinson
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2-ohm amps - reliability & bang for buck

#1 Post by Charles Jenkinson »

This is a slight tangent topic to a comment on page 2 of the following thread.

http://billfitzmaurice.info/forum/viewt ... =6&t=20250
Grant Bunter wrote:
Bas 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.
That's a great point Bas, and not one I ever considered :)
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.
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.

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...
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.

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.
2xJ12L (3012HO) switchable/melded
2xT30

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byacey
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Re: 2-ohm amps - reliability & bang for buck

#2 Post by byacey »

Grant Bunter wrote:
Bas Gooiker wrote:I would advise no one to run all their cabs off one amp or amp channel. If one of your drivers dies in a series parralel configuration you will screw up the whole line.
This is true, but at the same time, if one channel on an amp fails, usually the good channel shuts down too, on many amps that share a common power supply.

This may prevent the speakers from sustaining further damage, but in a show situation, the end result is the same - no sound is, no sound.

The other problem with running series / parallel is the extra calculations required to set the limiters.
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escapemcp
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Re: 2-ohm amps - reliability & bang for buck

#3 Post by escapemcp »

Charles Jenkinson wrote: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.
But that quoted 540W is going to be for a sine wave tone... music ain't a sinewave, so you'd get your safety margin from that. You are on about using 75% of the capability of the amp for safety, but IIRC most music only uses about 1/3 of the available power from an amp (can someone add something here about crest factor :D !!)

I think... :wink: :roll:

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Re: 2-ohm amps - reliability & bang for buck

#4 Post by Grant Bunter »

Hi Charles,
Thanks for opening this in another thread and not sidetracking the OP's :)

Since I opened the can of worms, I'll try better to explain what I was trying to say, and respond to some of your comment.

Amp manufacturers and reliability data:
The basic premise here will be that if an amp manufacturer releases model X amp with 2 ohm overall load capability, then the (final) R&D test model will have survived a 2 ohm load for a period of time at the testing frequency (usually) specified in it's literature. In same cases that will be that, in others, extensive testing may have been undertaken.
How many attempts at having to revise the circuitry etc to get to the final test model will never be known.

We all know the Crown XLS series is rated to 2 ohm loads.
There was a thread a while back, where one of the forum members said that, with 3 sub cabs/channel, with a Crown XLS amp, that, under that load the amp was performing well, but since they were also running the software, noted that the amps temperature was increasing rapidly.
As you note, the load per channel was 2.6ish ohms, and the amp should be able to handle a 2 ohm load, but in that particular situation, the owner decided that there was potential for failure, or thermal shutdown, and only runs 2 cabs/channel on that amp.
So I guess that's an example of real world experience Vs lab testing.

You gets what you get, if your amp is only 4 ohms load capable, so be it.
(Apologies, I thought that Sync amp had some massive output BTW)
I use a 4 ohm capable old iron amp for my subs (nominally the load is 5ohms/channel in my case) and these amps have been going hard since the 80's.
BUT, ideally, I would have 2 ohm load capable amps, simply because I'm not then operating the amp towards it's tolerances.

IITP. You need to select nominal driver impedances and internal and external cab wiring methods to derive safe impedance loading for the equipment you have, or intend to get.
If you have a 8 ohm amp that can do 4 ohms, ideally it would better to run the amp at an 8 ohm load than a 4 ohm one, and you would choose drivers and wiring methods accordingly.

The bit about headroom.
I didn't mean eliminates the need for. As I said, brick wall limiting eliminates headroom.

There are plenty of people who like to have some headroom running their amps. ie power over and above required power.
I (and the respondents) discussed that brick wall limiting actually eliminates headroom in a thread I created ages ago.
It seems this is either not widely known, or ignored.
The point is that it is redundant to buy a eg 2000W/channel amp (not bridged), simply because, once you brick wall limit, you don't have access to the wattage available in the amp.
When you pay x amount of money per watt, don't buy more than you need to.
Having said that, there is a school of thought that says if you only using up to half the power available, you're running the amp low in it's duty cycle...

Driver selection:
I'll say it anyway :oops:
What's the point in buying lab12's if you can't take advantage of the extra voltage they can be given?
The BP's can be limited to 35V, safely. Mine are and work fine. Despite the buy once, cry once calls, and the displacement is king calls, and the go premium driver calls, it simply doesn't make sense to waste the money on drivers whose potential can never be utilised with the amp you have, unless you plan to upgrade your amp later.

Having said that, if you have 42V available, I would brick wall limit 1dB, probably give you 39-40V. If your Otops are premium loaded, that would be a good setting on both channels...
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Re: 2-ohm amps - reliability & bang for buck

#5 Post by sine143 »

the crown xti 4002 starts to complain a little with 3 t48s per (10 ohm loads equal 3.33 nominal). one gig (although it was quite hot in the venue, about 85 degrees F) I had the PSU Temp up to about 70C. I do not know what temp the thermal shutdown occurs. the very next night I ran 2 cabs per side (this venue was about 75 F ambient temp) and could not even break 40C on the PSU temp, although I was driving them to similar output levels (I try and maintain about -3 on my peaks using a custom panel in system architect).
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

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escapemcp
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Re: 2-ohm amps - reliability & bang for buck

#6 Post by escapemcp »

Totally with you on the 'headroom' (wrong word!) thing for amps (where you buy a 2ohm amp and only ever run it at 4ohms)... this is what I am doing with my iNuke 3000DSP. If these 2ohm tests have been done by a manufacturer, I bet they weren't running 2ohms in a hot and sweaty club (as sine mentions), where the temperature delta of the amp/heatsink to the surrounding air wouldn't been anywhere near as much as if running the amps in a much cooler environment (back in the manufacturer's test room). It could be that reduced ability to shift the heat that could end up sending your amps into thermal protect/failure.

And +1 on the limiting eliminates the need for headroom thing.... I have been thinking this for ages and you have now confirmed this :D

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Charles Jenkinson
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Re: 2-ohm amps - reliability & bang for buck

#7 Post by Charles Jenkinson »

Thank you for the replies fellas.

Sine, good to have the data on a running amp.

Grant, I'd antipated needing a sub amp at some point so wasn't too worried about getting the lab's. I'll definitely consider a 2 ohm capable amp, though i do like the 1U size of the synq amps. May get old iron for subs.

Blessings.
2xJ12L (3012HO) switchable/melded
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Re: 2-ohm amps - reliability & bang for buck

#8 Post by Michael Murphy »

https://photos-5.dropbox.com/t/0/AAAMKl ... e=1024x768

I ordered an IPR 1600 non DSP and got this yesterday> :D

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escapemcp
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Re: 2-ohm amps - reliability & bang for buck

#9 Post by escapemcp »

pumpsfast wrote:https://photos-5.dropbox.com/t/0/AAAMKl ... e=1024x768

I ordered an IPR 1600 non DSP and got this yesterday> :D
I can't see the pic... what did you get... IPR3000?? :D DSP?? :hyper: Crown?? :fruit:

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Re: 2-ohm amps - reliability & bang for buck

#10 Post by Michael Murphy »

Lol, escape. I got a brand spankin new IPR 1600 DSP version peavey amp, paid 278US. It was from jim laabs. I was looking for one on ebay and they had the non DSP one as an open box, 1 customer store demo so I figured the price was right and bought it. To my surprise and delight they sent a new DSP version, another flippin manual to read and device to learn! :fruit:
emailed them and basically said thanks!

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Chris_Allen
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Re: 2-ohm amps - reliability & bang for buck

#11 Post by Chris_Allen »

pumpsfast wrote:Lol, escape. I got a brand spankin new IPR 1600 DSP version peavey amp, paid 278US.
Nice! hope it works out for you.
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escapemcp
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Re: 2-ohm amps - reliability & bang for buck

#12 Post by escapemcp »

pumpsfast wrote:To my surprise and delight they sent a new DSP version, another flippin manual to read and device to learn! :fruit:
emailed them and basically said thanks!
KICKASS! :hyper:
Loving the DSP on my Behringer amp... means that I can run my whole rig off of a single 5kg amp if I want/need to.

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Re: 2-ohm amps - reliability & bang for buck

#13 Post by Michael Murphy »

Yeah, the IPR DSP has many features and at only 7lbs :D , and yes it can run my 2 T39's x 2 OT 12's. I like how the manual states values in volts, 46 is the max, just fine for the lab 12's. It really does everything a BFM set needs, would be a great start for a weekend warrior.

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Re: 2-ohm amps - reliability & bang for buck

#14 Post by netwerks »

escapemcp wrote: If these 2ohm tests have been done by a manufacturer, I bet they weren't running 2ohms in a hot and sweaty club (as sine mentions), where the temperature delta of the amp/heatsink to the surrounding air wouldn't been anywhere near as much as if running the amps in a much cooler environment (back in the manufacturer's test room). It could be that reduced ability to shift the heat that could end up sending your amps into thermal protect/failure.

And +1 on the limiting eliminates the need for headroom thing.... I have been thinking this for ages and you have now confirmed this :D
I think the other consideration as Grant pointed out is to purchase higher power amps with the mindset that they would be running far below their max rated voltage swing which ensures they are idling along in lower power mode in these types of conditions which results in the amp running cooler overall to avoid thermal issues.

I do not know how valid this approach is is but would love to hear real world examples from users.

I can tell you from my experience that fans run pretty hard on my XTI4000 even when limited @ <50v and I know it will do much more than voltage than that. :)

sine143
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Re: 2-ohm amps - reliability & bang for buck

#15 Post by sine143 »

ii run the fans full speed at all times in the xti 4k lol.
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

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