Hi

Soon I will be looking to purchase a high power sub amplifier to power six WSXs modded to fit an Oberton XB1500. I was originally looking at an FFA 10000 but upon realising that the Obertons were in fact 1500watts, I am back to the drawing board! I intend to purchase this amp second hand and have a budget of around £1200-£1600 (so not a K20 ;-;). Have looked at an E90 but people on here don't have alot of good things to say about them!

While I agree that double RMS + 3db is an extorniate amount of power to feed drivers, I struggle to believe that any more than 1/3 would kill drivers. I generally feed mine 1.5x RMS with careful limting settings.

toastyghost wrote: 1/4 power for horns, 1/3 for reflex is my general rule. Or less. It depends on the box.

This goes against everything I've ever read regarding how much power to feed drivers ! So you're suggesting I feed the Obertons 375 watts of power? That seems crazy!

Big amps are great for high output as actual program material has a high crest factor, but it is still best to use an RMS limiter set much lower so you dont feed the drivers too much power.

Your "1500 watt" speaker is rated to survive 2 HOURS, in OPEN  AIR and with a 6 db crest factor signal (somebody correct this if wrong!).

Now with some modern music is not uncommon to see 3db or even less crest factor in bass, so this brings your speaker to 750 watt before meltdown, but still for two hours and in cool open air. Enclose it in a box that keeps the heat inside and run it for 12 hours straight and 750 watt will still cook it. So 1/4 for horns and 1/3 for reflex boxes, that are obviously vented seems safe (and pros like Toasty or Danley engineers say this, not me).

Ideally your limiting should allow levels to rise with higher crest factor material, so better dsp allow you to have 

- a quick peak kimiter , could be around program or even more, depends on the enclosure, the goal is to keep excursion in check and protect speakers from very fast transients that could cause mechanical damage

-an rms limiter that lets fast transients (like a kick drum) tru to preserve dynamics, timing (as always) is frequency dependent. This keeps the average level in a safe thermal zone but allows more through than the last

-thermal limiter , very attack long times, maybe 5 6 seconds under 100Hz, kicks in only when the threshold is reached for a long time, so only with high duty cycle/low crest factor  program.

Drivers are rated in voltage,  as per AES test these days,  those obertons are tested at 89V RMS long term, so setting a limiter a little below that should keep them safe, bear in mind they are tested in free air so in a small closed chamber they will build up heat more easily.

What amp you use is up to you, the higher the voltage the louder they will get but a carefully set RMS limiter should keep them safe thermally.

Unfortunately most budget processors do not have an RMS limiter, just a peak limiter,  i am working on a solution for that ;)

Yes 6dB crest factor pink noise is used but you will not find much music program with long term crest factors much lower than that, 3dB is a continual sine wave mastered at 0dB and despite what people say im yet to find a tune with that in, there is always some dynamic.  

The 1500W rating is v^2/re ,   on the old AES test it was V^2/ nominal impedance but they changed to so they could give bigger numbers, and now more high power bass drivers are designed with a lower RE to exploit this and yeild a bigger power number...  but 89Vrms ^2 / RE is "1500w" program is defined as 2x that and peak is 4x, as the 6dB crest factor signal will have peaks at 178V / "6000W"

But you should look for at least a peak and an rms limiter to still protect the system without loosing too much performance.

Timebomb wrote: A lot of the time when people say "i feed x drivers with 1000W" thats not really whats happening,  it might be an amp capable of giveing 90V rms at 8 ohms / "1000W"  at clip but with signal crest factor and resistance rise they might only be getting 100W of actual power.

Hallelujah 

And that's why some great systems still run off 900w PPX's etc...Just well looked after systems kept out of danger zone. A few DB down at peaks that's all

I can call it 1100 watts power or 89 volts into 7.2 ohm , am I missing something? (I think you know more than me, not being a prick)

the power limiters are set lower because supposed to kick in later and protect from heat buildup, while the rms limiter, set higher, will keep the driver close to where it's happy but still not protecting fully from intense and continuous abuse.

If you don't have powersoft or linea you have to choose between extreme safety , so setting your rms limiter to 1/4 to act as a power limiter, or give it a higher limit to do rms limiting , but you are now allowing some risk.

It seems like all of those limiters are vitally important, yet, to my knowledge, only very high end DSPs have them. Is there any way i can set such limiting with a dbmark DP24?

Kind of, an RMS voltage limiter will protect from long term abuse, that is what they are for, and set right they are in effect are a power limiter.

The difference with those "true power" limiters is they are actually measuring current delivered, so can calculate the actual power delivered to the speakers and be set as a power rating rather than a voltage rating.  imo they are not really required as it can be very hard to say how much "true power" a speaker can take, and drivers are rated in RMS voltage anyway. 

An RMS voltage limiter set at 70V will act similarly to the true power limiter set at 1/4 power as those points are both around about the same, when the coil warms up 70V long term RMS limit into say 12 ohms is only about 400W of real power, and resistance will get higher than that as the coil gets hotter, when the coil is cooler then it will let more power / current flow, as resistance is lower, drivers in effect compress the actual power level drawn but if you get them to hot they will blow, there is a point of diminishing returns though. 

There is a lot of things people say and ways manufacturers specify things that can make it confusing,  if you try to forget power and think of it in volts it gets simpler,  unfortunately with a DP24 the best you can do is set the peak limiter and estimate a minimum signal crest factor and hope the signal does not get to dense for to long to heat up the drivers too much.

How do you convert a power rating in watts into volts?

so for a 1500w driver with 5.3 ohms RE  sqrt (1500x5.3) will give you the RMS voltage the driver was tested at.  

using peak limiters alone will not stop you during voice coils, and if used poorly can actually significantly increase the long term average power sent to your drivers.

without top of the range limiting, you have to think old skool - good driver / amplifier matching and listening to your rig when it is running - if it sounds happy it usually is...

Peak limiters are fine though,  i have run systems for many years on peak limiters, shortest attack and longest release for maximum and very very rarely blown anything, i tended to set the peak limiters lower though, with an RMS limiter in place so you are thermally safe you can open up the peak limiter to just deal with over excursion or clip prevention.

I use clip limiters set slightly above the maximum output of the amplifier so it can achieve maximum Voltage swing but stops it the signal turning into a complete square wave!  However ultimately the limiter is me.  If I'm just tickling the limit lights occasionally then I take that to be the system running at maximum level. If I start seeing more than a brief flash every few seconds then it's time to turn it down.  The only difference is if I do leave a system unattended then I'll normally wind the limiters back a few dB to a more conservative level and probably increase the release time too.

As for the question of how much headroom, well it depends of course!  Mainly on the style of music.  I do a lot of live work and for that I like lots of headroom because of the high crest factor, especially on mids and highs.

Just get K20, or PL380, or 2x Void Inf8MK2.

I've heard FFA10s, E90s, Crown ITECH 8s.

IMHO, None of them provide the lows AND SPL, Like the above.

All done.

Yeah bob in if your up this way, im normally about,  i will do some more refined presets for my systems when the new processors are ready but its looking like the new year now... 

It wont work. After bass ends limiter will reset and count attack again. It may not turn on at all. Also limiter turning on after few second  of bass would be annoying. Device has to have memory.

What are the maximum temperatures you see on powersofts?

How does it change with copper VC, aluminium and CCAW?

toastyghost wrote: Your drivers will still be able to be burned by 300-600w LONG TERM power. The rating alongside a driver is measured in ‘easy conditions’ with band limited high crest factor pink noise. It is not a real representation of power handling apart from in maybe a well tuned reflex box.

Sorry gen0me, you've completely lost me Why is that formula needed ? As in what does it actually show? I can gather a rough idea from the context but I'd ideally like more than just a rough idea ! You've also used some symbols that I've simply never encountered before such as ωL, ΔT and while we're at it what is Vamp? (the voltage an amp gives out ??).

Hard not to feel like an imbecile but I am so desperate to fully understand this that despite feeling as such, I simply have to ask. TIA

That was much more helpful! Don't mean to be ungrateful to Gen0me but i feel like the above needed to be read before I understood what you meant. Yes, when you put it like that there isn't alot too it but when phrases such as "burning out your voice coils" and "expensive recone bills" are used to describe a concept, I just had to make sure I understood it 110%. Thank you

Vamp is the voltage an amp gives out.

Δ = delta = difference.

This is to show how much power of an amp that was supposed to give kW is really being taken by the speaker just in standard working conditions.

ΔT is the difference of temperature. Lets say ts parameters were measured on ambient temperature speaker in 20°C. Than when voice coil heats up to 120°C its resistance will grow by ΔT* temperature coefficient. So for copper voice coil that has temperature coefficient ~ 0,4%=0.004 [Ω/°C] and ΔT=100°C the Resistance will grow to Re + 100*0.004Re= 1.4 Re

Forget it. I figured out different way.

On left reasonable reflex. On right reasonable horn. Horn could use speaker's excursion a bit more.

18SW115 has Re=5.3ohm which on 170°C will give 5.3*1.6=~8.5 ohm

Here are impedance charts after changing Re in ts parameters to 8.5ohm as effect of rising voice coil temperature from 20°C to 170°C.

Power on the speaker would be P=U*I*cos(θ)/2

So if the amp was on spec measured on resistive load than

P=U^2/(2*R)

U^2=2*P*R

Knowing Z from hornresp we can calculate I=U/Z

Power on the speaker will be: I*U*cosθ/2

Power=U^2*cosθ/2*Z=2*P*R*cosθ/2*Z=P*Rcosθ/Z

R is impedance on which amp was measured

P is amp power. I assume that above that power thd rises a lot as I am using this power to estimate amp max peak voltage. The above equation on power from current, voltage and angle is for sinusoids.

Z is impedance from hornresp

θ is angle between Voltage and current, taken from hornresp

Can also scale power through efficiency and get separately acoustical power and heat.

So for 2kW amp here are the charts:

Notice that 18SW115 has very low Re as for 8ohm driver.

Link below is to download a powersoft tech note re limiters which may be of interest.

I think klippel have a paper describing a way of modeling the thermal characteristics of a driver to accurately predict thermal compression with a view to designing a system to prevent thermal overload.

Another method is to drive the loudspeaker at low level and take an fr measurement, then increase the level and check output equals the input, at the point the loudspeaker is outputting 3dB less than the added input demands then you have reached max input for most loudspeakers. 3dB may be a bit much for some loudspeakers, PD for instance give a power compression rating of 1.6dB at rated power for the 1850 IIRC. I think toastyghost posted a link to a method a while back.

Note the bit about power factor and it's effect on the VC temp.

I dont know where this discussion went ,but from first hand experience with xb1500s .6 now 8 , ram bux 5.0 ran them pretty hard/loud but was riding the clip for whole nights,got tired of that and got a k20.

Now thats running them properly with 0 red lights in sight and lots of control.

Dont have experience with other lightweight amps,but in the end you can get away with lesser headroom for a long time if its a quality amp,but a k20 just feels right you know .

Also depends how are you gonna run them,our parties/jobs somehow always end up full tilt in the end.I reckon 6wsx wont need to be ran full tilt if youre sensible, unless massive case of not enough rig for the gig.

Oh goody, back to actually talking about amps..

As thread title, requested...

I'd love a K20 but just simply can't afford it. Seems to be the only lightweight worth getting really, except other K series. Guess I'll have to pay with my back aswell as money and cop some Inf 8s. I'm sure 6 WSX doesn't neeeed to be at full tilt but seen as this is ultimately a party stack I wouldn't mind crankin it up a tad :D Will be interesting to see how the Oberton likes the WSX...

Holy ... that hardly looks like an amplifier and more like something you'd use to power a city

When I swapped my bass drivers from 6th order bandpass (two large impedance  peaks in there workjng range) into ported horns that partially damped the upper impedance peak my amps ran much cooler, so totally agree with what your saying.

 I assume you are referring to

odc04r wrote: it is better to push 200% more drivers 50% of their capabilities vs 100% of drivers to their limit for a happier result all round

when I said I'd be running my WSXs "cranked up"? Fear not gen0me, I heeded all the advice and information in this thread very carefully and simply meant that for a few short points in the session I would push them closer (not TO) their safe limit. In general, I will be running this system relatively conservatively because before I start trying to squeeze every last db out of my drivers I feel I need to gain the neccesary experience to be confident doing so.

+1

Funny you mention the Ram BUX 5.0. A friend had 2 of those running 8 x 18" Beymas (not sure what model) and wasn´t convinced. He then swapped the Rams out for 2 x Crest 8001´s - supposedly less wattage, but swears that the system now sounds better - and louder.

Like you say, a quality amp is always better.  

not when you look at the scale on the ammeter - which looks like 15A at the top...which at 240V would give you a maximum total output of around 3Kw assuming 85% efficiency - which it probably isn't.

 anyone looked inside? Maybe there is something else hiding inside...

Yeah but

yeah but........

They're REGGAE WATTS.....!!

If its anything like most reggae amps and pre's what is inside is mostly air amd a spaghetti mess of wiring! But that's all part of the fun.

James Tengo wrote: Reggie Watts?

Don't put fingers in amplifier outputs. Not even as an experiment.

Haha - yes, a matter of taste really. I can´t say I like them at all, especially the newer lightweight stuff. Really horrible. 

Reggae Watts are heavier