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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 16th Jan 2019, 2:26 pm   #1
Zelalla
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Default B112D Active Speaker 1000W????

I recently purchased a pair of these speakers. I've not yet powered them up.

I note they are rated to 1000W, and the specifications state that thats 300W to the tweeter and 700W to the Woofer. It uses a Class D amplifier, and a switched mode power supply
the sales literature show a graph of input (mains) to output power efficiency comparing the Class D amp with a conventional Class A amp, which shows wattages from 1 Watt to 100Watts. The plate on the rear of the speaker clearly states its power consumption (from mains) is 110W.

Have Behringer found some miraculous way of getting 1000W of electrical output power from 100W of input? This would solve the worlds looming energy crisis! This would enable us to reduce our greenhouse emissions by 90% This would permit the development of perpetual motion machines...

Back in the real world methinks their marketing department are getting creative with how the define a Watt!!!!

Pro-Audio equipment is normally rated in Watts RMS. there is an international standard that defines that a piece of kit must be capable of running a "simulated Music Signal" of band limited pink noise (to the frequency range of the device), with a crest factor of 10 for 8 hours without being damaged.

A crest factor of 10 represents 10 dB of head room for transient peaks. In a 100W amp and speaker, a crest factor of 10 means it can tolerate transient peaks which would produce 1000W instantaneous input from the amplifier to the speaker.

That is therefore a 100W RMS device, consuming 110W electrical power, with lots of headroom for transients.

Rule by which to interpret headline specifications: If it doesn't say RMS after a claimed wattage the figure is nonsense. "Peak" has a defined meaning, and "PMPO" is often quoted but is not clearly defined, the true RMS wattage of such systems can often be 1/10 - 1/100 of the claimed value.

I expect this nonsense in domestic all in one "hifi" systems - not in semi-pro audio equipment!
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Old 16th Jan 2019, 5:03 pm   #2
mhennessy
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Default Re: B112D Active Speaker 1000W????

This comes up from time to time. Here's a recent thread:

https://www.vintage-radio.net/forum/...d.php?t=152840

Firstly, let's not say "Watts RMS" - there's no such thing. Unfortunately, "continuous average sine wave power" is a bit of a mouthful, but that's the correct term. The pink noise testing you refer to is probably "AES power".

Opinions vary on what a good value for crest factor (or PMR, preferably), but 20dB is a rule of thumb I like, based on my observations of well-recorded music. I've seen 14dB stated as a standard, but I've not read up on where that comes from.

This is the separation between the peak powers and the average powers. Headroom is the difference between peak level and clipping point, which is different, but easily confused. The headroom varies with the setting of the volume control; the PMR for a given piece of audio is the same, whatever the volume setting (assuming no clipping).

Anyway, as the mains power draw will be based on the average power delivered to the load, I'd say that the mains power rating isn't as silly as it seems.

You'd never play a sine wave at full power through that speaker. If you did, the amplifier would overheat (despite being class D), assuming the PSU could supply the power without overheating or current limiting. Also, the voice coils would overheat too. Not to mention your hearing

I have a Berhinger NX3000 - this is something like 450 watts per channel into 8 ohms. It claims to do 3000W when bridged into 4 ohms. Astonishing for the £140 I paid! And all the more impressive when you consider that the mains inlet is just a standard IEC rated at 10 amps. Look inside, and there's no way the fan and heat sinking is able to deal with the heat from a 3kW amp, but it's easily OK for 10dB less than that. I let it play into my dummy loads for a few hours when it first arrived - I put a Steely Dan CD on repeat and turned up the volume until it started to clip. My dummy loads barely warmed up - the instantaneous peaks were around 450W, but I'd be surprised if the average power per channel was 40 watts. Probably less than half of that, in practice. The speed-controlled fan stayed at its slowest speed (still too noisy, frankly!) during this time, and the air coming out of the amp was still at room temperature. So if I did use this amp to drive subs, which might be more heavily compressed, then it would probably cope just fine...

Quite simply, these sorts of things are sold for use with audio signals - they are not lab amplifiers designed to drive sine waves into their rated loads at full power. If they were designed to do that task, then they would be grossly over-engineered for the job they were sold for, and that's just as bad as under-engineering, frankly.
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Old 16th Jan 2019, 10:19 pm   #3
kevinaston1
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Default Re: B112D Active Speaker 1000W????

Salesman watts.

The technician says it produces 80W r.m.s.

The salesman thinks this will not sell with a figure like that, so multiply it by ten and round it up, then call it 1000W Peak Music Power.

I used to repair Lab Gruppen amplifiers. Believe me, 1000W in a room is very painful, and will damage your ears if you use it for any length of time.

Kevin
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Old 16th Jan 2019, 11:24 pm   #4
mhennessy
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Default Re: B112D Active Speaker 1000W????

No, based on my measurements of my NX3000, I doubt that Berhinger will be lying. They are a reputable company, despite what some of their critics might claim. They (Music Group) own Lab Gruppen, BTW.

When playing back music (both channels driven into 8 ohms), the NX3000 gives about 85V peak, which is pretty scary! This is the peak voltage that equates, give or take, to 450 watts continuous average sine wave power (not "watts RMS", please).

However, if you tried to play a sine wave through this amplifier with the same peak voltage, I wouldn't expect it to reach 85V peak because of PSU sag. Also, I would expect it to warm up (and possibly even shut down after a period of time). None of that makes it a bad amplifier. Who listens to sine waves?

As I've tried to explain, there is a world of difference between a sine wave and music. A sine wave has a PMR (or "crest factor") of 3dB. Audio signals have a much larger PMR - perhaps 20dB, which is a factor of 100. So my 450 watt amp playing that Steely Dan CD - where the peaks are reaching 85V - might well be delivering an average level that's less than 10 or 20 watts.

I mentioned earlier how cool my dummy loads got during that test (several hours). When I built them, I could get them much, much hotter than that with a dual 30V, 2A bench PSU - just 60 watts per side. I've included a couple of pictures of the load, just to give to the idea. Note the CD for scale. These are pretty serious Each of those big resistors is 1 ohm, 50 watts, so there's 4 ohms between each of the pairs of terminals. The bottom two smaller resistors are 15 ohms each.

Anyway, this is hugely significant because it's the average level is what determines how much energy the power supply has to provide, and also how much heat is generated - both in the amp and in the voice coils.

An amplifier that is designed to deliver its rated power with a sine wave is over-engineered for use with music. That does not make commercial sense, especially in the highly competitive PA market.

All the best,

Mark
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Old 17th Jan 2019, 10:02 am   #5
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Default Re: B112D Active Speaker 1000W????

There was an article about a 1000 watt amplifier back in the 60's in one of the leading magazines when 10 watts was a lot of power from a transistor amp. We had people coming into the shop asking about this and they crept away somewhat embarrassed when we pointed out the date on the mag - April 1st.
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Old 17th Jan 2019, 10:45 am   #6
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Default Re: B112D Active Speaker 1000W????

This is a classic: http://sound.whsites.net/dynamic-range.htm

I linked to Rod's version because of his comments about the issues raised, but the original scan can be found on Keith's site: http://www.keith-snook.info/wireless...nt%20Noise.pdf
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Old 17th Jan 2019, 11:13 am   #7
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Default Re: B112D Active Speaker 1000W????

George’s name is wonderful, also like the comment about purchasing the adjoining houses.
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Old 17th Jan 2019, 3:07 pm   #8
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Default Re: B112D Active Speaker 1000W????

Is there a bit O'Veering off topic here?
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Old 17th Jan 2019, 3:26 pm   #9
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Default Re: B112D Active Speaker 1000W????

Out of interest and to put it into perspective I measured the voltage on my stereo amplifiers output a few minutes ago while listening to "The World Service" the reading was less than 100mV RMS, V^2/R (R is 8 ohms) gives a shade over a whole milliwatt (per channel). Assume the 'speakers are 5% efficient and I have two the sound is 10 microwatts.
 
Old 17th Jan 2019, 4:57 pm   #10
mhennessy
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Default Re: B112D Active Speaker 1000W????

As Rod says in the article I linked to, 5% efficiency equates to 99dB/W/m, which is rather high for a hi-fi or radio speaker. Depending on what your speakers are, you could probably knock 10dB or so off that figure.

Here is a handy set of examples: https://en.wikipedia.org/wiki/Sound_..._sound_sources

10uW is about as loud as a hairdrier, according to that. Go down 10dB, and it suggests a radio or TV

How did you measure the RMS voltage? While the number you got makes the point, it's worth saying that True-RMS multimeters are only accurate with crest factors of 3:1 or less typically (about 10dB). And they often have a limited frequency response. Measuring audio programme level is surprisingly complicated if you want to be accurate.

An average power of 1 watt (2.83V RMS) fed into an 89dB/W/m loudspeaker is pretty loud in a domestic room. Quite possibly enough to clip a 100 watt amp if you're playing material that hasn't been overly compressed. The original 1985 release of "Brothers In Arms" is a good example - play "Money For Nothing" in Audacity and note that the difference between the RMS and peak levels (PMR) approaches 30dB at times. The remastered version is nowhere near as dynamic, of course...

To get the same levels in an auditorium or outside space, which is where we came in, of course, the power levels go up dramatically. Luckily, PA speakers are more efficient that hi-fi speakers. In the local arts centre where I help (capacity just over 300), we have 450 watt amps driving the 96dB/W/m LR main speakers (ignoring subs, fills and monitors). To compete with a drum kit, that's actually a bit marginal.

Quite apart from the size of the space you're trying to fill, live music tends to be more dynamic than recorded music (unless you're being a bit heavy-handed with the compressors), so lots of power is a basic requirement.
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Old 17th Jan 2019, 5:40 pm   #11
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Default Re: B112D Active Speaker 1000W????

Quote:
How did you measure the RMS voltage?
With a Voltcraft VC265. How efficient are Tannoy DC4s ? (lovely spoken word 'speaker BTW).
 
Old 17th Jan 2019, 6:09 pm   #12
mhennessy
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Default Re: B112D Active Speaker 1000W????

VC265: Max crest factor 3:1. Frequency range 45-1kHz. If it uses the ubiquitous DTM0660 chipset, it'll be exactly 3dB down at 3kHz.

Tannoy DC4: 87dB/W/m, according to the manufacturer.

Incidentally, Tannoy are also owned by Music Group.
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