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BEHRINGER KM750 & KM1700 official specifications vs actual specifications

djtetei

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I was interested in acquiring some additional information about those two models from the manufacturer before making a decision to buy, because I wanted to ensure at least 3 dB of headroom between the speakers rated average power and the amplifier rated average power, so here are my findings:

Behringer KM750 specifications state a voltage gain of 32dB. However, if we do the math, the published voltage gain value doesn't add up.
The specifications states that the KM 750 delivers 200 watts into 8 ohms with an input sensitivity of 0.775 Volts.

Output voltage formula: sqrt (power x impedance)
Output voltage calculated: sqrt (200 x 8) = 40V
Voltage gain (amplification factor): output voltage / input voltage = Av (amplification factor)
Voltage gain (amplification factor) calculated: 40 V / 0.775 V = 51.62
Voltage gain (dB) formula: 20log(Av)
Voltage gain (dB) calculated: 20log(51.61) = 34.25 dB

The calculated voltage gain is 2 dB higher than the specified voltage gain.
The only scenario the specified voltage gain is 32 dB is if the input sensitivity is, in fact, 1 Volt.

Furthermore, if we take the officially specified input sensitivity (0.775 V) and voltage gain (32 dBU) and do the math, we arrive at a different result for the output power of 119 watts, which is less than the officially specified power into 8 ohm load.

So, the following question arises: when input sensitivity of 0.775 V is selected, the maximum input voltage required for maximum rated power is 0.775 V (0 dBU) or 1 V (+2 dBU)?


The following scenario applies to Behringer KM 1700, also.

Update:

On 29.06.2022, MusicTribe Customer Solutions Specialist Mr Kyle Johnson replied to my support ticket, and his answer is as follows: "The 200W is the peak power not the RMS, the calculation should based on the RMS 130W for KM750 and 310W for KM1700. Also, the peak power is actually about 210W."

This is important information and should definitely be included in the product's user manual.

Starting from this, suppose we now have a peak power of 210W into 8 ohm load.
Calculate the peak voltage: SQRT(210*8)=40.987 Vpeak
Calculate the RMS voltage: 40.987*0.707=28.977 Vrms
Calculate power (RMS): SQR(28.977)/8=104.95 W
Calculate amplification factor (X) for 0.775 input sensitivity: 28.977/0.775=37.389
Calculate dB voltage gain: 20*LOG(37.389)=31.454 dB

As you can see, the statement about 130 W RMS doesn't hold up.

Amplifier power is calculated, not measured.

A Voltmeter measures voltage in volts. An Ammeter measures current in amperes. An Ohmmeter measures resistance in ohms. Any two of these measurements will allow calculation of amplifier power (in watts).

If you search MusicTribe knowledge base articles, under Behringer brand you will find an article called "What is RMS" with the following statements:

"We no longer list our amp power ratings by RMS as these tend to not give true results as tests are always done using signal generators and specific waveforms which don't reflect in comparison to music, music comes at fuller frequencies and non linear dynamics which of course as I'm sure you're aware is nothing like a test tone generated from a signal generator...As a rule of thumb, you can assume RMS is around half the peak value."

Of course music comes with broad frequency range and nonlinear dynamics, because music is mixed and mastered in a specific way, to ensure tonal balance and a specific dynamic range to make it sound good. Its purpose is to be listened and not to be used as a test tone for audio equipment capabilities and limits, although there are certain instruments that can put an audio equipment to the test. On the other hand, test tones are created and used specifically for testing and measurement of audio equipment capabilities and limits. By using test tones and filtered noise waveforms able to stress and measure the audio equipment capabilities and quality of assembly, manufacturers ensure the customer's piece of mind, knowing that when the specific equipment is used with music, it will never reach the operational limits, unless it is used by reckless or unprofessional people. A 0 dBFS test tone with a crest factor of 3 dB is able to push an amplifier or a loudspeaker to its limits, if played long enough, compared to a music track with a crest factor (dynamic range) of about 14 dB, because the latter will never bring an amplifier to its current limits, unless one crazy dude decides to drive the input or output stage into overload. As many of you know, music is mixed and mastered with different dynamic range, according to the author or the mastering engineer tastes, resulting in dynamic range values between 6 and 20 dB, which makes it difficult to be used as a test reference. You could use music as a test reference if all music tracks are mastered to the same dynamic range (crest factor) and loudness target level, but that is not the case. Therefore if a certain audio equipment manufacturer choose to publish peak values for power ratings, it can also publish the calculated average power output relative to the measured RMS voltage output and RMS current output of its equipment, under specifically stated test conditions (proprietary or standardized), and stand behind its statements, ensuring the proper sound system design and implementation for a potential customer. In my experience, failing to disclose usefull information to the customers and failing to provide a solid customer support for parts, warranty and technical feedback is a sure way to destroy a brand's image and affect its business future, even if that particular brand is making good efforts to offer competitive products in terms of functionality.

Anyway, as a conclusion, it seems that if you want to match your speakers RMS / continous power rating with a Behringer amplifier power rating, you should expect "about half" of the declared power ratings.

Therefore, the calculated parameters for Behringer KM 750 and Behringer KM 1700, based on published specifications are as follows:

Behringer KM 750:

Peak Power / channel @ 8 ohm: 200 W
Peak voltage: SQRT (200 X 8) = 40 V
RMS voltage: 40 X (1 / SQRT(2)) = 28.284 V
Average continous power @ 8 ohm: SQR(28.284) / 8 = 100 W
RMS current: 100 / 28.284 = 3.535 A
Peak Power / channel @ 4 ohm: 400 W
Peak voltage: SQRT (400 X 4) = 40 V
RMS voltage: 40 X (1 / SQRT(2)) = 28.284 V
Average continous power @ 4 ohm: SQR(28.284) / 4 = 200 W
RMS current: 200 / 28.284 = 7.071 A
Amplification factor for 0.775 V input sensitivity: 28.284 / 0.775 = 36.519
Voltage gain for 0.775 V input sensitivity: 20 X LOG (36.519) = 31.250 dB
Amplification factor for 1.4 V input sensitivity: 28.284 / 1.4 = 20.203
Voltage gain for 1.4 V input sensitivity: 20 X LOG (20.203) = 26.108 dB

Behringer KM 1700:

Peak Power / channel @ 8 ohm: 500 W
500 W
Peak voltage: SQRT (500 X 8) = 63.245 V
RMS voltage: 63.245 X (1 / SQRT(2)) = 44.721 V
Average continous power @ 8 ohm: SQR(44.721) / 8 = 250 W
RMS current: 250 / 44.721 = 5.590 A
Peak Power / channel @ 4 ohm: 800 W
Peak voltage: SQRT (800 X 4) = 56.568 V
RMS voltage: 56.568 X (1 / SQRT(2)) = 40 V
Average continous power @ 4 ohm: SQR(40) / 4 = 400 W
RMS current: 400 / 40 = 10 A
Amplification factor for 0.775 V input sensitivity: 44.721 / 0.775 = 57.742
Voltage gain for 0.775 V input sensitivity: 20 X LOG (36.519) = 35.229 dB
Amplification factor for 1.4 V input sensitivity: 44.721 / 1.4 = 31.943
Voltage gain for 1.4 V input sensitivity: 20 X LOG (31.943) = 30.087 dB

Feel free to express opinions, share knowledge or other useful information about Behringer KM 750 and KM 1700 amplifiers.

Thank you!
 
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sergeauckland

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I don't know those amplifiers specifically, but have a fairly extensive experience of Behringer products generally. Their specifications are, shall we say, somewhat different to what I've measured, so can't say if the specs are wrong, or are just measured in a way that produce different results.

The way I've approached their products is to buy them, measure them for myself, and if the performance is adequate for the job they're intended to do, I keep them, if not, they go back. So far, I've only ever sent back two of their USB audio interfaces, as the ADC part had high distortion at anything above -3dBFS, and so useless for the job I needed which required driving close to 0dBFS. If it wasn't for that requirement, they would have been OK as recording interfaces, which to be fair is what they're sold as.

S.
 
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djtetei

djtetei

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I don't know those amplifiers specifically, but have a fairly extensive experience of Behringer products generally. Their specifications are, shall we say, somewhat different to what I've measured, so can't say if the specs are wrong, or are just measured in a way that produce different results.

The way I've approached their products is to buy them, measure them for myself, and if the performance is adequate for the job they're intended to do, I keep them, if not, they go back. So far, I've only ever sent back two of their USB audio interfaces, as the ADC part had high distortion at anything above -3dBFS, and so useless for the job I needed which required driving close to 0dBFS. If it wasn't for that requirement, they would have been OK as recording interfaces, which to be fair is what they're sold as.

S.
Thank you for your answer!
Sometimes, depending from country to country and dealer to dealer, it's not easy to buy a product and send it back, especially if you have to buy it from abroad, that's why over the years, although I put some Behringer products to good use, I avoided buying their amplifiers, not because of durability issues, in particular, but mostly because of their customer service policies, regarding warranty claims, parts availability and especially technical feedback. All those years, I relied on products from JBL, Crown, QSC and Yamaha for everything regarding sound reinforcement, for obvious reasons, although, sometimes, I would have loved to try some amplifiers from Behringer to assess their value, given the fact that the brand owner put some good efforts, lately, to improve their product lineup.
Regarding your remark about Behringer audio interfaces giving distortions, I wouldn't, especially, blame them, because analog to digital converters, in general, do not like levels over -6 dBFS, given the fact that you have a reference level of -18 dBFS to -24 dBFS to work with, keeping the top as headroom for unexpected peaks in the signal. As long as the digital audio interface offers a respectable signal to noise ratio, there is no real reason to drive a signal to the ceiling, because of digital domain editing capabilities, like normalisation and compression.
 
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sergeauckland

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Regarding your remark about Behringer audio interfaces giving distortions, I wouldn't, especially, blame them, because analog to digital converters, in general, do not like levels over -6 dBFS, given the fact that you have a reference level of -18 dBFS to -24 dBFS to work with, keeping the top as headroom for unexpected peaks in the signal. As long as the digital audio interface offers a respectable signal to noise ratio, there is no real reason to drive a signal to the ceiling, because of digital domain editing capabilities, like normalisation and compression.
I agree with the general principle, when doing live recordings I always allow at least 10dBs headroom above peaks, exactly for the reasons you mention.
However, in my case, I wanted the interfaces for making measurements, where the S/N ratio had to be maximised and I couldn't 'waste' 18-24dBs.

I take your point about difficulties in sending stuff back, I suppose we're fortunate here in the UK that I can buy a lot of stuff from Amazon who readily take things back at either no cost or little cost, and this has forced other dealers to offer similar terms.

S.
 

LTig

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[..]
Regarding your remark about Behringer audio interfaces giving distortions, I wouldn't, especially, blame them, because analog to digital converters, in general, do not like levels over -6 dBFS, given the fact that you have a reference level of -18 dBFS to -24 dBFS to work with, keeping the top as headroom for unexpected peaks in the signal. As long as the digital audio interface offers a respectable signal to noise ratio, there is no real reason to drive a signal to the ceiling, because of digital domain editing capabilities, like normalisation and compression.
Nope. An ADC must be able to accept levels at or even slightly above 0 dbFS. If not I consider it broken by design. The maker could sell it as ADC with 1 bit less resolution and specify its max input level accordingly.
 
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djtetei

djtetei

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@sergeauckland One thing I learned over the years, working with digital audio workstations and audio interfaces, DJing, mixing or mastering music, is that they are made to emulate the behaviour of analog consoles, so the fact that you encountered those distortions at levels higher than -6 dBFS is not a surprise, given the nature of the digital beasts design and concept. They are not ment to be used at those levels, even if their system dynamic range is "theoretically" available, the usable signal to noise ratio zone, sometimes called "the sweet spot", is lower.
Regarding your remark about Amazon, yes, you are lucky to have it in the UK, but, theoretically, we, in Romania, can also send back products brought online, because the EU rules apply also in our country. The difficulty comes from the various dealers or online shops who, sometimes, refuse to behave in a professional manner, leading to time spent resolving an issue and convincing them to obey the European laws.
 
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DVDdoug

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an input sensitivity of 0.775 Volts.
Is that a problem? Line Level isn't usually tightly defined/controlled but most outputs have enough voltage and most inputs have enough sensitivity that everything usually works together. (The exception is with some balanced inputs on pro equipment that expect a higher level.)

Anyway, as a conclusion, it seems that if you want to match your speakers RMS / continuous power rating with a Behringer amplifier power rating, you should expect "about half" of the declared power ratings.
I don't even trust RMS specs! From what I recall, Amir tested a Crown amp and it failed to meet its power specs. Before that, I would have trusted Crown.... It was "close" but I would have expected at least 1 or 2 Watts over the spec. Most good electronic equipment is specified so that every sample off of the assembly line meets or exceeds the published specs.

I trust speaker ratings even less! Even an honestly-rated speaker can't take the full-continuous rated power into the tweeter. And if it's a 3-way it might not handle full-power continuous power into the woofer, since the power normally is divided between all of the drivers. But luckily, music and program material are dynamic and we are rarely running our amplifiers at full power (and hopefully not driving them into clipping).
 
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djtetei

djtetei

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@LTig In digital domain there is nothing above 0 dBFS, there is no such thing as +1, +2 or +X dBFS. It is a brickwall. Hit it and you have "clipping".
 
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djtetei

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@DVDdoug Both in live sound reinforcement and in home audio, I can accept a difference of no more than 1 dB between the specified rated power and "hands on" power.
 
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djtetei

djtetei

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I don't even trust RMS specs!
In my case, I have to be able to trust the average power output of an amplifier, within 1 dB tolerance, because in live sound reinforcement I have to be able to drive that amplifier to a certain level 24 hours a day, 7 days a week and the "beast" heart has to be able to deliver the required current without missing a beat.
 

LTig

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@LTig In digital domain there is nothing above 0 dBFS, there is no such thing as +1, +2 or +X dBFS. It is a brickwall. Hit it and you have "clipping".
Look for intersample overs. Usually those are created during digital processing, and since some DACs are able to reproduce them it makes sense to also enable ADCs to handle them properly.
 
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djtetei

djtetei

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That is exactly why, during mixing or mastering in digital domain one has to work with the highest bit depth, at least double the sample rate and use true peak metering to prevent possible intersample peaks to actually hit the 0 dBFS ceiling.
During analog to digital conversion, also, one should never push a signal to the 0 dBFS ceiling.
 
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LTig

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That is exactly why, during mixing or mastering in digital domain one has to work with the highest bit depth, with at least double the sample rate and use true peak metering to prevent possible intersample peaks to actually hit the 0 dBFS ceiling.
During analog to digital conversion, also, one should never push a signal to the 0 dBFS ceiling.
You're absolutely right but shit happens ...
 
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djtetei

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Absolutely, shit can happen, but, then, the problem is behind the desk...;)
 
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djtetei

djtetei

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If anyone is interested and wants to study Behringer KM 750 and Behringer KM 1700 schematics, you can find them in the attachment.
 

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  • Behringer_KM750_schematics.pdf
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Wolf11Man

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Thank you for the manual. Normaly impossible to get from Behringer. It is a mix of KM750 and KM1700 pages, in the lower right corner of each page is the model No. visible, if you enlarge the PDF.
I have a KM750, while I silenced the fan I measured the supply voltage, as far as I remember it was enough for 280W/4 Ohm. This transformer driven A/B amp is simply not heavy enough for more power. Anyway, a very nice amp, as I got mine for €130.
 
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djtetei

djtetei

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it was enough for 280W/4 Ohm
That being continuous power?
Did you measured the voltage supply connected to a 4 ohm load, both channels driven?
 
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Wolf11Man

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Important: I mention the KM750, not the KM1700, as the later is a class H amp and switches supply voltages.

No, I only measured the supply voltage. This will give me an idea what peak power the amp might be able to deliver into a certain load. Sure, only for a short time, mainly dependend on the size of capacitors. This may be OK for a typical HT miss use of a PA amp. HT amps usualy deliver full power only into one channel. All 5 or 7 driven, the output is often only 25% of the advertised power. Still they work well.
What I measured on my amp made it hard to reach the Behringer "maximum power" rating, using some serious calculations.
You may define such a "peak power" for maybe 50 milli seconds, with 100% distrotion, but such number has no use in real life. Like shorting the power supply on the speakers and calling it "peak power"...

So for me I calculate this (hypotetical) peak power as the supply voltage (55V if I remember right), minus average 3 volt (drop at transistor stages, wires and resistors).
For example (52V/1.4)^2 divided by loudspeaker impedance like 4 Ohm gives 340 W until the power supply breaks down, what happens instandly (transformer is not heavy enough in the KM750, which gives some very rough indication of its capabilities). Both channels driven makes it even worse. As I only use mine to power two 4 Ohm/ 150W rms subs, they are perfectly OK for music and home theater. If I had needed a 200W/8Ohm rms amp, I would be disapointed.

Certainly the power numbers of the Behringer amps are not measured by technicians, but invented by marketing guys. From my personal experience this breed is less trustworthy than any used car dealer.
If you take this into account, the Behringer products are still a verry good deal, considering price and the extremely fair warranty. If you are clever, you may use them professionally for 3 years and then resell them, which in the end saves you 70% on expensive "top brands".
The iNuke amps are the worst in this power play. A 3000 W rated amp can not even deliver 300 clean rms watts into an 8 Ohm speaker. Anyway, the DSP versions are a very good way to a light and compact PA system for semi-professionals or HT users. Just include this fact into your decission if you buy one.

Some PA reviewers do not measure amp power, but connect walls of real loudspeakers and play some reference tracks. Then they judge how loud the amp can play without quitting. That gives some idea how it really performs. Not very scientific but practical for an honest review. If such a thing exists...
Today it is too easy to design an amp that deliveres huge power in a test situation, but shuts off in real stage situations after 2 minutes.
 

Wolf11Man

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PS you could not do 2x400W rms /4ohm with this amp anyway, as the capacitors are only rated 63V.
I consider mains overvoltage, wheight of transformer and typical load /voltage behavior of an unregulated trnsformer power supply. Does not match up...
 
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djtetei

djtetei

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@Wolf11Man Thank you very much indeed for sharing your experience with the KM 750.
Earlier, this month I opened a support ticket at Behringer to ask for more details about the real life capabilities of the KM750 and KM1700 and Behringer representative answered as follows:
- Behringer KM 750 would be able to deliver about 130 W continuous / 210 W peak at 8 ohms
- Behringer KM 1700 would be able to deliver about 300 W continous at 8 ohms
The reason I made the inquiry was to give Behringer a try and offer it the chance to prove itself, both at declarative level and on the field.
Until now I never used a Behringer amplifier as I never has problems with the Crown models I use.
About two days ago, I opened another support ticket at Behringer to ask for details about the standards, methods and guidelines they follow or abide by regarding their amplifiers power ratings.
I still wait for an answer from them and I will post their point of view.
 
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