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opus jody View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote opus jody Quote  Post ReplyReply Direct Link To This Post Posted: 12 June 2022 at 9:55am
IDK the answer, but speaker impedence isn't actually constant, it's frequency dependent.

Improvised Hardware Music http://vimeo.com/user9389813/videos
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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 12 June 2022 at 10:45am
What I meant was that when comparing power delivered into a speaker, impedance is a constant.

At whatever frequency, providing you are using the speaker and the same box, the load presented to the amplifier is the same.




Edited by Randy Bohannon - 12 June 2022 at 4:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 12 June 2022 at 1:48pm
Originally posted by Randy Bohannon Randy Bohannon wrote:

Originally posted by toastyghost toastyghost wrote:

Originally posted by opus jody opus jody wrote:


Bridging:
Setting the amp for bridge mode links the 2 channels in the amp, so that the 2 channels have one, much higher output, but it can typically only drive 8ohm = one driver.

It's basically a cheap trick to turn a low power 2ch amplifier into one higher output channel, or a way of getting ridiculous wattages into a particularly high power single cone / sub (like in car audio), and I've yet to hear a bridged anp that sounds as good as 'normal' 2ch mode.


wweeeeeeellllll the thing is the Watts aren’t what you’d really want more of. The peak voltage capability is what makes the speaker move and handle the peaks for dynamic, good music. Bridging was / is a way to get an amplifier to be able to handle the exceptional peak voltage demands for unclipped music transients.

The AES75-20222 (M-Noise) peak SPL testing standard has a good example; a loudspeaker with an 8-ohm nominal impedance and AES power rating of 200W covering the midrange (anything above 500Hz) needs 400V of unclipped peak voltage swing to avoid being limited by amplifier capability when playing most music signals.



A Crest Factor of 10 is equivalent to 20dB from RMS to peak.

These numbers aren't just plucked out of thin air either. They're the result of analysing a lot of music files and live concerts.

I’m trying to work this all out so please bear with me if my questions are silly.

Isn’t it same thing to talk about power and voltage in this context? Given that speaker impedance is a constant, x volts equals y watts doesn’t it or have I missed something?

A crest factor of 20dB on 200w average… that’s 20k isn’t it?!




isn't a music signal crest factor of ~10db on the POWER of the signal not the voltage.

this seems to say so under 'test signals' section where they talk about a 12dB crest factor on power
Loudspeaker SPL Expectations and Reality | Danley Sound Labs

this suggests a range of 6dB-20dB on power - but surely 20dB is on stuff like classical recordings not rock or dance music
Understanding The Nuances Of Crest Factor - ProSoundWeb
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Post Options Post Options   Thanks (1) Thanks(1)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 12 June 2022 at 10:14pm
Originally posted by Randy Bohannon Randy Bohannon wrote:

What I meant was that when comparing power delivered into a speaker, impedance is a constant.

At whatever frequency, providing you are using the speaker and the same box, the load presented to the amplifier is the same.





No it isn’t. The electrical impedance changes with the acoustical load, including temperature increase and other non-linear behaviours of the transducer and cabinet.

Regardless of this; you also need to consider the difference between apparent power and real power. This is super important since loudspeaker power ratings are calculated from the measured voltage and nominal (or lowest) impedance in the passband - depending on the testing standard used.

20dB crest factor is also very prominent in popular music, at the high frequencies. I suggest reading the AES75-2002 standard document and the papers related to the M-Noise test signal.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sam012 Quote  Post ReplyReply Direct Link To This Post Posted: 14 June 2022 at 12:34am
Originally posted by fatfreddiescat fatfreddiescat wrote:

Not sure what your paying for the RMX's but could look at an FFA, save a lot of lugging, those RMX's make my back heart just looking at them.

The Blue Aran Jam amps are £1250 for the K16, I understand there's difference in quality between K16 + FFA6004 but my inexperience fails me completely in which would be better at this price point. 

The JAM amps haven't cropped up as being problematic from my googling?

Would running 8ohm @ 1600w not be better than FFA which is 4 ohm @ 1500w?

To answer my own question after some thought, the only benefit really is the extra ~100W of headroom for £700 less but opting for a chinese made amp (numbers below) over picking say a FFA 6004

The main amp picking issue I'm having is seeing anecdotal comments saying stuff like the "k10 sounds bad imo, the k20 is better" so I sort of have ADHD on which amp to finally decide on - as the search goes on the budget goes up and up, bringing me back to maybe I should just get the cheaper JAM amp

K16 £1250
4 channel mode:
8 ohm: 4 x 1600W
4 ohm: 4 x 2800W
2 ohm: 4 x 3500W

Soundgear Saturn 16 £1080:
8ohm: 4 x 2100w
4ohm: 4 x 4200w

FFA - 6004 ~£1800 ebay
8ohm: 4 x 900W
4 Ohm 4 x  1500W 



Edited by sam012 - 14 June 2022 at 1:10am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote VECTORDJ Quote  Post ReplyReply Direct Link To This Post Posted: 14 June 2022 at 4:24am
QSC Amps are A+
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KDW32 Quote  Post ReplyReply Direct Link To This Post Posted: 14 June 2022 at 8:28am
Originally posted by sam012 sam012 wrote:

I'm debating buying 2 x QSC RMX 4050a but a bit confused on the specs

Running 4 x Void V12 1000

I couldnt find any info on a void V12 1000  did you mean 18 or have I missed so something googling? 
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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 14 June 2022 at 4:42pm
Originally posted by toastyghost toastyghost wrote:

Originally posted by Randy Bohannon Randy Bohannon wrote:

What I meant was that when comparing power delivered into a speaker, impedance is a constant.

At whatever frequency, providing you are using the speaker and the same box, the load presented to the amplifier is the same.





No it isn’t. The electrical impedance changes with the acoustical load, including temperature increase and other non-linear behaviours of the transducer and cabinet.

Regardless of this; you also need to consider the difference between apparent power and real power. This is super important since loudspeaker power ratings are calculated from the measured voltage and nominal (or lowest) impedance in the passband - depending on the testing standard used.

20dB crest factor is also very prominent in popular music, at the high frequencies. I suggest reading the AES75-2002 standard document and the papers related to the M-Noise test signal.

Thanks for taking the time to explain it further. :)

The impedance load that a particular speaker presents, in a particular box and assuming the same programme material is a constant if all that is being varied is the amplifier(s) testing it, surely? 

Thanks you for the references, I couldn’t track down a public domain copy of that paper but read up on The idea behind the M tone and it makes sense to me. The ran a few tracks through a spectral analyser and can see how they arrived at their conclusions.

The 20 dB crest factor you mentioned makes more sense l, being primarily a function of high frequency content, as the average power content of this portion of the musical spectrum is lot lower in power than than the lower frequencies.

So, if I have understood correctly, if the average programme rms if the woofer is 200w, the tweeter might be getting 10w and the 20dB crest factor on 10w seems more realistic.

Why does that mean quoting power in voltage, which is independent of impedance and voice coil/cabinet reactance, is that preferable to power, which accounts for impedance by factoring in current, or indeed VA and phase which would be needed to calculate real AC power? 


Edited by Randy Bohannon - 14 June 2022 at 4:42pm
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