Hi Ho!
...back again....
During last time I had again the chance to do some examinations for
my SubWoofer project.
Active system with SMPS and Class-D amp.
During my last examinations I was curious about the power crest factor.
This ratio is important for me because especially the SMPS will have to handle high peak power, but the thermal design does not need to allow 1kW all the time.... and I guess the speakers voice coil has also some sort of privat opinion regarding survivable average power...
I measured some power crest factors in my current sub woofer, in order to get the information about the music program behind all the filters...
I "measured" the speaker signal for 5sec. with 2ks/s.
2ks/s is OK to measure the low frequency signal of a sub, but
5 sec. is just a short sequence from the entire song. I played
around and the values seem to be quite reproducable at various
positions of the songs.
I just measured the voltage and calculated the power.
...yes, you are right the real power might be different due to
the complex impedance of the speaker...
But just for getting a feeling about the power ratio, this method should be OK.
My findings for the power crest factor ...so far:
"Eye In The Sky" by Alan Parson : about 24
"Without Me" by Eminem: about 20
Some ordinary pop song with additional noise from the radio (still searching title....) : about 16
Attached "Eye In The Sky".
Would be interesting to hear which ratios you might have observed.
Cheers
Markus
...back again....
During last time I had again the chance to do some examinations for
my SubWoofer project.
Active system with SMPS and Class-D amp.
During my last examinations I was curious about the power crest factor.
This ratio is important for me because especially the SMPS will have to handle high peak power, but the thermal design does not need to allow 1kW all the time.... and I guess the speakers voice coil has also some sort of privat opinion regarding survivable average power...
I measured some power crest factors in my current sub woofer, in order to get the information about the music program behind all the filters...
I "measured" the speaker signal for 5sec. with 2ks/s.
2ks/s is OK to measure the low frequency signal of a sub, but
5 sec. is just a short sequence from the entire song. I played
around and the values seem to be quite reproducable at various
positions of the songs.
I just measured the voltage and calculated the power.
...yes, you are right the real power might be different due to
the complex impedance of the speaker...
But just for getting a feeling about the power ratio, this method should be OK.
My findings for the power crest factor ...so far:
"Eye In The Sky" by Alan Parson : about 24
"Without Me" by Eminem: about 20
Some ordinary pop song with additional noise from the radio (still searching title....) : about 16
Attached "Eye In The Sky".
Would be interesting to hear which ratios you might have observed.
Cheers
Markus
Do I understand that you're measuring crest factor, as defined as the ration of the Peak to the RMS value of a waveform, of an audio signal? I deal with crest factor with my work on power supplies and inverters. A crest factor of 2.5 to 3 is considered high. You've seen a C.F of 24 with an audio signal? I'm not in a position to dispute your data. I'm just amazed that it could be that high.
Crest Factor - definition?
I agree with d3imlay. When I was in the UPS / power protection business "Crest Factor" was defined as the ratio of the peak current drawn by the load over the RMS current drawn by the load. If the UPS was powering a simple load then the "sine wave" crest factor of 1.414 would apply and little consideration was given to the UPS "Crest Factor" capability.
However if the UPS was powering a complex load (switching power supplies, wierd lights, some lab / medical equipment) then cosideration had to be given to repetitive peak currents drawn by the load. This could produce crest factors as high as 2 or 3 which meant that the UPS had to be able to deliver repetitive current peaks 2-3 times the RMS value.
A little long winded I know but I wonder whether we are talking about the same thing.
ChocoHolic seems to be talking about a type of music dynamic range capability and has termed it as "Crest Factor". This is outside the definition that I learned. Not saying it's not correct as often the same words are understood differently in different applications.
So ChocoHolic are you defining the power peaks contained in a music sample when compared to the average or are you defining something else?
Cheers
I agree with d3imlay. When I was in the UPS / power protection business "Crest Factor" was defined as the ratio of the peak current drawn by the load over the RMS current drawn by the load. If the UPS was powering a simple load then the "sine wave" crest factor of 1.414 would apply and little consideration was given to the UPS "Crest Factor" capability.
However if the UPS was powering a complex load (switching power supplies, wierd lights, some lab / medical equipment) then cosideration had to be given to repetitive peak currents drawn by the load. This could produce crest factors as high as 2 or 3 which meant that the UPS had to be able to deliver repetitive current peaks 2-3 times the RMS value.
A little long winded I know but I wonder whether we are talking about the same thing.
ChocoHolic seems to be talking about a type of music dynamic range capability and has termed it as "Crest Factor". This is outside the definition that I learned. Not saying it's not correct as often the same words are understood differently in different applications.
So ChocoHolic are you defining the power peaks contained in a music sample when compared to the average or are you defining something else?
Cheers
Crest Factor
So there's a need of crest factorization.
The Crest Factor in audio amplifiers is defined as"
"The ratio of Peak amplitude of Musical Transient in terms of voltage TO continuous average amplitude of musical signal at -3dB point "
The Crest factor ranges from 3 to 20 in professional amplifiers, provided with less power supply sagging.
regards,
kanwar
So there's a need of crest factorization.
The Crest Factor in audio amplifiers is defined as"
"The ratio of Peak amplitude of Musical Transient in terms of voltage TO continuous average amplitude of musical signal at -3dB point "
The Crest factor ranges from 3 to 20 in professional amplifiers, provided with less power supply sagging.
regards,
kanwar
Crest Factorisation
ChocoHolic's view seems to be ralated to signal sources rather than an amplifiers specifications.
"The ratio of Peak amplitude of Musical Transient in terms of voltage TO continuous average amplitude of musical signal at -3dB point " also seems to relate to the signal rather than the amplifier.
So how can a crest factor be applied to an amplifier?
Is it related to the SOAR of the output stage i.e current capability for 100ms 10ms 1ms etc? Or Workhorse are you talking about the dynamic range of the amplifier that is normally expressed in dB?
I know that some amplifiers are rated for momentary peak current capability, is this the "crest factor" for amplifiers?
Cheers
ChocoHolic's view seems to be ralated to signal sources rather than an amplifiers specifications.
"The ratio of Peak amplitude of Musical Transient in terms of voltage TO continuous average amplitude of musical signal at -3dB point " also seems to relate to the signal rather than the amplifier.
So how can a crest factor be applied to an amplifier?
Is it related to the SOAR of the output stage i.e current capability for 100ms 10ms 1ms etc? Or Workhorse are you talking about the dynamic range of the amplifier that is normally expressed in dB?
I know that some amplifiers are rated for momentary peak current capability, is this the "crest factor" for amplifiers?
Cheers
I think you need to evaluate the frequency content of the program material also. Depending on where the energy is mostly concentrated you will gain some “dynamical power” by having a higher non loaded rail voltage and more caps. This gives you a lower RMS output power, but it might sound better.
Of cause this is a question of budget, and some might argue that the biggest transformer and the most caps you can fit into the chosen enclosure will be the optimal choice.
A friend of mine Peter John Chapman did an AES paper on the frequency content of different program material, I don’t remember what it is called, but try looking it up.
\Jens
Of cause this is a question of budget, and some might argue that the biggest transformer and the most caps you can fit into the chosen enclosure will be the optimal choice.
A friend of mine Peter John Chapman did an AES paper on the frequency content of different program material, I don’t remember what it is called, but try looking it up.
\Jens
Hi Ho!
Sorry that I did not look to this thread that long.
I am glad to see that there were coming more answers.
Great.
Yes of course, I borrowed the naming crest factor.
And definition in regard is not very clear.
I defined my power crest factor as:
cfp = max. instantanious power / average power
mathematical this is equal to
cfp = (Umax^2 / R) / ( Urms^2 / R ) = Umax^2 / Urms^2
The voltage crest factor would range between 4.4 - 5.
The same with the current crest factor, if we assume constant
resistive load (stupid assumption).
For the PSU this large ratio means that you will need a supply that
can deliver very high power for some time without sagging. Typical for around 0.1 s ... 0.3 s. But thermally you do not need to design it for continous peak power.
In a regulated SMPS this will give the provision for much smaller
designed inductive components. You will have to be able to handle the full power without saturation in storage magnetics (flyback or boost preregulator) and provide good coupling in forward magnetics. But thermally the demands are much more relaxed compared to continuos power applications. This will allow smaller
core sizes with higher number of turns with thinner wire (less number of strands in HF-litz) as long as the leakage inductances are
acceptable.
@Jens:
Yes , I agree to your sight that the frequency content is important.
In my application (subwoofer) the frequencies are low and peak load durations 0.1s...0.3s are that long, that the required caps would blow the planned geometric size of my subwoofer....
@Peranders:
Would you call music something discontinous or even interruptive?
Sorry that I did not look to this thread that long.
I am glad to see that there were coming more answers.
Great.
Yes of course, I borrowed the naming crest factor.
And definition in regard is not very clear.
I defined my power crest factor as:
cfp = max. instantanious power / average power
mathematical this is equal to
cfp = (Umax^2 / R) / ( Urms^2 / R ) = Umax^2 / Urms^2
The voltage crest factor would range between 4.4 - 5.
The same with the current crest factor, if we assume constant
resistive load (stupid assumption).
For the PSU this large ratio means that you will need a supply that
can deliver very high power for some time without sagging. Typical for around 0.1 s ... 0.3 s. But thermally you do not need to design it for continous peak power.
In a regulated SMPS this will give the provision for much smaller
designed inductive components. You will have to be able to handle the full power without saturation in storage magnetics (flyback or boost preregulator) and provide good coupling in forward magnetics. But thermally the demands are much more relaxed compared to continuos power applications. This will allow smaller
core sizes with higher number of turns with thinner wire (less number of strands in HF-litz) as long as the leakage inductances are
acceptable.
@Jens:
Yes , I agree to your sight that the frequency content is important.
In my application (subwoofer) the frequencies are low and peak load durations 0.1s...0.3s are that long, that the required caps would blow the planned geometric size of my subwoofer....
@Peranders:
Would you call music something discontinous or even interruptive?
ChocoHolic said:
Some music has deep sustained bass - Pink Floyd seems to love shaking the room. The Vangelis soundtrack for Blade Runner is another example: it has several seconds of a 25 Hz (I think, the scope's elsewhere) sinusoid about 1 minute into track 1. If your subwoofer uses a Linkwitz transform to extend F3, that'll push your supply requirements higher than with music.
If you're using the subwoofer for home theatre, then you're looking at some demanding requirements when Ahnuld blows something up or Tom Cruise shoots down a Bad Guy.
http://www.svsubwoofers.com/faq.htm#moviedemos
is a good site for frequency/time/amplitude measurements of movie bass.
Francois.
Good point!
I should include Pink Floyd to my measurements.
My current design plans would limit the time extend by
the speed of thermal heat up of the magnetics. So one minute
1kW will probably be still in range....
But also the speakers voice coil will be critical!
The sadhara is specified for 1kW, but this IEC test has also
a crest factor and thermal average power is 25% of the stated values.
Movies:
I remember one movie, which gives crunching and deep rumpling for an quarter of an hour: Space Cowboys, Clint Eastwood's guy's chilling around on the asteroid....
I guess every subwoofer has it's limits.
On the other hand: Two sadhara cubes in normal living room should
be acceptable. I do not need continously 130db/15Hz.
BTW:
I also did my measurements at a subwoofer which extends f3 from
156Hz down to around 15Hz. Quite mad, but it works..... If you appreciate to deal with several kW in a normal living room.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=25015&highlight=
The results did not differ that much. The reason is that the power spectrum is already heavily dominated by the bass in the normal signal.
I should include Pink Floyd to my measurements.
My current design plans would limit the time extend by
the speed of thermal heat up of the magnetics. So one minute
1kW will probably be still in range....
But also the speakers voice coil will be critical!
The sadhara is specified for 1kW, but this IEC test has also
a crest factor and thermal average power is 25% of the stated values.
Movies:
I remember one movie, which gives crunching and deep rumpling for an quarter of an hour: Space Cowboys, Clint Eastwood's guy's chilling around on the asteroid....
I guess every subwoofer has it's limits.
On the other hand: Two sadhara cubes in normal living room should
be acceptable. I do not need continously 130db/15Hz.
BTW:
I also did my measurements at a subwoofer which extends f3 from
156Hz down to around 15Hz. Quite mad, but it works..... If you appreciate to deal with several kW in a normal living room.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=25015&highlight=
The results did not differ that much. The reason is that the power spectrum is already heavily dominated by the bass in the normal signal.
ChocoHolic said:
You're a nut, and I mean that in the nicest possible way!
Seriously, one of the reasons for reasonably efficient systems is to avoid dynamic range compression. Copper has a positive temperature coefficient, and if your voice coils run up to 80C (which is pretty darn hot), their resistance will increase by about 30%, increasing the system Q by roughly 30% and also lowering your efficiency by a couple of dB.
That's why horn systems tend to sound so lively - unless you run them at insane volumes, the power dissipated in the voice coils is low enough that thermal compression is a non-issue.
Anyway, looking at your pentagon, the cabinet shape is almost irrelevant at subwoofer frequencies. Assuming crossover at 100 Hz, and say you want to keep away from internal resonances an octave above xover, say 200 Hz, you then are working with a wavelength of about five feet (1.5 metres). The most obvious resonance is a half-wave between opposing panels, so if you keep the subwoofer dimensions below 2.5 feet (0.75 metres), the cabinet shape drops out of the equation even at an octave above xover. Panel stiffness is far more important.
On the other hand, once you set up your sadharas, you can use those nice little Dynaudios for mid-bass above your subwoofers.
Then the cabinet shape becomes of more interest, but that's a discussion for another time.
Cheers,
Francois.
... a theater? 
Sorry, no. I just love to play around and check out
if ideas do work.
I am coupling the subwoofer around 45Hz.
....just adding what my normal speakers cannot handle.
Subwoofers which are coupled above 60Hz, always give me the
impression that there is a separately placed bass source.
Yes, it's clear that the small size does not allow resonances at
the operating frequency. No matter, which cabinet shape.
But I loved that design idea... and still do.
Thermal time constant of the voice coils is high, so it does not compress some single bass sequences.
11 voice coils with 75mm diameter need some time to be heated.
Even if playing with a 1.2kW amp.
So thermal compression should no be audioable here.
Quite different from firing one 100mm voice coil with
1kW as it is usually done..
Of course if playing loud full power for a long time then
the Q will rise (not so critical, as I run the system more than 2 octaves below it's resonance) and the efficiency may drop 1.1db...
Hm, I guess except during testing... the voice coils probably never saw temperatures above .... hm , no idea ... probably not above
25°C = ambient + 0 .....
Don't ask why I need two sadharas......
Sorry, no. I just love to play around and check out
if ideas do work.
I am coupling the subwoofer around 45Hz.
....just adding what my normal speakers cannot handle.
Subwoofers which are coupled above 60Hz, always give me the
impression that there is a separately placed bass source.
Yes, it's clear that the small size does not allow resonances at
the operating frequency. No matter, which cabinet shape.
But I loved that design idea... and still do.
Thermal time constant of the voice coils is high, so it does not compress some single bass sequences.
11 voice coils with 75mm diameter need some time to be heated.
Even if playing with a 1.2kW amp.
So thermal compression should no be audioable here.
Quite different from firing one 100mm voice coil with
1kW as it is usually done..
Of course if playing loud full power for a long time then
the Q will rise (not so critical, as I run the system more than 2 octaves below it's resonance) and the efficiency may drop 1.1db...
Hm, I guess except during testing... the voice coils probably never saw temperatures above .... hm , no idea ... probably not above
25°C = ambient + 0 .....
Don't ask why I need two sadharas......
Yes, my pentagon sub has a overall time constant around 1h.
For thermal equivalent schematic I would propose two staggered
RC time constants. In fact I did not examine this in detail.
Your simulation would be interesting for me!
I measured my voice coil temperatures by resistance measurement
at 15Hz. at this frequency you see quite accurate the same values
as Rdc (rechecked, of course).
I needed this values, in order two find the proper value for a slow average power limiter.
...and had to wait for about 2..3h in order to get stabilized values....
But we can make a simple calculation to get a brief idea about the
intial thermal ramping of the voice coils if fired with 700W.
700W is the value which matches to the max. linear excursion.
Let's assume that all of the 700W is transferred to heat.
Let's further assume that the speed of temperature rise
is limited by the thermal capacity of the voice coils.
No heat dissipation to the magnet.
The Esotecs have a moving mass of 15g. Aluminium voice coils
and aluminum coil wires..!
Let's guess about 10g of the 15g are the Aluminium of the voice coil
and wire (No chance to figure out the exact value).
Specific heat capacity of aluminium is 900 J / (kg x K).
Eleven Esotecs have 0.11kg aluminium.
700W for 1s makes 700 J.
Hm, so when fired with 700W, then the voice coils may heat up
with approx. 7 Kelvin / s ....
If we pick the temperature coefficient of aluminium (same as copper)
==> +38% every 100 Kelvin
We get about 2.7% increase of the resistance per second.
Means, a dynamic compression that makes a fading
of about 0.116 db every second.
Hm, OK... now I have a value.
But no idea if this is audioable......
For thermal equivalent schematic I would propose two staggered
RC time constants. In fact I did not examine this in detail.
Your simulation would be interesting for me!
I measured my voice coil temperatures by resistance measurement
at 15Hz. at this frequency you see quite accurate the same values
as Rdc (rechecked, of course).
I needed this values, in order two find the proper value for a slow average power limiter.
...and had to wait for about 2..3h in order to get stabilized values....
But we can make a simple calculation to get a brief idea about the
intial thermal ramping of the voice coils if fired with 700W.
700W is the value which matches to the max. linear excursion.
Let's assume that all of the 700W is transferred to heat.
Let's further assume that the speed of temperature rise
is limited by the thermal capacity of the voice coils.
No heat dissipation to the magnet.
The Esotecs have a moving mass of 15g. Aluminium voice coils
and aluminum coil wires..!
Let's guess about 10g of the 15g are the Aluminium of the voice coil
and wire (No chance to figure out the exact value).
Specific heat capacity of aluminium is 900 J / (kg x K).
Eleven Esotecs have 0.11kg aluminium.
700W for 1s makes 700 J.
Hm, so when fired with 700W, then the voice coils may heat up
with approx. 7 Kelvin / s ....
If we pick the temperature coefficient of aluminium (same as copper)
==> +38% every 100 Kelvin
We get about 2.7% increase of the resistance per second.
Means, a dynamic compression that makes a fading
of about 0.116 db every second.
Hm, OK... now I have a value.
But no idea if this is audioable......
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