60 Degree DIY Mid Hi - AKA PM60

Re: 60 Degree DIY Mid Hi

Art Welter said:
The AES measurement we are talking about uses a peak-to-rms voltage ratio of 2:1, limiting the 12 dB crest factor pink noise to a 6 dB crest factor.
Back in the "olden days" (pre-1984), the "RMS watts" used to test speakers were sine waves (same as used for rating amplifiers) which have a crest factor of 3 dB.

I'm so old that if there is not a reference to AES I still assume a sine wave for "RMS" watts...
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Yes but the AES measurement is calculated from the RMS voltage squared divided by the minimum impedance. So if the load was a resistor the AES and "RMS" power would be the same. Accordingly the AES and RMS ratings are similar. The AES measurement uses one octave of shaped pink noise. I think the RMS test was done a 1KHz ...

Given that the AES is made in free air, its arguable the power handling should be measured in the actual enclosure over the nominal operating band, and referenced to the nominal impedance ... similar to what EAW do - http://eaw.com/docs/6_Technical_Information/StudyHall_and_TechNotes/Power_Handling.pdf
 

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Re: 60 Degree DIY Mid Hi

So after reading and re-reading the responses...it's still clear as mud. I was under the understanding the 4594 could use the c8/8 passive crossover, just as commercial speakers that are using the 4594 do with relative ease. With that being said, it appears I should just ditch the passive crossover and run HF and VHF on their own amp channels and frequency limit? Set the VHF to 50w with a 200w peak and the HF to 100w with a 400w peak... Sound like a plan?
 
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Re: 60 Degree DIY Mid Hi

Jason Allen said:
So after reading and re-reading the responses...it's still clear as mud. I was under the understanding the 4594 could use the c8/8 passive crossover, just as commercial speakers that are using the 4594 do with relative ease. With that being said, it appears I should just ditch the passive crossover and run HF and VHF on their own amp channels and frequency limit? Set the VHF to 50w with a 200w peak and the HF to 100w with a 400w peak... Sound like a plan?
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I think you could do either; it’s just that you will get more protection if you run it the BMS 2-way. How loud do you need to run? If it’s as loud as you can then I would go 2–way with the BMS.

2- way will also give you slightly better sound quality, ... just noticeable ... most people are happy with the sound quality of the passive crossover.
 
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Re: 60 Degree DIY Mid Hi

Thank you for the reply Peter. I am only trying to properly power the 4594 with no regard to total volume, but more so getting the box properly powered. I have read many responses and yet to get such a to-the-point answer. I would rather run it with the passive crossover for simplicity. So if I run the passive crossover, I should supply it with 100w with a 500w peak? And frequency pass band from about 650hz on up?
 
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Re: 60 Degree DIY Mid Hi

Peter Morris said:
The AES measurement uses one octave of shaped pink noise. I think the RMS test was done a 1KHz ...
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A 1kHz (or any frequency) sine wave has a crest factor of 3dB, twice the average power of the AES compressed and shaped pink noise signal having a 6 dB crest factor. Average power of double the AES rating will burn up a driver, unless the heating raises the impedance high enough so the delivered voltage does not result in too much power, but relying on thermal compression to protect high frequency drivers is pretty "iffy".

A "long term" limiter (which may be "short" in terms of one second) set to the AES "wattage" should be OK as long as the crest factor of the music played is greater than 6 dB, which would be the case for most mid/high musical content, but would be 3 dB too high for safety in the LF portion of many EDM tracks that have 3 dB or less crest factor below 100Hz.

Since high frequency acoustical feedback can go as low as 3 dB crest factor (rather quickly...), to be safe I'd still recommend 1/2 the AES for "long term" limiting, and up to double AES for "peak" limiting.

The Powersoft tech sheet linked in post #493 has guidelines on page 8 and 9 as to what is "long" in terms of attack/release times for various generic frequency ranges and driver types.
 
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Re: 60 Degree DIY Mid Hi

Art Welter said:
A 1kHz (or any frequency) sine wave has a crest factor of 3dB, twice the average power of the AES compressed and shaped pink noise signal having a 6 dB crest factor. Average power of double the AES rating will burn up a driver, unless the heating raises the impedance high enough so the delivered voltage does not result in too much power, but relying on thermal compression to protect high frequency drivers is pretty "iffy".

A "long term" limiter (which may be "short" in terms of one second) set to the AES "wattage" should be OK as long as the crest factor of the music played is greater than 6 dB, which would be the case for most mid/high musical content, but would be 3 dB too high for safety in the LF portion of many EDM tracks that have 3 dB or less crest factor below 100Hz.

Since high frequency acoustical feedback can go as low as 3 dB crest factor (rather quickly...), to be safe I'd still recommend 1/2 the AES for "long term" limiting, and up to double AES for "peak" limiting.

The Powersoft tech sheet linked in post #493 has guidelines on page 8 and 9 as to what is "long" in terms of attack/release times for various generic frequency ranges and driver types.
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Hi Art, here's what I don't get..... the AES specs as explained in the EAW paper previously linked, say that measured RMS voltage is used, and that measured voltage is then used at minimum impedance to determine wattage.
I don't get what crest factor has to do with it....RMS is RMS ???

I realize AES is full of crap in a number of dimensions...one octave pink, true pink has 14db crest, minimum impedance, survival defined as less than 10% permanent damage to specs haha...but still doesn't measured RMS=RMS despite the waveform??
 
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Re: 60 Degree DIY Mid Hi

Mark Wilkinson said:
I realize AES is full of crap in a number of dimensions...one octave pink, true pink has 14db crest, minimum impedance, survival defined as less than 10% permanent damage to specs haha...but still doesn't measured RMS=RMS despite the waveform??
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Pink noise has unbounded (i.e. infinite) crest factor - on a very very long time scale! The common misconception that it has e.g. 12dB crest factor probably came about because basically all real world signals have a 12dB crest factor. Sounds crazy, but real signals as presented to loudspeakers are pretty tightly band-limited. A signal with lots of peaks will have the sine components that created them misaligned by the phase shift inherent in that band-limiting, reducing the peak to average ratio. A super-dense heavily limited signal, unless it is literally a single sine wave, will have some of its separate components aligned by that same phase shift - creating a higher peak to average ratio. Anyway, you can pretty much count on 12dB crest factor for music.
 
Re: 60 Degree DIY Mid Hi

Mark Wilkinson said:
Hi Art, here's what I don't get..... the AES specs as explained in the EAW paper previously linked, say that measured RMS voltage is used, and that measured voltage is then used at minimum impedance to determine wattage.
I don't get what crest factor has to do with it....RMS is RMS ???

I realize AES is full of crap in a number of dimensions...one octave pink, true pink has 14db crest, minimum impedance, survival defined as less than 10% permanent damage to specs haha...but still doesn't measured RMS=RMS despite the waveform??
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Exactly (other than as noted by Bennett) The whole point of using RMS Volts is that it can be used to determine the heat caused by the applied voltage even if it is not a sine wave.
https://en.wikipedia.org/wiki/Root_mean_square
 
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Re: 60 Degree DIY Mid Hi

Bennett Prescott said:
Pink noise has unbounded (i.e. infinite) crest factor - on a very very long time scale! The common misconception that it has e.g. 12dB crest factor probably came about because basically all real world signals have a 12dB crest factor. Sounds crazy, but real signals as presented to loudspeakers are pretty tightly band-limited. A signal with lots of peaks will have the sine components that created them misaligned by the phase shift inherent in that band-limiting, reducing the peak to average ratio. A super-dense heavily limited signal, unless it is literally a single sine wave, will have some of its separate components aligned by that same phase shift - creating a higher peak to average ratio. Anyway, you can pretty much count on 12dB crest factor for music.
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Thx Bennet, so I take what this means, is that the pink noise crest factor is really a function of whatever confidence interval we are imposing on the data (via hard limiting of the pink peaks I guess?).

I'm getting that we choose a crest factor that is designed to replicate crest factors measured (in music), and that 12db works.
I'm left wondering if maybe 12db works for live sound because the economics of amps and speakers have been, and still are, designed to support 12db, ..........and maybe no more????
Is there any difference in crest factor between amplified and unamplified music? Or with cinema sound? I see in this Meyer paper that a number of cinema folks use 14db or so. https://www.meyersound.com/pdf/cinema_technical_papers/cinema_calibration_tech_report.pdf

This also made me realize I've been confusing crest factor, with average music level vs transients.
If I'm thinking straight, I now see that crest factor is an instantaneous relationship between a waveform's RMS and peak values. And that avg music level vs transients is time dependent, more like avg RMS to peak RMS. From posts I've read, I'm thinking many of us with lesser experienced have suffered this confusion..
 
Re: 60 Degree DIY Mid Hi

Mark Wilkinson said:
Hi Art, here's what I don't get..... the AES specs as explained in the EAW paper previously linked, say that measured RMS voltage is used, and that measured voltage is then used at minimum impedance to determine wattage.
I don't get what crest factor has to do with it....RMS is RMS ???

I realize AES is full of crap in a number of dimensions...one octave pink, true pink has 14db crest, minimum impedance, survival defined as less than 10% permanent damage to specs haha...but still doesn't measured RMS=RMS despite the waveform??
Click to expand...
What crest factor has to do with it is a square wave with the same RMS value has twice the average power of a sine wave, which has twice the average power of the AES 6 dB crest factor pink noise, which has twice the average power of 12 dB "normal" pink noise, which is roughly the equivalent of compressed pop music.

As an example, in a listening test recently burned up a speaker rated at 40 watts AES. It sustained musical peaks of around 800 watts (80 volts peak RMS) producing over 126 dBA, but would have burned up in the same time period with a sine wave of 40 watts (17.9 volts RMS) at only 105 dB.

Bottom line for speaker protection is to use 1/2 AES "wattage" for long term limiting (slow attack and release), and (around) twice AES for peak limiting.

Art
 
Re: 60 Degree DIY Mid Hi

Art Welter said:
What crest factor has to do with it is a square wave with the same RMS value has twice the average power of a sine wave, which has twice the average power of the AES 6 dB crest factor pink noise, which has twice the average power of 12 dB "normal" pink noise, which is roughly the equivalent of compressed pop music.

As an example, in a listening test recently burned up a speaker rated at 40 watts AES. It sustained musical peaks of around 800 watts (80 volts peak RMS) producing over 126 dBA, but would have burned up in the same time period with a sine wave of 40 watts (17.9 volts RMS) at only 105 dB.

Bottom line for speaker protection is to use 1/2 AES "wattage" for long term limiting (slow attack and release), and (around) twice AES for peak limiting.

Art
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A one volt peak square wave has an RMS value of 1 volt; what we call a one volt sine wave has a 1.414 volt peak and an RMS value of 1. Both will produce the same heat when applied to a load (resistive).

Assuming you are using a quality processor it will use RMS detection to calculate the limiting, (this is what the Lake does) the shape or crest factor does not matter for determining the amount of heat the speaker is subject to.

There are basically two failure modes for a speaker, heat and exceeding the mechanical limits of the speakers design. It’s also important that any of the peaks that the RMS limiting functions permit, do not allow the mechanical limits to be exceeded and break the speaker. The Lake has peak limiting to take care of that.

There is also another fact you should take into account. If you continually driver a speaker close to its limit it won’t fail straight away but it won’t last long and you may suffer some form of early fatigue failure.

I do however think that a practical implementation is as you and Bennett suggested … about 3 dB less than the limits.
 

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Re: 60 Degree DIY Mid Hi

Peter Morris said:
A one volt peak square wave has an RMS value of 1 volt; what we call a one volt sine wave has a 1.414 volt peak and an RMS value of 1. Both will produce the same heat when applied to a load (resistive).

Assuming you are using a quality processor it will use RMS detection to calculate the limiting, (this is what the Lake does) the shape or crest factor does not matter for determining the amount of heat the speaker is subject to.

I do however think that a practical implementation is as you and Bennett suggested … about 3 dB less than the limits.
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Crest factor is the peak amplitude of the waveform divided by the RMS value of the waveform.

When expressed in decibels, crest factor and PAPR (peak-to-average power ratio) are equivalent.

The PAPR is most used in signal processing applications. As it is a power ratio, it is normally expressed in decibels (dB). The crest factor of the test signal is an important issue in loudspeaker testing standards, it is usually expressed in dB.

The minimum possible crest factor is 1, 1:1 or 0 dB for a DC or square wave signal, they have double the average peak-to-average power ratio of a sine wave (3.01 dB PAPR) and therefore will heat the voice coil (or resistor) twice as much.

This is the reason why clipping an amp will burn up drivers more than an unclipped amp. The voltage is no greater when clipped, there is just more average power delivered, and the harder the amp is clipped the closer it comes to delivering twice as much (+3dB) more average power than it's sine wave rating would indicate.

The AES compressed pink noise signal PAPR is 6 dB, half the PAPR of a sine wave, and about twice PAPR of (compressed) music.

Run a 700 Hz square wave through your Lake RMS detection and your driver will dissipate about 12 times more power (heat) than with music.
Don't believe it? Put your finger on an 8 ohm load resistor and try some acoustic music through it at limiter threshold, then repeat with a square wave and you will feel the difference a lot faster than it has taken to read about it.

Art
 
Re: 60 Degree DIY Mid Hi

Art Welter said:
Crest factor is the peak amplitude of the waveform divided by the RMS value of the waveform.

When expressed in decibels, crest factor and PAPR (peak-to-average power ratio) are equivalent.

The PAPR is most used in signal processing applications. As it is a power ratio, it is normally expressed in decibels (dB). The crest factor of the test signal is an important issue in loudspeaker testing standards, it is usually expressed in dB.

The minimum possible crest factor is 1, 1:1 or 0 dB for a DC or square wave signal, they have double the average peak-to-average power ratio of a sine wave (3.01 dB PAPR) and therefore will heat the voice coil (or resistor) twice as much.

This is the reason why clipping an amp will burn up drivers more than an unclipped amp. The voltage is no greater when clipped, there is just more average power delivered, and the harder the amp is clipped the closer it comes to delivering twice as much (+3dB) more average power than it's sine wave rating would indicate.

The AES compressed pink noise signal PAPR is 6 dB, half the PAPR of a sine wave, and about twice PAPR of (compressed) music.

Run a 700 Hz square wave through your Lake RMS detection and your driver will dissipate about 12 times more power (heat) than with music.
Don't believe it? Put your finger on an 8 ohm load resistor and try some acoustic music through it at limiter threshold, then repeat with a square wave and you will feel the difference a lot faster than it has taken to read about it.

Art
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Art ... sorry mate, but your not understanding RMS :)~:-)~:smile: or I'm not understanding your point ?? https://www.quora.com/Why-are-RMS-Root-Mean-Square-values-used-in-AC-circuits if its the same RMS value the shape of the wave form does not matter - it will produce the same amount of heat.
 
Re: 60 Degree DIY Mid Hi

Peter Morris said:
Art ... sorry mate, but your not understanding RMS :)~:-)~:smile: or I'm not understanding your point ?? https://www.quora.com/Why-are-RMS-Root-Mean-Square-values-used-in-AC-circuits if its the same RMS value the shape of the wave form does not matter - it will produce the same amount of heat.
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You are right, I misunderstood RMS as it relates to crest factor and wave shape, and was also under the mistaken impression that AES2-1984 "watts" are peak, when they are (or should be..) RMS. I also overlooked that the AES rating is free air for loudspeakers, and based on the minimum impedance, which for a free air speaker will be much lower than the average impedance, making the thermal rating higher than it typically would be in a cabinet.

Compression drivers are tested on a device which reasonably simulates the acoustical loading of a horn for the test, so their AES rating should be more indicative of real world use.

It is interesting that B&C's power ratings use a "continuous" rating double the RMS, when the speaker has met the AES2-1984 specification the peaks it withstood are four times the RMS rating.

BMS, on the other hand, shows the RMS wattage, and then "Peak" four times (or more) the RMS rating.

At any rate, as Bennett said "Fuuuuuuuuuck Peak", and use half the AES rating for long term compression.

Art
 
Re: 60 Degree DIY Mid Hi

Art Welter said:
You are right, I misunderstood RMS as it relates to crest factor and wave shape, and was also under the mistaken impression that AES2-1984 "watts" are peak, when they are (or should be..) RMS. I also overlooked that the AES rating is free air for loudspeakers, and based on the minimum impedance, which for a free air speaker will be much lower than the average impedance, making the thermal rating higher than it typically would be in a cabinet.

Compression drivers are tested on a device which reasonably simulates the acoustical loading of a horn for the test, so their AES rating should be more indicative of real world use.

It is interesting that B&C's power ratings use a "continuous" rating double the RMS, when the speaker has met the AES2-1984 specification the peaks it withstood are four times the RMS rating.

BMS, on the other hand, shows the RMS wattage, and then "Peak" four times (or more) the RMS rating.

At any rate, as Bennett said "Fuuuuuuuuuck Peak", and use half the AES rating for long term compression.

Art
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The BMS 4594 is interesting – they quote the power at 150W AES above 400Hz and 1000W peak above 500Hz. I assume the 1000W peak is to provide information about the mechanical strength and Xmax capabilities of the driver. Most compression drivers would have the diaphragm hitting the phase plug with that sort of input power at a 500Hz crossover point.
 
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