Power needs across audio spectrum in active setup

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One good way has been pointed to for years in my signature line. ;)

Do you really need 116dB average out of a domestic sub? Meaning peaks of 130dB or more? That's kinda nuts unless you have a really big room. Then you'd want multiple drivers anyway.

Yep, i thought you'd say that about sig line :)

Yeah, that kinda bass is kinda nuts, but damn it's so much fun :D
For me, it completely changes the emotional impact of many tunes.

Current room is about 8-9k cu ft. Standard sub rig is a pair of ppsl dual 18"s.
Outside, or every now and then inside when I'm '99 shades of crazy', i pull in some horn loaded subs to augment.
 
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I can't see RMS as static unless we're talking periodic waveforms, it's certainly not for music or even pink noise.
So over some measured time interval, it will have an average value, a minimum value , and a maximum value which i was calling peak RMS.
I'll use the term maximum RMS from now on to avoid confusion.

I measure these three RMS values fairly often, for both music and pink noise.
I've found pink as dense as it is, can measure +3dB maximum RMS to averaged RMS over given intervals.

It's one of the issues I have with substituting a sine wave as a surrogate to determine amp voltage like in your test. Misses the temporal RMS maximums, I think.
The second is using a single frequency surrogate to represent the average of all the passbands' voltages.

In my world, all 0dBFS means is that I don't have any digital clipping; it doesn't have anything to do with the maximum output of any particular passband.
When you say "maximum RMS" (which again is not a proper term), are you referring to the crest factor?

Crest factor - Wikipedia
 
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Sure a music signal can have different average levels if you look at different parts of the song. Take any Cat Stevens song, it's a long crescendo from beginning to end. :)

But that's not what I'm talking about and not a fair measure. If you take the average level of a whole song - you have what? A long term average of 2-4 minutes. How far is that average below peak? That's the peak to average ratio. Now look at the average of each track on an album. With genres like rap, pop, rock, jazz, country - you'll find the average levels pretty constant across the album. That's what mastering engineers do to keep the song to song volume consistent.
 
When you say "maximum RMS" (which again is not a proper term), are you referring to the crest factor?

Crest factor - Wikipedia

No, not crest factor at all. That's a well defined terminology / relationship between peak and RMS.

When I say, 'maximum RMS', I mean RMS compared to RMS....and to be exact with the relationship to average RMS...

...the average RMS value over a time period, compared to the maximum RMS value within the same time period.

Hope that makes sense......do you know a more proper term for that?
 
.....the FTC stepped in and came up with the 1/3 power 1 hour preconditioning requirement prior to full power testing. BGW was OK with it Dynaco's position was that it was a little too much.
Interesting article---thanks for the link. I had to laugh at Dynaco's position, though---I had a Dyna 400 and it was a real P.O.S.---that damn thing blew up on me so many times that I finally just got tired of replacing the output transistors time and again and I just dumped it in the nearest recycling bin. It did sound pretty good....when it was working!! My Peavey CS-800, on the other hand, has been a brute and never failed in all these years---a really robust design!
 
Thanks for checking on me Chris. The different numbers come from this:

I started with 40 volts peak, and and counted a typical RMS value 12dB below that, or 40/4=10 volts.
You started with 40 volts peak and lowered that by 12 dB to get 10 volts peak. Then divided by square root of 2 to get 7.07 RMS.

I counted the RMS values as 12 dB below peak, you counted peak as 12dB below peak, and figured RMS from that. Thus a 3dB difference.

Makes perfect sense, thanks.



It might be worth having a look here: https://www.powersoft.com/wp-content/uploads/2019/03/Powersoft_AN_Power_Sharing_RackAmps.pdf

Scroll down to Table 2 (or read the whole thing if you like, but it's not particularly relevant to this thread) and it shows the expected dynamic range for different passbands.
They haven't given crossover frequencies, though.

I'm also not entirely sure where we ought to plug those numbers into the equations, if anywhere.

Chris
 
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Thanks for the link, I just looked at table 2. We don't know the crossover frequencies or the test signal, but the crest factors do look close to what I've seen with moderately compressed pop that sits at the typical -16dB. The lower the frequency band, the lower the crest factor.
 
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Wow, had no idea about LUFS. Good stuff.
Yes, it's quite a step forward in determining loudness levels. The K-weighting takes into account the sensitivity of the ear, while the gating eliminates the worries of differing RMS across the song or track.

The K-weighting would not be used in our situation of figuring out the peaks and averages of each band. The gating could be useful but I have not found it to be a big deal with most music tracks. For dialog it could make a significant difference.
 
Very much appreciate the help. Directionally, it seems I would be ok. If the midrange demands 0.15 or 0.30A it's basically still ok as the 2A3 can deliver 4W and I'd like to keep it under 2W and hopefully under 1W.

Even if it took 0.3A to deliver the target 95dB SPL (cell B4), at 0.6A it would deliver 98dB, at 1.2A it would be at 101dB. Seems ok, unless I need to factor in additional 15dB for peaks and then target would turn to be 95+15=110dB and the setup wouldn't suffice.

So B4 is supposed to be RMS and the calcs account for peaks too, right? Then ball park 100dB at 1.2A would be enough, even starting from twice the current demand the spreadsheet calculated.
Updated version here
 

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Makes perfect sense, thanks.



It might be worth having a look here: https://www.powersoft.com/wp-content/uploads/2019/03/Powersoft_AN_Power_Sharing_RackAmps.pdf

Scroll down to Table 2 (or read the whole thing if you like, but it's not particularly relevant to this thread) and it shows the expected dynamic range for different passbands.
They haven't given crossover frequencies, though.

I'm also not entirely sure where we ought to plug those numbers into the equations, if anywhere.

Chris

Sorry I missed this post. Thanks for the link.

Looking at table 2, they note 19.8 dB peak vs average for high frequency. I realize we don't know where their "high" frequency starts. Am I right to interpret that if my goal is to listen at [say] 90dB SPL for the high frequencies, then I need an amp with 20dB headroom playing clean? So a 2A3 with a 102dB sensitivity tweeter wouldn't cut it.

It would work, however, if my goal was to listen at 84dB at high frequencies, so then I would have 20dB headroom so that peaks took up to 2W or 50% of rated power. This is good food for thought. Need to go back and check the posts where music was plotted and showed high frequencies demand lower SPL for music material.

I guess I'll come back to the midrange being the constraint, yet good to be improving my understanding.

BTW, was the above reasoning ok? :eek:
 
If you are listening to the tweeters at an average SPL of 90dB, or even 84 you must have a large room. Have you ever tried to measure?

I am not. I was using it as reference only. When I listen to music I mostly do at 85 to 90dB SPL weight C, which of course is an average of all frequencies and average over time.

From the spectrum analysis you posted on #41, high frequency is about 14dB below midbass and subs when a given SPL is measured while playing music. So definitely my tweeters aren't operating at 90dB on average.

From the same spectrum analysis I recall midrange was 6dB down from midbass and subs. So if I take 90dB SPL measured on a radio Shack handheld at the listening point, then probably the midranges are playing at 84dB. If the midranges were 100 dB sensitivity, then a 2A3 amp would have 18dB headroom (per table 2 on the above link) playing at 2W/50% rated power. This assumes 103dB SPL at 2W which works back into 0.03W at 85dB SPL.
So I would be measuring 90dB at the listening point and the 2A3 driving the midranges would be cruising and with appropriate headroom.

of course all of this is IF I had a proper 100 dB sensitivity midrange, which is another subject altogether!!
 
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Ha ha, yes! 100dB/watt midrange is probably going to be horn loaded. Maybe there is a direct radiator mid that can do 100dB across its bandwidth, but I don't know it.

Your numbers above look about right to me. I suppose that you could mesure SPL section by section to get a better idea.
 
Yeap. I'm starting to experiment with MTM for midrange and tweeter, where the midranges are two B&C 8PE21, that are spec'd at 98dB sensitivity by the manufacturer, so roughly I'm assuming 1 dB less than spec'd and twins to provide 100dB. Of course MTM with 8" mids...isn't exactly mainstream. Let alone throwing a huge tweeter in between: Beyma TPL-150H...time for experimentation, which I'm doing on a separate thread.

A lot of variables up in the air: MTM or TM, which drivers, which amps, room. I'll decide MTM vs TM and drivers first, then I will go for amps. But this thread has helped me mature the way to think about amp needs. And I'll be treating the room, especially the ceiling, so also something to consider when thinking MTM and lobbing effects.

Fun!

Thanks for helping in my learning!!!
 
Here's some power and voltage measurements of an active 4-way that may be of interest.

The 4-way consists of a double 18" bass reflex sub,
and the PM60 top which is a double 12" horn loaded mid,
around a bms 4594he coax CD on a xt1464 horn.

Frequency ranges, measured sensitivity, and specified nominal and measured nominal impedance are in the upper chart section.

The lower section shows the volts, amps, and wattage to drive each section to equal SPL.

The measurement technique is to put processing in place for all 4 bands such that there is flat frequency response across the entire 30Hz-20kHz spectrum.

I used 2.0v as the reference voltage, since both the sub and mid sections are 4 ohm nominal on the spec sheet.

For about 1 min, i take an average SPL-flat measurement, against an average 2.0v rms pink noise signal.
So both SPL and voltage are averages taken over the same interval,
and become the actual measured sensitivity of the entire band.

I measure current the same way, an average over the same time interval.
A little ohms law, and i get actual measured nominal impedance of the entire band.

This is just RMS...i think next time i'm set up to do this sensitivity process, I'll try to grab some peak voltage readings. But to me, even without peak, the trend is pretty clear as to where power and headroom are needed.
 

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