How big of an amp?

[etc6849]

I know my RF-83's I sold had nasty impedance swings in the lower frequencies.  A speakers impedance is never going to be 8 ohms, and if it drops to 4 ohms at certain frequencies it's going to require twice the wattage for a given voltage and if the amp's voltage rails aren't high enough to output that voltage at that impedance clipping will occur (whether I hear it or not) since P(t) = V(t)*V(t)/Z.

 

I remember when I bought an ATI AT2007 amp and put it on my RF-83's I immediately noticed an improvement in clarity and a reduction of harshness at peaks versus using my AVR only (even though a lot of folks on forums say there is no improvement).  Perhaps this is due to the higher voltage rails or the beefier power supply an external amp provides...

 

I have since switched to Emotiva XPR-1 mono blocks driving some used Palladium P-39f's.   When I playback tracks with a very high dynamic range (DR) I swear I hear less harshness at the peaks of certain tracks versus even my AT2007 multi-channel amp.  It is definitely there, although I only notice it on a few tracks out of a 50 demo tracks I have listened to many many times.  In fact, playing back some movies I've even seen the VU meters on these 100 lb mono blocks peak at 9-10/12 lights, and I can't help but wonder was my 200 watt @ 8 ohm multi-channel amp clipping before?  EDIT: the VU meter lights up like this even with my P-39f's crossed at 80 Hz to my subs.

 

Unfortunately, I suspect that even my AT2007 multi channel amp was clipping on my P-39f's during these types of transients as ChrisA pointed out that my P-39f's 3-4 ohm impedance dips at some lower frequencies:  http://www.stereophile.com/content/klipsch-palladium-p-39f-loudspeaker-measurements#GW4sqHo8o68YSMiY.97

Plus the VU lights on a 1000 watt mono block really light up at these same peaks, could my smaller multi-channel amp have been clipping...?

 

But, what is the proper mathematical way to consider playback of a track with a DR of 45dB (as measured by the Foobar2000 DR plugin) in a room with a noise floor of 55dBA?  Obviously one unit is signal related and the other is acoustic (SPL).  Should one assume that the quietest part of the track is at the room's noise floor?  Maybe it makes more sense to use a weighted average DR for a given track compared to typical playback level (75-80dBA for music and movies ~85dBA for me), then use one of the existing website calculators to plug in the peak SPL + some headroom to avoid clipping?

 

Seems this issue is even more complicated with things like room gain, reduction of SPL wrt to listening distance, impedance swings, non-ideal power supplies in smaller amps and AVRs, etc...

 

I still want to try one of these low wattage amps in an active bi-amp setup though!  Do these 1 watt amps really have better IMD for mid-range frequencies versus bigger class A/B amps?  I know typically these large class A/B amps have a lower S/N ratio at 1 watt, but the XPR-1's were still 91dB:  http://www.audioholics.com/amplifier-reviews/emotiva-xpr1-amplifier/emotiva-xpr1-amplifier-measurements

 

Here's another test showing the mid-range IMD for the XPR-1's:  http://hometheaterhifi.com/reviews/amplifier/power-amplifier/emotiva-xpr-1-monoblock-power-amplifier/

 

PS:  Please don't reply that I just need a 20-40 watt amp for my speakers unless you can explain why this is true taking more things into account than just the one sensitivity number Klipsch provides for the P-39f's (consider a 10 foot distance to the MLP, how dynamic/transient a given track is, impedance swings at low frequencies, etc). 

 

I want to be able to playback tracks with up to 45-60dB of DR or whatever the highest real world DR for music and movies is, and want to ensure my amp never clips.  I also don't have a bass bin like I used to anymore.  No doubt a 20 watt amp would sound fantastic on the La Scala's I sold, but how big of an amp should I be using for my P-39f's?

 

I had every intention of buying these big mono blocks used on ebay just to try and resell them later for more money (to cover transportation cost) when I didn't hear a difference.  But this slight difference I'm hearing makes me want to keep them...

 

It'd be great to understand/confirm mathematically or theoretically why I'm hearing these differences on tracks like the Chesky Record's dynamic drum test in a dry room at 3 feet (Foobar2000 DR plugin stated ~45dB of range) when I play the track back at an average in room SPL of 85-90dBA.  I try to be objective as possible, but have no way to ever do a fair A/B comparison with only a few second lag.  I am hearing a difference at peaks on tracks I've heard 100's of times though, so I'm pretty sure it's not my mind playing tricks on me.

Edited December 16, 2015 by etc6849

[Frzninvt]

There is no replacement for displacement.  Headroom does and will make a huge difference!  People that think that the single power supply in there AVR is enough for even the most efficient Klipsch speaker are only fooling themselves.  I compromised and replaced my two monster DBX BX-1 configurable amplifiers with a Sherbourn 7 channel true mono block amplifier.  That said the huge power supplies and headroom available in the DBX units made them superior to even the 115lb Sherbourn 7/2100A monolith.

 

I did run a nice pair of McIntosh MC-30 tube amps on my Klipschorn's while they sounded fabulous at low to moderate levels they could not complete with the horsepower of the big DBX amps.

 

Edited December 17, 2015 by Frzninvt

[etc6849]

Wow, just looked up the DBX BX-1 you mention.  Nice amp!  I wouldn't mind having one for my sides and backs.  I only have three XPR-1's right now (FL, C, FR), but put up some wanted ads.  Seems like a nice amp for what they sell for used.

 

I would not have believed a post like yours before I owned one of these monster amps, but I am hearing the same thing you are describing, and seeing the VU meter almost peak on these XPR-1's, even with my P-39f's crossed at 80Hz, seems to confirm it.

 

Seems there's a few typical causes of clipping: 1. power supply can't supply what's needed 2. clipping of the voltage or current waveform.  This wikipedia article does a good job of explaining/confirming the power supply cause you are talking about and this is probably the most common I think from what I've read on the forums:  https://en.wikipedia.org/wiki/Clipping_%28audio%29

 

I honestly thought folks who had these big amps were crazy until I listened to some of my most dynamic tracks on these mono blocks (at what some would say is high volume).  The biggest difference I'm hearing is with dynamic movie tracks.  Arguably, 98% of my music collection sounds the same to me.  Of course, movies are nearly impossible to compare as I don't re-watch a movie 100 times, so who knows.

 

I did run a nice pair of McIntosh MC-30 tube amps on my Klipschorn's while they sounded fabulous at low to moderate levels they could not complete with the horsepower of the big DBX amps.

[Frzninvt]

Damping factor, rail amperage capability and available power supply capacitance also play a role.  Here is a link to the user manual for the DBX BX-1.

 

http://vintagedbx.free.fr/owner%20manual/bx-1.pdf

 

It is stable to 0.1 ohms damn near a dead short and has tons of headroom.  Check out the specs on the thing.  I regret parting with them as they are rare and hard to find in good condition.

Edited December 17, 2015 by Frzninvt

[xxJPMxx]

I know my RF-83's I sold had nasty impedance swings in the lower frequencies. A speakers impedance is never going to be 8 ohms, and if it drops to 4 ohms at certain frequencies it's going to require twice the wattage for a given voltage and if the amp's voltage rails aren't high enough to output that voltage at that impedance clipping will occur (whether I hear it or not) since P(t) = V(t)/Z.

 

Your assumptions are incorrect. Consider the amp a voltage source with say an output impedance of .5 ohms. If reactance of the speakers dips to 4 ohms at a particular frequency the current increases not the voltage. If anything the voltage will drop due to the increase in current creating a larger voltage drop across the amps output resistance.  A perfect voltage source will have an output impedance of 0, meaning no matter the load the voltage will always be the same but the current will just increase, voltage stays the same. This is why most amps don't like a short circuit at the output.

 

Rail voltage has nothing to do with anything.

Edited December 16, 2015 by xxJPMxx

[etc6849]

I like your thinking here.  It sounds like you are proposing I use a circuit similar to what's below to model how a real world non-ideal amp behaves?

 

Doing this shows that the voltage across Zspkr would indeed drop (due to the additional voltage drop across Rout as Iamp(t) is increased as Zspkr drops).  This seems like a decent way to think of it to me, thanks!

 

I think the rail voltage comes into play when this new current demanded by the lowered Zspkr cannot be adequately supported by the amps power supply.  This would lower the rail voltage of the amp.  I think this would result in clipping depending on if Vamp(t) is greater than this new lower rail voltage.  Is this the right way to think about it?

 

 

Consider the amp a voltage source with say an output impedance of .5 ohms. If reactance of the speakers dips to 4 ohms at a particular frequency the current increases not the voltage. If anything the voltage will drop due to the increase in current creating a larger voltage drop across the amps output resistance. A perfect voltage source will have an output impedance of 0, meaning no matter the load the voltage will always be the same but the current will just increase, voltage stays the same.

Edited December 16, 2015 by etc6849

[xxJPMxx]

It sounds like you are proposing I use a circuit similar to what's below to model how a real world non-ideal amp behaves? Doing this shows that the voltage across Zspkr would indeed drop (due to the additional voltage drop across Rout as Iamp(t) is increased as Zspkr drops). This seems like a decent way to think of it to me, thanks!

 

Yes you got it now

 

 

I think the rail voltage comes into play when this new current demanded by the lowered Zspkr cannot be adequately supported by the amps power supply. This would lower the rail voltage of the amp. I think this would result in clipping depending on if Vamp(t) is greater than this new lower rail voltage. Is this the right way to think about it?

 

Depending on the amps power supply yes the the increased current demand could drop the rail voltage; e.g. The amp's power supply has a high impedance out.  My main concerns are usualy the speaker coil and the the amps output active device. FIrst the speaker coil. Let's say you have an "8 ohm" speaker rated at 100 watts. You look at your amp and see it is indeed a 100 watt amp @ 8 ohms. Let's just say the amp is a perfect voltage source and the speaker impedance plot shows it dips to 4 ohms at 100Hz. The speaker's voice coil could be blown due to the amp delivering 200 watts at that frequency.  Now let's think about the amp. The increased current could cause the output device to exceed it's rated power dissipation and or current rating and it goes poof.

[babadono]

Welcome to the Wonderful World of Headroom!! You will love it here(hear) I predict.

[etc6849]

Thanks!  I was thinking about this on the way home and finally remembered it finally from circuit theory 12 years ago! 

 

If I remember right, we modeled this resistance as Rinternal or Rin as it is a resistance internal to a non-ideal voltage source.

 

So if someone is reading my previous post Rout should really be Rin for the purposes of clarity.

 

Yes you got it now

Edited December 16, 2015 by etc6849

[garyrc]

Paul Klipsch said you need peaks of 115dB "at your ears" to simulate "The blood stirring sound of a symphony orchestra."

[xxJPMxx]

So if someone is reading my previous post Rout should really be Rin for the purposes of clarity

 

I think Rout or Ro is fine and most likely the most accurate description. I usually label them Rout and Rload like this;

 

[etc6849]

If 115dB is what I need, this means I really do need a big amp according to this online calculator.

 

I have read online some music such as a symphony can have a DR of 60dB, so this makes since if you assume a room's noise floor is 55dB (55dB + 60dB= 115dB).

 

Definitely some of the movies I've watched this week and last sound really really good and have benefitted from the bigger amps.  This is a subjective comment though.

 

 

Paul Klipsch said you need peaks of 115dB "at your ears" to simulate "The blood stirring sound of a symphony orchestra."

 

[babadono]

60dB = 1,000,000X. so if the loudest is at 1000watts the softest is at 1 milliwatt. A live performance by a symphony may have 60db dynamic range, a recording of such..... nah

[garyrc]

 

If 115dB is what I need, this means I really do need a big amp according to this online calculator.

 

I have read online some music such as a symphony can have a DR of 60dB, so this makes since if you assume a room's noise floor is 55dB (55dB + 60dB= 115dB).

 

Definitely some of the movies I've watched this week and last sound really really good and have benefitted from the bigger amps.  This is a subjective comment though.

 

amp size calc.png

 

Paul Klipsch said you need peaks of 115dB "at your ears" to simulate "The blood stirring sound of a symphony orchestra."

 

 

You probably need 115 dB only for the leading edges of peaks.

 

babadono is right, it would be unlikely that an ordinary music recording would have 60 dB dynamic range over the noise floor, especially vinyl or a normal CD, because of the nature of the medium in the case of vinyl, and since dynamic range restriction is often used when recording both vinyl and CD.  A SACD, maybe, because they know audiophiles are listening.  Several Blu-rays we have run in our HT at near reference may have reached that level for a moment at a time.  We read 110 dB on an analog SPL meter, "C," "Fast." and those can read as much as 13 dB too low on sharp dynamic peaks, because of needle balistics.

 

Many people do not really mind hearing some of the noise floor.  Under those circumstances, playback can be turned up untill one gets big peaks that conceivably might have leading edges of 115 dB.  Don't try this unless you have a peak reading meter and are using extreme caution.

 

According to a Scientific American article from 1941 (Peck), I think the old movie Fantasia (in Fantasound, which was optical 4 channel stereo with 96 sources, commissioned by Walt Disney) the peaks read 75 dB over whatever the noise floor was in the theater during test runs ... I think I remeber that the noise floor was 35 dB, so that would be 110 dB peaks ... in 1940.  A couple of my old college professors (one of whom became an audio engineer) saw it back then and said it was "overwhelming," and "hypnotic."

Edited December 17, 2015 by garyrc

[Quiet_Hollow]

You probably need 115 dB only for the leading edges of peaks.

...and only in the mid-bass and bass ranges.

 

115 dB SPL at anything above 300 Hz parts an entire FOH like the Red Sea. Seen it happen in person. Very unpleasant experience.

[etc6849]

I agree.  I wish vinyl would just die already.  Its DR is definitely inferior to what a CD can do.  As my original post stated, the highest track I have measured 45dB for DR, so I believe you guys.

 

I think movies are a different animal though and may exceed 60dB of DR, I just haven't analyzed a movie sound track before to know for sure.

 

it would be unlikely that an ordinary music recording would have 60 dB dynamic range over the noise floor, especially vinyl or a normal CD, because of the nature of the medium in the case of vinyl, and since dynamic range restriction is often used when recording both vinyl and CD.

[Frzninvt]

You can increase that DR on LP's with an older DBX 3BX-DS or 4BX Dynamic Range Expander/Controller into the CD range and improve the transient/impact (percussion) attacks by up to 12db.  They can also be used on CD's if transition levels are not set too aggressive.

4bx.pdf

Edited December 17, 2015 by Frzninvt

[etc6849]

I'm concerned only with transients/DR as my post points out.

 

I'm not sure what frequencies a gun shot or explosion in a movie would have...  Have you done an FFT or spectrogram to see what frequencies are involved or is your post talking about a pure sine wave?  I definitely have no plans of ever sending a pure sine wave through my speakers at 115dB!  That'd be nuts...  All of my REW testing is done at ~90dBA or lower.

...and only in the mid-bass and bass ranges. 115 dB SPL at anything above 300 Hz parts an entire FOH like the Red Sea. Seen it happen in person. Very unpleasant experience.

[garyrc]

 

I'm concerned only with transients/DR as my post points out.

 

I'm not sure what frequencies a gun shot or explosion in a movie would have...  Have you done an FFT or spectrogram to see what frequencies are involved or is your post talking about a pure sine wave?  I definitely have no plans of ever sending a pure sine wave through my speakers at 115dB!  That'd be nuts...  All of my REW testing is done at ~90dBA or lower.

 

 

...and only in the mid-bass and bass ranges. 115 dB SPL at anything above 300 Hz parts an entire FOH like the Red Sea. Seen it happen in person. Very unpleasant experience.

 

 

I would bet that explosions have a leading edge attack of somewhere between 80 and 200 Hz, with rumbles all the way down to 15 Hz or lower.  I've played a few -- just out of curiosity -- through the sub only (80 Hz and down) and get a tremendous "oom" of the "baoom."  No "ba." With the sub off, the "ba" of the "baoom" comes through my Khorns when they are set for 80 Hz and up, and "small," for movies.

[babadono]

etc6849,

 You sure said a mouthful when you stated "what a CD CAN do".  Problem is it is hardly ever used to its potential. Google 'loudness wars' if you have never done so before. Its enough to make you ill.