Crown vs Rotel

[PENG]

You can't even get more than a 20dB peak at reference level of 85dB. If the system is calibrated to 75dB using a -30dBfs pink noise the maximum peak at 0dBfs is 105dB. The only way you'd need more headroom is if you set the fronts to large and ran the LFE channel into the fronts, in which case you'd need 115dB of headroom, but good luck finding a floor standing speaker that can cope with 115dB of low frequency content without major distortion or physical damage to the drivers. Even most large subs fail to do that and it usually requires multiple subwoofers. Even Klipsch's thx ultra speaker system, which has actually been designed to play at reference level without distortion, includes dual subs.

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If I remember right he has a Marantz SR5010, and that has maximum volume of +18, that means he can go above reference. It also depends on the recording/mastering level of the source material.

Another thing I am not 100% about is how exactly THX defines that 20 dB peak, do they mean maximum SPL average, or maximum SPL peak in the source material, i.e. movie (same principle applies to music too, just different numbers)? This may sound crazy but you never know until you see the definition in fine print. I googled this very hard and came up with nothing, time to give them a call but I doubt they know that too. To me, peaks are peaks, and it should mean just that literally. So hopefully whenever someone (from THX and other standards committees etc.) refers to "peak" they mean the absolute maximum peak of the signal, not the maximum average of the signal in the material.

I don't ever listen to reference level myself, though it is nice to be at least 20 dB below the amp's clipping point regardless of what I listen to.

 

[Verdinut]

You can't even get more than a 20dB peak at reference level of 85dB. If the system is calibrated to 75dB using a -30dBfs pink noise the maximum peak at 0dBfs is 105dB. The only way you'd need more headroom is if you set the fronts to large and ran the LFE channel into the fronts, in which case you'd need 115dB of headroom, but good luck finding a floor standing speaker that can cope with 115dB of low frequency content without major distortion or physical damage to the drivers. Even most large subs fail to do that and it usually requires multiple subwoofers. Even Klipsch's thx ultra speaker system, which has actually been designed to play at reference level without distortion, includes dual subs.

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Actually, I am using 3 subs, one in each front channel, and each one has a power rating of 500 watts. With 3 QSC RMX850a's which I plan to get, there wouldn't be much of a problem reaching with the three a peak SPL of 115dB, and this without excessive distortion. The subs are Dayton's RSS390HF-4 15 inch transducers.

My setup will provide a total acoustic gain of 13.8 dB: Corner placement of L & R speakers = 6dB, active bi-amping of the 3 front channels = 3dB and 3 identical speakers = 4.8dB.

In addition, I calculated to see what SPL the two 5 inch mid-woofers in each cabinet would be able to put out. They should be able handle a peak SPL of 110dB without audible distortion (Total Sensitivity of 90 dB/watt and combined power rating of 60 watts).

According to Altec acoustical engineers, in the situation of a full orchestra, the main power demands fall between 250 Hz and 500 Hz, the frequencies which have to be handled by those mid-woofer drivers. The main power demand will shift down in frequency when I'll be playing a pipe organ recording with 16 and 32 foot stop notes.

Since I will be listening to music at an average SPL level of 80 dB, I should have ample headroom for both music and movies.

 

[lovinthehd]

You can't even get more than a 20dB peak at reference level of 85dB. If the system is calibrated to 75dB using a -30dBfs pink noise the maximum peak at 0dBfs is 105dB. The only way you'd need more headroom is if you set the fronts to large and ran the LFE channel into the fronts, in which case you'd need 115dB of headroom, but good luck finding a floor standing speaker that can cope with 115dB of low frequency content without major distortion or physical damage to the drivers. Even most large subs fail to do that and it usually requires multiple subwoofers. Even Klipsch's thx ultra speaker system, which has actually been designed to play at reference level without distortion, includes dual subs.

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What makes you think that calibration results in an avr's ability to limit peaks?

 

[Verdinut]

I have done some reading too since, and I am now also quite comfortable of their class AB amps. The thing about class AB is, as I mentioned before, one can choose the quiescent point to barely qualify to be called class AB. It is much more complicated to control the bias to the point where the amp can actually operate like class A at least for the first few watts, or higher in the higher end ones.

Looking at the specs for the RMX850a, QSC publishes typical THD at less than 0.03% at 10dB below rated power for the whole 20-20K frequency range, and the same distortion level at full rated output for frequencies 1 kHz and below, for both 8 ohm and 4 ohm loads. I have a tendency to believe that it most likely works as a Class A amp up to the -10dB level. That could mean 28 clean watts in Class A at 4 ohms where most of my music content would be. Wouldn't that be amazing?
The real fact is that the published specs by pro audio amplifier manufacturers are quite more conservative than that for most audiophile products. I am really anxious to get my first one within the next 2 weeks.

 

[PENG]

Looking at the specs for the RMX850a, QSC publishes typical THD at less than 0.03% at 10dB below rated power for the whole 20-20K frequency range, and the same distortion level at full rated output for frequencies 1 kHz and below, for both 8 ohm and 4 ohm loads. I have a tendency to believe that it most likely works as a Class A amp up to the -10dB level. That could mean 28 clean watts in Class A at 4 ohms where most of my music content would be. Wouldn't that be amazing?
The real fact is that the published specs by pro audio amplifier manufacturers are quite more conservative than that for most audiophile products. I am really anxious to get my first one within the next 2 weeks.

I highly doubt it runs in class A at all. It's likely just AB from 0 to rated output, nothing wrong with that if done well. You can email them for a direct answer.

 

[Verdinut]

I highly doubt it runs in class A at all. It's likely just AB from 0 to rated output, nothing wrong with that if done well. You can email them for a direct answer.

I will soon.

 

[yepimonfire]

If I remember right he has a Marantz SR5010, and that has maximum volume of +18, that means he can go above reference. It also depends on the recording/mastering level of the source material.

Another thing I am not 100% about is how exactly THX defines that 20 dB peak, do they mean maximum SPL average, or maximum SPL peak in the source material, i.e. movie (same principle applies to music too, just different numbers)? This may sound crazy but you never know until you see the definition in fine print. I googled this very hard and came up with nothing, time to give them a call but I doubt they know that too. To me, peaks are peaks, and it should mean just that literally. So hopefully whenever someone (from THX and other standards committees etc.) refers to "peak" they mean the absolute maximum peak of the signal, not the maximum average of the signal in the material.

I don't ever listen to reference level myself, though it is nice to be at least 20 dB below the amp's clipping point regardless of what I listen to.

Maximum peak for a single channel at 0dBfs. In 5.1, that means just on the speaker level the maximum output could be as much as 120dB if all channels were driven simultaneously at full scale level. I know listening at -15dB full scale translates to 90dB, yet during an intense scene with all speakers going full blast I've maxed at 105dB. The level is in reference to the digital full scale, if a digital pink noise is -30dBfs than that gives you 30dB of headroom from 75dB. I can't possibly imagine listening at +18dB even if the source was highly dynamic, and I like it loud. 80dB for music is more than adequate for me and between -15dB and -10dB is good enough for movies. Dynamic music such as classical is also good at about -15dB

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[yepimonfire]

Actually, I am using 3 subs, one in each front channel, and each one has a power rating of 500 watts. With 3 QSC RMX850a's which I plan to get, there wouldn't be much of a problem reaching with the three a peak SPL of 115dB, and this without excessive distortion. The subs are Dayton's RSS390HF-4 15 inch transducers.

My setup will provide a total acoustic gain of 13.8 dB: Corner placement of L & R speakers = 6dB, active bi-amping of the 3 front channels = 3dB and 3 identical speakers = 4.8dB.

In addition, I calculated to see what SPL the two 5 inch mid-woofers in each cabinet would be able to put out. They should be able handle a peak SPL of 114dB without audible distortion (Total Sensitivity of 92 dB/watt and combined power rating of 60 watts).

According to Altec acoustical engineers, in the situation of a full orchestra, the main power demands fall between 250 Hz and 500 Hz, the frequencies which have to be handled by those mid-woofer drivers. The main power demand will shift down in frequency when I'll be playing a pipe organ recording with 16 and 32 foot stop notes.

Since I will be listening to music at an average SPL level of 80 dB, I should have ample headroom for both music and movies.

Yeah those subs based on that number will certainly hit 115dB. The 92dB sensitivity is at 1m. At 2m that drops to 86dB, at 3m about 82dB, so now in order to reach a 114dB peak in the midrange per channel, you'd need 1400w. A 105dB peak would require 180w, but nobody uses just one speaker, so you really only need 90w. This is assuming the music is played at reference level and the entire signal is in the midrange, which it isn't, so you'd likely only need a few watts program and maybe 60hz for peak. Drivers can generally handle 3x the rms power rating for brief peaks, so you're well in the clear. If the music is played back in multichannel and you've got a solid 120wpc I'd imagine you'd be able to get 120dB peaks. For two channel, maybe if enough power were available, but you're also using decent 3 way floorstanding speakers with subs.

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[yepimonfire]

What makes you think that calibration results in an avr's ability to limit peaks?

Well, I suppose you could turn the volume up past 0dB. Try playing a full bandwidth pink noise at 0dBfs, at 0dB you'll get about 108dB in two channel mode.

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[PENG]

Maximum peak for a single channel at 0dBfs. In 5.1, that means just on the speaker level the maximum output could be as much as 120dB if all channels were driven simultaneously at full scale level. I know listening at -15dB full scale translates to 90dB, yet during an intense scene with all speakers going full blast I've maxed at 105dB. The level is in reference to the digital full scale, if a digital pink noise is -30dBfs than that gives you 30dB of headroom from 75dB. I can't possibly imagine listening at +18dB even if the source was highly dynamic, and I like it loud. 80dB for music is more than adequate for me and between -15dB and -10dB is good enough for movies. Dynamic music such as classical is also good at about -15dB

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I don't disagree with you at all, not in principles.

 

[Verdinut]

Yeah those subs based on that number will certainly hit 115dB. The 92dB sensitivity is at 1m. At 2m that drops to 86dB, at 3m about 82dB, so now in order to reach a 114dB peak in the midrange per channel, you'd need 1400w. A 105dB peak would require 180w, but nobody uses just one speaker, so you really only need 90w. This is assuming the music is played at reference level and the entire signal is in the midrange, which it isn't, so you'd likely only need a few watts program and maybe 60hz for peak. Drivers can generally handle 3x the rms power rating for brief peaks, so you're well in the clear. If the music is played back in multichannel and you've got a solid 120wpc I'd imagine you'd be able to get 120dB peaks. For two channel, maybe if enough power were available, but you're also using decent 3 way floorstanding speakers with subs.

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I readjusted the mid-woofers sensitivity figure to 90dB/1w/1m. At a distance of 9 ft, since I have 3 identical speaker cabinets at the front, just with a total amplifier peak output of 192 watts for the high frequency portion only since I will be actively bi-amping the 3 front channels, I could easily get 110dB. The L & R speakers are placed in a corner with an acoustic gain 6 dB. Those figures were obtained with a reliable peak SPL calculator on the web.

 

[lovinthehd]

Well, I suppose you could turn the volume up past 0dB. Try playing a full bandwidth pink noise at 0dBfs, at 0dB you'll get about 108dB in two channel mode.

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I don't know where you're going with that but has nothing to do with the avr limiting anything.

 

[Bucknekked]

Do you have neighbors?

Peng
The most important thing to know about your neighbors is what it sounds like when they unlock their gun racks. When you hear that sound, knock the volume control back a couple of clicks.

I just read this entire thread. I had an interest in the QSC and the Crown amps during the last month. I believe one of the posters in this chain pointed them out to me to consider. I did so. What I read in the comparisons is the build quality on the QSC appears to be of a higher standard than on the Crowns. Hence, harder to cause a failure with rugged or intense use as one of the posters here highlights. Both series of amps appear to have very good $/value ratios.

What an interesting discussion. I appreciated being able to read an entire thread without someone throwing mud at someone else.

 

[slipperybidness]

Peng
The most important thing to know about your neighbors is what it sounds like when they unlock their gun racks. When you hear that sound, knock the volume control back a couple of clicks.

I just read this entire thread. I had an interest in the QSC and the Crown amps during the last month. I believe one of the posters in this chain pointed them out to me to consider. I did so. What I read in the comparisons is the build quality on the QSC appears to be of a higher standard than on the Crowns. Hence, harder to cause a failure with rugged or intense use as one of the posters here highlights. Both series of amps appear to have very good $/value ratios.

What an interesting discussion. I appreciated being able to read an entire thread without someone throwing mud at someone else.

We have a local night club in town, on their ads in the entertainment periodical, they always tout "Soundsystem by QSC".

I suspect that QSC likely did the work at a discount, with the catch that it must always be advertised in that manner.

Just an FYI, and that's the only place I've ever seen this.

 

[jinjuku]

The situation is that I am going to use those inefficient amps in an apartment with a limited number of AC circuits, only one 15 amp line for the full living room. I am planning to use the bedroom circuit for two of the 850's and the living room one for the center channel. Note that, according to the indications by QSC, at 1/8 rated power with pink noise which represents typical program with occasional clipping, with a 4 ohm load, this amplifier draws (both ch. driven) 4.5 amps. Imagine with the 1450, the power consumption is up to 6A.
I know that electricity is cheaper in Montreal than in Ontario, but the electrical supply limitation in my apartment has to rule. I don't intend to use the kitchen stove circuit !
With regard to the fans, I read that QSC would have quieter fans available at a very reasonable price. Should I be annoyed with the noise, I will surely look into that possibility of replacement.
Cheers,

Why would you need that much amplification in an Apartment?

 

[Verdinut]

Why would you need that much amplification in an Apartment?

There is the question of the availability of less powerful and dependable amps at a reasonable price. The $/w ratio of pro audio amps is hard to beat. As mentioned in a previous post, the QSC power amps have gain controls which I'll be able to adjust.
Classical music and opera recordings nowadays have a wider dynamic range than recordings of the 20th century. A dynamic peak of 30dB and maybe more is possible with classical music. Such situation would demand 1000 times or more clean amplifier power.
Finally, it is always better to have more headroom available than not enough.

 

[Johnny2Bad]

Certainly they are both representative examples of their topology, but I have no trouble discerning a difference in sound between a Crown Class D amp and a Rotel Class A/B unit. Your mileage may vary.

 

[Johnny2Bad]

I highly doubt it runs in class A at all. It's likely just AB from 0 to rated output, nothing wrong with that if done well. You can email them for a direct answer.

Class AB describes a topology whereby the amplifier runs in Class A at low output power then switches to Class B at some point typically based on the bias point of the output devices. It's not exotic by any means, but yes, it does run in Class A under specific circumstances. Exactly at what output this occurs is up to the amplifier designer; it's relatively rare for the amp to operate in Class A at relatively high power but it is not unheard of.

However with most consumer-grade amplifiers the switch to Class B happens at a fairly low output power point. Taking the maximum output of the Rotel into consideration, it's extremely likely that it does not run in Class A for long ... too much heat, and difficult to support very high output power.

The reason this is the case can be summed up fairly easily ... pure Class B sounds terrible (although not as bad as Class C would).

At the crossover point (where the output devices switch halves of the waveform through the zero crossing point) a Class B amplifier will have crossover distortion into the tens of %. So Class AB hands off this critical point to a Class A topology (which is capable of zero crossover distortion), making Class AB a high quality topology suitable for High Fidelity use.

 

[Verdinut]

Peng
The most important thing to know about your neighbors is what it sounds like when they unlock their gun racks. When you hear that sound, knock the volume control back a couple of clicks.

I just read this entire thread. I had an interest in the QSC and the Crown amps during the last month. I believe one of the posters in this chain pointed them out to me to consider. I did so. What I read in the comparisons is the build quality on the QSC appears to be of a higher standard than on the Crowns. Hence, harder to cause a failure with rugged or intense use as one of the posters here highlights. Both series of amps appear to have very good $/value ratios.

What an interesting discussion. I appreciated being able to read an entire thread without someone throwing mud at someone else.

You can't hear the sound of the gun racks, because your music is too loud!

 

[panteragstk]

Peng
The most important thing to know about your neighbors is what it sounds like when they unlock their gun racks. When you hear that sound, knock the volume control back a couple of clicks.

I just read this entire thread. I had an interest in the QSC and the Crown amps during the last month. I believe one of the posters in this chain pointed them out to me to consider. I did so. What I read in the comparisons is the build quality on the QSC appears to be of a higher standard than on the Crowns. Hence, harder to cause a failure with rugged or intense use as one of the posters here highlights. Both series of amps appear to have very good $/value ratios.

What an interesting discussion. I appreciated being able to read an entire thread without someone throwing mud at someone else.

It really depends on the series of QSC and Crown amps. There are so many you can't really make a blanket statement of "QSC seems better than Crown". I would say to compare similar priced amps and go from there. Crown goes way up into the high end and I'd think those are going to be some pretty fantastic amps. Same with QSC.