Monoblocks for theater?

[AudioThesis]

Matt, that was a good theory, but it does have some flaws in actual application (sorry). If you want to look closer at it, just look at driver sizes and power handling capabilites. There are reasons why subwoofers can eat up gobs of power while a midrange is often limited to 100-200 watts. Go to the tweeters and it gets even lower. The power spectrum is not linear and much of that energy to reach peak levels is at the lower frequencies. If you can cut those off from other speakers, you are thus alleviating the strain on those components. The higher the frequency cutoff, the less power needed for ACTUAL use.

 

[AudioThesis]

To better explain what I'm saying - power is not linear with the frequency. There is an inverse relationship there that can and will vary with recording, but it is fairly consistent in its relationship. Hopefully this link will provide a decent insight, but I'm struggling to find proper papers to support it right now.

https://archive.cnx.org/contents/9c...lassification-by-genre-power-spectral-density

 

[Matthew J Poes]

Matt, that was a good theory, but it does have some flaws in actual application (sorry). If you want to look closer at it, just look at driver sizes and power handling capabilites. There are reasons why subwoofers can eat up gobs of power while a midrange is often limited to 100-200 watts. Go to the tweeters and it gets even lower. The power spectrum is not linear and much of that energy to reach peak levels is at the lower frequencies. If you can cut those off from other speakers, you are thus alleviating the strain on those components. The higher the frequency cutoff, the less power needed for ACTUAL use.

It isn't theory and the link you listed has nothing to do with speaker power consumption. This is ohms law and my comment came from a number of speaker designer experts, one of which has a PhD. Speakers do not draw more power inverse to frequency (more at lower levels).

The reason for the higher power handling is solely an issue of efficiency. LF drivers are less efficient than high frequency drivers typically. Remember that efficiency is relative to a frequency. A subwoofer might claim to be 88db efficient. If at 20hz in a 2 cubic foot box its free air response is 78db's, where at 100hz its 88db's, then the efficiency at 20hz is 78db's. By comparison a tweeter would have fairly flat efficiency response and thus draw a fairly consistent amount of power at all frequencies, with the exception of its impedance peak. To produce a flat response you need to add 10db's. If at 100hz it needs 1 watt, then at 20hz to achieve the same level, it will need 10 watts. That is the cause of the problem, its all efficiency. If you look at the transfer function of a crossover you can quickly see why speakers with no bass EQ have this problem. A speaker wouldn't have a flat response if you didn't apply what's known as baffle step compensation, so once you add that in, the lower frequencies are drawing more power.

What you posted is precisely the misconception that I see on forums. It has been publicly refuted by Earl Geddes and Mark Seaton, among other experts. Additionally, as was suggested to me as proof, you can model this in spice to see exactly how much power is being drawn at any given frequency.

 

[AudioThesis]

I don't think you understand the point. I'm not arguing your theory at all. The problem is application. It assumes that ALL frequencies are getting the same power levels at any given time. It doesn't work that way. Bass gets emphasized with the recordings so removing those frequencies frees up that heft.

This isn't about efficiency but about the recording and the playback requirements based on the frequencies being passed. The lower the frequency, the higher the power draw because of the recording itself.

 

[AudioThesis]

Let's use classical as an example. At 20 hz, the draw in dB is -60ish. At 80 hz, the draw is at -80ish. Assuming approximations, that is 20 db freedom now allowed for the amplifier to push the rest of the frequencies. That is huge!

Again, the efficiency argument that you make is valid, but it doesn't touch on the actual issue in the application.

 

[Matthew J Poes]

I don't think you understand the point. I'm not arguing your theory at all. The problem is application. It assumes that ALL frequencies are getting the same power levels at any given time. It doesn't work that way. Bass gets emphasized with the recordings so removing those frequencies frees up that heft.

This isn't about efficiency but about the recording and the playback requirements based on the frequencies being passed. The lower the frequency, the higher the power draw because of the recording itself.

I think you need to provide a graph that extends beyond 140hz showing the musical spectral density to make that point. Unless I misunderstood the range on that graph, it wasn't clear what they showed and that it could make the point you are making.

Mark Seaton specifically had stated research into the musical energy content actually being concentrated in the midrange. I've not seen graphs of this. If you like I can check with both him and Geddes to get a better scientific answer.

I can say this, I think you are making the same point I made, but it doesn't change what I said either, and what you said still contains errors. What I think you are basically saying is that producing more simultaneous tones draws more power. That is true! I said that too. What you are also saying, which I'm saying is not true, is that a speaker uses more watts to produce low frequencies than high frequencies. That is not true. Even if the balance of frequency energy is tilted toward the lows, it still doesn't change how much power is consumed by the speaker at those frequencies. It just means that over time more of the power is being consumed to produce low frequencies. That has nothing to do with power handling and is not why tweeters and midrange drivers handle less power. That is due to efficiency.

So my point was that you need a lot of power for movies, what you showed doesn't change that. Your mains still need a lot of power because for a main speaker to produce 105db's, regardless of the spectral density, requires the same amount of power. for a low efficiency speaker, its 1000's of watts. If there is an explosion and the explosion contains content that extends from 5hz through 1khz, then the 1khz portion will still draw 1000watts to hit the targeted 105db's. In the bass there is more information and it is louder but then ITU standards are 115db's below 100hz or so, and for lots of reasons that go from LF efficiency to also now needing to produce 10 more db's, we need way more power.

 

[AudioThesis]

See my post prior to yours. My argument that I'm struggling to find documentation for is that the recording itself is not a flat-measuring source. In order to make the argument for movies, you would need to know what they emphasize and given the sound I'm accustomed to in movies, I expect those emphasized frequencies to fall in the sub bass arena. As you can see from the graphs I provided, it does vary depending on a multitude of factors, but its the best example I could find right now.

Think about it like this - how often do you associate dynamic and powerful sound with a huge spike of midrange or treble? While I realize dynamics have nothing to do with frequencies, we associate it with pressurizing energy most often - of which the bass is responsible for.

 

[Matthew J Poes]

See my post prior to yours. My argument that I'm struggling to find documentation for is that the recording itself is not a flat-measuring source. In order to make the argument for movies, you would need to know what they emphasize and given the sound I'm accustomed to in movies, I expect those emphasized frequencies to fall in the sub bass arena. As you can see from the graphs I provided, it does vary depending on a multitude of factors, but its the best example I could find right now.

Think about it like this - how often do you associate dynamic and powerful sound with a huge spike of midrange or treble? While I realize dynamics have nothing to do with frequencies, we associate it with pressurizing energy most often - of which the bass is responsible for.

The frequency energy of a dynamic is not flat but its also not concentrated only in the bass. The standard for movies allows for 115db's of headroom in the bass and 105db's in the mains. It is expected that the bass range has more output. That doesn't change the peak output needed in the midrange. The spectral energy of an explosion or giant footstep or whatever is mostly concentrated in the bass, but again, if this is an all out peak and we see 115db's in the bass and 105db's in the midrange, then the midrange is going to be consuming a ton of power. The density is irrelevant to that point as that is just an efficiency issue.

I really do think I understand what you are saying and I do think I agree that movies and music have elevated energy in the bass. However the other side of this is that there are a lot more midrange frequencies too, and since this is the average power over time for a band of frequencies we are calling bass, midrange, treble, in the end, the lets say 140hz to 20khz range still contains a lot more overall energy than just the range from 20hz to 140hz.

 

[AudioThesis]

We are on the same page now. My main hangup was that if 105 was your target threshold then you would reach it quicker with the bass and not need as much power with your midrange. The clarification on the 105 vs 115 helps tremendously. EDIT - I see you included that but somehow I missed it.

Carry on and pretend this never happened.


Cheers gents

 

[AudioThesis]

Most home speakers I've seen have an efficiency around 87 dB. 84 and 85 tends to fall in line with most high quality monitors I see. In order to get to 105 dB at 1 meter, you are looking at 32 WPC. Factor in that you are sitting roughly 4 meters away and you need to increase it by a factor of 4. So that's 512 watts to maintain a reference of 105 dB at roughly 12 ft with 'no headroom'.

I think the numbers are a bit high in your original post, but please correct me if I am wrong.

 

[Matthew J Poes]

I don't think your 32 watt number is right. I came up with the same calculation as you did for the 32 watt starting number in terms of the 11-12db loss at 4 meters. However, an 85 db speaker sensitivity would need 85 watts to hit 105db at 1 meter. An 87 db speaker needs about 55 watts at 1 meter. The 87 db speaker would need 850 watts to hit 105db at 4 meters.

http://myhometheater.homestead.com/splcalculator.html
Try this, or
https://www.crownaudio.com/en-US/tools/calculators#amp_power_required

As both gave me the same values, as did my phone app calculator.

The crazy high value I gave was based on adding in the suggested 3db's of headroom above the peak you intend to produce to avoid any chance of clipping. 1200 is with no headroom, so depending on how your amp clips, if any movie ever exceeded that you might clip, and then the Crown calculator let me put in .5db's, which is how I got 1500.

I called 85db's average because that's what Sound and Vision and Stereophile seem to call average. I have not measured as many speakers as they have. Keep in mind that both of those magazines have found manufactures seem to fudge the sensitivity values or give them based on what you get with the speaker against a wall, which gives a boost. Or they are just being dishonest, who knows. In any case, they come up with lower values. I'm measuring those Pioneer Andrew Jones Towers right now, they are just around 84db's based on my measurements. They specify 87db's. They also claim 6 ohms, what I see is a solid 4 ohm speaker.

 

[Talley]

So w/ the XPA-7 hooked up not the krell.... with my now second HSU sub installed... playing Fury tank battle scene at -5 leaves me very satisfied.

Obviously I wouldn't know better until that time comes but until it does... right now I have zero reason to upgrade anything. Sounds wicked and the second sub really added a special element. The bass really attacks you now and it acts like nothing stresses it either.

I also was hitting 107-109 peaks at -5db volume. C weighted of course so probably most of this is bass. I'd have to turn off the subs and see what the speakers get. At -5db with the emotiva driving them there is a hint of harshness i the upper frequencies but maybe thats because right now my Dirac is targeting flat. I could adjust it from here and see how it turns out.

 

[AudioThesis]

I'm one degree off. Should be 64/1024. In a theater, are you actually looking to reproduce 105 db consistently at the listening position? That seems dangerous. I get reference levels as a guideline but wow.

I'm trying to understand the approach of the Home Theater enthusiast. To me while the reference is exciting, its not an enjoyable experience at those levels. I need to see what my normal listening preferences are in regards to decibel levels.

 

[Talley]

When I listen to music I'm normally at the 80-85db mark with peaks in the 90 range is all. However if you have a movie going and your listening to an average of 85db there could be instantaneous peaks during gun fire or explosions that with adequate equipment would hit peaks over 110db.

You would never know it unless you had a system capable. I can tell you for a fact that my speakers are a limit for me for movies. But for music they do really well. It's a trade off I think.

 

[AudioThesis]

For a dual purpose system there always is a trade off. I started more HT oriented, but then I heard what a good pair of speakers on a tube amplifier was capable of and I've gone completely 2 channel since. I never got deep enough in HT to understand the approaches and so I'm trying to catch up now.

I know I would never dream of a 105 dB session but if that is the goal, then a solution is needed. I still don't think monoblocks are a necessity for your system.

 

[Talley]

For a dual purpose system there always is a trade off. I started more HT oriented, but then I heard what a good pair of speakers on a tube amplifier was capable of and I've gone completely 2 channel since. I never got deep enough in HT to understand the approaches and so I'm trying to catch up now.

I know I would never dream of a 105 dB session but if that is the goal, then a solution is needed. I still don't think monoblocks are a necessity for your system.

Again HT has way more aggressive dynamics than music. How many times you hear guns/explosions or roaring prop airplane zipping by in a music track. Two totally different animals.