Importance of Center channel Amplification in HT System

[john_k_antony]

Hi,

I just wanted to start a discussion, if its really worth , regarding the amplification needs of the center channel in a 5.1/7.1 home theater system. For the sake of discussion, lets assume that all the front speakers (Left, Right and Center) are similar in specs (sensitivity, impedance, power rating, frequency response etc) except for the fact that the center channel is a "dedicated" center channel speaker with MTM horizontal configuration while the Left & Right are vertical floor standers, but from the same manufacturer and same model.

With my limited experience listening to 5.1 system, I have observed the following

1. Bass content fed to center channel and surrounds are much lesser than the bass sent to the main L & R speakers in a typical 5.1 movie track.

2. You need more power to reproduce bass SPL than you need to reproduce the same SPL for mids and highs.

Now that center channel and surrounds reproduce mostly mids and highs most of the time and rarely deep bass, do they need the same continuous amplification power that is required for the main L & R channels?

The whole idea of this discussion is to understand the need for a 200w/ch, 5 channel amplifier vs a 200w/ch, 2 channel amp for the fronts L & R and 100w/ch 3 channel or 5 channel amp for center and surrounds. Do the center channel require the same power as the front L&R and do they need the same amplification head room as the front L & R.

I would also like to hear your experience of having heard the deep bass content being fed to the center channel similar to that of front L & R channels that requires a lot of power amp head room.

Please ignore this discussion if this doesn't make any sense to you guys .

Thanks,
John.

 

[sash]

John, my experience on this is mixed. Try "Life of Pi" and "MI-Ghost Protocol", you'll find a hell lot of dynamic range in the center channel - including decent amount of bass.
While some movies are mostly dialogues. Considering these movies are relatively new and probably represent today's trend, i'm afraid you might need good amount of amplification to sustain dynamic range in the center channel too.

 

[Audio_Freek]

Hello John,

Lets start up understanding on Why the 5.1 or 7.1 are superior Than Stereo setup.I know few FM's Raise their hands that "I Love \Prefer Even Movies for my Stereo".But BY experience,I would Say Center Channel is Vital for Movies.Thats the reason even Entry level HT would be good for Movies,Just give Liveliness.

So Why?

Movies are Build with Lot to listen and Not just Feel Normally Like Music. So DIALOGUE are the vital for any Movies.I am Just speaking about the Generic Films and For Action the its different Story.

We cant expect Clear Voice of the Pilot when Helicopters is rumbling in a action sequence in Stereo. As all would agree Most of the time the Mid range get over capped by the Low range or High-range.

When Central channel gives only Mid and High (I Would Prefer Only Mid and Slight of High and not too Much)

The Surrounds and Front shall carry the Remaining Frequencies and Leave Low for SUB anyways.

I dont like 5.1 anyways, rather I go with 3.1 Center+2 Rear+Sub.

SO while watching the Movie I expect the Dialogues and related Sound Coming just in Font of My face and the Other Surround effect coming from Rear so it should be Much real(Could be my assumption though)


I Do tried to with Equalizer to Boost some Base for Center channel and then The Original clarity for the Voice was been Missing.

This is my assumption or my experience and not a STATEMENT FOR debate.

 

[Nishanth]

Before the introduction of Dolby Digital in AV receivers, the power rating in AV receivers were higher for the front channels and lower for the surround channel. But the trend changed with the introduction of Dolby Digital which has five discrete full-bandwidth channels. Films started making use of Dolby Digital's full-bandwidth channels and the trend of AV receivers having equal power rating for all channels started.

Hi,


1. Bass content fed to center channel and surrounds are much lesser than the bass sent to the main L & R speakers in a typical 5.1 movie track.


Now that center channel and surrounds reproduce mostly mids and highs most of the time and rarely deep bass, do they need the same continuous amplification power that is required for the main L & R channels?

Like Sash pointed out there are also movies which have bass content in the surrounds and center. But then having equal power for all channels is not just for bass reproduction, but is mainly to create a seamless sound field for modern day film mixes and is especially very important for multi-channel music.

But in the end it come down to personal preferences, if your usage is mostly for 2 channel music or for content with very little surround content then you can always go for a more powerful dedicated amp for the fronts. There are people with set ups like these, so the idea of having more powerful fronts does make sense to some.

 

[Santy]

As far as I have observed, the centre carries more bass frequencies than any other channel (other than the sub ofcourse). Bass upto 100 hz can be somewhat located so when there is an impactful sound in the movie, they have to come from centre unless the action is towards left or right side of the screen. Below that frequency, the sub kicks in anyways.

My speakers do distort when I drive them beyond limits and when it happens it is the centre that is affected the most. Many 5.1 speaker designs have a smaller centre purely to address the placement issues. Otherwise ideally it must be exactly of same specs (and orientation) as the other two main speakers as it is the case with many top end HT systems.

Regarding your amp query. Well, a 200W amp is not simply 100W more than a 100W amp. Be it stereo or monoblock or multichannel, usually OEMs reserve superior technology and better quality components for their bigger models in their product line because they are not fully justified to be used in low powered amps. People buying low power amps have budget constraints so it would go against the idea of entry level system when expensive technology/ components are used in it. At the same volume level, a 200W amp is most likely to give not only higher fidelity but also better quality than a 100W amp for the same reason. Actually depending on what we are comparing, the difference could be substantial. They also have better headroom which is essential for movies or music with demanding passages. In smaller amps you have to drive hard to achieve same SPL which introduces distortion. In the Emotiva models, you could see how vastly the design / technology / specs vary between UPA-500 and XPA-5. The later has discrete amplification, a meaty power supply ( almost as heavy as the other amp!), balanced inputs etc..

Coming back to the topic, the centre channel as sash said carries most of the 'action' so it is ideal that it is given equal treatment as the fronts. This is purely my understanding, I could be very well be wrong. And I agree with Nishanth, if your primary use is music, then such a setup is perfectly alright even with the compromises made..

 

[john_k_antony]

Thank you guys for the great inputs. Really appreciate it. I was thinking about all the comments mentioned by you guys above till I saw something in real life. My recent experience with KEF speakers and Denon AVR.

I had the exact same LCR speakers - KEF Q300 and was playing different movie contents, Hollywood, Bollywood and Malayalam.

In most of the cases, I have seen my front L&R struggling for breath while the center channel speaker is "chilling out" and was making good SPL for the dialog and songs to match the background music / effects coming from front L & R.

I have tried clips from following movies

1. Avengers
2. Hero (Jet Li)
3. Gladiator
4. Avatar
5. Life of Pi
6. Some Hindi and Malayalam movie song sequences where I saw the front L & R is given heavy bass content and vocals were coming from center channel.

This observation made me think that center and surrounds may not require that much of an amplification, even for heavy action sequences.

Now I am thinking something different, during heavy sequences, the front L&R speakers were taking all the juice from Denon and there was hardly any amplification power left for center and surrounds from Denon . So except the front L&R, all the other channels were not getting enough power.

Is this assumption true that if I have a 100w/ch, 5 channel amp and only connect 3 channels, I get 130-140 w/ch for each of the 3 channels?

Thanks,
John.

 

[Santy]

In most of the cases, I have seen my front L&R struggling for breath while the center channel speaker is "chilling out" and was making good SPL for the dialog and songs to match the background music / effects coming from front L & R.

Quite possible.. It quite depends on the movie / scene / sound mixing.
Did you set the fronts to large and centre to small?

Is this assumption true that if I have a 100w/ch, 5 channel amp and only connect 3 channels, I get 130-140 w/ch for each of the 3 channels?

No it won't. Amps would always have a maximum capacity per channel.

 

[john_k_antony]

Quite possible.. It quite depends on the movie / scene / sound mixing.
Did you set the fronts to large and centre to small?



No it won't. Amps would always have a maximum capacity per channel.

Hey Santy,

After I burned my KEFs, I NEVER kept the speakers to Large or played in Pure Direct Mode. All speakers are set to Small and cross over was at 80Hz for LCR and 100hz for surrounds.

Regarding the amp max capacity, I also thought all amps would have a cut off for the max power per channel, no matter how many channels are driven.

Surprisingly, Emotiva is saying that their amps can deliver more power per channel if less number of channels are driven in a multi channel power amp. I guess they are just BS ing . One thing I might probably gain is that the storage capacitance will be now shared by lesser number of channels. Not sure if that makes a big different!

-John.

 

[spirovious]

In most of the cases, I have seen my front L&R struggling for breath while the center channel speaker is "chilling out" and was making good SPL for the dialog and songs to match the background music / effects coming from front L & R.

Many times Center channel sensitivity is higher than Front speakers.That can be another reason.

 

[kanwar]

In our professional theatre installs we usually keep the centre channel power same as L+R channels. The centre channel like others is 3 way active always. 150 HF, 500 MF, 2kW LF[with LF HP at 80hz, below its handled by SUBs]. This simply states that you need a good dynamic range for center channel also, therefore its good to have same power specs for center channel as well.

So accordingly in home HTs the Center channel should be of same power as L+R.

 

[john_k_antony]

Many times Center channel sensitivity is higher than Front speakers.That can be another reason.

In my experiment, all the L-C-R speakers were exactly the same - KEF Q300 bookshelves. Meaning the center channel had the same sensitivity as the main L&R. In my new setup, center channel is 98db sensitive and main L&R are 97db.

-John.

 

[john_k_antony]

In our professional theatre installs we usually keep the centre channel power same as L+R channels. The centre channel like others is 3 way active always. 150 HF, 500 MF, 2kW LF[with LF HP at 80hz, below its handled by SUBs]. This simply states that you need a good dynamic range for center channel also, therefore its good to have same power specs for center channel as well.

So accordingly in home HTs the Center channel should be of same power as L+R.

Kanwar,

Thank you very much for the info.

Just curious, in a typical multiplex, do they have just one big center channel speaker or they have an array of speakers behind the screen for center channel? Are they custom made or branded ones like JBL/Klipsch?

Thanks,
John.

 

[kanwar]

Kanwar,

Thank you very much for the info.

Just curious, in a typical multiplex, do they have just one big center channel speaker or they have an array of speakers behind the screen for center channel? Are they custom made or branded ones like JBL/Klipsch?

Thanks,
John.

John,

See this pic, this is 3-way fully active system, normally this is more than sufficient for center channel, 3 of such units are used behind the screens for L + R + C. If the hall area is very big which is rare owing to multiplexes are of average size, we sometimes do parallel installs as well. Subwoofers are placed in stacked configuration depending on the LF needs.

Sometimes the hall is more of a cascaded stage with a screen much much bigger, there the use of line arrays is usually done which focus on specific areas of audience for dedicated coverage but that is beyond the essence of this thread.


Brands like JBL these days is more of a mass market consumer products oriented, the precision engineering is lost long ago. We have much better brands when it comes to proper pro-audio.

 

[spirovious]

So accordingly in home HTs the Center channel should be of same power as L+R.

Yes,I experienced same when I connected power amp to fronts and center to AVR,due to less power,I felt center effect with lower sound quality and less dynamic.

 

[ranjeetrain]

1. Bass content fed to center channel and surrounds are much lesser than the bass sent to the main L & R speakers in a typical 5.1 movie track.

Not necessarily. Depends on the mix.

2. You need more power to reproduce bass SPL than you need to reproduce the same SPL for mids and highs.

Correct!

The whole idea of this discussion is to understand the need for a 200w/ch, 5 channel amplifier vs a 200w/ch, 2 channel amp for the fronts L & R and 100w/ch 3 channel or 5 channel amp for center and surrounds. Do the center channel require the same power as the front L&R and do they need the same amplification head room as the front L & R.

I would also like to hear your experience of having heard the deep bass content being fed to the center channel similar to that of front L & R channels that requires a lot of power amp head room.

Center channel is critical. Especially with Hollywood movies. You can't even watch a move like "Source Code" without the Center channel. You will need to down-mix to stereo, such is the dependence on the center channel.

Re power: In ideal condition you need equal power for all channels including surrounds.

Usually, surrounds are unused. But such is the need of power that when you need current at an instance you need it, right then. It isn't like "since the amp hasn't been working for last 30 minutes for these two channel, it can deliver higher current for this scene". When you need current you need it right then. There is only one solution. If the power rails of an amp has been designed with variable loads for different channels in mind.

In ideal condition you need equal power for all channels but practically it depends. People even watch movies on a two channel system and they are very happy. How about that?

So it really depends on how much sophistication do you want for movies. Ideally you should have enough power (if not equal) for all channels.

 

[manoj.p]

I am in the camp of identical L-C-R performance. Same speaker, same cable and same amp gives you a seamless front soundstage. Once I went this route, I can never think of doing it otherwise.

Also, it would be cool to have identical surrounds. Gives a seamless all around bubble sound. ;-) But I do understand it may not be achievable in all situations.

 

[john_k_antony]

I am in the camp of identical L-C-R performance. Same speaker, same cable and same amp gives you a seamless front soundstage. Once I went this route, I can never think of doing it otherwise.

Also, it would be cool to have identical surrounds. Gives a seamless all around bubble sound. ;-) But I do understand it may not be achievable in all situations.

Even this was my plan, and tried to implement the same, with in my budget constraints. But I failed with that, may be because I chose the wrong speakers and amplification. This was my first setup

L-C-R : 3 x KEF Q300
Surr : 4 x KEF Q100
Sub : 1 x Velodyne EQ Max 12.

Amp : Denon 2310.

The above setup failed miserably in my room and I had to let it go. Now with my budget constraints, I had to settle with the following. I had to eat into my budget for stereo upgrade and get the following .

1. Klispch RB-81, 5 channel package : RB-81 II Home Theater System | High Quality Home Audio by Klipsch and use KEF Q100 for rear surrounds.
2. Emo XPA-200 for mains, Emo UPA-500 for center and side surrounds and let my Denon 2310 power the KEF Q100 rear surrounds.
3. Get my Velodyne EQ Max 10 from my living room and put it in the HT room to complement the EQ Max 12 already there.
4. Use Oppo - 105 as the pre-amp and use the 7.1 analog out.

I know that, I might not get any sonic improvements, however, I am pretty sure that I will not burn my speakers and my amps wont go to clipping mode with the above setup even at higher volumes :lol:

My dream upgrade is something like this

1. Identical 3-way L-C-R with 3 mono block power amps.
2. Identical 3-way Surrounds, if possible same speakers as L-C-R or speakers very very close to the L-C-R specs and use 2 x 2 channel power amps. I think 4 mono blocks for surrounds is an over kill
3. MINIMUM of 2 identical Subwoofers, if possible get 3 or 4 of them
4. Get a top of the line Pre-Pro, something in the range of Emotiva XMC-1

-John.