Choosing A Centre Speaker

The Center speaker is the most important speaker in your system for Home Theater.

What's " LOBING"


2 centres do not give you a better central voicing. A single high quality centre always does better. Hence I changed my system a few months ago based simply on the desire to get a better centre speaker.


This will give you an idea on why 2 centre speakers are seldom used:


http://www.hometheatershack.com/forums/home-theater-audio-video-news/364-center-channel-speakers-part-2-a.html





Look around the local retailers and web dealers for speaker systems. You'll find most 5.1 speaker systems build a center speaker that matches the other speakers in the system, about the same size drivers etc. Some speaker systems will give you the option of larger front speakers. For home theater this isn't necessary, although larger speakers with larger woofers can produce deeper bass the speaker should be set to "small" in the receiver. The small setting means that sounds below the crossover frequency will be diverted to the subwoofer. A typical crossover is 80Hz. So, the front speaker won't produce any of the lower bass instead those sounds will be diverted to the subwoofer. If you have a competent sub in your system the effect of setting your speakers to the "small" setting will produce more bass. We won't delve too much into bass management, that's another topic. Suffice it to say that for Home Theater it's a good idea to set all your speakers to "small" even if you like to switch it back for dedicated two channel (music) sources.


The center speaker arrived back in the days of Dolby Pro-Logic. Dolby Pro-Logic was the improvement on Dolby Surround that had a problem with hard to hear voices. By giving the midrange its own dedicated speaker dialogue in film could now compete with splashy sound effects and musical scores that dominated the front and rear speakers in a surround system.


The center speaker is responsible for reproducing sounds in the range from about 500 to 5000 Hz. This isn't a hard limitation of the center channel just an estimate of the midrange. In a 5.1 system the center channel can receive sounds from any frequency.


There is a lot going on in that center channel. Not just voices but a lot of sound effects too. Virtually anything that goes on front and center to the camera's perspective can be heard through the center channel. A frail center speaker will rob explosions, gunfire and all those other splashy effects of the bang they should have, despite the big sub and giant front left and right speakers.


One of the most common complaints when you have a center speaker that isn't up to the task is muted voices. Dialogue gets drowned out when the action or musical score gets loud. Chances are the center speaker isn't able to produce enough midrange or the midrange has some dispersion problems which can be associated with the speaker's build.


Sound Speaker Build Quality


One of the classic "cheap" center speaker builds is the MTM (midrange, tweeter, midrange) build. This is a two way design. One tweeter sits between two woofers. Since this design has no midrange it's already off to a bad start. To make an effective center channel speaker of this design is a challenge to the speaker's builder. The design opens you up to acoustic dispersion problems called the lobing effect.


Lobing is a bend in a circle. The circle of sound from your speakers should converge on the audience. But if your center speaker is exhibiting lobing it's difficult to accurately judge the sweet spot. The net effect is the midrange suffers.


Look for a center channel speaker that has a midrange and tweeter stacked on top of each other with woofers on either side. This is a three way design and isn't usually found in the most budget speakers. Most manufacturers only build their top end center channel speaker in the desired three way design.


Not to pick on Paradigm, a fantastic Canadian speaker manufacturer. But you must go well up Pardigm's product line to get into a three way center. If you can afford it you'll be glad you did. The mainstream line is the Monitor series, they're an excellent buy. But the CC-370 (pictured at the top) is an MTM design. I have not auditioned them or put them through the test. To really determine if they exhibit lobing problems you'd have to try it for yourself in your own livingroom. But I would automatically avoid that speaker when looking to spend a bit of money on a quality design.


To get the three way design you have to go two rungs up the Paradigm ladder to the CC-570. The 570 is part of Paradigm's "Reference" series of audiophile quality speakers. The 570 is an amazing speaker that will knock you back into your seat. The CC-370 is a $300US speaker where the CC-570 retails at almost a grand.


Think of it this way, a center speaker should include a midrange! A real center will make a dramatic difference for movies. For two channel music (CD, MP3 etc) it can only serve to fill in the central soundstage, not exactly a critical job if you have well positioned front speakers. But, if you've upgraded a two channel stereo to 5.1 surround for Home Theater and skimped on the center speaker reasoning you'll upgrade it later, you might be wondering why some soundtracks seem robbed of oomph and sometimes dialogue is a bit thin. Well, later is now.

This speaker is the centrepiece of a good HT system, and we should give it the utmost attention if The Home Theatre Experience is the most important aspect of our sound system.

Some useful info:

A little info on centre speakers & lobing:

http://www.avsforum.com/forum/showthread2.php?t=686371&goto=newpost

Here is the message that has just been posted:
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Sooo... Regarding that product announcement... Well, this is the reason why we have a policy not to comment on future product announcements: The product has been delayed, and I can't tell you when to expect it (just as I never should have given you this expectation!) Just to make myself feel better, it wasn't my call alone to allow the teaser to be made, but in hindsight it was a mistake. I know some of you will feel "cheated" by me for teasing and not delivering, but this is what it is, and giving you more information now would only repeat the same error. SORRY!! Shoot me now.
Anyway, that should not hold me back from giving you the promised answer regarding our view on center speakers and lobing. However, it is not a simple one.
First off, I would like to say that there is no way to "handle" lobing in a horizontal center speaker without causing drawbacks. If there were, we would not be discussing it.
Any speaker with a horizontal driver alignment will have some degree of lobing. This is a physical fact, and while different alignments will cause different degrees of lobing, they can't be completely avoided. This means that if you want to completely eliminate it, you need to change the alignment. As mentioned, there will be drawbacks to any of the available choices, either sound quality wise, economically, or practically.
You can arrange the drivers vertically. If space allows, this can be a very good choice, but most people need (or want) a relatively low profile speaker to place below or above a flatscreen tv. For a no-compromise solution however, this is probably the best choice. It also allows for three identical front speakers. Note: Three physically identical speakers do not sound identical if one is closer to the floor, or mounted horizontally etc. So the goal of three completely identical speakers in the front can only really be realized by using an acoustically transparent projection screen. Please notice that we DO offer a solution for this purpose: Any speaker in our passive home audio lineup, from Emit to Evidence, can be bought as singles at a 10% surcharge. If you always dreamt about using a Consequence as a center channel speaker, we're not the ones holding you back. There is no acoustical arguments to not using any speaker that you find usable as left and right speakers, as a c
enter channel. Practically though, for many this will not be an option.
You can use a fullrange or coaxial driver. Whichever variant, this causes limitations and/or acoustical artifacts that are in our view much more severe than lobing, and not compatible with the performance we want to present to our customers.
You can use a single midrange, still in a horizontal alignment, either as a 2-way with one mid/bass, a 2.5-way, threeway or similar. This is actually not a bad choice, however, you don't eliminate lobing - you change it to something that may or may not be more acceptable.
You can use a three-way with a small midrange below the tweeter, and bass drivers . Aligned properly, this can minimize lobing (depending on the crossover to the bass drivers). However, it is not without cost: You have to use a small midrange, that might not have the performance of a larger one. You have an extra crossover frequency and a more advanced crossover, which isn't always a good thing if you are cost-constrained (which you basically always are!)
There are also possibilities within the "normal" horizontal 2-way alignment, that will minimize (but not eliminate) the issue without necessarily causing these drawbacks: Using a relatively low crossover point to the tweeter - which is done in most Dynaudio speakers anyway. Also, placing the mid/bass drivers as close together as possible decreases the amount of lobing.
To conclude, to answer how we handle lobing, there are two overall answers: First, We do not design a center speaker with the specific purpose to eliminate lobing. We design it to deliver the best overall performance. This is a balance between a lot of different factors, and so far we believe that the amount of lobing left in our center speakers is negligible, compared to the sacrifices that would have to be made to completely eliminate it. This balance is sometimes bent in different ways depending on the needs, and I am not saying that the solutions we have now will be used in any Dynaudio speaker ever. It's just to say that the overall performance is our goal, not the individual benchmarks. In our judgement, there are other, more pressing concerns that might not be as easy to visualize, but has at least as much impact on the performance.
Second, if you really want a no compromise setup, the best center speaker is a third speaker identical to your left and right speaker.

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The centre speaker is the lynchpin and does about 80% of the work: