Center Channel: One driver, or two?
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New member Username: KingdufusBeantown Post Number: 3 Registered: Apr-04 | Hi all, Just trying to understand speakers. What is the difference between a center channel speaker that has one driver (I think i'm using the term correctly, it means one "speaker" inside, right?) compared to another speaker with two identical drivers? Assuming they have the same frequency range, is one better than the other, and why? |
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Jan Vigne Unregistered guest | Your question could mean several things and therefore require different answers. If, in the simplest form, you have a full range (one) driver the biggest effect (particularly in a center channel speaker) is the declining dispersion of the driver as the the sine wave length of the ascending frequency becomes smaller than the dimension of the driver itself. In that situation the speaker will narrow its dispersion and the higher the frequency the more directional the sound will become and if you are not sitting on axis (right in line with the speaker) you will hear less high frequency content than a two driver system where one driver (the tweeter) is of a smaller dimension. |
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Silver Member Username: John_aPost Number: 812 Registered: Dec-03 | Awesome, Jan! Lester, most conventional speakers have two or more "drivers", the things that produce the sound. The "tweeter" is the driver takes the high frequencies, while the "bass/midrange driver" takes the lower frequencies. They get given the different frequencies by the "crossover", which is a small piece of electronics, inside the box. That describes a "two-way" speaker. The reason for this is it is nigh on impossible to make one driver (at least an electromagetic one - most are) that can cover the full frequency range at all well. Sometimes the "Bass/midrange" is divided, too, into a "mid-range driver" and a "bass driver", the latter aka a "woofer". This is a "three-way" speaker. Sometimes you can have three drivers for a different reason: because there are two identical bass/midrange drivers in the box. This is common in centre speakers, in which case the two bass/midrange drivers usually sit on either side of the single tweeter. Hope that helps. |
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New member Username: KingdufusBeantown Post Number: 8 Registered: Apr-04 | Thanks John and Jan for your answers. I'm now wondering about the three driver center channel that John describes. Why would you need two identical drivers on opposite sides of the tweeter? Does that help with dispersion? |
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Silver Member Username: John_aPost Number: 841 Registered: Dec-03 | Lester, I do not know the answer to that. I could make a guess, which is that a center speaker needs to be small, so you may get more good bass-midrange out of a slim box if you double-up on smaller drivers, putting them in a line. Some of the excellent, single, bass-midrange drivers in main speakers are whacking big things, and would need a speaker box no-one would want on top of their TV. Jan will know better than me, I am sure. |
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Anonymous | Almost all of the center channel speakers I've ever seen have the dual woofer arrangement. Generally center channel speaker enclosures are relatively small, so I would think that the dual woofer design provides somewhat better bass response, and placing the woofers on either side of the tweeter would provide a more symmetrical sound field coming from the speaker. With the center channel generally being wide and short for aesthetic purposes, it could be possible to audibly locate the drivers if only one woofer was present to one side of the tweeter. Human hearing is much better at placing sounds across the horizontal plane as opposed to a vertical plane. In the case of my center (BIC Acoustech series) the center and mains have identical drivers - dual 6 1/2" woofers and a 6 1/2" mid-high horn. |
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Silver Member Username: John_aPost Number: 843 Registered: Dec-03 | Anon, I agree. I use a KEF KHT 2005 for the centre speaker. It has one bass/midrange, and one tweeter. These drivers are mounted with the tweeter is inside the bass/midrange, so they are on exactly the same listening axis. They bump up the bass with small reflex port. It sounds darned good. |
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orbit Unregistered guest | I was about to buy an Orb speaker system. I enquired with their consultant about their center speaker -tweeters and woofers in particular. This is what they replied: "it has no separate woofer and tweeter, so it doesn't need a crossover. All crossovers affect sound quality, and this is especially true in the frequencies of the human voice. So, we believe a center channel without a crossover is the best possible design choice. " I just wanted your comments on this. Am I being taken for a ride? Is this common in speakers of this small size? |
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Silver Member Username: John_aPost Number: 849 Registered: Dec-03 | orbit, With conventional, electromagnetic speaker technology, you cannot reproduce the human voice, across its full frequency range, and at the same volume as the human voice, with one driver. Old AM radios had one electromagnetic driver, but it was no good for accurate reproduction of sound. In a perfect world you would not have a crossover, I agree, but I see no way round it with speakers that work on electromagnetic coils. Please post some more info or a link to Orb speakers, and I will have a look, and see if they have something to say on this. |
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orbit Unregistered guest | Hi John A., Here is a link to the tech specs for these orb speakers I was refering too- http://www.orbaudio.com/index.asp?PageAction=Custom&ID=25 |
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Fezin Unregistered guest | I disagree John...a sub/sat system can definitely use a full range driver as the center channel (or two in the case of the Orb Mod2 center channel), and rely on the subwoofer for very low frequencies. The Orb speaker plays as high as other speakers with a tweeter, so the high end response is not an issue. So, if we are talking about bass response, then the issue becomes one of driver and cabinet size. If you want a giant center channel, there is no doubt that a center channel with a 6" driver will have lower bass extension than any small speaker, including the Orbs. But, if the Orbs are playing flat from 100hz to 18,000hz and the subwoofer is playing everything below 100hz, I do think you can have a center channel that is just 2 full range drivers and no tweeter. |
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baseballfan Unregistered guest | While the Orbs look interesting they are only flat down to 120hz, so localization of sounds from the sub is going to be an issue since human hearing can localize from about 85hz to 90hz and up. If you have the sub in a back corner some of the sounds that should be coming from the center will be heard coming from elsewhere. If you can place the sub next to the TV or at least somewhere between the front speakers then it probably would be OK. |
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Silver Member Username: John_aPost Number: 860 Registered: Dec-03 | Fezin, Good point. Yes. Thanks! Even a conventional two-way speaker can have the cross-over at 200 kHz, I think, so a crossover at 120 Hz, and the sub taking the bass, is certainly possible. But I also agree with baseballfan: I am sure it works, but there are trade-offs. That spec (120hz - 18,000hz (+/- 3dB) would not do for a conventional speaker - computer speakers and transistor radios have ranges like that. Also, DTS and DVD-Audio specify "full range speakers all round" and that Orb is definitely not that. Even down to 80 Hz still counts as "small" speaker. |
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Orbit Unregistered guest | Thanks for all your response. John A, after you have compared the orbs to computer speakers I am hesitant to spend any money on it. I must admit that I was sold on to the orbs more from an aesthetic point of view rather than performance. That said I guess there will be a compromise as far as sound quality when it comes to small speakers. In your opinion would you know of any small satellite speakers for HT that would perform better than the orbs? I have a small room and will be using a HK AVR230 receiver. |
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Fezin Unregistered guest | John...you ever hear the Orb's? If so, I doubt you'd be comparing them to transistor radios. Quite frankly, that comment is pretty lame advice. It's funny how people can make a judgment like that based on specs, when most companies lie about specs. I prefer to make judgments based on the performance, and the Orbs blew away my friend's Snells that were way more expensive. Better, tighter bass. Much better clarity and soundstage. Not to harp on the specs thing, but even the $100 HTIB in Walmart probably claims to be 20-20,000. I give Orb credit for posting real specs. I saw on avsforum.com that someone actually tested them and they came out in line w/ the #s on the website. Most other speakers tested over there fall way, way short of their posted specs. Also, you have to judge the Orb as a system, with the subwoofer, and every single review I've ever read by a person that has HEARD the Orbs has been overwhelmingly positive. It's absurd to tear them down based on specs. Orbit -- your best bet is to take them up on the home trial. If you are looking for a small speaker, these are a great choice, and everyone on here is comparing them to much bigger (and maybe more expensive) speakers. While there are probably compromises with small speakers, the Orbs also have the benefits that come with their design, and the overall performance is certainly top of the line. The home trial is how they hooked my friend, and by extension, me. Once you hear them, you will see for yourself, they really are the best small speaker out there, and they sound big and full and have great imaging. In a small room, like you said you have, I think you will be blown away like I was. An important point that also shouldn't be forgotten -- Orb didn't skimp at all on the sub, and a lot of other HT systems do. The SPL for a sub that size is phenomenal, and it really, really sets the system apart from others. |
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Silver Member Username: John_aPost Number: 866 Registered: Dec-03 | Orbit, Fezin, No, I have not heard the orbs. I was not giving advice, just trying to work out the answer to orbit's original question. My point was only that the centers, working alone, have a comparable frequency response to computer speakers and transistor radios. That seems to be correct, and is based purely on following the link. But the orb centres do not work alone in that system, and they could well sound excellent working with their compatible sub. I personally prefer a wider range from all main speakers, crossover or not. BTW my original point "one driver will not reproduce the human voice" still stands. Normal, adult, male voices can go to about 70 Hz, I think. I will back off from a recommendation, Orbit. I make no claims to have done comparative tests. I like the centre I've got. That's all I can say. The sub as the source of all bass in the system up to 120 Hz is not a way I would choose to go, partly for the reason baseball fan describes, partly because I prefer the sub to handle just the LFE channel. But I know "small"-speakers-plus-sub is a favoured solution for many people. It also avoids having large speaker cabinets around the room! |
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Fezin Unregistered guest | Didn't mean to come off so snotty, having re-read my post, by the way  I think you can cross the Orb's at 100hz pretty well, that is what my system has them at, and I think the specs said they were less than -6db at that point. I think we all make some good points...Orbit, no matter what you get, I still say get something that you can hear in your own room and have the choice of returning w/ no questions asked. I think you'll be pretty surprised by the performance of the Orbs, but whether you wind up w/ Orb or anything else, make sure you can give them a listen at home, in your room and with your receiver and cables. I've given up on in-store demos since speakers never, ever seem to sound the same at home (sometimes better, sometimes worse, sometimes just different). |
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Silver Member Username: John_aPost Number: 870 Registered: Dec-03 | I agree with you, Fezin. In my opinion, that is good advice. Orbit: A dealer who will allow you to do a home trial will not sell stuff you can buy from a dealer who doesn't , except at a higher price, and no-one chooses to pay more. I will predict you can only buy Orbs from good dealers! |
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Jan Vigne Unregistered guest | Lester - If you are still in this you can research the three speaker arrangement by doing a Google search for "D'Appolitto". It is the name of the engineer who proved the mechanics of this type of arrangement. It requires specific palcement of the drivers in relation to each other and a specific design in the crossover to insure the wide dispersion characteristics this design is noted for. The arrangement is meant, originally, for a vertical array but the results vary little when the speaker is used horizontally. In most center speakers, my guess would be marketing drives the design of many speakers as much as sound quality does. Orbit - In response to your original question about crossovers, yes, you were being given bad advice. It would be wonderful if speakers could be constructed to the ideal of a point source. A driver so small that all frequencies could come from one point in space as they do in a musical instrument. Unfortunaely, the laws of physics say that is a real world impossiblity. The closest speaker I am aware of that operates "like" a point source is the Quad electrostatic. A panel speaker that is about 42" high and wide. A speaker like the Orb will have to push the driver very hard to extend its operating range to the frequencies stated if they are to achieve any reasonable levels of volume. Materials and computer aided designs have changed the speaker market dramatically in the past decade but the laws are still the laws. Distortion will inevitably set in and become a noticebale problem as volume rises. Dispersion, as mentioned above, is a problem I have seen no one over come so you will need to be seated on axis (right in front of the speaker) to hear the upper frequencies without a roll off of the relative levels. This is the reason for crossovers and two way designs. The crossover in some of the most respected speakers of the last four decades have been very complicated affairs that were used to actually tailor the response of a driver to eliminate the inherent irregularities of its frequency repsonse (think Theil and the venerable LS3/5a from the BBC design). This type of design makes for what is termed a reactive load (as opposed to a resistive load) because the amplifier has to slug its way through all those resistors, capacitors and inductors. It is not something you would wish on your average reciever. Some of the best small, inexpensive designs of the past and present have used a crossover that was no more than a capacitor and a resistor to keep the deep bass from the tweeter and to match the level with the more inefficient woofer. The woofer was allowed to mechanically roll off its response as the frequency rose(something all drivers do by their very nature). The crossover point is somewhere around 2,500 - 3,000 Hz since this is the lower limit for most 3/4 - 1" tweeters before they start to increase in distortion. This simple design solves many more problems than it creates and has been the basis for many successful speakers through the years. The lack of a crossover sounds like a marketing gimmick to me. Something to hang their hat on. If they feel so strongly about crossovers, why do they have a crossover between the satelites and the subwoofer? But never take anyone else's opinion as the truth on any subject. It is just that; an opinion. Go listen for yourself and judge with your own ears. Just judge with your ears, not your eyes. Quite a few small speakers are sold on how much sound they can get out of a speaker that size. Don't let the size get involved. Many a small speaker has ended up in a bedroom system after you realize, several months down the road, just how much sound they can't get out of a small box. If you are satified these are the speakers you can live with, for whatever personal reason you might have, then you should buy them, take them home and love tham no matter what. Do not let specifications get involved. For more on this read my response to "Harman Kardon" in the amplifier section of this forum. Specs can be almost anything you want them to be and they still tell you nothing. Lastly, if you are in need of a small satelite system give the Energy Take 5.1 system a listen. I'm not plugging the Energy's but they have earned a reputation as the best small speaker set up out there. Judge for yourself how the Orbs do against one of the best in that class. |
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Silver Member Username: John_aPost Number: 878 Registered: Dec-03 | Amen. No more to say. Awesome, once again. |
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baseballfan Unregistered guest | Jan's post is spot on. I wasn't slamming the Orbs as I've never heard them. All speakers make compromises of some sort, and small satellites compromise by having a relatively high crossover to the sub. Whether that compromise is outweighed by other positive factors is something that only your own ears (and eyes, since size is likely a factor) can decide. And there is nothing inherently wrong with using the sub to augment the bass outside of the LFE channel - my front mains go down to about 35Hz, but in my room I think the overall sound is better by letting the sub handle everything below my receiver's 90Hz crossover. This puts less stress on the amplifier as well. |
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Silver Member Username: John_aPost Number: 880 Registered: Dec-03 | Yes, I agree with that, too, baseballfan. I have nothing else I can add. I will come back to read. |
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Silver Member Username: John_aPost Number: 883 Registered: Dec-03 | Yes, I agree with that, too, baseballfan. I have nothing else I can add. I will come back to read. |
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Silver Member Username: John_aPost Number: 884 Registered: Dec-03 | So I thought... Sorry about that! |
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Orbit Unregistered guest | Thanks a lot for all your detailed feedback. Jan, that was a great insight! As you all suggested I will try out the orbs and compare it with other similar systems. I'm forced to go with the small speakers - WAF problems. But given this size limitation I would like to get the best performing one in this category. Jan, once again thanks for that recommendation on the Energy Take 5.1 If any of you are aware of any other sat systems worth a try please could you let me know. |
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