Drivers in tower speakers

Discussion in 'Speakers & Subwoofers' started by Steve Matulich, Apr 5, 2004.

  1. Steve Matulich

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    Why do some tower speakers have only 1 tweeter & 1 woofer while others have 1 tweeter & maybe 3 or 4 other drivers?

    More drivers may look aesthetically superior but does it necessarily mean they sound superior?

    What are the pros & cons of each?

    Cheers everyone!

    Steve.
     
  2. JimIroc

    JimIroc Agent

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    It all depends on the design. In many cases it's marketing. In other cases, it's a legitimate design consideration. In all cases, it's a comprimise, and somewhere a designer or design team chose a particular design based on their goals and which comprimises were most important to them.

    A typical 2-way is basically the simplest design, so we'll use that as the "reference" that the others will be compared to.

    So, what happens if you add another driver to make a 3 way? Well, the crossover is more difficult to design. Expense goes up. If the crossover design isn't very good, it can smear the sound around the crossover point, and with 2 crossovers, that's twice as many places in the band range where it can happen. An advantage is that the midrange driver is free to do its job without having to reproduce the bass, which can clean up the midrange. Likewise, you can use a bass driver that doesn't have to deal with midrange frequencies, so you can choose/design a driver that's best suited just for bass. Likewise, a 4-way or 5-way design is just a more complicated example of the same type of thinking.

    What about some of these other designs with 2 identical woofers? A lot of them are a 2.5 way, which means that it's basically a normal 2-way design, with an extra woofer that plays up to a certain frequency below that of the other woofer. This design has some pretty big benefits, at least in my eyes. To get good bass response out of a 2-way design, you've got to include a baffle step compensation circuit, which basically attenuates everything above a certain frequency (typically around 500-800hz) by 3 to 6dB. To learn what baffle step compensation is, do a google search. It's pretty interresting. ANYWAY... with a 2.5 way design, instead of attenuating everything above 700hz to provide a flat frequency response, a second woofer is added to play from 700hz and down. This 2nd woofer will increase output below 700hz by 6dB, effectively eliminating the baffle step. The drawback to this design is that the 2nd woofer is going to have a 90* phase shift with respect to the main woofer, which can cause some issues. Since you don't have to attenuate a 2.5 way as much as a 2-way, you wind up with a speaker that has higher sensitivity. This requires less amplifier power to achieve a desired output level.

    There's also another design that's very popular with the DIY community, but not so much with consumer speakers. it's called a D'Appolito configuration. It's still a 2-way design, but uses 2 parallel-wired woofers, one above the tweeter and one below. This design increases sensitivity by 6dB. While you still need a baffle step circuit on the woofers, generally you don't have to pad the tweeter as much. You also get the benefit of both woofers projecting a phantom image from the same location as the tweeter. This can provide better imaging. It also works well to limit vertical dispersion, so floor and ceiling reflections are minimized. But, for the same reason, this type of configuration isn't ideal for a center channel, because when tilted on its side, horizontal dispersion is comprimised. Unfortunately, due to size limitations, the overwhelming majority of center channel speakers use a D'Appolito configuration. As with the 2.5 way, sensitivity tends to be higher with these compared to a 2-way, so you don't need as much amplifier power to drive them.

    All of these designs have their pros and cons, and all can provide great (or terrible) results, depending on the quality of the design and the quality of the components used.
     
  3. gene c

    gene c Producer

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    From a "how does it sound?" perspective, more is usually better. All else being equal of course. A perfect example is the Polk R30 and R50. The R30 has one tweeter and one 6 1/2" woofer. The R50 has the same tweeter and two of the woofers (and is about 8 inches taller) and the difference in sound is hugh. Of course the new RTi series is much better, but the R30 and R50 were better for this comparison. The other benefit's are power handling and input sensitivity. The more drivers a speaker has, the more power it can handle. And to a lesser extent, the SPL seems goes up a little. As for why this happens? Don't have a clue. Gene
     
  4. ChrisWiggles

    ChrisWiggles Producer

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    I would disagree with this wholeheartedly.

    In fact, I probably wouldn't move beyond 2-way stand-mounted monitors unless I were reaching beyond the $5K point for a pair of speakers.

    IMO, if anything more drivers is totally irrelevant on its own to the sound of the speaker. More drivers can have more bass output, sure, but the overall sound will have to suffer at a fixed price. Plus it is much much more complicated to design crossovers and driver placement and interaction with 3 way designs and designs with many drivers.

    The sound is the most important, and there are many ways to get there. Many drivers can be done extremely well, but so can small 2-way speakers. Listen to the speaker with a variety of music, and make your choice there. I think you'll find if you listen carefully, you'll end up preferring smaller, more accurate speakers than big bass-capable speakers that sacrafice accuracy for SPL output.
     
  5. Chris PC

    Chris PC Producer

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    Its all about trade off's. A large tower with only one woofer is actually making the most of that single woofer with a large enclosure. More drivers aften equal more efficient. More woofers almost always mean more bass volume, as in, as the volume and power goes up, the bass does too, and usually lower bass extention too. More drivers also = higher power handling.

    Often 2 way designs are good because, as others have mentioned, they are simple.

    I myself have 2 1/2 way towers and they sound great to me. Out of curiosity, I'll compare them with my 2 way surrounds. Its a good test because they have identical drivers.
     
  6. Chris PC

    Chris PC Producer

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    Aside from a noticable drop in efficiency and less bass, I didn't notice a huge difference. Certainly didn't sound "better" than my towers. My towers are identical except they have 2 additional 6.5" woofers covering 500 hz to roughly 32 hz (well, technically all three woofers work away at 32 to 500 hz, with the mid/woofer operating 32 hz to 2500 hz where the tweeter takes over). Mine are 2 and a half way.
     
  7. gene c

    gene c Producer

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    Does this mean all multiple-driver towers below $5000 a pair don't meet your standards? If so, me and you are looking at this from completely different perspectives. Anyway, I'm making my comparison's within the same brand. In doing so, I stand by my comments. Wholeheartedly! [​IMG] Have a great day! Gene
     
  8. LanceJ

    LanceJ Producer

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    A two-way is a good choice IMO if you don't move beyond an 8" woofer but if you like listening at consistantly high volumes but still desire accuracy, I would advise buying that 2.5 way speaker or better, the 3-way version. Why? Because a single woofer aggressively pounding out the bass notes is going to negatively affect the important midrange frequencies (whether b.m. is used or not); large woofers just can't move as quickly compared to a lightweight 4" or 5" mid driver; and large woofers have problems with narrow midrange dispersion (i.e. "beaming").

    And a dedicated midrange driver can be optimized to reproduce only one set of frequencies, rather than trying to get the woofer to be a jack of all trades. And before someone reminds me [​IMG] I am very aware one of my favorite speakers, the Large Advent, is a two-way with a 10" woofer. I do think it sounds good (because of very specific woofer and tweeter designs and their crossover points) & it does have compromises but the positives outweigh these, especially when taking into account its price.

    These days so many manufacturers are run by the company's bean counters I think you don't see as many true 3-ways as in the previous decades since they do cost more to design/produce (though computer modeling techniques have brought down the cost of research & development a lot) and they might feel the 2.5 way is "good enough", particularly in the very competitive mid-fi market.

    LJ
     
  9. ChrisWiggles

    ChrisWiggles Producer

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    No, I'm not saying that at all. I too would RATHER have a floorstanding, full-range version of my speakers (they are dynaudios). But take a given budget level, I am a big music fan, and the overall quality of the sound is more important than the bass extension. I listen to a HUGE variety of music, so bass extension is quite important for me, and for the small speakers I do have, they pound out a *LOT* of bass. I do have an SVS to help out down low as well a little bit.

    But I'm saying that at this given price, I could have spent $1500 on a pair of floorstanders, but not had the same sound quality because I'd have to move down a line to afford it.

    Same thing applies, say there were a floorstanding version of my speakers (there aren't mine are audience 52SE). It would probably cost a thousand dollars more, and with that much added expense, I could afford a different stand-mounted speaker at a higher pricerange, that would be far superior. And so I'd go for that one instead.

    I'd ALWAYS *prefer* to have a floorstander for the added bass capabilities, but the added expense of that usually allows you to step up to a better stand-mounted speaker isntead, and that improvement is more important than the added bass. If I get a bass urge, I take my receiver out of S. direct, and turn up the SVS and rattle my walls. And then I can return to the previous SQ whenever. You can't really *add* quality sound like you can bass with a subwoofer with the same ease.

    I hope that makes sense?
     
  10. gene c

    gene c Producer

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    Thanks for the clarification. I was hoping that's what you meant but wasn't sure. I was comparing a $35k BMW 318 to a bigger $45k 525. You were comparing that 318 to a $35k Chevy. The BMW is much smaller, but a better driver. I was comparing speakers from the same maker at different price points, you were comparing different makers (and sizes) at the same price. Now that I fully understand what you meant, I agree. Wholeheartedly![​IMG] Gene
     
  11. JimIroc

    JimIroc Agent

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    I won't disagree that typically a speaker like the R50 may sound better than the R30, but I will disagree with *why* it sounds better.

    For one, the drivers in the R50 aren't the same as what's in the R30, assuming that it is truely a 2.5 way and not a 3 way. If it's a 2.5 way, it would have 1/2 the impedance of the R30, which it does not. If it's a 2.5 way, that means it uses a pair of 16 ohm woofers, and I have yet to see a pair of drivers with different voice coils that have identical t/s specs. They differ somewhat. Even if they had identical t/s specs, the different impedance, as well as a different baffle step compensation approach (extra woofer instead of crossover design) will require an entirely new crossover. I would be willing to bet this different crossover has more to do with the different sound than anything else.

    This brings me to my next point. Who in their right mind would pay more for the R50 over the R30 if it sounded exactly the same? I guarantee that they were designed to sound different. It all boils down to marketing, at least at the price point that the polks are aimed to fill.

    Oh, and I'd rather have the $35k chevy over any $35k bmw... although that's an intirely different arguement. :p
     
  12. Chris PC

    Chris PC Producer

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    I like the 1/2 way speakers (as in 2 and 1/2 way). In my towers, the tweeter covers above 2500 hz. The three 6.5" woofers cover from the bottom most bass up to 500 hz, with the top most ,mid/woofer covering all below 2500 hz. You still have two crossovers, but the 3 identical drivers create a nice blended sound. Those drivers don't have to move too much either, even at low frequencies, as the cabinet is big. I may have noticed a somewhat more point source effect from the two-ways, but I don't think I liked it. It made the sound boxy. My towers create a nice full sound with good imaging.

    I admit though, that I often wonder what happens with three woofers all working together on the bass from 500 hz and below. But then I lean back and turn off the lights and my theories vanish. It sounds good so I forget about my curiosity and listen more. I just want more bass [​IMG]
     
  13. gene c

    gene c Producer

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    I have no idea if the R30's and R50's have different crossovers, baffles, impendence or anything else. If they are different it's for one reason...they added another woofer. And how about this. It seems that most 5.1 speaker packages do the same thing. The center channel has two mid's and a tweeter where as the surrounds use one mid and tweeter. My center has two 4" 8 ohm's wired in series and the surrounds use one 4" 8 ohm wired straight to the connecter. The crossovers look the same but who knows. I hooked them up as L/R and turned the receiver to stereo and the center sounded better. Smoother vocals and and a bit more bass. I'm sure the bigger inclosure had a lot to do with it, but I also think the extra mid played a big part as well. This was confirmed when I dis-connected one of the mid's from the center and wired the other straight to the connector. This caused a little drop in bass and a big loss in the added smoothness that was there before. My conclusion is two woofers/mid's generally sound better than one. Why? As I said in my first reply, "I haven't got a clue". In my opinion, it just does. Gene
     
  14. Steve Matulich

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    Speakers which have 1 tweeter & 3 woofers - do those woofers have music/voices coming out of them or do they just act as a 'subwoofer' with "doof, doof, doof" coming out?

    What about the towers which have 1 tweeter, 1 midrange & a powered sub.

    Does having the powered sub allow more power from the amp to be distributed to just the tweeter & midrange thus making the speaker sound much richer?

    Just another thing, if clarity is sometimes a problem with the centre channel why do they not have 2 tweeters?
     
  15. Chris PC

    Chris PC Producer

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    Like my speakers with 1 tweeter and 3 woofers, two woofers are just that, woofers, operating 500 hz on down, one mid/woofer is operating from 2500 hz on down. One of the main reasons for this is because it blends well. As to how much vocal comes out of the woofers at 500 hz and below, I'm sure some voice comes out, it all depends on the frequency. Time to look at a graph showing instruments and frequency ranges.
     
  16. JimIroc

    JimIroc Agent

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    Of course it sounded different! With one speaker disconnected, the impedance presented to the crossover changes (it doubles), which will completely goof up the crossover. All this proves is that an incorrect crossover sounds worse than a correct one, which I don't think was ever in question.

    Your experiment had too many variables to prove anything. It would be like saying that more kids drown in swimming pools than in drinking glasses due to the pool having more water, while completely ignoring the fact that a kid can't fit into a drinking glass.

    Your "little drop in bass" is most likely a 6dB loss due to losing the 3dB added efficiency due to having a 2nd driver, as well as losing 3dB of amplifier power due to the higher impedance of a single driver compared to a pair of paralleled drivers. Your lacking midrange is due to the same issues, as well as the crossover not being able to function as intended, which would have reaked havoc with the frequency response and probably allowed all of the upper frequency cone breakup resonances to be clearly audible.
     
  17. Michael__M

    Michael__M Stunt Coordinator

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    Nice thread - Good info Jim [​IMG]
     
  18. gene c

    gene c Producer

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    Ya, this did turn out to be a nice little thread. Even if my little experiment didn't prove anything, I still enjoyed doing it. I still think the main reason they add another woofer is to push more air and hopefully lower the frequency response. Some makers, like Cerwin-Vega, just use a larger woofer, some add another of the same size. But who thought this would produce so many emotional and intelligent responses? Even if I didn't teach much, I did learn a little. Gene
     
  19. JimIroc

    JimIroc Agent

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    more woofers don't lower the frequency response. If each woofer has a -3dB point of 45hz, then the pair has a -3dB point of 45hz. You can't get more bandwidth by adding more of the same thing.
     
  20. gene c

    gene c Producer

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    I was waiting for you to say something like that! The R30 goes to 45hz and the R50 to 40hz. So is the lowerer response is due to the crossovers, ohm's, baffles and such or do you think the two woofers are not identicle as I thought they were. And while I'm at it, would two identicle woofers increase the spl over one at the same HZ? And thanks for taking the time to sharing your knowledge. Gene
     

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