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Woofer question: One big versus several small?

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  • jcandy
    replied
    Originally posted by Rory Buszka View Post
    Multiple small speakers enjoy wider usable bandwidth, especially when reflex loaded, and also especially when very high SPL is not required to fill a large space. A 6.5" two-way bookshelf speaker can be designed to provide bass extension down into the "subwoofer" range (below 50 Hz), but it is much harder to make a 15" speaker play smoothly and cleanly into the midrange without cone breakup; the designs you see using 15" drivers in a two way speaker are focused on high sensitivity but they are mitigating cone breakup outside the piston band, and paper tends to do this well, but there are still compromises in the time domain and in power response flatness. The wide bandwidth achievable from smaller speakers is part of why the Phil Jones Piranha bass cabinets work well and also why the Ampeg SVT 8x10 bass cabinets set the standard for bass punch among non-exotic, front-loaded designs. Multiple small speakers with wide bandwidth can also be arranged in a manner that produces a desired dispersion characteristic, such as a column or line array.
    The first part of the post was really excellent! Very good, clear explanation of the mechanical differences. But I found this last paragraph puzzling. You seem to be comparing large-woofer 2-ways with multiple-small-woofer 2-ways, which is an odd comparison. Large-woofer 2-ways are well-known to be problematic and require special attention. The analysis changes when you consider, instead, a small-woofer 3-way against a classic large 3-way -- something like a Harbeth 40.2. Here the woofer/mid and mid/tweeter radiation patterns are well-matched at the crossover frequency and I would not know how to improve on this design, and at lower cost, by using only 6" midbass drivers in place of the 12" woofer. I think this is precisely the point of Charlie's post.

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  • Rory Buszka
    replied
    Typically:

    One large speaker will be more cost effective than multiple smaller speakers with the same excursion capability. This is because you need multiple motors, and there start to be practical limits to how small and cheaply you can make those motors. They don't get to be much smaller, or any shallower, than their counterparts on large speakers, so you still need more steel and more magnet for your motors. This also increases weight for the multiple small driver design.

    One large speaker will have less distortion reproducing high amplitude bass signals because of the ability to use a larger diameter spider and wider surround rolls with less Sd penalty, and those wider surrounds and larger spiders become less nonlinear at high excursion because they are not being yanked to their limits.

    One large speaker will be more efficient than multiple smaller drivers with equivalent Sd because of lower moving mass per unit piston area. Smaller speakers can be built using smaller voice coils and motors but as stated above there start to be practical limits to this. You can shrink the components but you have trouble shrinking the mechanical clearances required, and that prevents reluctance in the magnetic circuit from decreasing in proportion to motor size, so you make less efficient use of the magnetic material.

    One large speaker enjoys more mechanical stability because the distance between the plane of the front and rear suspension is larger for a given cone angle, giving the driver more "wheel base" to prevent rocking of the voice coil assembly, and this enables smaller mechanical clearances to be used in the larger speaker, also improving utilization of the magnet in the motor assembly.

    One large speaker will have difficulty reproducing a wide bandwidth without cone breakup effects (FR ripple at the upper operating limit) because of the higher moving mass and the greater bending/buckling stresses in the cone, so it is best restricted to low frequency operation over a narrower bandwidth, such as in a subwoofer. A speaker employing a large woofer will also need a large midrange driver capable of playing low enough to meet the woofer with low distortion and high SPL because of the woofer's more restricted upper bandwidth limit.

    Multiple small speakers enable a variety of form factors not possible when using a larger speaker, and you can get more motor force per unit area when you need a high-force design (more newtons/ampere of driving current) to drive a small vented box, for example. If the cost is not as much of an issue, multiple smaller drivers with relatively large-ish motors enable smaller vented or passive radiator loaded enclosures.

    Multiple small speakers enjoy wider usable bandwidth, especially when reflex loaded, and also especially when very high SPL is not required to fill a large space. A 6.5" two-way bookshelf speaker can be designed to provide bass extension down into the "subwoofer" range (below 50 Hz), but it is much harder to make a 15" speaker play smoothly and cleanly into the midrange without cone breakup; the designs you see using 15" drivers in a two way speaker are focused on high sensitivity but they are mitigating cone breakup outside the piston band, and paper tends to do this well, but there are still compromises in the time domain and in power response flatness. The wide bandwidth achievable from smaller speakers is part of why the Phil Jones Piranha bass cabinets work well and also why the Ampeg SVT 8x10 bass cabinets set the standard for bass punch among non-exotic, front-loaded designs. Multiple small speakers with wide bandwidth can also be arranged in a manner that produces a desired dispersion characteristic, such as a column or line array.

    Leave a comment:


  • jcandy
    replied
    Originally posted by charlielaub View Post
    So far the discussion about more smaller or fewer larger woofers has focused around total displacement, or how to arrange more smaller woofers. This is completely ignoring the fact that larger woofers are just better at producing bass. Smaller woofers that can "play low" will less efficient and they will typically (generally speaking I mean) have higher distortion for the same SPL level even when using multiples of them with the same cone area. On balance, to make that larger woofer "play nice" you will need a larger cabinet, sometimes much larger. It really depends on how low in frequency you were planning on reaching with the loudspeaker and at what SPL. Low and loud more or less requires large drivers. If you are targeting a more "monitor" like F10 of 60Hz, then a single 6.5" will probably do just fine. OTOH, 30Hz and below at room filling levels is another matter.
    I think the way you have stated the claims about efficiency are arguable, but I totally agree with the bottom line that "larger woofers are just better at producing bass". This is just a practical reality. Of course, one could custom-make small drivers with abnormally large moving mass (for low Fs) and huge Xmax and perhaps achieve a result that is more comparable. But existing systems with multiple small bass drivers are simply outperformed by large-woofer 3-ways.

    I am a bit saddened by what seems to be the latest trend in consumer loudspeaker form factor: a tower loudspeaker using multiple 6.5" class woofers. Compare a current example of this (how about the B&W 804 D3) to the good old days of a 3-way monkey coffin or a speaker like the B&W 801, which used one larger (12" ?) woofer in a big cube below the mid and tweeter, which were in separate enclosures. This is just not a great approach, and I think it's more a matter of market forces (e.g. shipping costs) that are driving the multiple-small-woofer-tower trend since they can be slimmer and lighter and each package will fit under the UPS/FedEx weight limit of 70 lbs and can be placed unobtrusively on either side of a large screen TV. Gotta have a market and an affordable price point to be successful in business.
    I agree completely

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  • billfitzmaurice
    replied
    Many of us still use large drivers to go low, they're just not mounted in the same boxes as the drivers that take over around 80Hz. It's the all in one box that was rendered obsolete the day Roy Allison first described the Allison Effect.

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  • Dave Bullet
    replied
    The real issue here is "similar other properties". Smaller drivers by and large cannot get the low Fs a bigger driver has. If you like electronica and need bass in the 20s, Good luck finding 6.5" midwoofer drivers that can dig that deep. More of a driver doesn't provide more bass extension (just louder). And each driver requires a requisite volume.

    Basically your Sd/VAS requirements determining box size become the same.

    The cost therefore of getting the same Sd might be cheaper with a larger driver over several smaller ones, all things being equal. This has already been stated.

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  • fpitas
    replied
    I'll comment, you can get useful vertical directivity by stacking small woofers. You can get a similar effect by using a fairly shallow crossover between a big woofer on the bottom and smaller woofers/midranges above. I use LR2 between my 15" bass drivers and the MTM of 6.5" midrange drivers above them, and get pretty good vertical pattern control down to 250Hz or so.

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  • Unbiasedsound
    replied
    Originally posted by fatmarley View Post
    Ask this question on pinkfishmedia and you will get completely the opposite answer, and I agree with them. Multiple small drivers don't sound as good as a single large driver. Male vocals from a large 8 to 10" driver sound better than smaller ones and the lowest frequencies sound more realistic on larger drivers.
    I agree. IMO a larger driver just sounds more full/robust and seems to produce lower frequencies more effortlessly then smaller ones.

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  • fatmarley
    replied
    Ask this question on pinkfishmedia and you will get completely the opposite answer, and I agree with them. Multiple small drivers don't sound as good as a single large driver. Male vocals from a large 8 to 10" driver sound better than smaller ones and the lowest frequencies sound more realistic on larger drivers.

    Leave a comment:


  • Unbiasedsound
    replied
    Same here I use to own many speakers with 12-18inch woofers as that was the in thing in the late 80's90's as bigger is better was the motto. lol I especially liked the 10-12inch woofer coupled to a 10-12 passive radiator type of loudspeakers including polk SDA1 or any speaker that used a passive radiator. I also liked the sound of Bipolar speakers like the Mirage M1 flagship and even Def techs until I heard Planars and Electrostats like Maggies and Quads. But after hearing Bertagni speakers I am hooked on DML's unique type of sound signature. So I guess its safe to say Ive always liked the sound of HUGE speakers.

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  • billfitzmaurice
    replied
    Originally posted by kevintomb View Post
    The advent of very affordable subs kinda was a game changer several years back.
    It changed my game back in 1972. That's when I designed and built my first sub/satellite system. As far as I know the first commercial example was done by Ken Kreisel in 1976. http://www.kreiselsound.com/timeline.php

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  • kevintomb
    replied
    Originally posted by Unbiasedsound View Post
    So basically you are saying is that people don't buy large driver 3 ways because its not required? I guess according to you every ones requirements are the same? Some people buy Klipsch large driver 3 way speakers and still use them with a sub. The only logical reason for people buying 2 ways instead of large driver 3 ways is due to space restrictions and aesthetics.

    If space restrictions and aesthetics did not matter at all then a lot of people would have a pair of 12" PA mains and a pair of 18-21 inch PA subs in there home. Or maybe a 7.1 PA surround sound in a 12X10ft. room LMAO
    The advent of very affordable subs kinda was a game changer several years back.
    There still is room for big 3 way speakers for sure, but the ability to hide a sub or two, altered what was possible in most average sized living rooms.

    I used to own some HUGE 4 way speakers with 18" woofers from the 60s and they were great in many ways.
    But now owing 2 nice subs, with some small sized 2 way monitors, im not sure I could ever go back to those huge boxes.

    I like thinking about those big old speakers, but the reality is my new stuff most likely sounds better and FAR easier to integrate.

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  • Unbiasedsound
    replied
    So basically you are saying is that people don't buy large driver 3 ways because its not required? I guess according to you every ones requirements are the same? Some people buy Klipsch large driver 3 way speakers and still use them with a sub. The only logical reason for people buying 2 ways instead of large driver 3 ways is due to space restrictions and aesthetics.

    If space restrictions and aesthetics did not matter at all then a lot of people would have a pair of 12" PA mains and a pair of 18-21 inch PA subs in there home. Or maybe a 7.1 PA surround sound in a 12X10ft. room LMAO

    Leave a comment:


  • billfitzmaurice
    replied
    A large driver 3 way used with a sub is a large driver, and along with it a large box, where it's not required. Of course there are exceptions, like PA mains loaded with twelves, used with PA subs loaded with eighteens or twenty ones.

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  • Unbiasedsound
    replied
    So basically are you saying that the lack of large driver 3 ways is due to room space and aesthetics? Or are you implying that a large driver 3 way cant be used with a sub and or not sound as good as a 2 way with a sub?

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  • billfitzmaurice
    replied
    Originally posted by charlielaub View Post
    Smaller woofers that can "play low" will less efficient and they will typically (generally speaking I mean) have higher distortion for the same SPL level even when using multiples of them with the same cone area. .
    That's not actually the case. Since sensitivity goes up by 6dB/volt with each doubling of driver count the opposite can be true. But the no free lunch rule applies, the driver cost will usually be higher with multiple drivers, and that's why they don't own the marketplace. As for the lack of large driver 3 ways, that's the result of using 2 way mains with 1 way subs. It's still a 3 way system, contained in more than one box. Since that offers the option to place the low frequency sources and higher frequency sources where each works best, which is almost never within the same footprint, it's by and large a better way to go.

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