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Woofer question: One big versus several small?

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  • Unbiasedsound
    replied
    Damn djg you looked younger then I imagined. LMAO

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  • djg
    replied
    Mounting biggest subwoofer in the world (32") on car roof - YouTube

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  • fpitas
    replied
    I think it's a case-by-case basis whether multiple smaller woofers of the same effective cone area can effectively replace a larger woofer. I needed a 15" driver to go below a 511 horn, but the drivers I saw that would be appropriate, going smoothly to the 800Hz crossover, and up to 1.6kHz without crazy peaks etc were expensive, starting at $300 or so. I ended up using four 8" 830869 Peerless drivers. Same cone area as a 15, but the overall price was lower. It's true the Xmax isn't what a typical subwoofer driver would give, but the pro drivers we considered didn't have a large Xmax either. The 8s were placed in a square pattern below the horn to give a similar polar pattern as a 15. Using the 8s allowed us to angle the front baffles, each vertical pair of 8s angling outwards about 14 degrees to help with baffle diffraction. The cabinet is tuned to 28Hz, so deep bass for music isn't much of a problem. So far everybody who has heard the system is impressed.

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  • windcrest77
    replied
    To recap my analogy of small and large woofers to bass guitar and stand up bass strings...

    String length of the bass instrument is analogous to the speaker diameter (short string = small speaker and long string = big speaker)

    String tension of the bass instrument is analogous to the speaker excursion (low-tension string = high excursion speaker and high tension string = low excursion speaker)

    The needed plucking force of the bass player is analogous to the watts you need to run the speaker (hard plucking of a loose string is needed to get the same power of soft plucking of a tight string = high watts to move long excursion vs low watts to move low excursion speaker). Additionally the stand-up bass has a "cabinet" so it needs no electricity. The bass guitar has no cabinet, it is a slab of lumber. The stand up bass is a big resonant cabinet.

    Slow bass of a bass guitar vs fast bass of a stand up bass is analogous to the slow bass of a long excursion woofer that achieves the same note via excursion vs the fast bass of a low excursion woofer that achieves the same note via size.

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  • windcrest77
    replied
    Originally posted by mikec View Post
    too much time to think---

    Has anyone listened to similar enough designs to decide if there's a noticeable difference?

    For example, nine 4" drivers or four 6" drivers would have same area as one 12". If all the drivers had similar properties would there be a difference?

    Would multiple smaller similar drivers have a higher total cost?

    Would the narrower baffle have an advantage?

    I cant give you a technically reasoned answer. But I can give you my cheap *** opinion after having attended Axpona this year and auditioned 100 or so systems. In a nutshell my wife and I preferred the sound of single large woofer systems 12 or 15 inch. Some were horn loaded, some bass reflex, none that I can remember were in sealed enclosures. Often times they were paired with horn loaded mid/high. Small or multi woofer dome tweeter System after system started to sound the same, too perfect, too clinical, with little apparent differences even at $20,000 price differential. The big boxes were just plain fun, especially on jazz with horns and stand up basses, Ella Fitzgerald, frank Sinatra, count Basie big band recordings from the 50's. Hearing the great baritone Joe Williams and the count Basie band we looked at each other and smiled. My wife and I are both dancers so we hear a couple live dance bands per week, big bands, small bands, all jazz related, often stand up bass, occasionally a slower bass like bass guitar (IOW bass with no attack) bass guitars don't swing too good. Some of our band even use a tuba player for the bass, 1920's Charleston bands. I trust my wife's ears, she isn't thinking of technicalities. After Axpona I visited here with my first post asking about doing a 15 inch system with horns and sensitive enough to hear the noise floor of my tube amps! I have a great deal of respect for folks here working all the math and voodoo, I'm not anti intellectual, a good large woofer speaker still needs that background. But this is just an empirical opinion.

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  • windcrest77
    replied
    Originally posted by mikec View Post
    too much time to think---

    Has anyone listened to similar enough designs to decide if there's a noticeable difference?

    For example, nine 4" drivers or four 6" drivers would have same area as one 12". If all the drivers had similar properties would there be a difference?

    Would multiple smaller similar drivers have a higher total cost?

    Would the narrower baffle have an advantage?

    I cant give you a technically reasoned answer. But I can give you my cheap *** opinion after having attended Axpona this year and auditioned 100 or so systems. In a nutshell my wife and I preferred the sound of single large woofer systems 12 or 15 inch. Some were horn loaded, some bass reflex, none that I can remember were in sealed enclosures. Often times they were paired with horn loaded mid/high. Small or multi woofer dome tweeter System after system started to sound the same, too perfect, too clinical, with little apparent differences even at $20,000 price differential. The big boxes were just plain fun, especially on jazz with horns and stand up basses, Ella Fitzgerald, frank Sinatra, count Basie big band recordings from the 50's. Hearing the great baritone Joe Williams and the count Basie band we looked at each other and smiled. My wife and I are both dancers so we hear a couple live dance bands per week, big bands, small bands, all jazz related, often stand up bass, occasionally a slower bass like bass guitar (IOW bass with no attack) bass guitars don't swing too good. Some of our band even use a tuba player for the bass, 1920's Charleston bands. I trust my wife's ears, she isn't thinking of technicalities. After Axpona I visited here with my first post asking about doing a 15 inch system with horns and sensitive enough to hear the noise floor of my tube amps! I have a great deal of respect for folks here working all the math and voodoo, I'm not anti intellectual, a good large woofer speaker still needs that background. But this is just an empirical opinion.


    as others have said large woofers simply "go lower" and have low-side headroom (foot room?). It's like if you compare the bass of a bass guitar where the plucked string is less that 3 feet long to the string of a stand up bass where the string is 6 feet long. For the 3 foot string to produce a low note it must be very loose, whereas the 6 foot long string can still be wound tight. Plucking the short string will still produce the note, but there will be no "attack" to the note because of such a loose string. It will be "slow bass". Whereas a 6.5 foot tall stand up bass when plucking that long tight string will produce an "attack" to the note that is exponentially louder than the 3 foot string on the guitar can ever produce. Musically this is what gives jazz "swing", the fast attack and decay of the bass with a 6 foot long very tight string. Large woofers can be "tight" with low excursion like the 6 foot string of a stand up bass. Small woofers need to be "loose" with high excursion to get the same note, like the short string of a bass guitar must be loose. So small woofers have "slow attack" in the bass, like a bass guitar has slow attack because it has such a short loose string, the compromise is to loosen the string a lot to achieve the same note. The compromise with a small woofer is to give it large excursion, but then it loses its attack to reproduce the same note as the large woofer which needs very little excursion, like a long but tight stand up bass string.

    Last edited by windcrest77; 07-11-2019, 07:40 AM.

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  • bradley.s
    replied
    Originally posted by Rory Buszka View Post
    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.
    Specifically with regard to my personal motivation for DIY, I think this overcomes the value proposition of large vs multiple small explained earlier in the post. If I was motivated to make beautiful speaker cabinets I'd lean toward larger woofers.

    That was a good post to help someone design and achieve their goals.

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  • billfitzmaurice
    replied
    Originally posted by AEIOU View Post
    I'm not quite sure how in your single mindedness you seemed to miss the fact that larger woofers do reach significantly lower
    I'm not quite sure how in your singlemindedness to disagree with me you seem to miss the fact that I said I use larger woofers, in subwoofers where they belong.

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  • AEIOU
    replied
    Originally posted by Chris Roemer View Post
    F3 (how low a speaker will reach) is not determined by Fs alone, it's determined by Fs and Qts. A large woofer w/an Fs of 20Hz (and a Qts around 0.40) CAN reach 20Hz (in a vented box), but so can 8" or 7" or 6-1/2" woofers w/an Fs of 30 or 40Hz (IF they also have Qts values in the 0.50 to 0.60 range).
    And in the real world. . . .

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  • Chris Roemer
    replied
    F3 (how low a speaker will reach) is not determined by Fs alone, it's determined by Fs and Qts. A large woofer w/an Fs of 20Hz (and a Qts around 0.40) CAN reach 20Hz (in a vented box), but so can 8" or 7" or 6-1/2" woofers w/an Fs of 30 or 40Hz (IF they also have Qts values in the 0.50 to 0.60 range).

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  • AEIOU
    replied
    Originally posted by billfitzmaurice View Post
    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.
    I'm not quite sure how in your single mindedness you seemed to miss the fact that larger woofers do reach significantly lower, simply because the have a much lower fs and the voice coil to do the deed. No problem finding a 15" woofer or even a 12" woofer that has an fs in the 20s. Try that with a 6.5" woofer! If you do have a 6.5" woofer that has an fs as low as the big boys, it will have such a heavy cone which makes it very inefficient. You struck out on this one Bill.

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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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