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Question for the acoustical experts: Why go with a 5" speaker array?

Discussion in 'Amps and Cabs [BG]' started by CodaPDX, Mar 23, 2009.

  1. CodaPDX


    Feb 2, 2009
    I'm an engineer, so while I'm relatively new to the bass guitar, I've already managed to spend an embarrassingly large amount of time in between work, practice, and rehearsals researching all the nuts, bolts, and juicy physics behind low frequency sound reproduction. Really interesting stuff for the mechanically-minded.

    I'm a little confused by the diversity of approaches to the design of high end speaker cabs, though. On one hand you've got traditionalists like Epifani and Bergantino that make the best of the relatively flawed approach that characterizes mainstream cabinet design. On the other you've got cabinets like the Big One and fEarful, designed from the ground up with solid acoustic engineering principles. And then way out in left field you've got the small speaker array approach characterized by Phil Jones Bass and MarkBass' smaller products. The first two groups I can understand - there's generally a compromise between what the market expects and what the acoustic engineer wants to deliver, and those two approaches represent different priorities along that axis. But the 5" speaker array approach? I have no clue, whatsoever.

    I mean, traditional 10" speaker arrays are already a hugely compromised approach from an acoustical standpoint with regard to the volume in the enclosure and off-axis performance in the higher frequencies. Maybe my understanding of the physics is incomplete, but wouldn't replacing 10" drivers with an equal area of 5" drivers only make your high frequency beaming problems worse? Also - barring drastically different design principles, the throw of the drivers has gotta be relatively less than a comparable 10" - that has to affect the overall SPL. People seem to love them, though.

    The catchphrase when talking about the smaller speakers seems to be "quicker response," but when you're talking about a speaker, isn't that basically just saying that it can reproduce higher frequencies without distortion, which isn't all that amazing a claim, nor does it seem like an advantage worth building a low-frequency speaker cabinet around. Is this a case of boutique audiophile snake oil salesmanship, or is PJB actually on to something?
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It depends on whether the cab is properly engineered or not. If the vertical lines of drivers to either side of the center line are low-passed so that the center to center distance of each line pair is no more than one wavelength within their respective pass-bands then there won't be any problem. If not the off-axis response would be horrendous.
  3. seamonkey


    Aug 6, 2004
    No expert, but this paper explains quite a bit.
    Even with 5" arrays, I'd expect that most wouldn't believe how much physical space each driver would still need.
    With 5" drivers, you'd still need to add tweeters, in their own array if you wanted to do full range.
  4. newbold


    Sep 21, 2008
    Phil Jones stuff has tweeters?
  5. as far as i can see, the multiple smaller drivers (ie 5") are more or less a gimmick. there's no advantage to using them. they are a way to separate themselves from others in the market, but not in terms of performance.

    having said that the specific 5" drivers may have certain properties that are better than common drivers of a larger size and they use multiples to achieve a high enough spl/power handling. one advantage could be stiffer cones. a larger driver may have a stronger motor which can handle a heavier cone, so one could add the extra weight to stiffen the cone, getting the same features but a different size. everything is a trade off in speaker manufacturing, and using a different speaker (but it could be the same size) can change the cabinets output.

    i went to a TB gettogether with my homemade 1x15 and an old valve amp from the 70's (Australian made, so no one really knew what to expect). when someone tried it they were surprised of the sound and thought it must have a HF horn or similar in it, because they were expecting a deep sound with very little high frequency. the speaker has quite a good amount of HF, and would be better than the common 4x10's off axis as well, as the overall cone surface isn't as wide. the

    as you can see, people have views on how speaker size effects sound, but they are only correct for certain speakers. these misconceptions sell those cabs.

    ps. this isnt saying those cabs are worse than other cabs, but they dont offer an advantage like many percieve. it is simply a point of differentiation in the presentation and marketing.
  6. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    The use of multiple small drivers is nothing new, and designs such as the "Sweet Sixteen" date back to the early 1960's. Bose later used this approach with their 800 series speakers. There are advantages and disadvantages to any design approach and multiple small driver designs are certainly no exceptions. Although good engineering is important, it must be kept in mind that sound is very subjective, and what sounds good to the player and the listeners is ultimately what's most important. For musical instrument amplification, we are often creating sound rather than just accurately reproducing it, and this can be two very different things.
  7. seamonkey


    Aug 6, 2004
    Peavey versarray is a good example of 2.5" drivers used in verticle line arrays, but just for the mids.


    Could you change out the 12" for a matrix of 5" or even 2.5" drivers? - sure if you used a crossover to make sure the matrix gets only lows and no mids. But I doubt you'd find any advantage over 12" drivers Peavey uses. I tried some in winisd and did find any worthy of use in a matrix as a woofer.
  8. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    For light bedtime reading, you might enjoy some of the articles at my little web page. I have a derivation of the speaker response equations, and some other odds and ends.

    In the frequency range where the cone acts like an ideal piston (up to maybe a few hundred Hz), sound pressure in the far field at a given distance is proportional to the product of cone acceleration and frontal area. At first glance, what the big cone gives up in linear speed, it gains in area. A closer look (at systems with comparable frequency response for instance) tends to hand the sensitivity advantage to the system with more cone area.

    I think that one effect of multiple small drivers is the ability to dissipate heat from the voice coils, suggesting the possibility of higher power handling. Of course if amplifier power is cheap, and you want to get loud, then there might be something to gain from this approach. On the other hand, the sheer quantity of material to fabricate multiple drivers might tend to bump up the overall weight of the system.
  9. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    If all the small drivers are driven fullrange, I can see a couple of potential problems - namely, narrow pattern and high frequency roll-off due to cancellation. But if the frequency response of the drivers is tapered properly, an array of suitable small drivers may perform very well indeed.

    And, they sure do look cool.
  10. CodaPDX


    Feb 2, 2009
    seamonkey - One step ahead of you - I've already read it. :D It describes the behavior of line arrays, not square arrays, however. Essentially it boils down to the fact that since line arrays essentially behave as a single linear speaker, they generate sound more efficiently in the near field (assuming a mostly horizontal room) than their clustered counterparts. The disadvantage with a square array is that it begins to approximate a planar speaker, which transmits sound unidirectionally instead of spreading it throughout the room.

    Interesting design on the Peavey, btw - kind of a cross between a traditional 2x2 array and the cross-fired line arrays on top of horns that Bill Fitzmaurice has on his website.

    fdeck - While smaller drivers would definitely dissipate heat more quickly than a larger counterpart, most of the information I've read has asserted that the primary limiting factor in bass amplification is driver excursion and not the power handling of the voice coil. And since the amount of air moved by a speaker depends on both it's area and the distance it oscillates through, all other things being equal you would need eight 5" drivers to equal the swept volume of a single 10". Given that only four 5" drivers fit into the same frontal area as a 10", this doesn't seem like that great of a deal. Granted, things are probably not equal in this case, and PJB probably uses drivers that are specially voiced for bass with a longer throw than a typical full range driver, but I'm still having problems seeing how four 5" speakers could generate the same SPL as a single 10". I dunno - maybe it just comes down to a sensitivity advantage. : \

    BTW, I've already read some of the stuff on your site, and I'm working my way through the rest. Good stuff!

    Is there a good reference text or similar place to start for someone like myself who's interested in learning more about the physics of what's going on between my bass and my ears?
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That 'If' is the entire key to whether drivers horizontally placed will work well or not, irrespective of their size. The Bose 802 previously referred to is a perfect example of how multiple drivers should not be used, as the 802 has no frequency tapering. For 30 years it's been almost universally reviled as one of the worst PA speakers ever created. OTOH the 402 OTOH works well, since the array is vertical and no tapering is required. So the end result is not a matter of using a lot of small drivers, it's a matter of whether one uses them properly.
    The Peavey array with horizontally placed woofers and midrange lines low passed below their 1 wavelength center to center distance is the same basic design as Christian Heil's V-Dosc array, which is now used by most high end PA manufacturers. Judging by the snail's pace at which bass cab manufacturers have moved since the '59 Bassman one can expect to see that level of engineering sophistication in bass gear around the beginning of the 22nd century.
  12. greenboy


    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Who will re-educate the bass players to accept this lightning-fast change? ; }
  13. buckminster

    buckminster Banned

    Apr 29, 2006
    Sacramento, CA
    I'll take my "relatively flawed" Bergantino any day...
  14. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    LOL! :D
  15. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Quite true.

    Your concern seems well-founded. Here's a way to think about it. Imagine a 10" driver divided up into four quarters. That's like having four 5" drivers. The original 10" driver shouldn't be any louder or quieter than the four quarters connected together.
  16. Brad Johnson

    Brad Johnson Supporting Member

    Mar 8, 2000
    Gaithersburg, Md
    DR Strings
    Has the OP tried any of the products in question?
  17. CodaPDX


    Feb 2, 2009
    Okay, yeah, the cone area is the same, but isn't the distance that the cone travels back and forth also a factor in the volume of the speaker, particularly at low frequencies? A 5" driver, assuming it's proportionally the same as the 10", would only have half the travel.
  18. depends on the driver itself. again its driver design, not driver size that effects things
  19. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    CodaPX, I don't think we can reliably assume that those 5" drivers have only half the travel of a 10". In fact, that would make no sense to me for the same reason it makes no sense to you.

    Eyeballing a picture of the driver, that looks like a double-roll accordian surround, so I would guess x-max is between 3 and 5 mm. That puts its excursion in the same league as many 10's, if my guess is in the ballpark. Nice ribbed metal cone, and probably has a good motor. I'm guessing that's not a cheap driver.

    That being said, I disagree with their overall design philosophy. In my opinion, radiation pattern is a first priority because it cannot be fixed after the fact by EQ or DSP.
  20. CodaPDX


    Feb 2, 2009
    Ah - that makes more sense. Not having designed or worked extensively with speakers, myself, I wasn't aware of the design considerations that went into determining a speaker's Xmax. As is so often the case, things rarely scale in a linear fashion.

    Thanks for the discussion, all. It's been most enlightening.

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