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speaker building question

Discussion in 'Amps and Cabs [BG]' started by link wray, Feb 18, 2005.


  1. I am designing a speaker cabinet. It is now tuned at 50hz, but somebody tells me that this makes the speaker extra vulnarable at this frequency because this is also the speakers fs. I believed it was common practise to tune the cab at the speakers fs. Any opinions?
     
  2. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    It is a common practice to tune the box to Fs. The problem is if Fs is higher than the lowest note you want to play; below Fs the driver is subject to overexcursion and associated distortion.
     
  3. Hm... the cab i am designing is a copy of Avatar's B212 (wich you can not buy in Europe), and the Avatar also is tuned to 50 hz and i heard of no problems with it. I also ran a few simulation of a typical 4x10 through win ISD and those all have to be tuned to 60 hz....no problems there either. I guess i will be safe as long as i do not put to much power through them. (wich also would mean that Avatars 1000 watt rating for the B212 is a bit optimistic)
     
  4. andruca

    andruca

    Mar 31, 2004
    Madrid (Spain)
    It's exactly what I think of this kind of cabs' "happy rating". You simply cannot sum the rated power handling of speakers. Because given certain cabinet designs speakers can exceed Xmax (or even Xmech) at a power rating WAY BELOW half the sum of power handling RMS rates.

    Let's impose some new kind of measuring for cabs, the WBF norm (Watts Befor Farting). And it would not only consist of one number, no!, cabinets shoud be measured in at least WBF30, WBF50, WBF125, WBF250 (all of them in every spec sheet!) for measures taken with 30/50/125/250Hz signals. This would be a fair power rating measurement! We'd exactly know at what point to expect a cabinet to fart given the range of frequencies our sound is more enhanced at. I'm absolutely serious about this. I even have thought of dBBF30/dbBF50/... which means what volume is the cabinet able to deliver before farting at a given frequency. Am I asking for too much? Can't these be seriously measured? Will I have to buy some SPL meter to prove this? I think these kind of measures have WAY more to do with the reality of cabinet behaviour!

    ANDRUCA
     
  5. The Avatar cabinets are a generic one-size-fits-all type design. It is not optimal engineering, but a concession to lowering manufacturing costs by using a single cabinet for 2x12, 4x10, and so forth.

    Since you are building a cab, why not do it right, and match it exactly to your driver? This will give you the best possible results.

    If you have a driver, use my spread sheet to calculate cabinet volumes. If not, use my spread sheet to find the appropriate driver, then build the cab to match.

    I prefer the SBB4 alignment, which tunes at Fs. This gives the lowest amount of group delay (mud) for nearly all drivers. The bass does roll off a bit higher, but it really only looks bad "on paper", and can be EQ'd as required. The positive side is the tight, fast bass you will get in the bottom end.
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Tuning fb to fs was de rigeur prior to 1970 or so but since the adoption of T/S parameters it's unusual for a box to end up that way, as having fs and fb the same is of no particular advantage in and of itself. Where the fb is placed is mostly a matter of what the desired response of the box is. For electric bass that usually means delivering maximum output from 60 to 120 Hz, as that's where most of the power requirement for electric bass lies.

    While the notion of having fb no higher than the lowest note being played seems logical, in fact this is not a requirement. The SPL of electric bass at 40 Hz is some 25dB down on average from that at 60 Hz. Since the SPL of the box goes down at a rate of 24dB/octave below fb even a 60Hz fb is quite adequate, as you'd have to go all the way to 30 Hz for response to be down by 24dB. An EVM15B in an optimally tuned alignment has an fb of 58Hz (and fs of 43 Hz), for instance.
     
  7. Thanks for all your answers people!
    I did not intentionally copy the avatar design, but by comparing speakers specs i decided the eminence delta 12 lf would be a good candidate. Then i ran into some problems with enclosure size, so i took a look at what commercial manufacturers use in their 2x12's and Avatar happened to be the first one i looked at. Since they also use the delta 12LF i ran their design through winISD and it seems to be a good compromise between portability and sound quality parameters. Its internal volume is 147 liters.
    I will see later if i can improve on this design, now i am at work so no winISD.
     
  8. I now tuned at 38 hz; results seem better.
     
  9. Sorry for posting in a thread that is half a year old, but it seemed better than opening a new one.
    I recently finalised the 2x12 design together with a friend who designs hifi-speakers for a hobby and has professional software for speakerdesign. We managed to make the design much smaller while still having the same bass response: it now is only 100 liters and has the drivers in a vertical alignment. So no longer an Avatar copy; drivers are still Eminence delta 12 LF's. A matrix eliminates cabinet vibrations and supports the drivers (they dont have a casted frame so this is good since they will be transported a lot). The matrix in this design turned also out to act as a Briggs-filter, wich will give the cabinet a better 'WBF'-rating (see above). The prof. software predicted the driver leaving the linear excursion zone at about 250 watts for the Avatar 212. This does not implicate the 'WBF-rating' for the Avatar is this low since not being 100% linear is not farting out yet, but it certainly proves Andruca's point (we also found that the Avatars drivers will not be in danger of mechanical failure under 1200 watts so Avatars specs are no bull****, they just dont tell you anything about farting out) . The drivers have been shipped, so in the next weeks the cabinet will be built. i will keep posting here and will possibly publish the design here if it turns out to be good in reality.
     
  10. I dont understand this: the fact that there is not much power in the basses' signal under 60 hz does not mean i want my speakers to reproduce it incorrectly...
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That's a perfectly logical statement and applies absolutely when you're referring to hi-fi speakers, whose job it is to faithfully reproduce a recording. It doesn't apply to musical instrument speakers, because those speakers are part of the instrument, and as such create sound, not reproduce it. Speaker coloration is part of the tone making machine, and one of the traits of electric bass speakers going back to the first time Leo Fender plugged in the first P Bass is that they don't have flat response to the fundamental, nor anything even close to it. Try using your head with a high quality full range hi-fi speaker and you'll see what I mean, they just don't sound the same. That doesn't mean you might not prefer the sound of an accurate speaker with your bass, what sounds good is all in the ear of the beholder.
     
  12. Well, i guess the cab will be pretty hifi-sounding then...
    Does any commercial manufacturer use a matrix in their cab ? or will this cab be the first one?
     
  13. Masher88

    Masher88 Believe in absurdities and you commit atrocities

    May 7, 2005
    Cleveland, OH
    Oh Boy do I agree! Stop with the "marketing schemes" and start with the real world applications!!!!!
     
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    What's a matrix?
     
  15. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The measuring standard already exists, as specified by the AES. In the hi-fi world bandwidth averaged SPL1m/1w, along with both the -3dB and -10dB frequency and full frequency response graphs are the norm rather than the exception with high quality speakers. The musical instrument loudspeaker industry in general just doesn't use it. The only consistent measurement you'll see is watts, which is meaningless. In the good old days- meaning before the FTC put an end to it- you couldn't even compare watts, as some used RMS, some EIA, some Peak, some 'Music Power'. The same speaker or amp could have anywhere from a 50 watt to a 500 watt rating depending which specification was used. Caveat Emptor.
     
  16. A lot of cabinet bracing; looks like this:
    [img:]http://www.speakerbuilding.com/content/1044/05_bracing.jpg
    [/img]

    I am aware it adds some weight...
     
  17. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That's called shelf bracing and you're a few decades down the road from being the first to use it. It is the best bracing method, also the most complicated to install. I find keeping free panel area at seven to nine inches width does the job in eliminating vibration in even the highest power subs. For a bass cab an unbraced width of up to 10 inches is OK, and that's using 1/2" Baltic birch, with heavier material up to a foot is OK. Take the weight you invest in the bracing to use thinner cab walls and you'll actually end up with a lighter box. 3/4" is the preferred material for commercial boxes not because it's better but because it's cheaper than properly braced 1/2" that carries a high labor cost.
     
  18. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Yep I prefer 1/2" walls + bracing.

    Just for fun, I built an unbraced cab with thin 1/2" walls, then crank it with a bass-heavy song. The vibrations made it dance across the room. It's also a waste of acoustic power.

    Bracing made the problem disappear. The box is still lightweight, and it reproduced lows much better. To get the same effect from thicker, unbraced walls, I had to use walls that were 1" think. That cab weighed a hell of a lot more than the 1/2" braced cab.
     
  19. The vast amount of bracing shown in the JPG above will most likely bring the weight of the cabinet close to that of 3/4" unbraced material. Despite the holes, I suspect a significant displacment occurs with that scheme. Build one, and stick it into a full tub of water, to find out how much it displaces. Then add that much more internal volume to the cabinet.

    Those with time and money on their hands might try using that bracing technique with 1/4" panels to realize some weight savings to compensate for all the work and extra material in the complex bracking scheme.
     
  20. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Whoa I missed the .jpg. Now that I've seen it, I agree, it's overboard. You don't need nearly that much bracing to eliminate panel vibrations.