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differences between 15" and 18" speakers

Discussion in 'Amps and Cabs [BG]' started by terraplane, Mar 22, 2003.

  1. terraplane


    Oct 14, 2002
    Italy, Palermo
    What is in your opinion the sound difference between a 15" and a 18" speaker? I play with a 15" cabinet, I want know something about 18".
    thank you!
  2. bentem


    Oct 18, 2002
    Rockville, MD

    You wont get as much definition or high end with an 18 as you would with a 15

    not that theres anything wrong with rumble:D
  3. TxBass


    Jul 3, 2002
    Frisco, Texas
    of course quality and specs (and the cabinet it's mounted it) all play parts...but bentem pretty much summed it up.
    15 = 1 x muff. 18 = 2 x muff.
    muff is a "Munjibunga term" that seems to cover speaker sound of these larger ones pretty well.:D
  4. LessWooten

    LessWooten Guest

    Mar 22, 2003
    Perrysburg, OH
    18 inch speakers have larger magnets and coils which allow them to handle more bass and a louder sound but, they do have a lower sound quality which is why so many bassists use 10's so unless uplay large theatres and stadiums stick with 10's and 15's~~
  5. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
  6. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    I love my 18. I would never run it solo, but with my 2x10 it sounds great. Gives off a ton of bottom. Used to use a 15, but it didn't have enough 'boom.'
  7. One thing I know, being satisfied with both 15's and 18's is...A really good 15= a mediocre 18...I used an 18 suited best for bass, and was happy, but when I got my new 15's, although suited best for PA, size wise(not friendly for bassists 3'x3'x2'), They put out the booty...I'm thinking of replacing the 15 in another box, for use as a bass cabinet until another cabinet comes along.Anybody got specs for a JBLD140F?

    In Bass:bassist:

  8. redneck2wild


    Nov 27, 2002
    Memphis, TN
    Typically an 18 moves more air than a 15 (partially because it has more surface area).
    An 18 usually requires a larger cabinet.
    There are some exceptions. There are some very good (and expensive) 15s on the market that can match some 18s. I have seen car audio 15s that are deeper than they are wide (giving them probably as much surface area as an 18).

    Some companies sell 15s and 18s with the same size magnet and voice coil. With the same size magnet and voice coil, an 18 will have a lower frequency response and will move more air than a 15 given the same amount of power.

    I have seen cheap 18s that are not equal to good 15s. But for the most part, Pro Audio 18s will give you more deep bass than Pro Audio 15s from the same manufacturer.

    There are many "cheap" 15s on the market that do not perform well for live sound reinforcement (search for car audio subs on the internet).
    There are far fewer non Pro Audio 18s.
  9. geshel


    Oct 2, 2001
    Actually, it doesn't work that way. Since the cone moves forwards and backwards (not "in" and "out"), not all that area is "applied" to pushing the air.

    Think of it this way. Take the really extreme case, where the woofer is like a mile deep (and 15" in diameter). The cone has a huge area. But, when it travels say 1/4" it's still not pushing much air. Because mostly the cone is moving (relative to it's surface) sideways! In the infinite case the speaker would effectively look like a really long 15" tube. Slide the whole tube forward and it's not going to push much air. In fact, it'll push the same amount as a perfectly flat 15" disk moved the same amount. The surface area that counts is the area facing the direction of travel, which is always about the area of a 15" disk (slightly less in reality).
  10. Lockout


    Dec 24, 2002
    I was wondering, if I biamp with an 18" for lows (that new Ampeg 18" cab), will it make the tone muddy?

    Or is all this talk of "muff" mostly about running them full range?
  11. Low end mud comes from several points:

    1) Driver performance, specifically the Group Delay.
    2) Driver quality, specifically the BL and Le factors.
    3) The venue

    Group Delay is the amount of time required for various frequencies to reach your ear. It gets worse as the frequency goes down. A large delay (25ms or more) is heard as distinct blur or "mud". GD is dependent on the box tuning and the driver parameters. Lower Qts drivers typically have better GD performance.

    The SBB4 alignment typically produces the least amount of GD in a vented cabinet, but at a cost of a larger box and somewhat rolled off bass. Sealed boxes, by far, produce the smallest amount of GD.

    Group Delay is the most severe at/below the tuning frequency of the box. A driver and box correctly tuned at 20 Hz will have much less (better) GD at 31 Hz. The lower tuning moves the GD peak below your operating range.


    Quality drivers typically have a high magnetic motor strength (Bl) to control the cone movement. The Le (inductance) is directly proportional to the amount of turns in the voice coil wiring. Voltage leads Current in an inductive circuit, so a higher inductance voice coil brings about a current lag in relation to the applied voltage. Current is what moves the cone.

    A larger voice coil inductance introduces a time lag and increases group delay. Long excursion subwoofer coils with high inductance values are prone to this. The opposite are the high efficiency, short coils such as the JBL E145. The 10" drivers are much "faster" partly due to the smaller inductance values in their voice coils. This is a trade-off with not having much Xmax (cone movement).


    The best drivers will still sound like crap, in a crap venue.

    I play a venue with brick side walls, glass windows, hardwood floors and drywall ceilings. Boom, boom, boom. I have to EQ my subs down -6dB at 63 Hz and lower to get away from the booming room. A Carvin RL210 or similar cab with no bottom works great in this venue.
  12. Petebass


    Dec 22, 2002
    QLD Australia
    Most of the demand for 18's comes from players who use more than 4 strings. For example, a 5 string has a fundamental of 31.5 hz on the open B string. Some 15's can get close to this but not many, so the 18's get a look in.

    I wouldn't even look at most car audio subs for any pro audio application. They have great frequency range but it's usually at the expense of sensitivity. In other words, it may very well be a 15" speaker that goes down to 30Hz, but it will often be 5-10db quieter than a pro-audio speaker when fed the same signal. You could get around this by having 2 speakers, but that defeats the purpose of going for the smaller speaker in the first place.

    Bgavin's comments are spot on, especially the part about room acoustics. I can't emphasise how much the room affects your sound. My G/F has just scored a gig as the in-house sound engineer at a popular pub in Sydney. The room resonates at 125Hz and it's frustrating. But at least it's consistent throughout the room. I've played in rooms where the stage is muddy but the dancefloor is the exact opposite, making it hard to adjust.

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