F3 of a sub??? What is this?

Discussion in 'Archived Threads 2001-2004' started by Charles J P, Apr 18, 2002.

  1. Charles J P

    Charles J P Cinematographer

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    CJ Paul
    This post is really long, with some background detail. For those of you who dont want to read the whole thing, I am looking for a 10" woofer with an F3 of 30Hz or less in a .8-.9 cu-ft enclosure for car audio application that is $50-$70. Any help?

    Normally I would post this in the after hours lounge since its really about car audio, or in the DIY area of I was building this myself (but I'm not). Since its just a question about passive subs and driver specs, I thought it might benefit the readers here that dont hang in the DIY area. I'm planning on getting a new car in October, and being the big impatient nerd that I am, I've already started researching the changes I'm going to make to the stereo. It will be a Subaru Impreza WRX wagon, and I am keeping the stock head unit. I will be using a 50X4 amp in three channel mode to power the fronts - which I will be upgrading - and a single sub (rear speakers will remain powered off head unit.

    So, any way. I go to the local car audio shop (the only one in town that I would trust to do an install on a brand new car) and let them know what my plans and that I dont plan on spending 1 or 2 grand on this, but just a few hundred dollars. So he shows me this JL Audio 10-W-0 sub (10" sub "zero" series is JL audios lowest series). They want only $100 for one 10" in a .8 cu-ft enclosure. I am unable to listen to the sub in this configuration since their listening room is setup for visual apeal not audio (Please dont say, "I would never buy from a place that wont let me demo" these guys win tons of awards for flashy installs, and due to the car audio market must cater to 16-20 yr olds with mom and dads money).

    So, to get to the point of the topic, I go to JLs website and look up the specs for this sub. The F3 in a sealed enclosure is like 43Hz. There is also a frequency response graph that shows that the sub drops off really high in a sealed enclosure, so I assumed that the F3 is the point that the sub is down 3db in a given enclosure (also the F3 was a different number for a ported box)

    Now, I dont want boomy bass, so maybe a sealed enclosure is good, but I'm not apposed to ported boxes except the boxes they had there were like 5 times the cost of the woofer ($250 for a vented box built custom for the JL woofers and only $50 for the sub on sale).

    So, is there any 10" woofer on the market that will do better than 40Hz in a 1 cu-ft enclosure without eating up my whole budget? It doesnt have to be big name... anything from parts express??? other DIY vendors? Basically the box and woofer are on sale for $50 each. I would like to stay under $120 so if I can find a more capable woofer for $50-$70 shipped (maybe asking to much?) then I could just go buy the box. Any thoughts?
     
  2. Harold_C

    Harold_C Stunt Coordinator

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    The JL Audio subs (both their drivers and their enclosures) are terrific. In fact, my home theater sub uses a JL 10W3.

    JL gives hones specifications. However, keep in mind that their specs are given with the drivers and enclosures in an open location (quasi anechoic). A car is like a living room in that it provides significant room gain. In fact, the car provides even more. Typically, you would expect to get an extra 20 dB at 20 hz just from the cabin gain in a car.

    A JL enclosure with a -3dB point of 40 Hz in the test lab would rock when installed in a car.

    Don't confuse the honest specs from a company like JL with the "ad copy" specs that you see from most subwoofer manufacturers. JL is killer at providing ALL of the engineering specs for their drivers.
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Your goal of flat response throughout the frequency range is understandable. But you haven't begun to consider cabin gain. Even in home theater applications, sealed subwoofers are designed to work with the natural room gain slope of 12dB/octave. But in a big home theater room, that gain begins at a fairly low frequency - maybe 25 or 30Hz.

    In a car its a whole different story. The cabin gain is still 12dB/octave but in such a small space its going to start at a much higher frequency (a pure guess would be 60Hz). So any subwoofer that's designed to be flat anechoic down to 30Hz won't be flat at all when you put it in your car. It'll likely be flat to 60Hz and rise to +12dB by 30Hz.

    My suggestion is to design it flat to 40 or 50Hz and let the cabin gain do its work.

    Since you're already designing the sub yourself, why not build it too? A small sealed sub is extremely easy, given access to a few tools. And it could be significantly cheaper. Consider the $25 Clarion 10" subwoofer from madisound. It would probably work well in very small sealed enclosures (0.5 to 0.75 cu ft). Its no Xmax champion, but should perform well.
     
  4. Mike boettner

    Mike boettner Stunt Coordinator

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    Ryan,
    The clarions are all sold out[​IMG]
    Mike
     
  5. Harold_C

    Harold_C Stunt Coordinator

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    Here's the data sheet for that driver in a .75 cu foot sealed enclosure. The second page of the PDF has a freq. response curve (with no cabin gain).
    JL Audio data sheet
    BTW, I am installing exactly the same thing in my car on with the slightly beefier 10W3 driver. The frequency response will be essentially the same, the beefier drivers just has a 2.25 inch voice coil instead of 1.4, more linear one-way excursion (.51 inch inches instead of .34), double the power handling, and a dual voice coil.
    Both drivers in that size sealed enclosure should be extremely musical. The reviews of the JL 10 inch driver combo in their seal enclosure of that size have been oustanding.
    I'm using the 10w3 driver in a 1.4 cubic foot vented enclosure in my home theater system. These are among the nicest subwoofer drivers I've seen. JL has their act together on their bass drivers. They are not cheap, but they are properly engineered.
    I would say that your local dealer made a very sound recommendation and that you won't go wrong.
     

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