IB Sub in a car?

Discussion in 'Archived Threads 2001-2004' started by Andrew S, Mar 24, 2002.

  1. Andrew S

    Andrew S Stunt Coordinator

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    I'm sorry if this is a stupid question, but I was just curious.

    After reading about how IB subs seem to offer excellent bass and have SPL levels that compare to other types of subs.. I was just curious if it was possible to use an IB sub in a car application? Would it be possible to mount the sub under the rear deck and cut a hole in the rear deck to put the vent? Again.. I appologize if this is a stupid question. I was just curious.

    Thanks

    Andrew
     
  2. Bob Ahlberg

    Bob Ahlberg Agent

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    Not a dumb question. In cars, that application is typically called "free air" rather than infinite baffle. There are subwoofers that are made particularly for that type of use. Three things to remember:

    1. They do not handle as much power in a free air installation.

    2. It is important to seal off the trunk from the cabin of the car very well. Air leaks will reduce performance.

    3. They do not usually give as high spl levels as a sealed or ported installation. This is usually related to power handling levels.

    With that said, you will also get some of the most musical bass you have ever heard in a car. Fewer response peaks and smooth rolloff to the lowest frequencies.

    Bob
     
  3. ColinM

    ColinM Cinematographer

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    I ran 2x10" free-air subs in my old 72 Cutlass.

    ELP never sounded so good!

    Get a good seal around the trunk, and some expanding foam for nooks.

    - C
     
  4. David Giles

    David Giles Stunt Coordinator

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    Okay, I know this is off topic from the original question, but I'm considering an IB for my home and am trying to learn as much as possible.

    Bob's three points are very interesting, and I'm just curious as to whether points 1. and 3. also apply to home IB installations.

     
  5. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    I was under the impression that IB subs just tend to be more efficient (sensitive) than sealed subs. Because there is less backpressure in the enclosure, the IB driver requires less power to reach the limits of excursion. This would be a good thing.

    But I don't see how it would reduce SPL any. The amount of low end bass it can produce should be dependent upon how much air you can displace. Take 2 identical drivers, put one in a sealed box and the other in an IB. At the excursion limits they both move the same amount of air but the sealed driver requires more power to do it.

    Am I off here?
     
  6. Jack Gilvey

    Jack Gilvey Producer

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    Right-on, Ryan. [​IMG] Deep bass is displacement limited, in an IB it just takes less power to get to max SPL/excursion at a given frequency. This is a good thing, but the concept of "power handling" is largely misunderstood.
    In addition to its other advantages, I think that one factor that contributes to the superior sound of an IB is that that it requires less power be delivered to the voice coils leading to less power compression and other non-linearites from heating the voice coils.
     
  7. Jeffrey Noel

    Jeffrey Noel Screenwriter

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    Now this sounds interesting as it would save so much space in the trunk. Just one question, exactly how would you set one of these up in the trunk?
     
  8. Brian Bunge

    Brian Bunge Producer

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    Jeffrey,

    Back in my car audio days I saw several IB setups. They usually consisted of a baffle made of 3/4" MDF or plywood mounted against the back seat or rear deck. The one issue is that you really have to find and seal up all other openings from the trunk into the cabin. That means any hole in the metal where any air can pass from one compartment to the next. Depending on the vehicle, this could be quite simple, or quite time consuming.

    Brian
     
  9. James Mudler

    James Mudler Stunt Coordinator

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  10. Mark Seaton

    Mark Seaton Supporting Actor

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    Hey guys,
    No question, IBs are a great solution for great bass while maintaining your trunk space. I have a pair of Tempests mounted IB in my '86 Cutlass Supreme. The main issue with IB drivers is that if you can find the right driver, you can achieve huge efficiency gains over small sealed box. A lot will depend on the range of frequencies you intend to use the driver at, but in general you want a fairly high efficiency driver with it's natural roll-off appropriate to mate to the cabin gain for your given size car. In my case, the trunk makes for a little more than 20 cu.ft. of rear enclosure for the pair of Tempests(mostly because I could make them fit [​IMG]). Basically this yields a rising response with decreasing frequency (sounds quite interesting) which I then correct with a simple, passive 1st order HP filter. Power requirements are indeed greatly reduced for very low frequencies with this setup. IN fact only about 1/10th the power is required for full output at 20Hz relative to 80Hz. Certainly should help with IM distortion and total current draw. Down the road I will likely find some more efficient drivers, but they do just fine right now. I am tempted to drop a pair of the Lambda TD-15X drivers in there though. Could put the 750W of power between the two to better use. [​IMG]
    Regards,
     
  11. Bob Ahlberg

    Bob Ahlberg Agent

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    Just a couple of comments to clarify some things: First of all, the original context was car audio where the objective for "some" is not just low bass, but very loud bass. With the cabin gain available in most cars, even subwoofers that are 3db down at 50hz in a sealed enclosure are flat to 20hz in a car. Nominally flat setups have a very strong rise below 80hz...depending on the car as much as 15-20db by 20hz. As you might imagine, between the cabin gain and the smaller area that you are trying to pressurize, levels of over 130db are fairly easy to hit with even just two 10" drivers. Still, very few free air setups are used specifically for spl...with the exception of the spl only vehicles which use modified IB arrangements to use multiple drivers.

    "Most" drivers used in an IB setting in car audio are made specifically for that purpose. (although some enterprising individuals are using a number of nanufacterers drivers in IB) It is true that drivers used IB will reach xmax at a lower power level...thus the lower power rating that a manufacturer puts on a design made IB driver. Also, in car audio, many drivers are designed to fit into small boxes. They "tend" to have a higher "Q" and higher fs than drivers that work well in free air or infinite baffle setups.

    Many of the drivers we look at here such as the Adire 12, 15,18" drivers and the BP drivers have a very low fs and work fairly well in IB. With all of that said, I have two Parts Express 12" dual voice coil drivers in a specially designed ported box that will bury a similar setup if used for IB. I can approach 150db in a ford explorer. (no, I am not inside it at the time) Please notice that I said nothing about sound quality in this last comparison.

    my .02

    Bob
     
  12. Andrew S

    Andrew S Stunt Coordinator

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    Thanks for all the replies.

    I was just asking because the other day I started reading up about IB subs and started thinking about how it would save trunk space like someone above mentioned... as well as the sound quality.

    People have mentioned using specifically designed "free air" drivers, but how would maybe a tempest work in an IB car setup? I know someone above mentioned two tempests in his '86 cutlass I think?

    Does anyone have any specific pros and cons as to using an IB design in a car environment?

    Thanks

    Andrew
     
  13. Jack Gilvey

    Jack Gilvey Producer

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  14. Bob Ahlberg

    Bob Ahlberg Agent

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    Well said Jack. In fact, if sound quality is no issue, the output of a vented box increases as the size of the vent increases up to about 1/2 sd. You end up with a very peaky box with huge output at the tuning freq of the box.
    Andrew...a Tempest should work well free air in a car as long as you have a solid baffle to mount it on and pay careful attention to sealing the trunk from the cabin of the car. [​IMG]
    Bob
     
  15. Mark Seaton

    Mark Seaton Supporting Actor

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    Hey guys,
    Go back up and re-read my post. I do have a pair of Tempests in my car with an MTX 500D on them. Mine is a wall built behind the rear seats. This does indeed leave most of my trunk un-touched, and available for toting a ContraBass [​IMG] or a few sets of clubs. My trunk works out to around 20 cu.ft. from some rough estimates. This just starts to load the pair of Tempests, and the resulting response rises with frequency below ~75Hz. The effective box is a little smaller due to the size of the cabin, but the cabin is still fairly large compared to the trunk. It followed models pretty accurately. You will want to correct the response of the system electrically. Get the response to be ~+3dB or so at 20 relative to 50-80Hz range and you should be set. A simple 6dB/oct. high pass filter did well for me. This can be done passively at the input of the amp, but will depend on the input impedance of the amp. I will be TEF'ing the sub later this week, as I've only measured to 15Hz so far. Due to the amp's internal high pass filter the resposne levels off 20-15Hz without any correction to the response, and is about +8-9dB at 20Hz relative to 70-80Hz. Nothing like a little headroom. [​IMG]
     

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