Sub box options (again)
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This is a discussion on Sub box options (again) within the Interior Mods forums, part of the Tech & Modifying & General Repairs category; Ok, I have two sealed 12" in the car right now, each one rated at ~94dB. When I went from ...

  1. #1
    Registered User 04blkWRX's Avatar
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    Sub box options (again)

    Ok, I have two sealed 12" in the car right now, each one rated at ~94dB. When I went from one to two, I know the sound didn't double (i.e. I'm no producing 180dB now). I'm not thrilled with the response so I was thinking about switching to a single 12 in a ported enclosure, which is rated at ~103dB max.

    I guess my main question is: how does the SPL increase when you add speakers? How does one ported sub compare to two sealed subs purely in volume?

    Sealed curve:
    Attached Thumbnails Attached Thumbnails sealed.jpg  

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  3. #2
    Registered User 04blkWRX's Avatar
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    Ported curve:
    Attached Thumbnails Attached Thumbnails ported.jpg  

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    Registered User Th3Franz's Avatar
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    Ok, there's tons of variables when it comes to SPL. Speakers are rated at a given sensitivity, which does not translate into straight SPL. Also, keep in mind that sound pressure level is a logarithmic decibel scale, so if you go from 100 dB to 101 Db, you're multiplying by a factor of 10.

    The biggest factor when dealing with SPL in my opinion is the box design in relation to the sub-woofers. If you build a huge ported box tuned low (like 35 Hz) with one or two subs it will get loud. What is your amplifier rated at? The amp you use makes a difference in how loud your system is. FYI, I'm hitting 140 dB with two 10" subs in a ported box with a 500W amp. I expect to hit a bit higher when I get a bigger amp.
    - F r a n z
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    Registered User 04blkWRX's Avatar
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    I have a 1000W peak amp. Right now its at 4 ohms so it's 200W RMS. I tried it at 1 ohm, 500W RMS but i didn't notice much differance so I put it back (plus the THD goes way up at 1 ohm). The speakers are Infinity Kappas 120.3DVC so they can handle 1300 max/300 RMS.

    My setup now is pretty loud overall but it sounds choked down low. If I build the box to the specs of Infinity do you think one ported will sound close to the volume of two sealed? I can't find any good literature about how the two subs add together.

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    Registered User FutureWRX15's Avatar
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    Ported in my opinion rocks sealed. I had a 10 Q Series Audiobahn in a sealed boxed. But the voicecoil locked and fried. Then i built a ported box thats kind of big but not to big. It makes a termendous difference in sound. Im also using a 12 now and can make those boxes for a single 12 pretty good now. Got the plans from the Wave Box from a store by us.
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    Registered User Th3Franz's Avatar
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    Considering your amp is not very powerful, I'd go ported with one sub. Generally to get a sealed setup to get loud it takes more power. Plus in terms of SQ I think at 4-ohm with a good ported setup you might get a better SQ/SPL setup since the THD is lower like you said. Also, what music do you listen to? If you listen to any rap or music that has quite low bass, then definitely go ported.
    - F r a n z
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    hmm, well here is my $.02.

    I would stay with the two sealed twelve's. The reason being is that with the given power, you are displacing more air than a single 12. Even though it is a ported design. Second, make sure your speakers are properly wired up to give a 4 ohm rating (series-parallel) and leave the amp mono. Lastly, ported enclosures are less forgiving than sealed enclosures, so there is a higher chance of damaging speakers.

    A note about db ratings. If one twelve has a rating of 94 db. Then by adding a second driver, your rating should theoretically jump to 97 db. measured with a one watt input at one meter (1w/m).

    Lastly the orientation of the drivers makes a difference as well. Which way are they pointed?

    so there, I hope it helps. Also, I dont know your background in this stuff, so please dont think that Im putting you down or being condacending in any way.
    "Failure is only an option for those who try".

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    Registered User 04blkWRX's Avatar
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    Aha! Silvertsunami had the answer I was looking for about combining two speakers to get 97dB (I don't know how you arrived at that number but I trust you ).

    My coils are wired correctly for the impedance I want. The cones are pointed to the back of the car.

    Th3Franz: how much power would you want to see? BTW, I listen mostly to metal, sometimes Rap.

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    well its actually a combo of common sense and some technical know how. First of all, to double the volume, you need to double the area of air moved. Second, a perceived doubling of volume is equivalent to three db increase. Unfortunately, this only applies to the sensitivity of the speakers. In real world, however, it does not always work that easily, especially when you go above 130 db. As Franz pointed out, it is a logarithmic progression and at that levels is takes that much more to increase.

    bottom line: stay with sealed, it is a better candidate for your musical tastes. However, I would always have to go with the more power, the better. Just dont get a 'no name' brand amp. There are a lot of companies that claim outrageous figures.
    "Failure is only an option for those who try".

  11. #10
    He simply abides. SD_GR's Avatar
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    The dB scale is such that doubling sound volume means an increase of (very roughly) 3 dB, not double the original dB value.

    The cleanest sound will come from an adequately driven system free of grounding problems and provided with a clean signal, and the system must be properly crossed over at a reasonable frequency. Also, the driver must be in a well designed enclosure that's as free of vibrations, nodes, port huffing noises, and other silly stuff as possible.

    Band pass enclosures don't fit with my preconceived notions of a good enclosure, so I am not a fan.

    The easy answer to your question is to find someone with a sub setup you like and copy it. The better, but harder answer is to learn enough to build a good one yourself.

    A terrific book on loudspeaker design is the classic "Loudspeaker Design Cookbook" by Vance ****ason.

    What you might do as a shortcut is find out all the technical parms of your chosen transducer and look online for a free application that will design either an acoustic suspension or a bass reflex enclosure for you. Then you can either build it or have it built. Keep in mind we're talking thick, braced MDF at the very least, so you'll be carrying a full trunk load around all the time.

    BTW an amplifier capable of sustained 200W RMS from 20 to 20KHz with something less than 0.1% total harmonic distortion should be able to drive even the most demanding speaker loads with some authority. I mention this to point out that the W ratings listed are a bit meaningless and really optimistic...
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    Registered User Th3Franz's Avatar
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    Did you say what brand amp you have? Having a amp that's at a higher power rating can't hurt. I know I want to switch out my current 500 W RMS amp for a 1000+ W RMS amp since my two subs are 400 W RMS a piece. When I crank it the amp gets really warm and I want to get a bit louder since I might compete and I might use my current amp to power some regular speakers.

    I've been very happy with my ported setup, but a lot of it is preference. I think my ported box has a good balance of sound quality and SPL. I definitely like having that extra octave down low compared to sealed box. If possible try hearing different setups of ported and sealed at a car audio shop and determine which one you like better.

    Also as slvrtsunami pointed out, cone area is a factor too. If you're really not decisive about which setup to go with, go with 2 subs in a sealed box and get a little bit bigger amp and you should be happy.

    Oh and the "Loudspeaker Design Cookbook" is a good resource.
    - F r a n z
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    loudspeaker handout. A classic refernce book!!! he did a very good job with it. I think I still have my copy.


    Franz: what do you compete in? and where is your box ported at? do you have a subsonic filter? do you still want my punch power 1000.2?

    sorry for the hijack...Franz pm me if you want.
    "Failure is only an option for those who try".

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    Registered User 04blkWRX's Avatar
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    Oh yeah, I have a Kenwood amp (this one)

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    hmmm, didnt realize the amps were one ohm stable. Just how do you have the speakers wired? are you running all 4 voice coils in parallel? (all the positives and negatives connected toghether) This will give you the max output of the amp.
    "Failure is only an option for those who try".

  16. #15
    Registered User Th3Franz's Avatar
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    Try wiring your sub-woofers at 1-ohm and seeing how loud they get and how warm that amp gets. 500W could sound the same as 200W up to a certain point. It depends on how you have the gains set and what volume you're playing at. Obviously if you crank it up you'll probably be able to notice the difference with 500W.

    Also, find someone who has an SPL meter if you're curious about the difference in loudness between the two configurations. It's always fun cranking it up and seeing how loud your subs hit.

    But, you gotta be kinda careful. Pay attention to how the subs sound/smell (if you smell burning that's bad. ) and the general temperature of the amp.
    - F r a n z
    Bucky with teh lime powah!

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