1 Box -- two 8" ported -- two 8" sealed

Discussion in 'Archived Threads 2001-2004' started by Joey Ford, Jul 24, 2002.

  1. Joey Ford

    Joey Ford Agent

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    I have four 8" drivers that I'm looking to enclose. My question is, if I tune the first half of the box by porting it (two 8") at 42Hz (according to the driver's specs)and seal the second half of the box (two 8") and tune it at 75Hz, am I going to run into any cancellation issues? Cancellation may not be the proper term? Distortion?

    Why am I doing this? Well, here's my thinking process...Could be right or wrong:

    By porting the first two drivers, I will accomplish a lower range of frequencies that will give me that rumbling feel.
    By sealing the second two drivers, I will get good "mid bass" that will accomplish that punchy sound.

    Am I totally lost here? Should I stick to porting the entire box?

    Thank you,
    Joey
     
  2. Brian Bunge

    Brian Bunge Producer

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    Joey,

    I'd decide on either ported or sealed, but not both. What is your intended application, HT, car audio? I get the impression your drivers have an Fs of 42Hz since you're talking about tuning to 42Hz. That's mighty high for HT use, so I'd have to assume it's car audio. Even if the application is car audio, I'd definitely go with a sealed enclosure and take advantage of the interior's natural cabin gain vs. porting the enclosure and having a huge peak at 42Hz.

    Brian
     
  3. Joey Ford

    Joey Ford Agent

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    Thanks Brian,

    Actually, it's for my HT/stereo listening at home. They are car woofers that I've had for some time. I have two of them in a ported box in my corner. They sound decent, but you can't ask alot from 8's.

    I want to make good use of them until I decide to upgrade. It's not a money issue, it's just having fun with what I have. I'm sure I will upgrade to 12's or 15's in the future.

    Your response was based on the cabin of a car. Can you give me a little more information port vs. sealed since it's a home enclosure?

    Is there any negatives to 1/2 ported, 1/2 sealed?

    Thanks
    Joey
     
  4. Joey Ford

    Joey Ford Agent

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    Oh, BTW -- I used WinISD freeware to get the specs of the speaker. I lost all the paperwork. It's Fs is 39.94.

    When I plugged in a ported enclosure, it resulted in 27.5 liters at a tuning frequency of 42.23 Hz.
    These measurements are based on one speaker.

    When I plugged in a sealed enclosure, it resulted in 13.6 liters.

    I'll admit, I'm green when it comes to looking at the charts. The -3db was at 75Hz.

    I wanted to include this data if it helped in dissecting the situation.

    Basically, with the vented enclosure, I will only hear/feel frequencies as low as 42Hz?

    With a sealed enclosure, 75Hz is as low as I will hear/feel?

    Thanks a bunch
    Joey
     
  5. Brian Bunge

    Brian Bunge Producer

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    Joey,

    I just don't see going with ported and sealed. Depending on the driver's specs and the enclosure size, a sealed enclosure will probably have lower group delay/better transient response. But a ported enclosure will give you more extension. You could build both and then decide which you prefer. Then build a new box to match the one you prefer for the other drivers.

    I never use the info. that WinISD spits out. I change it to see if I can get a better response curve. Do you have any of the specs for the woofers? If nothing else, maybe the model number will allow us to look them up on the company's website.

    If the driver's have an Fs of 39.94Hz and you tune to 42Hz then you'll have very little output below 42Hz. A ported enclosure has a 24dB/octave rolloff below the tuning frequency of the box. Most people tune at or just below the driver's Fs. The driver "unloads" below it's Fs, so it's very easy to damage it with frequencies below it's Fs in a ported enclosure. A sealed enclosure has a 12dB/octave rolloff, so you'll still get some decent output below 75Hz.

    See if you can get the specs and I'll try some simulations to see if we can get anything decent. Otherwise, you'd be better off springing for something like a Dayton DVC 12" driver or Adire Audio Tempest. It'll bury those 4 8" woofers I'd imagine.

    Brian
     
  6. Bryan Michael

    Bryan Michael Supporting Actor

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    the sweetist sub box i had was a 12 inch sub hitting into a sealed box with a vent on the back side but the problem was it was big and it got wrecked whin i got hit just had the box in trunk if you want to pound and maybe distroy subs make a box like this you cant hear the sub overextend that much and you get less thd too
     
  7. Mark gas

    Mark gas Second Unit

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    I would just go with a sealed box or you could try a ABC box to get a mix of high spl and good sq.
     
  8. Joey Ford

    Joey Ford Agent

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    Brian,

    Here are the specs:

    Qts = 0.38
    Vas = 33.0L
    Fs = 39.94Hz
    Re = 3.27ohm
    Xmax = 0.007m
    Z = 4.00ohm
    Qms = 4.07
    Qes = 0.42
    SPL = 88.80dB
    Pe = 220W
    dia = 0.203M

    Let me see if I have this straight. A sealed enclosure will play below it's tuned frequency because it doesn't roll off as fast as a ported enclosure. BUT, it will not play as low as a ported enclosure. So, in a typical HT setup, I would miss alot of sound/vibration because of this frequency cutoff in a sealed enclosure. You're suggesting that I go with the sealed enclosure because the sound will be cleaner and will make use of the room's accoustics?

    Let's forget about future upgrades to 12" or 15" drivers please. I want to know the "BEST REASONS" for sealing vs. porting these drivers in my home. I had them ported in my truck years ago and they literally sounded "cleaner" than any system I ever had. I've had two 12's, four 18's, and four 15's at different times. Of course, the larger drivers would play lower, but these 8's were awesome! The key was porting the box in order to get the 8's to play low. I turned more heads and dropped more jaws than you could imagine. Out of hundreds of people who auditioned my system, no one had ever heard of using 8's and most had to see the woofers in order to believe that was source. Now, I realize the cabin gain had alot to do with this. So, that is why I'm here seeking advice.

    Thanks
    Joey
     
  9. Brian Bunge

    Brian Bunge Producer

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    OK, here's what I'm getting in a sealed enclosure. An 8L (roughly .28ft^3) enclosure per driver gives a Qtc=.7 and an F3=83.86Hz.

    A 1ft^3 ported enclosure tuned to 40Hz has an F3 of 39Hz. If you were going to mount them all in the same enclosure I would wire them in a series/parallel configuration to get a 4 ohm load, put them in a 4ft^3 enclosure, and use three 3" ports 7" long.

    I think I'd go with the ported enclosure over the sealed. While you will get pretty good ouput from 35Hz and up, there will be virtually nothing below that point.

    I guess they will work for the time being, but at some point you'll definitely want to upgrade to something that's better suited for the home environment.

    Brian
     
  10. Joey Ford

    Joey Ford Agent

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    Brian,
    I appreciate all of your efforts. It's nice to be able to come to a location and swap ideas and dry the wetness behind the ear [​IMG]
    FYI: The box that I threw together is 1ft^3 with two 8" drivers. I used a 3" port that is 13.5" long. I stuffed it with poly-fill and I'm running them in 4ohm stereo with a Soundstream DA-2 amp 350w X 2. It sounds decent. From my calculations, this tunes the box to 35Hz. I guess I screwed up a bit and need to shorten the port length by 5 inches to tune the box to its proper 40Hz frequency.
    In the mean time, I can begin working on the new enclosure.
    One last question if you don't mind?
    On the above mentioned box that I made, the drivers are stacked vertically in an elongated pentagon shaped box. The port is running vertically from the top while the drivers fire from the front. Does port direction make a difference? I know you should keep the end of the port at least 4 inches away from the inside wall and/or driver. The best sound comes when I point the drivers towards a corner wall. I'm wondering if I do the same on the new box, but have the ports coming out the opposite end towards the listening area.
    What do you think about this?
    Thanks
    Joey
     
  11. Bill Fagal

    Bill Fagal Stunt Coordinator

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    Hey Joey,

    Others have given you some pretty good advice, but I'll try to cut to the quick of your original question: Why not run sealed + ported?

    This is a recipe for funky response for two reasons, as I see it:

    1) Yes, the sealed half will give you mid-bass and the ported will give you lower extension, but even if you tune both halves for flat response, the combined response will not be flat. It will probably show a mid-bass hump (the sealed territory) dropping 3dB to a slightly declining plateau down to the tuning freq. (ported territory). What's more...

    2) Do a WinISD sim of your drivers in sealed and ported alignments. Now click the phase plot tab. You'll see that at lower frequencies the phases of the two systems diverge markedly. The combination of these two phases roll off the combined response, creating a "suckout" on the lower end. (Caveat: I don't have software running to predict the phase of the port output, which dominantes the cone output in the ported system near the tuning frequency, so your mileage may vary.)

    Hope this helps.

    Bill
     
  12. Joey Ford

    Joey Ford Agent

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    Thank you Bill for the explanation.

    Brian, could you please take a look at my last question above?

    Thanks
    Joey
     
  13. Brian Bunge

    Brian Bunge Producer

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    Joey,

    I think that would be fine. If it sounds best to you with the drivers firing into the corner then do that. I don't think the direction the port is firing will have much of an affect.

    Brian
     
  14. Seth_L

    Seth_L Screenwriter

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    I have a pair of Wharfedale Sapphire Blue 89 speakers. They are a sealed/ported hybrid. The tweeter and the midrange are sealed and play down to 150Hz. Then it has two ported cones below that comprise the rest of the speaker. The ported chamber is both front and rear ported. They sound really good.

    I suppose because they're not really overlapping in frequency response they don't have the same issues that Joey might encounter?

    Seth
     
  15. Brian Bunge

    Brian Bunge Producer

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    Seth,

    Because they are not overlapping is exactly why you don't have the problems that Joey would encounter.

    Brian
     

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