What designs for my tempests?

Discussion in 'Archived Threads 2001-2004' started by Mark Wilson, Dec 18, 2002.

  1. Mark Wilson

    Mark Wilson Agent

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    Hi all, I happen to have 2 tempests that need an enclosure. I also have a 250 watt plate amp. I'm very interested in the thought of a sonosub, and can get sonotube rather cheap in my area. I of course want tight bass for music, and loud low bass for HT.

    I was thinking of building 2 sonosubs, and putting one in each corner. The enclosure would be a 20" diameter 48" high peice of sonotube. That yeilds just a little below 250 liters. I would then tune them to 12 Hz. I only want them to play from about 60-70 Hz down. They'd be about 12' away from each other.

    I'm planning on tuning them that low, and with that size, because that's what size a sealed enclosure with a QTC of .6 would have. (I could easily plug the port, making it sealed if I wasn't happy with the vented config) Also, with it tuned so long, it has a really nice smooth roll off, and an F3 of 25 Hz or so. Plus, with it tuned so long, excursion is much reduced, compared to tuning it to 20 Hz. (Also, during movies with extreme low freqs, I don't have to worry about cone movement below the tuning of the sub, I don't expect there'd be to much info below 12 Hz)

    Any significant problems anyone can spot? Will that provide me with tight 'feel it in your chest' bass? Will I require any polyfill, and if so, how much?

    As for the weak amp, I plan on getting a QSC RMX1450 power amp. That'd provide them with 450 watts each (into 4 ohms) or if I needed/wanted more, I could bridge it which would produce 1,400 watts into 4 ohms (I'd just have to use one voice coil of each sub then)

    Would that make a nice sub amp? I'd just have to wire my RCA plug into an XLR (supposed to be very very easy, I'm not worried about that at all) One thing I am worried about, is, will the voltage/impedance from the RCA output of the reciever (Nad T752) be 'good' enough for the XLR inputs of the pro amp? I know some people have issues using RCA's because the voltage of the outputs on receivers is so low compared to what the inputs of pro gear expect.
     
  2. Jon Torres

    Jon Torres Second Unit

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    Using some rough numbers from WinISD, you're looking at a very long port. With a 6" wide port, you're looking at a 55" port. With 2 4" ports, it would be about 50" long. That's using the entire 250 liters which would be reduced by about 25 liters from the displacement of the ports further lengthening the port. Your best bet would be to tune higher or use a bigger enclosure, maybe 24" sonotube. IMO
     
  3. Pete Mazz

    Pete Mazz Supporting Actor

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    Tuning that low, you may as well just build a sealed sub.

    If you want it to make any appreciable difference, try a 15 Hz tuning. Port length becomes reasonable and the slightly higher tuning adds some output in the audible bandwidth.

    Pete
     
  4. Mark Wilson

    Mark Wilson Agent

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    No worries about the size of the port. I'm a little confused, using a 4" port, I was getting a length of 23" or so.. (Using WinISD pro)

    Sides, it _is_ a big piece of sonotube. To make up for the lost displacement, I can add a few inches to the overall length of the tube. (20" is very cost effective, any wider, and it gets a lot more expensive, a lot quicker)

    I would go with a sealed sub, but the excursion was _a lot_ higher then in the ported design. If it's going to sound close to the same, why use the design that will bring my subs close to botteming out, when I could use the vented design, which will leaves my subs at a nice healthy excursion.
     
  5. Keith Martin

    Keith Martin Auditioning

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    Mark,
    John T. said two 4" ports not a single. Yes, a single 4" may be 23" but we all know it's not enough displacement.
    I personally went with two 4" ports over the single 6". The deciding factor was simply that it was left over from the Shiva I did a year earlier.
     
  6. Joe Sabato

    Joe Sabato Auditioning

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    I am thinking about buying the same amp and had the same concerns. I spoke to a local company that sets up systems using pro gear and I was told it would be no problem. The advice I got was to get a RCA to 1/4" unbalanced adapter ( Radio Shack), and then use a 1/4" to XLR connector with a balancing transformer built in; that should keep noise issues down. The amp needs 1.15 V for full output which should not be a problem for the receiver.

    BTW I am in the process of "re-cycling" some 20 year old AR towers that I have been using for subs by installing a Tempest (surround rot has set in). I have one Tempest already and will set it up next week to see how it works out; they are 120 liter towers which gives a Qtc of .7 sealed which should work out well for movies and music.
    If I am happy, I will do the other the same way. Good luck with the project.
     
  7. Matt Tucker

    Matt Tucker Agent

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    I use a "pro" amp for driving my subwoofers. I have a Carvin DCM1000. It has 1/4" inputs as well as XLR, so I bought a rca to 1/4" adaptors. The input level conrtols on the Carvin are set about 40% up. Plenty left. If you don't have 1/4" inputs then the above suggestion sounds good of using the dual adaptors.
    Matt
     
  8. Ted_Polzin

    Ted_Polzin Stunt Coordinator

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