2 Port Plugged on a SVS Subwoofer

Discussion in 'Speakers' started by lyradWong, Sep 22, 2004.

  1. lyradWong

    lyradWong Extra

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    Hi All SVS Sub Owners / Ron or Tom (SVS),[​IMG]

    Does anyone know what is the maximum SPL when 2 port plugs are used on a SVS Subwoofer?

    Example: 25-31PC-Plus

    Am I still able to play it at Reference Level?

    My hall size is 24'L x 14'W x 8'H (7.1m (L) x 4.2m (W) x 2.4m (H)), but listening area is on one side that is 13'L x 14'W x 8'H (3.9m (L) x 4.2m (W) x 2.4m (H)).

    In fact, I don't really play that loud at reference level, most at -10db ~ -15db, but some of the DVD that I played only -20db when I found it really loud at certain section.

    The reason why I asked this question is that I prefer to have a better feel (REAL Deep Bass) of the LFE from the Sub, 2 port plug used (if I use 25-31+) to achieve and feel of 16hz bass effect (or even lower if I can) but I worried that I might spoilt (bottom out) the Sub when I play it loud, said Reference level (just in case that I need to crack it up to this extend some day).

    I read the SVS manual stated with 2 port plugged I can acheive 16hz bass playback from the sub but only few db loss at the upper bass but I will like to know what is the maximum volume (SPL) I can play?

    If 25-31PC-Plus cannot achieve Reference Level when 2 Port Plugged? Can PC-Ultra, PB2-ISD or PB2-Plus can do so when 2 Port plugged and go deep to lower bass?

    Or the new PB12-ISD can reach 16hz or lower without plugged and play at reference level? [​IMG] But I really don't expect this for a budget SUB but just curious to ask.

    Million thanks to whoever assist me to clear my doubts.[​IMG]

    Your sincerely,

    Lyrad

    PS. Hi Ron or Tom, actually I sent an email to SVS tech support but I am not sure whether any of your staff has receive it. Anyway I am trying my luck here and hope to get advise from any experts who can help.
     
  2. Edward J M

    Edward J M Cinematographer

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    If you want to play bass at 16 Hz or deeper at the loudest volumes possible, you would be better off with a 16-46PC+.

    The 25-31PC+ and PB2 series all have a native tune of 25 Hz and will work optimally with all ports open. If you plug one port, the sub will still work very well, but you are losing some system sensitivity and output above the new tuning frequeny. Plugging two ports and lowering the tune still further really starts to limit the maximum output the subwoofer is capable of delivering.

    A 25-31PC+ with two ports plugged can provide a reasonable approximation of a 16-46PC+ at lower volumes, but at higher volumes, the 16-46PC+ will easily outgun the 25-31PC+ (with two ports plugged) in the 12-18 Hz region.

    If you want maximum output in the 12-18 Hz region, I would stick with the 16-46PC+. In that size listening area, it should be able to play at Reference Level if properly calibrated.
     
  3. lyradWong

    lyradWong Extra

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    Hi Edward, thanks for your advise.

    Unfortunately due to WAF and the look, 16-46PC+ is definitely OUT.

    Losing a few db is not really an issue to me (I think), but will you be able to advise what is the MAXIMUM Volume that those selected Sub (25-31PC+, PB2-ISD, PC-Ultra and PB2+) can play?

    I downloaded the manual of PB2-ISD and PB2-Ultra and 25-31PC+ from SVS website and found this documents inside the manual. (Suprising that PB2+ does not have this document).

    First of all, let me said that I am not good at reading graph chart. Please correct me if I am wrong here.

    PB2-ISD Tuning Chart
    I added 3 Cross X and the marking A, B and C on it.

    [​IMG]

    The cross at A shows the Subwoofer freq response with no port plugged, about 30hz, it can play near to 0db.

    At B cross, with 1 port plugged, about 25hz, it can play near to -2db.

    At C cross, with 2 port plugged, about 18hz, it can play near to -5db.

    Am I right?

    PB2-Ultra Tuning Chart
    Same thing that I added 3 Cross X and the marking A, B and C on it.

    [​IMG]

    This chart (PB2-Ultra) looks almost the same as PB2-ISD.

    The cross at A shows the Subwoofer freq response with no port plugged, about 30hz, it can play near to 0db. Same as PB2-ISD?

    At B cross, with 1 port plugged, about 25hz, it can play near to -2db. Same as PB2-ISD?

    At C cross, with 2 port plugged, about 18hz, it can play near to -5db. Same as PB2-ISD?

    25-31 PC-Plus Tuning Chart
    I added 2 Cross X and the marking A and B on it. There is no curve indication for 2 port plugged.

    [​IMG]

    The cross at A shows the Subwoofer freq response with no port plugged, about 25hz, it can play near to 0db.

    At B cross, with 1 port plugged, about 16hz, it can play near to -9db.

    As I said I am not good in reading graph chart, please correct me if I am wrong. And I am not here to find fault with SVS.[​IMG]

    From the PB2-ISD and PB2-ULTRA chart, can I said that BOTH with 2 port plugged, the maximum volume output level is -5db?

    Hope anyone of you can advise me.

    Thank you so much.

    Lyrad


    PS. Hi Ron/Tom, I already got the reply from Erik (from SVS). Though he recommend me getting the PB2-Plus but I just think that the information/answer doesn't really clear my doubt. However I appreciate with his quick respond with my mail.[​IMG]
     
  4. MingL

    MingL Stunt Coordinator

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  5. lyradWong

    lyradWong Extra

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    Hi Jag (MingL), Thanks.

    You seems to be always around with Xtremeplace and here. Anyway good to hear from you.

    Any comments for the above charts?
     
  6. JohnSmith

    JohnSmith Supporting Actor

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    I don't think you can work out just how loud a particular subwoofer will be IN YOUR ROOM by looking at a graph plotted outside.

    With a room that big I don't think plugging two ports is a good idea.

    Perhaps a 20-39 PC Plus or a PC Ultra, with one port plugged? And if you run out of steam with one port plugged, go back to 20hz tune.
     
  7. lyradWong

    lyradWong Extra

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    Hi John,

    Thanks for your advise.

    At least a guide. I need a guide to tell me what is the Max Volume level I can play in order not to bottom out the Subwoofer.[​IMG]

    So I know my Sub will be SAFE to play at that volume level.
     
  8. MingL

    MingL Stunt Coordinator

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    The size of the room will determine how loud the sub can go. A sub in a small room will be able to give more SPLs than in a large hall. Sub placement will also affect the ultimate loudness. So, its tough to theoretically calculate how loud a sub will go before it bottoms out as many practical factors can affect it acutal SPL.

    Proper placement can do wonders to create the feel of infrasonics.

    Say, wouldn't a 2 port blocked PB2 be underported to serve 2 12" drivers?
     
  9. lyradWong

    lyradWong Extra

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    Hi MingL,

    Thanks. Sure I agree and you have the point.

    But individual has it own taste of bass, right? And, 2 port plugged still utilise both drivers.

    [​IMG]
     
  10. MingL

    MingL Stunt Coordinator

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    I'm just cautious that underporting creates other problems...... I mean its like 2 12" drivers forcing air our of a 4" port.

    Comments anyone?
     
  11. Edward J M

    Edward J M Cinematographer

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    Your hall is 2700 ft3. Your listening area (within that hall) is 1500 ft3.

    How loud a subwoofer can play in any size room if dictated by several variables like room acoustics (standing waves and associated peaks/nulls), sub placement, the presence or absence of room gain, and the distance from the subwoofer to the listener.

    If my experience with the PB2+ and the PB2-Ultra is any indication, you should be able to hit about 120-122 dB (>25 Hz) at the listening position in the 25 Hz tune. My estimate would be 117-119 dB (>20 Hz) in the 20 Hz tune, and 114-116 dB (>16 Hz) in the 16 Hz tune.

    Port noise in the 16 Hz tune "might" be an issue at very high volumes if the source material actually has strong content in the 14-18 Hz region that is not otherwise masked by other content at higher frequencies.

    If you hear port noise in the 16 Hz tune at your preferred playback volume, then I advise running in the 20 Hz tune which will still give you solid extension to 15-16 Hz in-room with much less of a chance for port noise to occur.

    Regards,

    Ed
     
  12. lyradWong

    lyradWong Extra

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    Thanks MingL and Edward,

    I think your advise will greatly help me to judge and I will try not to exceed the playback limit.[​IMG]

    Beside PB2+ and PB2-Ultra, is it not adivisible to have 2 port plugged in 25-31PC-Plus, PC-Ultra and PB2-ISD?[​IMG]
     
  13. Edward J M

    Edward J M Cinematographer

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    The native tune of the 25-31PC+ and PB2-ISD is 25 Hz. Plugging two ports to obtain a 16 Hz tune limits the efficiency of the units and they are not really operating optimally. Sure, they can do it, but expect a loss of sensitivity and overall output, and the onset of port noise will occur sooner on some source material.

    If you want deeper extension with maximum efficiency, look at the 20-39 series, which has a native 20 Hz tune with all ports open. Ditto for the PC-Ultra (which uses a 20-39 cylinder). You only need to plug one port on the PC-Ultra for a 16 Hz tune, so you'll still have 2 open ports and good air flow with less chance of port noise.

    Until you actually hear how deep an SV plays even in the 25 Hz or the 20 Hz tunes, I wouldn't fixate on the 16 Hz tune at a "must have". For nearly all people, the 20 Hz tune is subjectively considered extremely deep, and will get to 16 Hz strong in most rooms.
     
  14. lyradWong

    lyradWong Extra

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    Hi Edward,

    I really appreciated your advise in this topic. I will narrow down my choice to both 20-39PC-Plus and PC-Ultra.

    Thank you so much.[​IMG]
     

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