SVS Port Block Tuning and Stereo Integration w/PSB Stratus Golds (Long)

Discussion in 'Speakers' started by James Edward, Oct 11, 2004.

  1. James Edward

    James Edward Supporting Actor

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    This is part-question, and part story-

    Over the weekend, I added an SVS 25-31PC Plus to my stereo system- Adcom amp, Adcom preamp, and PSB Stratus Gold speakers. I am currently running the Golds full-range, and setting the SVS crossover at 40Hz(it's lowest point).
    Gain on the SVS is set at about 8 o'clock(very low). No port blocks are in place, with the sub tune at 25Hz. Using a sound meter and a test disc, I got response at 20Hz, down by about 6 db compared to 25Hz. I currently have the subsonic filter set to 16Hz.

    This arrangement is an unqualified success. There is not even a hint of chestiness in vocals, I guess due to the low crossover point. Even though the Golds go down to 36Hz, the extra weight added by the sub is phenomenal. I am loving the sound. At the low crossover point, you cannot come close to localizing the sub.

    But I am curious about one thing- does anyone feel that adding a port block to lower the tune to 20Hz would make much of a difference? This is a music-only, 2 channel system, and is often played fairly loud. Does the lower tune substantially degrade the power handling capabilities of the sub? Room size is about 16x20 feet with 10 foot ceilings.

    BTW, the reason I run the Golds full range is that I have never come close to feeling that they were at their limits in the 8 years I've had them.

    Any thoughts appreciated. Thanks.
     
  2. Ilkka R

    Ilkka R Second Unit

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    No port plugs and ss filter at 16Hz, not a good combination. You will easily bottom your driver. I'd say put one port plug in and set ss filter to 20Hz. You'll get straight response at 20Hz and below.
     
  3. Edward J M

    Edward J M Cinematographer

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    Agree with the above poster on the 3/16 mismatched tune - a recipe for disaster at high volumes. Also if you are not applying any correction factors, then your response curve will be misleading. When you state 6 dB down at 20 Hz, is that with the meter correction factor or not?
     
  4. James Edward

    James Edward Supporting Actor

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    Good point- I did not factor in meter correction. So, I'm probably getting 20Hz in my room with three ports open- I guess I'll leave it as is.

    I'm going to change the SS filter to correspond with the port situation and see what readings I get. I have not bottomed the driver so far, but why chance it...

    Thanks for the responses.
     
  5. Edward J M

    Edward J M Cinematographer

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    I can't remember what the RS meter CF is at 20 Hz, but I think it's around 6 dB anyway. I'd bet you are close to flat in the 3/16 mismatched tune.

    Moving the tune switch to 25 Hz will start to ramp down the response and also will apply less EQ on the very bottom end. So I would expect the response to be maybe -2 dB at 20 Hz (with correction factor) in that size room in the 3/25 tune.

    If you want legitimate 20 Hz performance with less distortion, then definitely plug a port and set the tune switch to 20 Hz. At anything but the highest volumes, you won't experience any compression.
     
  6. Ilkka R

    Ilkka R Second Unit

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    It is 7.5dB at 20Hz, so it is very close to flat. More than flat actually.
     
  7. Robert Hoffman

    Robert Hoffman Stunt Coordinator

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    I'm curious about setting the crossover at 40hz. I haven't had time to play around yet, but my new Joseph Audio RM25s are rated down to around 30 hz. I thought I had read before that setting a crossover that low could cause some issues with bass cancellation? I also have a 25-31PC+. Is the best way to check to just pull out my RS meter and run a frequency sweep with Avia and check for any dips?
     
  8. James Edward

    James Edward Supporting Actor

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    I thought that the SS filter was only a filter- I didn't realize it added EQ. OOPS! I'll change it right now...
     
  9. James Edward

    James Edward Supporting Actor

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    OK- If anyone is still reading this thread:

    Here are my meter corrected values from 20 - 100Hz, with the SS filter set to 20Hz, and one port blocked.

    20Hz- 83db
    25Hz- 82db
    31.5Hz- 82db
    40Hz- 81db
    50Hz- 75.5db
    63Hz- 81.5db
    80Hz- 77.5db
    100Hz- 77db

    Question: Do you feel that this is an appropriate response curve for 2 channel music? I know that it has been suggested by some that a gradually increasing curve is a good thing in an HT system- would the same apply for music?

    I suppose if I raised the crossover point slightly from 40Hz I would somewhat eliminate the dip at 50Hz. On the other hand, perhaps this curve is pretty good?
    Any thoughts please... Thanks
     
  10. Ilkka R

    Ilkka R Second Unit

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    That is very good. You don't have BFD hidden right? [​IMG]
    That little dip at 50Hz isn't really a problem, but of course you can try to raise the crossover and see what happens. Try something around 60-80Hz.
    IMO flat curve is best for music and increasing curve (house curve) for HT.
     

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