out of curiousity (SVS question)

Discussion in 'Speakers & Subwoofers' started by James L, Dec 30, 2003.

  1. James L

    James L Auditioning

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    Hello,

    I was wondering if anyone out there knows if there is a high pass crossover in the PC+ amp? If so, at what frequency is this set and how steep is the slope (goes for both low level and high lever inputs/outputs). I'm just trying to think of the best compromise to set up my system for both music and movies. I'd rather not use the LFE output of my receiver because it's fixed at 100hz. Thanks in advance!
     
  2. Edward J M

    Edward J M Cinematographer

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    Yes, there is a filter in the PC+ BASH amp. There is also a filter defeat switch. The filter is variable from 40-120 Hz. I don't know what the filter rate is, I'd ask Tom V. at SVS. My guess would be 2nd order (12 dB/octave) for both high/low pass.

    While 100 Hz is a tad high, I still think the benefits of using digital BM greatly outweigh a slightly high xo frequency. The SVS can easily handle a 100 Hz xo. If you place it between the mains, localization shouldn't be much of an issue.

    Regards,

    Ed
     
  3. Rudi B

    Rudi B Stunt Coordinator

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    Actually, it's second order on the line levels, and first order on speaker level, both around 80Hz. At least for the PB2+.

    Unfortunately, first level highpass for speaker level outputs is mostly useless. At least I've noticed this when toying with my SVS in friend's system, poor bookshelfs were choking with bass.
     
  4. Edward J M

    Edward J M Cinematographer

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    The filter is variable from 40-120 Hz, you select the frequency.

    Rudi - Did you measure or calculate the filter rates on the line level and speaker level inputs? BTW, I love your Bass Archives website - nice work. [​IMG]

    For a HT application, James would still need to set all the speakers to small anyway, except for the L/R fronts which would be set to large, and the sub would be set to off/no. Setting all the other speakers to small will give him a 100 Hz xo on them, so I don't see much of an advantage in using the filter in the SVS to lower the xo to 80 Hz (or w/e) for the mains. I still recommend digital BM and a 100 Hz xo. Or perhaps an ICBM is a good idea.

    Ed
     
  5. Rudi B

    Rudi B Stunt Coordinator

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    Nope, Tom V. My testing in that system was this past weekend, so of course I had to ask him. [​IMG]

    And 80Hz crossovers are fixed for *outputs*, input is of course variable.

    And, thanks. Too bad that I can't find any new *really* satisfying movies to plot. Terminator 3 was a disappointment (non-stop rumble), X-men 2 in DTS was really nice with great dynamics, but nothing revolutionary like Finding Nemo [​IMG]
     
  6. Dustin B

    Dustin B Producer

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    Rudi did the asking, but to clarify what he saidthe high pass on both the line level and speaker level connections will be fixed at 80hz. The low pass on both is what's variable from 40-120hz. No idea on the slopes (you'll have to ask Tom) except that the high pass on the speaker level will be 1st order. Guess is low pass is 2nd for both and high pass is 1st on both.

    You're pretty much always better off using the receiver for bass management even with a 100hz crossover. Only amps like the Adire HS series or subs like Rel or some other ridiculously priced (considered high end; some of which have decent output some of which don't) subs have good flexible bass management built into the sub.

    The other option is to find an external line level crossover unit.
     
  7. Edward J M

    Edward J M Cinematographer

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    Thanks for clarifying that on the filter network. Good information to store for future reference. All the more reason to stay with digital BM, IMO.

    I find 2nd order at 80 Hz to be a nice compromise between protecting bookshelf size speakers, and still allowing them to contribute "some" bass down to about 60 Hz or so. All my surround speakers have an F3 of around 50-55 Hz anyway, so it works well for me, and I have not noticed any really bad FR anomalies using a 2nd order high pass at 80 Hz when doing in-room FR sweeps.

    Try the Daredevil barfight scene in DTS. If you run your PB2+ in the 20 Hz tune, you will note there is a few seconds of very strong infrasonic stuff (when he is tumbling in the air and also when the bartender is crawling behind the bar for cover) that the 25 Hz tune cuts out. I would be interested to see just how low that scene goes. A lot of people guess certain scenes (like the Ring Drop in FOTR) are infrasonic when they really are around 23-25 Hz.
     
  8. Edward J M

    Edward J M Cinematographer

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    Dustin - I'd like to pick yor brain while this thread has your attention.

    Why would the line level or speaker level filter network on the sub amp have a fixed high pass at 80 Hz and a variable low pass? I'm not doubting what you said is correct, it just doesn't make much sense to me.

    If the L/R speakers are being high passed at a fixed 80 Hz, then why would the low pass be variable? Conceivably, the user could set the low pass filter to say 40 Hz and create a large hole in the FR between 80 Hz and 40 Hz, particularly if the high pass filter is second order.

    Intuitively, one would think that the variable filter on the amp should set and control both the high and low pass filter points, analogous to how a typical digital BM filter network works in a pre/pro or AVR.

    Any light you can shed would be appreciated.

    Thanks,

    Ed
     
  9. James L

    James L Auditioning

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    Hey thanks for all of your input guys! It looks like I'm getting bit by the upgrade bug again (first the sub, now the electronics!) and I'm gonna see what is out there with a more flexible bass management system. I guess I'll just fiddle around in the meantime with different setups. I'm interested in what Dustin has to say in reply to Edward above.
     
  10. Dustin B

    Dustin B Producer

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    Cost. From Adire's site. 250W plate amp with plain jane crossover stuff.

    http://www.adireaudio.com/diy_audio/...ers/ava250.htm

    200W plate amp with excellent line level crossover options (the amp itself is a little better too). Notice there are no speaker level connections. Not possible to do speaker level in a variable fashion. And to do it properly each amp would have to be costum designed for the speaker it was to be used with.

    http://www.adireaudio.com/diy_audio/...iers/hs200.htm


    And it isn't really all that different in most receivers and pre/pro's with adjustible crossover settings. Ones with the same crossover point for all speakers work as you would expect, but those that allow different crossover points for different speakers don't work as you expect. This article is an excellent read.


    http://www.hometheaterhifi.com/volum...rs-9-2002.html
     
  11. Rudi B

    Rudi B Stunt Coordinator

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    Ah, I just had to rent it. [​IMG]

    http://bass.jawmail.org/index.php?p=daredevil

    Sounded nice with a 3 ports / 20Hz tune, but nothing really earth-shattering. Finding Nemo is still the king, IMHO.

    As for infrasonics: I'd say that even an SVS PB2+ is too wimpy for satisfactionary < 20Hz reproduction. Mostly because it is tuned to 25Hz with all 3 ports opened, a pair of 16-46CS+ would rock probably for that. I'd opt for a Servodrive Contrabass for real infrasonics, tho. [​IMG]
     
  12. Edward J M

    Edward J M Cinematographer

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    Thanks for the waterfall chart, Rudi. [​IMG]

    Maybe not earth shattering from a sheer amplitude standpoint, but nevertheless as I suspected there is a bunch of short-interval, high-amplitude peaks squarely centered in the 15 Hz region in the minute following the 23:05 waterfall chart. That's the stuff the 25 Hz tune cuts out, but the 20 Hz tune captures perfectly.

    I have found the PB2+ in the 20 Hz tune to have very strong and satisfactory output in the 15-20 Hz region. On the Sound Hound organ CD, I have pushed it hard enough on the 16 Hz notes to shake everything in the room, and even the walls/windows upstairs. Those two huge flared (both ends) 4" vents can still move a lot of air before audible port compression becomes an issue.

    When you plug a port and drop the tune switch to 20 Hz, you really need to increase the sub calibration level about 2-3 dB to retain the same level of impact you had in the 25 Hz tune. While I'll concede a pair of 16-46+ subs would have a max output advantage in the 15-20 Hz region, the PB2+ still rocks very strong in that region when tuned to 20 Hz.

    Take a look at the FR charts - at 16 Hz in the 2/20 tune the PB2+ is up about 15 dB over the 3/25 tune. In the 2/16 tune, the advantage grows to over 20 dB. Note, the 2/16 tune is a mismatch of port and tune switch settings and leaves the sub more vulnerable to bottoming and is not recommended by SVS. If you do experiment with non-conventional (i.e., 3/20, 3/16, 2/16) mis-matched tune configurations, keep things moderate and sensible.

    Regards,

    Ed

    [​IMG]


    [​IMG]
     
  13. Rudi B

    Rudi B Stunt Coordinator

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    Ed,

    I was toying with infrasonics on the Pomp & Pipes CD (I'll have to plot those too sometime) sometime ago, and I found out that the 16Hz organ's tone was much stronger with the 20/2 tuning than with 16/1, even with +3dB to the sub. The charts say otherwise, but I was probably at +100dBs, not 90. [​IMG]

    One port ain't quite enough for 1/16 and loud! I even managed to produce some port noise, which was a first with the SVS. But I'd like to toy with the 2/16 tune on that recording until I find the limits...

    BTW, what exactly happens when you play tones under the tuning frequency of a bass reflex system? I assume that the ports cannot move enough air thru then, so the air in the box compresses and puts additional pressure on the drivers?
     
  14. Edward J M

    Edward J M Cinematographer

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    Not quite.....this article explains it well.
    http://www.hometheaterhifi.com/volum...ayporting.html

    I agree - in the 16 Hz tune, the PB2+ can indeed troll VERY deep (down to 11-12 Hz), but with only one flared 4" vent, it is underported and output will be limited before audible port compression occurs.

    The 2/20 tune (or 2/16 if you are careful and moderate) is a far better choice and will give you much more airflow and SPL and still provide deep extension well into the teens and will be perfect even for 32 foot pipe organ music.

    Regards,

    Ed
     
  15. MingL

    MingL Stunt Coordinator

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    Rudi,

    Pomp and pipes definately have a few heart stopping moments where the pipes play way below 20hz. My favourite track is track 3, with infrasonics somewhere near the 6:15 mark. This same catchy tune is also featured in XLO/Reference Recording's "Test & Burn-in CD"

    Lately, I have been experimenting with my 16-46PC+ at 12 hz tune. I've always been using it at stock tune, but I realise that the sub is running with less distortion at 12hz tune, and even verified using spectraplus RTA.
     
  16. Edward J M

    Edward J M Cinematographer

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    That's funny Ming, I was blasting Pomp and Pipes last night at about -5 RL in the 20 Hz tune with the PB2+. Awesome.

    Your comment about the lower distortion is interesting. At what frequencies did you observe this phenomenon?

    At an identical playback level, I would expect lower THD in the 10-15 Hz region with a port plugged as compared to the stock tune with all ports open.

    Above 15 Hz, the stock tune should exhibit less THD due to less thermal power compression and less port compression - again at the same exact playback level.
     

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