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Questions about a new sub amp

Discussion in 'Speakers' started by Brad Russell, Feb 12, 2007.

  1. Brad Russell

    Brad Russell Well-Known Member

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    My PSB Subsonic III has had its second amp go bad and I can't seem to get any help from PSB so I'm coming here for advice. A new plate amp from parts express is arriving today and I have a couple of questions. When I took the old amp out there were 3 wires coming out of the seal chamber. 1 black and 2 red. I think this means the driver has two voicecoils? When I measure the resistance, I get the same 3.8 ohms whether I measure one set of wires or with the to reds combined. The PSB amp of course had hook-ups for all three wires - I'm not sure if the new amp (500 watt BASH) will have this set up. I can't seem to find out any more info from the web. Anybody familiar with this amp or the PSB drivers. Since PSB won't return e-mails I'm not exactly sure about the driver set-up. Also, anybody know what effect switching from a 180 RMS watt amp to a 500 RMS watt amp will have on the sub?

    Thanks!

    Brad
     
  2. Arthur S

    Arthur S Well-Known Member

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    Hi Brad

    Please don't hook anything up until someone with enough experience has a chance to read about your situation and advise you properly...you could destroy the driver if you make a serous mistake... please keep in touch with me.
     
  3. Robert_J

    Robert_J Well-Known Member

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    Have you pulled the driver out of the enclosure and looked at the connections on it? Just because you have a 3 wires doesn't mean you have a DVC. I can wire up a quad voice coil speaker with two wires.

    By using a larger amp, you are now able to move the cone of your sub more. That means you can probably drive it past its maxinum excursion rating. That leads to torn spiders and deformed voice coils. Be careful with your levels. Second, the amp in your PSB may have had some EQ built into it. The PE amp will have a relatively flat response to 30hz. So your sub may sound better/worse/different. That leads me to my third point - yes, the PE BASH amp has a filter so it only plays signals above 30 hz. You need to look at the sheet of paper that comes with the amp and swap resistors to adjust your boost/ssf appropriately.

    -Robert
     
  4. Arthur S

    Arthur S Well-Known Member

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    Hi

    I completely agree with Robert_J.
     
  5. John Garcia

    John Garcia Well-Known Member

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    The PE amp is 273w RMS @ 8Ohms, 500 is for 4 Ohms AFAIK, though it will still allow you to push that driver harder than it was intended to IMO.
     
  6. Brad Russell

    Brad Russell Well-Known Member

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    Thanks for the responses! I'll see if I can pull the driver tonight although that may require ruining the cloth cover. It does not have a standard grill cover. I have a couple of questions based on your responses:
    The amp is sitting on my porch and I'm still at work so I haven't seen the instructions but PE spec sheet says it is 500 watts RMS at 4 ohms from 22hz on up. Is the 30hz filter a default setting?

    As far as overexcursion goes, isn't that really just a matter of volume? Right now I have a BFD hooked up to it and I was getting pretty good response to about 22hz. Unless I really crank it, won't the additional power just allow me to control it better?

    Thanks for all the help!

    Brad
     
  7. Robert_J

    Robert_J Well-Known Member

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    Based on the included sheet and the PDF instructions at the PE web site, the default setting for the sub-sonic filter is around 30hz. It gives you the resistor values that you need to change that to anything you want.

    And yes, excursion is based on power and frequency. If you find that you can now easily overpower your existing sub, then we can recommend replacement drivers as well.

    -Robert
     
  8. Brad Russell

    Brad Russell Well-Known Member

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    Thanks again for all the help. I was able to pull the sock up and remove the driver. I still don't know if there are multiple voicecoils but there are only one set of terminals for the driver. The + cable splits into to leads so you end up with 1 neg and 2 positive connections to the PSB amp. I just replaced the + wire with the one that came with the amp. I would guess it is a single voicecoil 4 ohm driver. I'm still a little confused about the 30hz filter. When I look at the spec sheet all I see are options for boosting response in a certain frequency range not removing a filter. Although, I'm also confused about the LFE switch. I have a BFD so if possible I'd like to eliminate any eqing at the amp. Can I just flip it to LFE and use the BFD?

    Thanks again for all the help. Also, I have to admit when I saw the driver my first thoughts were about replacing it. Although, I'm not sure I'm ready to start trying to calculate all the numbers to figure out a replacement driver.

    Thanks again!

    Brad
     
  9. Robert_J

    Robert_J Well-Known Member

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    Based on this PDF, the default resistors are R17=10K and R18=60K. Look at the 2db bass boost table. The default values closest match is the last line of that table. 2db boost at 36-40 hz and a filter set at 30.6 hz. I suggest that you change the values to R17=18K and R18=68K. That's 1db of boost and the filter set at 20 hz. Some people have rigged switches to change the values without pulling the amp or even wired plugs to the amp so resistors can be changed at any time.

    The LFE switch just disables the low pass cross-over. That doesn't eliminate the boost or the high pass.

    If you aren't in the mood to do all of the math, post details about the enclosure. Ported or sealed? What's the net enclosure volume? What size is the driver? What's your budget? TC Sounds is having a sale on a lot of their drivers right now. the db500 12" starts at $75.

    -Robert
     
  10. Brad Russell

    Brad Russell Well-Known Member

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    Thanks for all the help. I'll study that PDF. The enclosure is approx. 1.6 cu/ft has a front firing 12" 4 ohm driver and two 2" ports in the rear. It also about a 14x14" piece of pink insulation. I measured the resistance of the driver at 3.8 ohms on my DMM. Eventually, I'm planning an IB sub for the theater and this one will move to my living room so I don't know if I want to so spend a ton on a driver but if there is one that make a marked improvement then I think I could get really interested. Also, why not go for a cut-off as low as possible?

    Thanks again!

    Brad
     
  11. Robert_J

    Robert_J Well-Known Member

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    Find the length of the two ports and I can determine the frequency the enclosure is tuned to. If you send the sub signals below the tuning frequency, the sub acts like it is in free-air. It takes very little to move it past xmax. With a sealed sub, it's different. The air inside acts as a spring to limit the driver's motion throughout the frequency range.

    -Robert
     
  12. Brad Russell

    Brad Russell Well-Known Member

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    I'd have to pull it apart for sure but I think they were about 6 inches. The owners manual says the freq. response is from 24-150hz. I think I was hitting a little lower with the help of a house curve by the BFD but I think it was droping off pretty quick after 22.

    Thanks again!
     
  13. Robert_J

    Robert_J Well-Known Member

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    Based on your measurements, that does sound like it is tuned around 24-25 hz. I'd set the amp's filter around 22hz to be safe.

    If you want to replace the driver, there are a few options. Seal up the port holes and drop in a TC Sounds TC-1000 12". They are on sale right now for $119. If you really want some output, a TC-3000 12" is on sale as well. It would perform great in that box but would need more power than the BASH amp could provide.

    -Robert
     
  14. Brad Russell

    Brad Russell Well-Known Member

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    So it sounds like I would not get really any more extention but maybe more spl? The room it is in now is about 2700 cu/ft. and I do have another 10 passive sub that I just bought the 300 watt BASH amp for that I'm planning on co-locating with it. In the future, when this sub moves to the living room it will essentailly open to the whole top floor (approx. 12800 cu/ft) so maybe beingt able to move more air might be worth the $120. Also, do you think the extra 4 mm of Xmax? Am I on the right track here?

    Thanks!
     
  15. Robert_J

    Robert_J Well-Known Member

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    I'm not sure what you meant by "Also, do you think the extra 4 mm of Xmax? Am I on the right track here?".

    With the TC-1000 on sale FOR A LIMITED TIME, I think it is very much worth it. If you decide to upgrade the enclosure to a sonotube, you could have a sub that falls in between the performance of an SVS PC+ and an SVS Ultra.

    To me, displacement is everything. With enough overkill you can keep distortion down to a bare minimum. That's why I'm talking to a guy that can get me eight 15" TC Sounds TC2+ subs (similar to the TC-1000) for an IB install. I'll be pushing them with 2,400w from a pro amp. All of this in a sealed, 3,500cf room.

    -Robert
     
  16. Brad Russell

    Brad Russell Well-Known Member

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    Sorry bad editing. What meant to ask is if you felt the difference in Xmax between the TC-1000 and the the db-500 was worth the extra $45? Also, I'm with you and planning an IB to replace this sub with. I'm thinking of starting with 2 Ficarudio 18" drivers with the potential to go to 6. Have you checked out the "Cult"?

    Thanks again.

    Brad
     
  17. Robert_J

    Robert_J Well-Known Member

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    Yes, the extra money for the TC-1000 is worth it to me. I have some 12" TC2+ models are that are VERY similar to the 1000 and they are awsome subs.

    Yes, I'm a member over at "The Cult". My ID is rlj5242. In fact, I'm selling some older TC2 15" subs over there to fund my upgrade plans.

    Those Fi subs look great. When you order, you can get Scott to customize them to work better in an IB application.

    -Robert
     
  18. Brad Russell

    Brad Russell Well-Known Member

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    Thanks for the help! I guess now I need to take some closer measurements to make sure that driver will fit.
     
  19. Neil Joseph

    Neil Joseph Well-Known Member

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    Speaking of PSB subs and plate amps, I have my own story from about 3 years ago. The sub started blowing fuses. I got the meter out and did some investigating and traced the problem to a small power supply card located within the plate amp. I phoned up PSB to try to get the card but they advised me that I would have to buy the entire plate amp at a cost of $100 less than the entire sub.

    The card has 4 power transistors on it so I got them from an electronics store and removed the old ones and soldered on the new ones. It still works to this day.

    Grand total = cdn$10
     
  20. Brad Russell

    Brad Russell Well-Known Member

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    Thanks for the suggestion Neil. I whish I had the knowledge to attempt a similar repair. My problem was a loud low rumble that would start a few minutes after powering on and then would continue even if there was no signal going to it.

    This is totally off topic but how does that black front wall work with the other tan ones? We are in the process of redoing our room for front projection and both my wife and are are leary of the dark colors. I'm willing to sacrifice for picture quality but I'm not sure my wife is.

    Also, Robert, if your deal falls through selling those drivers drop me line.

    Thanks,
    Brad
     

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