Caps for enhanced bass management.

Discussion in 'Archived Threads 2001-2004' started by Paul K, Mar 7, 2001.

  1. Paul K

    Paul K Auditioning

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    I have a Sony da50es receiver which has limited bass management. The problem seems to be that the crossover setting for redirecting bass from the mains to the sub is set too high (100 or 120 hz depending on who you talk to). I have mid-size front mains which reproduce bass well except that they choke on the really deep bass put out by 5.1 material. The problem is that if I set my mains to "small" on my receiver, thus redirecting the bass to the sub, I seem to be lacking mid-bass. Movies sound good, but music sounds very thin. If I set the mains to "large", I get much fuller, better sounding bass, but the mains choke on the really deep bass put out by 5.1. My intended solution is to keep my mains set for "large" and use the appropriate capacitor in-line with the speakers to filter out all bass below a certain value, say 75hz. Can anyone tell me whether this is feasible, and if so, exactly what type and value of Capacitor I would need for this purpose. My speakers are 8 ohm.
     
  2. Patrick Sun

    Patrick Sun Studio Mogul

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    Just a cursory number crunch gives me a value of 265uF for the capacitor. That's a big cap! That's a starting point, it be be
    I used 1/(2*pi*frequency*resistance)=1/(2*3.14159*75*8) to get that value.
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  3. Phil A

    Phil A Producer

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    Paul - you can also look at www.audioc.com/accessories/Hipass.htm. They make high pass filters for $29 fixed at either 65 or 85HZ and give you instructions on your choices without preamp outs.
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  4. Patrick Sun

    Patrick Sun Studio Mogul

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  5. Paul K

    Paul K Auditioning

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    Thanx for the reply's. That link gave me the information I needed. Unfortunately, my receiver lacks preamp inputs so I can't use their filters, but the capacitor they recommended sounds like exactly what i was looking for.
     
  6. Jon_R

    Jon_R Stunt Coordinator

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    I did this very thing yesterday. While listening to some tunes loud, I noticed the port on my R10s, see webpage, was huffing. Now that I have a sub, I don't need my bass to be reproduced by 2 5 1/4 speakers. Being a very poor college student, I actually ventured to best buy hoping for some cheap caps. I found some in the car audio section for $10 total. No doubt low quality, but they do what I want. 199 micro farad, they seem to not entirely cut out 85, but when I A/B them it significantly cut down on airflow, and thus bass.
    Just my 2 cents.
    Jon
     
  7. Timmy

    Timmy Stunt Coordinator

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    if you use a cap, it goes in series with the woofer positive lead with your specific project ( in case you didn't know).
    If you retain the "large" setting and limit your mains bass drivers low end, understand you will create a hole. Your best bet is to specifically nail the bass drivers 3db down point and limit it starting there. It would be a WAG unless you was able to verify with instrumentation where your caps indeed do start to roll off.
    If you could verify your mods, and you did eliminate the frequencies at which your receiver/speaker combo "chokes", it would probably make a noticeable difference in bass tightness.
    I have had 2 different mfgrs mains connected to my 50ES; a not so efficient Infinity Ref 6, and now a more efficient PSB 6T. On both these speakers, I never noticed the problem you are having. Have you tried changing the "4 ohm/8 ohm" switch to see if it improves things?
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  8. Paul K

    Paul K Auditioning

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    I'm learning quite a lot from this post. You speaker building guys are my hero's!
    Plugging the 200mf cap recommended by audioc into Patrick's equation yields a frequency cutoff of about 100hz. That's what I get now from my receiver, so I wouldn't gain anything from using that value. I believe that I will need a cap of at least 300mf. I think I will follow Timmy's recommendation about finding the exact level at which my mains choke. I think Avia has a bass sweep test tone that might help me determine this.
     
  9. Patrick Sun

    Patrick Sun Studio Mogul

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    If you go this route, make sure you get a cap that's rated for high power, like 250V to 400V.
    The polypropylene caps might be overkill for a choke, you might want to go with mylar or at worst, electrolytic caps (the cheapest, and not very large in physical size).
    The poly caps be huge (and expensive), maybe larger than the size of toilet roll's inner cardboard roll if you want a 300uF cap.
    A good poly 200uF cap is about 4.33" tall, 2.5" wide in diameter, and $45.
    If you can't find a 300uF cap, get a 200uF and a 100uF and parallel them to get the 300uF value of capacitance.
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  10. Paul K

    Paul K Auditioning

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    I just thought I'd update you all on how I made out with this little tweak. I purchased 3 of the following for my 3 identical mid-size mains and center speakers:
    http://www.partsexpress.com/pe/pshow...=027-096&DID=7
    Using the formula previously posted above yields a 65 hz cutoff for my mains so I set the crossover on my sub to 65 hz. After installing these caps in-line with the positive terminals on my three front speakers, I re-calibrated my subwoofer using Avia and a sound level meter. I originally calibrated my mains to 70 db and my sub to 77 db using the output control on the back of my sub. Afterward, I played some bass heavy music and fine tuned a little more, turning down the "woofer" level on my 50es to -2. At that moment, suddenly the music sounded right. Bass sounded tight and balanced. My system achieved a level of transparency that It never had before as my sub blended perfectly with my mains. Before, I guess I had one note bass and couldn't strike a balance between boominess and thinness no matter how I adjusted the sub. My bass has never sounded this good and musical. I must say that this has to be the best $20 I've ever spent on my system.
     
  11. Chris Hoppe

    Chris Hoppe Stunt Coordinator

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    You should keep in mind that a single cap inline with the speaker is only a 6db/octave highpass filter. Most receivers will do 12db/oct or 18db/oct.
    This is a very slow rolloff! For example, an 18db highpass at 100Hz will actually be playing less enerygy at 50Hz than a 6db at 200Hz! The 18db/100Hz will be down 18db @ 50Hz, and the 6db/200Hz will only be down 12db!
    The upshot of which is that you probably want a higher target frequency than you thought.
    Also, go ahead and use those cheap caps from best buy. Just wire a good 1Uf poly cap of some kind in parallel with it. That cap will conduct better at the frequencies the electrolytic cap is supposedly having trouble with. The audibility of this is debatable, but you might as well.
     

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