How do I solder resistors/inductors in center speaker (?)

Discussion in 'Home Theater Projects' started by Bart_R, Jul 18, 2004.

  1. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Hi everyone,

    I recently purchased a (second hand) mordaunt short center speaker (905c), but I'm not satisfied with the higher frequencies. It sounds too harsh and peaky at times, imho. I've been using all sorts of different settings and connections to try and solve this, but nothing works.

    I'm thinking now about building something into the speaker that will block the highest tones from going to the tweeter. I did some reading on the internet, and it seems like I need either an inductor or a resistor. It's still not clear to me what should be used. Can somebody help me with this? What would I need? Also, does somebody know of a site that tells/shows you how to insert such an inductor or resistor?

    [Also, is it worthwile to do this and can it be done to begin with by a non-professional (I mean, I can have it done by this store, but that will cost me...).]

    Thanks [​IMG]
     
  2. Chris Keen

    Chris Keen Stunt Coordinator

    Joined:
    Aug 14, 2002
    Messages:
    117
    Likes Received:
    0
    Trophy Points:
    0
    Could you wire in an adjustable L-Pad of some sort?
     
  3. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Hi Chris, thanks for responding.

    Hmm, wiring in an L-pad, eh? Well, to tell you the truth I have no idea. I'm very new at all this, so please bear with me. [​IMG]

    I've read about L-pads, but I barely know what it is or does. Anyway, are you saying that this is the thing I should use in my particular situation? Also, what exactly do you mean by "wire in"? Does it just involve connecting it to the internal wires (by twisting/connecting the different wires together) or does it involve some soldering?

    Bart.
     
  4. Wayne A. Pflughaupt

    Moderator

    Joined:
    Aug 5, 1999
    Messages:
    6,185
    Likes Received:
    51
    Trophy Points:
    9,110
    Location:
    Katy, TX
    Real Name:
    Wayne
    Some L-pads require soldering, some don’t. If you get one intended for in-wall mounting, it probably wouldn’t require soldering.

    As far as what to do for your problem, it depends on what you’re really trying to accomplish. If you’re trying to roll off the highest frequencies, that’s essentially a passive crossover and will require a network of capacitors and chokes. The values and configuration of the elements would depend on the slope and turnover frequency you wanted. It could be inserted in front of the speaker – i.e., between the amplifier and speaker. That would be most practical placement, although inserting it between the speaker’s crossover and tweeter would be more efficient.

    If all you need to do is reduce the level of the tweeter, the L-pad would do. An L-pad is essentially a high-powered variable resistor. It would have to be inserted internally, in-line on the positive speaker lead, between the crossover and tweeter. You could then dial in the amount of high frequency reduction you wanted.

    High frequency reduction could also be accomplished “mechanically,” by taping cloth over the tweeter. This could accomplish both level reduction and roll-off, determined by the type and thickness of the material used.

    Regards,
    Wayne A. Pflughaupt
     
  5. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Hi Wayne.

    Thanks a lot for the info. All your options sound viable to me. It's not really clear to me (yet) what the different effects between the alternatives are. What is the difference for example between a high frequency reduction via an L-pad and rolling off the highest frequencies through a network of capacitors and chokes? Doesn't that do the same?

    If all the options pretty much do the same, I'd go for the easiest and cheapest option.

    How does one apply a passive crossover in front of the speaker? I take it you would be "doing something to" the cable (between amp and speaker), right? How does this work, though? Anyway, it would be a nice safe option (since I wouldn't have to open up the cabinet).

    Is dialing in a frequency reduction with an L-pad as easy as setting a switch? This would be great as I could experiment with the amount of reduction I need.

    Does this cloth taping thing actually work? I mean, do sounds from the tweeter still sound clear enough in this manner (despite the dampening of the higher frequencies)? This sounds like the easiest solution. If this works (and doesn't leave permanent "damage") I might give this a try to start with. Does envolve putting some cloth over the entire tweeter? From the outside of the speaker? Also, what kind of cloth and how to tape it?

    Sorry for the 20 questions, btw. Oh and I haven't even properly explained what I'm trying to accomplish here. Maybe this can narrow it down a bit.

    You see, the problem is this: higher pitched voices or just agitated/screaming voices can have a harsh sound to them. Especially the letter "s" (and "t") can sound distracting. I figured there is a "problem" with higher frequencies, or at least with the tweeter. I'm not sure if my assessment is right, and if it is if I need the frequency to be rolled off or reduced, but there you have it...

    Thanks so far [​IMG]


    p.s. I am not unwilling to do some soldering, it's just that I never do it so it would take some more reading/research and a little practice (since there is the danger of damaging the inside of the speaker)
     
  6. Wayne A. Pflughaupt

    Moderator

    Joined:
    Aug 5, 1999
    Messages:
    6,185
    Likes Received:
    51
    Trophy Points:
    9,110
    Location:
    Katy, TX
    Real Name:
    Wayne
    Bart,

    Hopefully making some of this a little clearer:
    This indicates problems between 2-10kHz. More precisely, the high-pitched problem would be between 2-6kHz, the sibilants between about 8-10kHz. Considering that you’re talking about virtually the entire range of the tweeter, you might be very happy with the results of an L-pad across the tweeter – i.e., reducing the tweeter’s overall level.

    Equalization can accomplish the same improvements electrically, if that’s an option – like the tone controls, if you have some dedicated to the center channel. A treble control that could be set down to 2kHz or so could shelve (reduce) the problem frequencies. If you have pre-amp ins and outs for the center channel, the ideal solution would be an outboard parametric equalizer, which could precisely and narrowly notch out the offending frequencies and leave everything else virtually untouched.

    Regards,
    Wayne A. Pflughaupt
     
  7. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Wow, you're really a life-saver! Thanks for the time you're taking out to help me with this.

    It seems like an L-pad would be a good solution. I will be looking into that then. (Do you happen to know of a website that tells and shows where/how to insert such an L-pad, preferrably with pics of the chip and L-pad?). Sounds like it will be easy enough to adjust the tweeter level. That's great, since one of my concerns was how I would be able to find the exact right resistor/inductor to insert in the speaker. I mean, if I wouldn't be satisfied I would have to take out the (perhaps soldered) thing and replace it. This L-pad sounds ideal in that respect (as well as others).

    I will go to the store tomorrow to try and get myself one of these L-pads. If this promises to be too complicated or costly initially, I might go for the cloth-solution first. I'd have to think about what to do with the tape, though, since I wouldn't want to rip off part of the tweeter(-material) when I take it off. Other than that it sounds safe enough.

    "quote:
    You see, the problem is this: higher pitched voices or just agitated/screaming voices can have a harsh sound to them. Especially the letter "s" (and "t") can sound distracting.

    This indicates problems between 2-10kHz. More precisely, the high-pitched problem would be between 2-6kHz, the sibilants between about 8-10kHz."

    Wow, that's great that you're able to pinpoint it like that. Anyway, I think I'm mainly talking about the sibilants here, but I'm not sure. In that case it might not be the complete range of the tweeter that's the problem. Nevertheless, I think an L-pad might be a good enough solution.

    Equalization sounds neat too. I have actually been thinking about this (or something like this). I was thinking about perhaps bi-amping (after bi-wiring) my speaker, so that I could control the higher tones myself. Are you basically talking about the same here? Still, I think this would get somewhat costly, wouldn't it? I would have to buy myself one of those pre-amp things (I take it you cannot use just any amp because it doesn't have speaker ins and outs, right?). And then I would also need this parametric equalizer... hmm. I like this solution, but I'm afraid it will get a tad bit pricey. (Does your speaker only need to be bi-wirable for this to be possible, btw, or are there more requirements?)


    Regards,
    Bart.
     
  8. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Well, I haven't got an L-pad (installed) yet, but I am trying the cloth-taping thing now.

    Turns out to be easier than I thought. At first I put the cloth on the wrong speaker. I somehow thought one of the big ones was the tweeter with the little (middle one) acting as some sort of bridge between highs and lows. But then no matter how much I taped it, nothing changed as far as higher frequencies go. So I listened more closely to the the different speakers/woofers, and I concluded that the little one must be the tweeter. So I only needed little patches of cloth. I first tried one little piece of some elastic cotton-like material. Wasn't enough, so I added something else (somewhat like the grill/front-fabric only thicker), which improved it further. Anyway, I still haven't found the right configuration, but it seems to be helping. I'm not sure if I want the whole tweeter output diminished like this (it sometimes seems too "muffled"), but it might because I just haven't found the right combination of cloth patches yet.

    Anyway, I'm going to see how this works out for a while. I might turn to other solutions but first I'll give this method a couple of more days.

    Regards,
    Bart.
     
  9. Wayne A. Pflughaupt

    Moderator

    Joined:
    Aug 5, 1999
    Messages:
    6,185
    Likes Received:
    51
    Trophy Points:
    9,110
    Location:
    Katy, TX
    Real Name:
    Wayne
    If you have bi-wiring capabilities it will be easy to connect the L-pad in front of the tweeter’s speaker terminals. Without bi-wiring capabilities, it would require installing the L-pad inside the speaker between the crossover and the tweeter’s speaker wires.

    Good luck,
    Wayne A. Pflughaupt
     
  10. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Thanks again, Wayne. An L-pad is looking better every minute [​IMG]
     
  11. Bart_R

    Bart_R Stunt Coordinator

    Joined:
    Nov 25, 2002
    Messages:
    120
    Likes Received:
    0
    Trophy Points:
    0
    Well, yesterday I got myself one of those L-pads (15 w) and hooked it up to the hf-cable going to my speaker, and well, I'm pretty pleased with it. You can easily change the amount of filtering or blockage with the turning knob, and I didn't have to open up the speaker for it, which is all good. I think I've found about the right setting now. It might be a little better if I could be able to just diminish a part of the tweeter frequency (and not the whole tweeter), but that would get too complicated (what with the whole network of capacitators etc.).

    Anyway, I'll do some more testing, but it looks as though this is a great little solution so far...

    Regards,
    Bart.
     

Share This Page