?s for the speaker/xover builders here

Discussion in 'Audio Hardware' started by markshan, Mar 8, 2008.

  1. markshan

    markshan Active Member

    Location:
    Pittsburgh, PA
    I just modded a set of bookshelf speakers. (Yamaha NS-A635A) The midranges were blown. I remembered having a box of old drivers in the basement. (I used to work at Radio Shack when I was in school and would buy disco drivers for pennies on the dollar.)

    I found a pair of cloth dome mids that fit the existing hole in the enclosure. I put then in and they were so much more sensitive than what they replaced that the cabs became quite "honky". So I replaced the existing tweeters with a pair of "linaeum" tweeters mounted on top of the cabs. I left the old tweeters in the cabs but disconnected the wires to them (just to plug the baffle holes).

    I really like the sound of this setup for the most part. The speakers sound much more articulate than they did before. However, there is still too much midrange.

    The cabs didn't have a proper crossover network, just high pass caps. I was told that this is all that is necessary, but I have my doubts. I am wondering if the frequency response on the 8" woofer goes high enough that it is playing some of the same frequencies as the mid, adding the peak that I hear. Would a proper 3 way network possibly (or even likely) help with this midrange problem?

    If I should add a crossover, that leads to question two. The add on linaeum tweeter is self enclosed, with terminals on the back and a high pass cap built in. If I add a crossover, will I need to bypass the enclosed cap? I didn't know if capacitance is additive, like resistance, or if having the second cap will only block the same low frequencies that the crossover is already handling. If it were easily accessible, i would remove it either way, but if I can avoid tearing this thing apart and not getting it back together that would be great.

    Thank you in advance for any help.
  2. JBStephens

    JBStephens I don't "drop needles" or "pull triggers".

    Location:
    Western NC
    Interesting. Typically, 8" drivers don't usually need a midrange driver, they will go high enough into the midrange on their own. In fact it's quite silly to have a 3-way system with an 8" woofer. I remember the soft dome mids from RS, they were pretty nice, I used them in a couple of systems back in the day. Knowing RS, there's a 2.2 uF cap on that outboard linaeaum (aww, YOU spell it) tweeter. I'm not familiar with that particular Yamaha speaker, but just from what you've described, here's what I would do. Wire the woofer directly, bypassing any crossover (if there is one). Then, hook the RS midrange to the tweeter wires of the Yamaha, ignore the midrange wires, and use the Linaum tweeter as the top end. If you've been inside the Yamaha cabinets, what are the cap values?
  3. markshan

    markshan Active Member

    Location:
    Pittsburgh, PA
    The linaeum does have a built in cap. That was one of my questions, will the value of the cap and the crossover be additive or will they both just pass high frequencies.

    The 8" 3-way is an odd design, but that is how they came. The mids on these cloth domes do sound nice though, so I want to try to make it work.

    The stock setup was woofer running full range, caps on mid and tweeter. I don't know those values as I already got rid of them in lieu of the caps that were on the Radio Shack drivers.
  4. See my replies to your questions in bold letters above

    HG :cool:
  5. markshan

    markshan Active Member

    Location:
    Pittsburgh, PA
    HG, your answer makes perfect sense, so perhaps I am just being anal here. These mids sound great. Can't I come up with a way to saddle the offending frequencies from this woofer instead of this midrange?
  6. To prevent bleed over of frequencies from woof to mid I use 3rd order crossovers and Zobel filters on all my homebrew speakers.

    You can do this, but you will have to build new crossovers. The cost would run you about $60 per speaker. This assumes that you use electrolytic, not mylar capacitors. I use nothing but non plarized electrolytics in all my crossovers.

    It would be interesting to determine the current balance of your drivers. You can do this as follows if you have an SPL meter and a pink noise recording:

    - Do one speaker first then the other. Disconnect the mid and tweet, play a pink noise recording and get a reading of your woof only with your SPL meter at your normal listening spot. Make a note of this reading.

    - Do not touch the volume control on your amp or preamp. Disconnect the woofer and hook up the mid. Play the pink noise recording and make a not of the SPL meter reading.

    - Do the same with the tweet.

    - Now you have a rough idea of which driver(s) you must adjust to balance your system. For example, if you get a reading of 80 dB on the woof, 85 dB on the mid and 75 dB on the tweet, you will probably have to bring your mids down a little and your tweets up.

    This is why I always recommend installing variable L-Pads on your mids and tweets. This will insure that your system is always in perfert balance. I check my speaker balance every 2 months.

    HG
  7. markshan

    markshan Active Member

    Location:
    Pittsburgh, PA
    Thanks again for all of the input. I am open to building a proper xover network and think that $60 would be in order to take these to the next level. I looked for 3 way xovers but couldn't find anything with the proper frequencies. The mid spec calls for a 1500-10k response, so I though a three way with points at 1500-1800 and 5k-8k would be appropriate. My only issue with building the xover is that I don't know how to determine the cap and choke values.

    I do not have an SPL meter.
  8. Here is the web address of a good crossover calculator that you can use.

    http://www.lalena.com/audio/calculator/apcxover/

    Once you plug in your crossover points, it will give you the values of the caps and inductors as well as a schematic diagram that you can follow.

    I forgot to mention in my previous post that the $60 crossover cost is based on using 18 gauge copper aircore inductors. You will be wasting your money if you use a heavier gauge.

    Are you sure your midrange frequency range is 1500-10K? 1500 seems high for the low end of a midrange driver. Most midrange drivers start out at 150-400.

    I like to set my low cross at 250-350 and my high cross at 2500-3200. This insures that the woofs are only covering the true bass frequencies, the mids only the true midrange frequencies and the tweets everything else.

    Look at this chart which shows the frequency distribution of various instruments:

    http://www.dak.com/reviews/Tutorial_frequencies.cfm

    Except for the pipe organ and piano, not many instruments produce fundamental frequencies over 3000. Thats why I try to set my high crossover in this area. Remember, I have variable L-Pads on my mids and tweets, so if I should want to bring my mids up or down, I want to be certain that only the mids will respond. Likewise, If I decide to bring my highs up or down, I only want the highs to respond.

    By the way, if your serious about building or tweaking speakers, you should eventually have an SPL meter. Radio Shack has a decent one for around $35.

    HG