Conference napalm::guitar

    I am ignorant of the theory involved, but my PA has bass cabinets with
    15" drivers and crossovers for (external) horns to augment the highs.
    It seems to work really well. 
    
    Greg

    For an ultra cheap, but very good sounding high end extender, try this:

    3 Radio Shack Piezo tweeters ($4.95 each, last time I looked), wired:

	    ========    ========    ========      Sort of back views
    +       | +  - |    | +  - |    | +  - |
    <---------o  o--------o  o--------o  o-------+
            |	   |    |      |    |      |     |
	    ========    ========    ========	 |
						 |
    -						 |
    <--------------------------------------------+


    These connect to the + & - of your 15's. Each of these piezo's can
    handle 70 watts peak (making this set up good for 210 watts) and around
    35 watts average power (105 watts). I use a very similar set up (only
    using 2 in a box that sets on top of a PA cabinet - actually one set for
    each side). Your Bass guitar won't hurt them (my cabinets have 15's in
    the also & I occasionally use them for Bass Guitar), and there is no
    other cross over network. If you later decide to add a drum machine,
    or mike a drummers symbols, these little buggers will add a lot to your
    PA systems sounds high end. I put mine in a particle board cabinet &
    spray painted the cabinet black before installing the tweeters. The
    advantage of keeping them seperate from your main Bass cabinets is that
    you can direct the sound better & control the occasional feedback that
    you might get by aiming them different. If you are worried that 3 won't
    be enough, just add another one or 2 in series. Sounds way too simple,
    but, mine have been in constant use for the last 5 years, without a
    single failure. Not bad considering that they get beat on almost
    every weekend of the year.
								Jens

    
    Re: .3
    
    The nice thing about piezo drivers is that they have a "natural"
    crossover so they won't attempt to reproduce any of the low stuff,
    and you can indeed daisy chain as many as you need.
    
    In addition to the little bullets, Radio Shack sells a piezo horn
    for about $15, which might be of interest as it would have slightly
    better dispersion characteristics.  
    
    If you want a high-end balance control, just wire a pot into the
     "+" line going to your tweeters and you can turn them down (but
    not up, of course) relative to your woofer.
    
    

    Thanks folks, that answers the question.  I think I'll use a couple
    of those RS horns & see how that works out.
    							joe

    I am interested in the solution that has been mentionned.
    I have a 90 watts trainsistor bass amp. (Carlsnro 90) which I use
    to play bass on. Recently I decided to learn guitar after 20 years
    of bass only activity.
    
    I would therefore want to use my existing amp, at least in the
    beginning and was considering to add some speakers to improve the
    hi-range.
    
    The solution seems acceptable however here are my questions.
    
    1. Do you simply connect the speakers in paralell to the woofer
    
    2. If so, is this not going to overload the amp, given that the
    woofer is a 4 ohms which is already the maximum that the amp can
    take.
                                                        
    Thanks.

    re: 878.5 - I'm not certain, but I think the piezos have a very
    high impedience, which, when connected in parallel with the relatively
    low (ie:4-8 ohm) impedience of the speakers, has a negligable effect
    on the overall impedience.  For example, if the piezo's resistance
    was on the order of 1K (just pulled that out of the air), placing
    it in parallel with an 8-ohm load would result in an overall impedance
    of (1000*8)/(1000 + 8) = 7.94 Ohms, which would probably not have
    much effect on the driving device.
    						jpb

    Correct, the piezo's are high resistance (I don't recall ever seeing
    it listed anywhere), but it is high enough to have negligable effect
    on the speaker impeadance. I like the cheaper ones over the horns, only
    because they cost less, and they can be added easily with out breaking
    the bank. The horns (like the RS horns) are nearly identical to the
    ones found in some Peavey P.A. systems & they wire them in series, and
    then connect directly accross the normal P.A. speaker.

							Jens

    The Motorola Piezo-electric devices have a very high impedance at
    frequencies below 3.8KHz, and it reaches 8 ohms at 100KHz. Models
    vary in output, and the small cheap horn, has the greatest at 103
    dB. McGee Radio has 'em for $7.95 ea., while RS has 'em for $12.95,
    but they're painted silver. They can be harsh sounding when really
    pushed, but they're a real inexpensive way to give a small system
    some definition in the top end. 
    
    Neal
     

    Ok,
    	Thanks again to all.  Now that I know what I want to put in the
    box, how about some info on the enclosure itself.  I know there
    are several notes on the subject, but none of them seem to provide
    exact dimensions, or a formula for computing them.  I realize that
    a really state of the art cabinet design would depend on the exact
    driver being used, etc., but I really don't need anything quite
    that advanced.  I guess all I really want is to be a little more
    precise than simply making a box that will accomodate the speaker
    (15").
    	I've heard some mention of Thiele design cabinets as being
    relatively simple to build.  Could anyone provide the inside dimensions
    of one of these?  Thanks again.
    						joe

    re: 878.8 - Where is McGee Radio?

    Does anybody know where I can buy grillecloth material?
    Central MA area.
    
    joe.

    re: .11
    I think Radio Shack still sells it, both in cloth and accoustically
    transparent 'foam'.
    
    chuck