mcmiller@uokmax.UUCP (Michael C Miller) (02/18/89)
Maybe this is a stupid question but here goes.... I want to build a sub-woofer for my stereo but I need some help designing the thing.. I can handle the low pass filters, (they are built and work well ), but I want to drive a single 15" speaker , not one per channel... Does anyone know of a passive summing circuit that will handle 120 watts per channel ? I've heard that tying the two filter outputs would be bad as one channel may try to "drive " the other and blow the amp. A circuit would be great, even a reference would help.. thanks..... sans -- < sans => mcmiller@uokmax.UUCP or mcmiller@uokmax.ecn.uoknor.edu > < Abe said 'where you want this killin' done ?' > < God said ' out on highway 61 ' >
sjb@dalek.UUCP (Seth J. Bradley) (02/20/89)
In article <2413@uokmax.UUCP> mcmiller@uokmax.UUCP (Michael C Miller) writes: >Maybe this is a stupid question but here goes.... I want to build >a sub-woofer for my stereo but I need some help designing the thing.. > I can handle the low pass filters, (they are built and work well ), but >I want to drive a single 15" speaker , not one per channel... > Does anyone know of a passive summing circuit that will handle 120 watts >per channel ? I've heard that tying the two filter outputs would be bad >as one channel may try to "drive " the other and blow the amp. You are correct in that you cannot just connect the two outputs together. I only know of three methods to implement a mono subwoofer: 1. Use an active crossover, sum the outputs and use a separate amp for the subwoofer. Not super cheap (you can get a decent amp for a little over $200 and a crossover/bridge can be built for around $60) but it is definitely the best. You get many advantages, like; sharper cut-off slopes, better damping, lower system I.M. This is what I use. 2. Use a dual voice coil subwoofer. Not much help if you already have the woofer! Most manufacturers use this technique, as it is the cheapest. 3. Use 1:1 isolation transformers between the outputs of the crossovers and the woofer. Audio grade isolation transformers are VERY hard to find (I've never been able to find them) and rather expensive. Dahlquist made/makes? an outboard crossover/ summer that used this technique. If you hunt around real hard you might be able to find one used. -- Seth J. Bradley UUCP: uunet!{lll-winken|ubvax}!dalek!sjb Internet: lll-winken.llnl.gov!dalek!sjb
passaret@brahe.steinmetz.ge.com ("Mr. Mike" Passaretti) (02/25/89)
In article <2413@uokmax.UUCP> mcmiller@uokmax.UUCP (Michael C Miller) writes: > Maybe this is a stupid question but here goes.... Stupid? No. Uneducated, perhaps. > I want to build > a sub-woofer for my stereo but I need some help designing the thing.. > > I can handle the low pass filters, (they are built and work well ), but > I want to drive a single 15" speaker , not one per channel... Good idea. Single speaker systems are easier to balance for a first-time project. Where are you crossing into the sub? What's the rest of the system look like? > Does anyone know of a passive summing circuit that will handle 120 watts > per channel ? Aaakk. You're processing the OUTPUT of your amp? Evil. Very Evil. You really want to do the low-pass and summing stuff in the pre-amp stage of the system. With a few op-amps and some discretes, you can build a really nice n-order filter (If you don't own the active-filter cookbook, buy it now). You also want to put in a sub-sonic filter (if there isn't one in the proc chain before all this). This will guard against one of the causes of "destructive excursion" (defined as throwing your voice coil across the room at high speeds). That really low frequency stuff will cook you if you're not careful. Once you've got the low-level signal, you can either run your amp in bridged mono, or buffer it and send it to both channels. I don't mean to get nosy here, but what kind of enclosure are you using for the woofer? Tuned or sealed? If tuned, what frequency? If you don't understand these questions, that's answer enough. Sorry if I seem a bit pedantic here, but designing speaker systems is a LOT more than just stuffing a driver in some box and putting power behind it. If you have more knowledge that I have assumed, I apologize, but it seems like you may be in over your head here. I've recently been involved in some sub-woofer design for a specialty audio house (not my work, I just stood around and said "wow" a lot), so a lot of this stuff is still in my brain. If you are interested in some advice re: enclosures and such, drop me a line with the model and specs for your woofer and maybe I can con them into using their design equipment for a little while. This got a little long winded, and it really belongs in rec.audio, but I don't read it any more (got tired of mercury filled speaker wire and black equipment panels). Ciao. - MM > sans > -- > < sans => mcmiller@uokmax.UUCP or mcmiller@uokmax.ecn.uoknor.edu > -- passaret@brahe.steinmetz.ge.com {whatever}!steinmetz!brahe!passaret