Redesigning Home Stereo Speakers

Hi all knowledgable gurus! I am currently redesigning my stero speakers for my home system, and need a little help.

I want a 5-way speaker system, plus a sub, using 2nd order passive filters.

My stereo is capable of driving speakers at either 8 or 4 ohms. It only has speaker outputs, no line outs. Power output 100watts RMS x 4 ch.

Questions:

1) How do I determine the output impedience of my stereo? I have software to design and simulate any filter design, but I cannot determine the filter's input impedience (same as the stereo's output impedience)  to use for the designs. I found that it affects the x-overs enough for me to worry about. What is the value commonly used for your charts or calculators for a 2, 4, or 8 ohm system?

2a) I am having problems finding my mids and tweets in a 4 ohm version. I know that using different resistances changes the filter designs, but does it also affect the other filters connected in parallel (i.e. the woofer and sub)? Remember, I want a 5-way system, so each filter will be connected in parallel to the output of the stereo.

2b)If it does affect it, what do I do to correct it?

2c) So basically, will I have any problem using 4 ohm subs and woofers, and 8 ohm mids and highs?

3) How would I implement a "volume" knob for each speaker in my passive x-overs?

4) How would I implement a "Bass Boost" switch in my subs or woofers using passive x-overs?

5) How would I make my x-over frequencies variable over a small range in this passive system?

6) Do you see anything you don't like about my x-over frequiencies I plan to use for a given size speaker? (The frequencies I plan to use are listed to the right of the speaker below.)

My 5-way system and subs will be made up of the following components (LPF=low pass filter, BPE=band pass filter, HPF=high pass filter):

Currently, I have purchased:

Subs: 2 - 15" - 4 ohm coils - desired x-over: LPF 60hz

Woofers: 2 - 12" - 4 ohm coils - desired x-over: BPF 50Hz - 260Hz

Other speakers to purchase:

Mid/Low: 2 - 6.5" - 8 ohm coils - desired x-over: BPF 250Hz - 1.1kHz

Mid/Mid: 2 - 5.5" - 8 ohm coils - desired x-over: BPF 1kHz - 3.1kHz

Mid/High: 2 - 4.5" - 8 ohm coils - desired x-over: BPF 3kHz - 6kHz

Tweeters: 2 - 1" - 8 ohm coils - desired x-over: HPF 5.5kHz

Thank you in advance for any help provided to my problems.

Hi KyferEz, impedance is relative to frequency, so with 2 woofers, 3 mids, and a tweeter all on one crossover network, the nominal impedance will most likely vary at different frequencies depending on your design and each speaker's nominal impedance. For example if you have a 4 ohm woofer playing at 80Hz and down, a 4 ohm midrange playing at 70Hz to 5000Hz, and a 4 ohm tweeter playing at 4500Hz and up, the lowest impedance would be 2 ohms between 70 and 80Hz and between 4500 and 5000Hz. Below 70Hz, between 80Hz and 4500Hz, and above 5000Hz impedance would be 4 ohms.

Although you plan to use variable filters, keep in mind that while your desired crossover frequencies may look great on paper, they can easily produce less than desireable results once constructed. For all that you want to incorporate into your speaker design, I'd strongly recommend visiting the library where you can find tons of detailed information on constructing home speakers and crossover networks. Also I'd recommend visiting Brian Steele's site here: http://www.diysubwoofers.org/  While his site's main focus is on sub woofer enclosures, he includes a lot of the information you're looking for. For passive crossovers in great detail, I'd recommend this site: http://www.passivecrossovers.com/

When you get them built, post a pic and let us know how you like 'em.

the12volt

Ok, Thanks.

I understand what you're saying, and I read everything at www.passivecrossovers.com and checked out www.diysubwoofers.org. Both great sites, thanks!

So, I can fix one design problem by setting the crossover points so that they don't overlap. The others I will have to research.

But I am on a tight schedule, (work full time, DeVry full time, and Married w/ Children) so I was wondering what a quick fix would be until I can devote more time to the x-over designs. I mean, I need to actually use the woofers I bought before the warranty runs out,  right?

Am I correct in thinking that using the charts would be the best idea until I can take the time to do the designs properly? What should I do about the imbalance in impediences of my mids/highs with my woofers? 4ohm woofers, 8ohm mids/highs. That still presents a problem doesn't it? What do you recommend for a quick & dirty fix?

Thanks again for taking the time to reply. BTW, I will send detailed pics and all when I get them done right. I really think your site is wonderful. This industry needed a really good site like this.