3-way plans (newbie question)

[atc747]

Hello there! I am a 3rd year university student studying philosopy and mathematics. What does that have to do with this post? I'm not sure...

Anyway, I'm interested in building some 3-way (or possibly) speakers and have done a fair amount of 'net research into crossovers, components, design, and so on. While I have a little bit of confidence that I would be able to design my own speakers that are okay, I am pretty sure there are plans out there that would be a lot better! I was surprised that I could not find a lot of plans, however, that included enough detailed information to build the speakers. (Measurements, crossover, recommended components, etc.) While I am sure people have asked similar questions on this forum, I was unable to find anything particularly useful (ie. links to a good plans website, recommendation of plans, etc).

I am not particularly interested in a kit... just the plans. I think I will learn more from the latter. And with plans I can get a little experimental to learn what's going on a little more.

I am looking for something in the range of 400-600$ USD, small 3-way speakers (maybe 1.5 - 2' high). I know 'sound quality' is subjective, but I like a warmer sound if possible. I have a rotel RX-602 amplifier, 35 watts RMS per channel. The speakers must be 8ohms minimum for this amplifier. I like the idea of an sealed box, but I am not sure about this. The speakers will be used in a small-medium sized bedroom.

Any thoughts, any help is really appreciated. Like I said I have done quite a bit of research and I think it's time I just went for it .

Thanks, and sorry if this is a really commonly posted question. I did my best to search for answers before posting.

Mike.

[omba]

http://www.audiodiycentral.com/sd300_jh3.shtml

I think this may fit your bill thogh it costs a little less than your budget.

[PowerCrest Labs]

Hi Mike,

I can help you design your bedroom speakers.....I've designed many enclosures before, with great results. ...Anyway.........what you need to do is perform some calculations based on your speaker impedance at the crossover frequency. What is the crossover frequency supposed to be you ask????? It typically should be at least 2 octaves above the speakers free-air resonance. That is why it is important to by raw speakers that provide you with these specs. I have the test equipment needed to test speakers, however I live in Winnipeg, so that doesn't help! Once you know your speakers free-air resonance you then know the crossover frequency. (for example 1 octave higher than 1000 Hz is 2000 Hz and 2 octaves higher than 1000 Hz would be 4000 Hz) Then you must find your speakers impedance at that frequency. NOT SO EASY!!! There are a few ways of doing this...I can guide you through the procedure if you want.....Please let me know.

Once you have the impedance at the crossover frequency, you then use the following formula

High Pass Capacitor Value in Farads=

159000/((Speaker Impedance)(Desired Crossover Frequency))

Low Pass Inductor Value in Henneries=

(159(Speaker Impedance))/Desired Crossover Frequency


Many people just use the "8 ohm" spec, and through that into the equation..THIS DOESN"T WORK.....If you measure the DC Resistance of your speaker it may be more like 7.2 ohms or something.....the manufacture measure the impedance at a specific frequency...such at 400hz which is quit common for woofers. Anyway...I just wanted to throw that in.

The above calculation is for a 1s order crossover. (which cuts off the frequency at 6db per octave) I can give you all the calculations up to 4th order (24db/octave) if you like.....just let me know how involved you want to get. And how much you care about doing this properly.

Justin
PowerCrest Labs
Winnipeg, Manitoba

[PowerCrest Labs]

Remember...The crossover values shown in the schematic are specifically calculated to the speakers that are part of that kit.....don't think any old speakers will sound ok using that schematic.....But If you want to go "seat of the pants method" thats up to you!


Justin
PowerCrest Labs
Winnipeg, Manitiba

[sreten]

http://www.speakerbuilder.net/web_fi...a/lyramain.htm

sreten.

[atc747]

Wow thanks for all the friendly replies

The links two the plans look pretty good.. and also tips from Justin if I'm looking to design. I just have to decide what to do (still).

I was thinking about this a little bit last night... I could get some compatible speakers for a TMW arrangement and use pre-made crossovers -- for the time being --, and then worry about making my own crossovers a little later (as an upgrade, replacing the pre-made ones). Looking at the two plans posted, I already have a few suggestsions for compatible speakers to use, about in the right price range too.

So along these lines... what do you think about pre-made crossovers? Say, the dayton's found on partsexpress (the price is right)... ? Will I be seriously compromising (potentially) quality by not getting the frequencies 100% ideal (for my tastes, I should probably add). If I am using crossovers, I suppose what I am left worrying about is enclosure design/volume. I have seen a number of calculators on the 'net for this... but would certainly run anything I was thinking about by the people here to see if there is something I am seriously missing.

I am just trying to get a sense as to what the things I need to take into consideration are... if I'm using pre-made crossovers, or not, or if I'm just building from plans.

Thanks again!

Mike.

[sreten]

Don't go anywhere near premade crossovers.

http://www.speakerbuilding.com/content/1030/

Is the best for substituting tweeters or another 4 ohm bass unit,
in a different cabinet volume but similar sensitivity of course.

Copying a good design to the letter is always a good idea.

sreten.

[atc747]

Okay I hear ya on the crossover -- !

A few questions about .. http://www.speakerbuilding.com/content/1030/ .. because I do think they are about what I'm looking for.

I think they are kinda ugly ... not too much of a concern but I wonder what my possibilities are for making them look nicer. I realize any little thing I do as far as shape goes is going to change a whole bunch of things around that I will be too inexperienced to compensate for. Maybe I'll just paint a happy face or mandelbrot fractal on it.

Nominal impedance: 6 ohms... not sure I understand impedance that well (only the basics). What does nominal mean? My receiver says 8 ohms minimum! I'm afraid of hurting it. Thoughts? (Rotel RX-602) There will be 2 other speakers hooked up at the same time (as in... 'main' and 'remote'... ) though they won't usually be used at the same time.

Looking at the crossover schematic.. woah, it looks pretty crazy to me Seems like things are just grounded all over the place. How does this work? Maybe I'll just take it on faith (which I'd be doing a lot of if I built these)... but what exactly do I ground to? Am I misinterpreting something here?

Thanks once again -- I've pretty much decided to find a good design and copy it... at least for these first pair.

Mike.