Bookshelf Speakers - General Help

[nrgy]

I am looking at building my first set of bookshelf speakers. I would like to start with building a 2.1 stereo system, and add on to it for a full 5.1 theater system later on. Much of this is confusing to me, but I'll try to ask the questions as best I can, with some of them being pretty vague and/or basic.

First off, I would like to build two small satelites, using a 3" driver, perhaps from Tangband or Adire. Also a tweeter from Vifa or another source. I'm not all that familiar with the different frequency ranges of everything yet, but I assume it is ok to couple a 3" driver and tweeter together, correct? For the most part this seems fairly straight forward, however I am very confused when it comes to crossovers.

I know what crossovers are used for, to filter out certain frequencies from reaching the drivers, but I'm not sure when it is necessary to use them. With any DIY bookshelf speaker such as the one I would like to make, are crossovers always necessary? If not, when are they not? The reason I ask is a briefly read something about using a plate amplifier on a subwoofer and not using a crossover, but this is all very vague.

Is there a typical/standard crossover design used in satelite speakers such as the one I would like to build? (ie. passive 1st order)

What are the typical cutoff frequencies for midrange drivers, tweeters, and woofers?

What is the Bass Z/ Tweeter Z?

I noticed PartsExpress has some prebuilt crossovers. Are there other prebuilt crossovers out there?

Does a program like WinISD do a good job a calulating the necessary parts for a crossover?

An active crossover, from what I gather, is a digital XO. So generally this is something you buy, rather than build correct. (except for the more advance DIYs I suppose)

How are most bookshelf speakers you purchase from stores like BestBuy, (ie. polk audio, klipsch) designed with regards to crossovers?

There is definatley a big learning curve to get over with this hobby, so I appreciate everyones help.

[mikee12345]

1) a filter will be required on the tweeter to avoid damage from playing low frequencies

2) a filter will be required on the woofer or midrange to prevent it from playing the high frequencies that the tweeter will do with less beaming

Xovers require fiddling around to get right.

Id buy a kit

buying commerical speakers is good because you can audition them THEN buy them-but you dont know what shortcuts/compromises they have taken..

id reccomend getting a loudspeaker design book
and finding some good reference sites on the net
im sure sone one will show a walkthrough website which shows how they designed their vifa midrange,for example

[coolkhoa]

I, too, would recommend you build a kit. But here's some info:

Bass Z and Tweeter Z refer to the nominal impedances of your drive units (usually 4, 6, or 8 ohms). There is no "standard" crossover used in satellite speakers, but most use simple, low-order XO's. WinISD and other simple programs use standard formulas to design the XO and are a good starting point, though you'd want to tweak it. AFAIK the speakers available at Best Buy, etc. use simple crossovers with cheap components (e.g. electrolytic caps).

[Timn8ter]

Some kits you may want to look at would be

Super Elf

Adire Kit 51

AV1

[Bose(o)]

If you're like me you'd build your own speaker and not buy a kit. If you'd rather have the safety net that a kit would offer, buy a kit. For me, buying a kit is buying someone else's work--yuck!

[Timn8ter]

If you're like me you'd build your own speaker and not buy a kit.

Agreed.

As for XO points they vary depending on the drivers. Most tweeters do not do well below 1000 Hz. Many XO points in two-ways tend to be close to 2000 Hz. If you want to use the W3-871 I would add a woofer rather than a tweeter. The upper end on the 871 is pretty good. Adding a 4 or 5 inch TB woofer with a simple inductor/resistor XO is usually enough.

[Bose(o)]

1. Purchase Drivers
2. Measure Frequency response+t/s parameters after break-in.
3. calculate, determine compromises, etc.
4. Build
5. Measure some more, tweak
6. Get some wine, candles, and Kenny G, Diana Krall, Norah Jones and listen 'til your heart's content.


Now, for helpful info: Assuming you're going to be using a Tangband W3871S you could x-o anywhere 3800Hz. because at that point the Frequency being produced is of 1/3 wavelength the diameter of the cone. This is the point at which beaming occurs. Though, if the natural roll-off of the driver lacks many distortions (breakup modes and such) then you could try a xo without an inductor. Depending on your listening tastes and measurements. Right now, I'd guess you'd be worried about which drivers to choose and how well they would integrate with each other.

PS, since these speakers may be used for HT you'll want to control vertical reflections as much as possible. So, in a 2-way config. you may want to place the mid-range driver above the tweeter to control positive vertical sound as the carpet on the floor and/or couch etc. would pad the negative vertical reflections.

Well, let's see how you do now.

[nrgy]

Thank you for all the replies. Things are becoming clearer, step by step. Regarding the cutoff frequencies, so if I enter a value of 1500 hz for the Bass Z, this means that any frequencies above this will be filtered, correct?

Likewise, if I set the Tweeter Z to 1500 hz, then any frequency below this will be filtered? If so, then I just need to remember that the cutoff for the woofers filter frequencies above the specified value, and for tweeters below the specified value.

Also, in a broad definition, the higher the filter order (ie. 1st, 2nd, etc.), the better filtering achieved by the XO?

As far as kits go, I was tempted for a moment to go this route, however I would like to learn as much about this hobby and figured getting hands on experience would be the best way to do this. A crossover kit would be nice however, but I suppose if these were available they would be somewhat generic. This is probably my weakest area, as I have no experience building these.

[sobazz]

Z refers to impedance...

[Bose(o)]

Your understanding of the cross-over point is correct. A higher-order cross over will have a steeper slope, think y=mx+b. It's not accurate, but if you know this then it will help.

Say, you choose to cross-over at 3000Hz. this means (for our example) that x=3000 is on the line y=mx+b. This line extends from this point and down to -infinity. The steepness of the line is dependent on the order of the filter. Say, we are using a first-order filter that means the slope is 6dB./octave. That means, at x=6000, y=reference level subtract six. and, by x=12000, y=reference level subtract twelve.

PS, keep reading and researching, but don't rush this--remember DIY is supposed to be fun not a money saving technique.