Selecting and Matching tweeters and woofers???

Discussion in 'Home Theater Projects' started by Ryan Peddle, Oct 23, 2005.

  1. Ryan Peddle

    Ryan Peddle Second Unit

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    I am looking for advice on what parameters to look at when trying to select a woofer and a tweeter for a DIY project. I've done much searching and I've read many small threads that didn't really provide me with the answer.

    I have a speaker building book, but it really doesn't go into that in any detail. I will be investing in some new reading material soon but until money permits me, the internet it is.

    I'm not looking for suggestions for drivers, just how to calculate a good pair for a 2 way design.

    OR

    If you know another website I may be able to discuss this further by all means send me that direction.

    I've had no real help from diyaudio.com btw. Not that it isn't a great site, just not enought people interested in helping a novice.

    Thanks in advance.
     
  2. ThomasW

    ThomasW Cinematographer

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    I know of no website that explains the entire process since it's a combination of science, experience, and magic... [​IMG]

    One important thing to know, is that measurements of the drivers mounted in the baffle where they're going to be used, are necessary for properly designing the crossover. This means you need test equipment before you can design and build speaker systems.
     
  3. Todd Shore

    Todd Shore Stunt Coordinator

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    A few thoughts...

    First, evaluate your experience level. Some drivers are harder to work with than others. Metal cone woofers with pronounced breakup can be difficult for the novice to tame.

    Second, what are your goals for the speaker? For instance, if you have a receiver or amp that can’t drive a 4ohm load then you’ll probably want to look for drivers with an 8 ohm nominal rating. If you like it loud and have a low powered amp then you’ll be looking at drivers with higher SPL. What size of cabinet? What frequencies are the most important to you? Bass, female vocals, sax, etc.

    As Thomas said, measurement equipment is almost mandatory. You can fudge by tracing the manufacturer’s graphs, but that will limit the overall quality of the finished speaker – you’ll have to have some luck to get a great speaker.

    Obtain and learn to use design software. WinISD for cabinet tuning and Speaker Workshop for crossover design are both free. There are also the FRD tools. In fact, a combination is probably required. Experiment using traced manufacturer SPL graphs until you can get a reasonably flat response out of different drivers. More than anything, this will educate you in what is important.

    Okay, back to driver selection.

    How much do you want to spend? Understand that the crossover can be 50% of the final cost.

    Look at what driver combinations other people are using. For a first timer, having other projects to reference is immensely valuable and gives you a fail-safe if you can’t get yours to work.

    Ignore any broad manufacturer/vendor claims as to what frequencies a driver can cover. A claim of 40-4000Hz doesn’t mean much.

    For a tweeter, the relevant number is its Fs. You’ll want your crossover to have the tweeter’s output down by around 24dB at that frequency. That means you’ll be crossing higher than that. Usually, at least double its Fs. Even higher if you are using shallow slopes.

    Let’s say that your tweeter has an Fs of 750Hz and you are using a 4th order crossover on the tweeter at 1500Hz. The woofer you select will need to have a post-crossover response that is almost a mirror of the tweeters post-crossover response with the reflection point being 1500Hz. A woofer that rolls off below that frequency certainly won’t work. If you are using a textbook 4th order on the woofer it would need to be fairly flat all the way to 3000Hz and have a smooth roll-off above that frequency. How do you determine that? By looking at the manufacturer’s graphs.
     
  4. Todd Shore

    Todd Shore Stunt Coordinator

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    A couple more thoughts...

    The sensitivity of the woofer and tweeter. You can pad down a tweeter but it is not practical to attenuate a woofer. So, the tweeter should be have greater or equal sensitivity than the woofer.

    But wait! If your speakers are in a box rather than in-wall you will lose output from the woofer at lower frequencies as it radiates into 2pi space so its output will need to be higher than the tweeter in order to get a flat combined response.

    Hmmm. Dealing with a BSC dip is not so simple if working from mfg's graphs. You'll need to either learn how to use the FRD BSC tool or bite the bullet, buy drivers, measure them in box and hope you get lucky with your selection.

    Generally, most people design in 3-5dB of BSC. That is, the woofer will output more in the 200-1000Hz range than the overall level of the tweeter. So, the woofer needs to be that much more sensitive than the tweeter. However, since the tweeter can be padded down, working with two driver's with similar SPL output can be made to work.
     
  5. Ryan Peddle

    Ryan Peddle Second Unit

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    Thanks Todd.

    Some people may look at your response and say...WHAT?

    I understood every word. I was more or less looking for a simple starting point.

    I am an Electronics technician which helps me understand the basic principles behind audio electronics, and until I get some money to buy my own equipment, I can go back to my school and use function and audio generators and my SPL meter and such.

    I'm not looking for a simple speaker project to do like a kit from a company. I'd like to start from scratch, make something that I designed. It seem like a big under taking, but I'm a little more educated in the field than most and am just starting to have the time and money to really educate myself in the audio loudspeaker field specifically.

    But with so many different product to look at, it's hard to find a starting point.

    I do have a few tweeters in mind but am still trying to narrow it down, and I'm set on a 1 or two woofers. I'll leave them nameless only because I am not looking for recomendations due to my desire to learn from error of my own.

    Anyhoo, thank again and keep the advice coming.
     
  6. ThomasW

    ThomasW Cinematographer

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    Ryan,

    Realistically this can't be done with a function generator and a SPL meter. You need a mic and the ability to make MLS (maximum length sequence) measurements.

    Unfortunately one can't successfully use the mfgr's plots, because most are anechoic or on a IEC standard baffle, and that's not how you're going to use the drivers.

    The cheapest way to get started is buy a Behringer ECM-8000 mic, $50, a Behringer U-802 mixer, $60 (this is used as a mic preamp and phantom power supply). Then chose from the many MLS software programs out there.

    This setup combined with a PC and a duplex sound card will allow you to make the accurate measurements needed for speaker design.
     
  7. Ryan Peddle

    Ryan Peddle Second Unit

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    Thanks very much Thomas. That was something I didn't know and equipment I wasn't aware of.

    See with me I am acually trying to learn and do the engineering part of loudspeaker building, not just build a random set of speakers. But because of a car accident my wife and I had and my wife being injuered and off work for the last 1.7 years I have more of less had no funds to really take a deep step into instumentation and education. Family health and well being always come before personal interest.

    But she, by the grace of God, has improved greatly and found her way to returning to work this past month.

    So I am slowly trying to start where I could have 2 years ago.

    Now that we are back to a two income house hold and my monthly commisions outside of my salary won't necesarily go directly to a bill, I might have an extra 50 bucks to save towards things/equipment like this.

    Again, thanks Thomas for your assistance.

    Another question.

    Like I had mentioned before that I had a few drivers in mind, but is there a real way to judge which tweeter/midbass may work together by looking at basic parameters (Fs, Qts, dB, Z, etc.) that way I can pick a few and purchase them for testing. Or is it like a shot in the night that you find two the work well together.
     
  8. Dean Mar

    Dean Mar Stunt Coordinator

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    Ryan

    You may find diyaudio.com a good source of information with many knowledgeable and helpful people.

    I have very limited knowledge and it always amazes me how helpful people are on this site as well as other sites.

    Thanks to everyone who shares their wisdom here and on other boards
     

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