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Old 20th September 2007, 11:15 AM   #1
ecl86 is offline ecl86  United States
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Default Specs VS reality

Can someone please educate me regarding secs of speakers. I've seen lot of 15" speakers that have specs from 20hz on up but how come only some certain speakers can only be used as subwoofers while the others can only be used as part of a 2 ways or 3 ways speakers. Why is that.....
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Old 20th September 2007, 01:54 PM   #2
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The parameters that decide that are

Mass
- High mass -> low Fs -> increased low frequense response.

VAS
- High VAS -> low Fs due to the "spring effect" -> increased low frequense response

Bl
- Low Bl -> the magnet don't have the power to hold the cone in a firm grip, so the element can move a bit more than indented at low frequense -> more air moves at low frequenses


High mass decrease frequense response in the upper regions due to the cone is too heavy that it does not have the time to move along the initial signal from the alplifyer.

A stronger magnet will reduce that problem slightley. Better is to use a lighter cone. For example, a mid-bass 15" has a typical mass of 50-70 g. A woofer has about 130-450 g

Regards / Petter
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Old 20th September 2007, 02:07 PM   #3
badman is offline badman  United States
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There's a lot in your question, but I'll give you a simplified run-down.

A speaker can be a number of types. Some are pure 'subwoofers', these are generally high mass, high inductance drivers, with severe breakup behavior (peaks in the response). Some are designed as woofers, meant to play cleanly up to 500Hz, but wanting a crossover above that. Some are meant to be midwoofers typically playing up to about 1 kHz, or even fullrangers (if you can call an extended band 15" a fullrange). Usually, the more efficient a 15" driver is, the more it's suited to wider-bandwidth usage, due to similar design constraints for both features (Low moving mass, etc). These wider range/higher efficiency units are typically 'pro' drivers, used for PA (I'm fond of them for home use too, as are many others, there's less 'style and voodoo' in pro drivers, they put the features where they count). So Pro 15"s are usually woofers or midwoofers, vs. subwoofers, or the freakishly rare "15" full range".

Subwoofers usually have multilayer voicecoil assemblies, heavy cones, and large roll surrounds. They're made to move far, dissipate heat, and not distort on large excursions.

Most "Hifi" (Seas, etc) 15"s are woofers, neither subs nor mid/fullrangers.

If a woofer's 'specs' have 'frequency range' it often is a good indicator that it's not a very high quality driver. The lowest frequencies a driver will reproduce are very much dependent upon the enclosure, which is why we use the Thiele-Small parameters.

The construction methods that lead to these things are issues like: driver stiffness (sometimes, a controlled distortion of a cone can be used to extend frequency response), the motor design (the magnet and voicecoil), the suspension (surround and spider) and even things like the adhesives used.

Your question could lead to a full-blown discussion of what makes a driver do what, but more likely, it'll get precious few replies: It's so broad that people often dismiss such questions, thinking "I'm not going to type it out, this guy needs to use some search engines".

Which, now, is what I recommend you do. Look over a lot of drivers, see what types of construction seem to be correlated to what usage, and read up on loudspeaker design. You'd be hard-pressed to find a better basic reference (and it does go reasonably in-depth) than Vance Dickason's Loudspeaker Design Cookbook. It's available at www.madisound.com
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