Frode Posted March 27, 2005 Share Posted March 27, 2005 Here's a post where djk explains more about the filter: http://www.diysubwoofers.org/talkshop/messages/35659.htm Frode Quote Link to comment Share on other sites More sharing options...
djk Posted March 31, 2005 Share Posted March 31, 2005 http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3271&item=5763572555&rd=1&ssPageName=WDVW Quote Link to comment Share on other sites More sharing options...
dragonfyr Posted March 31, 2005 Share Posted March 31, 2005 Just a few thoughts... Is the total woofer enclosure tuned utilizing T/S parameters, etc. or is it simply of a size convenient to match the LS? Also, to what frequency is the enclosure tuned? Do you have any thoughts regarding the bass response as it nears the free air resonance of the woofer, as at that point the woofer (in a bass reflex configuration) is completely undamped acoustically! You are then totally dependent upon the electromechanical damping of the voice coil and amp. Not a nice quality assuming tight defined bass is desired for the lower two octaves and bass reflex. Even IF you are using a Crown Macro-Tech 2400 or 3600 with damping factors above 3000 to drive the woofer! A bass reflex loading affords a little better efficiency over acoustic suspension loading while adding slight bass extension...but they have severe limitations one you exceed that... Quote Link to comment Share on other sites More sharing options...
djk Posted April 1, 2005 Share Posted April 1, 2005 "Is the total woofer enclosure tuned utilizing T/S parameters, etc. or is it simply of a size convenient to match the LS?" If you had read all the posts, you would know that this has be analyzed to death with several drivers and different port tuning frequencies, plus as a sealed system, and an assisted vented system. BassBox 5.183 was the primary tool. "Also, to what frequency is the enclosure tuned?" Depending on the woofer, from 28hz~35hz. "You are then totally dependent upon the electromechanical damping of the voice coil and amp. Not a nice quality assuming tight defined bass is desired for the lower two octaves and bass reflex. Even IF you are using a Crown Macro-Tech 2400 or 3600 with damping factors above 3000 to drive the woofer!" Total red-herring. It doesn't matter what the output impedance of the amplifier is unless the DF goes below about 20. You have fallen victim to marketing hype. The REAL DF involves the sum of all generator resistances: speaker wire, woofer inductor, and the BIG ONE of the DC resistance of the woofer. The amplifier output impedance of 0.000001 ohms is meaningless with the over 6 ohms in series with a typical 8 ohm speaker. "Do you have any thoughts regarding the bass response as it nears the free air resonance of the woofer, as at that point the woofer (in a bass reflex configuration) is completely undamped acoustically!" Wrong again. The woofer is most under control at Fb, it progressivly unloads both above and below there. The port becomes the main radiation resistsance. "You are then totally dependent upon the electromechanical damping of the voice coil and amp." The amp never was really in the picture, see DF above, its always been surround, spider, and radiation resistance (in this case, the port). "Not a nice quality assuming tight defined bass is desired for the lower two octaves and bass reflex." Another wrong statement. Build a simple high and low pass filter set. Run some square waves throught them and look at on a 'scope. The low pass output starts at zero* and slowly rises to 180* Where it drops straight down. The high pass goes straight up at zero* to about double the amplitude, then slowly falls to 180* 'Punch' and 'slam' in the bass are a function of how well the highs are integrated with the system. "A bass reflex loading affords a little better efficiency over acoustic suspension loading while adding slight bass extension..." A bass reflex has no improvement in No% over a direct radiator, they have EXACTLY the same mid-band efficiency (how could it? its the same driver.a port only inverts the phase over a narrow range, a 1/2 oct or so). A B6 alignment has a bass extension of 1-1/2 octaves compared to the SAME driver in a sealed box, that is hardly 'slight'. Don Keele has a paper on this, it is still available from JAES. "Direct Low-Frequency Driver Synthesis from System Specifications," J. Audio Eng. Soc., (Nov. 1982). "but they have severe limitations one you exceed that..." dB Keele: The vented sixth-order system can handle full rated power a full octave below the closed box system (note: his examples were a 15" driver for the direct radiator and an 8" for the 6th order, and the 8" still handled the power better). I seem to remember designing in a high pass filter at Fb...did you miss that too? Quote Link to comment Share on other sites More sharing options...
djk Posted September 5, 2007 Share Posted September 5, 2007 "A bass reflex loading affords a little better efficiency over acoustic suspension loading while adding slight bass extension..." Posted by djk ( M ) on July 25, 2005 at 00:55:59 A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB). A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB). A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB). Classical music at mid hall can reach levels of 0.2W at 30hz. This requires 112W, 56W, and 22.4W for the above systems. To keep FMD below an annoying level (3%) would require a 300hz crossover and a nominal frame size of 15", 10", and 8", with a Bl of 29.6, 13, and 6.7 All data calculated per DB Keele and PW Klipsch. Quote Link to comment Share on other sites More sharing options...
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