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<blockquote data-quote="Phil Graham" data-source="post: 49520" data-attributes="member: 430">Re: Need subs that will do 20hz-40hzEric,Hoffman&#039;s iron law is very much in effect for this circumstance. For a vented box the acoustic efficiency is directly proportional to the box volume, and the cube of F3. This means that cutting a F3 by an octave (e.g. 40Hz to 20Hz) reduces the efficiency by factor of 8. There is a reason that 30Hz is the historical (self-imposed) low boundary for commercial sound reinforcement.Personally I would recommend against using vented boxes for this. Modern vented boxes are already at the point where the port behavior falls apart before the quality drivers run out of excursion. This will only get worse at lower frequencies. Horns and re-entrant (e.g. tapped) horns have better performance in this regard. The air velocities at their throat, where the opening is smallest, tend to be lower. This is perhaps the biggest advantage of these systems.Also, if you move to a horn, you should take advantage of their increased sensitivity in the upper bass, and use them for the entire subwoofer bandpass. They will have superior sensitivity to your existing vented cabinets, and require less space. No need to add an extra crossover point, amps, and boxes.The question then becomes &quot;what do you want to spend?&quot; and &quot;how much room do you have?&quot;</blockquote>

[QUOTE="Phil Graham, post: 49520, member: 430"] Re: Need subs that will do 20hz-40hz Eric, Hoffman's iron law is very much in effect for this circumstance. For a vented box the acoustic efficiency is directly proportional to the box volume, and the cube of F3. This means that cutting a F3 by an octave (e.g. 40Hz to 20Hz) reduces the efficiency by factor of 8. There is a reason that 30Hz is the historical (self-imposed) low boundary for commercial sound reinforcement. Personally I would recommend against using vented boxes for this. Modern vented boxes are already at the point where the port behavior falls apart before the quality drivers run out of excursion. This will only get worse at lower frequencies. Horns and re-entrant (e.g. tapped) horns have better performance in this regard. The air velocities at their throat, where the opening is smallest, tend to be lower. This is perhaps the biggest advantage of these systems. Also, if you move to a horn, you should take advantage of their increased sensitivity in the upper bass, and use them for the entire subwoofer bandpass. They will have superior sensitivity to your existing vented cabinets, and require less space. No need to add an extra crossover point, amps, and boxes. The question then becomes "what do you want to spend?" and "how much room do you have?" [/QUOTE]

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