I need a little assistance. Someone has asked me to design them an enclosure for their Dayton Titanic MkII 1002 subwoofer. I am predicting a bass-reflex box volume of 3972.6 in.^3 tuned to 28 Hz to provide bass down the Titanic's lower limit of 25 Hz. I am noticing extremely high group delay near the enclosure's tuning frequency, on the order of 32ms. Is this something I should be worried about in trying to give a subwoofer that will still give halfway decent transient response? I don't want to design this person a boom box if I can avoid it.
Looks about normal. It's why ported systems and me do not get along...
See:
http://www.adireaudio.com/tech_papers/sub_gd.htm
See:
http://www.adireaudio.com/tech_papers/sub_gd.htm
Group delay is a relatively useless tool for bass design unless you have a good understanding of systems analysis using LaPlace Transform techniques - and then it only has limited usefulness.
32ms is not extremely high for a sub that goes to 25Hz.
All you need to do to avoid a boom box is make sure you measure the parameters and design so that there are no peaks in response. Whether it booms is largely dependant on room placement and room modes (i.e. size) and how much absorption there is at low frequencies. Room modes have a delay on the order of seconds, by the way....
Systems with high delay ring near the delay peak - you aren't going to hear 25Hz ringing......
32ms is not extremely high for a sub that goes to 25Hz.
All you need to do to avoid a boom box is make sure you measure the parameters and design so that there are no peaks in response. Whether it booms is largely dependant on room placement and room modes (i.e. size) and how much absorption there is at low frequencies. Room modes have a delay on the order of seconds, by the way....
Systems with high delay ring near the delay peak - you aren't going to hear 25Hz ringing......
BAM said:
Parts Express recommends a box of 1.5 cu ft tuned at 25Hz, which is very close to what you calculated.
They also sell a kit that uses a sealed 3/4" MDF box with outside dimensions 14 1/4 cubed, as described in the Dickason book. That uses an amp with a 6dB 30Hz boost. They say it has an F3 "around 24 Hz when room loaded."
D.
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