Bass-Reflex Group Delay

BAM · 17th October 2003, 01:27 PM

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.

biggerdog · 17th October 2003, 02:13 PM

Looks about normal. It's why ported systems and me do not get along...

See:

http://www.adireaudio.com/tech_papers/sub_gd.htm

Ron E · 17th October 2003, 04:56 PM

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......

Dave Jones · 17th October 2003, 05:42 PM

Quote:

Originally posted by BAM
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.

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.

BAM · 17th October 2003, 10:26 PM

I am designing this for a person who did not want the lower output of the sealed box. Thanks for your responses, I appreciate it.

mikee12345 · 19th October 2003, 11:22 PM

my jbl 33hz 175L EBS tuned sub has about 30ms GD

personaly it sounds great

dont go crazy over getting perfect graphs,
follow ppls reccomendation ..
just KNOW what they are when u build it then u can make your own decision about how much is too much.

17th October 2003, 01:27 PM	#1
BAM diyAudio Member Join Date: Sep 2001 Location: Carmel, IN; West Lafayette, IN	Bass-Reflex Group Delay 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.

17th October 2003, 04:56 PM	#3
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	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...... __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

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17th October 2003, 02:13 PM	#2
biggerdog diyAudio Member Join Date: Oct 2003 Location: MA	Looks about normal. It's why ported systems and me do not get along... See: http://www.adireaudio.com/tech_papers/sub_gd.htm

17th October 2003, 10:26 PM	#5
BAM diyAudio Member Join Date: Sep 2001 Location: Carmel, IN; West Lafayette, IN	I am designing this for a person who did not want the lower output of the sealed box. Thanks for your responses, I appreciate it.

19th October 2003, 11:22 PM	#6
mikee12345 diyAudio Member Join Date: Nov 2002 Location: NZ	my jbl 33hz 175L EBS tuned sub has about 30ms GD personaly it sounds great dont go crazy over getting perfect graphs, follow ppls reccomendation .. just KNOW what they are when u build it then u can make your own decision about how much is too much.

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