How can I change group delay

[Rik]

I've modeled a sub in Bass Box Pro using the Dayton HF 12". The box I modeled is a cylinder with a 16" x 36" interior and a 4" x 20" port with flairs on both ends. The problem I have is that the model is showing excessive group delay... actually it's a real nasty spike right at 20hz. Is there a way I can "fix" this spike without going to a sealed sub?

 

[jonnythan]

Hey I just finished building that exact sub.. with a 3" port instead of 4" though. I found some "minimum perceptible" group delays (it varies with frequency) online and my numbers were *well* below these. I had a spike at 15Hz with 31ms at 20Hz.

 

[jonnythan]

BTW, you can lower the tuning frequency but either way it doesn't seem like an issue at all.

 

[WmAx]

Group dealy is severely over-rated. Another example of people drawing conclusions based upon speculations and in result hyping the issue beyond relevance.

I present to you control samples:

http://www.linaeum.com/downloads/misc/gdelay/

Read the .txt file in the directory for file details. Use [1] WinABX freeware audio *compare software in conjunction with your computer connected to a high quality reference headphone(no room effects) that has a very low frequency response. Use the original reference file and compare to the files simulating a sealed and ported system group delay and roll off characteristics. At best, you may detect very subtle difference(s) upon repeated listening.

*Note: it is critical that you use the blind test software for the comparison in order to minimize psychological bias.

-Chris

[1] WinABX Freeware
http://www.kikeg.arrakis.es/winabx/

 

[Rik]

Okay, I don't have to worry too much about group delay. So as long as the freq resp is flat and the vent velocity is low I'm good? Or is there anything else I have to look out for while modeling a sub?

 

[jonnythan]

Okay, I don't have to worry too much about group delay. So as long as the freq resp is flat and the vent velocity is low I'm good? Or is there anything else I have to look out for while modeling a sub?

Excursion is something to look at, but in your situation it won't be an issue.

 

[Rik]

Hey I just finished building that exact sub.. with a 3" port instead of 4" though. I found some "minimum perceptible" group delays (it varies with frequency) online and my numbers were *well* below these. I had a spike at 15Hz with 31ms at 20Hz.

Hey post some pics of your build up... so I can steal some ideas. So you took some measurements of the actual sub once it was built? Seriously, if you don't mind I would love to see how it turned out.

 

[jonnythan]

There are some preliminary pics at http://jonnythan.com/subwoofer

I spent a couple of days patching a small leak or two around the base because I forgot to seal up from the inside, but it works great now. Tomorrow I will cover the outside in carpet, like an SVS sub. I will have better pics from outside in the sunlight after it is completed tomorrow.

I cannot *believe* how loud it plays. I fired up the Avia disk, and with the gain on my 250W amp at 1/2, the *entire house literally shakes* like mad at 25Hz with the receiver volume at -15. It keeps playing down to the 20Hz on the disc, with the house still shaking, when I can no longer hear it.

When it's turned that far up and rattling the house at 25Hz, there's a little bit of port noise, I'm afraid. I should have gone with the bigger port, but I'll be quite surprised if I ever play it that loud. It was quite ridiculous