Tuning BR below Fs?

[00600]

I'm planning on building another box for my sub, its currently in a 5.75cu ft box slot ported to ~28hz. I love the way it sounds, but I'm considering tuning the new box around 18-20hz to extend the low end for HT use. I'm just worried about over excursion.

Here are the specs:

Fs: 31.8Hz
Vas: 5.779cuft
Qts: 0.191
Qms: 7.923
Qes: 0.196
Le: 0.001mH
Re: 3.6
Sd: 201sqin
Xmax: 0.626in
Sens: 96db W/M
Pmax: 1600W RMS


Here's a screenshot from SpeakerWorkshop, the black trace is the current enclosure, and the red trace is tuned to 18hz. I realize it will take a ton of power to make up the 5db difference, but I'm only running ~200-250W through it now, I don't have a problem pushing that up to 800W-1KW.

Any thoughts?

[simon5]

There's not much problems about tuning below Fs except overexcursion.

Did you check the excursion versus power curve with WinISD or something else ?

I doubt you could use 1000W and still stay within the excursion limits...

[Dr.EM]

Definately check your excursion in WinISD.

This lower tuned enclosure should complement room gain better though and might not require any boost. Should sound less "boomy" but group delay will increase

[00600]

Just D/Led WinISD Pro, pretty neat program.

Here are a few enclosures modeled along with my L/R speakers.

The pink is my main speakers.

The red is the manufacturer's spec box for my sub.

The gray is the current enclosure I'm running.

The blue is the same enclosure tuned to 18Hz.

There's a 90Hz highpass on the mains and a 90Hz lowpass on all the subs.

It looks like I won't run into an excursion problem until I get around 13Hz, maybe a mild highpass around 15Hz would help.

That's running 500WRMS through the sub to reach the same reference level as my mids and highs just under their excursion limit.

How does group delay and phase work into this?

[00600]

excursion

[00600]

group delay

[00600]

phase

[00600]

Originally posted by Dr.EM
Definately check your excursion in WinISD.

This lower tuned enclosure should complement room gain better though and might not require any boost. Should sound less "boomy" but group delay will increase

I was surprised at how little "boom" there was in my current setup compared to most HT systems I've heard. it doesn't have the usual 40-60HZ boom that really annoys me, but instead it had infrasonics that I never noticed before- which really make me grin.

Thanks for the input guys.

[simon5]

Looking at the group delay curve, you push the peak lower in the passband. I think you will be fine. I guess that enclosure is going to be huge ?

Good luck !

[00600]

Originally posted by simon5
Looking at the group delay curve, you push the peak lower in the passband. I think you will be fine. I guess that enclosure is going to be huge ?

Good luck !

Huge? Its 14"x21"x53" with the slot at the base and the sub 1/3 the way up 12X53" side.

The new enclosure will be 19"x19"x39, with either the sub firing out one end and the ports (round this time, for tunability) firing out the opposite end. Either laying on its side, or standing up vertical. I haven't decided yet (downfiring versus corner loading).

Or I may build it with the driver in the 19"x 39" side downfiring.

Comments are always welcome.