Tuning BR below Fs?

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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?
 

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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?
 

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Dr.EM said:
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 said:
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 ? :D

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.
 
simon5 said:
BTW, what is that driver ? It has interesting parameters.

I guess you'll need to use long ports with big diameters to have low vent noise no ?


The driver is a late 90's Cerwin Vega Stroker 18", sold for car audio competitions, I have a strong feeling its just a relabeled PA driver.

The ports will be 4" diameter, two ports roughly 34" long, I'll use DWV PVC pipe with a few bends in it.
 
00600,Loud is Beautiful said that' all right.the TQWT is a better choice for 18 hz and it's not difficult to design. But before u build please carefully to check your roof and your floor. because it's very high. sometime may be higher than your roof.:D About phase and group delay are difficult to explain. u build a lot u will know by yourself.

:) /TW
 
00600 said:

Am I missing something?

Apparently.

I'm curious, how did you arrive at such a large, long pipe? What program are you using to sim it? None of the typical vented box calculators such as WinISD can do it with any degree of accuracy, especially WRT vent area/length since they assume a ~uniform particle density throughout the cab, i.e. one with dimensions that has a theoretically perfect acoustic ratio.

Regardless, just so we're on the same 'page', TQWT ~ defines the inverse of a simple constant area expansion horn, i.e. just as it needs an increasing expansion ratio (ER) from the throat to the mouth (St : Sm), ergo its length increases with increasing ER, so goes the TQWT's inverse closed : open cross sectional area (CSA) compression ratio (CR), ergo its length decreases with increasing CR.

Bottom line, the TQWT shouldn't require any more net Vb than the sum of your MLTL + vent Vbs and maybe less depending the desired XO point/slope, yet its various performance specs will be superior overall due to better acoustic damping. The trade-off is a deep notch at its 3rd harmonic and strong pipe resonances above it along with a vented alignment's 4th order roll-off , so its effective HF gain BW is much more limited than typical vented alignments without a high stuffing density that will attenuate much of its gain, but for < ~100 Hz XO points it's not a problem.


Thawach said:

.....because it's very high.

That's what multiple folds are for ;), with the dividers doing double duty as very effective bracing, ergo if void free plywood construction is used it shouldn't be all that heavy for its bulk. I mean you could design it so that the driver loaded the walls/floor corner and the vent the walls/ceiling corner, but a folded one with the driver and terminus (vent opening) at floor level has much more placement flexibility, though of course at the expense of taking up more floor space.

GM
 
LOL:D :D :D :D GM! because u my joke is not joke. i told very high but u tell me high/2.LOL 00600 if u want high/2 TQWT that u can use speaker calculus program from mhsoft,i ever saw. 00600 please believe me about high+extension=super high LOL okay GM the next project sometime i want the deep bass. it's sure!! TQWT


:) /TW
 
GM said:


Apparently.

I'm curious, how did you arrive at such a large, long pipe? What program are you using to sim it? None of the typical vented box calculators such as WinISD can do it with any degree of accuracy, especially WRT vent area/length since they assume a ~uniform particle density throughout the cab, i.e. one with dimensions that has a theoretically perfect acoustic ratio.

Regardless, just so we're on the same 'page', TQWT ~ defines the inverse of a simple constant area expansion horn, i.e. just as it needs an increasing expansion ratio (ER) from the throat to the mouth (St : Sm), ergo its length increases with increasing ER, so goes the TQWT's inverse closed : open cross sectional area (CSA) compression ratio (CR), ergo its length decreases with increasing CR.

Bottom line, the TQWT shouldn't require any more net Vb than the sum of your MLTL + vent Vbs and maybe less depending the desired XO point/slope, yet its various performance specs will be superior overall due to better acoustic damping. The trade-off is a deep notch at its 3rd harmonic and strong pipe resonances above it along with a vented alignment's 4th order roll-off , so its effective HF gain BW is much more limited than typical vented alignments without a high stuffing density that will attenuate much of its gain, but for < ~100 Hz XO points it's not a problem.




That's what multiple folds are for ;), with the dividers doing double duty as very effective bracing, ergo if void free plywood construction is used it shouldn't be all that heavy for its bulk. I mean you could design it so that the driver loaded the walls/floor corner and the vent the walls/ceiling corner, but a folded one with the driver and terminus (vent opening) at floor level has much more placement flexibility, though of course at the expense of taking up more floor space.

GM


here's a link to the .xls file I used:

http://82.95.237.142/mhsoft/downloads/TQWPmetric.zip

I just changed the blue parameters to match my driver, and changed the 1st harmonic to 18Hz.

I spent two weeks playing with Hornresp last year, trying to model a folded horn for this driver, but the low roll off always ended up worse than just running it in a BR.

I'd like to keep the enclosure as small as possible, 1.5' x 2' x 4' MAX, that way it either has a small footprint, or I can use it as a shelf.

Around the time I was modeling the horn, I was also reading a whitepaper on TQWTs, it seemed like tuning was very hit and miss, and since I didn't have ANY enclosure at the time, and I had never done a slot ported box, I figured I'd take the easy one.

I'm looking for a response curve as flat as possible, as low as possible, around 110-120db to match with my mains.

I was thinking about a Linkwitz Transform, but it didn't seem like the driver was well suited to it either.

I'm just trying to improve upon what works. Though I'd be willing to try a TQWT if I knew more about it.

Thanks again.
 
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