Extended Bass Shelf box

[emilimo701 10+ year member]

So I have a daily driver in-cabin sub, a Polk SR124 in a sealed 1.4 cube box.

But soon I will be on the market for a subwoofer system to use for tailgating, looking for the best open air response.

My goals, in order, are:

1) low frequency extension

2) sound quality

3) loudness/SPL

i realize that I will probably have to upgrade my electrical, but i'll save that for another time, as i may not have to. right now i'm just looking for a basic direction

for the sake of efficiency, and since i will have the space, i will be looking for a 15" sub at the very least. ideally, the setup will be be two 12" or one 18" if i can find an 18 that fits the bill

i'm not too picky on the SPL requirements, as long as it's more than just "low end fill". basically, the bass will be the centerpiece. i will probably be flanking the sub(s) with a pair of 6x9 full range coaxials (i'd love to try a pair of CADENCE CVSL69).

the theory behind an Extended Bass Shelf enclosure is summed up here:

Audio Innovation - by Dan Marx www.danmarx.org

i found a good thread explaining subwoofer box "alignment" design here:

what is underdamped and overdamped ? - diyAudio

to quote a useful post,

The goal of the optimum vented box design is to select a vented box volume that will achieve the smoothest or flattest amplitude response in combination with a tuning frequency for the vent which will yield good bass response. Many consider the B4 or 4th-order Butterworth alignment originally described by A.N. Thiele to be the ideal maximally flat design. It has a 24 dB per octave roll-off and a system Q of 0.7 but it is possible only when the Qts of the loudspeaker equals 0.4 (assuming a box leakage loss or QL of 7). As Qts sinks below this value, the optimum vented alignment shifts toward a QB3 (quasi third-order Butterworth) alignment. As Qts rises above the B4 value, the optimum vented alignment shifts toward a C4 (fourth-order Chebychev) alignment.

i found a good site that will graph approximate open air frequency response curves for all three alignments stated in the above post...

Subwoofer Box Enclosure Design Calculator - Sealed Ported Bandpass Closed Vented

...there are three radio buttons that you will see that select this. the "natural" alignment recommended for subwoofers with QTS around .40 is the radio button labeled SBB4. the alignment optimized for low-QTS woofers, 3rd order butterworth, is the raido button labeled QB3. the alignment recommended for high-QTS subs, the fourth-order Chebychev alignment, is the radio button labeled SC4. This fourth-order Chebychev alignment is what I believe Dan Marx is referring to with his "Extended Bass Shelf" box design.

Just for an example, I was thinking of purchasing two Phoenix Gold RSDC subs. Plugging them into WinISD, it recommendeds by default a box size of 112 liters per woofer, with a tuning frequency of 22Hz. The frequency response curve resembles the ideal "shelf" with a sharp rolloff with an incredibly low -3dB downpoint of under 20Hz. when plugged into the AJ designer box calculator, this recommendation of box volume and tuning frequency most resembles their SC4 (extended bass shelf) alignment.

So this leads me to a few questions. The "AJ designer" box calculator lists the EBS "Chebychev alignment" as having the most "degraded response" out of the three alignments. does this mean that sound quality will be sacrificed? and if so, how much will it actually matter in a tailagting application?

another question is, why would WinISD recommend, for the RSDCs, 3.9 cubic feet per sub at a tuning frequency of under 22Hz? What is the largest box size, and lowest tuning frequncy you would give these subs? and answer that question in regards to low low frequency extension for rap tracks, with a slight contradictory emphasis on sound quality

Click to read more...

 

[RAM_Designs 5,000+ posts]

winISD does that to give you a flat response, and sometimes has some pretty weird boxes. Like 18" Fi SSD needing a ~17ft^3 box tuned in the low 20's...or my old 21" sub needing ~3ft^3 at 40hz.

Just tinker with it see what kind of response curves you get. Normally if I can be flat from 30-70hz, I'm good...an f3 somewhere in the 20's will suffice for pretty much any music.

 

[galacticmonkey 5,000+ posts]

Forget WinISD and all that other graphing stuff. It doesnt apply at all once the box is in a car.

Just get a good ported or bandpass box design and you will be happy.

 

[RAM_Designs 5,000+ posts]

Forget WinISD and all that other graphing stuff. It doesnt apply at all once the box is in a car.
Just get a good ported or bandpass box design and you will be happy.

Blindly building a box(or at least not knowing what to look for in the t/s) is a crap shoot. If you know how your cabin peaks then you can design around that. Also some subs just do not perform well in certain applications. Just an example: high qts/low fs subs in a normal mid-30's ported box will be very peaky in the 40's and have a big drop off in low-end. Large boxes tuned low work better for those kinds of subs(as far as trying to get some sort of even response).

 

[galacticmonkey 5,000+ posts]

You use your graphs and computer and Ill "guess" and we will see who has the louder box.

 

[RAM_Designs 5,000+ posts]

You use your graphs and computer and Ill "guess" and we will see who has the louder box.

Didn't know we were building fart boxes here. //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

He wants an EBS box, being loud isn't the point...it has "shelf" in there for a reason. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[galacticmonkey 5,000+ posts]

By louder I mean louder overall.

 

[hispls 5,000+ posts]

If space isn't an issue use a PA type driver in a horn loaded alignment.

 

[RAM_Designs 5,000+ posts]

By louder I mean louder overall.

Whatever you say there champ. //content.invisioncic.com/y282845/emoticons/uhoh.gif.c07307dd22ee7e63e22fc8e9c614d1fd.gif

 

[emilimo701 10+ year member]

Forget WinISD and all that other graphing stuff. It doesnt apply at all once the box is in a car.
Just get a good ported or bandpass box design and you will be happy.

dude did you even read past the first sentence of the post? this won't really be a daily driver sub. i'm looking for something for a flat free air response. even if it were a daily, and considered cabin gain, i still wouldn't want to throw it in "any" box

 

[emilimo701 10+ year member]

winISD does that to give you a flat response, and sometimes has some pretty weird boxes. Like 18" Fi SSD needing a ~17ft^3 box tuned in the low 20's...or my old 21" sub needing ~3ft^3 at 40hz.
Just tinker with it see what kind of response curves you get. Normally if I can be flat from 30-70hz, I'm good...an f3 somewhere in the 20's will suffice for pretty much any music.

yeah i noticed this -- that elcosure calculators will recommend seemingly extreme specs on one end of the spectrum or another. so i wonder if the calculators are "imperfect" and that you should stick with recommended specs (for example not using more than 5 cubes for a single 15"... not tuning below 28Hz or below 32Hz if the sub has higher Fs ...etc). but the fact that usually the calculators recommend bigger boxes and lower tuning frequencies makes me believe that the manufacturers recommend smaller boxes than ideal for the sake of saving space, and higher Fb for sake of making the sub seem more efficent in the critical frequencies.

I have researched up on pro audio in general, away form the domain of car audio. And 90% of the time, the ported boxes I see have lower tuning frequency than the resonant frequencies of the drivers they hold. And they also cite box calculators like Leap as being pretty accurate for what they are worth.

I just got a 15" Audiopulse Axis. I'm thinking of using that for this project, since its low Fs and high power handling make it a good candidate.

I'm on vacation right now (why am i on CA? good question) and before i left I did the calculations... 4 cubes at 23Hz i think?

let me know how this would potentially work!

 

[RAM_Designs 5,000+ posts]

It'll be a low-end monster for sure. I love the sound of TC subs, but the only thing about them that I hate is their damn high inductance on most of their models(the Axis being one of them, 9mH!). Because of the high inductance, larger boxes become even worse for quick transient passages because of the higher group delay associated with the larger box.

 

[emilimo701 10+ year member]

It'll be a low-end monster for sure. I love the sound of TC subs, but the only thing about them that I hate is their damn high inductance on most of their models(the Axis being one of them, 9mH!). Because of the high inductance, larger boxes become even worse for quick transient passages because of the higher group delay associated with the larger box.

So would you recommend a smaller box? All ported boxes have a greater group delay in the

 

[RAM_Designs 5,000+ posts]

So would you recommend a smaller box? All ported boxes have a greater group delay in the
I noticed it in my 15" TC-3000 that I had. I believe the inductance was higher in the 3000 series though, something in the 13-15mH range. It was originally in a 4.25ft^3 at 32hz box, switched to 3.5ft^3 at 34hz and could notice a difference in "quickness"(I hate to use words like that). It was pretty peaky in that box, and looking back I probably should have tuned around 28-30hz. IMO, small low tuned boxes will work best with something like the Axis. Just fiddling with winISD and you can see how the smaller box will affect the group delay in any situation. I'd shoot for 3-3.5ft^3 tuned to 28-30hz, but I really do prefer a more flat, musical kind of response that doesn't have me wanting to turn down my sub level because of peaks in certain songs.

 

[emilimo701 10+ year member]

I noticed it in my 15" TC-3000 that I had. I believe the inductance was higher in the 3000 series though, something in the 13-15mH range. It was originally in a 4.25ft^3 at 32hz box, switched to 3.5ft^3 at 34hz and could notice a difference in "quickness"(I hate to use words like that). It was pretty peaky in that box, and looking back I probably should have tuned around 28-30hz. IMO, small low tuned boxes will work best with something like the Axis. Just fiddling with winISD and you can see how the smaller box will affect the group delay in any situation. I'd shoot for 3-3.5ft^3 tuned to 28-30hz, but I really do prefer a more flat, musical kind of response that doesn't have me wanting to turn down my sub level because of peaks in certain songs.

yeah, Audiopulse web site is still up. they recommend between 3.0 and 4.2 cubic feet. based on the T/S numbers, at 3.2 cubes the Axis (at QTS of .40 for "true" butterworth) will react in Butterworth alignment (which supposedly gives best transient response?), and at 4.0 cubes it will have a Chebyshev alignment for an optimally flat SPL shelf, both at just about 22Hz Fb. So Audiopulse seems to be spot on with their recommendations.

I think i'm going to shoot somewhere down the middle, 3.6 cubic feet. It should get low, sound good. And with a couple thousand watts of power pushing it, should get loud too //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif