Two 18" BTL's in 4.7 cubes per driver after port?

[valin 0]

I just picked up two BTL 18's, dual 2's, fully loaded, and will be running them off of two modded Memphis Mojo MC-2000d amplifiers (1 on each driver at 1 ohm), approx. 3000 watts each. In my vehicle, which is a 2007 Toyota FJ Cruiser, I don't have a whole lot of useable space to work with and still maintain practicality, so the enclosure is going to be a bit tight for specs. I will run the subs inverted to try to save as much airspace as I can, but I only have a total of 11.2 cubes to work with, before port displacement. I will be able to run 4.7 cubes per driver after displacement, while running more than sufficient power to the drivers, at 3000 watts per. Fi recommends 5-8 cubes. Running the two 18's will give me 44% more cone surface area than running two 15's........so am I wrong to think that it would be more beneficial to use 44% more cone surface area and cut back slightly on space than to drop down to 15's?

This is going to be a daily setup, and I am more than likely going to build it with a removeable port so I can also tune it for SPL for comps. Subs will be facing up, inverted, and the port will be facing backwards with 3-3.5" to the tailgate of my SUV.

Can I get away with running these drivers with the airspace I have available? This is the first time I've run 18's, and Fi BTL's. Thanks in advance for the help guys.

I have asked this question in other locations.....i'm just looking for more opinions. Thanks in advance guys!

[George 0]

my buddy is running 2 18" bl's off ~3k in 6 cubes each tuned to 32hz. i had the same setup in my explorer except each sub had 5.5 cubes tuned to 33hz.

my single 15" BTL in 4.5 cubes at 33hz, off of 3k has more low end than either of them.

i would REALLY try to get as much space in there as you can if your trying to get any low end out of them. i would of stuck to the 15's. i made the mistake of buying a pair of 18's trying to squeeze them in a box to small and was unhappy with them.

Edited October 23, 2007 by George

[valin 0]

Ok, I can probably get it up to 13.81 cubes, before port displacement. It won't look as good in the vehicle, but it'll have to do.

What should I tune the box to for daily? I was thinking 32 hz.

So, if I go with 165 sq. inches of port (the minimum 12 sq. inches per cube), how long would the port have to be for 32 hz? Is this enough port size?

What are your box recommendations?

I really appreciate the help guys.

[George 0]

13 cubes with 168^2 of port and a 35hz tuning will mean a 17.61" length port

13 cubes with 168^2 of port and a 35hz tuning will mean a 23.61" length port

personally i would go with a 35hz tuning and see how much extra space you can give them by sacrificing a little port length. theyll still get PLENTY low at a 35hz tuning. your better off trying get low end with enclosure volume and sacrificing a little port length than vice versa.

also you can try to use aero ports. they will let you use roughly 50% of the required port area, give your subs quite a bit more volume.

try to see if you can give each sub 6.5+ cubes after displacment each. like i said it will be a lot easier to use the aeroports to regain some volume.

Edited October 23, 2007 by George

[valin 0]

What would I need to run for Aeroports to maximize output, and tune down to 32 or 35 hz?

[BKOLFO4 29]

35 Hz is a low enough tuning on those drivers. . .

For a port with that much area, I would assume you would do a big slot port.

Do you have any overall dimensions for the box? I would be glad to help you with a box design.

Brian

[valin 0]

The box is a "T" shaped enclosure to go around the wheel wells. The bottom is 42" wide, 23" deep, and 10.5" tall. The top of the box is 53" wide, 23" deep, and 12.5" tall. Subs up, inverted so they don't take up internal volume, port back. Hopefully this link for the image works.

Clicky for the box

[valin 0]

Thanks alot. I really appreciate the help.

My old system consisted of two 15" Memphis M3's in a 7 cubic foot enclosure, tuned to 44hz. They were powered by one Memphis MC-2000d Mojo amp. It wasn't nearly deep enough, but it hit fairly hard. I was pushing a best of 149.7 db, on an older mic (i'm not sure which one). It really fell off hard on the lows.

I've been watching some vids of people doing the infamous "hair trick", and would love to be able to do that. Time will tell i suppose.

[George 0]

Thanks alot. I really appreciate the help.

My old system consisted of two 15" Memphis M3's in a 7 cubic foot enclosure, tuned to 44hz. They were powered by one Memphis MC-2000d Mojo amp. It wasn't nearly deep enough, but it hit fairly hard. I was pushing a best of 149.7 db, on an older mic (i'm not sure which one). It really fell off hard on the lows.

I've been watching some vids of people doing the infamous "hair trick", and would love to be able to do that. Time will tell i suppose.

i would keep the aero ports in mind man. by most tests done by members, you can get by with 50% of the port area you want, by using aero ports over slot ports.

3 6" ports are equal to 84^2in which is equal to about 168^2in of a slot port.

4 6" ports are equal to 112^2in which is equal to about 224^2in of a slot port.

this will allow you to give those drivers as much room as possible while still giving adequate port area because your gaining volume but minimizing port area, while not sacrificing performance.

a 35hz tuning will work fine with these subs. my 15" btl at 33hz gets lower and louder than my buddies 15" XXX 15" at 29hz. and its a widley known fact that the xxx is a low end monster.

[BKOLFO4 29]

Aero ports will definitily work great, but (3) 6" ports is $$$

How far is it to the back wall using those dimensions, 3-3.5"???? You may want subs and drivers facing up.

The dimensions you gave, with (3) 6" aeros, 15" long, subs inverted, top baffle 1.5" thick, would be around 11.25 ft^3 tuned to 33-35 Hz (not sure of the end correction factor with those 6" aero ports and I approximated the volume gained with the subs inverted).

Should work out really nice. . .

Brian

[George 0]

Aero ports will definitily work great, but (3) 6" ports is $$$

How far is it to the back wall using those dimensions, 3-3.5"???? You may want subs and drivers facing up.

The dimensions you gave, with (3) 6" aeros, 15" long, subs inverted, top baffle 1.5" thick, would be around 11.25 ft^3 tuned to 33-35 Hz (not sure of the end correction factor with those 6" aero ports and I approximated the volume gained with the subs inverted).

Should work out really nice. . .

Brian

yea, thats really the only reason i dont like aero ports. the price is bad. but i usually base my recommendations on what i see the person using.

i mean 2 18" btl's and 3kw a piece and the electrical to back it up to me, means you got a little bit of change, so aeros would be the least of your worries lol.

i prefer slots because they are cheap and im usually never constricted on space anyways

[valin 0]

Yes, I have 3-3.5" to the rear hatch. I don't see there being a problem with that. Steve Meade only had about 3" to the rear hatch in his Tahoe, with twice the drivers, and 16000 watts of power. I'm going to check in to Aeroports right now. Thanks guys.

[valin 0]

Ok. I've been looking into the 6" Aeroports, and found some calculators.

http://www.audiogearreviews.com/tech/tools...r-rectangle.asp

Using this calculator, and a box width of 48" as an average, 22.25" tall for the double baffle, width of 23",

leaving me at 12.01 cubic feet total before displacement. Each driver takes up .26 cubic feet, so I adjusted the box dimensions to accomodate for another .52 cubes, for a total of 12.53 before displacement.

With three 6" Aeroports, it is giving me a length of 11" for a tuning frequency of 33hz.

[BKOLFO4 29]

Did you use 12.53 as the volume? You have to subtract the volume displaced by the ports, which is almost 1 ft^3. when you subtract that volume, the ports get longer, more volume is then displaced. . . Also, I don't think you gain as much inverting as you lose with them installed non-inverted. Quick calculation - volume inside the cone is 1/3 * area of the base * height.

you also gave me a total height of 23" (12.5 + 10.5) above, which is 20.25" internal with a double top baffle.

But it looks like you are on the right track and should be able to figure it out from here. . .just wanted to point out a couple of things you should double check. Messing up the port tuning on the high side can lead to over excursion and damaged drivers. . .

Edited October 25, 2007 by BKOLFO4

[valin 0]

Using a double baffle on top would give me a total of 20.75" in height. The 18" subs displace 0.26 cubic feet per driver, right off of the Fi site, so by inverting them I would be saving 0.52 cubes. The calculation program takes the volume consumed by the ports into account, as well as volume taken up by drivers (although it uses 0.33 cubes per driver). It's kinda nice actually.

To achieve my acutal volume of my enclosure, which 12.01 cubes before displacement, I have to use 48 wide, 22.25 tall (to make up for the extra top baffle), and 23 wide. The program then wants to take up 0.66 cubes for the sub volume, so I have to add that back in. So, i ended up using 48 wide, 23.4 high, and 23 wide, just for the program to give me total volume in the enclouse after driver displacement at 12.01. Then, using three 6" aeroports at 11" long give me 84.82 sq. inches of port area, and a tuning freq. of 33Hz, and consuming 0.63 cubes of space, leaving me with a total of 11.38 cubes after all displacement. If I ran two 8" ports, they would be 14" long for 33Hz tuning, giving me 100.53 sq. inches of port area. The 8's would consume 0.92 cubes, leaving me with a total net of 11.09 cubes.

Some people are saying that with using aeroports, you still need the same port area as using slot ports.....not half like what George mentioned. I have been trying to find this elsewhere to verify, and I am having trouble understanding why this would be. If that was the case,

Where is a good place to purcahse the aero's?

[BKOLFO4 29]

aeros take less. . . Not sure on the 1/2, but less. I remember David at RE running (2) MT 15's with just (4) 4" aeros and doing 154's if Iremember correctly on the score.

Inverting the subs. . .I am sure it is close enough, but the sub inside the box displaces more air than you gain when you invert them. Inside the box, the motor structure, basket, etc. take up airspace. You do not gain that with them inverted. All you gain is the 14" hole in the 1.5" thick wood and the volume inside the cone. Like I said, I am sure it is close enough, but it is not automatically the amount that would normally be displaced.

Brian

[valin 0]

Where can I purchase the Aero ports?

[valin 0]

Thanks alot guys, I really do appreciate the help in this.

[George 0]

Using a double baffle on top would give me a total of 20.75" in height. The 18" subs displace 0.26 cubic feet per driver, right off of the Fi site, so by inverting them I would be saving 0.52 cubes. The calculation program takes the volume consumed by the ports into account, as well as volume taken up by drivers (although it uses 0.33 cubes per driver). It's kinda nice actually.

To achieve my acutal volume of my enclosure, which 12.01 cubes before displacement, I have to use 48 wide, 22.25 tall (to make up for the extra top baffle), and 23 wide. The program then wants to take up 0.66 cubes for the sub volume, so I have to add that back in. So, i ended up using 48 wide, 23.4 high, and 23 wide, just for the program to give me total volume in the enclouse after driver displacement at 12.01. Then, using three 6" aeroports at 11" long give me 84.82 sq. inches of port area, and a tuning freq. of 33Hz, and consuming 0.63 cubes of space, leaving me with a total of 11.38 cubes after all displacement. If I ran two 8" ports, they would be 14" long for 33Hz tuning, giving me 100.53 sq. inches of port area. The 8's would consume 0.92 cubes, leaving me with a total net of 11.09 cubes.

Some people are saying that with using aeroports, you still need the same port area as using slot ports.....not half like what George mentioned. I have been trying to find this elsewhere to verify, and I am having trouble understanding why this would be. If that was the case,

Where is a good place to purcahse the aero's?

a lot of people also talk out of their ass lol.

i trust Loyd Lowry (bigbassman) and djman37 (off ca.com) in their testing over most.

a 4 inch aero port has the transfer ability of a slot port of roughly 25 sq inches..

that's in personal testing done by me.... and that's why a single 4" aero was used.. and to go even further.. numerous woofers on hand.. reccomended a 4" port for their designs..

also.. having a large port area requires a long length.. and there can be losses in doing bent ports..

and to do 2 4" aero's, would have required a bent design... no thank you

Loyd L.

and this is a direct quote from djman37

what is NOT factored in is how much the flared ports slow down the air and to what area that translates into in the slot port world. I have a figure of 50% - 60% port speed reduction, so the aero's, to me, act like bigger ports.

I got away with 2 6" aeros for 2 DD9515s.

both are members i would trust over most.

Edited October 26, 2007 by George

[DevilDriver 28]

http://www.soundsolutionsaudio.com/forum/i...?showtopic=7546

Lower down the page, I give an example where vent velocity is decreased by approximately 56%. These things can be calculated pretty easily.