what would be louder

[djjdnap 78]

So Im tryin to come up with a design for my 18's and im stuck..

I can either have 122.5 inches of port at 5.5 cubes at 34hz

or

70inches of port at 7.4 cubes at 28hz

im leaning towards the 1st one

or i can have even more space and just use aero ports

thoughts?

[dbjunior 0]

depending on sub id try something in between. what sub is it

[djjdnap 78]

MT's

edit.. sorta found my answer

THE RIGHT PORT AREA, THE DD PORT

(back to top)

Most modeling programs that simulate box responses were written for home audio use. They are not suited for high output systems. The port area defaults are inadequate. The port area must be commensurate with cone area. If the port velocity gets too high, the port no longer functions as a port, you end up with a leaky sealed box, double bad.

Lets say we have a 12 inch speaker in a box, roughly 100 sqin of surface area. Many programs and manufacturer sites will suggest a 4" diameter port for a 12" vented box. A 4" diameter port has about 12 sqin of area. This is about an 8-1 ratio of cone area to port area. If the 12 inch cone moves 0.25", the port must move 2.0". It can handle this, but when the cone is moving 1.0", the port must move 8 inches! Now you've got a leaky sealed box.

You need more port area for a clean sounding, high output system. The DD port formula is this: 16 sqin of port area per cubic foot of box volume. The port should be 16 inches long. Remember, the port is tuned to the box volume, not the sub(s).

This formula was derived from 1000s of hours of in-car testing and 1000s of installs. It works. It takes into account the need for increasing port area for increasing cone area. When combined with our DD subwoofer box requirements, you'll end up with the perfect match.

and neither one of them work for that formula

[helotaxi 46]

The "DD answer" is a generalization as well. The sub, power, box volume and tuning all dictate the required port area.

[djjdnap 78]

well i know a smaller box can take more power...

but i have heard that a smaller box can be louder than a bigger box sometimes, so im thinking about giving that a try.

after some more calcs i found i can get a 8cube box wt abotu 120sq inches of port...i think thats what ima go with

[KU40 173]

I'm not sure I follow the comparison. Those are two very different boxes and would yield very different results. I would understand more if the tunings were similar.

Is that 8 cubes total or per sub? What are you after with this setup (lows, loud, efficient, etc)?

[slim2fattycake 85]

have you tried using WinISD?

[djjdnap 78]

its 8cubes total minus displacement.

And i know they are different that was the question of the thread which would be louder, which is what im going for.

It was more of a question as should i sacrifice space for port area or port area for space...and which one would be louder.

So as taxi said somewhere in between and the 8 cubes and 120 seems to fit the equation as 8*16=128, and the multiplier range is from 12-16 so its right in that range 0f 96-128in of port area

checkin out winisd now

[djjdnap 78]

lol, the MT still doesn't have any known parameters..dammit

[95Honda 486]

I don't care what anyone says, a smaller box will never be louder than a larger box unless you are talking a much higher frequency (seriously higher), it's impossible. I know a bunch of people may argue this, but it is plain hoffman's iron law.

Many times people make the mistake of saying the smaller box was louder simply because they changed something else irrelevant (like the amplifier being more happy with a new impedance curve) or they have just moved the alignment peak closer to the vehicle's resonance. Additionally, if you have a smaller box and tune it drastically higher, than it will peak higher than the larger box tuned lower. BUT if you tune the large box as high as the small box, it's peak will always be higher. Period.

Model any sub, make the box bigger and watch the peak...

The whole port area vs box size is completely faulty logic. Port area is soley dependant on driver displacement, tuning frequency and power used... In the big scheme of things, box size plays a very minute role in this... The only reason many companies do (publish) this is because they know people will put their BIG subs in BIG boxes and will need BIG ports to keep compression to a minimum.

As far as which one will be louder? Model them and look at the peak in Fr, more than likely, which ever one has the highest peak will be loudest, assuming the peak is around the vehicle resonance...

Edited October 8, 2008 by 95Honda

[KU40 173]

5.5 cubes for 2 18s is way too little space. Even 8 cubes is too little IMO. You need a bigger box overall.

[lee 2]

Well, even though staying within known specs is safe, if you're willing to take some risks and know what you're doing, can pay off somewhere. Look at Steve meade, his 18s are in 5 cubes each and do extremely well. yes, he does have about 5k to each, alot of why the combination works in small enclosures. also seen a single 18 in over 11 cubes doing well with different intentions.

Both above and below usual requirements for most 18'' subs. good results can be had if done with proper design constraints.

[mlstrass 1]

I don't care what anyone says, a smaller box will never be louder than a larger box unless you are talking a much higher frequency (seriously higher), it's impossible. I know a bunch of people may argue this, but it is plain hoffman's iron law.

As far as which one will be louder? Model them and look at the peak in Fr, more than likely, which ever one has the highest peak will be loudest, assuming the peak is around the vehicle resonance...

apparently hoffman doesn't show up at SPL comps a smaller enclosure will increase power handling which can increase SPL, especially when burping with a ton of power. A bigger enclosure will be more efficient, can't argue that, but at some point it will become a hindrance as too much power will cause the sub to bottom out. a smaller enclosure is the reason meade can push 5k to each of his subs as the box helps to control cone movement.

Either box is WAY on the small side for the MT's. I've done a single 18 in 8.5cubes and it slammed off 2k of power. I recently did 2 15" MT's in 9cubes and it hits very hard also. These are daily boxes that get loud and hit low.

I'm currently running 4 15" HDC's in 12cubes (threw in a wall in 4 nights for a show), so way on the small side also. It doesn't hit the lows very well, but does move a ton of air. I only have 1.5k of power per sub and they'd easily take 3k+ in this size enclosure.

Smallest I've done 2 18's in is 10.25cubes and it does very well with 2k per sub. All boxes mentioned are 16^2 of port area per cube.

You could always try it and see, but I think you're going to choke those subs to death and be disappointed.

[djjdnap 78]

i think they'll work wt 4cubes...

I had 2 18in Sx's in a sealed box, it was about 8cubes total as well wt half the power i have now.

And it was pretty loud..

now i have the same cubes and can still port them, and 2x the power, i think ima be happy...

[KU40 173]

i think they'll work wt 4cubes...

I had 2 18in Sx's in a sealed box, it was about 8cubes total as well wt half the power i have now.

And it was pretty loud..

now i have the same cubes and can still port them, and 2x the power, i think ima be happy...

sealed and ported are two different beasts. Box requirements differ.

[manbeer 0]

if you only have 8 cubes i would keep it sealed.

[djjdnap 78]

well ima go wt some aero ports instead of slot port.

that gives me a lil less than 10.5cubes after displacement, then 4 6in aero's, give me 144in of port

i figured subs faced back and ports up

[SpeakerBoy 64]

What car?