Large or small box for straight SPL Box

[shizzzon 461]

Why is it that some companies suggest a larger box for Fart boxes then others recommend smaller boxes for Fart boxes?

What's the difference? Why would a large box work for one sub and not another and vice versa?

[KU40 173]

Perhaps it has to do with the parameters of the sub.

[///M5 2,833]

Drivers are all designed for different implementations. Optimizing for what the companies marketing departments feel will sell. On top of that of course some companies misrepresent the optimal enclosure for marketing purposes as well.

[Aaron Clinton 2,372]

Some companies will provide "high output" box suggestions, where others will provide peaky SPL competition box sizing. Also depends on the limits of the driver.

[shizzzon 461]

see, i can understand how the specs of a speaker will affect the box requirement for a great pure spl box... but some competitors swear that no matter what subs they use, small boxes and LOTS and LOTS of port area is the best way vs larger box with however much port area you wanna use.

That's why i am dumbfounded to try and understand this.

Yes there are companies who suggest the opposite of each other but there are competitors also who swear by the small box design.

[///M5 2,833]

And you believe what you were told by these competitors why?

[topgun 262]

Just because someone 'competes' doesn't mean they know a damn thing.

[///M5 2,833]

Or that they will even tell you truth. I am still curious why you believe these guys. From your other posts it seems to me like you are misled really often, perhaps we can use this example to find out why.

[Aaron Clinton 2,372]

Many competitors get off on playing coy and sometimes will miss lead people because they are afraid of competition. As if they know something so unreal, they are too cool to share it.

Where on the other hand, some guys are great and will help out and give ideas and suggestions.

[shizzzon 461]

ok, well u guys think it's a lie then i'll continue to go with bigger is better.

[3stagevtec 2]

i had a pair of Audiopipe TXX 15"s in separate 5.4cu.ft boxes tuned approx 46Hz, 111sq.in of port area.. my best score with that setup was 151.6dBs

i then made a direct swap over to a pair of DC Level 4s and my score dropped to below 150dB (149.x).. i then lengthened the port to lower the port tuning, the longer port reduced the net internal volume to 4.1cu.ft and the tuning freq dropped to approx 41Hz.. ended up making the exact same 151.6dB with that new setup..

those boxes were very tall though, so there were considered a wall by the IASCA rules.. judging from those results, i'd say that driver design plays a factor in box size..

after saying that, i've seen competitors obtain crazy scores from using the small box / huge port formula.. Jacob (Sundownz) has hit in the 154 (or was it 155) dB range with a single 15" nightshade in a pretty small box..

[Duran 387]

i had a pair of Audiopipe TXX 15"s in separate 5.4cu.ft boxes tuned approx 46Hz, 111sq.in of port area.. my best score with that setup was 151.6dBs

i then made a direct swap over to a pair of DC Level 4s and my score dropped to below 150dB (149.x).. i then lengthened the port to lower the port tuning, the longer port reduced the net internal volume to 4.1cu.ft and the tuning freq dropped to approx 41Hz.. ended up making the exact same 151.6dB with that new setup..

those boxes were very tall though, so there were considered a wall by the IASCA rules.. judging from those results, i'd say that driver design plays a factor in box size..

after saying that, i've seen competitors obtain crazy scores from using the small box / huge port formula.. Jacob (Sundownz) has hit in the 154 (or was it 155) dB range with a single 15" nightshade in a pretty small box..

The Nightshade suspension won't handle a large enclosure with alot of port.

[3stagevtec 2]

With my pair of Audiopipe 15"s, the 1st boxes i used was around 4cu.ft net tuned around 42Hz each. powered by a pair of Sundown 1500Ds, i made 149.0dB

I rebuilt those boxes to ~5.6cu.ft net tuned the same 42Hz and scored 150.5dBs with an estimated 1600 - 1700W going to each. The subs did not reach their mechanical excursion limit

my take on the above is i gained sensitivity by using the larger enclosures, hence the increased score..

Now if i was running both 1500Ds to just 1 15", chances are that 5+cu.ft would not have provided enough damping to the sub and it would have quickly reached its mechanical excursion limits. In this case, a smaller box (=stiffer air) will be needed to keep the sub under control..

but if only 1 1500D is used, the larger box should be superior..

so i figure power has something to do with it as well..

[Aaron Clinton 2,372]

ok, well u guys think it's a lie then i'll continue to go with bigger is better.

I never said that. It really has a great deal to do with the approach, equipment, vehicle, class, association etc.

Guys like Terry Brocks are using very small, super strong, massive aeroport, enclosures. But guys like Randy Kubeck are using many drivers, in huge enclosures. Both are using a tremendous amount of power.

[BKOLFO4 29]

Never built a fart box, but just thinking about box designs I do every day, you can really change the peak output you achieve by varying box size for a given port tuning, burp frequency, etc. If I do a quick comparision of the same sub in the same box volume with 2 different tuning frequencies, I get X output for one of them, and Y output for the other. If I make the box smaller for both of them (smaller but both still the same size), the peak output increases for the higher tuned box, but decreases for the lower tuned box. This is just random example, but it shows how box size and tuning work together if you want to achieve the highest possible burp score.

I really do not see how manufacturers can even recommend anything but a starting point. . .There really is not a good final recommendation unless someone has already tested the same vehicle, same amount of power, same subs, same enclosure, etc. for your best burp score.

Long story short - As it has been said many times - the only way to build a fart box is build, test, rebuild, test, . . . . keep going until you are happy with the results or you do not see anymore improvement.

[shizzzon 461]

ok, in your example, leaving port area the same but decreasing internal net volume will cause the port to peak at a later stage...

Maybe just a couple Hz but definitely later on.

I need to fill some volume in my box just to see if something remarkable happens, hehe.

[BKOLFO4 29]

In my example, I made the box volume smaller and changed the length of my port so that the port tuning frequency stayed the same. . .

The only parameter I varied was internal box volume. . .

Making the box small and raising you tuning frequency at the same time may or may not help. Knowing the peak your need for you vehicle and the ACTUAL MEASURED tuning frequency of the port is very helpful. If you get the port tuning above the peak you are looking for, it will most likely be a bad thing, unless the box size is somehow off. . .I have seen it happen in one install. Port tuned to 58 Hz, output peaked at 54 Hz. If I was guessing, I would think a different size box and the correct tuning for the lower peak would have been even louder, but that is just my guess.

That is why I like building loud street beaters. . .to maximize a fart box that is competitive now days is just too much time and work for me. I barely have enough time to build what I want to build. I like to design, build, take simple measurements, make adjustments as needed and go. . .

Brian

[shizzzon 461]

ok, i understand you now, so what's a good piece i can use to displace volume in the wall for testing?

I know it can't be anything soft.. i was thinkin of some small empty cardboard boxes but dont know it's effect.

[///M5 2,833]

Sandbags, easy to make them any volume you want.

[bland 0]

Manufacturer recommended spl boxes might be large because they still want the box to be safe for the guy who build it to get loud at a comp then assumes it would be safe to pound on it all day since it was so loud. They're not going to recommend a box that will blow the sub playing it daily.

From what I've been learning in spl, smaller boxes generally work well, but the smaller you go the more power you need to get the sub moving and pressurize everything. There's always a trade off. Right now I have a 2.4 cube box for a 15" on 4400 rms watts. I want to try a little bigger to leave some more room for the port to breath.

Best way to tune is throw out all the calculation programs. Build a medium sized box with some external aero ports, and just start the longest you have and keep working down till you find the sweet spot. I think I'm tuned about 5hz above my peak on my current box. Never actually calculated it.