Enclosure Myths

[brakefluid]

I making a few hypothesis statements based on my very small level of trials runs as well as readings. I stand to be corrected and i will edit where i am wrong for the benefit of learning. I may even show my bass "stealth" build.

1. A sub cannot blow because it is in a slightly smaller ported box. You may overpower a sub in a small ported enclosure in an effort to get more bass that would cause failure. If the sub was completely out of a box or a sealed one then there may not be proper cooling of the coil.
The main point being that the sub cannot blow under the same conditions but in a smaller enclosure. It just wouldnt sound as good.

2. In a fibreglass enclosure rigidity is more important than thickness.

3. There is not much difference in acoustics in mdf and ply. Mdf is however more dense but more flexible while ply is less dense but more rigid. Mdf is cheaper and more versatile to work with.

4. A lower wattage sub of same volumetric size will not play louder than a higher wattage of one in the same enclosure.

5. A larger than spec ENCLOSURE does not make the sub sound louder. The larger PORTS in a spec enclosure does.
Eg. A sub 1cube spec enclosure was placed in a 2 cube enclosure will sound the same. However if the sub was placed in a 1 cube enclosure with an additional 1 cube of port (tuned properly of course) it will make the world of difference.

6. Polyfill does not make a difference in how loud a sub plays.

[ruffneck_12]

1. Yep, same enclosure and power wouldn't blow a sub. However too high of a tuning frequency without a subsonic filter could do some mechanical damage.

2. In any enclosure rigidity is better than thiccccness. I rather 0.75" mdf over 5 inches of wet toilet paper.

3. correk for the most part, MDF dust harmful af though

4. yeah it would, Generally doubling power gives +3db. Frequency response is a different thing. It may be louder or softer at a specific freq

5. Nah, play around with WinISD, you can control the volume of the box with the mouse and see the graph in real time. As the volume increases the graph peaks around the tuning frequency.

6. Correk for the most part. It mightn't be a perceived difference in loudness, but it does absorb energy and would be detectable with instruments or in the simulation (bass box pro for eg).

[- Rovin's car audio -]

few days ago a customer come with a locally made 8" T-line he bought from some guy selling it online , it had a long dacron sheet running INside d port , apparently was added in b4 d enclosure was assembled

i didnt get to hear it as d guy said it didnt sound good as another regular slot port he also bought cheap online & had no sub in it as he was going to resell it .... what yall think of that 1

[nick639v2]

^ man prob say it does make the bass sound smoother cuz the air getting cushioned .

Seems like everyone and they grandfather with this t-line box now too

[Brian Steele]

few days ago a customer come with a locally made 8" T-line he bought from some guy selling it online , it had a long dacron sheet running INside d port , apparently was added in b4 d enclosure was assembled

i didnt get to hear it as d guy said it didnt sound good as another regular slot port he also bought cheap online & had no sub in it as he was going to resell it .... what yall think of that 1

Two things:

1. Almost all the car audio "T-lines" that I've seen online have been designed using classical method for designing a straight TL, which are both flawed and obsolete. Any time you instructions starting with "set the cross section of the line to be the same as the driver", that's the classical (and flawed) approach.

2. The "classical" approach did call for damping the line with some sort of fill (probably to damp out the nasty resonances caused by putting a driver in a box that it's totally unsuited for).

[kavaninho]

few days ago a customer come with a locally made 8" T-line he bought from some guy selling it online , it had a long dacron sheet running INside d port , apparently was added in b4 d enclosure was assembled

i didnt get to hear it as d guy said it didnt sound good as another regular slot port he also bought cheap online & had no sub in it as he was going to resell it .... what yall think of that 1

Two things:

1. Almost all the car audio "T-lines" that I've seen online have been designed using classical method for designing a straight TL, which are both flawed and obsolete. Any time you instructions starting with "set the cross section of the line to be the same as the driver", that's the classical (and flawed) approach.

2. The "classical" approach did call for damping the line with some sort of fill (probably to damp out the nasty resonances caused by putting a driver in a box that it's totally unsuited for).

Yup Loudspeaker Cookbook mentioned those two points you brought up!

That straight cross sectioned line was just the basis to the start of horns which employ the 1/4 wave theory and adjust the line so as to have an unbiased output.

NB those ported boxes with flared ports don't qualify as horns. I'm seeing alot being passed off as back loaded horns.

[ruffneck_12]

Not much people can actually design a good ported box, much less for a T-line

"yeah dawg the whole box is the port just make it to fit meh trunk"

[Brian Steele]

NB those ported boxes with flared ports don't qualify as horns. I'm seeing alot being passed off as back loaded horns.

I've heard them referred to as "Big Vent Reflexes", or BVRs. Like end-loaded TLs, they usually feature a nice big notch in the midbass frequencies. Not really a design I'd use in a car audio environment.

[nick639v2]

NB those ported boxes with flared ports don't qualify as horns. I'm seeing alot being passed off as back loaded horns.

I've heard them referred to as "Big Vent Reflexes", or BVRs. Like end-loaded TLs, they usually feature a nice big notch in the midbass frequencies. Not really a design I'd use in a car audio environment.

You still have the build post for the gallery setup u own? The tuscon na.. looking to try my hand on the sub

[Brian Steele]

You still have the build post for the gallery setup u own? The tuscon na.. looking to try my hand on the sub

That was just a concept build, using a cheap 12" PA driver, so peak output is limited. But it does sound good up to that limit

[Zetski]

Correct me if I'm wrong...

Myth: all subs sound good in a t line enclosure..

I heard an IA 15 in a well built t line enclosure but it still did not roll off as smoothly as the HCCA 15 in a regular slot port. The IA was loud but the HCCA still had a more robust deep bass.

[ruffneck_12]

All subs can sound good in a t-line to a point.

But the box has to be tailor made for that specific sub. And the size requirements might be ridiculous for some subs so a ported box might sound better than a T-line of the same size

also well built is different from well designed eh. Million screws and bracing doesn't help a poorly designed box sound better.

[Rovin]

its funny to judge a sub based off other ppls work

i have owned\used IA subs & imo if u tune them high u wasting a good sub , like most american brands they were built for their market : to hammer d lows with alot of smooth overall output , not what locals do to them ex tune it 45hz for loudbass

my daily use sub is 12 IA Li tuned to 23hz [tuned to flat response - for IN car bass according to MY personal taste] , everybody face go like when they ask whats it tuned to , but when they hear it on those extremely low bass songs & bass boosted songs they understand & surprised at how nice it sounds , even on high bass & normal pop songs too ....

[Brian Steele]

i have owned\used IA subs & imo if u tune them high u wasting a good sub , like most american brands they were built for their market : to hammer d lows with alot of smooth overall output , not what locals do to them ex tune it 45hz for loudbass

I usually advise that, if you're going to build a vented sub, tune it to the lowest frequency you want to produce. If you don't know the answer to that, then choose 32 Hz . Cabin gain makes up for a lot of issues in car audio....

Having said that, for a lark I recently built an offset TL that was tuned to 48 Hz, using the same cheap PA 12" driver that I used for my POC TH design. It actually didn't sound too bad with normal music (not that re-bassed stuff which stretches the term "music" just a little), and properly filtered (i.e. to make sure nothing below Fb got through to it), it actually didn't sound to bad.

I've attached an FR test I recently did with my car audio subs (2 12" Alpine Type Rs in a sealed cabinet, wired for a 2 ohm load), my POC3 TH loaded with an Eminence Kappalite 12" 4 ohm driver, and POC6, the 48 Hz offset TL described above. Both the POC3 and POC6 TL were MORE sensitive than the Alpine Type Rs above 50 Hz, sometimes up to 6dB more up to 100 Hz. Below 50 Hz the POC6 TL dropped off a bit faster (obviously because of the 48 Hz tuning), but the POC3 TH kept up with the Alpines all the way down to 30 Hz.

For raw SPL the Alpines will likely win (duh - two 12" drivers with 20mm Xmax, vs. one 12" driver with 9mm Xmax (the Eminence) and one 12" driver with 5mm Xmax (used in POC6), but we're talking about drivers that at least are double the total cost that are pulling up to 4 times the power at the same input voltage. Damn.

BTW, the FR curves also show that going with a 30 Hz vented sub for my car might be a better fit for it, but that's a whole other discussion. Plus I don't mind trimming the output at 50 Hz a bit with EQ so I can enjoy flat response down to single-digit frequencies

[brakefluid]

There is no acoustic advantage between slotted and pvc ports absolutely none.

There are however advantages and disadvantages as far as the actual construction of the enclosure goes. Basically slotted ports are easier to fold in the enclosure. Pvc ports are more versatile to work with in irregular shaped enclosures.

[brakefluid]

An enclosure does not give a sub more or less wattage. It can just sound louder/quieter and various frequencies.

[ruffneck_12]

An enclosure does not give a sub more or less wattage. It can just sound louder/quieter and various frequencies.

It can change mechanical power handling though.

A sub in a smaller sealed box can handle more power because the cone moves less. So you can really dump more power than you would in a large high tuned ported box which bottoms out easier.
(guess which one sounds louder though, hint : not the box with loads of power dumped into it)

Of course more cone movement is better for cooling, but heat damage is relatively slower than the coil former just slapping the back of the magnet.

but yeah you right otherwise

[- Rovin's car audio -]

There is no acoustic advantage between slotted and pvc ports absolutely none.

There are however advantages and disadvantages as far as the actual construction of the enclosure goes. Basically slotted ports are easier to fold in the enclosure. Pvc ports are more versatile to work with in irregular shaped enclosures.

provided that either has same amt of port area ...

[ruffneck_12]

A round port better IMO

Acoustics and sharp edges is like oil and water. (unless you're building sound traps for an anechoic chamber)