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Jroo
12-18-2011, 10:11 AM
Finally received my 18w6 from credence. After talking with a few people, sealed seems like the way to go. It also doesnt seem like going bigger than the 1.7 to 2 cube range or ported gets you any benefits. I was kicking around the idea of a 1 to 1 ratio 4th order. Im thinking 1.9 sealed and 1.9 ported with a tune around 45 and 50 square inches of port? Looking for smooth response with some very good low end. Do you think that would be a good start?

hispls
12-18-2011, 10:31 AM
I knew a guy who ran these bandpassed back when they were current. Half the bed of his pickup ported into the cab, IIRC sounded really loud but didn't do much 50hz and up, no idea specs of the box, but I would advise not to tune too low unless you have some brutal midbass to handle 55hz duty..

RAM_Designs
12-18-2011, 02:37 PM
Do a box with an interchangeable port so that you can alter the port size and tuning. Also, specs show that they'd want something around 3.5-4ft^3 sealed. Vas is super high since it's an old 18" sub, so they're going to need some room to get low in a sealed box.

duanebro
12-18-2011, 04:03 PM
Looks ok, But you should tune it higher - 55-58hz. Shrinking the ported side to 1.5cf will lower spl a bit, but smooth the rolloff down to 30hz. If you aren't concerned about that (below 40) I'd leave the sizes alone. You should get a extra 4db or so out of your BP vs sealed 4 cf. And less excursion.

wenn_du_weinst
12-18-2011, 04:09 PM
these subs like huge boxes. sealed it needs like 5-10ft
bandpass would probably be much smaller. I wouldn't do a 1:1 ratio I'd go for a traditional 2:1

pro-rabbit
12-18-2011, 04:34 PM
these subs like huge boxes. sealed it needs like 5-10ft
bandpass would probably be much smaller. I wouldn't do a 1:1 ratio I'd go for a traditional 2:1

I suppose we are back to disagreeing on everything again. :crap:

wenn_du_weinst
12-18-2011, 04:40 PM
it's a slightly revamped HT sub. It needs to over come the weakness in the motor.

pro-rabbit
12-18-2011, 04:43 PM
it's a slightly revamped HT sub. It needs to over come the weakness in the motor.

So you are not taken into consideration that the sub is built/designed to work as a whole. The soft parts and the motor work amazingly well together. Trying to make this into something it is not will only end with a damaged driver from a wide range of causes.

wenn_du_weinst
12-18-2011, 04:44 PM
So you are not taken into consideration that the sub is built/designed to work as a whole. The soft parts and the motor work amazingly well together. Trying to make this into something it is not will only end with a damaged driver from a wide range of causes.
How many have you owned? Of course they work well together, they still like big boxes and ran at rms power.

pro-rabbit
12-18-2011, 04:48 PM
How many have you owned? Of course they work well together, they still like big boxes and ran at rms power.

More then you I'm sure. I have also installed tons of them(my first ever audio job was for a JL dealer). I have found the exact opposite to be true actually. We never see eye to eye on building anything or enclosure designs. I'm ok with that though. Always good to have your own thoughts and not just go with what others suggest or say.

Micksh
12-18-2011, 04:48 PM
We built a bandpass for one as a test box...sounded good, but I agree, not much upper bass. Definitely could be a low-end monster, which is what we are going for in the build we will be doing. The new one we will be trying is a 1-1.6 s-p ratio, efficiency looks good, just need to watch the excursion at low frequencies. We shall see...

duanebro
12-18-2011, 06:02 PM
I like this discussion about bp boxes. I'd love to see what worked the best for you. I tried to model this with a 12 db transfer function starting at 80 Hz. This changed my design a lot. I changed the ported side to 2.4cf tuned to 66 Hz. The problem is that I don't know what the cabin gain is in the op's car. So this could sound like crap! Is there any way to figure this out? Or a good guess at least?

galacticmonkey
12-19-2011, 12:03 AM
You would get a pretty good range if you threw it in roughly 3-3.5 sealed and about 4.5-5 ported. About 80in^ of port tuned in the mid 40s would give a solid response from the upper 20s to the 70hz rang, I'd imagine.

Jroo
12-19-2011, 09:22 AM
I think Im going to stick with the sealed JL recommendations for now. I based the sealed side of the bandpass of the 1.7 to 1.9 sealed JL likes. To be honest, I dont want to end up with a 6 or 7 cubic foot box. Just correct me if Im wrong. Larger the sealed side, the lower the lower it usually plays? The larger the ported side, usually an increase in effeciency? I also know your port tuning plays into this, but a great deal of how low and how loud you play is decided by the size of your sealed and ported in a bandpass?

duanebro
12-19-2011, 10:08 AM
A 4th order band pass box is like a high tuned vented box, plus a sealed box below tuning. This give more effeciency as the ported side gets bigger. But this is only for the higher end of the fr. Below a point in the boxes response the sealed side takes over. The ported side has unloaded at this point and the box acts like a sealed design.

Moble Enclosurs
12-19-2011, 04:46 PM
I like this discussion about bp boxes. I'd love to see what worked the best for you. I tried to model this with a 12 db transfer function starting at 80 Hz. This changed my design a lot. I changed the ported side to 2.4cf tuned to 66 Hz. The problem is that I don't know what the cabin gain is in the op's car. So this could sound like crap! Is there any way to figure this out? Or a good guess at least?

Yes and No lol. There is a way to figure this, but guessing.........no. Luckily, due to the size of the average vehicle, compression is much higher where resonance and below, as expected, it a smoother gain than in larger areas, BUT still exact dB levels are difficult to obtain to get an accurate response....though pass-band curves are constant. So, saying a 12dB gain per octave below 80Hz will be correct in a few frequencies, but the complete gain may be off and the dips and curve may be much different than a steady gain. usually, the peak resonance(which does exist, though some engineers may disagree) will occur not at wavelength, but near half and quarter wave within a vehicle. This is why the quarter wave theory CAN be correctly utilized. (notice the "can be"). Since quarter wave resonances are design dependent as well, they may cause either cancellation, or out of phase banding resulting in much lower output than calculated. These are the things to be careful of when dealing with transfer functions. I mention this, because it seems you also have a passion for designing and hope you do well. So, for the OP, with 6th order designs, cabin gain can easily make or break the output. Just make sure that this can be accounted for in the process. Some get lucky when they have a LOT of room to deal with, and to tell you the truth, the now-common tapped design can be utilized much like a quasi-6th, which can be easier to design than a standard 6th with equal efficiency and pass-band operation. SO, those who do not know the deal around a conventional 6th, may want to explore the quasi design as well-and if you o not know how to figure for its response.....I recommend doing some trial and error. You may be surprised at how much easier it is for those who do not have all the information available to obtain a good response from a quasi design. Such design can be equal to the output of a tapped horn, with a compression chamber opened to the Horn path...this would create a quasi-like output.

Jroo
01-09-2012, 01:45 PM
I was messing around using the bandpass calculator on carstereo.com. Anybody use this before? I know this is trial and error, but trying to figure out how accurate it is and how much tweaking I would have to do?

Car Audio - Bandpass Subwoofer Box Design (Fourth-Order) (http://www.carstereo.com/help/Articles.cfm?id=27)
This is what I entered for the 18w6

Enter Qts= 0.384
Enter Vas (ft3 )= 9.00
Enter Fs= 20
Choose an S Factor= 0.6
Enter Desired F3(L)= 26

Gave me this below

Vf =(ft3 )= 1.911
Vr = (ft3 ) Qbp = 2.292
Fb = Hertz Passband = 26-75.79 hz
Fb= 44.39
Gain = (dB SPL@1W/1M) 0.9

Moble Enclosurs
01-09-2012, 04:21 PM
I can tell you with the specs that I have for that driver, using my own calculations, that a tuning of 37Hz is recommended for the 4th order design. And it looks like in order to reduce cancellation at the port opening at higher frequencies, that a larger sealed area is needed instead of a larger ported area. And the length of the port needs to be pretty long to reduce phase cancellation to a listening point UNLESS, you face the box towards the back of the vehicle, then you can use a more normal design type of a 4th with the ported part larger than the sealed part, where the phase will account for the placement of the driver.
It doesn't look like this driver will work too efficiently without the need to adjust the chambers like I mentioned. Otherwise, you will be getting a normal response output that will not sound much different than any other 4th order that is not concentrated on spl output.

With a near 130-180 phase response, I am getting volumes of sealed: 3.75 cubic ft, and ported:4.35 cubic ft. and a port area of 64 cubic inches with a length of 18.12inches. Most would disagree with the smaller port area, and I agree to this with the exception that it is needed to control cancellation. BUT, even a larger port area and a longer length will give similar results in this case. Just more commonly used.

Now, for accounting for phase control, I am getting a 5.3 cubic ft sealed and 1.77 cubic ft ported with a longer port with the same cross-sectional area. The 64 cubic inches of port is ok due to the power handling of this driver, and its xmax being commonly small compared to more modern 18" drivers. So, highest compression, without distortion is possible with this driver using only a, 18x3.75" opening, or even a 10" round port. And in the case of the 18x3.75, that is good because the ratio is less than 5:1. And any ratio below 8:1 for my figures are acceptable.

Micksh
04-23-2012, 09:38 PM
It took awhile, but finally posted a teaser pic of the 4th order bandpass in the general discussion forum....