box for rsdc124

Juggernuts · Post by **Juggernuts** » Mon Sep 06, 2010 5:25 pm

I understand now....I'm just looking for a happy medium because I listen to everything, but i want to be able to play some rap for a lot of bump as well. Wondering how big of a port I should use...

Post by **Jacampb2** » Mon Sep 06, 2010 5:48 pm

12voltjunky wrote:basically you could keep the vent the same size and use 2 vents or you could make the vent twice as large (6" wide).

No, that is not true, as pointed out, that will change the tuning frequency. Using two vents 3"x9.3" with a enclosure w/ 2x's the volume will maintain the same tuning frequency, but using one 6"x9.3" vent will not.

12voltjunky wrote:ports essentially work based on their internal volume (like the box itself).

No, not true again. I'm not picking on you, this is a mistake a lot of people make, but the important thing is the ports cross sectional area (2d area of the port cross section) and the effective length (typically a center line measurement of the port. If you find the area of your two 3" diameter circles, you will find that it does not equal the area of one 6" diameter circle. That is why the length would have to change to maintain the same tuning frequency.

So, to switch from a round to slot port, you calculate the cross sectional area of the recommended port, and then make a slot with the same cross sectional area, as long as the area is the same, then the recommended length will be the same as well.

If you want me to explain more, I will. If you think I am wrong, well, do some research on how a bass reflex enclosure really works...

I agree with audiophyle as well, 46Hz is way to high to tune the box. IMS, I tuned my box for about 28Hz, and it is stupid loud and low. If I ever get time for it, I am going to put my 3 RSDc12's back in a sealed box.

Later,
Jason

audiophyle_247 · Post by **audiophyle_247** » Mon Sep 06, 2010 5:50 pm

You wont have any problems with two 12's, shits gonna be loud friend.
Dual RSDc 12's? Yeah these are not your average sub.

Build the largest sealed box you can live with & brace the hell out of it, you need it to be bomb proof. That will give you a good solid low end with plenty of output. If you need more than that you're crazy, and require a ported box. lol

Juggernuts · Post by **Juggernuts** » Mon Sep 06, 2010 8:40 pm

Ok, sealed is what i'm looking at going then. For SPL the manual says .72cu per sub and the woofer displacement is .13cu. So a total of 1.44cu, added in with the woofer displacement (.26cu) i'd need the box at 1.70cu total. Should I round off to 2.0cu and call it a day or leave it at 1.7cu? I'm just curious if the bigger the sealed box=lower notes.

Post by **stipud** » Mon Sep 06, 2010 8:49 pm

Bigger box = louder on lower notes indeed!

I would suggest at least 2 to 2.5cuft.

audiophyle_247 · Post by **audiophyle_247** » Mon Sep 06, 2010 9:53 pm

stipud wrote:Bigger box = louder on lower notes indeed!

I would suggest at least 2 to 2.5cuft.

^^ Exactly what he said!

12voltjunky · Post by **12voltjunky** » Tue Sep 07, 2010 12:53 pm

Without totally hikacking this thread can jcampz comment on tuning freq...?
I would like to know if the 28-30 Hz tuning mentioned above accounts for cabin gain?
I am also trying to learn more about bass reflex designs. I really want to know about mltl designs too!

Juggernuts · Post by **Juggernuts** » Wed Sep 08, 2010 9:46 am

Hey that's fine i dont mind if you ask a question

.

Speaking of question, this is my last one before I build my box. I want to have the most space possible so I was going to build a short rectangular box and put one sub on each end of it. Is that going to be a problem as far as sound quality or performance goes? I didn't know if i needed to have both subs on the same side of the box. If i stick them on the ends I can make the box considerably shorter and just have it be a little taller to still keep my 2.5 .cu. plus this way the box wont take up my whole back seat.

oldschoolfan · Post by **oldschoolfan** » Wed Sep 08, 2010 10:48 am

You don't want the subs right up against a surface. As in one inch away from the side of the car. The face of the subs should be at least half the diameter of the sub away from a flat or similar surface. This will prevent "loading" against the sub. Remember, the sub moves in and out while working. If it is too restricted on the outside of the enclosure you are actually working against the tuning of the enclosure you built.

Juggernuts · Post by **Juggernuts** » Wed Sep 08, 2010 11:53 am

I understand that, and the subs won't be up against anything, what I mean is having one sub on each end of the enclosure. One sub would be facing each door but it would have a good foot and a half space in-between the sub and door. I was just worried if having the subs facing like that would affect anything....the cones would be facing away from each other and the magnets would be facing each other, with about 12 inches between them.

Post by **ttocs** » Wed Sep 08, 2010 1:20 pm

I am about to build a box that sounds similar and have none of these fears.

Juggernuts · Post by **Juggernuts** » Thu Sep 09, 2010 6:12 am

Box is built, im carpeting today

Post by **kg1961** » Thu Sep 09, 2010 6:23 am

Juggernuts wrote:Box is built, im carpeting today

Pics
let me know how you like them
what amp are you using again?

Post by **Jacampb2** » Thu Sep 09, 2010 11:29 am

12voltjunky wrote:Without totally hikacking this thread can jcampz comment on tuning freq...?
I would like to know if the 28-30 Hz tuning mentioned above accounts for cabin gain?
I am also trying to learn more about bass reflex designs. I really want to know about mltl designs too!

The first little bit of this I already replied to 12voltjunky in response to the question he PM'ed, which was basically the same as the quote above...

Some people will try to predict it and tune for a perfectly flat response, but frankly, the math is beyond me. Cabin gain typically has a corner frequency of 70-90Hz, and spl increases by approximately 12db/oct below the corner frequency. The corner frequency is dictated mostly by the size of the vehicle with lower corner frequencies yielded by larger vehicles.

So, with a bass reflex enclosure you are going to be tuning below the corner frequency regardless, by knowing how the transfer function applies in your specific vehicle (its not always exactly 12db/oct because of damping material, vehicle sealing and other factors) you can predict a enclosure tuning frequency that will yield a specific in vehicle response, but personally I would tune the enclosure where I wanted, and if I was competing for sq, I would tune the system the conventional way with a rta and eq.

As for the reason behind tuning lower than what you normally find as the manufacturer's recommendation, well, it was touched on above. The short answer is that subwoofers loaded by a bass reflex enclosure playing at or above the enclosure tuning frequency behave as if they are in a sealed box with a passive radiator. When the subs play bellow the enclosure tuning frequency the vent unloads and the subs behave as if they are in free air. Bellow the tuning frequency the output will drop quite steeply, and you risk seriously damaging the subwoofer if it is driven hard in this condition. So, if you want to have good low end response, tune for the lowest frequency that you want to hit on a continual basis. Keep in mind that normally the manufacturer suggested SPL tuning frequency is the frequency there the subwoofers are going to produce the most SPL and the SQ tuning typically is tuned so that the enclosure has the flattest response. If you tune for a much lower frequency there is a good chance that your enclosure response will have some dips and valleys.

The longer explanation is basically about why/how a vent works. Most people think that a bass reflex enclosure is a purposefully leaky sealed enclosure. This is not the case. At or above the enclosure tuning frequency the air in the vent is trapped there. The friction of the air against the walls of the vent keep the air trapped in place. This causes the trapped air to act as a passive radiator reinforcing the subwoofer output. So basically, if you put a bigger hole in the enclosure, you need to increase the length of the vent to provide the same amount of friction for the air within, thus maintaining the same tuning frequency. Bellow the tuning frequency the air in the vent is not moving fast enough for the friction to keep in trapped and that is when we say the vent unloaded. If the friction cant keep the air trapped, then your box is simply a big leaky sealed enclosure.

Vent size is not hugely critical to a point. You can tune almost any area port for almost any frequency. There are limits, mostly not due to being able to calculate it, but due to being able to build it. You can easily end up with a vent that will not physically it in an enclosure. To a point, even this doesn't matter, as the port does not have to be fully enclosed in the enclosure, and it can make turns and such inside as long as you calculate it's length properly. The big thing that will bite you is on small ports, it is possible to end up with a vent air speed which is to high due to a small vent and then you will have lots of audible noise from the vent. Most of the software for designing bass reflex enclosures will calculate maximum port air speed and let you know if it is to high or not.

Lastly, vent size does not make a whole lot of difference in output. If you took an enclosure and tuned it for the same frequency with both a 6" and 3" diameter vent (remember, the lengths are drastically different) both enclosures will exhibit the same frequency response, the only difference is going to be the maximum airspeed in the vent. The 6" diameter vent will have a much lower air speed than the 3" vent. Neither one is likely going to be audible, but going down to like a 1.5" diameter vent tuned for the same frequency is likely going to produce audible port noise. A lot of people think that a larger vent will be louder, this is simply not the case. Remember above when we talked about the air trapped in the port acting like a passive radiator? Well, if you consider the vent area to be the surface area of a passive radiator, that radiator can do the same amount of work whether it be 3" or 6", it is simply the excursion that changes. Obviously there are limits to a true mechanical passive radiator, but we don't have the mechanical suspension and cone to deal with in our air trapped in the vent. Bottom line is as long as the air speed stays within reason calculate your vent size for what will fit in your design.

There really should be no trial and error necessary, unless it is to find the tuning frequency that you feel is the best. Remember, you are tuning the enclosure, not the subwoofer, an enclosure will have specific behavior regardless of what driver you put in it. You absolutely have to calculate based on internal enclosure volume and as mentioned before, the volume of the vent that is inside the enclosure, and the displacement of the driver(s) also has to be subtracted from the internal volume of the enclosure. Also, ports that use one or more walls of the enclosure as part of their structure will have a longer effective length than one that is free standing in the enclosure. I cannot remember the approximate additional length, but I think I recall it being 1/2 of the vent height being added to the vent length. Vent length is measured down the center-line of the vent through any bends, not along any one wall unless it is a straight vent.

I highly recommend downloading WinISD pro and modeling your enclosures in there. Last I knew it was free, the "pro" version is in "alpha" but it runs pretty well and has a lot more features than the normal version. WinISD will calculate your vent air speed which is a nice bonus as well. You can find instructions step by step on how to use it by just google searching. The software itself doesn't come with any "how to" information and there is not much outside of online tutorials to learn to use it. I typically calculate my vent's manually (I can dig up the formula if anyone wants it) and then I model the enclosure in WinISD to verify my math (definitely not a mathlete here...).

*edit for vent frequency/enclosure calculation* I put it in the equation solver of my HP48Gx so that I could easily solve for any variable. Here is the formula:
Fb = .159 * Sq.Rt.((( Av * ( 1.84 * 10^8 )) / ( Vb * ( Lv + ( .823 * Sq.Rt.( Av ))))).

Where:
Fb is the tuning Frequency in Hz
Av is the vent cross sectional area in square inches
Lv is the Vent length in inches
Vb is the enclosure volume in cubic inches

*/edit*

Good Luck,
Jason

12voltjunky · Post by **12voltjunky** » Thu Sep 09, 2010 3:19 pm

^thanks for the lesson. now i just need to read it a couple more times and determine what i do and don't understand.

thanks again!

Juggernuts · Post by **Juggernuts** » Thu Sep 09, 2010 4:01 pm

12voltjunky wrote:^thanks for the lesson. now i just need to read it a couple more times and determine what i do and don't understand.

thanks again!

Ha, I know how you feel, except I'm on a "slightly" newer level

I've been taking pics, I'm about to go outside and install my radio. The head unit I got is the Sony GT740UI which got awesome reviews and i'm pretty impressed so far with how it looks. Luckily my dash only requires two bolts being removed to get the whole dash off! Gotta love a Dodge.

My amp is the Planet Audio TQ1601...I was going to go with a Power Acoustik or SPL amp, but someone mentioned to look at the actual fuses instead of the claimed wattage, especially if the amp isn't CEA compliant. The SPL and Power Acoustik both had 60amps total, and the TQ1601 i'm getting has a whopping 140. Even when I went to Knukonceptz.com to order my wiring package they stated the best way to see an amps true output is to go by the fuses because it's something a manufacturer can't fake without putting their product in jeopardy...So I'm hoping this holds true and I get some decent performance from my amp

Juggernuts · Post by **Juggernuts** » Sat Sep 11, 2010 7:49 am

Hey guys, i'm having some problems....I have everything hooked up, but when I turn my truck on the amp turns on for about a second then goes off. Is this going into protection mode? I'm going to try grounding it better but i'm not sure if that's the problem....THe only way I can tell the amp even comes on is the whole top of it lights up like the fourth of july (it's supposed to, i looked it up lol) for a brief second then switches off. I gave up last night because I worked on this thing for 6 hours and I was dead tired afterwards...Please help me troubleshoot. Thanks

Post by **Jacampb2** » Sat Sep 11, 2010 9:45 am

First of all, the fuse thing is a good rough gauge for an amplifier of reasonable quality, I have not had any experience with planet audio, but I don't think I would use their fuse rating to rate one of their amps. If it is a class d amp and somewhat reasonably efficient, 140 amps is a lot of current draw, probably somewhere in the neighborhood of 2kW output. Maybe it is, maybe its not, but don't use the fuse thing as a hard rule, some companies will not hesitate to endanger both you and the product to make it look better.

Anyhow, amp powering up and right back down, my guess is that the in rush current is to high and three amp is shutting down because the ps did not come up fast enough. What did you end up using for power and ground wire? A poor ground cold definitely cause this, but so could a problem with the amps power supply... Do you have the subs connected already? A shorted or improperly wired driver could cause it to shut down as well. Did the instructions specify how the amp would signal a fault condition? Do you have a constant 12vdc on the remote lead? There is a slim chance that it could be a head unit issue w/ the remote turn on lead, I could test by jumping the amps + lead to the remote in, and see if it stays on.

Good luck,
Jason