an audio confusion conclusion *Lots of PICS* :D

[SHOZ123]

How about some foam rope "caulk" from a building supply store. It comes in various thicknesses and is cheap. You can even secure it with hot melt......

 

[NoSlo]

I have to disagree with your box design though, just because you can plug the numbers into a box design program doesn't mean it is going to make a great sounding sub. First of all, I don't see cabin gain figured into either of those box designs, and secondly, just because a ported is louder, does not mean it is going to sound better. It sounds like you have some experience with car audio, so I don't want this to seem like I am talking down to you, because that is not what I am doing. But the sealed box will have a much more natural and controlled sound in comparison to that ported, as is evident by the big peak on the ported enclosures graph, versus the nice smooth **** for the sealed.

Also, an f3 of 33 hz is way lower than you need for an 8 inch sub in a car environment. 33hz might be a good tunign frequenciy for a larger sub, perhaps a 12 or a 15, but it is going to be pushing the limits of a small sub. Especially since the Fs of the polk unit is 43 hz, tuning below the free air resonance of the sub is a big no-no.

Notice that Polk tuned the box to 60hz. This is why you are showing the sub reaching maximum excursion at 40w of power. If you increase the tuning freq, you will get a smaller box with better power handling, and the cabin gain will take care of boosting the lower freqs. As for using two different sized ports, that's just bad practice, how did you come to those two sizes? I don't see that information in the box program on that either. The following is the information on the polk site, notice the graphs for both in car response, and anechoically. Notice that in car in a sealed enclosure, the subs will play an average of about 83-84 db with 1 volt of power below 100 hz. Note that anichoically, it will drop off very quickly. These two response graphs show the effects of a speaker being in a car audio environment, aka very reflectivce, and an environment lacking any reflections. .35 cubic feet sealed will provide more than adequate bass. Yes, a ported will be louder, but once again, look at the product specifications on Polk's site, .6 cubic feet tuned to 43 hz. A lot different than what you are showing.

Wow, what a rebuff!

Anyway, there are a couple of things I will address:

The subwoofer port is tuned to 40Hz, this is the Fb parameter. The F3 point of 33Hz is where the frequency response is down 3dB. If the port was tuned to a higher frequency, the +3dB peak you see in frequency response would be even more pronounced, and low frequency power handling would be comprimized. If it was tuned to a lower frequency, the peak would be smoothed out but the speaker would not be as efficient at the 40-60Hz range where we need bass. Nothing wrong with a 8" subwoofer design that has +- 3dB frequency response down to 33Hz.

The more bumpy graph is power handling. This shows a crazy peak at 40Hz, 126dB, but it only matters that the curve is above the 116dB line, because 116dB is the the max dB power that can be made by the 230W amplifier.
The increased power handling in the ported box is because around the resonant frequency, the cone of the speaker actually moves far less. The speaker excites the air spring of the port and doesn't need to move as much. Think of holding a Slinky(tm) from the top. At the right frequency you can move your hand up and down just a little bit and the slinky will spring up and down far more than you are moving your hand. That is why the sealed box can't handle as much power, the only way it can make a certain dB level is purely by moving the cone/voice coil, and at lower frequencies the 8" woofer just can't move enough air by itself to make much sound. 40 watts of power is all it needs and can handle to get to the maximum excursion of the speaker at 40Hz (a subwoofer 'benchmark' frequency). Regardless of what type of box it is in it will have the same excursion limit at the same frequency and that is it's maximum power level that can be radiated.

A sealed box can sound better, if only because the design doesn't have to be as precise and you don't have to design around port noise produced by having too small of a port. The port recommendation I listed are to use EITHER 3" OR 4" port, not both ports at the same time. The longer 4" port would be better because the air velocities will be lower and it will have less port noise, but it will be harder to fit in the box because of its longer length. They will both tune the box to the same frequency. Always comprimises.

I've found that the manufacturers (JL Audio, MTX, and it looks like Polk) spec recommended boxes on the small side - the small box is a selling point. However, you will see that on the top right, the software is showing an optimum box size of 1.493 cu ft for a flat response down to 24Hz for this speaker. I tuned the box to a higher frequency however, because with that 'optimal' box, the excursion power handling dips below the 116dB/230W around 35-50Hz.

I'm only showing the box curve because the box is the only variable I'm messing with (not changing cars or subwoofers). The modeling software shows the in-car curve to have a peak at 25Hz or so.

 

[93medusa]

Alright, your post is making more sense to me now, especially the 2 port thing, I was like wtf is this guy talking about?

What software are you using btw?

Anyway, It's not worth arguing back and forth about this. I'm pretty sure that he can get pretty good results with the recomended enclosure by polk, and still maintain his power handling (i know in kicker literature they specify the power handling for a given application ie ported, freeair, sealed).

Sealing the cone of the subwoofer off from the rest of the trunk is probably the key to fixing the problems he's having in the rear deck? You do agree with that right? I think you said it first anyways.

Live and learn...

Dave

 

[SteedaSVT]

yes you guys are way to smart for me... Im dumbfounded

 

[shoteen95]

awe, i just remembered i promissed lots of pics in this thread..well..when i'm back home this weekend i'll take some for you guys..cause i personally love looking at sho related pics..maybe i'll try and fab up some kind of seal for the enclosure while i'm at it..

 

[93medusa]

f U Steeda! You can chime in any time! you probably know 10 times more than either of us.

 

[SteedaSVT]

you guys are doing perfectly fine... if i see something or think of something I chime in.

 

[93medusa]

haha douchenozzle!

 

[Redline]

Finally! someone has found it!

I try to tell people its there (I am using it) and it seems like no one believes me...

Good luck on the setup.

Forgive my ignorance, but what is this second plug?

 

[shoteen95]

haha douchenozzle!

well thats a new one

Redline,
the speakers in our cars are dual wired, there's a second plug tucked up in the dash that bypasses the amps in the trunk and goes straight to the speakers..its a free alternative to buying the metra bypass harness that bypasses the amps. take a peak at a read deck speaker, you should notice 2 pair of wires (4 wires) running into the connector for the speaker

 

[93medusa]

well thats a new one

Yeah, it's a good one. You should work it into your list of insults

Redline, if you are talking about the stock harness behind the dash, there is one for the power connections, and another for the speaker connections.

Dave

 

[NiNeTy Fo SHO]

Forgive my ignorance, but what is this second plug?

With the factory setup, the head unit has 2 main plugs in the back of it (dont count the plug for the redundant controls, the antenna, or the optional cd player) One plug being the "power" plug. It contains power (12+), remote turn on (ACC), ground, and antenna remote (this wire makes your antenna go up when the radio comes on). This plug is re-used when installing an after market head unit.

The second plug has a different shape than the first plug. It takes the signal to the amps in the trunk (basically a set of RCA's) It goes to the amps, then out the speakers. If you reach into the dash, towards the steering wheel, there is a second speaker plug that looks just like the "power" plug. This plug goes directly to the speakers, bypassing the amps, so it can be used with an aftermarket head unit...and makes wiring 10 times easier and cheaper because you dont have to buy the amp bypass wire...and it sounds much better in my opinion as opposed to using the factory amps.

A way to verify that your car has this second plug is to look at the speakers in your rear deck, you will notice 2 wires going to the positive side, AND 2 wires going to the negative. One set of wires (a pos.and a neg.) come from the amp in the trunk, and one set comes from this second plug.

To get the second plug, I couldnt see it, but knew it looks just like the power connector...reached around, located it, and with a little tug (there is something that barely holds it out of the way) pulled it through the dash and wired it in.

Hope this helps...please advise if any info. is wrong...

The older vehicles (my 88 f-150 for example, 90 sable) use the same wiring connectors to install an aftermarket head unit. The older vehicles use the same power plug and the "second" plug in our cars is the first plug in them...because they dont have amps located outside the head unit.

 

[Redline]

Ok, cool, thanks for the info. I should look and see what mine is using. The guy I bought the car from had removed the factory sub and put in a Infinity 10". I'll have to check it out and see how he wired it.

 

[RAYJAY]

To seal the sub to the rear deck try to use cap tape (its the black foam tape used to put a cap on a truck if you need more than one layer just stack it to get a ggod seal

jeff

 

[shoteen95]

To seal the sub to the rear deck try to use cap tape (its the black foam tape used to put a cap on a truck if you need more than one layer just stack it to get a ggod seal

jeff

thanks for the idea...i still havent messed with it, since i just finished school last friday..do you think you could find an example of this product online? i've never really seen this before..or really know what your talking about