I plan on using one of the cubby holes for a subwoofer enclosure, just because it makes for such a clean install and takes no space away from the rear cargo compartment.

I got the idea from reading this thread by member "rmp"
http://forums.corvetteforum.com/audi...-c6-coupe.html

As you can see, this member used the plastic cubby box in the rear cargo area of his Corvette as the enclosure for an 8" sub speaker.

What he did was line the sides and the bottom of the plastic cubby box with Dynamat and then mounted his 8" sub driver on MDF board and secured it to the top of the cubby with adhesive. What this indicates to me is that this sub enclosure is of the "Sealed" box type.

Although Ported subs can be more "boomy" than a Sealed sub, they are more efficient and don't require as large of a driver as the Sealed subs do.

The cubby of the Corvette is only 0.4 cu. ft in total area, and we are only using a small 8" driver ... I am thinking that adding a round port tube to the top of the sub (next to the driver) will then, obviously make this a Ported sub.

I also did some calculation as to the size the port needs to be when used in a box with a volume of 0.4 cu. ft and a sub driver of 8" ... To tune the sub to 33 Hz (optimum for a sub), the port tube needs to be about 1" in diameter and have a length of 4".
Calculator: http://www.carstereo.com/help/Articles.cfm?id=31

This 1" D x 4" L tube could be easily installed in the MDF board next to the speaker driver, and will only extend just a little less than 4" down into the cubby hole.



BTW ... I am also a little concerned of the fact that the cubby box is made of plastic, which I think is a poor material for a Sealed sub box. Because of the higher pressures and more resonance associated with a Sealed subwoofer, I think plastic is not a good material at all (just not rigid enough) ... plastic would be much better suited for a Ported sub.

... The spec sheet on the CDT Subwoofer Speaker (model# HD-800CF) that I plan on using says it can be used in either sealed or ported boxes.

What do you folks think about this (sealed or ported)?

.

 

1" by 4" might get you some port noise. Does the driver do well in such a small enclosure ported? If so, port it. Hate it? Plug the port.

You still need a rigid enclosure... regardless of type. Ported and sealed will suffer.


The thing that really makes my eyebrow jump is the Fs of the CDT subs are in the mid 40hz range. That's a little unusual.

Typical quality 8" subs usually have an Fs of 30hz or lower.

 

I found the T/S params and did some modeling on this speaker. I did NOT shrink to account for the volume of the sub and the port.

Also with 7mm of Xmax and a high Fs, I really wouldn't have very high hopes for this sub. An Arc 8 would be a much superior driver in this situation. It has an FS roughly half that of the CDT sub as well as more than double the mechanical movement.

(I chose this sub for comparison because I know it works well in small ported enclosures)



Yellow is CDT ported.
Orange is CDT Sealed.

Bright Cyan is Arc ported.
Dark Cyan is Arc sealed.

The grey section represents the crossover set at 80hz.



Notice that the arc sealed slightly outperforms the ported CDT in the same size enclosure.

Notice that the arc ported significantly outperforms the ported CDT.

One interesting thing to note is that -3db for the sealed CDT is at 75hz. That's just abysmal. Given the typical crossover point at 80hz... It's already lost 2.33db! Remember that doubling power on a sub is 3db. Think about that for a second.


I don't mean that you should avoid the CDT for the arc specifically - just that the CDT is not the right driver for this application. In fact, after playing around with box sizes sealed and ported - I'm not sure what application it's actually good for. The final test is an ear test, and this is all software simulation based on math... but it's generally very good math that can provide a very close visual to what you can expect to hear.


Also, while it looks like they are all the same volume this program doesn't really estimate SPL. 0 for the arc might be 120db, and it might be 110db for the CDT.




Anyway, as mentioned, the 3db drop on the sealed CDT sub is 75hz.
Vented, it's 60hz.

By comparison, the ARC sealed is -3db at 56hz!
Vented, 42hz.

Though notice the peak in the response on the ArcPorted example. It really does not like to be in a box smaller than .6ft^3 Might result in a little boominess. Then again, cabin gain might smooth it out nicely. Hard to say without installing it!


(PS, probably the smallest you want to go is a 2.75" port. Length? 35 inches. If you wanted to try to get away with a 2" port, we're talking 18 inches. 1" is definitely going to get you port noise.)

 

That was alot of good info you provided, but some of it over my head.

The problem with a 2" port is that is needs to be 18" long ... How do you put an 18" long piece of plastic pipe into a cubby that's only 7 inches deep?

After reading more on sealed vs ported speakers, I am now convinced that ported speakers really need a fairly large box, and the cubby is certainly not a large box.

Maybe doing it like it is shown in the link I provided (sealed box) is the best approach. Sealed boxes work better than ported, if a very small box is selected (at least that's what I understand)

I will take your word for it about the CDT sub ... I guess there would be better choices for this particular application.

I would like to know if the guy "rmp that originally made the "cubby subwoofer box" is still happy with the results. Does he still post here?

Ron,

 

Sealed is a heck of a lot easier to work with, and it's true that you generally need a large box. .6 ft^3 is pretty darn small as far as ported boxes go.

You can also tune higher. The higher the tune, the shorter the required port. (but the faster it drops off.)

I really would look at the Arc 8 for a small sealed application. I believe we have a couple of Arc dealers on the forum now. Dennis @ DD mods and Rick @ Raamaudio.

I know ID made the arc 8, so I'm not sure if it's still available.

I run a pair in my daily driver in .35 each @ 150 watts per sub and people think I have a 12" sub in the car. (But it's also a compact wagon. These subs weren't quite as loud in my c5.)

 

Kale ...

I was looking at a few other 8" speakers too (Boston Acoustics, Polk and JL Audio)

All are 4 Ohm (per voice coil), and all in the same basic price range.

The deal is, some have single, and some have dual voice coils. I don't know which is best for my application.

Also, the "Xmax" (millimeters) range from .75mm to 20 mm. Also, I don't know what is best for my application.

Sensitivity also ranges from a low of 83.9 dB to 90.7 dB. (I do know that the higher the number, the more efficient the speaker).

Here is a Product Comparison link to these subwoofers:

http://www.sonicelectronix.com/compa...imageField.y=5

Any thought on any of these subs?

Ron,
____________________________

EDIT:

There are 2 Polk speakers that are the same except one is single and the other dual voice coils

Also, there are 2 Boston Acoustics ... same speaker, except one is single and the other has dual voice coils

And the JL Audio with just a single voice coil

.

 

Do you have an amp yet? Ohms/voice coils are designed for flexibility.
Here's a whole lot of ****in' info. http://mobile.jlaudio.com/support_pages.php?page_id=163

Xmax: More is better. Generally speakers with more xmax also have higher power requirements. Xmax means: How far does the cone move?
You have to be careful here - some manuf. measure "peak to peak" and some "one way linear xmax." Generally higher end brands default to one-way xmax. Peak to peak is just one way x 2.

Sensitivity: Sort of useless unless comparing 2 speakers from the SAME manufacturer. People measure this differently. 85.8db on an ARC might measure 88.9 db the way Sony measures it.

Looking at those subs, if they were my only choices, I like the Polk mm840. 20mm on an 8" speaker is good. However, that could be peak to peak. In any case, that makes it 10mm which is about as good as the rest.

It also likes a sealed box of .35

FS is under 40hz, which I like to see.

-3db is at 46hz, so overall, for $100, it doesn't seem like a bad sub at all. I'd give it ~300 watts.

 

This is just going to be a modest system. Here is the amp I would like to buy to power the small 8" subwoofer:


Rockford Fosgate 1-Channel Sub Mini-Amp
Model: PBR300 X1

RMS Continuous Power @ 4 ohms:........''.75 watts x 1
Peak Power Output (watts x channels).'''..300 x 1
Frequency Response:.......................''.....20 Hz - 250 Hz
THD @ Rated MS Power:....................''....0.2%
Signal to Noise Ratio:..........................''..85 dB
Low/High Pass Crossover Freq:...........''...35-250 Hz
Low-Pass Slope (dB/octave):.............''....12 dB/oct
_________________________________

Again, Polk makes that 4 Ohm sub speaker I mentioned above in either a single voice coil (MM840) or a dual voice coil (MM840 DVC)

I checked on the Polk website ... both speakers have an Xmax of .75" and both have an efficiency of 90 dB.

The only major difference was that the single voice coil sub has a Resonant Frequency of 35 Hz, while the dual voice coil sub has a Resonant Frequency of 43 Hz

Which sub do you think would be best for use with my fairly small amp? (the single or dual voice coil sub)

Ron,

 

If you get that amp, I'd go with the dvc so you can wire it in parallel for the 2ohm rating of 150w, or better yet find a dual 2ohm sub and wire it at 1ohm for 300w

http://www.bcae1.com/spkrmlti.htm

 

Agreed. You need a "dual 2 ohm" sub to get a reasonable amount of power from that amp.

 

Well, the Polk MM840DVC is a dual 4 ohm deal, but like Mark said, since it is has dual coils, it could be wired in parallel to increase it's output.

Again, I am not attempting to make this audio system bone crushing loud. All I want is something that is clearer / cleaner sounding than the 'muddy' sound of the OEM non-Bose system that's in there now. And I just thought that adding a little extra lows from a sub would make the system just a little more pleaseurable without the bass being overwhelming ... i certainly don't want this to sound like a big boom box playing rap music.

Maybe even the single 4 ohm voice coil sub driven by my little 75 watt per channel sub amp would certainly add some bottom end to the music ? ? I would be happy with just a little "tight" / clear (non-booming) bass added to clean sounding mids and highs. I just don't want alot of heavy bass to overpower the rest of the music.

Anything has to be better than that OEM system that's in there now.


BTW ... The OEM audio system in my Camry sounds alot better than the OEM system in my 2011 Corvette. If I could just make this system sound as good as the OEM system in the Camry, I would be happy.

 

75w would be a mousefart.
150w - you would probably still be adding bass boost to make it sound right.
300w - just right to give you a little bit of low frequency reinforcement.

 

I mentioned it in your other thread - definitely go with a dual 4 ohm subwoofer, wired in parallel if you're going with the Fosgate amp (2 ohm load to the amp = 150 watts), or dual 2 ohm subwoofer (wired in parallel, 1 ohm load = 300 watts). 75 watts will be underpowered, and why leave power on the table if you need it? Since that amp is brand new, it's hard to say how it will hold up at a 1 ohm load, or how hot it will run, etc. I'd run it at 2 ohms myself... But I never like to push my equipment to it's limits.

 

I did this, using a CDT 8" But, I added a bit more to the box via adding a second 1" layer of MDF to the top and used 3/4 MDF instead of 5/8". I followed his instructions to a T, and it just wasn't working for me. I added polyfill to 1/3 rd of the cubby and that really helped, but was still missing something the very low end. I then added another 1" MDF layer to the top. I cut it the size of the cubby, and then cut the inside of it out, leaving in inch wide area in which to screw it down. That made a big improvement.
Take his picture # 2 and cut out the entire middle of his 5/8" - 13 1/2 x 8 7/8.
Is it as good as my 10" dual coil JL in a custom box, no, but my goal was to add better bass than the Blose and retain room in the hatch area by not filling it with a big box and get better quality at the low end.
I definitely accomplished that.
Using Hotel California from Hell Freezes Over as my test song, it definitely picks up the low end and sends a very clear and nice sound.
A vast improvement over the Blose
I have been considering adding another 1" frame to it to make the box bigger, but time hasn't been there.
I am running a Kicker 350x4 with the rears bridged that puts 175W @ 4 ohms into the sub.
Is this the best sounding solution on the planet, definitely not. But for an 8" that consumes no space in the hatch area, to does a decent job and is a definite improvement over the Blose. Based on Kale's diagram the CDT is not that good. When I picked up the CDT, the 8" choices were pretty limited. Looks like there is a wider/improved selection at this point.

 

Thank's to all the info everyone here has helped me with, I think I have decided to go with a complete different set of amps:

I think I am going to use the following amps in my audio system:

JL Audio (Monoblock Amp)................ Slash V2 250/1v2

Class:........................................ ..........D
RMS Continuous Power @ 4 ohms:......... 250 Watts x 1
Frequency Response:............................ 5 Hz - 250 Hz
THD @ RMS Continuous Power:.............. 0.05%
Signal to Noise Ratio:............................ 95 dB
Low-Pass Crossover Freq:..................... 40-200 Hz

$220

_______________________________________


JL Audio (4-Channel Amp)................. Slash V2 300/4v2

Class:........................................ ..........AB
RMS Continuous Power @ 4 ohms:......... 70 Watts x 4
Frequency Response:............................ 5 Hz - 30,000 Hz
THD @ RMS Continuous Power:.............. 0.03%
Signal to Noise Ratio:............................ 109 dB
Low-Pass Crossover Freq:..................... 50-500 Hz

$370


Maybe a better choice?

.

 

id do a single amp with bridged rear fir sub. more info later when i have pc access

 

check out the new rockford fosgate mini amps that dennis at dbldmods has

 

That's what I was going to use, but the 75 watts x 1 RMS Continuous Power @ 4 ohms on the sub mini-amp just isn't enough.

That's what we have been disscussing here a little bit.

 

Ron, Try one of these and be done.

http://mobile.jlaudio.com/products_amps.php?amp_id=596
http://mobile.jlaudio.com/products_amps.php?amp_id=537

 

JL generally makes good amps, but you can get better quality for less dollars. I would also steer away from class-d full range amps myself.** Or amps like the PDX. I have a PDX - it ended up in my DD with my spare speakers. I replaced it with the amps below pretty quickly after attaching nice speakers to it...

This is what im running. I have two of these: One bridged for my midranges. (350x2)

One for my tweeters with the other 2 channels bridged to a sub. (90x2 + 350x1)

http://www.arcaudio.com/productdescr...ies/ks3004.asp

It would be 350watts on a 4ohm sub. Headroom is good.



I think either Dennis or Rick can get it for you.



**The advantages are: They are small and power efficient. The disadvantage is: They don't sound very good.