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-   -   enclosure help (http://www.diyaudio.com/forums/car-audio/45037-enclosure-help.html)

blyth18md 5th November 2004 07:02 AM

enclosure help
 
Ok well i picked up a couple(2) mcm 55-2421 8's to play with. And well when i tried to design a box i couldnt seem to get the specs to work well for me. I was wondering if anyone here is familiar with the driver and are willing to take a shot desinging the enclosure.

They will be going in a 82 Camaro z28. I listen to mainly classic rock...but occasionally like some hip hop. a few things i like to carry in the car are...Pink floyd, Zeppelin, The doors...Jedi mind tricks, jurassic 5, blackalicious...sublime,slightly stoopid

I have plenty of power for the subs and can pretty easily go to 2-3Cubic ft total for both subs.


RMS Watts 120
Peak Watts 240
Frequency Rsp 20HZ-1KHZ
Imp/Ohm 4.00
SPL (db) 87.00
Free Air 24.70 HZ
QES .190
QMS 12.640
QTS .180
VAS 39.400 LT
RE 3.400 OH
XMAX 16.000 MM (I have read that this is either a generous exaggeration or it equates to 8MM one way)

sdoom 5th November 2004 08:00 AM

From what my little program calculated in a closed box you should go with 25-30 liters (~26-31quarts). That will deliver most sound pressure

http://stephankresser.homepage.t-online.de/MC_1.JPG

If you decide to use a vented box : 40 liter (~41quarts) and use a 10cm port (4" diameter). Lenght should be 15cm (~ 6")

http://stephankresser.homepage.t-online.de/MC_2.JPG

richie00boy 5th November 2004 09:06 AM

Nooo! That ported design is no good :) Firstly, look at the HUGE peak -- it will sound terrible. Secondly, it's tuned to only just under 50Hz which will result in it shaking itself to pieces if you send it much bass.

The very low Qts of the woofer tells you that it's not suited to closed box, unless you can live with very early roll off.

The low VAS and Qts of the woofer tells you that the box will be small and will probably be difficult to accomodate a port of sufficient length. The answer is to use a passive radiator.

sdoom 5th November 2004 12:03 PM

but it will only run from 60Hz downwards (assumed he uses a 50-60Hz low pass filter) , If I make the enclosure smaller the shown curve will move towards 80HZ , then he will have no low bass at all unless he pumps a lot of power into the woofer

muhy3 5th November 2004 01:50 PM

What richie00boy is correct, the +/- 5dB peak at 50Hz is too large, at most you should be looking at +/- 0.5dB (at least that's what I look for). The larger the peak, the more unballanced it will sound.

I have tried modelling a suitable enclosure for your subwoofer, but it seems that no-matter how I mess around with the volume or tuning frequency, the peak is always very large, and that affects the rest of the spectrum as well quite horribly. Perhaps someone with more experience could model a ported enclosure otherwise stick to a sealed enclosure for the flattest response.

blyth18md 5th November 2004 01:50 PM

Keep the advice coming. Im starting to get a bunch of folks telling me to just sell the subs and get "better" ones because they cant find a design that works.

Tell me more about the passive radiator, im willing to give it a shot. if that may help things move more smoothly.

I have plenty of power an audio art 200ms, if i dont need a ton. And an audio art 200.2rxt if i need a "little" more.

As far as spl levels, im not really concerned about sheer loudness, i want just a decent sub stage. Output is always a plus, but i want quality first.

Thanks for being so helpful to a forum n00b

richie00boy 5th November 2004 03:09 PM

The design by sdoom will simply destroy itself as a subwoofer as the tuning needs to be lower than 40Hz to prevent unloading of the cone.

I'll add another voice to the crowd telling you to sell them. 99.9% of the time you are better with a single driver with the same total cone area as multiple smaller ones, as it will have lower Fs and higher excursion.

You have two choices if you keep it: passive radiator or sealed.

Finding passive radiators is not easy. You could make one to suit those eights out of an old 10 or 12 inch driver with good excursion, knocking off the magnet and adding mass to the cone to tune it. Box size should be about 20-25 litres. Note that's a 10 or 12 inch PR per eight...

You could have a play with a sealed box, but it would need some EQ. This could be (in order of ease of design & build) high-pass filter with high Q, Rod Elliot EAS circuit, or Linkwitz Transform. Box size should be about 15-20 litres.

sdoom 5th November 2004 04:16 PM

Hi guys.

Like another guy said, the peak will actually always be there. It gets more flat when the enclosure gets smaller, but then the port length is longer than the enclosure would be (using a 4" port) , and I am afraid when he uses a smaller port diameter he would probably hear the air flow.

Besides, the drawing shows the max. volume the speaker CAN produce where the limit is set by the max. displacement. The curve does NOT show the efficiency factor, where the peak is not that big.

I tried to calculate a bandbass-box , but there the curve shows even worse. If fb is set higher around 70Hz the bandpass gets better and is flat, but again, no lowbass at all then. It seems that those speakers are better be used for mid-bass operation.

blyth18md 5th November 2004 07:54 PM

Well digging through some posts and running a yahoo search netted me this post. Though I believe it was in a non-car audio section they did seem to find a PR that works with these subs.

http://www.diyaudio.com/forums/showthread/t-13259.html

If some one has more info on the RCM stuff let me know.

Lets keep this going guys. I really want to give these things a try and if they comparable to the tangbands they should be pretty nice if i can get them spec'd up.

REDSKIN 5th November 2004 09:51 PM

Just thought I'd chip in. I was all set to make a small box and use a PR instead of a port until I got some negative feed back that made me think. Check out what BAM has to say in this thread...

http://www.diyaudio.com/forums/showt...threadid=42305

I would also say IMO not to worry about small peaks in response graphs on sub sims, or concern yourself with linkwitz transforms or similar (IN THIS APPLICATION). You are about to put this into a car that will no doubt have it's own sub amp complete with it's vast array of hp filters and eq and your head unit will also have some if not a lot of eq possibillities, more than enough to deal with a small peak.

There is also the small question of massive cabin gain, that if factored in will make your reasonably smooth response look like the Andes.


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