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Howdy all! I was tasked with putting together a surround system on a real budget for my father in law. I decided to go with the fabled Micca amazon speakers. Just cause I want to hear them vs my little Polk T15 bookshelf speakers. Picked up 2 sets of the bookshelf Miccas and one center. For the sub I decided DIY would be fun, and I have a spare BASH 300 in my closet of treasures. I googled up the HD-1200 CFS from CDT Audio, because it was a good visual match for the other speakers. I queried the tech staff for a home theater enclosure recommendation and the gave me a "4cu.ft. box with a 3" port that is 6.43" long".
Can someone tell me what tuning frequency that box/port will give me? Thanks!! I've included a link below the pic in case anybody wanted to look at the specs. On sale for $69.

http://www.cdtaudio.com/sep_components/subwoofers/hd1200cfs.htm
 

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I googled up the HD-1200 CFS from CDT Audio, because it was a good visual match for the other speakers. I queried the tech staff for a home theater enclosure recommendation and the gave me a "4cu.ft. box with a 3" port that is 6.43" long".
I can't effectively model a subwoofer but I can tell you something doesn't sound right about that port info. A 4 ft^3 box with a port which isn't even 6.5" long sounds odd to me. If you have an enclosure that size it stands to the reason the port would be quite a bit longer.
 

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Discussion Starter #3
Yes, I was concerned too, they appear to be primarily a car audio maker. Wondering if that isn't a 30+hz for a car... I emailed back to tech support asking for the tuning, but no reply yet. Only been half a day, but it is Friday.....
 

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According to WinISD the 3" wide x 6.43 long port in 4cuft is a 23.45hz tune. This may be fine but maybe not. Without T/S parameters it is hard to design a subwoofer at all. Without knowing Vd or how much air this driver can move we dont know if this port is large enough for this driver. If it is too small you will hear a lot of chuffing or air turbulence from the port being forced too much air for the port to handle.

So 23hz is probably just fine for a tune but this may also be too small of a box or too big. Also make sure you have a Hpass in place so you dont ruin the driver when playing notes that are lower than the port tune.
 

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Discussion Starter #5
Thank you very much for that, kind sir!! If I may be super opportunistic, these are the driver specs. Have the time to check them? If it is of use, I plan to drive this the Parts Express version of the Bash 300 I picked up on sale last year.
Specifications
Cone Carbon Fiber
Diameter: 12” (250mm)
Sensitivity: 87.5 dB
Power Handling: 250 WRMS (500W Pk)
Frequency Response: 10 ~ 400 Hz
Nominal Impedance: 4 Ohms
Voice Coil Diameter: 1.95” (49.55mm)
Peak Xmax: 15mm
Magnet Weight: 50 Oz
HD-1200CFS 12” Subwoofer
Technical Data
Free Air Resonance: 28.4 Hz
Voice Coil DC Resistance: 3.93 Ohms
Voice Coil Inductance @ 1 kHz: 2.75 mH
Mechanical Q (Qms): 5.9
Electrical Q (Qes): 0.543
Total Q (Qts): 0.497
Compliance Volume (Vas): 84l; 2.96 ft3
Moving mass, Diaphragm: 138 Gr
Motor Force Factor: 13.35Tm
 

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So far the cabinet size looks fine. I have a 120l cabinet tuned to 25hz and it will take about 400watts to hit Xmax. It does need a hpass at 22hz though. Now the main problem with the design is that this will have audible port noise when pushing it to its limits.(Xmax)

With a 6" wide port you would need a 24.25" long port with 400watts you will hit about 34m/s. You want to stay around 20-25 if you can. Sometimes when in a car or outdoors you can get away with higher velocities. In a quiet setting like a home it is best to stay near 25m/s. So it is still a bit small but when not pushing the design to its limits you will be just fine with port velocity. 200watts is about 23m/s. BUT with a single 3" port and only 200watts you would be at 86m/s.

So ya bigger port is needed for sure.
 

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Discussion Starter #7
Thank You! That's a honkin' large port. Should look cool. :grin2: Seems like I read that Bash had a hpf. I'll have to look that up again. Thank you again.
 

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I'm just wondering if the stated T/S parameters of this driver are to be believed, e.g frequency response 10-400 hz, Xmax 15mm (one way or peak to peak? ) given the image displayed in the first post. The magnet size and suspension look rather lean.
 

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Discussion Starter #10
Ya got me as to their honesty. Never heard of CDT, just did a google on carbon fiber subwoofers and this came back as a good visual match to the Micca's. Plus a $69 sale price. This chart was in their pdf of box options if means anything to you scientist types.
 

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If you could find a way other than the cone appearance to match the design of the miccas, may be with the color scheme of the box you plan to build, you could use a sub with proven performance such as infinity 1260W reference in a similar box(maybe grill covered), similar volume and for a similar price to get satisfaction. There are many of such builds on this and other forums.
 

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Discussion Starter #12 (Edited)
Well, I already pulled the trigger on the CDT. Should be here in four days. I think I'm just going to put it together and see how she rolls. I may learn a lesson on impulse sale buys, or I may learn CDT makes a good lil' 12 in sub. I will report my findings, or more like my impressions, cause those cool tests guys run with mics and laptops are still above my pay grade.
FYI- shipping weight is 12lbs and ships from California.
 

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FYI- shipping weight is 12lbs
Must have missed it but did you say one sub or two? A single 12 inch Subwoofer driver usually weighs from 18 pounds up to as much as 45.. Two subs are better than one, OTOH two errors are worse than one. Still it'll be interesting to see how you fare. Please don't forget to report back.
 

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Discussion Starter #14
Howdy, again! If I chose to do a pair of 3" ports, instead of a 6", would it be as simple as halving the 6" port length? Thanks again for the help!
 

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Two 3 inch diameter ports will definitely be much shorter than a single 6 inch port but realise that a 6 inch port is up to 4 times the surface area of a 3 inch one so you lose a lot of port area in that swap and the port airspeed will drastically increase.
 

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Yeah, going from a single 6" port to two 3" ports will increase your air velocity, possibly to the point of causing audible distortion. But the benefit is that you can get away with ports that are about half the length (very general rule). If might be the difference between ports that fit in your box and ports that don't. Remember that the port counts against the internal box volume, so the 6" port that is twice the length accounts for a much larger loss in box volume (and consequently a bigger box).
 

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Discussion Starter #18
Thank You, Kind Sir! Finishing build today. And to be consistent with the rest of the build on this one, I have used a housecat patterned throw pillow for stuffing. Stolen from my Mother-in-Law. Father-in-Law mounted the driver well with screws and hurricane nuts while I was away. Logo on the dust cap several degrees from horizontal. Bless their hearts... LOL
 

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Discussion Starter #19
Ran the Pioneer MCACC and it wasnt really impressing me except on super deep hits. Went digging in settings and found that it auto set (or didnt correct) the front speakers to "small" setting. Changed that and BAM!!! Have not got up for hours. Flipping between Harry Potter & Transformers movies. Bass changes everything. ?
 

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