[althore]

Hello,
I am in need of a new sub. Unfortunately, I only have a budget of $300. While doing research on buying a used sub I ran across a DIY build and have chosen to go that rout. This is my first build so please forgive my questions.

My Room:
15'x12' listening area
24'x12' total room size (there is no wall in between my living room and kitchen)
8½' ceilings
sub placement will be restricted to the back corner of listening area

System:
Denon AVR-5700
RBH TK-5 Towers and center
Mirage nanostat surrounds

My listening habits are 50/50

I have purchase an original Tempest 15"($60) to start and was thinking of building a sealed enclosure.
I have been playing with Winisd and believe that a 22"Wx20"Dx18"H box is what I need. Also I have been looking for an amp and found the Foster WF-100K. According to the literature two of these can be bridged for 220W at 8 Ω.

Now for the questions. Is a sealed sub the best way to go for this speaker? If so are my dimensions correct? Are these amps OK or should I look for something else. I have also read up some on the BFD and would like to know if it will help with the response for movies? Any help or suggestions would be appreciated.

 

[Mike P.]

22"Wx20"Dx18"H is about 3.2 cu.ft. net and much too small for any HT application. A pair of Foster WF-100K's can be bridged for 8 ohms but the sub can't be wired for 8 ohms since the sub is dual 8 ohm coils. Your only option with two amps is run each amp per coil and get 80 watts from each amp for a total of 160 watts. The default boost in the Foster amps would need to be eliminated.

4.8 cu.ft would have a Q of .707. Powered by a Bash 300 watt amp for $149 it have a 6 db advantage at 20 hz over the smaller box and Foster amps.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-750

 

[althore]

Thanks for the reply. My graphs are turning out different than yours. It must be user error on my part. I have a cousin who is a DJ and she is letting me use her Peavy CS800X. The ratings are:
Stereo Mode: 2 Ohms : 600 Watts RMS x 2
Stereo Mode: 4 Ohms : 400 Watts RMS x 2
Stereo Mode: 8 Ohms : 240 Watts RMS x 2
Bridge Mode-Mono: 4 Ohms: 1200 Watts RMS
Bridge Mode-Mono: 8 Ohms: 800 Watts RMS
Rated Output Power: 4 Ohms: 0.03% THD: 400 Watts RMS
Rated Output Power: 8 Ohms: 0.02% THD: 240 Watts RMS
Slew Rate: Stereo Mode, Each Channel: 40 Volts/uSec
Slew Rate: Stereo Mode, Each Channel: 80 Volts/uSec
Total Harmonic Distortion: Less then 0.03% 20 Hz to 20 K at rated power 4 Ohms

Is this OK to use? If so how would I wire the coils?

 

[Mike P.]

Whatever amp you use will need a hi-pass filter (rumble filter)to block the lower frequencies from causing the sub to bottom out. The modeling I posted above has a hi-pass filter at 18 hz to both graphs. That's probably the difference you are seeing.

If you want low end output for HT you should consider a ported box if box size isn't an issue.

 

[althore]

The biggest I can go is 22"W x 33"D x 23"H. Would a ported design sound as clean. Also, Winisd keeps crashing on me (vista). Is there another program that would work?

 

[Mike P.]

Whether any sub sounds clean or not depends on how the sub is interacting with the room. This is where the REW software does its job by showing you where the issues are. Some issues are corrected by proper sub placement in the room and other are corrected by the use of a BFD to help smooth out the frequency response.

There are known issues with WinISD and Vista, another program you can try is Boxnotes.

22"W x 33"D x 23"H would have a net volume of about 7.5 cu.ft. Tuned to 20 hz with 2 4" flared ports, the ported model would have a 6 to 7 db advantage in the 18 to 30 hz range, definitely worth it for HT in your overall room size. Both models are shown with the P.E. Bash 300 watt amp.

 

[althore]

OK. WINISD Beta seems to work for me. It is telling me that the two ports you recommended should be 19.5" long. Is this correct? Also, a high pass filter was mentioned earlier. Is that built into an amp, can it be done with a BFD or is it a separate component that I will have to purchase? I have downloaded boxnotes and it looks like a cool program. Sorry for all the questions.

 

[Mike P.]

19.5 inches each for straight ports and 20.5 inches each for flared ports. The high pass filter of the Bash 300 amp is at 17.7 hz, perfect for this setup.

 

[althore]

So you would recommend the 300 Bash amp over my free Peavy amp?

 

[Mike P.]

I have no idea on the quailty of the Peavy CS800X. You could try looking up some reviews on the unit. If it doesn't have a HPF at around 20 hz then you'll need to add one the the Reckhorn B2

http://www.creativesound.ca/details.php?model=B-2

The advantage of the Peavy amp is it has enough power to power a second sub if you want to add another one in the future.

 

[althore]

If I use the bash amp I can make the cabinet 39" deep. Would this change the port size? The flared kit at PE will only go up to 17". Thanks for all your help Mike.

 

[Mike P.]

If I use the bash amp I can make the cabinet 39" deep.

Why would the cabinet need to be deeper for the amp?

You can extend the ports by using a schedule 40 white PVC coupling. They are a couple of dollars.

 

[althore]

I do not need to build a bigger cabinet. I was planning on putting a vertical rack on the back for the Peavy. The RCA is run in the wall to the back of the room for the subwoofer so the amp has to go back there. Since I will go with the bash I can make the cabinet bigger. Would the extra 6" deep be better? Also, what are your thoughts on down fire vs front fire. Thanks.