John's NHT 1259 Subwoofer Blog

Adventures in building the ultimate subwoofer...

After first reading about the virtues of the NHT 1259 subwoofer five years ago, I knew that I had to create something with it eventually. Never having the time or the money, I kept putting it off until just recently. Since I have upgraded everything in my Home Theater system except the sub, I have finally taken on the challenge. Although I have a lot of experience building R/C aircraft, I have never taken on a woodworking job of this scale before. At the start of the project, I had a limited selection of tools: a drill/driver, a dremel tool, and a bench sander. A quick trip to the pawn shop and $50 later, I owned a router, an orbital sander, and a set of wood clamps. My whole goal for this project is to keep costs down without sacrificing build quality. Madisound offers a DIY system based around this sub for around $550. I want to beat this by at least $150....
note about tools: I don't really consider the price of tools that I buy part of the cost of the project since they pay for themselves over time. I did try to keep tool cost to a bare minimum.
I decided on building a sealed box type sub from 3/4" MDF (Medium Density Fiberboard) with 1/2" oak plywood exterior. A lot of my ideas came from another 1259 project on the internet here. The dimensions came out to be 26 1/2 " x 19" x 19", mainly to try to match my other tables. This yielded an interior volume of about 3.5 cubic feet after bracing. This seems to be the ideal size for the NHT driver as a compromise between low end extention and power handling. To drive the 1259  I will use an Apex Senior 350 watt subwoofer amp from Apex Jr website (Steve rocks!). I chose this amp because it has the power I need to drive the NHT in this enclosure, and the price was great (159.99 as opposed to 225.00 for a less capable amp from Madisound). Parts Express has a smaller version of this amp for $128...I figured it was worth $32 for 100 more watts.
Day One. I just ordered my NHT 1259 from Madisound for exactly $161.03. Can't wait to get it. Having no way to cut MDF, I took my little pad of figures to my local Lowe's and hoped for the best. Thank god for Josh and his trusty panel saw. He cut all my MDF perfectly and charged me nothing for the cuts.  Bought some 1 1/2" partice board screws too. $25 for screws and wood. Got home and clamped it together.....this is going to be big and heavy :-)
Today I clamped the box together and and made sure all joints were tight before I drilled all the screw holes.  For bracing I decided to use a sheet of 3/4" MDF with a 10" hole cut in it for a middle brace while using MDF 2x2s (I used 1x2s laminated together) to brace front to back...$10 at Lowe's.
I went to Home Depot today to look around and found a clearance on mildly warped 1/2" oak plywood. A 4x8 sheet for $20! They cut it for me and I discarded the warped pieces. What a find! Finished gluing the brace pieces together.
I started fitting the braces in the box today. Very time consuming. My bench sander is really helping with this. To finish the cabinet, I plan on cutting the oak plywood to the exact dimentions of the sides, then putting in 1/2" quarter round oak molding to finish it off. $14 at Lowe's.
I recieved my NHT driver today. I am reveling in the glory..... I haven't had much time to work on the project for a few days.   Braces are fitted and main brace hole is ready to be cut. I should be able to start gluing soon. I intend on using screws to hold it together until the glue sets. I will then take out the screws, drill out the holes, then glue 1/4" dowels in the holes. For cutting the big holes, I didn't want to invest in a hole cutting jig for my router so I built my own.
Okay, forget about taking out the screws and putting in dowels. I used Gorilla Glue for the main butt joints and boy is it strong. Those screws are there to stay. Unfortunately, Gorilla Glue expands when it cures and it caused a couple of the braces to split. I filled the splits with slow cure epoxy and that was the end of that. Before gluing up the sides and braces, I cut the driver hole partially to aid in routing it after I install the veneer. I can't cut the hole for the driver until after installing the oak plywood since I need the little hole in the middle to rout the plywood.
Lots of "hidden costs" are popping up. I am not going to pay $25 for polyester stuffing! I am told that "Mountain Mist" fiberloft fiberfill is very similar to high-end acoustic polyester. I got two pounds at my local Jo-Ann hobby store for $8. Also paid $6 for Gorilla Glue and $4 for more screws (this thing has 100 screws in it). I ordered the amp today. It should be here by Monday or Tuesday. I glued and screwed the top on the cabinet today and started filling the countersinks with wood putty. I will be out of town until Sunday.
Got my amp yesterday. I couldn't do anything else until the amp got here so I could be sure the hole was the right size. All screw holes have been putty filled. I plan on using #10 hex screws and T-nuts to secure the amp and 1/4" hex screws and T-nuts for the driver. The amp looks like it is built very well.
Yesterday I trimmed all of the plywood panels to fit on the finished box. I glued on the top oak plywood panel also. Since I dont have clamps long enough for this panel, I piled on every heavy object I could fit on it. To take out some of the warp in the plywood, I routed several grooves in the back of the panel to allow the wood to flex better.
I got a lot done yesterday. All of the plywood panels are now in place. I routed the hole for the driver and installed the T-nuts. I couldn't take the suspense any more so I installed the acoustic stuffing, mounted the driver and amp, and cranked this puppy up! I must say that this amp is capable of driving this speaker very easily (on Avril Lavigne's "Skater Boy" I bounced the voice coil on the back plate....oops). In my apartment, subs do well with a little corner loading. Once the new sub was in place it was amazing! This thing is capable of hitting very,very low. Using a test CD, I found my F3 to be about 25 hz. The sub is almost done. All I have to do is install molding and spikes, then finish the wood. :-)
Well, after listening to this sub for the last two days I am very happy with the results. Don't get the impression this is some "ghetto pounder" sub that pumps out huge volume of muddy bass within a small bandwidth. This speaker is refined, accurate, and very low. It is capable of recreating the sub-harmonics that give recordings that "live" feel (especially live recordings!). I am sad that I must take out the driver and amp so that I can finish the cabinet. My old sub is an Audiosource SW15 that is barely better than nothing. I am excited to get my new sub finished!
Yesterday I was able to install all of the molding. It was easier than I thought it would be. Once again my bench sander proved it's worth by allowing me to make all the miters perfect. I am currently putty filling all the cracks and sanding the box. I am still trying to decide on a finish. I think Minwax Red Oak stain will do the trick
I had a busy weekend so I haven't had much time to work on the box. Sanding is the most boring thing about this whole project. Still undecided on what kind of finish I will use. More soon....
Well, I had a can of Minwax Pecan Satin polyurethane in my closet so I decided to use it. Looks good so far....
The pecan was a little too light so I put on a couple of coats of olde maple polystain. Minwax polystains are great since you can vary the shade as you go.
As soon as the spikes get here I can finish this project.
Well, it is finally done. A little over a month of construction time was well worth it. I can truthfully say that the reason I was so sucessful is that I was very methodical about every step of construction. You can't rush into anything.
I must say that I am very proud of myself. This sub integrates seamlessly into my system. My current home theater system includes:
Modded Xbox
Pioneer Elite DV-47a DVD player
Sony TA-E9000ES Digital Processor
Sony TA-N9000ES 5 Channel Amplifier
Energy Veritas 2.1 front speakers
Audax custom rear sattelites
The final cost of the box came out to $145. The cost of the driver and amp was $320 making a total of $465. Although this does not reach my goal as it is, if you consider what I would have had to pay for shipping on a Madisound kit, I reached my goal of beating thier price by $150 or more. The cabinet I have built is incredibly strong and heavy. It weighs over 100 lbs and is much better quality than almost all other subs on the market.
I now have much listening and breaking-in to do. I will post periodic updates for days to come, but as it stands, this project is done.
Well, after a couple of months of listening to this monster I am very happy indeed. You literally cannot tell where the sub is in the room. When I play a dvd with Dolby Digital or dts, I have to turn down the volume of the sub (I do this on my preamp, not the sub itself). In the Matrix Revolutions, when the hovercraft is flying over it feels like it is flying over my apartment. I am now building a grill for picture soon.

Thanx for visiting my site. If you have any questions or comments, you can email me at

NHT 1259

Apex Senior Amp

Here are the raw materials

Starting to frame it together

The driver arrives! This should blow chicks clothes off.

This is my homemade circle jig. Works great!

Gluing of sides and braces complete.

Amp hole finally cut

Gluing on the plywood panels

Testing in listening environment

Starting to look like a piece of furniture.

First coat of polyurethane.

Ta daa! My finished subwoofer!

Electronics Central