The Darren K Home Theater System was designed for a friend of mine as a home theater system. The goal of the design was to produce a set of speakers offering excellent home theater performance, while keeping the cost as low as possible. The fronts, centers, and rears are completely shielded, allowing them to be placed pretty much right next any type of cathode-based monitor. An MTM design across the fronts was decided upon, not really for any particular reason, other than aesthetics and for some extra bass and overall output capabilities compared to a straight MT. The results of this system were very good, making this very versatile as either a home theater or as a music-only system.

Peerless 811435 1" Neodymium Tweeter

This tweeter has been touted to have good excursion, and good power handling in a small package. One of the biggest benefits of the driver is the very small faceplate which is great for MTM's and in general. It has a somewhat drooping extreme upper end response, but I don't see this as a bad thing for a home theater application.

#299-712 High-End Shielded 6.5" Buyout

This woofer is very simple and well built. One of the nice things about it is that it is pretty much un-bottom-able. It has a nice progressive spider that really puts a stop to things when they are getting out of control. Funny thing is that it says Definitive on the side of the basket. Not sure what that's all about...

#295-190 Dayton 15" DVC Subwoofer

An outstanding value and an extremely versatile subwoofer. It features a hefty 15 or 16 mm of Xmax, dual 8 ohm voice coils, and a very rugged construction. This driver will move a lot of air and will produce good amounts of bass in any normally sized listening room. This driver will soak up all that the 300-794 plate amp will dish out, and then some.

A great all-around subwoofer amplifier. It is capable of 250 watts or so of output into 4 ohms. One of the nice things about this amp is that it has a user-adjustable bass boost (albiet its a little tricky). I also like that it has excellent thermal shutdown protection which make it virtually impossible to destroy. However, due to the low impedance of the 15" DVC, this amplifier will shut down fairly easily if fed continuous test tones with this woofer. But, on real-world home theater signals, I haven't heard of many problems.

#300-794 250W Subwoofer Amplifier

All of the cabinets were made out of 3/4" MDF joined at the edges using a standard butt joint reinforced with biscuits. As I always swear, the biscuit method will produce a superior joint when compared to most standard methods when dealing with MDF. Everything was assembled with Elmer's yellow wood glue and clamps. No fasteners were used in the cabinet construction except for driver and terminal mounting. The larger front, center, and subwoofer cabinets feature a single large brace connecting the sides, top, and bottom. It was made of a single piece of 3/4" MDF with holes in it. The rear cabinets did not use any bracing due to the small size and lack of serious activity within the cabinets.

All of the cabinets were lined with a layer of Parts Express lightweight vinyl damping sheets (#268-035). This material does do a very good job at deadening panel resonances. There is a very audible difference in the amount of ringing in a panel before and after application of the damping material. Once the walls were lined, the sealed cabinets (center and rears) were stuffed with Acousta-Stuf. The front ported cabinets have the walls lined with a thin layer of pink fiberglass. I find that for ported cabinets, not much works better than the good old pink stuff. Of course, for those of you worried about getting little glass shards into your lungs and eyes, convoluted foam may be substituted.

The finish on the cabinets is a Wilsonart gloss black laminate. The laminate is available in custom sized sheets that can be special ordered at most major building and cabinet supply shops. I ordered a batch from Home Depot, which took several weeks to arrive, but was pretty nice. I also ordered some from a local kitchen supply shop, which also took about the same amount of time. The cost from both sources was roughly the same, about $3.00 a square foot. As you can imagine, there is a decent chunk of change sunk into the finish on these cabinets.

The laminate is applied very simply with contact cement directly onto bare MDF. I applied the laminate before making any cutouts for drivers or terminals. The Wilsonart was cut to size, roughly 1/2" oversize to allow some room for error. Remember, since you are applying this with contact cement, once you start to place your laminate onto the cabinets, if you are off by a fraction of a degree in alignment you could be in trouble. I used a short-knap foam paint roller to apply the contact cement to both surfaces, and it worked quite well. I found that it was important to use a few applications along any MDF end grain, as it tended to soak up all of the adhesive very quickly. This process was very fast and I was able to do one side approximately every 1/2 hour or so. Needless to say I had several cabinets going at once, as this would still take a while going one side at a time. After applying the laminate, I gently rolled the surface with a heavy duty 3" rubber roller. This seemed to do the trick to get some good adhesion between the layers.

Once the laminate was secured on one face, the edges were trimmed with a flush trimming bit. From there, the next side was glued and affixed, going over the adjoining edges with a flush trim bit as needed. I proceeded from the sides, to the top and bottom, to the front and back. After all portions of the cabinet were covered, the edges were neatened up with a 27 degree or so laminate beveling bit. This is great because it removes all jagged edges and removes any possibility of snagging an edge on carpet or clothing. The exposed ends of the laminate were given a once-over with a black permanent marker to help darken the seam up. While the seam is still visible, as long as the joint is clean and tight, it still looks very good.

The gloss laminate is very scratch resistant and will withstand most abrasions other than those with sharp metal or stone objects. It does pick up fingerprints very easily, but these can be cleaned very effectively with Windex and a paper towel.

Cabinet Dimensions

Crossover

Front

The front crossover uses the woofer and tweeter in an MTM configuration on a flat baffle. To achieve good driver integration in the crossover region a topology that may seem slightly unusual was employed. Here is the schematic, both the woofer and tweeter are connected in the same polarity. (The "positive" side of the input goes to the "positive" terminals on the woofers and tweeter.)

As you can see, there is a single inductor on the woofer, using a 1st order electrical network with no impedance compensation. The characteristics inherent in the driver and their configuration minimized the need for complicated baffle step correction. The tweeter employs a third order crossover with an L-pad. This combination yields decent integration between the woofer and tweeter in the crossover region. A few phasing issues remained due to the phase changes the woofer was experiencing towards the upper frequencies, but, as stated before, the goal was simplicity.

The resistor in parallel to the tweeter was added later, as the speakers were overly bright for home theater use in my opinion. This value could be played with by the designer to change the upper frequency response. A value approaching infinity (a.k.a. no resistor) will yield a flat frequency response, while decreasing the value will attenuate the tweeter response more and more. Again, the 10 ohm resistor yielded a somewhat laid back sound for normal music listening, but was great for HT. If I was using these for music, I would probably use a somewhat larger value.

The crossover components consist of Dayton polypropylene capacitors throughout, and Perfect Layer 18 gauge inductors. The series resistor is a Mills, (which tends to offer a cleaner high frequency sound) and the parallel resistors are Dayton non-inductive sandcast pieces.

Measurements

This is the 0 degree and 30 degree off axis response horizontally on the MTM fronts. A slight ripple remains in the response of the woofers, this is attributed to the combination of driver response and baffle diffraction situations. You can see that the on-axis response shows a pretty laid back top end. As indicated by the 30 degree curve, the off-axis response is quite good on these speakers-- this may help explain their above-average imaging capabilities.

Frequency response with the tweeter in phase and out of phase. As can be seen, the reverse null is fairly deep, but is somewhat scraggly because of the shallow roll-off on the woofer. Forcing the crossover point lower and/or using a conjugate network may help clear this up.

The overall nominal impedance is definitely 4 ohms, but it is fairly friendly since it does not dip below 3.5 ohms anywhere. Note that the upper end of the vertical axis is 30 ohms.

Center

The center channel speaker uses the same drivers as in the fronts, except in a sealed enclosure. This speaker was designed to be used in a "horizontal" configuration (which is generally frowned upon, more on that later). The same basic crossover as used on the fronts was used for the center channel. However, because in most instances the center channel would be used on an extended baffle such as a TV or entertainment cabinet, a slightly smaller inductor was used on the woofer. This should help keep the same general midbass and midrange characteristics as the fronts. Ideally the tweeter response should be adjusted accordingly, but since the majority of the content in the center channel will be coming from the midbasses, this discrepancy was ignored.

Measurements

Yuck! Look at how bad the off-axis response of a horizontal MTM is! This is why no one in their right mind would use this design for a center channel. Granted, these effects can be minimized by the use of a low crossover point, and extremely close spacing of the woofers; however, this problem will still exist to a certain extent. This speaker was designed as such at the request of the recipient, I tried to argue against it, to no avail. I chose to use the same basic topology and crossover frequency as in the fronts to maintain a consistent soundfield. I figure, hey, as long as he's sitting right in front of the TV, its all good.

Again, the tweeter-reversed-phase situation looks pretty good

The same basic impedance curve as on the fronts, with a single sealed-box Fb hump.

Rears

Crossover design was not too bad. Possibly the biggest challenge was dealing with the baffle step. Because of the way the woofer rolls of very slowly, a large hump kept appearing between the end of the baffle step effects and the beginning of the low-pass filter. This required some fairly drastic baffle step work. Frankly, without getting rid of that hump in the 800 Hz to 1K region, the midrange sounded very bloated, nasally, and just not good. Here is a schematic of the final XO:

Sorry about the crude drawing, but I think you get the point. Here's a quick picture of the physical crossover.

This board was simply hot-glued into the bottom of the cabinet. Inductors are 18 gauge perfect layer, capacitors are Dayton polypropylene. Notice the choice of the Dayton sandcast resistors. I think in all but the most critical applications, these are acceptable. If I was making a reference system, I would probably replace the two in line with the tweeter with a Mills resistor, but for this price point, I figured why bother. Again, layout could possibly be made a little better, but for ease of installation, and the law of diminishing returns...

Measurements

As you can see, there is a very slight peak in the frequency response of the tweeter at 5K. If you wanted to get crazy with the design, you could probably throw in a notch filter, but since you are most likely going to be off-axis anyways, you can see that it pretty much goes away.

Frequency response again with the tweeter in reverse polarity. This was measured within a few degrees of the axis between the woofer and tweeter. Not too shabby I would say.

The impedance dips a bit low considering the 8 ohm impedance of the driver. I believe this can be attributed to the funky baffle step circuitry. But, in its home theater use, it probably won't see anything under 100Hz anyways. Overall though, this is a fairly uniform impedance profile.

Subwoofer

The subwoofer filtering functions are all accomplished via the internal adjustments within the #300-794 amplifier. The bass response was tailored by adding what is equivalent to 5 dB at 23 Hz. This corresponded to an 18K and 220K resistor in the rumble filter circuit. Bass response with this boost yielded a very nice F3 of just over 30 Hz. The low-frequency response below this point dropped off relatively slowly until below 20 Hz.

Listening Impressions

Fronts

The front main speakers are a very good speaker for both home theater and music listening. While they are slightly lacking in low bass response, their outstanding imaging and extremely clean midrange more than make up for it. The power handling is also excellent, the fronts can easily chew up a few hundred watts a piece and get up to near concert levels in your living room. With a slightly brighter top end (as discussed in the crossover section) these would be great 2-channel speakers. In a home theater system with a subwoofer, these sound excellent and I cannot envision making any significant changes to their design or construction.

Center

While the center channel does sound good directly on-axis, it does exhibit somewhat poor performance off-axis. If your listening room is such that the majority of the listening will occur within 15 degrees in either direction, you should be fine. Even at 30 degrees off-axis where the response is missing most of the midrange, it still does not sound horrible in a movie situation, though there is definitely something "funny" sounding.

Rears

Probably the thing that sticks out first about this speaker is the lacking bass. On some music such as jazz or classical-type stuff, it sounds very good, and you would probably never miss the low end. But, on rock music that relies on the bass guitar to carry melody, one can definitely tell that there is some stuff missing. Its really not all that bad though, but it is just a concern. Personally, if I was going to use these as a stand alone speaker, I would probably go ported with the woofers.

The midrange is very good on these, detailed, but not overly forward. I think these could compare favorably with pretty much any of the "budget" bookshelf designs that you will find. The tweeter also seems to let a lot of detail shine through. It is not the most "refined" that I have heard, but again is a good solid performer, especially for the price.

One of the better attributes of these speakers is their image/soundstage abilities. I am finding instruments firmly locked in locations between the speakers. The overall width and height of the soundstage is also very good. You almost start to get that "headphone" feeling from these that I consider good, meaning that it sounds like the music is just in your ears, and not coming from a speaker.

Subwoofer

The 15" DVC and #300-794 plate amp make a respectable combo. With the proper bass boost, the sound is very clean and tight. It is definitely not boomy, as it is very difficult to tell exactly how loud you have the woofer turned up. I would consider the sound quality "refined and under control." The only downside to this system is the lack of headroom on the amplifier and its difficulty in driving the relatively low impedance load the 15" DVC presents.

Overall HT system

As a complete system, the performance these speakers offers is outstanding. They are flexible in design, and will perform well either in HT duty or for 2-channel stereo. The satellites and the subwoofer blend together very well, and neither is the weak point in the system. The timbre matching from speaker to speaker is also excellent, with a virtually seamless soundfield across the front. Sound levels greater than you will find in most movie theaters can be achieved with ease. While the impedances of the various speakers are roughly 4 ohms a piece, they are for the most part quite efficient and will not require a ton of power to get to decent levels. However, since the rears are 7-8 dB less efficient than the fronts, they will need to be turned up on the receiver or processor most definitely.

Conclusions

This was a very successful project, and in my opinion worthy of duplication. Using the rears as stand-alone monitors and the fronts as stand-alone 2-channel stereo speakers would both work well. The system as a whole is definitely worth building (I'm tempted to build another set), especially if a vertical center channel speaker can be accommodated. All-in-all, considering the budget, this is a nice system.