HDX In-Wall Powered Subwoofer

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It's a common problem. You need some way to power the .1 channel in your surround sound recordings, or maybe you simply want to add deep bass to a room's existing stereo speakers, but you can't, or don't want to, take up any additional space. Our unique in-wall subwoofer and digital amplifier design is the perfect, affordable solution.

Sure, other so-called "in-wall subwoofers" have been around for a while, but most designs typically fall into one of two categories: 1) they are simply an in-wall speaker where the tweeter (high frequencies) has been removed, or 2) they require a significant reconstruction of your wall in order to place the subwoofer's "cabinet" inside. With the former, the sound improvement is no better, and often worse than that achieved by using a good quality in-wall speaker with an 8" woofer, such as our HDX-R80. With the latter, the cost of the cabinet-style subwoofer and the cost of having it professionally installed and amplified is exorbitant- $600-1500 is not uncommon.

Our approach with this new design was to find a solution somewhere in between. It requires a combination of a high quality driver, solid mounting system, and a separate digital amplifier. We use a 10" long-throw aluminum driver in order to achieve those really deep frequencies that make watching movies and listening to music so much more lifelike. But this driver pushes enough air and produces enough impact that it was not possible to simply install it in the same manner as our other in-wall speaker models. Through careful planning and design, we created wooden in-wall braces that cleverly fit through the hole cut-out and mount directly to your existing wood studs. Once in place the subwoofer can be securely installed with four screws that sandwich the drywall between the braces and the speaker frame.

Our SDA-120 digital subwoofer amplifier was also carefully designed with features that allow the amplifier to be connected either directly to the LFE (subwoofer) output on your home theater receiver OR "in-line" using the speaker cables already in place for existing speakers in a room. And with some pre-planning, it is possible to easily add this subwoofer into any zone of a whole-house audio system. Watch the video.

And because it is difficult to discern the location from which low frequencies (below 80Hz) emanate, you can place the subwoofer almost anywhere in the room and still achieve good results. The grille and frame can also be painted making the speaker virtually disappear in your room's decor. Of course, for best performance, some locations in a room are better than others and if you'd like assistance with speaker location, please call us at our toll free number. We're glad to help and are certain you'll find our experienced support reps a great, and free, resource for helping make your home audio project a success.


  • 10" aluminum cone with butyl rubber surround for long life
  • Power handling: 120 watts RMS, 150 watts program
  • Frequency response: 34 Hz - 200 Hz
  • Flush-mount grille and frame provides clean, professional appearance
  • Reinforced resonant-absorbing ABS polymer frame
  • Moisture-resistant design includes powder-coated aluminum grille that will not rust
  • Grille and frame can be painted to match any decor
  • Impedance: 4 ohms
  • Sensitivity: 88dB
  • Dimensions: 12 3/8" x 12 3/8"
  • Hole Cutout: 11 1/4" x 11 1/4" template included
  • Special wood braces included and required; will work with wood studs spaced 15" to 18" on center (note: most walls are built with studs spaced at 16" on center)
  • Minimum install depth: 4"
  • Weight (without amp or braces): 15 lbs
  • Includes 120 Watt RMS High Efficiency Digital Amplifier with:
         LFE (subwoofer) RCA-type Input
         Hi Level (speaker level) inputs and outputs
         Level Control
         Phase Switch
         Auto-on capability with dual color LED indicator (amber:stand-by; blue:on)


Dolby® (a pioneer in the world of surround sound) has a really great interactive tool for explaining speaker placement in a 5.1 or 7.1 setup. Here's the link . . .

Room Layout and Speaker Placement

We are available to answer your questions via email and our toll free line: 866-HTD-AUDIO (866-483-2834), M-F 8am-6pm Central Time.

When choosing a set of speakers for your home theater, start with the center channel. On average, the center channel reproduces 50% of an entire movie soundtrack and over 90% of the dialogue. Choose a center channel speaker that fits your space as well as your budget.

Next, choose the front left and right speakers. Ideally, these should be as close a match sonically to the center channel speaker as possible. The front three speakers create the front soundstage similar to the way a pair of stereo speakers creates the soundstage in stereo music. If the front three speakers are not well matched, the soundstage starts to fall apart- imagine listening to stereo with a large wooden speaker in the left channel and a small plastic speaker in the right channel and you get the idea. So if you select the Level TWO Center Channel speaker, it is best to buy the Level TWO Main speakers in order to achieve the best sonic match and thus the best soundstage. Similarly, if you plan to use an in-wall speaker for the center channel, then your best match for the front left and right channels will come from two other in-wall speakers. If your situation does not allow for a perfectly matched set, you can still achieve decent imaging and panning effects as long as the speakers are not too different. Just be aware that without a matched set you are straying from the best possible audio performance.

Moving on to the surround speakers, again, the ideal setup is to use the same speakers in the back left and right as used for the front left and right. However, it is difficult to establish a "side" soundstage between the front and back speakers so having the back speakers match the front speakers is not nearly as important as having the front three match. Often, our customers who choose Level THREE for the front speakers, opt for Level TWO speakers or Middies in the back because of space considerations. The result, while not exact, is perfectly fine because we design these speakers for a similar tone.

For similar space and cosmetic reasons, in-wall speakers are often used in the back even though regular cabinet-style speakers are placed in the front. This is also acceptable, just be aware that the tone will be different so you are exchanging a little bit of sound quality for aesthetics. Should you go this route, choose an in-wall speaker that is designed to be as close in tone as possible so that panning effects are not distracting. We recommend using the HD-R65 (high definition round) or HD-W65 (high definition rectangular) when combining with our Level TWO or Level THREE cabinet-style speakers.

Finally, a Powered Subwoofer is necessary for reproducing the unique Low Frequency Effects channel recorded in most of today's movies. It can also help augment the lowest frequencies in every channel. We recommend you consider how well the powered subwoofer blends with your main speakers in music listening when selecting the most appropriate sub. Speaker drivers are typically built in the following sizes: 4", 5.25", 6.5", 8", 10", and 12". In general, you'll want to get a powered subwoofer that is 3 "sizes" larger than the driver found in your cabinet-style main speakers (or at least 2 sizes larger than found in your in-wall speakers). That is why our Level TWO Main Speakers (5.25" driver) are best matched with the Level TWO Powered Subwoofer (10" driver), the Level THREE Main Speakers (6.5" driver) are best matched with the Level THREE Powered Subwoofer (12" driver), etc.

A powered subwoofer, by definition, includes an amplifier. The signal sent from the home theater receiver/processor to the amplifier is therefore a "non-powered" signal that needs to be shielded from its surroundings. Shielding prevents unwanted interference, specifically a 60 Hz "hum" from nearby electrical wires, from being picked up and amplified. We offer a shielded powered subwoofer cable in lengths of 3 feet, 12 feet and 30 feet. All current HTD powered subwoofer models have been designed with the amplifier separate from the subwoofer cabinet, i.e. the amplifier is not built-in to the cabinet. Among other benefits, this allows flexibility in where the amplifier can be located. In most cases, you will want to place the amplifier very near the home theater receiver and use the short, 3 foot shielded subwoofer cable. Then, you can run standard 14 gauge speaker cable to the subwoofer location. Alternatively, you can locate the amplifier near the subwoofer cabinet (our Level TWO and THREE subwoofers are designed with a slot underneath in case you choose to place the amplifier with the subwoofer cabinet). In this type of installation, you will need to run the longer 12 foot or 30 foot shielded subwoofer cable to the subwoofer cabinet and then add a short length of standard 14 gauge speaker cable to connect the amplifier to the subwoofer. Keep in mind that the amplifier will need an electrical wall outlet near the subwoofer cabinet. This is obviously not a requirement when the subwoofer amplifier is located close to the home theater receiver.

The other speakers in a surround sound setup (front left, center and right plus all of the surround speakers) do not have amplifiers built-in. Instead, they are powered by amplifiers in the home theater receiver. It is difficult for an amplified signal to pick up interference, so regular, unshielded speaker cable will do. We recommend 14 gauge cable because, in our experience, it is difficult to notice an improvement with even thicker cable. When running cable behind a wall or in the ceiling, most building codes will require that you use UL rated CL-3 cable which has a higher fire retardancy than clear jacket cable. We offer this type of cable as well.

Many people still cling to the idea that a powered subwoofer is only necessary if you are using small bookshelf speakers. While a powered subwoofer can, and usually should be used to assist in the bass reproduction of every channel, its main purpose in home theater is to reproduce the Low Frequency Effects (LFE) channel. This channel (the ".1" in a "5.1" or "7.1" recording) was introduced with Dolby Digital and DTS and offers a completely unique conduit for low frequency information and effects. If you don't have a powered subwoofer, you're completely missing out on this exciting stream of low frequency information.

The LFE channel dramatically improves the impact and emotion of scenes in all types of movies. Imagine missing out on the resonance of the approaching T-Rex in Jurasic Park, not feeling the rumble of an earthquake, or missing the low tone that penetrates your body just before the bad guy jumps out at you in a scary movie. Emotion is often conveyed through a movie's soundtrack and a powered subwoofer makes the most impactful low notes really hit home. Invest in a good powered subwoofer- you'll be glad you did.

The definition of a "transmission line" differs depending on who you ask or what you read. A simple port by some definitions is a type of transmission line. But we distinguish our designs from simple ported designs because we don't just cut a hole in the cabinet and insert a straight plastic tube.

Instead, we build a channel in every cabinet that goes inside the cabinet and up at least aportion of the back wall with a length that is equal to a minimum 1/12 the desired wave length. In same cases this transmission line wraps around inside the cabinet. The difference is obvious in the improved bass performance (both depth and control) of our speakers.

Our longest transmission line, relative to the cabinet size, is seen in our Level TWO Powered Subwoofer.

We do not publish all of our mechanical drawings because we consider this proprietary, but we do show this cut-away as a good example of a key difference in our cabinet designs. This feature is only seen in much more expensive brands. Our lower price is simply the result of our business model of selling our products only direct to consumers.

It is also significant to note that all our cabinet-style speakers are "front ported". This design allows you to place your speakers close to, or even directly against, a back wall without negatively impacting bass peformance. While a front port design costs a little more to manufacture, its importance becomes apparent (especially in home theater setups) when determining the location of your speaker.