Product Review

Thiel SmartSub SI-1 Subwoofer Integrator

Part I

February, 2005

John E. Johnson, Jr.


Click on Photo Above to See a Larger Version



● Solid State Electronic Integration Between Main
    Speakers and 1-16 Subwoofers

XLR and RCA Inputs and Outputs; Speaker-
    Level Inputs

● Parameter Settings: Mode, Number of
    Channels, Number of Subwoofers, Amplifier
    Gain, Speaker Type, Low Frequency Limit,
    Sensitivity, Damping, Low Frequency
    Extension, Low Frequency Level, Crossover
    Frequency, LFE Level
● Dimensions: 2" H x 17" W x 9" D
● Weight: 10 Pounds
● MSRP: $4,400 USA


Thiel Audio


For those of us who love having deep bass for our music listening and home theater experiences, we know that a major problem plaguing our setup is that blending the subwoofer to the main system is difficult. For one thing, the subwoofer must handle the low frequencies for at least two channels, and if in a home theater, it has to handle all five channels. Secondly, we usually have to place the subwoofer close to a wall, which loads the room differently than if the subwoofer were placed farther away from the wall.

So, what often happens is that the deep bass is there, but it sounds like a separate component rather than being "integrated" into the whole sound.

In conjunction with Thiel Audio's recently introduced SmartSub SS1, SS2, SS3, and SS4 subwoofers, they also have introduced the SmartSub SI-1 Subwoofer Integrator, which is designed specifically to solve the problems mentioned above. The SI-1 is for use only with Thiel subwoofers.

We reviewed the SS2 subwoofer using the Integrator, and now report specifically on the Integrator itself.

The Design

The SI-1 is a very attractive accessory, standard rack width but only 2" high. The chassis is brushed aluminum. But, don't let the diminutive size of the Integrator fool you. It has an enormous array of features.

On the front panel are numerous LEDs that indicate the selection of all the options. Beginning on the left (photo of the left end of the front panel shown below) are indicators for the "System". For Mode, you can choose either Augment or Crossover. Selecting Augment will leave the main speaker signal alone and simply add to the bass. Crossover mode lets you send all of the low frequencies to the subwoofer and the frequencies above the crossover setting (see text description several paragraphs below) to the main speakers.

For Channels, you can choose between Mono and Stereo. If Stereo, then you connect two sets of inputs and outputs on the rear panel instead of just one if you choose Mono. Either way, though, you can use just one subwoofer, which is the next item in the menu. You can have multiple subs, up to 16(!).

The Main Amplifier Gain is a number that represents the amount of dB gain between input and output of your power amplifier. It goes up to a maximum of 40.

In the Main Speakers Menu, you set the Type as either Sealed or Reflex (ported or passive radiator), the Low Frequency Limit as the frequency that your main speakers have at their 3 dB down point (speaker specifications usually list this as the frequency response 3 dB, so you use the frequency at the - 3 dB number in this specification). The Sensitivity is next, which would be something like 87 dB in your speaker specifications sheet. The Damping Factor (the "Q") of your speakers is dialed in next in the menu. It ranges from 0.5 to 0.9. If your speaker spec sheet does not list it, you can use 0.8 for sealed enclosures and 0.7 for ported (reflex) enclosures.

In the middle of the panel are the Readout, shown below as "20" with respect to the Low Frequency Limit LED that is active in the Main Speakers Menu shown above, and then the LED indicators for a category called "Performance". The Low Frequency Extension setting is for how low you want the subwoofer to play. So, this is the subwoofer cutoff frequency. It will limit low frequencies in subwoofers that have trouble with, say, reproducing anything below 25 Hz, and can improve the performance of such subs. The Crossover Frequency setting is used when you select Crossover in the System Menu. Setting it to, say, 60 Hz (you can select from a range between 40 Hz and 99 Hz), will send all frequencies above 80 Hz to your main speakers and all frequencies at 80 Hz and below to the subwoofer. You would use this most often with bookshelf speakers rather than floor-standers. The LFE Level lets you have a separate path for LFE signals from receivers than the low frequencies going to the main speakers. Its level adjustment is used to balance LFE bass with main speaker bass.

On the right hand side of the panel are the buttons to select from all the options. This includes Store and Recall Preset (you can save your parameter settings and recall them from six memory banks), and then the Select Next and Select Previous for scrolling through the various options. The Increase and Decrease buttons change the values in each option. Once you have all your options selected, you would press Store Preset to save them in memory.

The rear panel is a sea of connections. I bet you never thought you could have so many possibilities for setting up your subwoofer(s). Well, that is what you are paying for here: details and flexibility that give you seamless integration between your main speakers with your subwoofer.

Beginning on the left, are two sets of binding posts that are used if you want to connect the speaker-outputs from your power amplifier to the Integrator rather than a line-level subwoofer-out. They are for use in the Augment Mode, and are shorted with bus bars in the factory setting. Leave them in if you are not using the Speaker Level Inputs, as this reduces noise. Remove them if you are going to use the Speaker Level Inputs. This is followed by the LFE input, XLR inputs for Left and Right channels, and Unbalanced Inputs for Left and Right.

In the middle of the panel are XLR outputs for Left and Right channels and Unbalanced outputs for Left and Right (these would be used when Crossover is enabled, going to the main left and right channel power amplifiers), and XLR outputs for Left Subwoofer and Right Subwoofer when using the Augment Mode. There are no speaker-level outputs for use in the Crossover Mode.

Below is shown the right hand section of the rear panel. The Left and Right Bridge Inputs are for use when you have more than one Integrator (for example, if you wanted to control subwoofers for the left and right front speaker channels and the rear left and right speaker channels. The Remote socket (a DB-9 connector) is for use with a remote control other than the hand held remote. AC power is grounded with detachable cord.

The remote control is one of the prettiest I have ever seen. It is made of the same brushed aluminum as the main chassis and appears to have been routed from a solid metal block. It has buttons for 6 memories, and for selecting different parameters as well as increasing or decreasing their values.

Go to Part II

Copyright 2005 Secrets of Home Theater & High Fidelity

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