Test Bench: Crystal Acoustics THX-3D12 Home Theater Speaker System
In the lab
Frequency response: (at 2 meters) front left/right: 65 Hz to 20 kHz ±3.9 dB center: 71 Hz to 18.3 kHz ±3.5 dB surround: 76 Hz to 15.3 kHz ±3.5 dB subwoofer: 39 to 116 Hz ±1.8 dB
Sensitivity: (SPL at 1 meter with 2.8 volts of pink-noise input) front left/right: 91 dB center: 89 dB surround: 88 dB Impedance (minimum/nominal): front left/right: 3.0/5 ohms center: 3.8/7 ohms surround: 4.5/7ohms
Bass limits (lowest frequency and maximum SPL with limit of 10% distortion at 2 meters in a large room): front left/right: 50 Hz at 87 dB center: 80 Hz at 89 dB surround: 80 Hz at 88 dB subwoofer: 25 Hz at 91 dB SPL 104 dB average SPL from 25 to 62 Hz 110.8 dB maximum SPL at 62 Hz bandwidth uniformity: 94%
All of the curves in the frequency-response graph are weighted to reflect how sound arrives at a listeners ears with normal speaker placement. The curve for the left/right front channels reflects response of the THX-T3 with the speaker standing on the floor averaged over a ±30-degree window, with double weight at 30 degrees (the most typical listening angle). The center-channel curve reflects response of the THX-C averaged over ±45 degrees, with double weight directly on-axis of the primary listener. The surround-channel curve shows the response of the THX-Dipole averaged over ±60 degrees. Both the center and surround speakers were measured on a 6-foot stand, which gives anechoic results to approximately 200 Hz. All measurements except those for the subwoofer were taken at a full 2 meters, which emulates a typical listening distance, allows large speakers to fully integrate acoustically, and (unlike near-field measurements) fully includes front-panel reflections as well as cabinet diffraction and floor-boundary effects (for floorstanding speakers).
Front Towers, Center, and Surrounds
The THX-T3 and THC-C share a slightly upward-tilted frequency response, differing mainly in that the floorstanding THX-T3's response exhibits a small floor-bounce dip. In both cases, on-axis response rises about 5 dB above 4 kHz, and fully twisting the tweeter away from a listener flattens on-axis response above that frequency. This means that the left and right channel speakers will likely work best for a centered listener when the tweeters are faced straight ahead and not angled toward the listener.
Both speakers have tightly controlled directivity, with only the extreme treble falling off with increasing listening angle. With a noise source it is easy to hear the tweeter as a separate source when the listener is nearby and elevated. Thus, the system may not be optimal for rooms that have elevated seat rows.
On the other hand, the THX-C is one of few center-channel speakers I've tested that exhibits no off-axis lobing at any reasonable listening angle, so all listeners will get timbre-matched sound without off-axis errors. While the aim-able tweeter seems like a great idea, the basic upward sloping bass-to-treble balance indicates there may be few situations in which it would be useful for more than a single listener.
The THX-Dipole surround speaker's response varies considerably depending on measurement angle. Surprisingly, it shows no sign of the on-axis "notch" typical of a dipole surround speaker, but instead displays a curious 5-kHz peak. Nonetheless, response averaged over the speaker's full radiating area is well matched spectrally to that of its brothers.
Bass limits for the THX-12SUB subwoofer were measured with it set to maximum bandwidth and placed in the optimal corner of a 7,500-cubic-foot room. In a smaller room users can expect 2 to 3 Hz deeper extension and up to 3 dB higher sound-pressure level (SPL). The only response difference between the VAR and THX settings is that the latter reduces levels by 9.5 dB. In either position the subwoofer has useable response up to 250 Hz, where it measured -6 dB. Dynamically, the THX-12SUB will deliver 106 dB SPL at 32 Hz or above, which is better than average.