THOR-CDX
THOR12400 with Celestion CDX1-1446/Dayton H6512
The THOR-CDX is a 53 liters Bass Reflex that uses the 12″ THOR12400 with the Celestion CDX1-1446 compression driver (CD) mounted onto one of my favorite horns, the Dayton H6512. For those not in the know, this H6512 is a copy of the JBL 338800 horn that’s used in their JRX Series.
 Fig 1 – THOR-CDX LP/HP Frequency Response
Fig 1 are the responses of the individual drivers. The Blue plot is the THOR12400 with a Low Pass network whereas the Red is of the CDX1-1446/H6512 with her High pass. Acoustically, they are crossing at about 2.2kHz. This is exactly the recommended minimum crossover frequency of the Celestion CD.
 Fig 2 – THOR-CDX Crossover Summation
The Black plot in Fig 2 is the summation of the crossover. The crossovers are summing properly as no cancellations are observed on either side of 2.2kHz.
 Fig 3 – THOR-CDX NULL
Fig 3 is the Null response when the CD wires are flipped across. It did not result in a well defined notch, suggesting that the phases are not well aligned. I wouldn’t worry too much about this because during auditioning, I did not pick up phasing problems.
 Fig 4 – THOR-CDX Frequency Response
The final Frequency Response of the THOR-CDX is in Fig 4. She is virtually flat from 200Hz~10kHz (+/- 3dB). There is a small depression at 2.5kHz due to the less than perfect roll-off in the CDX1-1446 but it’s inaudible.
 Fig 5 – THOR-CDX Step Response
The Step response in Fig 5 indicates the woofer is fairly close to the CD. Her apex is at 131 microsec, after which she decays quite well.
 Fig 6 – THOR-CDX ETC
Her Energy Time Curve (ETC) plot shows the woofer loses her energy by 481 microsec (Fig 6). This indicates good damping.
 Fig 7 – THOR-CDX Harmonic Distortion
The THOR-CDX treble Distortion (Fig 7) is impressively low. 2nd Harmonic is 0.130% and 3rd is lower at 0.067%.
 Fig 8 – THOR-CDX Excess Phase
The Excess Phase (Fig 8) shows some phase rotation in the treble. However, it’s not detrimental to the sound.
 Fig 9 – THOR-CDX Excess Group Delay
Her Excess Group Delay is only -12.1 microsec. This is exceptionally low, suggesting the bass does not lag the midrange.
 Fig 10 – THOR-CDX Impedance
The THOR-CDX is a friendly load. Her Nominal Impedance is 8Ω. Lowest impedance is about 6.5Ω at 1.5kHz. Modern power amplifiers rated for 4Ω output should have no problems driving her.
THOR-CDX Sound
I’m surprised at the sound of the THOR-CDX. I’m not a fan of PETP diaphragms of which the Celestion CDX1-1446 is but I’m a convert after working with her. She actually sounds very sweet. None of the brightness that Titanium diaphragms are noted for. She sounds closer to my Emilar EC-175.
In the midrange, vocals are not shouty and there’s no shrill in the female singers. Sibilance sounds natural, not over-emphasized or over-suppressed until the music sounds dull. Bass is punchy and doesn’t lag behind the vocals.
Though I designed the THOR -CDX for PA, she is good enough for HiFi. Her Sensitivity of 96dB (1W 1m) is ideal for Tube Amplifiers and Home Theater. If more bass is desired, a subwoofer can be added. Either that or use my BassEQ. I developed that kit especially to address this issue.
The THOR-CDX will be offered in a kit form sometime in early spring next year. It will include the THOR12400 woofer, a Celestion CDX1-1446, a Dayton H6512 horn and a Fully Assembled Crossover on a PCB.
THOR-CDX for HiFi
 Fig 11 – THOR-CDX HiFi Frequency Response
For the benefit of users that prefer not to add a subwoofer, I re-worked the crossover for more bass. Fig 11 is what the response looks like with a new crossover.
To get this, a Baffle Step Compensation (BSC) network was used. With the midrange lowered, the bass loudness increased. That’s the way it’s done with passive crossovers.
I also needed to address the CDX1-1446 otherwise she’ll be too hot. To decrease her volume to match the midrange, I installed a L-Pad. The new Sensitivity is now about 90dB as opposed to 96dB in the Pro version. This is a small sacrifice for convenience. Adding a subwoofer and a plate amplifier will increase the cost which not everyone is prepared to do.
During auditioning, I am very pleased with the music. I can listen to this HiFi version all day. Highly recommended.
Unless otherwise stated, all measurements were made in Full Space (4pi). Mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied. |
