Time Alignment (CHP-70-P Gen2 with Audax TW010E1)

Time Aligning the CHP-70 with TW010E1

There are different ways to time align drivers. Most common is to either move the woofer forward by using a step or to tilt the speaker backwards. The idea behind this is to align the acoustic centers of the two drivers so that the sound emitting from individual drivers reaches the ear at the same time.

From my previous post, the null response (Fig 1) of the CHP-70 and the TW010E1 indicates the acoustic centers to be quite close. Instead of adding a step for the CHP-70, I decided to tilt the speaker back to see whether it will work. This is the method used in the Thiel.

Fig 1 – CHP-70 with TW010E1 Null response

Fig 2 – Time aligned null response

After some adjustments, I finally got the null to look like in Fig 2. This is what I’m after, a deep, symmetrical notch.  Once I got the null, it is time to measure the step response. Fig 3 is the previous non-time aligned step. 

Fig 3 – Step response of CHP-70 with TW010E1

Fig 4 – Time aligned Step Response

Fig 4 is the step response with the speaker tilted back. The difference is remarkable. Gone is the time gap between the tweeter and the woofer. What is recorded is a single, fast transient. The tip of the transient is almost at zero whereas it’s about 100 msec in Fig 3. 

Fig 5 – Time aligned response of CHP-70 with TW010E1

The final frequency response is shown in Fig 5. There is still room for improvement. Right now, I’m having too much of a midrange presence. It is a good +5dB. On playback, it is not objectionable once the bass is added in. If I want a more accurate response, I’ll need to flatten the response from 1kHz ~ 8kHz. This must be done carefully. A speaker can be made flat yet sound lifeless. 

Fig 6 – Tilting the Speaker

Fig 6 shows how I did the time alignment. I lifted the front of the speaker by 1.5″ to get the null in Fig 2. This is strictly through trial and error and lots of measurements. From here, I can calculate or measure the angle that I need to slant the front baffle. Obviously, this angle is only applicable for the CHP-70 with the TW010E1 only. 

But it’s more than just tilting the speaker. The height of the microphone has a direct bearing. I found that the axis of my microphone coincides with the top of the CHP-70 basket for the best null response.

Part 1 – CHP-70 with Audax TW010E1
Part 2 – Time Alignment
Part 3 – Correcting Baffle Step

Note:
Enclosure used is 1.7 liters Sealed Box stuffed with Polyfill.
Crossover is available on request. Free for DIY. Not for Commercial use.
Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.