Monday, May 28, 2007

2. Driver linearization

Driver linearization. What is that?? Basically, when you apply crossover to the drivers, you are separating the drivers so that each of them is reaponsible for a ceratinly frequency only. The frequency part the driver is responsible is totally control by the crossover. For example, a crossover can control the mid so that it will only output the frequency from 500Hz to 1500 Hz. At both ends of the crossover is a slope. This is the area where one driver is being taken over by another driver.

However, as you can see in the picture, the area between the slope is a straight line. The crossover ASSUME that the driver will behave perfectly and will always produce 0dB within the crossover range. However, this is not true. Not many driver are as perfect as that. Driver linearization allows actualy measurement on the drivers and incorporate these characteristics into the crossover. In other words, when the driver is output less amplitude, the DSP will kick it harder so that the actualy outout will be 0dB, when the driver is output too much, the DSP will pull it down abit. So the final output will be as predicted. Please see the following graph of my crossover for mid driver after linearization.

You can see the the program has too "pull" my driver down a bit in order for it to produce perfect response.
Actual setting up:
This is more complicated and there are a few changes I need to make. At the moment, I am using UcD180 to drive the drivers. it just happened that Raven 2.0 is a ribbon and to DC, it is pretty much shorted. This will active the current protection of UcD180 and the amp will be muted. At first, I add the 27uF caps in series with the output of the UcD, I can play the tune but I heard a loud "pop" when I switch on the amp. This happens because the Ucd has 2V DC output when not loaded. The cap is charged up and was discharged when the /on is pulled to ground. To solve the problem, I replace the cap with a 2ohm resistor and all problem soved. But the tweeter is not not protected from the DC.... Lets pray.

It has been one month and the tweeter is still here!

1. Crossover Generation

For my speaker, I use Linkwitz-Riley 96dB/octive. This is very steep and I am trying to achieve a very clear sound. The setup is fairly simple and the crossover can be generated in a 5 minutes!

However, the crossover over method used by Acourate is very different from other electronic crossover system. It has a linear pass filter. For details, you need to read the white paper here Acourate give me the best crossover filter

Continue with Acourate

It has been a while since I have time to paly with this toy again. Well, a few changes to my life
1. New speakers are finally here
2. New kid
3. New job

The last 2 have negative impact on my hobby but the first one is a good drive.

The new speaker is a 3 way design with Raven R2 as the tweeter and At as the mid and bass. I have also made 2 x w210 as a coner woofer/sub. Now, if I want to hear any music, I have get moving. And this comes to the power of Acourate.

Acourate comes with many function but basically, it can be devided into
1. Crossover generation - this is by no means simple steep slope LR or B filter. It is minimal phase. To understand the beauty of it and why it is the best crossover system than active and passive, you have to check out the white paper here.

2. Driver linearization - When you buy expensive speakers, the manufacturer will try to mactch the drivers for you so that the left and right is balanced (so they say). But when you DIY speaker, the drivers are not matched. Even when they are matched, they don't behanve exactly the same manner as the crossover anticipates. Driver linearization analyse the drivers behaviour and give it an extra push when the amplitude is sagging and hold itback a little when it is too excited. This way, the driver will be matched both side and follow the behaviour the crossover predicts

3. Digital alignment - This is used to align the tweeter, mid, woofer and sub so that the sound arrive to the ear at the exact time.

4. Room correction - All the benefits of digital room correction I mentioned before are incorported here!