Sunday, January 20, 2008

Drivers alignment

We are moving on the drivers alignment again. To make things a bit easier for me, I set up another XO with L Bressels 10th order filter and no parallel setting. In other words, each driver is only responsible for one section of the frequency.
Sub - up too 120Hz
woofer - 120 - 500Hz
mid 500 - 2000Hz
Tweeter - 2000Hz to 22000Hz

Note that these settings are arbitury and for alignment only. There is also a trick and that is drivers are delayed from the other one by 1000 taps. This is to ensure that the individual peaks can be seen later. Once this crossover is setup, it is then used in the colvolver engine and the logsweep is played for the following conditions
Sweep with all drivers
Sweep with no tweter
Sweep with no mid
Sweep with no woofer
Sweet with no sub

The following picture is the frequency and time domain of all the graphs.

I know, very difficult to see. Here is the blow up picture of the nomid and nowoofer
As you can see from the time domain graph, the pulse from each driver are seen clearly. Now we can than measure that exact location for each driver in terms of taps.
Left: 3125, 4010, 5005, 6000
Right: 3123, 4010, 5005, 6000

Now, we need to check the relative delay reference to the sub
Left:0, 885, 1880, 2875
Right:0, 887, 1882, 2887

Now, we need to compensate the 1000tap delay we set at the crossover
Left:0, -115, -120, -125
Right:0, -113, -118, -123

Negative means delay. The above number means the tweeter arrive to the mic first.
The delay is
Left:0, 115, 120, 125
Right:0, 113, 118, 123

Now align the tweeter:
Left:0, 115, 120, 125
Right:2, 115, 120, 125

Now, this can be used in the crossover setting and all the drivers become perfectly aligned. How do I know whether it make sense? lets look at the delay between the sub and the woofer for the left channel 115taps. 1/44.1K x 115taps = 0.0026sec. Sound travels at 300m/s so the delay is about 0.0026 x 300 = 0.782m which is exactly what I got physically!

There is one more thing I need to do - alignment between the left/right speaker. How? "you can generate a logsweep with Acourate: stereo L/R together. If you record it and convolve it with the inverse logsweep then the resulting pulse should have only 1 peak. Otherwise you have different distances."

Will post the results later

Tuesday, January 15, 2008

Crossover with Sub / Woofer 50/50 split

Previous, I get the gain of my woofer to 30% and the gain of my sub to 70% hopping to get better sound and avoid suck out. But as you can see on my previous post, I actually got booming. Today, I changed the crossover to 50/50 split I can hear a more authoritative mid bass and nice very low bass. Basically, the bass is more defined and more tight. The follow graph is the measurement with the new setting

You can see that the lower bass is not as exaggerated and the booming is less. The character of the AT driver becomes more prominent as well. I will settle as this for the time being.

Monday, January 07, 2008

More on Driver linearization

After listening to the Bressels standard filter for a few months, it is time for me to move forward to drivers linearization again with this filter. It took be 2 hours for the measurement and adjustment. During the linearization process, it was noted that the mid is actually quieter than the tweeter by about 6bB. After the linearization, the high is not as forward as before, the mid is clearly and the whole range becomes more balanced. The finer details is alot more easier to detect.

What you can see here is the frequence response of the whole speaker after driver linearization but without any other adjustment measured at the listening position. So, you are looking at the driver response + the room effect. You can see that the mid and high are quite smooth already. This is the part that is least affected by the room. There is a dip at the 200Hz of about 8dB. This is beacuse the woofer is not linearlized. The lower bass is also exaggerated giving a slight booming. All these will be corrected later on with room correction.

Also note that the lower cut off is now about 25-30Hz. Giving pretty good bass.

The above diagram shows the target curve I plan to use. This will be the first test, trying to make the target as flat as possible. Later on, I can make it to any shape I like. I can even exaggerate the mid range for vocals etc.

The next step I need to do is dirvers alignment. In the following graph, you will see the time domain of the driver response.

Now, you can clearly see the 3 spikes which represents the woofer, the mid and the tweeter not aligned properly. The sub reaponse is also hiding inside somewhere. With proper digital alignment, we should be able to get the spikes aligned.