Preliminary Investigation of the Audez'e LCD-3 and LCD-2 Page 2
Here's where things start to get a bit messy. I mentioned at the start that I've been measuring some Sennheiser HD 800s for a system characterization experiment. Here are the left and right THD+noise plots for the HD 800 with measurements taken on three different days during the same period I was measuring the LCD-3 headphones.
Here are the THD+noise at 90dB measurements of the four different LCD-3 headphones.
First, you'll notice the LCD-3 measurements are a lot more noisy and erratic than the HD 800. This measurement is very sensitive. If a truck goes down the street outside my house you'll see it here. It's also possible that noise on the incoming AC line might disturb these measurements. (I do have power conditioning, but I simply can't guaranty how well it performs.) It's exactly these kinds of results that have me investigating the performance of my system.
The problem is, while I do see some variability in the HD 800 THD plots of about the amplitude I'd expect, the variability of the LCD-3 plots is far wider. I usually leave the room during the THD plots, but in a couple of cases I was in the room sitting quietly watching as the plot was being taken. In one case (2312454C), I saw the elevated and noisy nature of the plot, and there wasn't any outside noise apparent. Plots like this could mean any number of things. To me, it looks like what I'd expect to see if something was rattling around inside the headphones around a certain frequency. For example, wires behind the driver might be moving about and making noise against something. That's just a guess though, just about anything could be going on. I don't really know what to say about the THD+noise graphs of the LCD-3s above, except to say the gear seemed to be working better than that when measuring the HD 800 (and other cans) that I was testing during the same period of time.
Apart from being erratic and noisy, some of the headphones exhibit a fairly wide noisy peak centered around 1.5kHz. It's not absolutely consistent, but this peak in THD+noise happens most on 2312260 and 2312476 --- the same two headphones without the frequency response step.
Let's look at some summary graphs ...