Production measurements with the final crossover.
Lets start with a simple on-axis measurement that you see with just about any loudspeaker. These are stand mounted loudspeakers, with my 28" stands the tweeter height is at 38". This is within the range of the average male in the seated position. All measurements are done as they would be used, stand mounted. Measurement distance is 53" with Liberty Praxis and shown 1/3rd octave smoothed.
I show data to 200Hz which is near the limit of what is accurate with my measurement method. I'll show near field data later for a better picture of the low-end. I have about 4-5db of baffle step designed into the crossover. Most of the ripples up top are baffle diffraction related. Wool felt or other methods should fill them in a little, or you can just leave them alone, off-axis they mostly go away and the audibility of diffraction effects are a topic of debate.
Here are the horizontal off-axis measurements. These are very important measurements for any loudspeaker design. I put very high priority on smooth off-axis response. Why? Because research shows that its very important. Not just for off-axis listening, but for on-axis also. Most of what your going to hear at the listening position is reflected energy so having the correct timbre REALLY depends upon the total in-room response.
This is on-axis (yellow), 15 degrees off-axis (red), 30 degrees (light blue), and 40 degrees (dark blue). You will notice the dip @ the crossover (1.6K). This is due to the narrowing of of the midwoofer's response off-axis transitioning over to the wide dispersion of the tweeter. The crossover is in this region so the main thing to look for is good smooth off-axis behavior. Good designs don't show large dips or strange frequency response anomalies. Up top, you see the narrowing of the tweeter's response as you move off-axis. This is determined by the size of the dome, 25mm in this case.
Next up is the vertical off-axis response. Believe it or not, vertical off-axis is less important than horizontal off-axis. Why? You have to ask God about it. He put ears on the sides of our heads rather than on our chin & forehead but I digress. Two graphs on this one because this got ugly with all the lines on one page.
Below the 38" measurement (towards the floor). Not much to report here. Measurements at 25", 30" & 38" for reference.
Above the 38" seated measurement is important too! These ranged from 38", 48" & 56" measurement heights. Note, these are from a measurement distance of only 50" so the 56" measurement is not reflective of a typical standing position. It would be the response aimed at your ceiling at any normal distance. The 48" would be a reasonable standing response from a 8ft listening distance. At this position the system is still +/- 2db which means it will sound very close to the same standing as it does in the sitting position.
Everyone seems to get excited about the low frequency performance of the XBL^2 drivers. By the way, the flat BL curve has nothing to do with low frequency response, outside of the fact that you need lots of clean stroke to achieve reasonable SPLs. Its still a matter of balancing the other properties of the transducer that gives you good low frequency performance that is clean, musical and balanced. Lots of clean linear stroke gives you much more usable headroom.
Most 6"-7" midwoofers wouldn't have the usable stroke to give you good output down this low. Most engineers choose T/S parameters such that they get to about 50-55Hz because that is all the typical 6"-7" driver will give you.
Note: These are REAL close-mic measurements (with the port merged with the EX-6.5). This is the ACTUAL response you will get from the loudspeaker in the PE 0.5ft^3 cabinet. These are not simulations. In addition, this is usable output. Usable means that ONE speaker is capable of 102db @ 1M before low frequency content will reach the usable x-max of the transducer. Translation for you non-loudspeaker geeks, you can turn them up and the woofer doesn't bottom, making nasty noises.
About 38Hz F3 without any room gain. In-room, I'd expect your going to see solid output @ 30Hz, depending upon your boundary conditions.
And finally, a speaker isn't much good if it requires a Krell to drive it.
Note: The low is around 350Hz @ 4.8 ohms. The high (ignoring the double hump from the ported box) is around 950Hz @ 7.4 ohms. Ignoring the resonant box (all ported alignments show the same behavior) this is very close to a purely resistive load that varies by +/- 1.5 ohm from 100Hz - 20K. Phase angle stays reasonable throughout. Its hard to tell from the graph but over 100Hz its better than +/- 20 degrees. You only go over 30 degree phase angle as you near the tuning frequency of the enclosure.
You can also see the bass tuning is around 35-36Hz. A 40-50W amp, even a tube amp will drive these with ease. Recommended power would be 40-100W. You can have more, but the loudspeaker won't benefit from >100W.
