EP500 Performance Tests
While subjective commentary can give good insights as to how a product performs and how the listener/reviewer perceives its performance within the confines of their listening environment, the proof is in the pudding so to speak. This is why it's always good to have some supplementary measurements and analysis to see if those measurements correlate to what we are hearing. Since frequency response can demonstrate the product bandwidth or tonality, this is a good start.
To go one step further, one must test this frequency response at various power levels to determine power bandwidth uniformity and freedom from excessive compression. With that in mind, we ran some frequency vs SPL tests (borrowed from our First Look Article ) on the EP500 at various output levels to validate Axiom's claim quoted below:
"Our DSP system wants things to go smoothly all the time - no bumps in the road. Using a digital roadmap, the XLF controls every frequency from 17Hz to 100Hz, never deviating more than +-1.5dB through this entire range."
EP500 SPL vs Frequency Plots 1 meter 4pi measurements
Thus the Axiom Audio claim about maintaining +/-1.5dB 20Hz to 100 Hz for the EP500 through the entire range is in fact true providing that the SPL output is kept to around 80dB (anechoic) which equates to about 91dB in a real room or +/-3dB under 92 dB (anechoic) which equates to about 103dB or so in a real room.
Editorial Notes on 4pi and 2pi Steradians Environments
4pi steradians describes a complete sphere. 2pi steradians describes a half a sphere or hemisphere. Therefore, when we measure outside on a pole we say we're measuring in 4pi. Or if we've got an anechoic chamber with a wire floor so that we are completely surrounded on all six sides by big ole fiberglass wedges we say that's 4pi. If we have a chamber with a hard floor into which we put a baffle and speaker, with the other five surfaces being those fiberglass wedges then that's 2pi. This is one way to measure an in-wall speaker. Similarly, if we go outside, dig a hole and put a speaker-in-a- baffle over that hole and shooting up, then we're measuring in 2pi.
1 meter in room measurement (ground plane technique, unsmoothed)
The green trace represents the EP500 while the purple trace is from my reference sub, the RBH 1010-SEP. Notice the EP500 has significantly more output below 25Hz. You can see the slight dip at the box tuning frequency of 24Hz in the EP500, but then the driver response below tuning is linearized via DSP processing to help extend the low frequency range. I noticed a slight bump of about 3dB centered at 44Hz, the second impedance peak in the open port response. I am uncertain of its cause and could only speculate that it indicates slight system overshoot which isn't uncommon with high mass drivers such as the one used in the EP500.
The purple traces represent the bass response of my dual RBH Sound 1010-SEP subwoofers while the blue trace represents all three subwoofers (dual RBH 1010-SEP's and the Axiom EP500). Notice the dip between 80Hz and 100Hz is virtually eliminated by adding another subwoofer into my system. Ideally four subwoofers strategically placed though out the room would yield bass nirvana for virtually all listeners, but three subs seem to do commendably well also.
