OK,

Here is what I found.  But first, a few disclaimers.  They test system is not calibrated.  Frequency identification is right on but the intensity scaling is relative not in dBs.  The sampling rate it uses is 11Khz so it can only give measurements up to 5500 Hz.  I looked at the range up to about 1kHz, but mostly concentrated on th erange up to 250 Hz.  The mic was placed at the mouth of the horn at its center.

The results (full size imperial):

There are noticable peaks at 70-75 Hz and less so at 100 Hz.  Also a peak around 250Hz.  The 250 I could hear and was gratified to find that when I engaged my equalizer (set by ear), the response got much flatter, although a bit heavy on the bass.  What can I say, I like a little bass.

As for the 75 Hz peak, it showed up in almost all configurations of the mic and speaker placement.

My imperial has one Dayton Pro 15" and one Eminence Gamma 15".  The Dayton is fs= 36 Hz, Qts = .37; the Gamma is fs= 33 Hz and Qts= .30

I also made use of an SPL meter and my old Carver test CD with 1/3 octave centered pink noise and measured the spl at about 1 meter from the speaker  .8 m from the floor.  Here are the  results:

Frequency (Hz) / SPL (dB)
25 / 60
31.5 / 63
40 / 66
50 / 70
63 / 73.5
80 / 74
100 / 73
125 / 73
160 / 76
200 / 79
250 / 81
315 / 81
400 / 82
500 / 84
600 / 85
800 / 85
1000 / 84.5

This is with the Imperial in the middle of the room, no corner or wall help for the bass and no equalization.

I found it interesting to note that I was picking up measurable subsonic output from the imperial during pink noise testing, and it wasn't from background noise.  Like 5-10 Hz!

What does it all mean?  Perhaps the higer Fs driver will help avoid the 70 Hz peak.  In listening that peak is not that noticable and almost never objectionable sounding.  The peak that I hear and dislike most is the 250Hz.  That's probably something going on with the back chamber or a cabinet resonance.

We'll I could keep writing but instead I'll wrap it up and answer any questions about what I tested you guys might have (that is if I can).

Jim P.

ps.  I had a student stop in after school because he wanted to hear the Imps turned up, something I can't really do during the school day.  I had Gary Glitter's Rock and Roll part whatever which is far from HI FI but has some decent bass.  I think he was stunned at the sound.  Now he's trying to figure out how to get one in his car.

Stv,

No standing waves noticed the way I had the speakers configured for testing, although I wasn't specifically looking (or listneing) for one.  The room is 30' wide by 50' long with lab stations in half an desks in the other half.  Tile floor, acoustic ceiling tiles and drywall walls.  Pretty reflective overall but the bass seemed pretty uniform.  Louder near the walls and corners as expected but no big nulls or antinodes.

Jim

Braggi,

I used 2 measurement methods.  The table of values was with a dB meter reading 1/3 octave pink noise.  I think this method was less sensitive to narrow peaks, smoothing the overall appearance of the response.  The FFT method showed very narrow bands of frequency almost individual frequencies, and with this method a peak showed up at 250 hz and also at 70Hz.  The 250 hz peak doesn't seem to show in the spl meter data, but it is there.

Jim P