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Fathom f112 Measurements

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Measurements were performed using the Sample Champion program developed by Paolo Guidorzi of Purebits. The program is a Maximum Length Sequence (MLS) program that can generate an impulse response from this pseudorandom signal. The Fast Fourier Transformation is applied to the impulse response to generate the system frequency response. The operating principle is the same as that of the well known MLSSA program.

Test samples were taken using 16 bit resolution with a 48 kHz sampling frequency. Fast Fourier Transformations were performed at 64K allowing for a frequency resolution of .73 Hz, which is more refined than even 1/24th octave resolution at the lowest octave; the A0 key on the piano has a fundamental frequency of 27.5 Hz.

IR 90dB_1m.jpg

Figure 1: Impulse response.

Figure 1 is the subwoofer’s impulse response. The basic shape of the curve is typical of low frequency driver; here we see a fairly smooth curve that decays within a few cycles indicating good damping characteristics.

FR 80dB_1m.jpg

Figure 2: Frequency response.

Figure 2 shows the nearfield frequency response for a sound pressure level of 80 dB when measured at 1 meter. Significant roll off starts to occur around 21 to 22 Hz based on this measurement, which is within reasonable measurement tolerance of the published specifications.

FR 90-109dB_1m.jpg

Figure 3: Power compression curves.

Figure 3 shows frequency response at various SPL levels at 1 meter. Measurements were taken nearfield with peak sound pressures of 90, 100, 105, and 109 dB when measured at 1 meter from the sub. Analysis of these curves must include some understanding of measurement and instrumentation limitations. Due to environmental conditions prevailing in a Chicago winter, ground plane measurements were precluded as a possibility and due to the high output capabilities of this sub, nearfield measurement of max SPL caused clipping of the microphone preamp as volume is increased.

Tests I performed indicate that the sub can get between 105 and 109 dB at 1 meter before compression using a wide band frequency input such as an MLS signal. Consideration of measurement accuracy at high SPL must be tempered with understanding that MLS testing is sensitive to any nonlinearity in the measurement, including from test gear. The microphone preamp indicated clipping at 109 dB under the maximum gain adjustment I could make, so it is very likely that the f112 can actually get higher than indicated by these measurements.

JL SPL Plot.jpg

Figure 4: Maximum in room SPL at 2 meters by frequency.

Figure 4 was provided by JL Audio with a reported maximum rms SPL output of over 117 dB for a single frequency, a 62 Hz sine wave, and 112 dB averaged over a range between 25 and 62 Hz with THD between 5.2 to 9.9% for various frequencies, in room at 2 meters.

For real world input signals, such as music, the frequency content will be somewhere between these two limits and correspondingly, the SPL output will also be between these two bounds. Either way, SPL that exceeds 109 dB is a substantial amount of output.

 

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Recent Forum Posts:

clubfoot posts on April 08, 2007 16:37
Review - broken link

The correct location for inf-rooms_3: http://www.infinitysystems.com/home/technology/whitepapers/inf-rooms_3.pdf
clubfoot posts on April 08, 2007 12:24
billy p, post: 260136
driving home on Friday a commercial from a local Toronto retailer made mention of the the new JL's having arrived. They went as far, as to call them the subwoofer of the Gods. Auditions will be for serious audiophiles only and by appointment only.
Then, again I'm not surprised because I would line up to have a listen .
Ps: I am serious, just don't have that kind of money.

Billy p
The local Toronto retailer would be Kromer and I just auditioned the f113 yesterday for a possible purchase at the end of the month. To me the f113 is not a WOW sub (spl) it is more of a “I didn't know those sounds/effects were there!” It is one of those rear audio components that reveals “stuff” that you could not feel before, because with this sub you do not need tactile transducers.

Go listen/feel for yourselves.
billy p posts on April 02, 2007 08:37
Hehe

driving home on Friday a commercial from a local Toronto retailer made mention of the the new JL's having arrived. They went as far, as to call them the subwoofer of the Gods. Auditions will be for serious audiophiles only and by appointment only.
Then, again I'm not suprised because I would line up to have a listen .
Ps: I am serious, just don't have that kind of money.

Billy p
jaxvon posts on March 28, 2007 20:23
gene, post: 258726
David's review and forum response has inspired me to request a review sample of their Gotham sub. Problem is I loath carrying a 300lbs sub up two flights of steps to my theater room, and knowing me, I'd want at least two of them

That's what JL's own top end demo room uses. Bryston electronics, PMC speakers, and two Gothams on the front soundstage.
no. 5 posts on March 27, 2007 20:06
billy p, post: 258756
I fully concur with post 14 & 18. Well said, no.5

Oh, stop… you'll make me all embarrased.

Thanks though.
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