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Subwoofer Measurements

Reviewed on: SoundStage! Access, September 2018

I measured the IW-S10EQ’s frequency response using an Audiomatica Clio FW 10 audio analyzer with the MIC-01 measurement microphone. For the frequency-response measurement I used the close-miked technique, with the microphone placed as close as possible (about 1/4”) to the woofer. For the power-compression measurement, I placed the mike on the ground 2m from the front of the sub.

I performed CEA-2010 measurements using an Earthworks M30 mike and M-Audio Mobile Pre USB interface with the CEA-2010 measurement software running on the Wavemetric Igor Pro scientific software package. Measurements recorded peak output at 2m. I measured the sub twice: once in a 48”-high box made with 6” studs 16” on-center (interior volume 2.08cf), and once in a box made with 4” studs but otherwise the same dimensions (interior volume 1.32cf). These enclosures reflect typical volumes encountered in in-wall mounting.

The two sets of measurements I’ve presented here -- CEA-2010 and the traditional method -- are essentially the same. CEA-2010 mandates that no matter how the sub is measured, the results must be scaled to the equivalent of a measurement at a distance of 1m using peak values. But the traditional measurement technique used by some audio websites and manufacturers reports results at 2m RMS equivalent, which is 9dB lower than CEA-2010. An L in the tables below indicates that the output was dictated by the subwoofer’s internal circuitry (i.e., Limiter), and not by exceeding the CEA-2010 distortion thresholds. Averages are calculated in pascals. (For more information about CEA-2010, see my “CEA-2010 Measurement Manual.”)

Frequency response

This chart shows the IW-S10EQ’s frequency response with the crossover frequency set to maximum and auto EQ off, and with the sub mounted in fake walls made with 4” and 6” studs. This isn’t the flat response we typically see from freestanding subs, because those subs are all factory-EQed for flat response -- something not possible with an in-wall sub because the enclosure volume is not known. However, it does show that the sub has usable response down to about 23Hz.

Modes

Above, you can see the effects of the app’s EQ modes. Their effects are pretty subtle: Cinema basically boosts the bass below 45Hz by about 1.5dB, while Music boosts the midbass by about 1.5dB in a peak centered at 72Hz.

EQ

This chart shows the effects of auto EQ with the IW-S10EQ placed in the corner of my listening room. The microphone was placed near my listening position, about 1’ from my head; I placed the smartphone in the same position when I ran the auto EQ. It definitely made the in-room response flatter, though it left most of the peak at 38Hz unaffected.

Power compression

This chart shows how the IW-S10EQ’s frequency response (measured here in Normal mode from 2m) was affected by increases in volume. I measured starting at 88dB, calibrated at 63Hz, then raised the level 3dB for each successive measurement. You can see that the function of the sub’s internal limiter doesn’t change significantly with frequency.

CEA2010 2.08

CEA2010 1.32

If you haven’t seen subwoofer distortion numbers before and are used to looking at amplifier distortion specs, some of these may look high. But in loudspeakers, and especially subwoofers, much higher distortion levels are the norm, though typically such levels are inaudible. The generally accepted threshold for audibility of distortion in subwoofers is 10% THD; CEA-2010 thresholds permit maximum distortion of around 30% THD.

The maximum output of the IW-S10EQ at higher frequencies isn’t impressive; from 40 to 63Hz, it’s roughly in line with what I’ve measured from some budget 10” standalone subs, and typically about 6dB lower than the best 10” standalone subs. But at lower frequencies it delivers output comparable to that of the best standalone 10” subs, and even delivers measurable output at 16Hz. This means you won’t get a lot of punch from a single IW-S10EQ, but neither will the sound thin out when you crank it up, as it can with subs that deliver a lot of output from 40 to 63Hz but much less from 20 to 31.5Hz. The IW-S10EQ’s output is a little lower from the smaller box made with 4” studs -- down an average of 3.7dB from 40 to 63Hz, and down 2.1dB from 20 to 31.5Hz.

CEA-2010 comparison

This chart tracks the CEA-2010 results of the IW-S10EQ (blue trace) compared with two standalone 10” subs.

. . . Brent Butterworth
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I measured the frequency response of the Monoprice Monolith THX Ultra 15” (product no. 24458) with an Audiomatica Clio FW 10 audio analyzer and MIC-01 measurement microphone, and in two different ways: the ground-plane technique, with the microphone on the ground 2m in front of the sub, and the result smoothed to 1/6 octave; and the close-miked technique, with the mike placed as close as possible (about 1/4”) to the woofer and ports, and the port responses scaled and summed with the woofer response. I show the close-miked results here because those graphs are clearer; the ground-plane results were within a couple of Hz of them. For the power-compression measurement, I placed the mike on the ground 2m from the front of the sub.

I performed CEA-2010 measurements using an Earthworks M30 mike and M-Audio Mobile Pre USB interface, with the CEA-2010 measurement software running on the Wavemetric Igor Pro scientific software package. Measurements recorded peak output at 2m. (For more information about CEA-2010, see this article.)

The two sets of measurements presented here -- CEA-2010 and the traditional method -- are essentially the same. CEA-2010 mandates that no matter how the sub is measured, the results must be scaled to the equivalent of a measurement at 1m distance using peak values. But the traditional measurement technique used by some audio websites and manufacturers reports results at 2m RMS equivalent, which is -9dB lower than CEA-2010. An “L” next to the result indicates that the output was dictated by the subwoofer’s internal circuitry (i.e., limiter), and not by exceeding the CEA-2010 distortion thresholds. Averages are calculated in pascals.

Frequency response

This chart shows the Monolith THX Ultra’s frequency response with the crossover frequency set to maximum and the sub set to Extended (rather than THX) mode. I’ll show the effects of the crossover and the THX mode in the next graph. You can see that the bass output gradually rises as more ports are opened, and that the response is pretty much flat up to 200Hz. With two and three ports open, the -3dB point (using the peak of the sub’s response curve as that +3dB reference point) is 14Hz. Even in sealed mode, it hits 16Hz.

Frequency response various modes

This chart shows the response of the crossover and the effect of the THX mode, measured with all of the sub’s ports sealed. The crossover frequency was 80Hz, and, as the chart shows, the control is accurately calibrated (not usually the case), and the low-pass function is about -22dB/octave. The THX mode reduces bass output by about 4dB at 20Hz.

Power compression

This chart shows how the Monolith THX Ultra’s frequency response is affected by increases in volume. I measured this with all three ports open in THX mode, starting at 106dB at 2m, calibrated at 63Hz, then raised the level 3dB for each successive measurement. You can see that the Monolith’s frequency response doesn’t change as it reaches its output limits; with many subs -- especially those with limiters that are set with higher thresholds, which allow greater distortion -- the bass response begins to weaken as the sub reaches the limits of its capabilities. Unfortunately, I had to return the sub in a hurry due to an upcoming trip, and didn’t have time to measure its output in the Extended (non-THX) mode, but based on the frequency-response measurements and what I heard, I expect the Extended-mode output measurements would average about 2dB higher than THX mode.

CEA-2010 ported

CEA-2010 sealed

Please note that if you haven’t seen subwoofer distortion numbers before and are used to looking at amplifier distortion specs, some of these may look high. But in loudspeakers, and especially subwoofers, much higher distortion levels are the norm, and typically are inaudible. The generally accepted threshold for the audibility of total harmonic distortion in subwoofers is 10%, and CEA-2010 thresholds permit a maximum THD of around 30%.

The Monolith THX Ultra’s CEA-2010 output numbers are excellent -- among the best I’ve measured for a sub of this size and configuration.

CEA-2010 comparison

This chart tracks the CEA-2010 results of the Monoprice Monolith THX Ultra (blue trace) compared with three other ported subs that are somewhat comparable: two 15” models (Hsu Research VTF-15H Mk.2 and Klipsch R-115SW), and one 13” model (SVS PC13-Ultra). The Monoprice doesn’t have quite as much output at higher bass frequencies as some models, but has more deep-bass output than the three other models, and a more consistent maximum output throughout the two octaves covered in the chart.

. . . Brent Butterworth
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I measured the Adante SUB3070’s frequency response using an Audiomatica Clio FW 10 audio analyzer with the MIC-01 measurement microphone. For the frequency-response measurement I used the close-miked technique, with the mike placed as close as possible (about 1/4”) to one of the woofers. For the power-compression measurement I placed the mike on the floor, 2m in front of the sub.

I performed CEA-2010 measurements using an Earthworks M30 mike and M-Audio Mobile Pre USB interface, with the CEA-2010 measurement software running on the Wavemetric Igor Pro scientific software package. Measurements recorded peak output at 2m.

The two sets of measurements I’ve presented here -- CEA-2010 and the traditional method -- are essentially the same. CEA-2010 mandates that no matter how the sub is measured, the results must be scaled to the equivalent of a measurement taken at a distance of 1m using peak values. But the traditional measurement technique used by some audio websites and manufacturers reports results at an RMS equivalent of 2m, which is 9dB lower than CEA-2010. An L next to the result indicates that the output was dictated by the subwoofer’s internal circuitry (i.e., limiter), and not by exceeding the CEA-2010 distortion thresholds. Averages are calculated in pascals. (For more information about CEA-2010, see this article.)

Frequency response

This chart shows the SUB3070’s frequency response with the crossover frequency set to maximum and the sub set for its Flat, Cinema, Night, and Music modes. Flat mode is indeed almost perfectly flat from 30 to 130Hz. Night mode basically lowers the output by about 3dB. Cinema mode boosts output by a maximum of about 3dB, centered at 80Hz. Music mode does the same, but centers the boost at 40Hz. The -3dB point (using the peak of the sub’s response curve as the +3dB reference point) is 18Hz, and the low-pass function of the SUB3070’s crossover is -24dB/octave.

Frequency response equalization

This chart shows the effects of the auto EQ processing with the SUB3070 placed in the corner of my listening room -- not the best spot for a single subwoofer if you want flat response, but it gives the auto EQ circuit a tougher challenge. The mike was placed near my listening position, about 1’ from my head; I placed the smartphone in the same position when I ran the auto EQ. In this case, the auto EQ processing seems to be making some pretty smart adjustments, flattening the response in general and ignoring the suckout at 73Hz, which is impossible for EQ to fill because it’s a cancellation -- the more energy you pump into it, the more will be canceled. Still, I was able to get a flatter curve using the parametric EQ function.

Frequency response power compression

This chart shows how the SUB3070’s frequency response (measured here in Flat mode from 2m) is affected by increases in volume. I measured starting at 94dB, calibrated at 63Hz, then raised the level 3dB for each successive measurement. You can see that the sub’s internal limiter seems to be most restrictive between 30 and 60Hz.

CEA-2010

If you’re used to looking at amplifier distortion specs, some of these may look high. But in loudspeakers, and especially subwoofers, much higher distortion levels are the norm, and typically are not audible. The generally accepted threshold for audibility of distortion in subwoofers is 10% THD; CEA-2010 thresholds permit maximum distortion of around 30% THD.

The output of the SUB3070 at 63Hz is, to the best of my recollection, the highest I’ve measured from a sub of this size. However, from there it falls rather quickly, albeit smoothly. Clearly, the SUB3070 is no home-theater bruiser; it focuses more on fidelity with typical music content, which seldom has much going on below 40Hz.

CEA-2010 comparison

This chart tracks the CEA-2010 results of the SUB3070 (blue trace) and three other subwoofers that are to some extent comparable, though all are less expensive. While at 63Hz the SUB3070 beats even the mighty SVS PC13-Ultra, its bottom-octave output is more akin to that of a typical, less-expensive 12” model.

. . . Brent Butterworth
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I measured the BasX S12’s frequency response using an Audiomatica Clio FW 10 audio analyzer with the MIC-01 measurement microphone. For the frequency-response measurement I used the ground-plane technique, with the microphone on the ground 2m in front of the subwoofer, and smoothed the result to one-sixth of an octave. For the power-compression measurement, I placed the mike on the ground 1m in front of the sub.

I performed CEA-2010 measurements using an Earthworks M30 mike and M-Audio Mobile Pre USB interface, with the CEA-2010 measurement software running on the Wavemetric Igor Pro scientific software package. Measurements recorded peak output at 2m.

The two sets of measurements presented in the Maximum Output table are essentially the same, just scaled differently to suit the two different reporting methods in common use for subwoofer output measurements. The CEA-2010 standard mandates reporting at 1m peak output, while the traditional reporting standard used by some audio websites and manufacturers reports results at 2m RMS equivalent. Thus, the CEA-2010 numbers are 9dB higher than the numbers presented under the traditional reporting standard. An L next to the result indicates that the output was dictated by the subwoofer’s internal circuitry (i.e., limiter), and not by exceeding the CEA-2010 distortion thresholds. Averages are calculated in pascals.

Frequency response

This chart shows the BasX S12’s frequency response with its crossover-frequency control set to maximum and to approximately 80Hz. You can see a small peak in the response at about 62Hz. This peak (which also showed up, to a lesser degree, in close-miked measurements) is insignificant; its effects will be swamped by the much larger effects of room acoustics, or possibly eliminated if you use a receiver or surround processor with auto EQ. With the peak taken into account, the ±3dB response is 26-119Hz. If you ignore the peak, the response is 22-155Hz. The crossover rolloff is -17.8dB/octave, -5.0dB at the 80Hz setting, which means that this control is more accurately calibrated than most subwoofers’ crossover-frequency controls.

Power compression

This chart shows how the BasX S12’s frequency response is affected by increases in volume. This is an excellent result -- the deep-bass output of most subwoofers is greatly reduced relative to midbass output at high levels. I measured this beginning at 100dB at 1m, calibrated at 63Hz, then raised the level 5dB for each successive measurement. Between 40 and 80Hz the level doesn’t increase significantly once it hits 110dB, though it does rise by a few more dB in the bass.

CEA-2010 ported

Please note that if you’re used to looking at amplifier distortion specs and haven’t seen subwoofer distortion numbers before, some of these may look high. But in loudspeakers, and especially subwoofers, much higher distortion levels are the norm, and typically are not audible. The generally accepted threshold for audibility of distortion in subwoofers is 10% THD, and CEA-2010 thresholds permit maximum distortion of around 30% THD.

CEA-2010 comparison

This chart tracks the CEA-2010 results of the BasX S12 (blue trace), compared with three other subwoofers priced in the mid-three-figures: the Outlaw Ultra-X12 (red trace, max output mode, $659), the Rogersound Labs Speedwoofer 10S (orange trace, $399), and the SVS PB-2000 (green trace, $799.99). The BasX S12 has 2-3dB more output than the identically priced (but 25% smaller by volume) Speedwoofer 10S in the second octave of bass (40-63Hz), and about the same output in the bottom octave (20-31.5Hz). Not surprisingly, the larger, more expensive subs outperform the BasX S12, but one could buy two BasX S12s for the price of one PB-2000.

. . . Brent Butterworth
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I measured the Ultra-X13’s frequency response using an Audiomatica Clio FW 10 audio analyzer with the MIC-01 measurement microphone. For the frequency-response measurement I used the ground-plane technique, with the microphone on the ground 2m from the front of the subwoofer, and smoothed the result to 1/6 octave. For the power-compression measurement, I placed the mike on the ground 1m from the front of the sub.

I performed CEA-2010 measurements using an Earthworks M30 mike and M-Audio Mobile Pre USB interface with the CEA-2010 measurement software running on the Wavemetric Igor Pro scientific software package. Measurements recorded peak output at 2m.

The two sets of measurements I’ve presented here -- CEA-2010 and the traditional method -- are essentially the same, but the traditional measurement technique used by some audio websites and manufacturers reports results at 2m RMS equivalent, which is -9dB lower than CEA-2010. An L next to the result indicates that the output was dictated by the subwoofer’s internal circuitry (i.e., limiter), and not by exceeding the CEA-2010 distortion thresholds. Averages are calculated in pascals. (For more information about CEA-2010, see this article.)

Frequency response

This chart shows the Ultra-X13’s frequency response in sealed and ported modes, and in sealed mode with its internal crossover set to 80Hz. The ±3dB response is 19-161Hz in sealed mode and 24-161Hz in ported mode. The crossover rolloff is -28dB/octave, -4.3dB at the 80Hz setting, which means this control is more accurately calibrated than most subwoofers’ crossover-frequency controls.

Power compression

This chart shows how the Ultra-X13’s frequency response is affected by increases in volume. This is an excellent result; with most subwoofers, deep-bass output is greatly reduced relative to midbass output at high levels. I measured this starting at 100dB at 1m, calibrated at 63Hz, then raised the level 5dB for each successive measurement. The frequency response remains essentially consistent at all levels, although because of the limiter, output doesn’t increase much above 120dB (green trace) except at very low frequencies.

CEA-2010 ported

CEA-2010 sealed

Please note that if you’re used to looking at amplifier distortion specs and haven’t seen subwoofer distortion numbers before, these may look high. But in loudspeakers, and especially subwoofers, much higher distortion levels are the norm, and typically are inaudible. The generally accepted threshold for audibility of distortion in subwoofers is 10% THD, and CEA-2010 thresholds permit maximum distortion of around 30% THD.

The Ultra-X13’s CEA-2010 output numbers are very good, and competitive with the leading subwoofers in its price range.

CEA-2010 comparison

This chart tracks the CEA-2010 results of the Ultra-X13 in ported (blue trace) and sealed (orange trace) modes compared with: the Outlaw Ultra-X12 (red trace, maximum output mode), the SVS PC13-Ultra (purple trace, ported mode), and the Hsu Research VTF-15H Mk2 (green trace). The Ultra-X13 is roughly comparable in ported mode to the SVS PC13-Ultra in ported mode, with a couple dB less output in the middle bass and a couple dB more output in the deep bass.

. . . Brent Butterworth
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