SSS.6.115 - Research Supplement: Flow-Through Silencers vs. Conventional Silencers. Head-to-Head Detailed Comparison - Nomad-Ti vs. FLOW 762 Ti vs. Thunder Chicken (Members Only)
/Dead Air Nomad-Ti, HUXWRX FLOW 762 Ti, and Q Thunder Chicken on a .308WIN Bolt Action Rifle with 20-inch Barrel
There are a variety of technologies implemented in modern rifle silencers. Principally, silencers reduce the severity of the signature produced by a small arm weapon system by modifying the propagation of combustion gasses such that they enter the ambient atmosphere at a lower temperature and pressure than they would otherwise, had a silencer not been installed on the weapon. These parametric differentials, along with the rate of gas propagation, dictate the resulting suppressed small arm signature.
The severity of a suppressed small arm weapon signature, to the human inner ear, is quantified by the PEW Science Suppression Rating (Figure 1). As the Suppression Rating is a Damage Risk Criterion (DRC), it only expresses the degree to which a human may experience hearing damage. Although complex signature characteristics are included in its computation, the end result is only a DRC. Suppression Rating Rankings can be found in Section 7 of the Standard.
The nature of human inner ear response, and human interpretation of such response, dictates further signature examination if one desires information outside the purposes of DRC use. For example, end users may be interested in “how a silencer sounds,” rather than in the hearing damage risk potential of using the silencer on their weapon. The two phenomena are not necessarily coupled for all users.
The Suppression Rating DRC allows the end user to group silencers with similar hearing damage risk potential on a variety of weapon systems. After such grouping, further analysis can provide insight into the aforementioned phenomena. To that end, three silencers evaluated by PEW Science are included in this members-only Research Supplement to examine relative First Round Pop (FRP) and overall sound signature suppression performance characteristics. The silencers in this group were selected for their very similar holistic sound suppression performance; their similar PEW Science Suppression Rating on a supersonic centerfire bolt action rifle. The three silencers behave differently, despite their similar performance. Silencers with similar suppression performance sometimes have very different flow restriction, or back pressure, partially characterized by the PEW Science Omega Back Pressure Metric (Figure 2). These are three examples of such silencers.
Fig 1. PEW Science Suppression Rating Scale
The published Sound Signature Reviews of these three silencers, with supersonic ammunition, are linked below:
Because the Suppression Rating is a DRC, it characterizes the postulated risk of hazard to bystanders, or the weapon operator, from a suppressed small arm weapon system. Despite achieving a similar Suppression Rating, some silencers may have certain signature characteristics that differ from others, and those differences are of interest to users, as noted above.
Furthermore, sound suppression performance of centerfire rifle silencers, particularly during the first shot, is of significant concern to many weapon system operators. High sound signature amplitude during the first shot from a suppressed weapon system is referred to as First Round Pop (FRP). Prior to the weapon system being fired, a sound suppressor is filled with air from the surrounding environment; this air occupies the internal silencer volume and supports ancillary combustion during the first shot. It is this ancillary combustion that may increase sound signature relative to subsequent shots. The FRP phenomenon is present and measurable in all suppressed systems unless the internal silencer atmosphere is purged such that ancillary combustion is not supported within the silencer.
Fig 2. PEW Science Silencer Relative Back Pressure Metric, Omega, For 30 Caliber Rifle Silencers
Typically, silencers possessing a very low Omega Metric exhibit lower sound suppression performance, but there are several significant exceptions. Although changes to gross gas flow rate (flow restriction, or back pressure) strongly correlates to sound signature suppression, there are other flow dynamics and frequency components of silencer sound signatures that result in varying signature severity to the human inner ear for a given suppressed system. These gas dynamics can significantly influence some signature characteristics. Furthermore, certain personnel may have preexisting hearing damage or other hearing sensitivity characteristics that differ from the 95th-percentile inner ear response with which the PEW Science Suppression Rating correlates. The impact of these differences on the human perception of silencer sound suppression performance has been quantified by PEW Science.
Section 6.116.1 provides an overall sound suppression performance summary at the muzzle and shooter’s ear.
Section 6.116.2 provides detailed comparisons of the sound signatures measured at the muzzle.
Section 6.116.3 provides detailed comparisons of the sound signature measured at the shooter’s ear.
Section 6.116.4 presents some concluding thoughts.
This research supplement is intended to provide more information to PEW Science members with regard to specific sound signature characteristics of the tested configurations in the aforementioned reviews and to help frame objective loudness comparisons between three supersonic 308 rifle silencers that possess similar holistic sound suppression performance. Both FRP and total sound signature suppression regimes are examined. This supplement is part of ongoing PEW Science small arm weapon system sound signature research.
6.116.1 Overall Sound Suppression Performance Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Q Thunder Chicken is postulated to sound the quietest, with the HUXWRX FLOW 762 Ti being the loudest, during the first shot. During the first shot, bystanders will most likely perceive the FLOW 762 Ti as “boomy,” with bystanders potentially perceiving the Nomad-Ti as having a “lower tone” than the Thunder Chicken.
The FLOW 762 Ti is noticeably louder than the Nomad-Ti and Thunder Chicken during FRP, to bystanders, across all frequency sensitivities of the human inner ear.
On average, the FLOW 762 Ti is postulated to sound the quietest to bystanders, with the Nomad-Ti being the loudest. Although the HUXWRX FLOW 762 Ti is quieter than the Nomad-Ti to bystanders, on average, it may still be perceived to bystanders as “boomy.”
On average, the Thunder Chicken signature is approximately 14% less severe than the Nomad-Ti signature, to bystanders. The Flow 762 Ti signature is approximately 17% less severe than the Nomad-Ti signature to bystanders, on average.
Shooter Perception:
To personnel firing the weapon, the Nomad-Ti is the quietest silencer during the first shot. The FLOW 762 Ti is the loudest to the shooter, during the first shot. During FRP, the Nomad-Ti may also have a “lower tone” to the shooter than the Thunder Chicken, as is postulated for bystanders.
Just like to bystanders, the weapon operator is postulated to perceive a more “boomy” signature with the FLOW 762 Ti than the other silencers, during the first shot. And, like the FRP to bystanders, the FRP to the shooter is postulated to also be more “harsh" with the FLOW 762 Ti.
Shooters with hearing loss above the 2,800 Hz range may perceive the sound delta between the Nomad-Ti and the Thunder Chicken to be imperceptible during FRP. These same shooters may also still perceive the FLOW 762 Ti to be more “boomy” than the other silencers, but not as “harsh.”
To personnel firing the weapon, on average, the overall signatures of the three silencers are very similar in severity. The Nomad-Ti is nominally the quietest to the shooter, on average, with the Thunder Chicken being the loudest to the shooter, on average.
It is postulated with a high degree of confidence that the weapon operator will perceive the FLOW 762 Ti to exhibit a more “boomy” signature with this weapon system than with the Nomad-Ti and Thunder Chicken, on average.
Shooters with acute hearing sensitivity above 4,000 Hz may note the Thunder Chicken to be slightly more “pleasing” or “less harsh” than the Nomad-Ti, on average. Some shooters possessing poor high frequency hearing sensitivity may perceive the Nomad-Ti to sound slightly more pleasing than the Thunder Chicken, due to the nominal difference in inner ear frequency response predicted between 1,000 and 2,800 Hz with the two silencers.
Normalized FRP and average performance is compared in Figure 3. Despite the composite Suppression Rating correlation, there are outliers in the detailed Suppression Rating correlation with FRP. Note that the maximum human inner ear damage potential of the silencer with the loudest measured FRP or Average signatures is used in each normalization. This allows strict relative comparison of all the silencers shown.
The data should be viewed with the following muzzle behavior note in mind:
The HUXWRX FLOW 762 Ti has the highest average muzzle Suppression Rating (28.0) but has louder muzzle FRP than both the Dead Air Nomad-Ti (average muzzle SR = 26.3) and the Q Thunder Chicken (average muzzle SR = 27.9).
At the Shooter’s Ear, the following notes apply:
The FRP signature of the HUXWRX FLOW 762 Ti is the most severe, by as much as 25% when compared to that of the Nomad-Ti. This occurs despite their very similar average shooter’s ear Suppression Ratings (41.2 and 41.3, respectively).
The FRP signature of the Q Thunder Chicken is 10% less severe than that of the FLOW 762 Ti, despite having an identical shooter’s ear Suppression Rating (41.2). Note that all three silencers possess very similar average signature severities to the shooter.
As noted, the relative the Muzzle and Ear Average and FRP measurements shown in Figure 3 are not comparable to one another. Muzzle numbers should be compared with muzzle, and ear with ear. This is a consequence of the chosen normalization and the hearing damage potential at the muzzle and ear being different (as with any silencer).
Fig 3. Normalized FRP and Average Performance Summary (Supersonic .308 Bolt-Action Rifle)
The data shown in Figure 3 is intended to present the likely human relative perception of FRP magnitude of the silencers to both bystanders and the shooter. It is important to note that the human inner ear responds differently to certain frequencies. On average, it is postulated that the relations in Figure 3 will directly correlate to human inner ear response. However, some users may have hearing sensitivity that is compromised or different than others in certain frequency ranges. Those phenomena are considered in this article.
The following subsections of this Research Supplement present in-depth comparisons of human inner-ear modeling response to the FRP and average sound signatures.
6.116.2 Comparisons of Muzzle Waveforms Measured in the Free Field
It is not always possible to determine relative, objective loudness from only the measured average peak sound pressure amplitude and measured peak sound pressure momentum transfer potential (impulse). Therefore, the Suppression Rating also considers physical ear response to measured sound signatures. The human inner ear responds to different sound pressure frequencies with varying sensitivity. Physically, these frequencies excite different regions of the basilar membrane within the cochlea. The human ear is typically most sensitive to sounds that excite the membrane near a frequency of 4,000 Hz. However, the ear may be exercised, and therefore damaged, at different physical regions. It is postulated that this inner ear response directly correlates to the perceived loudness of suppressed small arms.
PEW Science Research Note: As stated in previous Research Supplements, it is important not misconstrue the frequency-domain data in this Research Supplement with a simple frequency analysis (Fourier transform) of the time-domain overpressure waveforms presented in the reviews. The data shown in this research supplement is the output from analytical human inner ear modeling with the measured test data used as free-field overpressure loading input.
6.116.2.1 FRP Muzzle Comparisons
Figure 4 presents the results of an inner ear analysis performed using measured sound overpressure waveforms from the first shots in the referenced tests. The curves show normalized physical response of the human inner ear as a function of basilar membrane location within the cochlea and corresponding sensitivity frequencies. Fig 4a shows the response on the vertical axis with a linear scale. Fig 4b and Fig 4c show the same data on a logarithmic scale, in the low and high frequency hearing response regimes, respectively. Note that the data is normalized; this lets you see the relative theoretical ear response for the silencers.
To personnel located 1.0 m left of the weapon muzzle, the Q Thunder Chicken is postulated to sound the quietest, with the HUXWRX FLOW 762 Ti being the loudest, during the first shot.
Fig 4a. Comparison of FRP Human Inner Ear Response - .308 at the Muzzle (Linear Scale)
Note that in the very low frequency response regime, the HUXWRX FLOW 762 Ti signature is much more intense than that of the the other two silencers. The Dead Air Nomad-Ti is more intense in that frequency response regime than the Q Thunder Chicken. This indicates that during the first shot, bystanders will most likely perceive the FLOW 762 Ti as “boomy,” with the potential for bystanders perceiving the Nomad-Ti as having a “lower tone” than the Thunder Chicken.
At a hearing sensitivity of approximately 4,000 Hz, the inner ear response to bystanders from the Nomad-Ti and Thunder Chicken is postulated to be extremely similar. Above this hearing response frequency, the FLOW 762 Ti is still the loudest, which is postulated to result in a “harsh” signature to bystanders during the first shot, when compared to the other two silencers. The FLOW 762 Ti is noticeably louder than the Nomad-Ti and Thunder Chicken during FRP, to bystanders, across all frequency sensitivities of the human inner ear.
It is possible that bystanders extremely sensitive to hearing response above 7,000 Hz may interpret the Thunder Chicken to sound nominally more “pleasing” than the Nomad-Ti, during FRP.
Fig 4b. Comparison of FRP Low Frequency Human Inner Ear Response - .308 at the Muzzle (Log Scale)
Fig 4c. Comparison of FRP High Frequency Human Inner Ear Response - .308 at the Muzzle (Log Scale)
PEW Science Research Note: Bystanders with hearing loss above the 7,000 Hz range may perceive the sound delta between the Nomad-Ti and the Thunder Chicken to be imperceptible during FRP. These same bystanders may also still perceive the FLOW 762 Ti to be more “boomy” than the other silencers, but not as “harsh.”
6.116.2.2 Average Muzzle Comparisons
Figure 5 presents the average results of an inner ear analysis performed using measured sound overpressure waveforms from all shots in the referenced tests. Again, the curves show normalized physical response of the human inner ear as a function of basilar membrane location within the cochlea and corresponding sensitivity frequencies. Fig 5a shows the response on the vertical axis with a linear scale. Fig 5b and Fig 5c again show the same data on a logarithmic scale, in the low and high frequency hearing response regimes, respectively. Note that the data is normalized; this lets you see the relative theoretical ear response for the silencers.
To personnel located 1.0 m left of the weapon muzzle, the FLOW 762 Ti is postulated to sound the quietest on average, with the Nomad-Ti being the loudest on average.
Fig 5a. Comparison of Average Human Inner Ear Response - .308 at the Muzzle (Linear Scale)
Note that In the lower midrange response regime, the FLOW 762 Ti and Nomad-Ti curves cross at 2,800 Hz. This highlights that although the HUXWRX FLOW 762 Ti is quieter than the Nomad-Ti to bystanders, on average, it may still be perceived to bystanders as “boomy.” The low frequency range inner ear response of the FLOW 762 Ti is still more significant than the other two silencers to bystanders, on average.
On average, the Thunder Chicken signature is approximately 14% less severe than the Nomad-Ti signature, to bystanders. The Flow 762 Ti signature is approximately 17% less severe than the Nomad-Ti signature to bystanders, on average.
Fig 5b. Comparison of Average Low Frequency Human Inner Ear Response - .308 at the Muzzle (Log Scale)
Fig 5c. Comparison of Average High Frequency Human Inner Ear Response - .308 at the Muzzle (Log Scale)
6.116.3 Comparisons of Waveforms Measured near the Shooter’s Ear
The sound signatures measured at the ear during the tests of each silencer are significantly different than those measured at the weapon muzzle and this difference is not only shown in the average peak sound pressure and impulse measurements, but also with inner ear analysis.
6.116.3.1 FRP Ear Comparisons
Figure 6 presents an inner ear analysis performed using measured sound overpressure waveforms at the shooter’s right ear from the first shots in all tests. Fig 6a shows the response on a linear vertical scale. Fig 6b and Fig 6c show the same data on a logarithmic vertical scale, in the low and high frequency hearing response regimes, respectively.
To personnel firing the weapon, the Nomad-Ti is the quietest silencer during the first shot. The FLOW 762 Ti is the loudest to the shooter, during the first shot.
The same exaggerated lower frequency inner ear response of the Nomad-Ti, relative to that of the Thunder Chicken, that was observed in the muzzle signatures is observed at the shooter’s ear. This indicates that during FRP, the Nomad-Ti may also have a “lower tone” to the shooter than the Thunder Chicken, as is postulated for bystanders.
Fig 6a. Comparison of FRP Human Inner Ear Response - .308 at the Ear (Linear Scale)
Again, the entirety of the inner ear response frequency range from the HUXWRX FLOW 762 Ti signature is more severe during the first shot. Just like to bystanders, the weapon operator is postulated to perceive a more “boomy” signature with the FLOW 762 Ti than the other silencers, during the first shot. And, like the FRP to bystanders, the FRP to the shooter is postulated to also be more “harsh".
This time, it is the Thunder Chicken and Nomad-Ti inner ear response curves that cross near a frequency of 2,800 Hz. This further supports the above postulation that the shooter will perceive the Nomad-Ti signature to have a “lower tone” than that of the Thunder Chicken, during the first shot.
Fig 6b. Comparison of FRP Low Frequency Human Inner Ear Response - .308 at the Ear (Log Scale)
Fig 6c. Comparison of FRP High Frequency Human Inner Ear Response - .308 at the Ear (Log Scale)
PEW Science Research Note: Shooters with hearing loss above the 2,800 Hz range may perceive the sound delta between the Nomad-Ti and the Thunder Chicken to be imperceptible during FRP. These same shooters may also still perceive the FLOW 762 Ti to be more “boomy” than the other silencers, but not as “harsh.”
6.116.3.2 Average Ear Comparisons
Figure 7 presents the average results from an inner ear analysis performed using measured sound overpressure waveforms at the shooter’s right ear from all the shots in the referenced tests. Fig 7a shows the response on a linear vertical scale. Fig 7b and Fig 7c show the same data on a logarithmic vertical scale, in the low and high frequency hearing response regimes, respectively.
To personnel firing the weapon, on average, the overall signatures are very similar in severity. The Nomad-Ti is nominally the quietest to the shooter, on average, with the Thunder Chicken being the loudest to the shooter, on average.
Despite the very similar maximum hearing damage potential of the three silencers to the shooter, on average, the FLOW 762 Ti still possesses exaggerated lower frequency inner ear response below approximately 3,700 Hz. This indicates, with a high degree of confidence, that the weapon operator will perceive the FLOW 762 Ti to exhibit a more “boomy” signature with this weapon system than with the Nomad-Ti and Thunder Chicken.
Fig 7a. Comparison of Average Human Inner Ear Response - .308 at the Ear (Linear Scale)
On average, the signature to the shooter from the Dead Air Nomad-Ti and the Q Thunder Chicken, on this weapon system, is extremely similar.
Fig 7b. Comparison of Average Low Frequency Human Inner Ear Response - .308 at the Ear (Log Scale)
Fig 7c. Comparison of Average High Frequency Human Inner Ear Response - .308 at the Ear (Log Scale)
PEW Science Research Note: Shooters with acute hearing sensitivity above 4,000 Hz may note the Thunder Chicken to be slightly more “pleasing” or “less harsh” than the Nomad-Ti, on average. Some shooters possessing poor high frequency hearing sensitivity may perceive the Nomad-Ti to sound slightly more pleasing than the Thunder Chicken, due to the nominal difference in inner ear frequency response predicted between 1,000 and 2,800 Hz with the two silencers.
6.116.4 Research Supplement Summary
Bystander Perception:
To personnel located 1.0 m left of the weapon muzzle, the Q Thunder Chicken is postulated to sound the quietest, with the HUXWRX FLOW 762 Ti being the loudest, during the first shot. During the first shot, bystanders will most likely perceive the FLOW 762 Ti as “boomy,” with bystanders potentially perceiving the Nomad-Ti as having a “lower tone” than the Thunder Chicken.
The FLOW 762 Ti is noticeably louder than the Nomad-Ti and Thunder Chicken during FRP, to bystanders, across all frequency sensitivities of the human inner ear.
On average, the FLOW 762 Ti is postulated to sound the quietest to bystanders, with the Nomad-Ti being the loudest. Although the HUXWRX FLOW 762 Ti is quieter than the Nomad-Ti to bystanders, on average, it may still be perceived to bystanders as “boomy.”
On average, the Thunder Chicken signature is approximately 14% less severe than the Nomad-Ti signature, to bystanders. The Flow 762 Ti signature is approximately 17% less severe than the Nomad-Ti signature to bystanders, on average.
Shooter Perception:
To personnel firing the weapon, the Nomad-Ti is the quietest silencer during the first shot. The FLOW 762 Ti is the loudest to the shooter, during the first shot. During FRP, the Nomad-Ti may also have a “lower tone” to the shooter than the Thunder Chicken, as is postulated for bystanders.
Just like to bystanders, the weapon operator is postulated to perceive a more “boomy” signature with the FLOW 762 Ti than the other silencers, during the first shot. And, like the FRP to bystanders, the FRP to the shooter is postulated to also be more “harsh" with the FLOW 762 Ti.
Shooters with hearing loss above the 2,800 Hz range may perceive the sound delta between the Nomad-Ti and the Thunder Chicken to be imperceptible during FRP. These same shooters may also still perceive the FLOW 762 Ti to be more “boomy” than the other silencers, but not as “harsh.”
To personnel firing the weapon, on average, the overall signatures of the three silencers are very similar in severity. The Nomad-Ti is nominally the quietest to the shooter, on average, with the Thunder Chicken being the loudest to the shooter, on average.
It is postulated with a high degree of confidence that the weapon operator will perceive the FLOW 762 Ti to exhibit a more “boomy” signature with this weapon system than with the Nomad-Ti and Thunder Chicken, on average.
Shooters with acute hearing sensitivity above 4,000 Hz may note the Thunder Chicken to be slightly more “pleasing” or “less harsh” than the Nomad-Ti, on average. Some shooters possessing poor high frequency hearing sensitivity may perceive the Nomad-Ti to sound slightly more pleasing than the Thunder Chicken, due to the nominal difference in inner ear frequency response predicted between 1,000 and 2,800 Hz with the two silencers.
This supplement is part of ongoing PEW Science small arm weapon system sound signature research. PEW Science thanks you for your support.
