SSS.6.124 - Research Supplement: Subsonic 300 BLK Suppression Performance - Flow-Through vs. Forward Flux vs. SURGE BYPASS vs. Conventional Silencers. Head-to-Head Detailed Comparisons (Members Only)

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HUXWRX HX-QD 762 vs. Sig Sauer SLH300Ti vs. Combat Application Technologies CAT/ODB/A1/718 vs. Surefire SOCOM300-SPS vs. Sig Sauer SRD762QD-Ti on a 300 BLK Bolt Action Rifle with 8-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.

Currently, there exist three different primary classes of rifle silencer technology:

  1. Conventional designs, in which shock and blast loads are significantly reflected in early time, rearward toward the muzzle orifice, with later time gas propagation significantly restricted to atmosphere. Examples of such silencers include the Q Full Nelson (6.99), Surefire SOCOM300-SPS (6.57) and the Otter Creek Labs Hydrogen (6.94).  These silencers use technologies such as legacy straight cone designs, elements of Surefire Total Signature Reduction®, and others.

  2. High Flow Rate designs, in which blast reflections in the proximal expansion chamber are redirected, reduced, or otherwise altered to reduce the influence on reciprocating weapon function, with later time gas propagation expediently venting to atmosphere. Examples of these silencers include the HUXWRX OSS HX-QD 762 (6.45) and the Sig Sauer SLH300Ti (6.107) which use HUXWRX Flow-Through® and Sig Sauer Forward Flux technologies, respectively.

  3. Hybrid designs, in which elements of both Conventional and High Flow Rate silencers are used, coupled with other technology variations and staged elements to provide parametrically varied performance attributes. Such attributes include the ability to reduce early time shock reflections while significantly altering the rate of proximal venting. These silencers may allow for minimal reciprocating weapon functional influence, while at the same time significantly suppressing signature to the operator and bystanders. Hybrid designs span a large range of the market in both brand and performance in different combustion regimes.  These silencers include the CGS Hyperion (6.71), CGS Hyperion K (6.50), the Surefire RC2 family, and others.  Technologies implemented in these types of silencers are varied, including CGS Hyperion Technology, elements of Surefire Total Signature Reduction®, CAT SURGE BYPASS©, and others.

The above three classes of silencers produce varied performance on different weapon systems and with different ammunition types. Of the three classes, the most significant overall performance potentials remain confined to Hybrid designs, in accordance with the PEW Science Silencer Sound Standard public research pedigree, to date. There exists a subcategory of this class of silencers, that is shown to demonstrate efficacy in multiple flow regimes. To date, the best example of such a subcategory includes silencers like the Combat Application Technologies CAT/ODB/A1/718 (6.22). These silencers not only combine performance parameters from all three classes, but have been shown to demonstrate so-called pressure agnostic behavior, in which input variation exemplified by both supersonic and subsonic cartridge combustion regimes both result in high signature suppression efficacy.

It is important to note that many silencers exhibit significantly different performance when using supersonic and subsonic ammunition.  PEW Science Research Supplement 6.115 presented a performance comparison of HUXWRX Flow-Through technology with that of Conventional designs, in the supersonic ammunition combustion regime.  The performances of the Dead Air Nomad-Ti, Q Thunder Chicken, and HUXWRX FLOW 762 Ti were compared in that article, in significant detail.

This Research Supplement compares a different group of silencers, in the subsonic ammunition combustion regime.  In general, increasing gross flow rate through a silencer can significantly reduce signature suppression performance, particularly with subsonic ammunition.  However, certain designs may significantly outperform others in this regard.  Quantifying these performance differentials is essential for characterizing hazards to the system operator and bystanders.

6.124.1 Quantifying Sound Suppression Performance

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, five 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 relevance to the above three rifle silencer technology classes. The five silencers behave differently, even despite some of them exhibiting similar performance quantified by the PEW Science Suppression Rating.  Their subsonic 300 BLK suppression performance provides an excellent case study comparing current rifle silencer technology (Figure 2).

Fig 1. PEW Science Suppression Rating Scale

The published Sound Signature Reviews of these five silencers, with subsonic 300 BLK ammunition, are linked below. Their technology class and subcategory or designation is noted:

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. Flow-Through, Total Signature Reduction, SURGE BYPASS, Forward Flux, and legacy baffle systems all respond differently to changes in muzzle blast pressure input.

Sound signature suppression is not the only performance attribute of interest to many users. Back pressure reduction is often paramount for reducing gas toxicity and weapon over-function. The higher flow rate models above do not represent an exhaustive list of silencers that may reduce back pressure; in addition to other existing silencers on the market, there exist new models such as the HUXWRX Ventum 762 and the Surefire SOCOM556-RC3. Both of these silencers are intended to exhibit higher gross flow rates, reduce over-function on reciprocating weapon systems, and reduce gas toxicity to the end user. The HUXWRX Ventum and Surefire RC3 use HUXWRX Flow-Through technology and a higher flow variant of Surefire Total Signature Reduction technology, respectively, to reduce back pressure. These two silencers will be evaluated by the PEW Science Laboratory at a later date.

In addition to flow rate, flash reduction, back pressure reduction, and overall signature suppression performance, 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. Suppression Rating Comparisons Of .30 Rifle Silencers Using PEW-SOFT 300 BLK Subsonic Test Data

Typically, silencers possessing a high flow rate also possess lower sound suppression performance with subsonic ammunition. However, there are significant exceptions. Hybrid designs have the potential to exhibit high performance in multiple regimes.

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 6.124.2 provides an overall sound suppression performance summary at the muzzle and shooter’s ear.

  • Section 6.124.3 provides detailed comparisons of the sound signatures measured at the muzzle.

  • Section 6.124.4 provides detailed comparisons of the sound signature measured at the shooter’s ear.

  • Section 6.124.5 repeats the performance summary.

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 five 30 caliber rifle silencers that use various technologies to suppress subsonic 300 BLK sound signatures. 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. PEW Science thanks you for your support.

6.124.2 Overall Sound Suppression Performance Summary

Bystander Perception:

To personnel located 1.0 m left of the weapon muzzle, the Sig Sauer SRD762QD-Ti is postulated to sound the quietest, with the HUXWRX HX-QD 762 being the loudest, during the first shot.

During the first shot, bystanders will most likely perceive the HX-QD 762, SLH300Ti, and CAT ODB silencers as “boomy,” with the potential for bystanders perceiving the CAT ODB as sounding “less harsh” than the other two silencers.  It is likely that most bystanders will perceive the SOCOM300-SPS and SRD762QD-Ti as generally “quieter” than the other three silencers, during the first shot.

On average, the signature produced by the Forward Flux technology in the Sig Sauer SLH300Ti may be interpreted as slighly more harsh than that produced by the Flow-Through Technology in the HUXWRX HX-QD 762. However, it is important to note that the signatures to bystanders from those two silencers are significantly more severe in this combustion regime than the signatures from the other three silencers, on average, and are also diverge from each other less than they do during FRP.

On average, to bystanders, the CAT ODB will likely still be perceived as somewhat “boomy” compared to the SOCOM300-SPS and SRD762QD-Ti silencers, but significantly less “harsh” than the HX-QD 762 and SLH300Ti. Bystanders with acute hearing sensitivity above 2,500 Hz may interpret the CAT ODB as sounding more “pleasing” than the SOCOM300-SPS, on average.

On average, the Sig Sauer SRD762QD-Ti signature is approximately 95% less severe than the Sig Sauer SLH300Ti signature, to bystanders, and 97% less severe than the HX-QD 762 signature.  On average, the CAT ODB signature, to bystanders, is approximately 92% less severe than the Sig Sauer SLH300Ti signature, and 94% less severe than the HX-QD 762 signature.  The Surefire SOCOM300-SPS signature is very similar in gross severity to that of the CAT ODB, on average.  Preexisting hearing damage will influence the presented perception differentials, as noted in the text.

Shooter Perception:

To personnel firing the weapon, the CAT ODB is the quietest silencer during the first shot. The HX-QD 762 is the loudest to the shooter, during the first shot.

To the shooter, the CAT ODB signature is lower than all of the other silencers, in absolute severity during the first shot, while the Sig Sauer SLH300Ti more significantly outperforms the HX-QD 762 in shooter’s ear hazard reduction during the first shot.

Below approximately 3,500 Hz, the Surefire silencer produces a more hazardous inner ear response than the Sig SRD silencer, and as a result, shooters with high frequency hearing loss may still perceive the Sig SRD silencer to be quieter. The same shooters with high frequency hearing loss may perceive the CAT ODB to be louder than the Surefire and Sig SRD silencer during FRP, even though the CAT ODB signature is objectively less severe. This is a function of the inner ear response differential below 2,500 Hz.

The CAT ODB is nominally the quietest to the shooter, on average, with the HX-QD 762 being the loudest to the shooter, on average.  The HUXWRX (OSS) HX-QD 762 is the loudest silencer (produces the most severe sound signature to the human inner ear) during the first shot and all shots on average, and it possesses this behavior to both bystanders and the weapon operator.

On average, the Sig SRD silencer is most likely slightly less hazardous to the operator than the Surefire SOCOM300-SPS.  The CAT ODB produces a signature that is slightly less severe than the Sig SRD to the weapon operator, on average.

On average, the Sig Sauer SRD762QD-Ti signature is approximately 26% less severe than the Sig Sauer SLH300Ti signature, to to the shooter, and 96% less severe than the HX-QD 762 signature.  On average, the CAT ODB signature, to the shooter, is approximately 27% less severe than the Sig Sauer SLH300Ti signature, and 97% less severe than the HX-QD 762 signature.  Just as during FRP, on average, shooters with high frequency hearing loss may perceive the CAT ODB to be louder than the Surefire and Sig SRD silencer, even though the CAT ODB signature is objectively less severe. This is a function of an average inner ear response differential below 2,000 Hz.  On average, the difference in signature severity to the weapon operator, between the CAT ODB and Sig SRD silencer is nominal.

Normalized FRP and average performance is compared in Figure 3.  Note that there are significant performance differentials shown.  In the technology classes noted above, High Flow Rate technology is shown to experience potentially severe signature suppression performance losses in the subsonic 300 BLK combustion regime.  It is for this reason that any Hybrid Design technology demonstrating efficacy is so significant in the research pedigree.  Recall the hybrid CAT SURGE BYPASS technology evaluated on a reciprocating weapon platform in Sound Signature Review 6.120.  In that white paper, the CAT ODB was evaluated on a 5.56x45mm MK18 - a short barrel automatic rifle.  The external gas momentum transfer and weapon kinematics presented in an atypical combination.  In summary, the system was able to exhibit significant signature suppression performance with low back pressure behavior.  

Other silencers exhibiting low back pressure behavior, like those using Flow-Through and Forward Flux technologies, do not present the same externally measured impulse accumulation behavior. The difference in external gas momentum accumulation rate is indicative of more direct venting to atmosphere in those designs. It is this direct venting that can significantly reduce subsonic 300 BLK suppression performance. To balance a low back pressure design such that it exhibits high signature suppression performance in both supersonic and subsonic cartridge combustion regimes, the design must minimize rearward early time shock and blast reflections, while at the same time relieving high pressure stagnation with forward gas flow, all the while either re-routing gas pressure through additional turbulent zones or creating favorable pressure differentials in the proximal geometry.  Technologies employing all of these characteristics are not as well studied as the aforementioned High Flow Rate (Flow-Through and Forward Flux) designs and Conventional (ported cone baffle) designs.  This white paper continues this research.

The data should be viewed with the following muzzle behavior note in mind:

  • On average, the Sig Sauer SRD762QD-Ti signature is approximately 95% less severe than the Sig Sauer SLH300Ti signature, to bystanders, and 97% less severe than the HX-QD 762 signature.  On average, the CAT ODB signature, to bystanders, is approximately 92% less severe than the Sig Sauer SLH300Ti signature, and 94% less severe than the HX-QD 762 signature.  The SRD762QD-Ti has the quietest FRP to bystanders.

At the Shooter’s Ear, the following note applies:

  • On average, the Sig Sauer SRD762QD-Ti signature is approximately 26% less severe than the Sig Sauer SLH300Ti signature, to to the shooter, and 96% less severe than the HX-QD 762 signature.  On average, the CAT ODB signature, to the shooter, is approximately 27% less severe than the Sig Sauer SLH300Ti signature, and 97% less severe than the HX-QD 762 signature.  The CAT ODB has the quietest FRP to the weapon operator.

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 (Subsonic 300 BLK 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.  Please note the silencer technologies shown in brown below the model labels on the vertical axis of Figure 3.

6.124.3 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 to 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.

6.124.3.1 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 Sig Sauer SRD762QD-Ti is postulated to sound the quietest, with the HUXWRX HX-QD 762 being the loudest, during the first shot.

Fig 4a. Comparison of FRP Human Inner Ear Response - Subsonic 300 BLK at the Muzzle (Linear Scale)

Note that in the very low frequency response regime during the first shot, there is a commonality in inner ear response characteristics from two distinct groups:

  1. Group 1: Conventional Design silencers, in which low frequency inner ear response is minimized.

  2. Group 2: High Flow Rate and Hybrid Design silencers, in which low frequency inner ear response may be exacerbated.

The above phenomena is best viewed on the logarithmic scale in Figure 4b and Figure 4c. Note that the HUXWRX HX-QD 762, Sig Sauer SLH300Ti, and CAT ODB signatures are more intense below 500 Hz. However, as inner ear response frequency increases, the hybrid design CAT silencer with SURGE BYPASS begins to present lower response.  At 2,500 Hz, SURGE BYPASS technology is is shown to begin to approach the severity of conventional silencers during the first shot.  At 4,000 Hz and above, SURGE BYPASS begins to meet or exceed performance of conventional silencer FRP.  This performance analysis is significant, due to the behavior of the Flow-Through and Forward Flux technologies employed by the HX-QD and SLH silencers presenting significantly more severe inner ear response over the entire frequency range.  This indicates that during the first shot, bystanders will most likely perceive the HX-QD 762, SLH300Ti, and CAT ODB silencers as “boomy,” with the potential for bystanders perceiving the CAT ODB as sounding “less harsh” than the other two silencers.  It is likely that most bystanders will perceive the SOCOM300-SPS and SRD762QD-Ti as generally “quieter” than the other three silencers, during the first shot.

Due to the aforementioned inner ear response crossing at 4,000 Hz, it is possible that bystanders extremely sensitive to hearing response above this frequency may interpret the CAT ODB to sound nominally more “pleasing” than the SOCOM300-SPS, during FRP.  It is likely that those same bystanders will interpret the SRD762QD-Ti as sounding slightly more pleasing than both.

Fig 4b. Comparison of FRP Low Frequency Human Inner Ear Response - Subsonic 300 BLK at the Muzzle (Log Scale)

Fig 4c. Comparison of FRP High Frequency Human Inner Ear Response - Subsonic 300 BLK at the Muzzle (Log Scale)

PEW Science Research Note: Bystanders with hearing loss above the 4,000 Hz range may perceive the sound delta between the silencers in Group 1 and Group 2 to be greater, during FRP. These same bystanders may also still perceive the CAT ODB to be more “boomy” than the Group 1 silencers, but not as “harsh” as the other Group 2 silencers, during FRP.

6.124.3.2 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 SRD762QD-Ti is postulated to sound the quietest on average, with the HX-QD 762 and SLH300Ti being the loudest silencers, on average.

Fig 5a. Comparison of Average Human Inner Ear Response - Subsonic 300 BLK at the Muzzle (Linear Scale)

On average, the signature produced by the Forward Flux technology in the Sig Sauer SLH300Ti may be interpreted as slighly more harsh than that produced by the Flow-Through Technology in the HUXWRX HX-QD 762. However, it is important to note that the signatures to bystanders from those two silencers are significantly more severe in this combustion regime than the signatures from the other three silencers, on average, and are also diverge from each other less than they do during FRP.

As with the FRP signatures at the muzzle, this data is best viewed on the logarithmic scales, below. Again, the CAT ODB presents exacerbated lower frequency inner ear response to bystanders, on average, but this response is less than presented during FRP. Interestingly, the signatures of the SOCOM300-SPS and the CAT ODB induce very similar inner ear response above 2,500 Hz, on average. This demonstrates the effects of more severe FRP from SURGE BYPASS than from conventional designs, to average bystander signature severity. The reader is encouraged to examine Figure 4b and Figure 5b to see this delineation.

On average, to bystanders, the performance gap widens between the Sig Sauer SRD762QD-Ti and the other silencers. This is to be expected, given the technology used and its low flow rate and significant shock and blast reflections in its proximal expansion chamber.

On average, to bystanders, the CAT ODB will likely still be perceived as somewhat “boomy” compared to the SOCOM300-SPS and SRD762QD-Ti silencers, but significantly less “harsh” than the HX-QD 762 and SLH300Ti. Bystanders with acute hearing sensitivity above 2,500 Hz may interpret the CAT ODB as sounding more “pleasing” than the SOCOM300-SPS, on average.

Fig 5b. Comparison of Average Low Frequency Human Inner Ear Response - Subsonic 300 BLK at the Muzzle (Log Scale)

Fig 5c. Comparison of Average High Frequency Human Inner Ear Response - Subsonic 300 BLK at the Muzzle (Log Scale)

6.124.4 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.

6.124.4.1 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 CAT ODB is the quietest silencer during the first shot. The HX-QD 762 is the loudest to the shooter, during the first shot.

The same exaggerated lower frequency inner ear response of the CAT ODB, relative to that of the SOCOM300-SPS and SRD762QD-Ti, that was observed in the muzzle signatures is observed at the shooter’s ear. This indicates that during FRP, the CAT ODB may still be perceived by the shooter as “boomy” compared to those two silencers, but it still produces an objectively less severe inner ear response to bystanders.

Fig 6a. Comparison of FRP Human Inner Ear Response - Subsonic 300 BLK at the Ear (Linear Scale)

As with the signatures at the muzzle, this data measured at the shooter’s ear is best viewed on the logarithmic scales, below.

The deviation between muzzle signature severity and shooter’s ear signature severity, is a function of sound field shape influenced by particle velocity and flow rate, forming the complete gas momentum transfer mechanisms. Impulse signatures delineating these behaviors may be examined in detail in each respective Sound Signature Review white paper. A summary of this behavior is easily noted by the reader using Figure 2 in this article (the gross muzzle and ear Suppression Ratings and how each compare to each other for each silencer). Due to the divergence in muzzle and shooter’s ear signature hazards, the following phenomena occur:

  1. To the shooter, the CAT ODB signature is lower than all of the other silencers, in absolute severity.

  2. The Sig Sauer SLH300Ti more significantly outperforms the HX-QD 762 in shooter’s ear hazard reduction.

During the first shot, the shooter may not only perceive the SOCOM300-SPS as quieter than the SRD762QD-Ti, but may also note a harsh component of the signature from the Sig Sauer SRD silencer (note the exaggerated inner ear response above 11.500 Hz in Figure 6c).  Below approximately 3,500 Hz, the Surefire silencer produces a more hazardous inner ear response than the Sig SRD silencer, and as a result, shooters with high frequency hearing loss may still perceive the Sig SRD silencer to be quieter.

Fig 6b. Comparison of FRP Low Frequency Human Inner Ear Response - Subsonic 300 BLK at the Ear (Log Scale)

Fig 6c. Comparison of FRP High Frequency Human Inner Ear Response - Subsonic 300 BLK at the Ear (Log Scale)

PEW Science Research Note: The same shooters with high frequency hearing loss may perceive the CAT ODB to be louder than the Surefire and Sig SRD silencer during FRP, even though the CAT ODB signature is objectively less severe. This is a function of the inner ear response differential below 2,500 Hz shown in Figure 6b.

6.124.4.2 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 begin to experience less overall divergence.  However, some trends in the analysis continue.  The CAT ODB is nominally the quietest to the shooter, on average, with the HX-QD 762 being the loudest to the shooter, on average.  The HUXWRX (OSS) HX-QD 762 is the loudest silencer (produces the most severe sound signature to the human inner ear) during the first shot and all shots on average, and it possesses this behavior to both bystanders and the weapon operator.

The exaggerated lower frequency inner ear response of the CAT ODB is now pushed further into the lower frequencies to the shooter, on average, and presents with divergence below approximately 2,000 Hz (reference Figure 7b). This indicates, with a high degree of confidence, that the weapon operator will perceive the CAT ODB to exhibit a more “boomy” signature with this weapon system than with the SOCOM300-SPS or SRD762QD-Ti, on average, but the signatures will be perceived by the operator to be much more similar in severity to each other after FRP.

Fig 7a. Comparison of Average Human Inner Ear Response - Subsonic 300 BLK at the Ear (Linear Scale)

It is likely that environmental variables, such as nearby reflecting surfaces, will significantly influence the relative perceptions of the weapon operator when firing this weapon system with these silencers, on average.  This is a function of muzzle and shooter’s ear Suppression Rating divergence.

On average, the signature to the shooter from the SRD762QD-Ti and the SOCOM300-SPS, on this weapon system, is reversed from that of the relative severity noted during FRP.  During the first shot, the Surefire silencer is most likely perceived as quieter to the weapon operator.  On average, the Sig SRD silencer is most likely slightly less hazardous to the operator.  The CAT ODB produces a signature that is slightly less severe than the Sig SRD to the weapon operator, on average.

On average, the operator will experience a closer relative severity between the HX-QD 762 and SLH300Ti on this weapon system than they will during the first shot. Both those silencers continue to present the most hazardous signature to the weapon operator on this system, on average. The mechanism by which the HUXWRX Flow-Through and Sig Sauer Flux Forward technologies achieve high flow rate are somewhat similar. The resulting similarities in human inner ear response in the subsonic 300 BLK combustion regime is reflected in this analysis.

Fig 7b. Comparison of Average Low Frequency Human Inner Ear Response - Subsonic 300 BLK at the Ear (Log Scale)

Fig 7c. Comparison of Average High Frequency Human Inner Ear Response - Subsonic 300 BLK at the Ear (Log Scale)

PEW Science Research Note: Just as during FRP, on average, shooters with high frequency hearing loss may perceive the CAT ODB to be louder than the Surefire and Sig SRD silencer, even though the CAT ODB signature is objectively less severe. This is a function of the inner ear response differential below 2,000 Hz shown in Figure 6b.  On average, the difference in signature severity to the weapon operator, between the CAT ODB and Sig SRD silencer is nominal.

6.124.5 Research Supplement Summary

This Summary is Repeated from earlier in the Article.

Bystander Perception:

To personnel located 1.0 m left of the weapon muzzle, the Sig Sauer SRD762QD-Ti is postulated to sound the quietest, with the HUXWRX HX-QD 762 being the loudest, during the first shot.

During the first shot, bystanders will most likely perceive the HX-QD 762, SLH300Ti, and CAT ODB silencers as “boomy,” with the potential for bystanders perceiving the CAT ODB as sounding “less harsh” than the other two silencers.  It is likely that most bystanders will perceive the SOCOM300-SPS and SRD762QD-Ti as generally “quieter” than the other three silencers, during the first shot.

On average, the signature produced by the Forward Flux technology in the Sig Sauer SLH300Ti may be interpreted as slighly more harsh than that produced by the Flow-Through Technology in the HUXWRX HX-QD 762. However, it is important to note that the signatures to bystanders from those two silencers are significantly more severe in this combustion regime than the signatures from the other three silencers, on average, and are also diverge from each other less than they do during FRP.

On average, to bystanders, the CAT ODB will likely still be perceived as somewhat “boomy” compared to the SOCOM300-SPS and SRD762QD-Ti silencers, but significantly less “harsh” than the HX-QD 762 and SLH300Ti. Bystanders with acute hearing sensitivity above 2,500 Hz may interpret the CAT ODB as sounding more “pleasing” than the SOCOM300-SPS, on average.

On average, the Sig Sauer SRD762QD-Ti signature is approximately 95% less severe than the Sig Sauer SLH300Ti signature, to bystanders, and 97% less severe than the HX-QD 762 signature.  On average, the CAT ODB signature, to bystanders, is approximately 92% less severe than the Sig Sauer SLH300Ti signature, and 94% less severe than the HX-QD 762 signature.  The Surefire SOCOM300-SPS signature is very similar in gross severity to that of the CAT ODB, on average.  Preexisting hearing damage will influence the presented perception differentials, as noted in the text.

Shooter Perception:

To personnel firing the weapon, the CAT ODB is the quietest silencer during the first shot. The HX-QD 762 is the loudest to the shooter, during the first shot.

To the shooter, the CAT ODB signature is lower than all of the other silencers, in absolute severity during the first shot, while the Sig Sauer SLH300Ti more significantly outperforms the HX-QD 762 in shooter’s ear hazard reduction during the first shot.

Below approximately 3,500 Hz, the Surefire silencer produces a more hazardous inner ear response than the Sig SRD silencer, and as a result, shooters with high frequency hearing loss may still perceive the Sig SRD silencer to be quieter. The same shooters with high frequency hearing loss may perceive the CAT ODB to be louder than the Surefire and Sig SRD silencer during FRP, even though the CAT ODB signature is objectively less severe. This is a function of the inner ear response differential below 2,500 Hz.

The CAT ODB is nominally the quietest to the shooter, on average, with the HX-QD 762 being the loudest to the shooter, on average.  The HUXWRX (OSS) HX-QD 762 is the loudest silencer (produces the most severe sound signature to the human inner ear) during the first shot and all shots on average, and it possesses this behavior to both bystanders and the weapon operator.

On average, the Sig SRD silencer is most likely slightly less hazardous to the operator than the Surefire SOCOM300-SPS.  The CAT ODB produces a signature that is slightly less severe than the Sig SRD to the weapon operator, on average.

On average, the Sig Sauer SRD762QD-Ti signature is approximately 26% less severe than the Sig Sauer SLH300Ti signature, to to the shooter, and 96% less severe than the HX-QD 762 signature.  On average, the CAT ODB signature, to the shooter, is approximately 27% less severe than the Sig Sauer SLH300Ti signature, and 97% less severe than the HX-QD 762 signature.  Just as during FRP, on average, shooters with high frequency hearing loss may perceive the CAT ODB to be louder than the Surefire and Sig SRD silencer, even though the CAT ODB signature is objectively less severe. This is a function of an average inner ear response differential below 2,000 Hz.  On average, the difference in signature severity to the weapon operator, between the CAT ODB and Sig SRD silencer is nominal.

This supplement is part of ongoing PEW Science small arm weapon system sound signature research. PEW Science thanks you for your support.