CA2160870A1 - Acoustical earmuff - Google Patents

Abstract

An earmuff cushion providing improved attenuation is described. The cushion is a foam material having a low static stiffness, and a high dynamic stiffness, which produces improved attenuation in the earmuff in which it is used.
Earmuffs made from the cushion and improved methods of making the cushion and the earmuffs are also described.

Description

WO 94/24185 .~ ~ ~ PCT/US94/03972 ~ -2160870 ACOUSTICAL EARMUF~

TECHNICAL FIELD
The field of art to which this invention pertains is hPArin~ pfo~;~ion, and sre~cifirAlly,rouctirAl e~-,-urr~.

S BACKGROUND ART
The use of earplugs and e~.nurrs are the two most useful ways to protect againsthPAring loss in those envif~l..n~ where noise levels are not able to be controlled within safe limits. In those areas where the use of earplugs is either il--possible or impr~rtirAl, the use of e~..-urr~ provides a means of redllcing sound intensity, in most ;~IC'Ai-~s to 10 a degree even greater than that provided by the use of earplugs. Other uses for noise eYcludin~ hPArin~ ~O~ include produr-in~ quiet for study, sleep, or audio pu~o3es.
rA.,.,..rr~ have advAnt~Ps for intc~..-il~nt use where co~ n~lo~~~ insertion andremoval of earplugs would be annoying or impr~tirAl. Also, ~urri tend to deliverhigher in-field noise ~.o~!;on in many high frequency noise en~ on...~n~ than most 15 earplugs. ~d~litinnAl pl~f~.~nce for eAllllllrr~ include use outdoors in cool w~thcr and use in dry ~1;---A~S.
~ 3en~11y, ~...urri have poorer low frequency AIIPnvAI;orl values than earplugs.
Part of the problem is be~ e at lower r,G luencies of 125 to 1000 Hz the e~---urr vibrates upon the ~....~.rr cushion and flesh in a ~wl~lping mode. Most w~ c are20 SPl~t~P~ of a soft combination of mAteriAl~ to achieve conformation to the head about the ear and claim co-nfo-L be~c~v~P of this ease of conçc~ Al;~n.
Most e~...ùrr~ are made up of a band s~tion~ a cup s~P~ti~)n~ and a c-v~hion sP~tiQn. The band section eYtPntl~ bGlwwn the pair of muffs, and holds the muffs snugly against the head of the wearer. The cup section is typically filled with foam mAtPriAl, 25 and in this combination of cup and foam is where the sound Allenl~AI;on takes place. The cushion section eYtPn-~ around the edge of the cup, and this cushion serves two pu~lJoses, to provide co---~-l to the wearer, and to form a seal to assist in kwping u..wanted noise away from the wGalGl's ears.

..t . ~ .t216087~) There is a constant search for ways to improve the comfort, sound ~tteml~tion characteristics, appeal~lce and designs of these earmuffs (note, for example, U.S. Patent Nos. 2,801,423; 4,260,575; 4,465,159; 4,471,496; and 4,682,374). In one of thesep~tt~ntc, Shaw et al. U.S. Patent No. 2,801,423, the cushion comprises a covering of 5 pliable or flexible but non-elastic material which forms a chamber around the periphery of the rigid cup. This chamber is ~ub~ ly gas ev~cu~t~A and partially filled with a liquid.
Shaw et al. later redefin~s the pr~re,.ed wall material as being polyvinyl chloride having a wall thickness of about 0.005 to about 0.01 inch and/or a dynamic Young's modules of about 5 X 103 p.S.i. Figure 1 shows the typical ~en~ ion achieved by an adaptation of this patent. The figure shows ANSI S3.19 Real ear attenuation vs.
Calculated Attenuation (C) for Safety Supply Model 258 Ear Muffs (Liquid Cushions as Per U.S. Patent No. 2,801,423).
The broken line on the graph inriic~t~s the calculated values and the solid line the 15 real ear values. Depths of 0 are formnl~t~ by the following formula:

Fo = AJVM X 35460 A = 72.84 cm2 V = 189.90 cm3 M = 116.08 Gm Fo = 92 Hz The present invention is di.~;~d to not only products, but m~t~ri~lc and metho~ls for producing such earmuffs which addresses the above concerns.

BRIEF SUMMARY OP THE INVENTION

The present invention is directed to an earll-urrcushion which provides improvedallenu~lion and ease of m~nnf~ctllre. The cushion is made up a foam m~teri~l which has a low static stiffn~sc~ and a high dynamic stiffn~cc. This invention simplifies construction which contributes to its ease of m~mlf~rtllre, retains ease of conformation about the ear and this same m~teri~l acts dyn~mi~lly very stiff reducin~ the motions of the earmuff cup.

Another aspect of the invention is an acoustical earmuff device cont~ining such a cu~hion.
Another aspect of the invention is a method of making such a cushion, through molding the cushion by passing the ingredients ~l.ough a mix/meter m~ ine into a5 mold, followed by crushing the molded cushion to provide increased ~eflP~tiQn characteristics while ~ in~ g dynamic ~l;rr.~s Dyn~mi~lly stiff cushions made by the above process when placed on low to u." volume e~lllurf~, the l)lere -~ d types, lead to ~r~m~ti~lly improved ~ttenl~tiQn results. These results exceed those predicted by equations normally employed for10 c~lc~ tion purposes.
These, and other aspects of the invention will become appare.lt from the following ~let~iled descli~tion.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows typical ~l~eu4~l;Qn of systems of the prior art.
Figure 2 shows a standard ~-,.urr co~ g a cu;,hio~ according to the present invention.
Figure 3 shows a flow chart of a mol(ling pr~cess for making c4shic~nc acccl.ling to the present invention.
Figures 4 and 5 show co...p~ ;sQns of REAT, IL, and c~lc~ tPd ~ .u .~;nn for 20 ~I~urr~.
Figure 6 shows static ~ofl~tion mP~llring a~p~
Figure 7 shows tr~ncmi~ihility m~sllring a~ s.
Figure 8 shows a t~n~mic~ihility m~mring system.
Figure 9 shows t~ncmi~ibility tr~ing~ for an e~h",urr.
Figure 10 shows controlling factors for e~lllurr ~ n~ ;5)n.
Figure 11 shows shapes of various et~",urrs.
Figure 12 shows a co...r~ on of REAT and IL values as a function of rrequellcy for an e~ rr.
Figure 13 shows a CG...p;.. ;~on of REAT to IL values as a function of fi~uency 30 for ea-",urr~.

..,j WO 94/24185 ~ 2 1 6 0 8 7 ~ PCT/US94/03972 .~
Figure 14 shows a co."y~ison of REAT to IL values as a function of frequency for earmuffs.
Figure 15 shows REAT co...pz~.;con.c Figure 16 shows REAT ~ ;cOI~c.

DETAILED DESCRIPIION OF THE INVENTION

The critical cG~ onent of the cllchion which provides the improved ~lle~...;.l;on in the e~lllur~is its stilfn~-cc char~cterictiG-c. The degree of ,lirr..~ss desired iS dependent upon the ability of the cuchion to form an acoustical seal against the head.
It has been found that m~t~.ri~l with a low static stiffnPcc, and high dynamic stiffnPcc, 10 provide improved ~ l;o~ according to the present invention. These ~l;rrne~
ell~r~t~ictics are defined in terrns of dynamic col-lple,. spring c4l.ct;.~-t (K~), static spring c~nct~nt (K,), and dynamic m~t~ri~l loss factor (~7).
In order to provide the improved ~ttenll~tion according to the present inventionit is ill~yO~ that the foam cuchionc have a dynamic spring co~ t of at least 30015 pounds/inch and a dynarnic m~tPri~l loss factor of at least 0.25, and yle~eldbly a dynamic spring col-ct~ of at least 1,000 pounds/inch. It is also i...po.~nl that the m~tori~l have a static spring cons~t of up to about 60 pounds/inch, and ~l~f~ably up to about 30 pounds/inch. While the cl~chi()nc according to the present invention can be made of any polymeric m~t~.ri~l having the above described ~lirr.~ c~-a~te icti~-s, 20 polyurel~,ane m~t~ri~l has been found to be particularly suitable, for e~mple, because of its stability in the presence of skin oils. And while any moldable polyu.cll.ane can be used, an espe~i~lly p.~f~.ed m~ri~l iS that clesc-rihe~ in U.S. Patent No. 3,377,296, the ~ os---e of which is incol~ldted by reference.

POLYURETHANE FORMULATIONS

The p efelled polyurt;lllane is diisocyai~ate based, preferably reacted with polyols with a portion being at least tri-functional, and having an iso~iy~late index of less than about 0.9.

r wo94n418s 2160870 PCTJU594/03972 According to Immergut and Mark (p~mticiz~tion and PlA~tiCjZ~r Processes, AmPrir~n C~hernir~l Society Publications);

~plActici7Ation, in general refers to a change in the thermal and meçh~nirAl pn~ ies of a given polymer which involves: (a) lowering S of rigidity at room le~ f---e; (b) lowering of tt;,.,~.~lule, at which S~I~S~ ;A1 dero,l--alion can be erræ~d with not too large forces; (c) increase of elhng~l;on to brealc at room ~ e; (d) incl~ase of the tollghnPcc (impact strength) down to the lowest t~ ~t..~e of serviceability. These effects can be achieved: (1) by col.l~ullding the given polymer with low molpcu1Ar weight co---l)oùnd or with another polymer: and (2) by introd~cing into the ori~in~l polymer a col~onGIllel which reduces crystAlli7Ahility and h~cr~s chain flPYihility. Il plActici7Prs have been broken into two types, intPrnAl pl~ctir-i7~prs and external pl~cti~i7~rs~ TntPrn~l rl~stiri7prs are actually a part of the polymer molocule - e.g., a second n~ o,--f~ is copoly--~Pri7PA into the polyma ~llUClulG thereby making it less o deled, and ll~ f~"G, more difficult for the chains to fit closely l~)gelllGr. This soften the polymer - i.e., lowers the glass trAnCitiorl t~.llr~.~ e ~g) or the modlllllc Usually, the intPrn~l pl~ctiri7Pr is a monomer whose polymer has good low telll~ ulG
~ ~.lies.
FYt~PrnAl plActiri7Prs are co",p. unds mixed in with the polymer which makes it more ~ifficult for the chains to fit closely togPthPr. This softens the polymer - e.g., lowers Tg or the modulllc FY~PrnAl pl~ctiri7prs are often ca~g<,lized as primary or seCon~l~ry dPfining degree of cc,...p~l;hility or in terms of it effi~ ncy or ~.IllAnf ~ce Polyul~ll,anes _re typically block co-polymers concicting of polyester polyols and/or polyether polyols reacted with iso~iy~nales having a functionality of 2 or more.
SometimPs the term polymers of iso~;ydnates is used to better define ~y~",s where water or amine lel...h-~lP~ co",po.~nds are reacted rP~s~llting in polyureas. Here polyult;ll,ane will be used all inclusively.

WO 94/24185 ~ i 216 0 8 7 0 PCT/US94/03972 When using a polymer polyol as a re~t~nt~ it is a pl~tici7p-r. Generally, the larger the polymer chain lengths for a particular type polyol the lower Tg. Types of polyols could also be referred to as having dirre~ t efficiençiPs. (Polyethers being more efflciPnt than polyesters.) Likewise, polyols could be considered more e-ffi~ient than 5 polyAminPs.
Monofunctional re~t~nts produce side chains which act as pl~cti--i7f rs However, they may be more or less effirient than the pl~cti-i7.o,r they replace. FYtPrn~l pl~ctici7p~r may be employed in polyur~ll.ane. Compatibility is quite illllJUl~t here and often a pl~felled approach has been to under index the system. The best way of 10 çn~l.ring co...paLibility is to use segmPnt~ of the polymer itself as pl~cti~.i7Pr.
UndçrinA~PYin~ is the in situ prociu~tion of eYtçrn~l pl~ctit.i7~r at the same time producin~ more A~n~ling polylllf-~ sp~mpntc. Undf rindeyin~ is not new to the art and was used in the early 1960's to produce soft foams for use in -,alll~ses and the like.
See U.S. Patent No. 3,377,296 and Cellular Plastics - Todcly's Technology, April 24 -25, 1963, "Te~hnQlo~y of Super Soft Flexible Ul~l.ane Foams~ by Dwyer, K~pl~n, Pirer and Stone.
The cllchinnc accG~ding to the present invention use di- and tri- functinn~
polyether polyols of varying mo~ r weight, lnderindeying and density adju~l~..f ~
as methorl$ of form~ ting co...l o~;Lionc which p~luce molted, dyn~mi~lly stiff, noise 20 eYclll-iin~ e~...)..rr ~ucl..ol-c At least a portion of the polyol used should have tri-function~lity (so as to produce a solid foam as opposed to simply a liquid polyu.~Ll.alle).
Surf~t~nt co~llbinAIionc are employed to .n~il-l;-in closed cells, a ~uil~.nent for noise eYçlu-iing ç~ ..rr cuchinnc. Lowering of the isocyanate index (NCO/OH) softens as does incl~ing polyol chain seg,.,~ length.
The cushions of the present invention will provide improvement in ~ nn both in use with the standard types of es.. ,.rr~ generally on the m~rl~t, but wilho~ll the bladders cull~nlly used.
In Figure 2, the cushion 1, is ~tt~h~1 to the seal plate 3, typically by a conventional p~s~u-~ adhesive such as an acrylic m~t~ri~l (not shown). The seal plate 30 is ~imil~rly ~ttaçh~l to the cup 4, again by convention~l m~th~ls such as ultr~coni~
welding. The hP~.lb~n~ S is attached to the cup, by typical mt~.h~nic~l means such as through a grommet (not shown), e.g. like those used in the convention~l E-A-R0 1000-~WO 94124185 ` 216 0 8 7 0 PCTIUS94/03972 3000 Model muffs. The foam liners 2 lining the inner surfaces of the cup 4, can be made of convçntion~l open cell foam materials, such as conventional pol~/urelhalles as are currently used. F.limin~tion of the cushion bladder provides the advantages of material savings and labor savings, in addition to the increased attenuation. Although 5 the foam according to the present invention can be used inside a conventional bladder system and some of the ~lle~ l;on advantages of the present system reali_ed, them~nllf~ctllring advantages would not be re~li7Pd.
The method for making the cushions according to the present invention can be described by reference to Figure 3. The re~ct~nt~ described in Table 1 are mixed in 10 conventional mixing ellui~,.--enL. This foam reaction mixture can be premixed and introduced into the mold or mixed as se~dle reactant sL,ea...s and injected as a single stream right into the plehedled mold, for eY~mrle in a conventional mix/meter mol~ing a~dlus, and is next introduced into the preh~t~l mold, c~ ing foaming to take place.
The injection can take place at low or high pl~S~u~eS r~nging from, for example, 50 to 15 300 pounds per square inch. The ~e~ is allowed to remain sufficiently high to cure the foam in the shape of the cu~hio~, and then the molded article is removed from the mold. It is then clushed to rupture some of the closed cells to allow at least some air flow. It is now ready to be either glued or otherwise affixed to the seal plate. As shown in Figure 3 the react~nts are first mixed (A), the ...i~lu~e is introduced into the 20 mold (B), the mixture is caused to foam (C), and the foam is cured (D), and the molded foam is next removed from the mold (E), and the molded foam is then crushed (F).

Polyol, catalyst, filler, pl~ctici7er, antifoam agent, surfactant and intern~l mold 25 release agents were premixed at room lelll~ldtule (see the Table 1 for specific compositions - the owners/sources of the tr~m~rk~lproducts are listed in Table 2).
The material was introduced into a pr~h~tç~ mold at a ~ dtUl'~ (about 500C) sufficient to cause foaming as part of a two stream introduction of materials (mix/meter m~chine). The isocyanate was added as the second stream. Cushions were then WO 94/24185 ~j~;J' ~ PCT/US94/03972 removed from the mold as quickly as possible to prevent puckering and crushed in order to open some of the as-formed closed cells. The cushion was bonded to the seal plate using convention~l p~es~ul~ sensitive adhesive. The liners were inserted, and the h.o~rib~n-l ~tt~rl~, all in conventional f~chinn. Testing was pe.~l,-,ed with the muff 5 to demonstrate the increased attenuation as ~ cu~ced below.

~ ' ' and Physic~ r t;~s for~ Siæ D,, ~ S~iffEar Muff Cushion ~n tF "' 1 2 3 4 5 6 7 8 9 10 11 12 13 LHT-240 56.00 56.00 56.0056.00 56.00 56.00 56.00 56.00 56.00 34.00 34.00 56.00 PPG-425 12.00 12.00 12.0012.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 LG-56 12.00 12.00 12.0012.00 12.00 12.00 12.00 12.00 12.00 34.00 34.00 12.00 Nia~c 11-34 100.00 Y-4347 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 1.20 3.60 3.60 3.60 L-45 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 1,4 E~ 1 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 I.S0 O
DE83R 18.60 18.60 18.6018.60 18.60 18.60 Antimony O~ide 6.20 6.20 6.20 6.20 6.20 6.20 Al Trihydrate 40.00 40.00 40.0040.00 40.00 40.00 Water 0.79 0.79 0.79 0.79 0.79 0.79 0.81 1.10 1.10 0.73 0.73 c M~lh~' Chloride 9.00 9.00 9.00 9.00 9.00 9.00 9.00 9.00 Ucar 154 1.98 2.75 Tinuvin 0.60 0.60 0.60 0.60 0.600.60 0.60 0.60 0.60 0.60 0.600.60 T-12 0.10 0.10 0.10 0.10 0.100.10 0.10 0.10 0.10 0.10 0.10 0.100.20 BL-I l 0.10 0.10 0.10 0.100.10 0.10 0.10 0.10 0.04 0.10 0.100.10 PPG-566 Green 0.90 0.90 0.90 0.90 0.900.90 0.15 0.15 0.15 0.15 0.15 83PC03 Brown 0.25 27A14 Red 0.01 llsonatel43L 47.2546.17 45.07 43.97 50.5747.25 47.25 47.25 47.25 26.86 39.24 43.26 47.49 ~
Ratio 3.49 3.57 3.66 3.75 3.263.51 1.91 1.91 1.92 3.96 2.53 2.291.94 1 O
C~O
Index 75.9374.17 72.40 70.63 81.2475.93 77.00 75.80 70.70 100.00 77.00 85.00 70.70 _~

s~ r ti~
Height (inches) 0.669 0.662 0.654 0.6620.701 0.651 0.673 0.662 0.655 0.656 0.654 0.662 0.660 Density (PCF)12.6 12.3 12.9 13.1 10.812.3 9.2 8.7 7.5 8.6 8.6 7.3 9.3 Def~i~m 12N 0.0510.123 0.154 0.240 0.0490.084 0.079 0.172 0.352 0.025 0.026 0.081 0.282 ~inches) O
F. (lbsli~ch) 82.7 18.3 11.7 57.753.5 35.6 16.4 108.5 12.5 34.910.00 ~ F ~'- 1 2 3 4 5 6 7 8 9 10 11 12 13 NRR(dB) Model 1000 24.9 25.0 25.1 24.8 25.1 24.3 24.1 24.S 23.6 17.2 22.1 23.1 Model 2000 27.3 27.0 27.0 27.6 26.2 æ.7 25.5 Mod~13000 27.7 27.7 27.8 28.9 26.2 27.7 26.3 26.9 24.4 27.1 29.5 T. ' '-~
Fn(Hz) 300 160 132 132 356 200 212 180 132 60 60 112 156 ~2 A or Lr (dB) 4.3 30 3.1 2.8 6.2 3.8 4.1 3.7 3.5 13.9 5.7 3.8 3.1 1 ~C~
K" (Ibs/inch) 9187 2613 1778 1779 12936 4083 4588 3307 1779 367 367 1280 2484 _~
'1 0.77 1.00 0.98 l.OS 0.56 0.85 0.80 0.86 0.90 0.21 0.61 0.85 0.98 Cushion Number 89A2 96A4 94B2 95C2 95D3 98A7 3B3 3C2 SAl 8B1 12C3 13A3 lSA2 LHl'-240 56.00 56.00 56.00 56.00 56.00 56.00 56.00 PPG425 12.00 12.00 12.00 12.00 12.00 12.00 12.00 LG-56 12.00 12.00 12.00 12.00 12.00 12.00 12.00 Nia,~c 11-34 100.00 Y4347 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 ~:\ .:;.
L45 3.60 3.60 3.60 3.60 3.60 3.60 3.60 3.60 1 ~ 1 1,4 r~ t l.So l.So l.So l.So l.So l.So 1.50 1.50 ~
DE83R 18.60 18.60 18.60 18.60 18.60 18.60 C::~
Antimony O~ide 6.20 6.20 6.20 6.20 6.20 6.20 ~1 T,il.~JIl~ 40.00 40.00 40.00 40.00 40 00 40 00 Water 0.79 0.79 0.79 0.79 0.79 0.79 1.10 Methylene Chloride 9.00 9.00 9.00 9.00 9.00 9.00 Uc~r 154 2.75 u Tinuvin 0.60 0.60 0.60 0.60 0.60 0.60 0.60 .

WO 94/24185 . , 216 0 8 7 0 PCT/US94/03972 - _ 8 ~ ~ _ o o o ~ ~ g o _ o ~

o~ o ~ ,, o ~, ooo ~X o_o O ~ ~ ~ ~ O ~ v~ ~r o o o ~ ~ t` o ~

_ O

~o ,,, ~ _ ~o o~ o o o o ~ ~ ~ o _ o ~, _ o ,_ ` o o o o ~ _ ~ o oo o o o o~ ` ~ ` -- oO~ 't o o o ~t ~ ~ o -- o Z ~

F 1~' / 14 15 16 17 18 19 20 21 Insertion Loss:
NRR(dB) Model 1000 25.3 24.6 26.2 25.8 25.3 26.4 26.4 20.7 M~del20D0 27.7 28.0 28.5 27.8 28.3 28.3 28.3 24.6 Model 3000 29.1 29.7 28.7 29.5 29.5 29.3 28.8 Fn (Hz) 164 200 336 324 256 208 504 84 A or LT (dB) 2.8 3.7 4.4 4.0 3.0 3.0 8.0 11.8 CX~
K~ (Ibs/inch) 2745 4083 11524 10715 6689 4416 2S928 720 C~
I.OS 0.86 0.76 0.81 1.00 1.00 0.43 0.27 Ci~himm Numbcr IOA3 ISB5 89A6 96B1 96C2 96D2 96A2 6C2 WO 94/24185 ~ 2 i 6 0 ~ 7 0 PCT/US94/03972 MATFDTAT.!~ SOURCE LIST

BRAND NAME SOURCE LIST FUNCTION EOUIVALENT WEIGHT

Arcol LHT 240 Arco ~L 1 Low MW Triol 234 Arcol PPG 425 Arco Cl 1 Low MW Diol 210 Arcol LG 56 Arco 1~' ' Medium MW Triol 1000 Arcol 11-34 Arco ~L 1 High MW Triol 1580 Y4347 UnionCarbide Cell S bi'i7P- _ L-45 (350) Union Carbide Cell Regulator 1,4 r - ~ ~. GAF Chain F ' 45 DE 83R Great T ~kes Chem Fire Retardant O~ide AmspPc ~L ~ -~ Fire Retardant ,~1 T.ih~.' Solem T ~ -- Fire T2. ~ .
hll,lLyl.,.. Chloride Dow ~ 1 Blowing Agent Ucar 154 Union Carbide Cell S ' 1i7pr 22.5 Tinuvin 765 Ciba Geigy HALS
Dabco T-12 Air Products Catalyst Dabco BL-ll Air Products Catalyst PPG-566 Dayglo Colorant Stantone 83PC03 Harwick ~ ' Colorant Stantone 27A14 Harwick 1~ 1 Colorant Isonate 143L Dow ~ 143 WO 94/24185 ~ 0 8 7 0 PCT/US94/03972 --Polyol, catalyst, filler, pl~tici7Pr, antifoam agent, surfactant and internal mold release agents were premixed and deg~d at room ~~ ul~. The is~y~late was added thereto, and the ~ ul~ deg~ once again. The m~t~ri~l was poured into a 5 mold at a ~nl~l~lule sl-fficient to cause foarning (e.g., about 50C). The formed cu~hion~ were then removed fronn the mold and ~ ce~ as set forth in F-~m, '~
above.

Al TENUATION ~ G/INSERTION LOSS TESTING

~ttloml~tion testing and Insertion Loss (IL) testing are conducted in acconlancewith ASA STD 1-1975 (ANSI S3.19), "~tho~ for the Mea~ul~.llent of Real-Ear E~ot~;nn of ~e~ring ~uleClolS and Physical ~ ;n~ inn of Lallllur~s". The artificial flesh supplied for the physical method did not meet the Shore 00 dwullle~ l~uil~.nent of 20 ~ 5 stated in the above procedure. Th~ rt;rul~, an artificial flesh made of silicone rubber was made having a Ille~uled Shore durometer of 20, being 0.385 inch thick and having a Knowles Electronic pinna over the micluphone center. The pinna was ol,lah~ed from ~n~ustri~l Research Products, Inc., a Knowles Comp~ny.
Insertion Loss testing employs an artificial test fixture (AI~F) having artificial flesh yielding insertion loss results for e~ .rr~ which are similar to those ~tt~ined using real ear testing at threshold (REAT). When using the ATF it should be renltl~bel~d ~at ~le~ lion results for better eallllurrs are usually bone c )nduction limited to 35 dB i about 2 at 2000 Hz.
The EPA has sPlected the NRR as a measure of hearing pl~tectol's noise recillcing capabilities. The range of noise reduction ratings for eYi~ting hearing ~ro~ ul~ is ap~ t~ly O to 30.
When estim~ting NRR from IL test results, we used 10 dB and 20 dB for minimllm 125 Hz insertion loss values for the E-A-R0 Model 1000 & Model 3000 e~u.nurrs r~eclively. These values were only lequiled for the normal e~.nurrs aslulrrs utili7ing dyn~mi~lly stiff c~-~hion yield higher values. Standard deviations of -wo 94/24185 - s2~ 1 6 0 8 7 ~ pcTluss4lo3972 .

3.0 are employed in calcul~ting estim~ted NRRs. This value is typical of measured values.
In several Tables, Q FREQ values are also listed. These values are the frequencies controlling the NRR. This means that changes at this frequency directly 5 effect the NRR while ch~ng~os at other frequencies may have no effect what-so-ever.
Insertion Loss measurements are only used in lieu of REAT measuremtonts.
Figures 4 and 5 show comp~isons of REAT, IL and calculated ~ttPml~tion for convention~l Model 3000 and Model 1000 E~lllur~s ,espe~ /ely. These Figures are used as a basis for using IL in lieu of REAT for the pul~ose of ev~ tin~ dyn~mi~lly 10 stiff cushions.
In Figures 4 & 5, C is the calc~ ted value, T is the result of 10 subject test, N
is the nominal limit due to bone co~uction and I is the insertion loss. The calculated ~l~e~ l;on obtained by del~""ining the frequency at 0 dB ~tten-~tion (Fo) using the eAprt;ssion:

Fo2 = A2/VM X 35460 Where: A = Area bounded by the cushion outer edge (cm2) V = Volume (cm3) M = Mass (gm) 20 In Figure S the increase in ~ l;on with frequency is applied using a 12 dB/octave.

STATIC DEFLECTION TESTING

Static deflection is Ill~suled on an appa dLus as shown in Figure 6. The apparatus consists of a platform 61 with an ~tt~rh~d adjustable electronic thickn~ gauge 62. The e~",u~ cup 63 has a hole 64 at the center of the top. At the top of the hole 25 is a flat plate 65 with ~tt~h~d hook 66 which protrudes through a hole in the platform so as to receive a 12.5 Newton weight 67.

WO 94/24185 .' ~ 2 i ~ 0 8 7 ~ PCT/US94/03972 The earmuff cup with cushion in position is placed under the electronic thickness gauge and the gauge is zeroed. Simultaneously to adding a 12.5 Newton weight to the hook a stopwatch is started. After 10 minutes the deflection is read from the electronic thickness gauge and recorded.
In these experiments the ea,lllurr cup employed is from an E-A-R0 Model 1000 Earmuff. The plate cup and hook weighs 90 gms exclusive of the cuchion TRANS~T.CSTR~T TTy TESTING

Tr~n~mi.~ibility measurements are taken using the fixture shown in Figure 7 and the equipment shown in the block diagld--- in Figure 8.
For this work it was shown that adding weight to the cup to a total weight of 1.00 pound (454 grams) using barium sulfate filled epoxy resin was nP~es~y to ensure adequate contact of the cu~hion to the platform. This total weight of 1.00 pound was employed during all tests.
Also, adequate stiffntoss of all connP~tion~ and of the platform itself must be assured so as to give a straight line output free of s~onda~ n~s to at least 1000 Hz. The platform used in this work was 5.0 inch (12.7 cm) ~ ",~le~, 1.50 inch (3.81 cm) thick brass.

The test procedure used (with reference to Figures 7 and 8) was as follows:

Place the e~...urr cup 71 with ~tt~t~hed cushion and mass on top of the shaker platform 72. Shaker 73 and stand 74 support the platform. With an input level of 0.2 G (~ler~tion of gravity, 32 feet/second/second) obtain a tr~n~mi~ihility curve having the cursor at the natural frequency. Read and record the natural frequency (Fn) in Hz and the amplific~tion (A) in dB. In Figure 8 the accelelu---elel (81) is co~ through the low noise cable (82) to the power/amplifier unit (83). The power/amplifier unit is connected to the signal output analyzer (86) which is connected to the audio amplifier (87) and shaker and stand (88). The accelerometer (84) is connected to the microphone amplifier accelerometer adapter (85) which is also connect~d to the signal output analyzer. The signal output analyzer is connected to the graphics recorder application package (89). The con~pollents are all commercially available, e.g., the accelerometer (81) is a PCB 303A02; the low noise cable is PCB Model PCB 002C05; the power/amplifier is PCB model 40DO6; the low noise cable can also be a PCB 003810;
the signal output analyzer is a Bruel and Kjaer Model 30282FFT; the audio amplifier a Proton model D540; the shaker and stand are MB Electronics Model ER1500; the accelerometer (84) is Bruel and Kjaer Model 4693; the microphone ~.,~l"plifier and accelerometer adapter are Bruel and Kjaer Model 2619 and W/JJ2615 respectively; the graphics recorder and application package are Bruel and Kjaer Model 2313 and W/827006 respectively. The cables are all standard commercially available low noise cables as described above. Figure 9 shows trAn~mi~ibility tracings for the E-A-R0 Muff Model 1000 with 3 di~Çerent cushions. In Figure 9 the standard is shown by curve S, the Hypol0 urethane / acrylic m~t~.ri~l is shown by curve A and the polyu~cll,ane m~teri~l of the present invention is shown by curve P. The Fn is directly related to the dynamic complex spring constant (K~) of the cushion and the ~mplifir~tion at lesol-Ance (A, sometimeS referred to as L~) to the m~tPn~l loss factor. Since the K~ and ~i vary with frequency, the exact weight of 1.00 pound (454 gram) must be used to dele""i~,e these values. K~ and il are c~lc -l~t~d using the following equations:
K~ = ( (Fn)V3.13 )W lbs./inch (W=weight in Ibs.) ~¦ ( 1 OLT/20)2 _ where L, = A = level of tMn~mis~ibility at resol-~l~ce (dB).

EARMUFF A~ NUATION

A ~implified ~ gr~m showing the controlling factors for earmuff ~tten~-~ti~ n isshown in Figure 10. Occlusion effect of the cushion/flush stiffness is shown by curve S, the mass by curve M and the bone conduction by limit by B and the stiffne~s surface area absorption by A. The frequency calcul~tions are as follows:

Low Frequency: Fo = A/2~ PC2/VM: PCV(27r)2 = 35460 : Fo2 = AVVM X 35460 WO 94/24185 216 0 8 7 ~ PCT/US94/03972 Where: Fo = Prequency e~ O dB ~ttçnl-~tinn A = area bounded by the cushion outer edge V = volume M = mass P = density of air C = speed of sound in air At very low frequencies (normally up to 125 or 250 Hz) the cl.chion/flesh s~;rr~e~ controls e~lllurr ~tlP~ l;on.
~A~Iition~lly, the occ~ ion effect causes a somewhat higher al)p~.lt ~ n~linn at the lower frequencies due to m~ ing by body noise when wearing a hP~ring ~rolec~r.
~ n~r~lly, this low frequency ~tiffnP!~s controlled ~ n~ n is thought to belimited by the low stiffnes~ of the flesh about the ear. Even the iu~hion .sl;rr~le~ is 15 limited by the balance bel~woen wearer colllfoll and the ability of the cu~hinn to l~r~duce an acoustical seal against the head.
The low rl~u~,ncy ~ nn~l;on from 125 to 1000 Hz can be predicted by c~ tin~ the rr~quen~ at 0 dB ~l~r~..u~l;on using the equations as described for Figures 4, S, or 10 and then extrapolating drawing a desc~-n-linf~ line increasing in ~ .n-.~;r~n by 12 dB per octave up to 1000 Hz. Above 1000 Hz ~IIlurr ~ l;on is controlled by the surface area of the cup, absolplion within the cup, sl;rr..-ss of the cup and at some frequencies (notably 2000 Hz) by bone conductinn. Bone con~uction or body u~nductinT~ is sound re~chin~ the inner ear by other paths besides directly down the ear canal.
Since e~lllur~ norrnally have large ~ttenll~ti~m values at frequencies above 1000 Hz, these frequencies yield adequate l~lu~lion and traditionally have l,r~senled little or no problems.
However, much lower ~ttenn~tion values are ~ttz~in~i at frequencies below 1000 Hz, and tll~lt;Çol~ increases in ~ttenll~tio~ within this frequency range can yield 30 ~ignific~nt increases in plu~ ion and in the res~lt~nt Noise ~ ction Rating (NRR).

wo s~ 8s ~! 1 6 0 8 7 0 rcTIusg4l039n NOISE REDUCTION RATING (NRR) The Noise R~lctis)n Rating (NRR), a variant of the NIOSH RC factor, is the - current EPA ~r~,~Gsed single number des~ ~r. The NRR is fully ~efinPd in EPA
(1979) Noise Labeling Requirements for Hearing Protectors, Federal Register, Vol.42, S No. 190, 40 C.F.R. Part 211, 56139-56147. A sample NRR c~lcu1~tion is demon~tr~t~
in Table 3. The key point to consider is that the NRR is subtracted from the measured (unplu~ d) C-weighted sound level to yield an effective A-weighted sound eA~SUlC;
for the employee. The idea of subtracting a noise reduction factor from a C-weighted sound level to find an A-weighted CAl)OSUle was first pr~posed by Botsford in 1973.
This "C-A conce~" is the i~ t col-----on ingredient in all of the succe~rul single nllrnher de~liplùrs pn~l~osed in recent years. As can be seen in Table 3, the NRR is the dirr~l~nce belwæn the overall C-weighted sound level of a pink (flat by octaves) noise sp~;llu~ll and rP~sulting A-weighted noise levels under the pr~te~lor. TheAl~u~l;Qn values used in the ç~lcul~tion are the .--~.~ ho,i.tc., ~ t;Qn values minus two ~nda~d deviations. This correction assures that the ~ u~l;on values used in the ~lc~ tion ~luc~lure are actually re~li7~hle by the majority of employees who cQn~:c~t;oucly and co~ ly wear their protectors. This coll~clion will not account for c.l,l)lo~lee misuse or abuse of the ~,ut~lu,~.

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~WO 94/24185 ~ 2 1 6 0 8 7 0 PCT/US94/03972 CUSHIONS SHAPES & SIZES -VS- INSERTION LOSS
Dyn~mic~lly stiff polyul~lhane foam earmuff cushions of Example 1 were made into various shapes shown in Figures llA through llH. In Figures llA through llFthe following cushions are shown in cross sections: the standard cushion (A); meAillm S cushion (B); thin cushion (C); tapered cushion (D); reversed taper (E); and large (F).
The back plates are shown with all cushions except for large (llG) and for largecushions (1 lH). The hole in the cushions lines up with the hole in the back plate. The upper portion of each cross section as shown is that normally cQnt~ ting the head.
Insertion Loss measured values for these shapes are shown in Table 4 with the 10 physical propelLies listed in Table 5. Of the various shapes as measured on the E-A-R~
Model 1000 Larll,urf several conclusions may be drawn:

1. All dyn~mi~lly stiff cushions are superior to normal Model 1000 cl-chion~ with respect to low fi~u~,n~;y ~llr~ l;on and e~ ed NRR.

2. The Reversed Taper cushions yield the highest low frequency insertion losses and NRR. This c~hitn is followed by the Thin, Standard and Tapered shapes l~es~ ely.

3. The Tapered cu~hion when inverted so as to give the same area of contact with the head as the Standard cushion gave similar results.

4. Crushing the foam c~-~hion had no ~ignifiç~nt effect on Insertion Loss.

20 5. The Reversed Taper, Thin and I~rge cushions all yielded higher high fr~4uency insertion loss.

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Est. Freq. t (db) Model2000 Thin/ 193 23.1 24.3 33.2 37.4 47.1 44.5 42.5 41.0 42.8 28.3 250 Model 2000 Thin /192 21.8 24.3 33.7 37.6 47.7 43.3 39.3 39.0 41.0 28.0 250 Model 2000 Tbin / 19~ 22.0 24.0 33.7 37.8 46.3 41.6 38.9 40.2 40.0 27.9 250 Model 3000 Thin / 185 24.8 27.0 36.0 39.7 48.0 42.0 37.3 40.1 41.0 29.9 250 Model 3000 Thin / 18~ 24.3 26.1 36.0 40.3 41.6 35.6 30.7 28.7 29.7 25.4 6+8K
Model 1000 Std. /2 18.8 21.7 31.7 33.6 43.6 36.5 34.8 39.4 42.0 25.0 250 Model 1000 Std. / 3 18.0 21.6 31.7 34.4 43.8 37.8 35.3 38.7 42.8 25.1 250 ~_ Model 1000 Std. / 4 17.3 20.6 30.2 36.5 44.3 38.7 37.5 41.8 43.9 24.8 250 Modrl 1000 Sld. / 5 ZO.I 23.0 32.1 33.3 43.4 32.8 33.5 37.1 40.4 25.1 250/3+ C~

Model 1000 Std. / 7 19.7 20.5 31.0 33.1 43.7 34.2 33.0 37.1 40.2 24.1 250 Model 1000 Std. /6 19.0 20.0 30.1 34.5 45.0 37.1 35.5 38.3 42.3 24.3 250 Model 1000 Std. / 8 19.4 19.8 30.5 35.8 44.0 37.9 35.8 38.5 42.0 24.5 250 Model 1000 Std. / 9 16.4 19.0 29.8 37.2 43.3 36.5 34.4 38.1 41.8 23.6 250 Model 3000 Std. / 2 24.3 26.1 35.0 39.3 47.6 33.2 34.3 38.0 39.0 27.7 3+4K

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WO 94/24185 2 i 6 0 8 7~ PCT/US94/03972 Of the various shapes as measured on the E-A-R~ Model 3000 e~.".lrr, a somewhat dirr~l~nt conclusion may be drawn. All dyn~mic~lly stiff cushions are superior to normal Model 3000 c~chionc for low frequency Insertion Loss but manyshapes do not result in higher estim~t~d NRRs. The Reverse Taper and Thin c~chi-~nc 5 are exceptions. The rest of the shapes end up with the 3/4 K Hz frequencies controlling the NRR and limiting further increase. Later ~A~ nl~ will utilize an optimized foam liner to further increase high rl~uency insertion loss. A total of 14 form~ tionc have been made into e~ rr c~chionc (See Table 1). Five of these form~ tiol~c Examples1 llllougll 5 are a series having high filler (flame lc~da, t) concenLI~tions being from 10 softest to hardest ~ tely. Test results of this series has been broken our in Tables 6 and 7 r~specli.~ely. The le .l~ g formations have changes as follows:

FOR~ULATION- F.~ ?lÇ CHANGE
6, 15, 1 Water added as part of Latex, UCAR

7, high index Filler & MeCl omitted, low water 8, med. index Filler & MeCl omitted, med. water 9, low index Filler & MeCl omitted, high water 21 High Mw Polyol and 100% index 10, 1,4 blJ~; n~l;ol High Mw Polyol and 100% index, drop 11 Increase conc. of high Mw Polyol, Decrease low MW Polyol of 3B

12 Same as 12C but increased index 11/12 No filler or MeCl, water added as UCAR 154, index as 95C, softest Of the above formulations the soft to hard series of S form~ ti( m are aimed at 25 produçin~ a cuchion in S~d~d or Thin cross-section which may help to define the upper limit of suitability for hardness i.e. lowest static deflectiQm FY~mple forml-l~tionc 21, 10, 11 and 12 are aimed at prod~lçin~ c~-chi( nc helping to define the lower limit of suitable dynamic sl;rr.---cc.

wo 94/24185 216 0 8 7 0 pcTluss4lo3972 .; ~ .... , --The ~ i..ing formulations are aimed at producing a series of lower density m~tt~ri~l allowing greater dçfinition of pn~r~,t;d physical char~rterictics. Table 8 list the Shore 00 Durometers of the various c.-~hion~ at 7C, 22C and 41C. This data isgiven as an ~lt~rn~te measure of hardness to aid those more f~mili~r with this measure.

S EQUIPMENT

Although most of the formulation were mixed in the laboratory for e~peAiçnr,e of ch~nging form~tions, some cuchion~ were produced using a convention~l mix/meter m~chine (e.g., Edge Sweets Foam M~rhine Model Flex-2H, Grand Rapids, MI). When using the foam m~rhine it was discovered that cu~hiollc should be made, colored and/or 10 coated for much less than by employing the pr~eS5CS used to make virtually all of the noise eYcJu~ling e~murr~ on the market today.
Cullently cG.n,--cr~ial e~--~urr cuchionc are made using a ...in;...---.. of two thin sheets of polyvinyl~lon~le or polyu,~l,ane, one of which is vacuum formed and filled with a cut-out donut of foam or a liquid followed by therrnal bonding and cutting off the 15 trim. R~ e of the low volumes normally employed, the ~l cess is labor int~nce, results in conci~lç~ble waste and is costly.
Table 1 show the form~ trJry and s--~ -y physical pr~ ies for Standard, M~illm and Thin sixed dyn~mir~lly stiff ea,...urr cuchion~ ely. Units are grams (and l~l.,~nt ratios as well).
Table 4 shows the individual insertion loss values as measured and are mostly used as ~u~ ing information for Table 1.
Tables 6 and 7 break out the physical ~ic,pe.~ies for the series of five cu~hionc varying from softest to hardest. These data show the Thin cushions to have least static ~lçfl~tinn, higher calculated NRRs and higher system natural frequencies (Fn).
The system natural rr~uel.cies (Fn) and ~mplific~tion at l~son~n~-e (A) values increase with increasing hardness.
Table 6 shows a normal cushion to have a (Fn) of 52 Hz with cushion from FY~mpl~ 11 being higher at 60 Hz. Cushion from Example 11 will be utilized later as an eY~mple of a good ~lro~.,.er.

WO 94/24185 ~ PCT/US94/03972 Cushion from Example 15 is an example of cu~hions yielding a large static deflection. This c~shion will be utilized later as an example of a good pelro~",er.
It should be noted that FY~mple formulation 15 cushions of the Standard size yields the highest insertion loss for that siæ. This along with con~ ;./e results for S the cl-chiol-~ from Example 14 in the Standard ~pAium & Thin siæs leads one to believe that the thi~kness as worn preferably should be less than 0.5 inch.

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STn~ CUSH~ONS

Av. ThicknessAv. Densiq Av.Fn Av.A
(In) (#IR3) (Hz) (dB) E%ample 4 Softest 0.534 14.1 170 2.9 E%ample 18 2"1 Softest 0.533 14.0 194 3.1 E%ample 17 3,~ Softest 0.537 13.6 242 3.5 E%ample 1 4~ Softest 0.540 12.8 318 4.4 E%ample 2 Hardoet 0.560 12.1 430 7.1 WO 94/24185 1 216 0 8 7 ~ PCT~U594/03972 CUSEIION SHORUE OO DURO~5ETER -VS- llEM}qERL~llUFUE
(Instant P~ ' O ) S CUSH~ON 7C ~2C 41 C
~"y~le 1 * 81 60 40 12 65 33 æ
1 * * 80 52 32 NonnL~ 61 50 40 * In-mold co~ed * * Shiny surface Al rENUATION TESTING - ANSI S3.19 Four earmuff cushions as alluded to earlier were selected for Real-Ear Attenuation Testing at Threshold (REAT) by ANSI S3.19 and co"ll~a ison made of those ~ttenll~tion results with insertion loss values. All alLe"uation results were in5 conformance with ANSI S3.19 except that five subjects were employed. Figure 12shows the co...l)a~ison of REAT to IL values as a function of frequency for Model 1000 E~"~lrrs with dyn~mi~lly stiff cushions, Example 11 (Std.). This figure shows the insertion law (IL) (calculated NRR=22) vs. Real Ear .Attenll~tion at threshold (REAT) (NRR=24) co~pa,ison for Model 1000 ear muffs with dyn~mi~lly stiff cuchion.c of o example 11. The bone cond~lctiol~ limited area is shown as B. These cushions were selected to be close to but superior to Normal Model 1000 cuchion.c. Tables 9 A and C show the individual subject data along with ~Lp~,lu~"iate calculations.

DIXONS OUTLIER TEST: EXTREME MEANS
Mean ~ ;on in dB across trials Subj. 125* 250 500 1000 2000 3150 40006300 8000 DVF 14.3 19.3 31.0 39.3 32.3 37.7 35.040.3 43.7 JEF 15.0 18.3 29.7 37.7 35.3 36.3 37.342.3 40.3 MG 16.7 18.3 26.7 36.7 34.7 37.3 36.340.3 44.3 BAK 21.7 23.7 27.0 37.0 36.7 37.7 38.342.3 43.7 JRM 14.3 17.7 28.3 36.3 31.7 36.3 37.038.7 39.7 I
Mean 16.4 19.5 28.5 37.4 34.1 37.1 36.840.8 42.3 Min. 14.3 17.7 26.7 36.3 31.7 36.3 35.039.7 38.7 2s Max. 21.7 23.7 31.0 39.3 36.7 37.7 38.342.3 44.3 *1/3 Octave-Band Prequency WO 94/24185 . 216 0 8 7 ~ PCT/US94/03972 -4t)-~~D O t` O ~ ~

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Wo 94124185 216 0 8 7 0 PCTIUS94/03972 Figure 13 shows the comparison of REAT (NRR=25) to IL values (calculated NRR = 25) as a function of frequency for Model 1000 Earmuffs with dynamically stiff cushions of Example S (Std.). C is the bone conduction limited area. These cushions were selected as having close to --a.~,inal static deflection for problem subjects. Tables s 10 A and B show the individual subject data along with ap~r~ ,ia~e calculations.

DIXONS OUTLIER TEST: EXTREME MEANS
Mean ~ ;on in dB across trials 0 Subj . 125* 250 500 1000 2000 3150 4000 6300 8000 DVF 10.7 19.0 26.0 34.3 32.7 28.0 31.7 31.3 34.3 JEF 20.0 23.3 31.3 36.3 36.0 32.7 33.0 35.3 37.7 MG 20.3 22.0 29.3 36.0 35.7 36.0 33.0 33.3 36.3 BAK 22.7 25.7 29.7 33.3 35.7 33.7 34.0 35.3 36.3 JRM 20.7 23.3 31.7 37.7 33.0 36.7 33.0 41.3 40.7 Mean 18.9 22.7 29.6 35.3 34.6 33.4 32.9 35.3 37.1 Min. 10.7 19.0 26.0 33.3 32.7 28.0 31.7 31.3 34.3 Max. 22.7 25.7 31.7 37.7 36.0 36.7 34.0 41.3 40.7 *1/3 Octave-Band Frequency WO 94/24185 . :216 0 ~ 7 ~ PCT/US94/03972 Z `

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WO 94/24185 45 I'CT/U594103972 Figure 14 shows the co"~ r;~on of REAT (NRR=29) to IL values (calculated NRR = 29) as a function of frequency for Model 3000 Earmuffs with dyn~miç~lly stiff cushions of Example 14 (Med.). The bone conduction limited area is shown as C.
These cushions were selectç~l because of their superior IL l~elroll"allce on Model 000 s Earmuffs. Tables 11 A and B show the individual subject data along with ~,r~liate calcul~tion~, DIXONS OUTLIER TEST: EXTRE~ME MEANS
Mean ~ ;on in dB across trials Subj. 125* 250 500 1000 2000 3150 4000 6300 8000 DVF 23.0 27.7 39.3 42.0 38.7 41.0 40.7 41.0 42.3 JEF 21.7 25.3 37.3 43.0 34.7 41.3 37.7 41.3 40.0 MG 23.0 24.7 36.7 41.7 40.0 40.3 38.0 39.3 41.0 BAK 27.3 31.7 38.3 44.7 44.7 43.0 43.3 41.0 39.3 JRM 24.0 27.0 39 7 43.7 33.7 40.0 40.3 41.0 40.0 Mean 23.8 27.3 38.3 43.0 38.3 41.1 40.0 40.7 40.5 Min. 21.7 24.7 36.7 41.7 33.7 40.0 37.7 39.3 39.3 Max. 27.3 31.7 39.7 44.7 44.7 43.0 43.3 41.3 42.3 20 *1/3 Octave-Band Frequency -4~
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Figure 16 shows a REAT co...1 ~. ;con for Model 3000 Earmuffs having 5 dyn~mir~lly stiff cushions (D) (NRR = 29) of FY~mrle 14 (Med.)as co---p~hc;d to the same e~.~urrs having their normal cuchionc (S) (NRR = 25).
All of these results from Figure l l Ihro~ll Pigure l 6 shows the close correlation belwæ1l REAT and IL and the superior pe1rol.-.ance of dyn~mic~lly stiff cllchionc over normal c~1chinnc.

COATINGS

Pinally, sample cushions were coated with an in-mold ~liph~tic sly blue polyu~lane, ~lirhlPY~ MPM-El80A. The coating was applied in-mold (spraying the mold, 10% solids cs~ ;1;on, al)L,ro,.i...~ ly one mil thick) prior to foam form~ tinn ~d~1iti~n (can also be applied ~ltprn~tely to the foam cuchiQ~ after pro~uction). Both 5 c~1;ng~ were re~con~hle with the in-mold coating having sll~ior looks and feel. The c11chionc spray-coated after production resulted in some absol~Lion into the surface.
Table 12 shows insertion loss test results in-1ir~tio~ that coated cuchionc yield the same improved low frequency ~le~ l;on and e,~ P~ NRRs as the unCo~tP~ dyn~mi~lly stiff cushions.

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WO 94124185 ~ 216 0 8 7 ~ PCT/US94/03972 In addition to increased attenuation, the cushions of the present invention provide improved ease of manufacture. Many e~ll,urr cuchionc have been made and tested most of which gave superior low frequency insertion loss and estim~ted NRRs. REAT andIL values as well as NRRs c~lc~ t~ from them ch~lr~ each other very well ~lthough s if questions should arise REAT ANSI S3. 19 values could be utilized as a referee. All foam cushions produced of molded polyu,~ll,ane on foam m~rhin.ory have an ease of m~mlf~ctllring advantage (which would also show itself as a low cost m~mlf~tllring advantage). Cushions having static ~ef~tic ~c of about O.OS inch or greater are ylerell~d for problem subjects with a static dçfl~tion of about 0.10 or more being more ~l~relled.
lo C~uchions having an Fn as tested in this report of about 52 Hz or more show equal to or superior ~lrollllance to normal cuchirnc. Cushion which deflect to a thir1~n~cc of about 0.5 inch or less when colllll~ssed (as measured by the static defl~tion test) are prerelled. C--chionc with increased contact with the head are pr~rclled. An eY~m t~
of this is the r~ ~d taper shape referred to in Figure 11 and Table 4 although other lS !~.;r~.Pc~fs are certainly applicable.
Applied CO5~ g~ espffi~lly in-mold coz~l;,-Ec may be adv~nt~eous. Placing molded dyn~mir~lly stiff cnchionc into current art bladders may also yield increased --~ ce but at higher cost. The total effect of ~mplifi~tion at l~sonAnce (A), is not totally und~-r~tood at this time. It is felt that c~chinnc having Fn about 52 Hz or less 20 may be useable as low cost cnchion~ of similar p~lrUl.-,~ ce to the prior-art. However, more highly resilient c~shinnc having Fn of about 52 Hz or less with A of 9.S dB or more may yield inferior ~ n~ ;nn.
From the above, it can be seen that the improved cushion of the present invention results in at least a 3 to 4 dB increase in ~ n-~;on over that obt~h~able with a25 conventional muff. In addition, the cushion of the present invention is easier to m~nllf~ctllre than convention~l muffs. For eY~mple, in addition of the ~limin~tiQn of a bladder, it can be formed directly onto a cushion seal end plate, if desired.

Claims (19)

1. An acoustical earmuff device comprising a pair of earmuffs fastened to opposite ends of a generally U-shaped connecting band, the earmuff comprising a rigid cupsection connected to the band on one side of the cup, and a compliant foam section on the other side of the cup for contact with the wearer, wherein the improvement comprises, using as the foam section a foam material having a low static stiffness, and a high dynamic stiffness resulting in an earmuff with higher attenuation.

2. The earmuff device of claim 1, wherein the foam section has a dynamic spring constant of at least 300 pounds/inch and a dynamic material loss factor of at least 0.25.

3. The earmuff device of claim 1, wherein the foam section has a dynamic spring constant of at least 1,000 pounds/inch.

4. The earmuff device of claim 1, wherein the foam section has a static spring constant of up to 60 pounds/inch.

5. The earmuff device of claim 1, wherein the foam section has a static spring constant of up to 30 pounds/inch.

6. The earmuff device of claim 1, wherein the foam section is a single molded piece.

7. The earmuff device of claim 1, wherein the foam is a polyurethane.

8. The earmuff device of claim 7, wherein the polyurethane is the reaction product of a diisocyanate and a polyol having an isocyanate index of less than about 0.9.

9. The earmuff device of claim 8, wherein at least a portion of the polyol has afunctionality of at least 3.

10. The earmuff device of claim 1, wherein the foam additionally contains a polyurethane coating.

11. The earmuff device of claim 1, wherein the cup is attached to the headband through a grommet made of rubber or other elastomeric material.

12. A one piece molded foam earmuff cushion for noise exclusion having a low static stiffness and a high dynamic stiffness resulting in higher attenuation when used in an earmuff.

13. The earmuff cushion of claim 12, wherein the foam has a dynamic spring constant of at least 300 pounds/inch and a dynamic material loss factor of at least 0.25.

14. The earmuff cushion of claim 12, wherein the foam has a dynamic spring constant of at least 1,000 pounds/inch.

15. The earmuff cushion of claim 12, wherein the foam has a static spring constant of up to 60 pounds/inch.

16. The earmuff cushion of claim 12, wherein the foam has a static spring constant of up to 30 pounds/inch.

17. The earmuff cushion of claim 12, wherein the foam is a polyurethane.

18. The earmuff cushion of claim 17, wherein the polyurethane is the reaction product of a diisocyanate and a polyol having an isocyanate index of less than about 0.9.

19. The earmuff cushion of claim 18, wherein at least a portion of the polyol has a functionality of at least 3.