▁co il ▁signal ▁wave form . ▁ ▁This ▁is ▁the ▁cru x ▁of ▁high - f idel ity ▁s tere o . ▁ ▁The ▁surr ound ▁may ▁be ▁res in - tre ated ▁cloth , ▁res in - tre ated ▁non - w ov ens , ▁polym er ic ▁fo ams , ▁or ▁therm op last ic ▁el ast om ers ▁over - m old ed ▁onto ▁the ▁cone ▁body . ▁ ▁An ▁ideal ▁surr ound ▁has ▁a ▁linear ▁force - def lection ▁curve ▁with ▁sufficient ▁d amp ing ▁to ▁fully ▁abs orb ▁v ibr ational ▁transm issions ▁from ▁the ▁cone / s urr ound ▁interface , ▁and ▁the ▁" t ough ness " ▁to ▁with stand ▁long - term ▁v ibration - indu ced ▁fat igue . ▁ ▁Sometimes ▁the ▁con ical ▁part ▁and ▁the ▁outer ▁surr ound ▁are ▁m old ed ▁in ▁one ▁step ▁and ▁are ▁one ▁piece ▁as ▁commonly ▁used ▁for ▁a ▁Gu itar ▁speaker . ▁ ▁Other ▁types ▁of ▁speak ers ▁( such ▁as ▁electro static ▁loud spe akers ) ▁may ▁use ▁a ▁thin ▁memb rane ▁instead ▁of ▁a ▁cone . ▁ ▁Micro phone ▁Micro ph ones ▁can ▁be ▁thought ▁of ▁as ▁speak ers ▁in ▁reverse . ▁ ▁The ▁sound ▁waves ▁strike ▁the ▁thin ▁dia ph rag m , ▁causing ▁it ▁to ▁v ibr ate . ▁Micro phone ▁dia ph rag ms , ▁unlike ▁speaker ▁dia ph rag ms , ▁tend ▁to ▁be ▁thin ▁and ▁flexible , ▁since ▁they ▁need ▁to ▁abs orb ▁as ▁much ▁sound ▁as ▁possible .