<PAGE>


THE SECURITIES REPRESENTED HEREBY AND THE SHARES OF COMMON STOCK ISSUABLE UPON
THE CONVERSION HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
AS AMENDED, NOR UNDER ANY STATE SECURITIES LAWS AND MAY NOT BE TRANSFERRED IN
THE ABSENCE OF AN EFFECTIVE REGISTRATION UNDER SAID ACT AND ANY APPLICABLE STATE
SECURITIES LAW OR AN OPINION SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION
IS NOT REQUIRED.

                                                                 August 28, 2000
                                                           Farmingdale, New York

                        7% SECURED CONVERTIBLE DEBENTURE

HEARING INNOVATIONS INCORPORATED ("Hearing"), a Delaware corporation, for value
received, hereby promises to pay to the Misonix, Inc., a Delaware corporation
(the "Holder) at the address set forth on the signature page hereof or at such
other address as the Holder may designate in writing, the principal sum of
$300,000 on August 27, 2002 in lawful money of the United States of America,
together with interest thereon from the date hereof or at the interest rate
hereinafter set forth until payment in full of the outstanding principal
balance, in accordance with all the terms of this Debenture. The principal shall
be made available to Hearing upon the execution hereof.

                                    ARTICLE I

                                 INTERPRETATION


1.1      Definitions. The terms used in this Debenture shall, unless there is
         something in the subject matter or the context inconsistent therewith,
         have the following meanings:

         (a)  "Accumulated Debt" at any time means the aggregate of the Loan
              Amount plus all interest accrued thereon at the time minus all
              amounts in respect thereof paid by Hearing to the Holder.

         (b)  "Business Day" means a day (other than a Saturday or a Sunday) on
              which banks are generally open for business in Farmingdale, New
              York.

         (c)  "Closing Date" means August 28, 2000 or such other date as Hearing
              and the Holder agree as the date for the execution and delivery of
              this Debenture.

         (d)  "Common Shares" means fully paid and non-assessable common shares
              with a par value of $.0005 per share of Hearing.

         (e)  "Consolidation Event" means any reduction in the number of Common
              Shares resulting from an alteration by any corporate means to the
              share capital of Hearing.
<PAGE>

         (f)  "Consolidation Factor" means the quotient obtained when the number
              of Common Shares immediately prior to a Consolidation Event is
              divided by the number of Common Shares immediately after the
              Consolidation Event.

         (g)  "Conversion Number" at any time means the quotient obtained when
              the Accumulated Debt at the time is divided by the Conversion
              Price at the time.

         (h)  "Conversion Option" means the right of the Holder hereunder to
              convert the Accumulated Debt to Common Shares.

         (i)  Conversion Price" at any time means the price at which Hearing
              will issue Common Shares pursuant to the Conversion Option,
              determined in accordance with Section 4.5.

         (j)  "Event of Default" has the meaning ascribed to it in Section 9.1
              hereof.

         (k)  "GSA" means a general security agreement between Hearing and the
              Holder granting to the Holder a second priority security interest
              in all the presently owned and after acquired property of Hearing.

         (l)  "Loan" or "Loan Amount" means a loan in the amount of $300,000
              made by the Holder to Hearing pursuant to this Debenture.

         (m)  "Permitted Encumbrances" means:

              (i)    liens or privileges imposed by law in respect of
                     obligations not yet due or delinquent such as carriers'
                     liens, warehousemen's liens and other privileges of a
                     similar nature; or liens for taxes, assessments or
                     governmental charges or levies not at the time due or
                     delinquent or the validity of which is being in good faith
                     diligently contested in appropriate proceedings; or
                     undetermined or inchoate liens, privileges and charges
                     incidental to current operations, that have not been filed
                     pursuant to law or that relate to obligations not due or
                     delinquent;

              (ii)   minor encumbrances, including without limitation,
                     easements, rights of way, servitudes or other similar
                     rights in land granted to or reserved by other persons,
                     rights of way for sewers, electric lines, telegraph,
                     telephone lines, oil and gas pipelines and related
                     facilities and other similar purposes, or zoning or other
                     restrictions as to the use of real properties, which
                     encumbrances, easements, servitudes, rights of way, other
                     similar rights and restrictions do not in the aggregate
                     materially detract from the value of the said properties or
                     materially impair their use in the operation of the
                     business of their owner;


                                      -2-


<PAGE>

              (iii)  the right reserved to or vested in any municipality or
                     governmental or other public authority by the terms of any
                     lease, license, franchise, grant or permit acquired by
                     Hearing by any statutory provision, to require annual or
                     other periodic payment as a condition of the continuance
                     thereof; and

              (iv)   the lien and security interest granted to Dan Purges
                     pursuant to the Senior Indebtedness.

         (n)  "Registration Statement" means a registration statement which
              registers the Common Shares to be issued by Hearing pursuant to
              the Conversion Option for sale under the Securities Act of 1933,
              as amended.

         (o)  "Repayment Date" means the date that is the second anniversary of
              the Closing Date.

         (p)  "Senior Indebtedness" means that certain Amended and Restated
              Secured Term Note dated September 1, 1999 by and between Dan
              Purges, as lender, and Hearing, as borrower, in the principal
              amount of $1,405,952.

         (q)  "Warrant" has the meaning ascribed to it in Section 3.1 hereof.

1.2      Headings. The division of this Debenture into sections and the
         insertion of headings are for convenience of reference only and shall
         not affect the interpretation of this Debenture.

1.3      Number and Gender. Words herein importing the singular number only
         shall include the plural and vice versa, and words importing the
         masculine gender shall include the feminine and neuter genders and vice
         versa.

1.4      Governing Law. This Debenture shall be governed by and construed in
         accordance with the laws of the State of New York without regard to the
         conflicts of laws principles thereof. Any legal action or proceeding
         with respect to this Debenture against the parties hereto may be
         brought in the Courts of the Supreme Court of the State of New York,
         New York County or the Federal District Court for the Southern District
         of New York, which Courts the parties agree to be a convenient forum
         for the resolution of any such legal action or proceeding, and each of
         the parties hereto hereby irrevocably submits to the jurisdiction of
         said Courts.

1.5      Severability. If any one or more of the provisions contained in this
         Debenture should be held to be invalid, illegal or unenforceable in any
         respect in any jurisdiction, the validity, legality and enforceability
         of such provision or provisions shall not in any way be affected or
         impaired in any other jurisdiction and the validity, legality and
         enforceability of the remaining provisions contained herein shall not
         thereby in any way be affected or impaired.


                                      -3-

<PAGE>

                                   ARTICLE II

                                  LOAN FACILITY

2.1      Loan Amount. Subject to all the terms and conditions herein, the Holder
         agrees to lend the sum of $300,000 to Hearing on the Closing Date.

2.2      Method of Payment. The Loan Amount shall be made on the Closing Date by
         wire transfer of funds to the bank account which Hearing designates by
         written notice to the Holder.

                                   ARTICLE III

                                FEES AND INTEREST

3.1      Commitment Fee. On the Closing Date, Hearing shall issue and deliver to
         the Holder as a commitment fee and in consideration of the execution
         and delivery of this Debenture by the Holder a warrant (the "Warrant")
         entitling the Holder, upon exercise, to purchase 66,667 Common Shares
         at a price of $2.25 per share (subject to adjustment), such Warrant to
         be irrevocably issued and in addition to all other rights of the Holder
         hereunder. The Warrant shall be substantially in the form of Exhibit A
         annexed hereto.

3.2      Rates of Interest. Hearing shall pay the Holder interest on the Loan
         Amount outstanding from time to time at a rate equal to 7% per annum,
         payable when the Loan Amount is due and payable, whether at maturity or
         by acceleration. Interest payments shall be made by separate check
         payable to the order of the Holder.

3.3      Calculation of Interest. Interest shall be calculated on the Loan
         Amount daily from the date of receipt of funds by Hearing on the basis
         of a 365 day year both before and after default and maturity.

                                   ARTICLE IV

                            REPAYMENT AND CONVERSION

4.1      Mandatory Repayment. Unless the holder has exercised the Conversion
         Option, Hearing shall pay to the Holder the Accumulated Debt on the
         Repayment Date.

4.2      Voluntary Prepayment. Hearing may from time to time prepay all or part
         of the Accumulated Debt, without premium or penalty, upon giving not
         less than ten (10) Business Days' written notice to the Holder
         specifying the amount of prepayment and the date for the making
         thereof; provided that the Loan Amount hereunder shall be permanently
         reduced by the amount of any such prepayment.


                                      -4-
<PAGE>

4.3.     Place of Payment. All payments of principal, interest, fees and other
         amounts payable under or by virtue of this Debenture shall be made to
         the Holder by payment as directed by the Holder from time to time. All
         such payments shall be in United States dollars.

4.4      Conversion. This Debenture shall be convertible at the option of the
         Holder at any time after the Closing Date and up to and including the
         Repayment Date if the Holder gives written notice thereof (the
         "Conversion Notice") to Hearing stating that the Holder has elected to
         convert all its rights under this Debenture including the Accumulated
         Debt at the time of the Conversion Notice into the Conversion Number of
         fully paid and non-assessable Common Shares, rounded to the nearest
         one-tenth of one share. If the Holder elects to convert all its rights
         under this Debenture then the Holder shall surrender this Debenture,
         duly endorsed on behalf of the Holder, at the registered office of
         Hearing at or after the time of delivery of the Conversion Notice.
         Hearing shall issue and deliver to the Holder a certificate or
         certificates for the number of Common Shares to which the Holder shall
         be entitled. The conversion shall be deemed to have occurred
         immediately prior to the close of business on the date of the surrender
         of this Debenture to be converted (the "Conversion Date"), and the
         Holder shall be treated for all purposes as the registered holder of
         such Common Shares as of that date. Hearing shall cancel this Debenture
         when surrendered to Hearing and shall so annotate its books and
         records. Upon the issuance and delivery of the Common Shares, the
         Holder shall have no more rights under this Debenture and shall be
         treated for all purposes as the registered holder of Common Shares as
         of that date. No fractional Common Shares shall be issued on the
         conversion of this Debenture. If any fractional interest in a Common
         Share would, except for the provisions of this subparagraph, be
         deliverable on the conversion of this Debenture, Hearing shall, in lieu
         thereof, adjust the fractional interest by payment to the Holder of an
         amount in cash (computed to the nearest cent) equal to the then
         Conversion Price multiplied by the fractional interest.

4.5      Conversion Price. Subject to section 4.6, the Conversion Price shall be
         $2.25 per share.

4.6      Adjustments to Conversion Price. Subject to section 4.8, the Conversion
         Price shall be subject to adjustment from time to time in the event of
         a stock split or stock dividend of Common Shares (any of which is
         referred to herein as a "Dilution Event"). Upon a Dilution Event, the
         Conversion Price shall be adjusted, rounded to the nearest US$0.01, to
         be equal to the Conversion Price immediately prior to the Dilution
         Event, multiplied by a fraction, the numerator of which is the sum of
         (y) the number of Common Shares outstanding immediately prior to the
         Dilution Event, including the number of Common Shares issuable upon
         exercise of all options, warrants, or rights, upon conversion of all
         convertible securities or upon conversion of all securities issuable
         upon exercise of all options, warrants, or rights for such convertible
         securities issued in all prior Dilution Events plus (z) the number of
         Common Shares that the effective price for any Common Shares issued in
         respect of the Dilution Event giving rise to this adjustment would
         purchase at the then Conversion Price, and the denominator of which is
         the number of Common Shares outstanding immediately after the Dilution
         Event, including the number of Common Shares issuable upon exercise of
         all options, warrants, or rights, upon conversion of all convertible
         securities, or upon conversion of all convertible securities issuable
         upon exercise of all options, warrants, or rights for


                                      -5-
<PAGE>

         such convertible securities issued in this and all prior Dilution
         Events. The effective price for any Common Shares issued in respect of
         any Dilution Event shall be the sum of all cash and the fair market
         value of all property other than cash, as determined by Hearing's board
         of directors in good faith and absent manifest error, received or
         applied to the benefit of Hearing plus, for options, warrants, and
         rights, the amount equal to the exercise price multiplied by the number
         of securities subject to such option, warrant, or right.

4.7      Record of Adjustments. Upon any adjustment of the Conversion Price,
         Hearing shall maintain at its registered office a statement, signed by
         the President and the Chief Financial Officer, showing in reasonable
         detail the facts requiring the adjustment and the Conversion Price
         after the adjustment.

4.8      Other Adjustments. If Hearing shall reorganize or reclassify its
         capital (other than a subdivision or consolidation of its outstanding
         Common Shares), consolidate or merge with or into another corporation,
         or convey all or substantially all of its assets to another
         corporation, this Debenture shall thereafter be convertible into the
         number of shares or other securities or property to which a holder of
         the number of Common Shares deliverable on conversion of this Debenture
         would have been entitled on the reorganization, reclassification,
         consolidation, merger, or conveyance; and in any such case, appropriate
         adjustments (as determined by the Board of Directors of Hearing) shall
         be made in the application of the provisions herein set forth with
         respect to the rights and interests thereafter of the Holder to the end
         that the provisions set forth (including provisions with respect to
         changes in, and other adjustments of, the Conversion Price) shall
         thereafter be applicable, as nearly as reasonably may be, in relation
         to any shares or other property thereafter deliverable on conversion of
         this Debenture.

4.9      Other Actions.

              4.9.1 Simultaneously with the execution and delivery of this
         Debenture, Hearing and the Holder shall execute and deliver an
         Amendment to Warrant Expiring April 14, 2001, in the form of Exhibit B
         annexed hereto.

              4.9.2 Simultaneously with the execution and delivery of this
         Debenture, Hearing and the Holder shall execute and deliver an
         Amendment to Investment Agreement dated October 14, 1999, in the form
         of Exhibit C annexed hereto.

4.10     Reservation of Shares. Hearing shall at all times reserve and keep
         available, out of its authorized but unissued Common Shares solely for
         the purpose of effecting conversion of this Debenture or exercise of
         the Warrant, the full number of Common Shares deliverable on conversion
         of this Debenture or exercise of the Warrant. Hearing shall, from time
         to time, in accordance with applicable law, increase the authorized
         number of Common Shares if at any time the authorized number of Common
         Shares remaining unissued shall not be sufficient to permit the
         conversion of this Debenture or exercise of the Warrant.



                                      -6-

<PAGE>

4.11     Issue Costs. Hearing shall pay any and all issue and other taxes that
         may be payable in respect of any issue or delivery of Common Shares on
         conversion of this Debenture or exercise of the Warrant.

                                    ARTICLE V

                                    SECURITY

5.1      Security. On the Closing Date Hearing shall grant to the Holder as
         security for its obligations under or by virtue of this Debenture a
         second priority security interest in all of Hearing's assets by
         execution and delivery of the GSA, in the form of Exhibit D annexed
         hereto.

5.2      Inconsistency. In case of any inconsistency between the provisions of
         this Debenture and the provision of the GSA, the provisions of this
         Debenture shall prevail.

                                   ARTICLE VI

                              CONDITIONS PRECEDENT

6.1      Conditions For Benefit of the Holder. The following are conditions
         precedent to the obligation of the Holder to make the Loan and the
         Holder shall not be obliged to make the Loan unless all of the
         following conditions precedent have been satisfied or waived in writing
         by the Holder as of the Closing Date:

         (a)  the GSA shall have been duly executed and delivered and
              registrations in respect thereof shall have been filed in all
              appropriate registries;

         (b)  the Warrant shall have been duly executed and delivered to the
              Holder;

         (c)  the Amendment to Warrant Expiring April 14, 2001 shall have been
              duly executed and delivered to the Holder;

         (d)  the Holder shall have received certified copies of resolutions of
              the directors of Hearing approving and authorizing this Debenture
              and the GSA;

         (e)  the representations and warranties contained in Article VII hereof
              were true and correct at the time they were made and continue to
              be true and correct;

         (f)  no breach of any of the covenants contained in Article VIII hereof
              has occurred and is continuing;



                                      -7-

<PAGE>

         (g)  no Event of Default and no event which, through the giving of
              notice or lapse of time or both, would constitute an Event of
              Default, has occurred and is continuing; and

         (h)  the making of the Loan is not contrary to any statutes,
              regulations, restrictions or rules of any competent regulatory
              authority having jurisdiction over the Holder.

                                   ARTICLE VII

                         REPRESENTATIONS AND WARRANTIES

7.1      Representations and Warranties. Hearing represents and warrants to the
         Holder that:

         (a)  Hearing is duly incorporated and validly existing under the laws
              of the State of Delaware;

         (b)  Hearing has all corporate power and owns all assets (including
              licenses) necessary in any material respect to carry on its
              business;

         (c)  the financial statements of Hearing for the year ended December
              31, 1999 and the quarterly financial statements of Hearing to and
              including June 30, 2000 fairly reflected the financial condition
              of Hearing as of the date of such statements and there has been no
              material adverse change in the financial condition of Hearing
              since June 30, 2000;

         (d)  there are no facts that materially adversely affect, or so far as
              Hearing can reasonably foresee would materially adversely affect,
              the properties, assets, conditions (financial or otherwise),
              business or operations of Hearing;

         (e)  Hearing is not in breach of or in default under any applicable
              law, statute or regulation of any jurisdiction where it carries on
              business or any agreement or instrument to which it is a party
              which in any way would materially adversely affect the ability of
              Hearing to meet its obligations under this Debenture or the GSA;

         (f)  there are no actions or proceedings pending (including appeals or
              applications for review), or to the best knowledge of Hearing
              threatened, before any court, arbitrator, administrative agency,
              referee or governmental body which, if determined against Hearing,
              would result in a change occurring in the properties, assets,
              conditions (financial or otherwise) business or operations of
              Hearing which would materially adversely affect the ability of
              Hearing to meet its obligations under this Debenture or the GSA or
              to carry on its business;

         (g)  Hearing has the corporate power and authority to enter into this
              Debenture and the GSA and to perform its obligations hereunder and
              thereunder;



                                      -8-

<PAGE>

         (h)  each of this Debenture and the GSA has been duly authorized,
              executed and delivered by Hearing and is a valid and legally
              binding obligation of Hearing enforceable against it in accordance
              with their respective terms;

              (i)    neither the execution and delivery of this Debenture or the
                     GSA nor performance in accordance therewith is or will
                     constitute a breach or a default under:

              (i)    any law, statute or regulation of any jurisdiction where
                     Hearing is carrying on business;

              (ii)   the charter documents of Hearing; or

              (iii)  any agreement or instrument to which Hearing is a party
                     which breach or default would materially adversely affect
                     (x) the ability of Hearing to carry on business, (y) the
                     legality, validity or enforceability of this Debenture or
                     the GSA or (z) the ability of Hearing to perform its
                     respective obligations under this Debenture or the GSA;

         (j)  Hearing has good and marketable title to all its properties and
              assets free and clear of all liens, charges and encumbrances other
              than Permitted Encumbrances;

         (k)  Hearing has paid on a timely basis with the appropriate
              authorities all federal, state and local taxes and any other
              amounts due to federal, state and local governmental authorities
              that are capable of forming a lien, charge or encumbrance in favor
              of such authorities against any of the assets of Hearing; and

         (l)  all necessary consents, approvals and waivers have been obtained
              to permit Hearing to enter into this Debenture and the GSA.

7.2      Nature of Representations and Warranties. The representations and
         warranties set out in this Article VII shall survive the execution and
         delivery of this Debenture and the GSA notwithstanding any
         investigations or examinations made by the Holder or its counsel, and
         the Holder shall be deemed to have relied on such representations and
         warranties when making the Loan.

                                  ARTICLE VIII

                              COVENANTS OF HEARING

8.1      Affirmative Covenants. Hearing covenants and agrees to and with the
         Holder that so long as the Accumulated Debt or any portion thereof is
         outstanding:



                                      -9-

<PAGE>

         (a)  Hearing will observe and perform all of the covenants, agreements,
              terms and conditions to be respectively observed and performed by
              Hearing in this Debenture and the GSA;

         (b)  the Holder will be provided with:

              (i)    the unaudited financial statements of Hearing for each
                     fiscal quarter end prepared in accordance with generally
                     accepted accounting principles ("GAAP") applied
                     consistently, within forty five (45) days of each fiscal
                     quarter end (not including the fiscal year end);

              (ii)   the unaudited financial statements of Hearing for each
                     fiscal year end prepared in accordance with GAAP applied
                     consistently, within ninety (90) days of each fiscal year
                     end of Hearing;

              (iii)  such other financial and other information relating to
                     Hearing as the Holder may reasonably request.

         (c)  Hearing will carry on and conduct its business in a proper and
              efficient manner, will keep all of its assets in a good state of
              repair and in proper working condition, and will keep or cause to
              be kept accurate books and records;

         (d)  Hearing will from time to time pay all rents, taxes, rates, levies
              or assessments, ordinary or extraordinary, and government fees or
              dues levied, assessed or imposed upon Hearing or its assets
              capable of forming a lien, charge or encumbrance on any of the
              assets of Hearing, as and when the same become due and payable
              unless their validity is disputed in good faith by Hearing and the
              Holder is provided security acceptable to it, acting reasonably,
              for the payment of same;

         (e)  Hearing will maintain its corporate existence and all
              registrations in jurisdictions in which it is carrying on
              business;

         (f)  Hearing will maintain all licenses and permits required to carry
              on its business and will not transfer, surrender or otherwise
              dispose of any such licenses or permits;

         (g)  Hearing will comply with all laws, regulations, rules and orders,
              the non-compliance with which could have a material adverse effect
              on its business or condition (financial or otherwise);

         (h)  Hearing will forthwith on becoming aware of same, provide the
              Holder with notice of the occurrence of any Event of Default or
              any event which, through the giving of notice or lapse of time or
              both, would constitute an Event of Default;



                                      -10-

<PAGE>

         (i)  Hearing will cause all the property and assets of Hearing which
              are of a character usually insured by companies operating like
              businesses to be insured and kept insured in such amounts as the
              Holder may reasonably require against loss or damage from any
              cause which is customarily insured against by companies carrying
              on like businesses with insurers approved by the Holder, with the
              Holder as a loss payee as its interest may appear, and will pay
              all premiums necessary for such purpose as the same shall become
              due and shall provide particulars of all such policies and all
              renewals thereof to the Holder, all such policies or contracts to
              be on terms reasonably satisfactory to the Holder;

         (j)  Hearing will maintain public liability insurance in such amounts
              as the Holder may reasonably require with insurers approved by the
              Holder, acting reasonably, and will pay all premiums necessary for
              such purpose as the same shall become due and shall provide
              particulars of all such policies and all renewals thereof to the
              Holder, all such policies or contracts to be on terms reasonably
              satisfactory to the Holder.

8.2      Negative Covenants. Hearing covenants and agrees to and with the Holder
         that, unless the Holder consents in writing, so long as the Accumulated
         Debt or any portion thereof is outstanding:

         (a)  Hearing will not grant, create, assume or permit to exist any
              mortgage, pledge, assignment, lien, charge, encumbrance or other
              security interest, whether fixed or floating, upon any of the
              assets of Hearing other than Permitted Encumbrances and the Senior
              Indebtedness;

         (b)  Hearing will not make any loans or advances to, whether secured or
              unsecured, or guarantee or otherwise become contingently liable
              for any obligations of any person, firm or corporation without the
              Holder's prior written consent, which consent may be withheld for
              any reason;

         (c)  Hearing will not in any fiscal year, except in the ordinary course
              of business, sell or otherwise dispose of any of its assets having
              in the aggregate a value exceeding $250,000 unless the proceeds
              therefrom are paid to the Holder on account of the Loan Amount;

         (d)  Hearing will not merge, consolidate, reorganize or become a party
              to any other transaction whereby all or substantially all of its
              assets become the property of any other person, firm or
              corporation or, in the case of a merger, of the surviving
              corporation resulting from the merger;

         (e)  Hearing will not change its fiscal year end; and

         (f)  Hearing will not pay salaries, management fees or bonuses except
              in accordance with existing contracts or usual industry practices.



                                      -11-

<PAGE>

                                   ARTICLE IX

                                     DEFAULT

9.1      Events of Default. The occurrence of any one or more the following
         events (each such event being herein called an "Event of Default")
         shall constitute a default under this Debenture:

         (a)  if Hearing fails to make any payment to the Holder due under this
              Debenture or the GSA, whether for principal, interest, fees or
              otherwise, for more than ten (10) Business Days after its due
              date;

         (b)  if Hearing defaults in the performance or observance of any
              provision contained in this Debenture or the GSA on its part to be
              performed or observed (other than making a payment referred to in
              clause (a) above) and such default continues for more than thirty
              (30) days after the Holder has given Hearing written notice of the
              default;

         (c)  the Holder, acting reasonably, is not satisfied on the basis of
              the financial statements furnished pursuant to Section 8.1(b) with
              the financial condition of Hearing;

         (d)  if proceedings are commenced for the dissolution, liquidation or
              winding up of Hearing, unless such proceedings are being actively
              and diligently contested in good faith by Hearing;

         (e)  if a default under any indenture or instrument evidencing
              indebtedness for borrowed money of Hearing shall occur and any
              such indebtedness shall have been lawfully accelerated or shall
              lawfully be or become due and payable prior to the date on which
              the same would otherwise have become due and payable;

         (f)  if Hearing is adjudged or declared bankrupt or becomes insolvent
              or makes an assignment for the benefit of creditors, or admits in
              writing its inability to satisfy its debts generally as they
              become due, or petitions or applies to any tribunal for the
              appointment of a receiver or trustee for it or for any substantial
              part of its property, or commences any proceedings relating to it
              under any reorganization, arrangement, readjustment of debt,
              dissolution or liquidation law or statute of any jurisdiction
              whether now or hereafter in effect, or by any act indicates its
              consent to, approval of, or acquiescence in, any such proceeding
              for it or for any substantial part of its property;

         (g)  if a receiver, receiver and manager, receiver-manager, custodian,
              liquidator or trustee (or any person with like powers) shall be
              appointed for all or any substantial part of the property of
              Hearing, provided that such appointment shall not constitute an
              Event of Default if and for so long as:



                                      -12-

<PAGE>

              (i)    Hearing obtains within two (2) Business Days of such
                     appointment an order of a court of competent jurisdiction
                     staying such appointment and such order (or a replacement
                     thereof to similar effect) remains in full force and
                     effect; or

              (ii)   Hearing disputes and continues to dispute such appointment
                     and provides or causes to be provided to the Holder, such
                     security as the Holder, acting reasonably, shall require
                     for payment of such sum as may be necessary to discharge
                     such appointment, and for the purposes hereof it is agreed
                     that the Holder, in determining whether any proposed
                     security is sufficient, may assume the validity of any such
                     appointment and of the powers purported to be granted to
                     the person so appointed;

         (h)  if any representation or warranty made in this Debenture by
              Hearing or any information furnished in writing to the Holder by
              Hearing before or after the date hereof proves to have been
              incorrect in any material adverse respect when made or furnished;

         (i)  if a writ, execution or attachment or similar process is issued or
              levied against all or a substantial portion of the property of
              Hearing in connection with any judgment against Hearing, as the
              case may be, in any amount which materially affects the assets of
              Hearing, as the case may be, and such writ, execution, attachment
              or similar process is not released, bonded, satisfied, discharged,
              vacated or stayed or unless being actively and diligently
              contested by Hearing, in good faith within sixty (60) days after
              its entry, commencement or levy;

         (j)  if an encumbrancer or lienor takes possession of any substantial
              part of the properties or assets of Hearing, unless Hearing
              disputes and continues to dispute such possession in good faith
              and provides to the Holder, such security for the payment of such
              encumbrance or lien as the Holder shall reasonably require;

         (k)  if an order is made or legislation enacted by any competent body
              having authority for the expropriation, confiscation, forfeiture,
              escheating, other taking or compulsory divestiture, whether or not
              with compensation, of all or a significant portion of the assets
              of Hearing and such order or legislation remains in effect and has
              not been stayed by a court of competent jurisdiction for a period
              of more than thirty (30) days from the date of pronouncement of
              the order or enactment of the legislation, as the case may be;

         (l)  if there has been a material adverse change in the businesses,
              operations, assets, financial or other condition of Hearing, since
              the date hereof;



                                      -13-

<PAGE>

         (m)  if judgment in excess of $50,000 is granted against Hearing in
              respect of which Hearing does not have insurance coverage and the
              same remains undischarged or unsatisfied after the time for appeal
              therefrom has expired without Hearing having appealed the judgment
              and obtaining a stay of execution of the judgment, provided that
              such judgment shall not constitute an Event of Default if Hearing
              provides or causes to be provided to the Holder such security as
              the Holder, acting reasonably, shall require for the payment of
              such judgment; or

         (n)  if Hearing declares a dividend on any class of shares other than
              as required on its issued and outstanding Series "A" Convertible
              Preferred Shares.

9.2      Termination and Acceleration. Upon the occurrence of an Event of
         Default and for so long as such Event of Default shall continue, the
         Holder may, by notice to Hearing, do any or all of the following:

         (a)  declare the entire principal amount of the Loan, all interest
              accrued thereon and all fees and other amounts required to be paid
              by Hearing hereunder, to be immediately due and payable without
              the necessity of further notice or demand for payment, presentment
              for payment, protest, notice of dishonor or any other notice
              whatsoever (all of which are hereby expressly waived) and proceed
              to exercise any and all rights under this Debenture and the GSA;
              or

         (b)  request from Hearing such additional financial, marketing, sales
              or other information (referred to herein as "Financial
              Information") as the Holder may reasonably request to permit the
              Holder to determine whether to waive the Event of Default. The
              Holder will keep confidential all Financial Information disclosed
              to it by Hearing hereunder and not copy, disclose or make any use
              of, Financial Information.

9.3      Remedies Cumulative and Waivers. It is expressly understood and agreed
         that the respective rights and remedies of the Holder under this
         Debenture and the GSA are cumulative and are in addition to and not in
         substitution for any rights or remedies provided by law or by equity;
         and any single or partial exercise by the Holder of any right of remedy
         for a default or breach of any term, covenant, condition or agreement
         contained in this Debenture or the GSA shall not be deemed to be a
         waiver of or to alter, affect or prejudice any other right or remedy or
         other rights or remedies to which the Holder may be lawfully entitled
         for such default or breach. Any waiver by the Holder of the strict
         observance, performance or compliance with any term, covenant,
         condition or agreement herein contained or contained in the GSA and any
         indulgence granted either expressly or by course of conduct, by the
         Holder shall be effective only in the specific instance and for the
         purpose for which it was given and shall be deemed not to be a waiver
         of any rights and remedies of the Holder under this Debenture or the
         GSA.



                                      -14-

<PAGE>

                                    ARTICLE X

                            MISCELLANEOUS PROVISIONS

10.1     Costs and Expenses. Hearing shall pay promptly all costs and expenses
         incurred by the Holder in connection with the preparation, execution,
         delivery and registration of this Debenture and the GSA, and in
         connection with arranging the establishment of the loan hereby
         established and reasonable out-of-pocket expenses of the Holder's
         counsel with respect thereto and with respect to advising the Holder as
         to its rights and responsibilities under this Debenture and the GSA.
         Except for ordinary expenses of the Holder relating to the day-to-day
         administration of this Debenture and not involving the preparation or
         review of any waiver, consent or amendment, Hearing further agrees to
         pay all reasonable costs and expenses incurred by the Holder (including
         reasonable fees and expenses of counsel, accountants and other
         experts), in connection with the preservation or enforcement of rights
         of the Holder under this Debenture and the GSA including, without
         limitation, all reasonable costs and expenses sustained by the Holder
         as a result of any failure by Hearing to perform or observe its
         obligations contained in this Debenture and the GSA.

             Any notice, demand or other communication to be made in respect of
         this Debenture may be made or given by personal delivery, registered
         mail or facsimile transmission to the parties as follows:

         (a)  if to Hearing:

              Hearing Innovations Incorporated
              9040 S. Rita Road

              Suite 2250
              Tucson, Arizona 85747
              Attention: President
              Fax No.: (520) 663-0018

         (b)  if to the Holder:

              Misonix, Inc.
              1938 New Highway
              Farmingdale, New York 11735
              Attention: President
              Fax No.: (631) 694-9412

        or at such other addresses or facsimile numbers as may be designated by
        written notice given by the other party from time to time.

10.3     Successors and Assigns. This Debenture shall become effective when it
         shall have been executed by the parties hereto and thereafter shall be
         binding upon and enure to the benefit of Hearing and the Holder and
         their respective successors and permitted assigns. Hearing shall not


                                      -15-

<PAGE>

         have the right to assign its rights hereunder or any interest herein.
         Subject to all applicable securities laws, the Holder from time to time
         (y) may grant a participation in all or any part of the Loan to any
         third party (a "Participant"), after notice to but without any
         requirement of consent by Hearing, and (z) with the prior written
         consent of Hearing (which consent shall not be unreasonably withheld),
         may assign all or any part of its rights and obligations under this
         Debenture to any third party (an "Assignee"). The Holder may give any
         Participant or Assignee copies of financial statements and other
         reports and all other information furnished to it by or on behalf of
         Hearing for the purposes of this Debenture. Without limitation of its
         obligations hereunder, Hearing shall, at its sole cost and expense,
         give such certificates, acknowledgments and further assurances in
         respect of this Debenture and the Loan as the Holder may require in
         connection with any participation or assignment pursuant to this
         Section. The Holder shall act on behalf of all its Participants and
         Assignees in all dealings with Hearing in respect of the Loan, until
         such time as an Event of Default occurs as a result of Hearing's
         failure to pay any amount on account of principal or interest owing
         under or by virtue of this Debenture. Save as aforesaid, any
         Participant or Assignee shall be entitled to the full benefit of this
         Debenture and the GSA to the same extent as if it were an original
         party in respect of the rights and obligations granted or assigned to
         it.

10.4     Entire Agreement. This Debenture constitutes the entire agreement
         between the parties hereto and cancels and supersedes any prior
         agreements, undertakings, declarations, commitments and
         representations, written or oral, in respect thereof.

10.5     Amendments. Any provision of this Debenture or the GSA may be amended
         only if Hearing and the Holder so agree in writing.

10.6     Further Assurances. Hearing agrees that it will, at the request of the
         Holder, do all such further acts and execute and deliver all such
         further assurances and documents as may be reasonably required by the
         Holder to carry out the intent of this Debenture.

         IN WITNESS WHEREOF this Debenture has been duly executed as of the date
first above written.

                                       HEARING INNOVATIONS INCORPORATED

                                       By: /s/ Arthur Przbyl
                                           -------------------------------
                                               Arthur Przbyl, President

                                       MISONIX, INC.

                                       By: /s/ Michael A. McManns, Jr.
                                           -------------------------------
                                               Michael A. McManns, Jr.
                                               President and CEO


                                      -16-