RECD Quick Reference (Real Ear to Coupler Difference)

RECD (Real Ear to Coupler Difference) – Quick Notes

  • Definition: RECD quantifies the acoustic difference between SPL in a standard 2cc coupler and SPL in the ear canal for a given hearing aid/earmold.

  • Purpose: allows REUR conversion factor to program a hearing aid in a test box rather than on a person’s ear; vent effect not measured in this process.

  • Key relationships:
    $$RECD(f) = SPL (canal) - SPL (coupler)
    Ear canal = RECD + SPL (coupler)

  • 2cc coupler simulates ear canal resonance; measurements span frequency to create a conversion factor.

  • Not limited to pediatrics; RECD used across ages.

Why Measure RECD

  • Predict real-ear output from coupler-based measurements.

  • Convert an audiogram (HL) to dB SPL using personalized RECD conversion factors.

  • Enables preprogramming of devices in a test box without patient presence.

  • Note: vent effects are not included in RECD.

Accuracy and Personalization

  • Personal canal volume and impedance affect SPL; RECD customizes conversion for precise fitting.

  • Differences due to canal size, perforations/PE tubes, middle-ear fluid, surgical changes, etc.

  • With RECD, ear canal SPL targets can be achieved within ~1 dB accuracy.

ANSI Standards (Formal RECD measurement)

  • Use either an ear insert or a custom earmold.

  • Standard requires use of HA-1 coupler; same coupler used for both measurements.

  • EAR insert measures ear canal resonance and the coupler’s resonance, or the custom mold measures both.

  • Historical cross-contamination concerns with materials like fun-tak; ANSI provides conversion factors between HA-1 and HA-2.

RECD Measurement Overview

  • Signal: pink noise; identical signal for both measurements.

  • The difference between ear canal resonance and coupler resonance provides the conversion factor.

  • The 2cc coupler simulates ear canal resonance when the conversion factor is added to the coupler resonance.

  • Terminology: HA-1 coupler resonance vs. ear canal resonance.

Step-by-Step RECD Procedure

  • STEP 1: Measure the coupler response using RECD transducer

    • Attach transducer to HA-2 coupler

    • On-Ear measures → RECD → coupler calibration

  • STEP 2: Connect the transducer to the foam insert to measure ear canal resonance

    • Probe tube insertion

  • STEP 3: Print results as graph and table

    • Includes real ear resonance, coupler resonance, and their difference

    • Reference line represents average RECD for the entered age

Check and Confirm Accuracy

  • The difference (ear vs. coupler) should be positive.

  • Negative low-frequency (LF) values suggest a slit leak; fix foam tip seal, ensure full expansion, or adjust tip size.

  • Aquaphor can improve foam tip seal.

  • Negative RECD results can occur with perforations or PE tubes due to combined outer and middle ear volumes.

  • If RECD < -10 dB in 4–6 kHz, probe tube blockage is likely.

Verifit 2 and WRECD

  • Verifit 2 uses wideband RECD (WRECD) with a 0.4 cc coupler to better mimic ear canal size.

  • TRIC adapter is used to attach the RECD transducer.

  • Expect negative LF responses on adults; ear canal resonance above 1 kHz should align with the 0.4 cc coupler response.

  • If WRECD above 1 kHz falls below the 0.4 cc response, this may indicate blockage or a blocked/pinched probe tube.

Documenting and Verification

  • Confirm accuracy by selecting an equivalent HA-1 RECD in Verifit to ensure no slit leaks or probe blockage.

  • Document HA-1 RECD values even if measured with HA-2 for future adult fittings unless canal changes occur.

Practical Use: RECD in Fitting and Lab Tasks

  • Use RECD to program devices in a test box (e.g., NAL-NL2 targets) and verify audibility.

  • Lab tasks commonly include:

    • Measure right RECD for one student and left RECD for another using inserts.

    • Confirm probe depth and print results (graph/table).

    • Fit a device in the test box using RECD values and verify targets.

  • For Verifit/RECD workflows, choose the correct coupler (HA-1 vs HA-2) per software version and setup recommendations.

Choosing Couplers and Software Notes

  • If software version is current, select HA-1 even if HA-2 is chosen on the setup screen.

  • Ensure consistency between the coupler used and the software’s expected RECD workflow.

Critical Concepts to Comprehend

  • RECD justifies improved fitting accuracy for every adult ear canal.

  • ANSI standards define RECD measurement workflow (ear insert or custom mold; HA-1 coupler; same coupler for both measurements).

  • Protocols: measure ear canal and coupler resonances with identical signals; compute the difference to obtain the conversion factor.

  • Interpret RECD in the context of ear canal volume variations, PE tubes, perforations, etc.

  • Differentiate expectations for Verifit 1 RECD vs. Verifit 2 WRECD.

  • Slit leaks and blocked probes adversely affect RECD; understand how to detect and remedy.