Trial objectives and design

This waitlist-controlled trial aims to explore the efficacy of a non-invasive wearable tinnitus device in reducing tinnitus symptoms in UK military veterans compared to a waitlist control group. This device is named TinniSoothe v1.0, Wearable Module & Docking Cradle, made in Britain. The manufacturer is TinniSoothe Limited. This waitlist-controlled trial will take place between October 2025 and October 2026. Our target sample is UK military veterans (n = 20) who have experienced tinnitus for at least three months prior to enrolment. Our primary objective is to evaluate the effectiveness of the non-invasive tinnitus device versus the waitlist control group in reducing the symptoms of tinnitus and mental health difficulties in UK veterans. The secondary objective is to explore whether improvements in tinnitus symptoms and mental health difficulties are maintained at later follow-ups for the immediate intervention group. Additionally, this study will explore whether the waitlist control group, once they receive the device, will experience similar or different rates of improvement compared to the immediate intervention group.

Sample size

A power calculation is typically used to determine the sample needed to detect an effect of a given size with a certain degree of confidence. However, since this is a pilot exploratory study, no sample size calculation has been performed. Following a pragmatic approach and building on prior studies of tinnitus (e.g., [17, 18]), we aim to recruit 10 veterans per group (total sample = 20). This sample size will allow us to address our research question.

Recruitment

Eligible veterans will be recruited from a sample of participants who previously completed a qualitative survey on their experience with tinnitus (submitted Journal of Hearing Science-under review) and elected to be contacted for future research on veterans. In the prior study (submitted Journal of Hearing Science-under review), recruitment was conducted through convenience sampling methods (social media feeds of a UK national veterans’ mental health charity called Combat Stress). In the current study, potential participants will be incrementally emailed by the research assistant, asking if they would like to participate. A maximum of 20 participants (the target sample of this study) will be emailed at a time to ensure no participant is invited to participate and then denied participation. This approach may introduce selection bias, as participants who elected to be contacted about future tinnitus research in the veteran population may differ systematically from those who did not consent to be contacted. To mitigate this, we will document all participant demographic characteristics and compare them to the broader veteran population. As this is an exploratory study, findings may inform feasibility and the design of future trials, which may incorporate broader recruitment strategies.

Screening and assessment

Potential participants will complete a brief screening survey in SurveyMonkey to confirm their interest in the trial and their contact details (i.e., telephone number and preferred time of contact). In this screening survey, participants are asked to confirm an experience of constant ringing or buzzing (bilateral or unilateral) lasting longer than three months. After completing the screening survey, eligible participants will receive the participant information sheet via email, followed by an individual phone call from the research assistant. During this call, each participant will be guided through the participant information sheet and given the opportunity to ask any questions. The research assistant will assess and confirm the potential participant’s suitability for this trial based on their current situation and their goals. If the research assistant decides the participant’s goals do not align with the current trial (e.g., they are not willing to use a noise device for a one-month period), the veteran will be thanked for their interest and given information about other potential support services. Eligible participants will be sent the baseline survey.

Inclusion and exclusion criteria

The full inclusion and exclusion criteria are described in Table 1.

Assignment of interventions: allocation and blinding

After eligible participants complete the consent form and baseline questionnaire on SurveyMonkey, participants will be randomly allocated to one of the two conditions: (1) the immediate intervention, or (2) the waitlist control. The asymptotic maximal procedure will be employed to randomly allocate participants [19], and randomised lists will be generated using an online tool (https://ctrandomization.cancer.gov/tool/). The outcome of the randomisation will be emailed to each veteran.

Interventions

Veterans randomised to the immediate intervention will be sent the device to their allocated address immediately, while those allocated to the waitlist control group will receive the device one-month post-randomisation.

At their scheduled time points, veterans will be sent the device to their registered address. As such, the location of this feasibility trial is in the participants’ usual environment. The package sent to their address includes the following: (a) user instruction manual, (b) module, (c) docking station, (d) necklace, and (e) clothing pin. The research assistant will personally call each participant to guide them through the setup and usage of the device. Participants will be asked to use the device for a continuous period of one month (i.e., wear the device around their neck during the day and dock the device to the docking station at night). The research assistant will be available throughout the trial period in case the participant requires any assistance with the device.

Questionnaires

Participants will be asked to complete a one-month post-randomisation questionnaire (i.e., 28 days post-randomisation) and a two-month post-randomisation questionnaire (i.e., 56 days post-randomisation). Though the baseline questionnaire will incorporate all measures (predictor and outcome measures), the one-month and two-month questionnaires will only include primary and secondary outcome measures (not predictor measures) to reduce participant burden. Specifically, the baseline questionnaire will include questions on demographics (e.g., age, gender), the Tinnitus Functional Index (TFI) [20], General Health Questionnaire-12 (GHQ-12) [21], Insomnia Severity Index (ISI) [22], Satisfaction with Life Scale (SWLS) [23], PTSD Checklist for DSM-5 short version (PCL-5 short version) [24], as well as the Patient Health Questionnaire-15 (PHQ-15) [25]. However, the one-month post-randomisation and two-month post-randomisation will only include the TFI [20], GHQ-12 [21], ISI [22], and the SWLS [23]. All measures are fully described below. Participants will be asked to complete a questionnaire assessing the device (e.g., the comfort level, how often they used the device) after they use the device for a one-month period (one-month post-randomisation for the immediate intervention group and two-month post-randomisation for the waitlist control group). Participants will be instructed that survey completion is voluntary, and all responses will remain anonymous. All surveys will be completed on SurveyMonkey, and participants will be contacted by the research assistant to ask them to complete the surveys. Consent will be reaffirmed at all questionnaire timepoints via SurveyMonkey. Participants in both arms will be free to withdraw from the trial at any point for no reason. Notably, participants may withdraw data at any point up to two weeks after the final questionnaire, after which data will be anonymised.

Outcome measures

An overview of the outcome measures collected throughout the study is illustrated in Table 2. The primary outcomes of the study include the TFI [20] and the GHQ-12 [21]. The TFI [20] is a 25-item measure of tinnitus symptoms that has been supported as a reliable and valid measure in assessing the severity and functional impact of tinnitus [26, 27]. Secondly, the GHQ-12 [21] is a 12-item measure of potential mental health issues, including depression and anxiety, and has demonstrated robust reliability and validity across populations [28, 29]. The GHQ-12 is included to capture the broader mental health difficulties that may co-occur with tinnitus symptoms. Additionally, secondary outcomes include the SWLS [23], a 5-item measure of life satisfaction, and the ISI [22], a 7-item measure of current sleep problems. Thirdly, predictor measures (collected at baseline) include the PCL-5 short version [24], a brief 4-item measure of the presence of PTSD symptoms according to the DSM-IV, and the PHQ-15 [25], a 15-item measure of physical health and somatic symptoms. All of the secondary measures and predictor measures have shown positive psychometric properties [22–24, 30].

Finally, the acceptability of the device will be assessed through a qualitative questionnaire administered post-intervention. This incorporates multiple dimensions of user experience, including the frequency of device use, satisfaction with various aspects of the device (e.g., volume, weight, instructions, usefulness, usability), and potential adverse effects. Participants will be asked about the integration of the device into their daily life, such as whether it helped them return to previously avoided activities, in addition to whether family and friends can hear the device, and if it bothers them. Further, participants will be invited to provide feedback, including the potential addition of alternative sounds (e.g., pink noise) as well as other recommendations and general comments on what they most like about the device. Finally, participants will be asked whether they would recommend the device to others and whether they would use it in the future. As such, this post-intervention survey will provide insight into user satisfaction, perceived effectiveness, and practical considerations. Responses will be a mixture of multiple choice and free text.

Planned statistical analyses

RStudio will be used to analyse the data. Descriptive statistics will be calculated for baseline, one-month post-randomisation, and two-month post-randomisation. Additionally, the effectiveness of the device will be assessed by examining changes in primary and secondary outcomes from baseline to one-month post-randomisation and two-month post-randomisation. Paired t-tests will be used to assess within-group changes from baseline to follow-up, and between-group differences will be assessed using independent t-tests. If the normality assumption for the Student’s t-test is not met based on the Shapiro-Wilk test, testing will be conducted with the Wilcoxon signed-rank test. For achieving superiority, the observed p-value must be < 0.025 for a one-sided hypothesis. Regression analyses will examine whether baseline predictor scores are associated with outcomes at one- and two-month post-randomisation. The qualitative results will be analysed using thematic analysis.

Adverse events reporting

Protocols for managing any risk or safeguarding concerns will be followed, and potential adverse events will be recorded and monitored in accordance with the study’s adverse-events protocol and Combat Stress standard operating procedures. Potential adverse events will be recorded and monitored by senior authors, and serious adverse events will be reported to the clinical lead within the organisation where recruitment is being conducted.

This study protocol describes the design of a waitlist-controlled trial which aims to assess the effectiveness of a non-invasive sound intervention in reducing self-reported symptoms of tinnitus between baseline and the one-month post-randomisation (day 28) among UK veterans who experience tinnitus. Findings from the proposed study will provide critical information on the effectiveness of this device in this population. As such, the current trial may provide a means to support an easily accessible, low-cost option for reducing tinnitus distress. Though this study will provide novel findings, limitations should be considered when interpreting the findings. Firstly, the convenience sample recruitment method could potentially introduce a sampling bias as the sample was selected from a prior study on tinnitus. Though this was an exploratory study, given the small sample of veterans, the representativeness is limited, reducing generalisability to the broader veteran population. Finally, the short follow-up period in this study limits the ability to evaluate the long-term effects of the intervention.

Ethics and dissemination

Participation in this study is subject to providing written informed consent. This study was reviewed and approved by the local ethics committee of King’s College London (LRS/RGO-24/25-48840). Throughout the trial, participants’ personal information will be password-protected, with access limited to the Combat Stress study team. Each participant will be allocated a unique ID number, which will be used for data storage and references. All personally identifiable information will only be seen by the Combat Stress research team, and data will be anonymised prior to analysis.

A manuscript describing the results of the study will be submitted to a peer-reviewed journal. Any published materials will be checked for potentially identifiable information.