The number of tourist attractions catering for people with hearing loss has improved in the last year, a charity has found.

However more than half of the 31 venues visited were not fully accessible for hearing aid wearers, according to Action on Hearing Loss Scotland.

The charity's "mystery visitors" found that nine of the 31 attractions had working induction loops at main ticket or customer information points, up from three of the 21 they visited last year.

But 19 of the 31 venues did not have working loops, which the charity said are essential to amplify speech over background noise for the 160,000 people in Scotland who wear hearing aids.

The Royal Yacht Britannia, Glasgow Science Centre, Edinburgh Castle and The Riverside Museum, Glasgow, were considered to have the most accessible overall experience for people with hearing loss - when staff support, deaf awareness and "reasonable adjustments" for people who are deaf or hard of hearing were taken into account.

Based on their experiences at the time of their visit, the mystery visitors considered Our Dynamic Earth, Dundee Science Centre, Kelvingrove Art Gallery, Camera Obscura and the National Museum of Scotland to be least accessible of the 31 venues for people with hearing loss.

Delia Henry, director of Action on Hearing Loss Scotland, said: "We commend the tourist attractions which have continued to be accessible, or improved their accessibility, for visitors who are deaf or have hearing loss in 2014. Some venues have taken the positive step of installing loops but, frustratingly for hearing aid wearers, haven't checked whether they are working properly or that staff know how to use the equipment.

"2014 has been a great year for the Scottish tourism industry and by making some simple, inexpensive adjustments or improving processes to get the best out of existing equipment or staff knowledge, 2015 can be an even better year for visitors with hearing loss."

Andrew Johnson, general manager of Camera Obscura in Edinburgh, said they were aware of the issues and are addressing them.

They have a hearing loop ready to be installed in the Camera Obscura chamber and have one on order for the front desk.

A spokeswoman for National Museums Scotland said: "National Museums Scotland takes access seriously and endeavours to cater for the needs of all our visitors.

"We have induction loops fitted at our information desks and in our auditorium and lecture theatre. 'Hearing Helper' radio aids are made available for tours and additional special tours and handling sessions can be arranged.

"We are currently investigating the circumstances of these findings and will ensure that the facilities we are committed to offering are available to our visitors at all times."

A spokesman for Glasgow Life said: "We are delighted Riverside Museum was considered to be one of the most overall accessible experiences for people with hearing loss.

"Kelvingrove Art Gallery and Museum offers a portable induction hearing loop at the main reception and specific tours on request for those who suffer hearing loss.

"We would be delighted to develop a working relationship with Action on Hearing Loss Scotland to understand how we can improve the experience of those with hearing loss when visiting the museum. A full access audit is available at www.disablego.com, detailing the facilities available at Kelvingrove Art Gallery."