Conclusions:

In terms of the testing results, how do these relate back to the aims of the project?

‘To use a suitable environment and viable equipment to test the offset bipolar loudspeaker’s frequency response in an anechoic chamber?’

As one the aims stated, the testing results were conducted using adequate equipment, which involved the ‘Room EQ Wizard’ software to produce frequency responses, as well as an Earthworks QTC 1 microphone to provide a response that covered the human hearing audible range of 20Hz to 20kHz.

In addition to this, the suitable environment was in fact a low RT60 drum booth room based at the University to get adequate control of what the characteristics of the speaker would produce. Unfortunately, as stated by (Richard Jacket, Senior Research Scientist, Acoustics and Sound in Air National Physical Laboratory, Teddington. Middlesex) in an email, he stated that due to operational costs it would be too expensive to use an anechoic chamber and that much control in terms of response would not suit this project. Therefore, the choice of using a drum booth was an alternative approach.

What was a success of this project and how?

– The graph results showed mostly flat responses throughout the majority of results. This showed that there weren’t significant problems in terms of the enclosure shapes. In addition to this, it proved that the damping used had resolved harmonic distortion from the rear waves of the drivers.

– Middle and high frequencies were very clear and concise upon listening to the speaker. This would have predominantly have been down to the loudspeakers overall length of 701mm to help to reduce the wrap around energy.

– Attention to detail in the building process significantly made the entire speaker extremely heavy and rigid in terms of gluing every surface and nailing every 20cms that helped give more presence from the drivers and not through the open ends.

What improvements could have been made to improve the outcome?

– More damping could been used especially more carpet felt to cover all the internal surfaces specifically towards to the open end making sure not to choke the open end. In addition to this, even to add more acoustic filling may help improve the low end response.

– Obviously due to simulation problems in the designing process, potentially in the future a more accurate prior simulation could be created through Martin J King’s transmission line worksheets to get an accurate simulation of the box and compare it with the results.

– With that in mind, this could potentially involve slight adjusting of the length of the TQWT lines that could potentially further improve its response.

– Testing the speaker outside as suggested by Richard Jacket at Teddington Laboratory could further distinguish the testing results. However, this encounters limitations as this current time due to the sheer weight and difficulty in moving the speaker.

– Having a more powerful amplifier to relate to the 90w power from each driver instead of the 20W Tube Amplifier used could potentially get a much more distinctive response from the drivers. However, due to price limitations, the low powered tube amplifier as stated during the project, was a compromise.

– Functionality could potentially be improved, in terms of connectivity. The use of XLR inputs and outputs could further make this speaker more usable, instead of line outputs from the tube amplifier. In addition to this, this could help remove the unnecessary and untidy AWG 30 wiring from the binding posts to the tube amplifier.