First Speaker cabinet measurement

After selecting the FaitalPRO 4FE32 (4", 4Ω, 30W, 91 dB, 2.2L@100Hz) as our loudspeaker driver, we were able to develop a first prototype of the housing. To facilitate future adjustments, we decided to create the CAD drawing parametrically. We chose FreeCad as CAD software, which is free and open source. The goal is to develop a housing that can be produced using conventional 3D printers, initially delivering as linear a sound image as possible, while also being printable with minimal material use and compatible with standard 3D printing equipment.

In the first step, we concentrate on the acoustic properties of an individual housing. The modularity and connection of several housings to form loudspeaker arrays will then be addressed in the next step as soon as the individual housing has sufficiently good sound properties.

Enclosure Prototype

The first housing prototype consists of a solid body, into which the driver can be directly mounted. The inner wall was reinforced with a mesh structure to reduce ringing. Additionally, an irregular surface structure was added to the inside to break reflections.

For the first print, we decided to print the housing with two different filaments: a common PLA filament and one with wood components, to compare them in initial measurements. For the first prints, we initially adopted the settings of the 3D print software Cura. The first two housings look good, and the printing process worked without any problems.

Measurements

To measure the housings, a Neumann KM 184 was set up in 1m distance from the speaker and AKG C 411 PP Contact mic was placed on the top of the enclosure. Then an exponential sweep from 20 to 20,000 Hz at about 80 dB was played and recorded for 60 seconds. Unfortunately, since no other room at the MDW was available at the time, we had to conduct the measurement in the experimental studio at MDW, which, with an approximate size of 30 square meters, is actually not very suitable for conducting a loudspeaker measurement.

Evaluation

After the initial evaluation using a Python script, the evaluation generally revealed that the measurements were significantly distorted by room resonances, as the space in which the measurements were conducted was not sufficiently large. In the future, these should be conducted in a suitably large room or, ideally, in an anechoic chamber.

Noticeable dips in both recorded spectrums were observed, which are likely due to weaknesses or natural resonances of the enclosure. It was evident that these were more pronounced in the case made from wood filament, suggesting that this material is probably not suitable for the production of loudspeaker enclosures. The next steps will be to optimize the housing so that the natural resonances are reduced and to find a suitable measuring method to reduce room resonances.