AcousticCheck: Hardware Overview

Which iOS device should we use?

AcousticCheck works on all Apple iPhones and iPads with at least iOS 16.4 installed. The microphones of all iPhones and iPads are equally suitable for conducting reverberation time measurements. Newer devices are simply faster in the calculations that need to take place.

Which Bluetooth speakers are best suited for measurements?

Due to the special characteristics of the acoustic test signal, theoretically all Bluetooth speakers are suitable for conducting room acoustic measurements with good accuracy. The choice of the right speaker depends on the type of rooms in which it is to be used. As a general rule, one can assume that larger speakers also play louder and are thus better suited for larger rooms. 

In practice, some, even expensive, speakers are not as well constructed as others, which has led us to examine some speakers more closely. These more detailed investigations are the subject of some articles that will be found here later.

First, we provide general guidelines on what to look for when choosing the right speaker and then list a few speakers that we consider to be well suited for the tested room volume.

How to choose the right speaker?

Usually, manufacturers do not provide much information about their speakers. Therefore, here are some specifications to look for to find the right speaker for measurement use:

Total Power / RMS Power in Watts: 20 W and above should be sufficient to conduct measurements in most typical rooms. This refers to 20 W per speaker channel. If the manufacturer does not provide any other specifications, the stated value refers to the sum of all channels of the speaker. Since most speakers are stereo speakers, having 2 channels, at least one speaker with 30 W (i.e., 15 W per channel) should be selected.

The "power" of a speaker can be seen as an indicator of the "acoustic energy" that the speaker can contribute to the room. The more energy the speaker can send into the room, the larger the room that can be measured with the help of the speaker.

Frequency Range: ~90 Hz to ~8000 Hz (if specified), thus all speakers that can operate below 90 Hz and above 8000 Hz are suitable for this type of measurements. Although not all speakers can reproduce frequencies lower than 90 Hz, most can play frequencies up to at least 13000 Hz. If the rooms to be measured are typical living spaces or one- to two-person offices, a speaker that only starts at 150 Hz should also be sufficient.

The "frequency range," sometimes referred to by manufacturers as "frequency response," indicates which frequency range the speaker can reproduce with a sufficiently high sound pressure level.

Mono or Stereo?: For room acoustic measurements, a mono speaker is usually preferred. However, since most speakers are stereo speakers - especially those with 360° radiation patterns - stereo speakers are also suitable. In AcousticCheck, from app version 1.2 onwards it is always possible to switch between playing the test signal in mono or over both stereo channels in the advanced options. Stereo playback is generally recommended for compact speakers, even if it is a mono speaker, as both channels are summed and the test signal can thus be played back louder.

Tribit Stormbox 2	Ultimate Ears Megaboom 4

Overview of some speakers we can recommend:

Which hardware is recommended for measurements with impulsive sources?

We would strongly advise you to measure with a Bluetooth speaker, as the countless advantages of the acoustic test signal outweigh the measurement with impulsive excitation. However, if you still insist on measuring with impulsive excitation or have no other choice and do not want to clap your hands, you have some other options.

A wooden clapboard - They come in different sizes and can achieve higher volumes than simple clapping, provided it does not trigger any old trauma from gym class in third grade.

A balloon - simply popping a balloon with a pin can also achieve higher volumes than typical hand clapping. Again, be careful not to bring up any bad memories of long-past birthday parties.

An origami popper - an origami popper is a paper-folded instrument that creates a loud noise by rapidly “snapping” it. The folding instructions are quite simple and the poppers can be folded in various sizes and with different paper thicknesses.

A gunshot - the name says it all - perhaps a bit extreme and a little too loud, and at this point, one should really ask whether measuring with a Bluetooth speaker might indeed be the better idea.

Is an external microphone needed? 

The use of external microphones, such as those sold by micW audio and Dayton Audio, offers an advantage in loud environments, but is not essential for measurement in typical rooms like offices and living areas, as long as unnecessary noise is avoided during measurement. If an external microphone is needed for measurement in particularly loud environments, it is available from manufacturers for any type of iOS device, regardless of whether a headphone jack (micW i436, Dayton Audio iMM-6), Lightning port (micW i437L), or USB-C (micW i437C, Dayton Audio iMM-6C) port is needed. 

MicW i436 Compact Class 2 Microphone with Lightning Adapter

For everyday measurements, the internal microphones of iOS devices are more than suitable for achieving accurate measurement results.

Is hearing protection needed?

Generally, the acoustic test signal does not need to be very loud to achieve good results. However, it may occasionally need to be a bit louder in large rooms to send enough energy into the room, so it is not a bad idea to have hearing protection on hand.

Is any other hardware recommended?

If you are using an external microphone, a (compact) microphone stand can be helpful.

A camera tripod can also be used as a stand for a Bluetooth speaker to be independent of available surfaces in the room such as tables and chairs and to position the speaker freely in the room. Such a tripod can also be easily modified by attaching a plate that is better suited for placing the specific speaker.

When measuring with the iOS device, having a power bank is especially a good idea for many measurements. We recommend capacities of 10000 to 20000 mAh to be safe.

Can a USB audio interface with measurement microphone be used with AcousticCheck?

Short answer: Yes! With an iPad Pro, it should work without issues.

Long answer: It is a bit cumbersome and will be described in detail in a later article.

Class compliant USB-audio interface with all the necessary accessories for the iPhone

Here is a list of the (maximum) necessary hardware:

• A (Apple) USB camera adapter - to connect a device with a USB-A port to the iOS device

• A (small) USB hub

• A USB-Y-Cable (2 male to 1 female) - to power the USB audio interface sufficiently using a power bank and connect it to the camera adapter

• A power bank - to provide enough power to the USB audio interface

• A class-compliant USB audio interface - to connect the measurement microphone

• A (XLR) measurement microphone - the actual reason why all this is being done

And that's it for our little hardware overview. Did we forget something? Do you still have questions? Feel free to contact us through our contact form or write us a nice little email.