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 well suited to carrying out reverberation time measurements. Newer devices are simply faster in the calculations that have to take place for this.

Which Bluetooth speakers are best suited for measurements?

Due to the special properties of the acoustic measurement signal, all Bluetooth speakers are theoretically suitable for carrying out room acoustic measurements with good accuracy. The choice of the right speaker depends on the type of room in which it is to be used. As a rule of thumb, it can be assumed that larger speakers also play louder and are therefore more suitable for larger rooms.

In practice, some speakers, even high-priced ones, are not as well constructed as others, which led us to investigate some speakers in more detail. These more detailed analyses are the subject of several articles that will be published here later.

Firstly, we give some general pointers on what to look out for when choosing the right speaker and then list a few speakers that we consider to be suitable for the room volume tested.

How do you choose the right speaker?

Manufacturers don't usually give out much information about their speakers. Therefore, here are some specifications that can be looked at to find the right speaker for everyday measurement:

Total Power / RMS Power in Watts: 20 W and above should be sufficient to perform measurements in most typical rooms. This refers to 20 W per loudspeaker channel. If no other information is provided by the manufacturer, the specified value refers to the sum of all channels of the loudspeaker. As most speakers are stereo speakers, i.e. they have 2 channels, at least one speaker with 30 W (i.e. 15 W per channel) should be selected.

The ‘power’ of a loudspeaker can be seen as an indication of the ‘acoustic energy’ that the loudspeaker can bring into the room. The more energy the loudspeaker can send into the room, the larger the room that can be measured with the help of the loudspeaker.

Frequency Range: ~90 Hz to ~8000 Hz (when specified), so any speakers that can play below 90 Hz and above 8000 Hz are well suited for this type of measurement. Although not all speakers can play frequencies lower than 90 Hz, most can at least play frequencies up to 13000 Hz. If the rooms to be measured are typical living rooms or one- to two-person offices, a loudspeaker that only plays from 150 Hz should also be sufficient.

The ‘frequency range’, sometimes also referred to as ‘frequency response’ by the manufacturers, gives an indication of the frequency range that the loudspeaker can reproduce with a sufficiently high sound pressure level.

Mono or stereo? A mono loudspeaker is usually preferable for room acoustic measurements. However, since most speakers are stereo speakers - especially those with 360° dispersion behaviour - stereo speakers are also suitable. In AcousticCheck, from app version 1.2 onwards, you can switch between mono playback of the measurement signal or playback via both stereo channels at any time in the advanced options. Stereo playback is generally recommended for compact loudspeakers, even if it is a mono loudspeaker, as both channels are added together and the measurement signal can therefore be played louder.

Tribit Stormbox 2	Ultimate Ears Megaboom 4

Overview of some speakers that we can recommend:

What hardware is recommended for measurements with a pulsed source?

We would strongly advise you to measure with a Bluetooth speaker, as the countless advantages of the acoustic measurement signal speak against measuring with pulsed excitation. However, if you insist on measuring with pulsed excitation or have no other choice and don't want to clap your hands, you have a few other options.

A wooden start flap - These are available in different sizes and can be used to achieve higher volumes than simply clapping, provided it doesn't trigger an old trauma from your third-grade PE lessons.

A balloon - simply popping a balloon with the help of a pin can also reach higher volumes than typical hand clapping. Again, be careful not to bring up bad memories of childhood birthdays long gone.

An origami pop bag - an origami pop bag is an instrument folded out of paper that makes a loud noise when it is quickly ‘snapped open’. The folding instructions are quite simple and the bangers can be folded in different sizes and from different paper thicknesses.

A pistol shot - the name says it all - perhaps a little too extreme and also a little too loud and at this point at the latest you should ask yourself whether measuring with a Bluetooth speaker might be a better idea after all.

Is an external microphone required?

The use of external microphones, such as those sold by micW audio and Dayton Audio, offer an advantage in noisy environments, but are not essential for measurements in typical rooms such as offices and living rooms, as long as you avoid unnecessary noise during the measurement. If an external microphone is required for measurement in particularly noisy environments, it is available from the manufacturers for any type of iOS device, whether you need a headphone jack (micW i436, Dayton Audio iMM-6), Lightning connector (micW i437L) or USB-C connector (micW i437C, Dayton Audio iMM-6C).

Compact class 2 measurement microphone MicW i436 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?

In general, the acoustic measurement signal does not need to be very loud to achieve good results. However, occasionally in large rooms it does need to be a little louder to send enough energy into the room, so it's not a bad idea to have hearing protection with you.

Is other hardware recommended?

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

A camera stand can also be used as a stand for a Bluetooth speaker in order to be independent of existing storage options in the room, such as tables and chairs, and to be able to position the speaker anywhere in the room. Such a stand can also be easily modified by screwing on a plate that is better suited for placing the speaker in question.

It is a good idea to have a power bank with you when measuring with your iOS device, especially if you take a lot of measurements. We recommend capacities of 10000 to 20000 mAh to be on the safe side.

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

Short answer: Yes! It should even work with an iPad Pro without any problems.

Long answer: It's a bit complicated and will be described in detail in a future article.

USB audio interface with measuring microphone and the necessary accessories for operation in the iPhone

Here is a list of the (maximum) hardware required for this:

• An (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 supply the USB audio interface with sufficient power using a power bank and to connect it to the camera adapter

• A power bank - to supply the USB audio interface with enough power

• Ein Class-Compliant USB-Audio-Interface - um das Messmikrofon zu verbinden

• An (XLR) measurement microphone - the real reason why all this is being done in the first place

That's it for now with our little hardware overview. Have we forgotten anything? Do you have any questions? We'll be happy to answer them via our contact form or by email.