Speaker enclosure resonance testing

[Kadent]

Hi all,

I'm currently designing a set of speakers using both mechanical de-coupling of the drivers, and constrained layer dampening of the enclosure walls.

Although most would argue that using your knuckles could provide sufficient data to determine weather or not the cabinet is inert, I'd like to perform some type of accelerometer test (similar to how stereophile conducts their CSD plots.

I was wondering if anyone has experience with doing these types of measurements, and if so, what hardware and software was used to do so?

Thanks all

 

[DanielT]

Here are some threads that address what you are thinking about:

Speaker enclosure vibrations - a few measurements with accelerometer

There are been quite a number of threads dealing with vibrations in speaker cabinets, both in relation to "speaker feet" and vibrations in enclosures themselves. I recently took out my ACH01 accelerometer to do some measurements, both speaker feet and enclosures. There was some initial...

audiosciencereview.com

Here, about the impact of different building materials and a bit about constrained layer damping. MAB shows, for example, tests, measurements he made:

Custom speaker enclosure, as innert as possible

So far, I've - braced my CLD cabinets, pushing the first (and only significant) resonance from 260Hz to 455Hz. - improved driver/case coupling by glueing in T-nuts for the woofer (and tweeter!!) The difference in clarity and voice/piano realism was immediately apparent with the added bracing. I...

audiosciencereview.com

What kind of speakers are you designing?

 

[Kadent]

Here are some threads that address what you are thinking about:

Speaker enclosure vibrations - a few measurements with accelerometer

There are been quite a number of threads dealing with vibrations in speaker cabinets, both in relation to "speaker feet" and vibrations in enclosures themselves. I recently took out my ACH01 accelerometer to do some measurements, both speaker feet and enclosures. There was some initial...

audiosciencereview.com

Custom speaker enclosure, as innert as possible

So far, I've - braced my CLD cabinets, pushing the first (and only significant) resonance from 260Hz to 455Hz. - improved driver/case coupling by glueing in T-nuts for the woofer (and tweeter!!) The difference in clarity and voice/piano realism was immediately apparent with the added bracing. I...

audiosciencereview.com

What kind of speakers are you designing?

I've read through the first thread, though I haven't read through the second. I will check it out. Many people use the ACH01, though that's not available anymore, which is a bummer since it has full range of bandwidth.

I'm building an active 2-way speaker. Usually to be used on smaller stands in living rooms, or possibly on a larger desk.

 

[DanielT]

Unfortunately, I can't help you there as to what is available to buy in the US in terms of measuring equipment and glue for constrained layer damping. Someone from the US can help you with that.

What I suspect, however, is that if you build physically small speakers, the need to use constrained layer damping is reduced. On the other hand, you don't need a lot of glue, so why not. I don't know how much such glue costs in the US, but I guess it will be quite cheap because so little is needed for your speakers.

By the way, if you are thinking of putting bitumen damping mats in your speakers, you will most likely have to glue them because the adhesive they are sold with is crap. That's my experience anyway.

 

[Kadent]

Unfortunately, I can't help you there as to what is available to buy in the US in terms of measuring equipment and glue for constrained layer damping. Someone from the US can help you with that.

What I suspect, however, is that if you build physically small speakers, the need to use constrained layer damping is reduced. On the other hand, you don't need a lot of glue, so why not. I don't know how much such glue costs in the US, but I guess it will be quite cheap because so little is needed for your speakers.

By the way, if you are thinking of putting bitumen damping mats in your speakers, you will most likely have to glue them because the adhesive they are sold with is crap. That's my experience anyway.

I've already sourced all materials and the CNC machine needed for cutting the materials. It will be an interesting build, so keep on the lookout for it in the next following weeks

It will be an interesting build as I'm using materials not commonly found in speakers. Moreso in the architectural industry, material used to support the foundation of homes. Very dense and stiff with high loss.

 

[DanielT]

You are serving up a cliffhanger there.

I will eagerly follow your building project. Good luck!

 

[MAB]

I usually use an impedance measurement of the speaker to find resonances, including cabinet panel resonances, internal standing waves, air leaks, etc.

The driver is very sensitive to resonances, so is ideal for detection of resonances relevant to audio. But finding the source between all of the thongs going on is not easy with a driver, just the existence and relative magnitude. For that accelerometers can be useful. Here is a good article on accelerometers for cabinet investigation:

Project 181

ESP - Project 181 - Audio frequency accelerometer for speaker testing (amongst other things).

sound-au.com

For what it's worth, I don't find much measurable or audible change in sound with cabinet construction techniques once I get to a good basic cabinet (Baltic Birch, moderately braced...) Most of audible resonance artifacts are standing waves, port resonances, etc.