Bass Tuning! Bose Acoustimas Series Woofers

Dr Amar G Bose started his career as a Professor in MIT. Later he would start the Bose Corporation by licensing his amplification algorithm for American military use & the likes of NASA. It was much later that consumer products like the Bose 901 series speakers hit the market. The 901 series speakers was a polarizing product as people in general either loved or hated it. The Bose 901 series speakers does hold some scientific promise, but was the result reflective of those published scientific papers? That's what makes it so polarizing.

Many years later, Bose moved away from conventional box speaker products and started moving in to the Acoustimass series of satellite speaker with sub woofer combo. Still very based upon the earliest premise of Direct/Reflect Sound Technology, but also add to the premise that low frequencies, a.k.a. bass becomes omni-direction below 80Hz. This comes at a time when urban living became more dense, homes got smaller, but people still wanted good sound with room filling bass. And judging by the Accoustmass series sales numbers, it was a home run!

Now, I know many audiophiles have some kinda beef with Bose, due to the construction & materials used, and that smoothing, well rounded, limited bandwidth sound ani't what we call hifi either. However, to the other 98% of the world population, that didn't really matter at all, despite those high price tags which resulted in fat margins. Fast forward to recent years, Dr Amar G Bose wanted to cash out, hence sold Bose Corporation to Apple Inc. Apple already own Beats By Dr Dre. And now Apple have merged both entities to become Beats By Bose!

I started with a little history & background of Bose, because I am squarely in the 2% of the worlds audiophile population, yet I am one of the few who loves Bose products for what they are today, lifestyle. My household is just all Bose sound mostly, in the non audiophile areas. And lastly, I find the Acoustimass bass modules, or woofers just so useful to have around, especially the passive ones. they are easy to integrate in to any existing sound system, and with guarantee extra room filling bass. What else do you want? Me, I always find the Acoustimass modules bass to be a little flabby, and when playing loud, port chuff becomes very apparent, especially the older series 1 models. Which is what I have exactly in my home office/study area.

And here, I set about doing something about that port chuffing sound. This DIY work is rather easy, and I think every Bose Acoustimass woofer user should try it. Do you know you can tone down that flabby bass & port chuff sound by just stuffing the Bose Acoustimass woofer? Here's a step by step guide how to do it. 

Bose Acoustimass series I bass module.

Once turn around, you will find back panel access screws & speaker input & output connectors.

You'll need to unscrew all the screws on the back panel, including those holding the 4 feet.  Do not unscrew the speaker terminal screws.

The back panel open, revealing all the internals inside, you will notice there is already some poly fill inside. Those white fluffy pillow fill. Just look at the materials used by Bose, woodchip board, crappy looking Pasar Road drivers & cheap x-over parts. Nothing special, but industrial grade only.

A closer look at the cross-over, all stuck to the rear panel.

Add more polyfill or pillow fill, there are generally 3 types on window fill, you can have foam or feather, both sadly are no good for this application. Then you have polyfill of various density, which will work for this case. What I have is of rather high density polyfill.

After filling the accessible side of the box to about 70% including the original polyfill. I stop and work on closing back the rear panel, making sure all the wires are still connected and in contact. As it quite common for Bose Acoustimas bass modules to fray & delaminate around the edges & corners of the box, so I wrap my module corner & edges with black duct tape to keep it protected. Even if the Acoustimass bass modules are designed to lie down, they can be placed in various positions, those liitel red feet you see are actually rubber door stoppers available from your local hardware shop. 

The bass quality after stuffing of polyfill in to the Bose Acoustimas bass module is tighter, cleaner and certainly less bass port chuffing effect. The immediate feeling is that the upper bass has been toned down, with slightly less kick and an overall bass volume reduction. So in essence, you gain some and you lose some. but for me it certainly an easy mod that takes just 20 minutes or so and it work a joy. Here are some other Bose Acoustimas bass modules that have gone thru similar bass tuning process.

Bose Acoustimass series III, I use this to complement the main hifi rig in my man cave. I loev this passive sub because even though it's one box, there is actually 2 units of  6.5 inch drivers inside running in stereo configuration! 

Here is how the Bose Acoustimas series III looks inside, still 2 units 6.5 inch drivers inside working as stereo pair. The box chamber design is totally different, but you can still access the box via the back panel where the speaker connectors are located. With simplified construction, all you need to do is to uncrew 6 screws in back panel to be accessible to the chamber which I have circled in RED. You just need to stuff the polyfill in to the chamber(as circled in RED) by 30-50% for bass tuning, results depends on your preference & room acoustics interaction.

I not only use Bose in my home, but also inside my car too. I use this Bose Acoustimass Canon in my car boot to augment bass to the OEM system in my car. I also need a 2 channel amp to drive this too. Again my main issue here is port chuffing & car interior panel vibration.

There are 3 chambers inside the bass canon. You can stuff polyfill in to the center chamber as circled in RED by 50-70%. As I preferred tight bass in my car, I filled the middle chamber by up to 70%. The chamber is accesi8ble via the tuning ports with end caps on the long port side. You just need to unscrew all the screws around the tube diameter on the end cap. For my interior panel vibrations, I added sound dampening materials to them. With panel vibration gone and bass tuning to very tight less, I some times can sit in my car, after reaching the destination. just to finish the song, before getting out!  

Bose Acoustimass Canon for home theater use. No I don't have this, but one of my buddies used to have it in his HT den, back then in the 1990's. These Bose Acoustimass Canons were considered high end at the time! I remembered my friend demo-ing Top Gun movies in his Dolby Digital 5.1 HT system. They were pretty convincing back then. However, the Bose Acoustimass Canon is very rare now, and hard to find in the used market.

There you go, now you know my fetish for Bose Acoustimass bass module!