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roubi 13th December 2012 01:11 PM

Bose Soundlink / Jawbone Big Jambox...

A question about those system (hopping I am in the right forum section but I think so).
How do they do to get so much "bass" and so loud in such small boxes with such small drivers?
When I use 3" drivers (like Monacor SPH30x) with 41hz Amp6 and a minidsp in boxes more than twice as big as the Soundlink for example, I don't get any low frequencies (below 120hz) and the volume is hardly the same as the Bose. They use 4 2" drivers and passive radiators but I wonder how they manage to get this low, even if I don't like the sound getting out of it.
Is it a question of big excursion drivers?

Thank you.

chris661 13th December 2012 06:38 PM

I'd say there's a few things they do.

First up, pick the tuning of the cabinet to give the impression of bass - no actual bass comes out of these speakers: a peak before roll off gives the impression that there's some low end grunt.

Next, DSP it to death. I'd expect compressor/limiters, frequency response shaping (including cutting anything below the cabinet tuning).
I'd also expect them to use the harmonic bass generator thingy - where the speakers play the correct series of harmonics, which allows the brain to fill in the fundamentals. Again, it's the impression of bass, without it actually being there.

Big excursion drivers lose efficiency, so this isn't much of an option when it has to be battery powered.



xrk971 13th December 2012 07:07 PM

The Jawbone JB claims a freq response of 60 Hz on the low end - that needs to be a real SPL measurable value rather than just fooling the brain with clever DSP'ing. I think they actually do use high excursion rubber surround 2 in drivers - there is a tear-down reveal video on YouTube and when the guy pushes on the driver, you see the big stroke (at least 5 mm) and you see the corresponding passive radiator bulge out. The low resonance freq of the passive radiator is achieved by clever use of mass added to it - in fact the Li-ion battery pack is the mass on the passive radiator. They also use a very stiff airtight structure made of 4 mm thick glass reinforced polycarbonate. There is no structural flex and all the bass energy goes to moving the passive radiator.
There is a lot of engineering in these things but the parts really don't cost that much. It would be a pretty cool DIY task to replicate. The problem is the custom passive radiator - tough to find a rectangular one. The closest thing I have found if the Logitech X-140 PC speakers - they have a rectangular passive radiator but it only gets down to 80 Hz - still pretty good.

Jawbone JAMBOX Explained - YouTube

Big Jambox teardown:
Jawbone Big Jambox Review and Teardown - YouTube

Soldermizer 12th September 2014 07:29 PM

I saw my first Jambox yesterday. I know nothing about passive radiators, but couldn't you take a normal driver or PR and put your own mass load on it (if that is a secret)? How would you calculate the mass? Trial and error works for me :)

Soldermizer 12th September 2014 07:44 PM

I watched the first video. It is a clever design. Now let's make the DIY knock-off version :rolleyes:

xrk971 12th September 2014 07:46 PM

You can model and simulate it - probably other packages out there but can easily be done in AkAbak. You can even use existing driver with voicecoil and turn it into a PR. Putting a resistor across VC allows tunable damping.

Soldermizer 13th September 2014 06:29 PM

I've read two wiki articles for passive radiators so now I'm an expert :rolleyes:

The PR is a close relative of ported, but superior overall. One said easier to design than Ported, the second said the opposite.

While it may not be the ideal driver, I am a Bose 901 ***** --er that should be "collector" -- the driver (i prefer the series I, II) might be good to experiment upon. As a practical matter, it had never occurred to me that a dead driver would be a good PR (provided of course it is not seized). I now regret tossing out my bum 901 drivers.

Experimenting with them would probably please the ghost of dearly departed Dr. Bose :)

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