Passive radiator for bass guitar?

[juliewarden]

Does anyone have any experience with using passive radiators for musical instruments? I was thinking of building a passive radiator box for my bass to keep the box small and get good lows from a 12" speaker.
The radiators I've seen are all foam surrounds and I'm thinking I'll be blowing the cones into the grill cloth 1st big notes I hit.
Why would I want to do this? I have a bassman with the crappy oxford 12" and I want to replace them with something that will give me good 40Hz response. The bassman box is very small, but it fits in my Camry, which is nice. Otherwise, I'll just replace the oxfords with a pair of eminence basslite 12s for about $160US.

[bear]

You will not keep the box "small" since the PR is the same as a port. You need the same size box as you would with a ported box with the same driver... maybe you can "squeeze" a little, but the main advantage to the PR is easier tuning. Otoh, if you use a 12" bass speaker, you want an 18" PR!! You can get away with a very very high linear throw PR at a smaller diameter, but it will be almost impossible to get away with a 12" PR... IF you use a HP (lo cut) filter below say 30Hz in your rig that makes it a bit easier all the way around... no extreme LF excursions (like when you slap?) to handle...

Getting 40Hz response will require some combination of power handling, surface area and box size. The max SPL you need dictates the surface area/power handling and then the box size - obviously it is easier to get low bass at lower volumes. Live gig volumes require something like the eminence higher power handling drivers and a boat load of power to permit some EQ to get the sense of low bass... but that still depends on the room size and the loudness you want/need.

sorry to say there is no box that fits in the trunk of the Camry that will fill a BIG room with loud bass... if there was it would be a product already.

Also, those boxes and drivers get heavy, fast...

Your best compromises will come by using a simulator and plugging in T/S parameters and looking at the EQ requirements, your power available (the amps) and the SPL max + headroom...

It gets complex fast.

So, if you have just a Bassman head, get the highest sensitivity driver you can with the best power handling, and hope it sounds ok in your box...?

No simple solutions for this...

_-_-bear

[Cal Weldon]

I've not thought about using it this way but I'll think you'll find that due to the nature of a PR system that the box size can be made smaller than your average ported. Maybe even as small as the sealed would be, hence the advantage in using them.

[bear]

Cal,

With serious EQ and HP filtering, yes, but then you need one of those 2kW power handling speakers to reach practical SPLs...

So at that point, why not just EQ and HP use an ultra high power handling speaker in a small box (get the T/S as best as possible too) and find urself a 3lb 2kW digital amp, skip the PR??

So, I'd just go with regular speakers... for live playing you can't have too small of a box and expect bass SPL, there's no way around it.

It's like asking if you can get thunder bass out of an 8" woofer - Carver tried, right? The max SPL is an issue...

_-_-bear

[chris661]

I tried getting 28Hz out of a pair of 8"s - they run out of excursion very fast...

I'm not sure about the PR idea - they're widely available, so why doesn't the industry use them?
Perhaps it's because ports take up a smaller area of the front, leaving more space for drivers...

[bear]

Most commercial PR using designs consist of dumb application, which results in less than optimum operation, which in turn results in less than fantastic consumer satisfaction. And they cost more than ports by a wide margin... I think that sums it up pretty much...

There's a saying: "no free lunch"

_-_-bear

[tinitus]

maybe think bandpass instead, and combine with midrange oriented midbass

[FoxInSocks]

I would have to agree with bear. There are a few really bad examples out there that have probably done a lot of perceptual damage to the concept.

I myself would never have given them a second thought until I recently picked up an old pair of JVC floor standing speakers with them in it (for free even!).

If this old pair of beaters is any indication, then you definitely do not want to give up on the idea. The quality of the bass really makes you sit up and take notice. The towers each have a single 8" woofer in them, and a 9x12" rectangular PR. You would swear there was also a subwoofer hiding somewhere in the room, filling in the bottom octave. It's quite amazing.

I'm definitely going to look in to building a PR cabinet for my own bass rig.

You can also use several PRs if you can't find a single one that's big enough... I've seen several boxes with the driver on the front, and a PR, same size as the driver, on each side.

[Andrew Eckhardt]

One of the other advantages a passive radiator does have is when the speaker parameters and desired response, maybe after mainly attempting to minimize overall size, call for a particularly small box and large/long tube. You can get to the point where a PR can actually make you a reactive loaded speaker that you can't otherwise have without putting the port on the outside of the box. (which doesn't actually take any less total volume, or necessarily become smaller either) If you're not particularly inclined to choose one or the other depending on ability to select passive radiator damping (which I think is pretty rare) or worry about things like whether you prefer suspension distortion over that of turbulent air and other funny noises that make their way through the port but not so much through a PR cone, there's hardly any difference, other than ports are cheap.

[bear]

There is a minor advantage to the PR vs. port below the resonant frequency of either. The PR acts more like a sealed box below the resonant frequency...

_-_-bear