Rumble from my OB sub

[Anthony]

Since the driver (and problem) is close to IB, I figured I'd post here:

I have an Exodus Audio 15" driver that was a closeout, supposedly good for OB/IB use. 27mm Xmax, great power handling.

Right now the VC's are in parallel for 4 Ohm load and driven by an NHT 400W amp (Class G or H I think, digital rail switching, AB output stage). The driver has no baffle now and is just sitting on the floor with some pillows holding it upright.

the bass is fantastic, except when it gets really low and the woofer bottoms out. Apparently the excursion really jumps at about 18 Hz.

So now I'm in the market for a new sub amp with a rumble filter, but cannot seem to find anything. Any advice here? I'd rather not build my own or use a passive one, but I definitely need something around 10 to 14 Hz to prevent this. It sounds awful and it may be hurting the driver.

Thanks,
Anthony

[brent_s]

Any plate amp will have you covered. By default, most of the amps at Parts-Express have the cutoff at 18ish hz, but changing the frequency and Q of the filter is simply a matter of swapping either a couple of resistors or 3 caps, depending on the amp...board level soldering required.

Elemental Designs is coming out with a gadget that has an adjustable/bypassable rumble filter along with a two band PEQ. Target price is $100, I haven't seen the time frame for availability.

I'm not sure if the BFD variants can be made to mimic a rumble filter. Also check the ART Cleanbox thread, IIRC it has a rumbel filter in it, but I can't remember the frequency.

-Brent

[Anthony]

Thanks for the advice.

I noticed that the amps on PE don't mention they have a rumble filter, but many of them had the instructions for modifying the filiter so I inquired. Turns out that all of their HPSA series amps have the rumble filter. That includes their one rack amp and two plate amps. I have a customer who wants the rack amp for his sono-sub, so I'll give it a test run and let you all know if it works (and if it does I'll pick one up for myself).

Funny that infrasonic filters used to be big in sub marketing and now even the amps that have it don't advertise it

[brent_s]

Looks like it's closer to production than I realized...eD eQ.2

[F1 fan]

Anthony wrote:

The driver has no baffle now and is just sitting on the floor with some pillows holding it upright....
except when it gets really low and the woofer bottoms out.

No kiddingWithout the restoring force of air that it would have if placed in an enclosure it has nothing but its suspension to control its excursion.

Apparently the excursion really jumps at about 18 Hz.

You have likely found the natural resonant frequency of the driver.You risk damaging your driver using it in this manner.