100+ dB at 10 Hz?

[Mark Holmes]

I have a 15 inch Tumult driver in a 2.9 cubic foot sealed box, stuffed with fiberglass. It is down firing, sits on about 4 inch feet, so that there is about 4 inches between the driver and carpet. It is in a 19.5x22.5x8 foot room, about 3500 cubic feet. A standard looking box subwoofer. I am using a BASSIS from Marchand Electronics to boost the low end rather than a Linkwitz Transform and a BFD for equalization.

It is replacing an SVS 20-39 PCi sub.

The goal was to get flat to 10 Hz with clean bass for movies and have a sub that would work well with Maggie 3.6s.

I still am working on getting the crossover right with the Maggies, but that is secondary to getting the low frequencies right.

The biggest problem is below 20 Hz. The SVS really did not have much output below 20 Hz. The DYI sub does.

What I am unsure of is what I am hearing below 20 Hz. I am hearing a “womp, womp, womp” sound from the sub at the lower frequencies. It is more prevalent with boost dialed in from the Bassis. I am concerned that what I am hearing is the driver bottoming out. I have no clue as to what a driver sounds like when it hits max excursion. I also did not expect to “hear” much below 20 Hz. More of that sort of pressurization effects.

Another problem is that when I plug the output in the spreadsheet, the correction factors give me huge output at 10 Hz. Is this really correct? Or could I have a Rat Shack meter that is way off that low. I have read that the meter is not that accurate at the lower frequencies.

So, am I bottoming out the driver, and could I really be getting over 100 dB at 10 Hz?

Hopefully the file is attached. The curves show the difference between 6 dB of boost and 12 dB of boost from the Marchand.

Thanks,

Mark

[PeteD]

What model SPL meter do you have? You may be using the old correction factor for a new meter, which would cause more apparent bass than reality in your curve at those low frequencies.

See correction factors here:
http://www.hometheatershack.com/foru...downloads.html

Regarding bottoming, I haven't heard it personally, but from what I hear...if it happens, there is no question it happened (clank!).

Is your sub in a corner?

Pete

[brucek]

You've altered the excel file to extend down to 10Hz.

Did you enter the correct meter calibration factors for the extra entries you've added.

The RS meter is reported to be somewhat inaccurate below 20Hz between different meters even with correction factors. That's why we limited the excel file to 16Hz......

brucek

[Josuah]

With a BASSIS in there, the whomping sound might very well be the driver bottoming out. Although it usually is accompanied by a clicking or clacking sound. I don't know your definition of whomp. :P

[MACCA350]

brucek wrote:

You've altered the excel file to extend down to 10Hz.

Did you enter the correct meter calibration factors for the extra entries you've added.

The RS meter is reported to be somewhat inaccurate below 20Hz between different meters even with correction factors. That's why we limited the excel file to 16Hz......

brucek

I think Bruce is on the right track, notice that the SPL drops by 10db from 28Hz-16Hz but then rises sharply by almost 20db from 16Hz-10Hz. I'd say the correction values below 16Hz are incorrect as you'd expect it to continue dropping.

I cant hear anything from my DD15 at 10Hz but I can feel the pressure in my ears and hear the windows rattle and see them flex. I tested using this SPL meter but I don't know what correction values to use, so these are uncorrected raw values(average not peak at the listening position). The DD15 also has a subsonic filter set at 15Hz

10Hz --- 88db
15Hz --- 100db
16Hz --- 106db

Maybe you should ask tzucc what 100db at 10Hz sounds like, he is getting 120db+ all the way down to 1Hz(3.7THD) with dual Rotary Subwoofers

cheers

[Mark Holmes]

I am using the old RS meter. And yes I did alter the file to include 10 Hz. At 10 Hz the correction factor is over 20! I really don't think I am getting 100 dB and do attribut that to the inaccuracy of the meter. It is loud though, you can feel it in the pressure on your ears.

The uncorrected values are at 80 dB at the listening position and over 100 dB at the driver.

I do not hear any clanking sound. But I do hear a rythmic sound. I would expect not to hear anything, especially that low. Just not sure how to trouble shoot this noise.

[Chrisbee]

Are you certain the sound is coming form the sub rather than some other object, surface or door vibrating in sympathy?

[Josuah]

It may also be distortion at a higher frequency, which is audible.

[O_ROD]

Almost sounds like the sub reaching it's excursion limits, which is very possible in a DIY sub reaching down to 10Hz w/ boost. Test the sub, when you hear the "womping" sound, back the gain down on the sub amp to see if goes away. If it does, your subs reaching it's Xmax.

Also, using boost to compensate for a lack of power will toast your sub. It'll start clipping without any warning. I've seen Tumults in 4+ cu ft sealed reach 8Hz at 100+ with over 600 watts.
Check out this one...
http://www.hometheatershack.com/foru...t-project.html

I think you can produce the same results with the right power and a bigger box.