Flat to 14 hz...possible with Paradigm PW-2200??? (1 Viewer)

[David Smith]

I have recently been messing around with my RS SPL meter and placement of my Paradigm PW-2200 subwoofer. Well, I finally found the best placement in the rear corner of my 17X12X8 room.

Now, when calibrating my sub to 80 hz, and using the corrected RS meter values, I'm +/- 5 db across the entire spectrum with 2 exceptions. First of all, I have an 11 db spike at 30 hz. That seems pretty normal.

Now, here's the weird part...I'm getting a 10 db spike at 18 hz (90 db's)and the fact that I'm still hitting 82 db's at least down to 14 hz using the corrected values is puzzling me too (I haven't made tones any lower yet)!

Is this possible, or am I doing something wrong? I'm scared to generate any more test tones any lower. I'm afraid I might actually be hitting 10 hz or something! hehe

Thanks! David Smith

PS I used a freeware tone generating software called NCH tone generator and just burned the files to a cd to play on my system.

 

[Dustin B]

I don't know what to say, except that 80dB is over 20dB under what the sub is capable of in the 30-60hz range. If you set the level to 100dB at 80hz and went down, you'd get very different low end results. The 18hz spike has to be another room mode like the 30hz one is.

I have measured the port on the PW2200 and calculated it was tuned to 30hz. With effective stuffing it may get down to 27hz, but definately no lower than that.

 

[Andrew Santos]

is it possible that you're hearing or measuring the harmonic?

 

[Brian Bunge]

Dustin,

It's my contention that most commercial subs aren't tuned much lower than 30Hz because of size restrictions. Below 30Hz port length just starts to get way too long for anything over a 2" diameter port.

Brian

 

[James Bergeron]

Brian, does the "size" of the port change teh tunning? The velodyne CHT-15 has a port that is the entire length of the front of the box about 2 feet long and about 2-3" tall.

 

[Brian Bunge]

James,

The larger the diameter of the port, the longer it will have to be for the same tuning frequency in the same sized enclosure. For example, a 3" port will be longer than a 2" port tuned to the same frequency. And the smaller the enclosure, the longer the port must be for a specific frequency. Box size is almost always an issue with commercial subs. So the tradeoff is to keep the enclosure size manageable and tune higher.

This is why a small enclosure cannot be tuned very low. Many times the required port length ends up being longer than the longest dimension of the enclosure.

Brian

 

[Geoff L]

In short, YES the diameter and length has everything to do with tune-ing.
Staying with the (Same Size Box Volume), the Smaller the Port diameter (Given the Exact Same "Port Length") tunes the cabinet Lower and the Larger the diameter will tune it Higher.
So you say why don't they just use a smaller diameter port and tune it deeper?
Well many problems arise from "Under Porting" a sub. One of the MANY problems is the air speed traveling threw the port itself. The air rushing threw the port can become audiable as a chuffing or whooshing sound.
The larger the "Cabinet Size, meaning Internal Air Volume" the shorter the port Length can be per the given tuneing point with the "Same Diameter Port".
These are simplified basics, but hold true regardless....
Seems Brian was posting the same time I was.. As always, Brian keeps it short & simple.

 

[Arron H]

Can anyone recommend a disc to measure sub output at low frequencies? Also, where can I find the correction values that you are supposed to account for when performing the measurements?

 

[Brian Bunge]

Arron,
I use the test disk from Stryke.
You can find the correction table for the Rat Shack meter in the second post of this thread.
Brian

 

[Arron H]

Cool. Thanks, Brian.

 

[Geoff L]

Arron,
You can pick up the Stryke Bass Zone test CD Vol-1 at,
www.Stryke.com
It has a large volume of sines (30-second a sine) from 10hz threw 20480hz along with Warbles & a full sweep from 1hz threw to 100hz. I think it's like $12.00 delivered to your door.
You can burn you own, someone may chime in with a good one as I don't know where to sed you. But their are some good ones out their.
RS METER correction values:
Do a quick search for the correction values. Radio Shack SPL meter. You should find what you need.
Edit:
Ok Brian, your just to quick!

 

[Tom Vodhanel]

In a smaller room(17x12x8)14hz isn't a stretch. The generic room gain formula is...
565/LB = RG (where LB is longest boundary and RG is the beginning of *room gain*).
So 565/17 = 33hz. In theory room gain adds 12dB/octave...but in real life...figure on 6-9dB/octave. Still...that is boosting things quite a bit by 14hz.
Now...the energy a SPL meter is going to measure isn't the same as clean output at that frequency Download Spectra(www.soundtechnology.com)and you'll be able to take some cool distortion measures using your SPL meter that might surprise you).
TV

 

[Dustin B]

I agree Brian, it's pretty much just plain stupid. The exceptions being some very expensive subs and SVS, Adire, Hsu.

The really bizzare part with the PW2200 is they could have tuned it much lower. The enclosure is right around 85L in net volume. But they put a slightly flared 5" port in it. They would have been much better off getting the tuning under 25hz with a nicely flared 4" port.

The PDR-10 I had before I built my Tempest was even worse. Tuned to just a little under 40hz with a 3.5" diameter port.

 

[Mark Seaton]

Hi David,
What you are descirbing is not absurd at all. In fact it makes a lot of sense depending on some factors of the construction of your room, etc. Your ~30Hz peak is from the 17' length of the room. Tom's explaination above is exactly the phenomenon which yeilds the rising response to the low end. This is the same phenomenon which is found in car audio systems where the subwoofer's response is boosted due to the volume and dimensions of the cabin. In the case of a home, the dimensions and volumes are just larger, and thereby the effect "kicks in" at lower frequencies.
Tom's formula is right, but I have found a better correlation to the longest diagonal as measured from upper to lower opposing corners of the room. Understand that the forumula Tom posted above figures the 1/2 wavelength corresponding to a dimension. The same formula gives you the first room mode peak correlating to each dimension of the room. The calculation Tom made explains precisely your 30Hz peak. Figuring the room's diagonal points to a corner frequency around 25Hz, which explains the large gain you are getting at very low frequencies.
My suggestion would be to give another try with the measurements, but this time place your subwoofer at the midpoint of the 17' wall. This should tame the 30Hz peak, and should slightly reduce the magnitude of the very low frequency gain. With the sub in this position, you will have to watch to see that your listening position doesn't show a peak at 60-66Hz, which is the 2nd mode corresponding to this dimension. If possible, moving your seat along this 17' dimension should allow you to find a spot where this isn't a problem.
Let us know what you find.
Regards,

 

[Brian Bunge]

Dustin,

I noticed something in testing a few small subs for a Bose Buster type system. I built a test enclosure approx. .77ft^3 and tuned it to around 40Hz. I used two different woofers; the PE Dayton 8" woofer and an MCM DVC 8" driver with aluminum cone (looks identical to those Axiom drivers in their subs).

The Dayton driver has much better extension than the MCM driver, but the MCM driver had more output in the 40-50Hz range. I'm sure the fact that the Dayton had an Fs around 30Hz and the MCM had an Fs around 45Hz made a big difference.

So I imagine designers know that many people will go for the "wow" factor of more output in a really small enclosure, even if it doesn't have as much extension.

BTW, the Dayton was even better in a 1.25ft^3 enclosure tuned to 28-30Hz, but how many people are going to buy an 8" sub that's over 1.5ft^3 externally when they see a 10" or 12" driver shoe-horned into the same sized enclosure?

Brian

 

[Michael R Price]

It's possible that when measuring those super low tones, your SPL meter was picking up distortion. When playing the signals under 20Hz, could you hear anything?

With a 27-30Hz tuning, the lower tones would cause huge cone movements that would probably create a lot of harmonics.

I don't think a sub tuned to 30Hz is going to be actually making much sound at 14 Hz. The PW-2200 is very good above 30Hz though.

 

[Shane G]

Your results are quite similar to measurements done by "Audio Ideas Guide" a Canadian magazine that did a review on the PW2200 in the summer 1998 Volume 18,#2.

A copy of this review can be obtained from the Paradigm website under the reviews section. They posted graphs of the subs response at various x-over settings and found the sub to be "+/- 1-1/2 db between 16 & 80 hz." Showing that this sub is quite a capable performer.

 

[David Smith]

Wow guys, thanks so much for all of the input! I'm gonna do some more testing and check out some more placement options and I'll let you know what I find.

PS As far as hearing anything at 14 hz, it's hard to explain, but I do think I could hear a little. I suppose that would be resonation and not actually the 14 hz tone though. I could definitely feel it though. It was literally shaking my couch. I had to make sure that my bass shakers were turned off twice!

One more thing, if I tame my 30 hz peak using a BFD or other, will it improve on the sound quality significantly? The rest of my bass curve looks really good actually.

 

[Sonnie Parker]

It could very well improve your sound quality. I had a peak of about 10 db around 32hz with my sub. Bringing that area down allowed me to hear and feel more of my sub as it sounded much better.

The BFD will give you some options.

 

[Arron H]

Brian & Geoff,
Thanks for the tip - I ordered the Stryke disc today.