Implementing the SW-12-16FR servo open baffle subwoofer driver

TRADERXFAN · « **on:** 22 May 2008, 03:28 pm »

I thought it might be helpful to have a thread dedicated to discussing the servo controlled, SW-12-16FR sub, in open baffle applications. There is quite a bit of general information going on in the "Best sounding subs on the market?" thread. Anyone else think this is a good idea?

As I am very interested in these subwoofers, I am hoping to learn more about how to implement them from Danny and Brian and the audiocircle as a group. Some of this may be redundant for what is on the open baffle circle itself, but I think that focussing on the specific driver, and this unique servo technology makes it somehthing different, as Danny put it " a completely different animal". Maybe it is not as tricky as it seems to be to me, but from what I have seen on a few posts here and information on the linkwitzlab site regarding open baffle dipole woofers, it is not a simple matter of plug and play. There needs to be some measurement and math done to correctly apply this. Then again, maybe when its used in the lower frequencies only, like <80 hz, you don't have to be that precise?

Some of the questions I have are in regards to:

What are the necessary input variables?

H frame design. How deep to make the frame? How that value determines resonance? How to control that resonance? -is the resonance eliminated when you cross over to the woofer below that resonant frequency?

How do you figure out the requisite shelving filter? I think it should be a 6db filter for a specified frequency range. Assuming stereo use do you need to know the mains in room response to merge these? If you have a shelving filter put onto the amp, does it replace the crossover adjustment or is there further refinement there.

I think becuase we have a "virtualization" of the thiele-small parameters that some of the math given on the linkwitzlab may need to be altered to use on this. Then again maybe not.

-Tony

WerTicus · « **Reply #1 on:** 22 May 2008, 05:28 pm »

I am very interested in a servo controlled ob subwoofer using these drivers myself, and so are a few others for sure.

However I don't think I have enough knowledge to contribute much to this forum

I'm going to start doing my homework now and hope to come up with a solid baffle design at some point to share with you all.

Danny Richie · « **Reply #2 on:** 22 May 2008, 07:02 pm »

FYI, I am testing a pair of these in a 14" deep W frame design.

No changes have to be made to the amp. It is plug and play.

I get good output all the way up to 300Hz from my measurements, and with the built in EQ function I can get flat response all the way down to 20Hz. In my room I didn't have to add gain with the EQ either. I had to take away some output at 28Hz to make it flat.

And it sounds incredible.

nodiak · « **Reply #3 on:** 22 May 2008, 07:14 pm »

Good thread idea.
Danny, that's sweet!
One of my main issues is about being able to keep the 3 woofer baffle short as possible. Both for general stealth options in the room, and so main speakers can be above without being too tall.
I don't like tall speakers myself. So that W frame is great. Also going above 200 hz would open possibilities for small mains.
Don

TRADERXFAN · « **Reply #4 on:** 22 May 2008, 07:55 pm »

Quote from: Danny on 22 May 2008, 07:02 pm

FYI, I am testing a pair of these in a 14" deep W frame design.

No changes have to be made to the amp. It is plug and play.

I get good output all the way up to 300Hz from my measurements, and with the built in EQ function I can get flat response all the way down to 20Hz. In my room I didn't have to add gain with the EQ either. I had to take away some output at 28Hz to make it flat.

And it sounds incredible.

Wow, that makes me feel a lot better. Sorry to be an alarmist!

Maybe, we could get a drawing of what you made, Danny, when you put the other plans together? Since we know THIS layout works

laserman · « **Reply #5 on:** 22 May 2008, 07:55 pm »

Don't forget to post pictures of your project here or in your gallery (with a link for us to click). That goes for you too Danny.

Thank you,
Lou

Danny Richie · « **Reply #6 on:** 22 May 2008, 08:47 pm »

Okay, I'll throw a bone.

It is just a test box. Don't ask what's above. It's top secrete.

nodiak · « **Reply #7 on:** 22 May 2008, 09:53 pm »

Nice Danny. How tall, ~ 20" ? How's the power handling of that pair compared to single sealed 4 ohm, a little better?
Don

Danny Richie · « **Reply #8 on:** 22 May 2008, 10:03 pm »

It is 23.5" tall. The "W" is a right angle. That made it really easy.

It takes all the power I can throw at it with no problem. It hits pretty hard, but does not load the room. It just sounds really, really clean.

TRADERXFAN · « **Reply #9 on:** 22 May 2008, 10:26 pm »

Danny, I must say you have this inimitable method of understated salesmanship...

Because after that last post, I put up my svs sub for sale...

http://www.audiocircle.com/index.php?topic=54889.msg490087#msg490087

konut · « **Reply #10 on:** 22 May 2008, 11:14 pm »

How ingenious! Will a cannon report make it jump? Oh,.....what's above? aa

laserman · « **Reply #11 on:** 23 May 2008, 12:39 am »

Hi Danny,

Thanks for the picture (I’m a visual kind of guy and that helped a lot) and for toying with us.

I guess you couldn’t help yourself because if you wanted to not play with our minds you would have cropped the picture so we wouldn’t have seen the mystery box.

Okay, so does one fire one speaker forward and one backward or can it go side-to-side ?

Can the “W” be wrapped in speaker fabric and then the top and bottom dressed with some solid wood end caps ?

I have more questions but I will wait till later.

Tony, I forgot to mention I appreciate you setting up this thread and your OB7 project looks fantastic.

Peace,
Lou

WerTicus · « **Reply #12 on:** 23 May 2008, 10:14 am »

call me old fashioned but its my opinion that a subwoofer should be used for sub bass

certainly if your crossing it off higher than 80hz you should be using two, and placement will be very important to not ruin the imaging of the stereo.

Obviously danny's super secret cut off image is an open baffle midrange and tweeter type of thing like this:

(at least that is my guess) So cutting off higher will work for such a design.

Ill be using mine below 50hz - 60hz only but i guess I'm not sure exactly where until i get them into the room and tweak it.

BrunoB · « **Reply #13 on:** 23 May 2008, 05:26 pm »

Quote from: Danny on 22 May 2008, 07:02 pm

I get good output all the way up to 300Hz from my measurements, and with the built in EQ function I can get flat response all the way down to 20Hz.

I have a strong resonance at 200 Hz with my dipole sub. Do you have any resonance issue with this W design? May be the resonance is above 300 Hz?

Bruno

TRADERXFAN · « **Reply #14 on:** 23 May 2008, 05:40 pm »

I was really surprised Danny didn't report a resonance. Maybe flat down to 20hz is not intended to mean from 300-20hz though?

maybe from 80 ish to 20 hz is flat?

Bruno, you seemed to have done some research on these things. Do you know of this calculation for the predicted resonance of an H frame based on the depth? This is what I found from Linkwitz's site...

http://www.linkwitzlab.com/x-models.htm#B

" The latter arrangement, called H baffle, is very practical for dipole woofer construction. It too has a severe resonance because the waveguide of effective length L in front and behind the cone sees large impedance mismatches at the cone and at the open end of the cabinet. The resonance occurs when L = l/4 = 0.25*v/F. (**see the site because the character used represents something different than this html code posts in this text)
For a baffle of D = 20" (0.5 m) length and with L = 10" (0.25 m) estimated, the resonance peak in the dipole output is at F = 0.25*v/L = 343 Hz. Even when the peak is removed by equalization, the H baffle should only be operated below this frequency. It is a compact baffle for woofer applications and I use it with slightly different driver arrangement for the PHOENIX."

One possibility I thought of is that the resonance might not be heard, in the range being measured, because having the drivers angled 90 deg towards eachother like that may have pushed the resonant frequency up higher than this simple calculation for the H-frame?
-Also, since the depth from the driver is not equal but varies from the front edge to back edge of either of the drivers in Danny's pictured layout, it is bound to be something different than this would predict.

Linkwitz says its an empirical finding. I wonder how high up the measurements went...

-Tony

Danny Richie · « **Reply #15 on:** 23 May 2008, 06:32 pm »

I was able to get a pretty flat response from 20Hz to 300Hz with no resonance at all.

Traderxfan,

Try applying that information to a box with a wider opening (22" tall by 13.5" wide) and only 13.5" deep and see what you get.

BrunoB · « **Reply #16 on:** 23 May 2008, 06:45 pm »

Quote from: Danny on 23 May 2008, 06:32 pm

I was able to get a pretty flat response from 20Hz to 300Hz with no resonance at all.

Traderxfan,

Try applying that information to a box with a wider opening (22" tall by 13.5" wide) and only 13.5" deep and see what you get.

Danny,

do you see any difference in the impedance plot of your driver in free air vs a pair of driver in the W frame?

Thanks,

Bruno

Danny Richie · « **Reply #17 on:** 23 May 2008, 07:12 pm »

Ask and you shall receive.

This is the impedance of the pair of woofers in the W frame box pictured. Does it get any better than this?

BrunoB · « **Reply #18 on:** 23 May 2008, 08:30 pm »

Quote from: Danny on 23 May 2008, 07:12 pm

This is the impedance of the pair of woofers in the W frame box pictured. Does it get any better than this?

Thanks for the plot!

According to Danny's web site, the Fs of a single SW-12-16FR is 23.8 hertz. From the impedance plot, the Fs seems to be 22 Hz. A decrease of only 2 Hz. A woofer placed in a folded frame, like U, H or ripole frame can show a drop of Fs up to 10 Hz (may be more, but this is what I measured with my own stuffed U frame), whereas in a I frame (infinite baffle), there is no Fs drop - it is like free air. I frame dipoles do not have an extra resonance (no folding). So, with only 2 Hz drop, I speculate that Danny's W setup has a mild folding around the dipole and that the extra higher resonance must be present but weak.

Quote from: Danny on 23 May 2008, 07:12 pm

Ask and you shall receive.

What about a full range waterfall plot?

Bruno

Danny Richie · « **Reply #19 on:** 23 May 2008, 09:03 pm »

I can't do any accurate waterfall plots in that low of a frequency range.

Also, any resonance for this size box should be well above the operating range of the woofers.