Fern and Roby: Rocket Dipole Subwoofer

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audiogurujax

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Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #20 on: 24 Mar 2017, 02:23 pm »
I have a question? I have always heard that you need high qts woofers or subs for open baffle applications then why is that the woofers used by the Linkwitz Orion has a QTS of .27 still is one of the best sounding woofers for OB applications?????

https://www.madisoundspeakerstore.com/approx-10-sub-woofers/seas-l26ro4y-10-subwoofer-4-layer-vc-d1004-04/

FullRangeMan

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Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #21 on: 24 Mar 2017, 02:33 pm »
I have a question? I have always heard that you need high qts woofers or subs for open baffle applications then why is that the woofers used by the Linkwitz Orion has a QTS of .27 still is one of the best sounding woofers for OB applications?????

https://www.madisoundspeakerstore.com/approx-10-sub-woofers/seas-l26ro4y-10-subwoofer-4-layer-vc-d1004-04/
Low QTS woofers need EQ, the Linkwitz Xover should do it.

Jazzman53

Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #22 on: 24 Mar 2017, 02:48 pm »
Greetings to all  As the designer of Surreal Sound's 5th row speaker and the Fern and Roby Rocket subs I feel I need to step in and make several clarifications.  The search for a woofer that was fast enough to make with an electrostatic speaker began in earnest in 2001.  I have tried thousands of dollars worth of woofers and ended up having DC gold build these woofers for us.  A 10 inch Wall Mart woofer isn't worth mentioning because it simply will not work.  The closest other 10 inch driver to the DC gold is the Morel 10 inch driver.  Prices are very close with both costing in the $150 to $175 dollar range each.   These are not Chinese made mass produced units.  It you care to actually measure the driver parameters the variation's of the cheep drivers is all over the place.  I would never base a design on there made up values.  If you want to read more I have posted several articles on Facebook open baffle site.  We have many electrostatic panel speaker owners who can attest to the speed of my design and yes they are the only woofers I have heard that integrate flawlessly.  We have shown these subs at Capital Audio Fest and Rocky mount.  Check out what the reviewers said.  If you want cheep then buy Chinese.  If you want good buy German Scandinavian (Morel is a Dynaudio based design) or USA made drivers  remember you GET WHAT YOU PAY FOR. We do a demo at the shows where we have a good set of speakers the the manufacturer say go down to 30 hertz and we put our subs in the room with them.  While the music is playing we turn off the Rocket dipole subs and everyone in the room has the same reaction. "What just happened" They are in disbelief.  The DC gold 9.5 is similar to our 10.  It is the same size.  We use a custom ultra low inductance, longer excursion coil with the same neo magnet.  I you actually check out people who have heard our bass check out the reviews by Scott Hull on the Surreal 5th row and Dagago.  Until you have actually heard what these subs can do there is really no point writing and opinion about them as way to many people do.  Again there is nothing like them that you can purchase anywhere else.  We guarantee they will match the speed of any electrostatic.  Hope to see you at an audio show.

Sir,
Your description of the woofer intrigues me greatly-- especially the "no spider" configuration.  And I'm wanting to ask if the "17 grams moving mass" ascribed to this woofer in another post was a typo because I've never seen a number that low published for a woofer of that size (or even smaller, for that matter).  I would assume a moving mass spec would have to include the spider's mass so perhaps the absence of a spider explains the low number (assuming it's not a typo).  That coupled with low inductance would indeed give serious speed! 

I would love to hear more about your woofer.   I build ESL's and I'm a DIY guy and I confess ulterior motives for asking if your company or DC Gold offers that particular woofer for sale as a lone driver.
In any case I'm intrigued and would love to hear any additional details about that woofer you might care to offer (LOVELY cabinet too, BTW).

Regards,
Charlie (a.k.a Jazzman)
http://jazzman-esl-page.blogspot.com/     

AJinFLA

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Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #23 on: 24 Mar 2017, 03:13 pm »
I have always heard that you need high qts woofers or subs for open baffle applications then why is that the woofers used by the Linkwitz Orion has a QTS of .27 still is one of the best sounding woofers for OB applications?????
High Qts gives "free" EQ for passive systems. Linkwitz designs are active, so he can pick any driver and EQ it to the desired final response. The benefit there is the driver can then be chosen for specific attributes, like silent mechanically during very long strokes (rare!), low distortion, high Xmax, etc, etc., rather than Qts.
Those attributes are extremely rare or non-existent with high Qts drivers, which are often inexpensive weak motor units. The exceptions being drivers from companies like AE, custom made specifically for passive OB use, but with advanced low distortion motors and silent operation.

Davey

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Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #24 on: 24 Mar 2017, 03:25 pm »
FYI, with SL's thoughts on this topic.
http://www.linkwitzlab.com/faq.htm#Q34

Dave.

JohnR

Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #25 on: 25 Mar 2017, 12:43 pm »
Once the driver is EQ'ed, doesn't the group delay end up the same (regardless of its starting Q)?

Davey

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Re: Fern and Roby: Rocket Dipole Subwoofer
« Reply #26 on: 25 Mar 2017, 03:58 pm »
The mechanical parameters of two different drivers will not change, but electronic equalization can force different amplitude roll-off behaviour and the phase-response/group-delay characteristics along with it.  So, within reason, yes.

The vast majority of speaker drivers (easily available to us today) are designed for some sort of box usage and are (generally) higher motor-strength (low Q) designs.  Using said drivers in open-baffle (free-air) configurations means conforming the roll-off to a more suitable rate with EQ.

If typical drivers were used in a "W"-frame application like the Fern and Roby, it would require three different forms of equalization.  A 6db/octave dipole correction, a driver Q-correction, and a resonant peak (notch) filter to account for the cavity resonance created by the enclosure.
These fellas seem to have selected a high-Q driver that (sort of) addresses the first two characteristics without the need for extensive equalization.

It seems an interesting design but, obviously, a good DIY'er can create something equivalent (or more likely superior) for much less money.

Dave.