Rocket driver construction? (1 Viewer)

[jad]

Does anyone know the makeup of the woofers used in the rockets, such as driver basket construction and/or magnet and voice coil size? Their web site says they're a custom designed long throw driver but does not give any other details.

 

[Bruce Chang]

Jad, it makes no difference whether a speaker uses dynaudio drivers and some cheap vifa drivers, it's the design of the overall speaker.

 

[SkiingNinja]

Bruce is right that the difference is in the SYSTEM and not just one part....but to answer your question, here is your answer from Dick Pierce:
Indeed they are custom drivers, with electrical, mechanical and
acoustical parameters tailored to the specific applications.
The customization is in several areas, the following being just
a partial summary of the specific tunings:
All the drivers have suspension and centering spiders selected
to achieve the required compliance so as to be matched to the
cabinet volume, enclosure tuning and cutoff frequency.
Drivers have had voice coils and magnets designed for specific
purpose. For example, even though they outwardly look the same,
the 6 1/2" driver in the RS 250 is NOT the same driver as in
the RS550 or the RSC200. The former is a nominal 8-ohm driver,
while the latter's use a nominal 13 ohm driver, so that two
can be used in parallel without an unduly low impedance resulting.
However, it is not a trivial task to change a driver's impedance:
it requires a very careful adjustment of wire size, winding length,
number of layers and the magnet itself to achieve both the desired
impedance at the same time as retaining other important parameter
values, such as electrical damping and efficiency.
Driver magnet structures use single-piece cold-forged, vented
pole-piece/back plate assemblies. Single piece forgings of this
sort have higher efficiencies (due to the elimination of a
potentially lossy high-reluctance gap between pole-piece and
back plate), resulting in higher voice-coil gap flux densities
and lower external leakage. One under-appreciated result of this
is that the entire magnet system can be placed at the most efficient
portion of the magnetization curve, and that contributes to better
long-term stability as well as achieving the required damping and
efficiencies with less hard magnetic material.
The vented poles of these magnets contribute to more uniform response
by eliminating the need to ventilate the voice coil chamber through
holes punched in the voice coil itself. The resulting increase in
stiffness of the voice coil reduces flexure at high frequencies.
The baskets for the woofers and midrange drivers are all carbon-steel
precision stampings. Much ballyhoo is made of the differences between
stamped and cast baskets, little of it having anything to do with
actual performance. Often claims are demonstrated by taking raw baskets
and examining how they "ring" when struck, but this highly unrealistic
"test" completely ignores the fact that once the basket is part of
an ASSEMBLY, including the much more massive magnet structure and
speaker front baffle, the basket itself is, at most, a small minority
contributor to the performance. For example, firmly attaching a basket
of ANY kind to a baffle largely eliminates resonances.
One of the properties claimed for die-cast aluminum or magnesium
frames is supposedly better resistance to water. That MIGHT be
an advantage for outdoor application, however, in working with
clients in that business, let me assure you that the appearance
of a cast aluminum frame that has been exposed to even light salt
air is NOT pretty.
I hope that helps
Sean

 

[rodneyH]

Wow, sean, you are all over the place!!

Also, don't forget the importance of the crossover network (which the rockets is supposed to be very good as well)

 

[Cam S]

I'd love to see some pics of the drivers used in these speakers if anybody wants to do so.

 

[Russell _T]

The data on the crossovers for these speakers just blows my mind. Mainly because I don't understand most of it. :b

 

[jad]

Thanks Sean, great reply. I think an audition of the Rs250 might be in order. Have you heard these with the Outlaw 1050?

 

[Russell _T]

Cam,
Gluegun just posted a picture of the Vifa tweeter on AVS under the Rockets thread. It's the black one not the silver one. Also, the Rocket loudspeaker site at AV123.com has cool animated pictures of the models with the grill on and off. If you touch your cursor to one of the pics, it removes the grill.

 

[Matt_Briol]

Here is a pic of the tweeter.

 

[Patrick Sun]

It looks mighty excited.

 

[SkiingNinja]

I inadvertently truncated part of Dick's reply on the driver makeup...here is the rest:

The basket design is inherently flush-mounting, contributing to smoother
on-axis response by reducing or eliminating secondary diffraction effects
due to sharp transitions. In addition, the rim design has inherently
better acoustic sealing properties than other baffle designs.

The cones are all proprietary coated-metal cones, the shape of which
are spherical segments. This shape is chosen because of its extremely
high mechanical stiffness. Combined with the inherent high internal
propagation velocity of metal leads to drivers of very wide bandwidth.
The coating provides appropriate mechanical damping.

The surround chosen are high-quality modified polybutadene allows with
high internal damping and provide suitable termination properties for
the cones. They have high linearity leading to low distortion and
very minimal memory effects. One positive side effect to this choice
of materials is that they do not suffer the deterioration found in
other surround materials.




Sean

 

[SkiingNinja]

I'd love to see some pics of the drivers used in these speakers if anybody wants to do so.

I plan on taking a whole bunch of high-resolution pictures @ my place of the speakers and drivers once I get it all set up.
Stay tuned
Sean

 

[SkiingNinja]

Thanks Sean. Have you heard these with the Outlaw 1050?

Sure I have. The 1050 does a great job. It has enough power to push slightly past ref levels anechoic while sounding clean. If you all remember, Mark used the 1050 to demo the Diva's at CES.


Sean

 

[Cam S]

The tweeter that the rockets use looks like the ones that are used in the new Polk LSi's?

 

[SkiingNinja]

They are the same design but are made with different materials...the Rocket Vifa is an upgrade of the one in the Lsi's.


Sean