Rocket speaker tweaks

Discussion in 'Hardware Lounge' started by Denton, Jun 5, 2007.

  1. Denton

    Denton Well-Known Member Donor War Zone Member Top Poster

    Danny Ritchie offers upgraded crossovers for the RS750 speakers as well as some other models. He also recommends using some of his No Rez foam along the ledge that overhangs the top front of the speaker. The foam in question is on the left in this photo: (the other is Black Hole 5)

    norez1.jpg

    Anyone use the foam or the crossovers? Any comments on effectiveness? Anyone know exactly how the foam is cut/shaped before application? In other words, what does the tweak actually look like when applied to the speaker?
     
  2. Max Yokell

    Max Yokell Well-Known Member War Zone Member Top Poster

    Don't know but if you experiment please post about your findings.

    Max
     
  3. Carl V

    Carl V Well-Known Member Donor War Zone Member Top Poster

    XO upgrades. Always a loaded question.
    Parts quality or is this a revision of transfer functions.
    If the former YMMV. I believe it's the latter
    & I'd believe you should hear a difference. I've had
    conversations with Danny & have been lead to believe that the
    Rocket line has been tweaked/improved with "better XO" design.

    BH5...No Rez.... VS other brands & types.
    I've used these...& no I haven't done a side
    by side compare & contrast. I've found BH5
    to be of some value in Sub enclosures. I've
    done a A/B with a few Monitors & found the differences
    minor & enclosure dependent.
    Some enclosures were mine and built along the
    lines of Northcreek...in other words substantial.
    The other enclosures were the Pre-made PE cabinets.
    These are nice 3/4 MDF with 1" MDF front baffles.
    I felt the addtion of No rez improved these. I placed
    no rez on the side & backs. Actually, I placed it only
    on the back 1/2 or 2/3 of the side panels. The front 1/2
    or 1/3 was covered with thinner PE dyna sheets & wool
    felt. I usually stuff the back portion with Acoustastuff.
    In other words I don't place a great deal of stuff in the
    immediate vicinity of the driver.

    Personally, I've found that the additon of extra bracing
    to be of greater benefit. The PE cabnets benefitted with
    addtional 'matrix' bracing. Even if you merely glue
    1x2 oak strips to side panels or .75x 1" BB ply to the panels.
    Enginners have known the benefits of "I" beams & "T" beams
    for years....not to mention the advantages of engineered
    Beams or trusses.

    Good luck & have fun.
     
  4. Denton

    Denton Well-Known Member Donor War Zone Member Top Poster

    I'm certainly familiar with using BH5 and other materials to deaden enclosures. If I understood this particular tweak correctly, the NoRez was added to the outside of the overhang or front face of the enclosure. I'm especially curious to hear comments from anyone who has played that game.
     
  5. Max Yokell

    Max Yokell Well-Known Member War Zone Member Top Poster

    From what I have read Danny was involved in the design the 850s and 1000s and did the xovers for them the 750s were a before him. I know that you can buy an upgrade for the crossover on the 200 CC to make it a 200 CC signature so it might be a similar thing.

    I bet that if someone shot him an e-mail he would likely show up here and fully explain it, but he might not know we exist yet since he wasn't active at HTT for some time.


    Max
     
  6. Denton

    Denton Well-Known Member Donor War Zone Member Top Poster

    Actually, Max, there are the Signature crossovers as well as two levels of upgrades available from DR ("Ninja"). These represent more than just upgraded parts. As I understand it, there is a change in crossover topology designed to suppress breakup in the small metal midbasses used in these speakers.


    http://www.skiingninja.com/750ninja.html
     
  7. Danny Richie

    Danny Richie New Member

    RS750

    Hi guys,

    Thanks for the invite to join in. I am sorry that it has taken me a few days to find the time to post a response. I will try to drop in here as often as I can.

    The RS750 got a complete re-design of the network. This is an upgrade that was in response to the demand from owners and is not offered through AV123. The RS750 is a discontinued model. The complete upgrade in various levels is available through the Skiing Ninja as noted.

    The new design limited the metal cone woofers to ranges that they were more optimal to cover and got them out of the break-up ranges that they were being allowed to play up into.

    The new design also limited the driver overlap and corrected the low impedance range that this was causing.

    The crossover point to the tweeter was lowered too.

    The frequency response is now much smoother, drivers are more acoustically in phase and off axis responses (horizontally and vertically) are now even, consistent, and free from out of phase cancellations.

    Parts quality upgrades were also a considerable improvement over the stock units even going with the most basic upgrade. This created a significant improvement as well.

    In regards to the overhang. There is an overhand of the top of the speaker that comes out over the tweeter. Surface reflections from this cause about a 1db peak in the response at 2.5kHz followed by a cancellation of about 2db in the 3.5kHz range.

    Added a piece of foam damping material right up under the overhang corrects the response problems that the overhang was causing. A thinly cut piece of No Rez works great here, however it will interfere with the grill if it is placed back on the speaker.
     
  8. Denton

    Denton Well-Known Member Donor War Zone Member Top Poster

    I'd say that pretty much clears it all up... :D
     
  9. Max Yokell

    Max Yokell Well-Known Member War Zone Member Top Poster

    But I guess since you did the cross over for the 850s I just got then they obviously should be perfect right. :)
     
  10. Danny Richie

    Danny Richie New Member

    As perfect as I can make them...

    You could upgrade the parts quality and step them up a few notches too.

    I think they turned out pretty well. Those are really nice speakers, especially for what they cost.
     
  11. Denton

    Denton Well-Known Member Donor War Zone Member Top Poster

    Okay Danny, now that we're talkin' about this stuff.... :) How many of the midbasses are handling the midrange in your design? In other words, is this a 3-way with some midbass(es) handling only midrange and some only bass, or is it a 2-way, or is it perhaps a 2.5-way?
     
  12. Danny Richie

    Danny Richie New Member

    The design is technically a three way.

    All of the drivers share the same air space though. This presented a challenge in that with all the drivers sharing the same air space they must all work together, in phase, and without electrical delay or they would be working against each other or adversely effect each other. But they can't all play together as a two way design because the acoustic centers are too far apart if they are configured that way.

    What I did to make it work was wire the woofers in a series parallel configuration with the top two woofers being paralleled and the bottom two woofers being paralleled than the two groups wired in series.

    Then I had to use a series network between the two woofer groups without using an inductor so that correct phase would be maintained. So what I have is a large cap bundle (161uF) by-passing the lower woofers. This lets the upper woofers get what will pass through the cap bundle (blocking the lower ranges) plus what will pass through the voice coils of the two lower woofers. This is like by-passing a cap value with a resister, except a resister is a linear load while the inductive reactance of the woofers make the resistance vary with frequency. It will have a minimum resistance level in the 12 ohm range. Basically all four woofers share the lower ranges equally, but as frequency increases only the upper woofers handle that range.

    This cap bundle that is by-passing the lower woofers also allows a path of least resistance to the upper woofers as frequency increases while allowing the lower ranges to pass unrestricted to the lower woofers and they share that load equally with the upper woofers. If I were to pick a range at which they equally play the same range then it would be near the 200Hz to 300Hz range.

    So the acoustic center at the upper crossover point is half way between the top two woofers. This still dictates a low crossover point. The breakup in the upper range of the woofers also dictated a low crossover point. Fortunately the tweeter had no problems being crossed at the 2kHz point.

    In the end it worked out really well.
     
  13. Denton

    Denton Well-Known Member Donor War Zone Member Top Poster

    Thank you for the explanation. This is a very unique situation, I believe, in that it looks doubtful anyone would have intentionally headed this direction if designing from scratch. (You had to make the best of an existing situation; it sounds to me like you have come up with an ingenious solution.) Would I be correct in assuming that the 760 crossover is an MTM at the top with the bottom two woofers handling the bass in a separate air space?
     
  14. Danny Richie

    Danny Richie New Member

    Yes you would.
     

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