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passive radiator q's

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  • Of course, it's not a bad idea to EQ a driver for more output on the low end, as long as your maximum SPL requirements are still satisfied. I'm sure you've heard the term "Linkwitz transform" in the past which is exactly this concept.

    SPL capability for any driver can be simply determined by surface area (Sd) and excursion. The sensitivity spec only determines how much power is required for a given excursion. For bass, get the biggest driver(s) that fit your space.

    I've done DSP 3-way in the past using a lower sensitivity subwoofer for the bass driver, the DSP provides the ability to give the low sensitivity subwoofer enough juice to meet the mid and tweeter's output.

    The DSP EQ can be incorporated in VituixCAD to the box model to simulate the combined effect, and if you have a mic available, complete DSP crossover design can be completed in VituixCAD and directly copied over to the miniDSP.

    Steve_Lee
    I'm not deaf, I'm just not listening.
  • edited February 2022

    For what you have in mind, I would go for RSS210HO instead for the extra few mm of xmax.

    To simulate the active DSP circuit in VituixCAD, first go to the options and select the miniDSP under the DSP System.

    For a simple example, I used a linkwitz transform block connected to the default driver. Loading driver impedance etc to the crossover is not important here for an active system.

    Then in the enclosure model, in the "align" tab, check the box to include crossover of driver and select the driver from the list. The EQ circuit is now applied to the cabinet model to provide the combined effect.

    You can right click on that LT block in the crossover and select "copy biquad coeffs" and then paste into the miniDSP software. Easy peasy.

    I'm not deaf, I'm just not listening.
  • edited February 2022

    The problem with a closed box and LT circuit will be the max output, green line here:

    The closed box above is 16.5L. Keeping with the RSS210HO and moving to a ported box, I haven't increased the box size much, only to 20L, and the max SPL capability in the low end is much improved with similar bass extension. Previous closed box max SPL is shown here as an overlay in blue:

    4thtry
    I'm not deaf, I'm just not listening.
  • impressive (amount of work you just did)- thx
    both at 30Hz ~82.5dB could 'liven up' even a large room
    looks like I'll pull out my old RatShack meter and get a sense of what level I've been listening to in my living room

    again, thx

  • again, I think you nailed it showing 85dB
    while cranking my stereo to play music at 90dB in my living room (vaulted and open thru kitchen and dining room) is fun, it’s too LOUD

  • I used the RSS210 in the sub portion of my Time keepers build, but I used it vented with the PE dsp plate amp so I guess that I'm no help. It's a solid little driver.

  • edited February 2022

    @tajanes said:
    again, I think you nailed it showing 85dB

    No...That SPL is just 2.83V reference, not important at all. The focus is on the green and blue lines up top. They are showing max SPL based on Xmax or Pmax, whichever comes first as the limiting factor. The point was to show that simply changing from a sealed cabinet to a slightly larger ported cabinet can gain you 10dB of extra output capacity at 30Hz.

    As I mentioned earlier, take the absolute SPL value in the cabinet model with a grain of salt, it's missing a lot of information to determine real in-room performance. Also keep in mind that average music SPL is a lot different than constant sine wave SPL. This is where "crest factor" comes into play, where music can often be in the 10-12dB range, meaning that the difference in SPL between the peaks and the average can be an order of 10dB, so if you want to hit 85dB average as an SPL goal, design the system to work to at least 95dB, and at listening position, not 1m.

    I'm not deaf, I'm just not listening.
  • edited February 2022

    Also, don't take the max SPL chart as complete accuracy either, especially below the tuning frequency. These cabinet models depend on T/S parameters that are defined as "at rest" parameters. The higher the simulated SPL, the greater the inaccuracy of the result, since the model doesn't have knowledge of the change in motor BL, and suspension compliance over the travel of the speaker. For this reason, they often show cone excursion throwing the speaker cone across the room below the port tuning frequency, where reality is quite a bit different. The max SPL chart will show the driver is xmax limited below the tuning frequency for this same reason as well.

    I'm not deaf, I'm just not listening.
  • Can I ask what port diameter and length your model showed?
    I've put the driver (the 8ohm HO unit) info into a couple of programs and getting undoable lengths

  • 3" port 27" long, you'll need to put a bend or fold in it, not impossible.

    I'm not deaf, I'm just not listening.
  • edited February 2022

    I modeled the RSS210 HO (4ohm) vs HF (4ohm) versions to comp drivers (even though HO 4 xmax 11 vs 12mm for the 8ohm, and the HF at 9mm) in a closed box, auto align to get best Vb fit for each.

    I then set V level to get xmax of drivers @ 26Hz (for the HO ~116w, and for the HF ~68w), then look at frequency of each driver at SPL 95.

    Interestingly the HF shows 31.9Hz @ 95 SPL and the HO shows 33.0Hz, so I'm seeing these as basically equivalent. While the HO provides a bit more room for adding eq amp power, it looks to require the extra xmax to stay even with the HF's output?

    So 1) what am I missing here, and if I'm basically correct 2) looks like the HF with its QTS .57 may be a better fit for a closed box than the HO QTS .40? And 3) maybe it just comes down to which driver sounds better- I've always thought (maybe incorrectly) that the more a driver needs to move the more distortion (hence size matters, but I want to keep to an 8 in driver for this project) so I'm leaning towards the HF.

    Thanks again for all the suggestions and input. I've only begun working with the modeling software.

  • edited February 2022

    @tajanes said:
    I modeled the RSS210 HO (4ohm) vs HF (4ohm) versions to comp drivers (even though HO 4 xmax 11 vs 12mm for the 8ohm, and the HF at 9mm) in a closed box, auto align to get best Vb fit for each.

    I then set V level to get xmax of drivers @ 26Hz (for the HO ~116w, and for the HF ~68w), then look at frequency of each driver at SPL 95.

    Interestingly the HF shows 31.9Hz @ 95 SPL and the HO shows 33.0Hz, so I'm seeing these as basically equivalent. While the HO provides a bit more room for adding eq amp power, it looks to require the extra xmax to stay even with the HF's output?

    So 1) what am I missing here, and if I'm basically correct 2) looks like the HF with its QTS .57 may be a better fit for a closed box than the HO QTS .40? And 3) maybe it just comes down to which driver sounds better- I've always thought (maybe incorrectly) that the more a driver needs to move the more distortion (hence size matters, but I want to keep to an 8 in driver for this project) so I'm leaning towards the HF.

    Thanks again for all the suggestions and input. I've only begun working with the modeling software.

    As far as the SPL comparison goes, you can simply observe the difference in max SPL to see that in a sealed cabinet you're not going to get much more out of the HO vs HF. Comparing the two, it looks like not much, but the difference is nearly 2dB extra output from the HO version, but it's natural response in a sealed cabinet is not great, it is more suited for a ported cabinet so you should use some EQ with it.

    In a ported cabinet, the HF version can get a lot more bass extension, but it also needs a big cabinet and max SPL becomes limited by Xmax. The HO on the other hand is quite happy in a smaller cabinet, not as much bass extension but can really belt it out.

    The comparison here is HF model in 60L cabinet tuned to 25Hz, and the HO model in 25L cabinet tuned to 30Hz. The area between the blue dashed max SPL and the green max SPL is the advantage of the HO model. The dip in the blue dash line is the HF model running out of Xmax.

    Both of those comparisons are not with equal overall frequency response, however the max SPL result doesn't actually change at all if you EQ the HO driver to provide the same frequency response as the HF, the max SPL is not dependent on frequency response, just a function of Xmax * surface area and Pmax. Both drivers have the same surface area, so advantage of max SPL goes to the HO for obvious reasons.

    The conclusion of this comparison would be that the HO provides quite an advantage >30Hz where the meat of the bass is, and in a much smaller cabinet. The HF can provide a bit deeper bass, maybe you would like it more for HT movie rumbles as long as the volume isn't too high.

    I'm not deaf, I'm just not listening.
  • edited February 2022

    And just because this thread started as a PR discussion, here's a comparison of the "losses" in moving from a port to a PR. This is the RSS210HO with the CSS APR-10. There is some small losses in the PR as it requires extra force to move it, and the rolloff is steeper, but IMO the real advantage is the surface area vs a port, 10" vs 3" means no chuffing or restrictions at higher SPL (as long as the PR is sized correctly), no port resonances, much less midrange leakage, etc.

    I'm not deaf, I'm just not listening.
  • Thx. again, and again, and...

    Per your detailed evaluations; looking at the 30 to ~45Hz area is leading me back to the HO, even in a sealed box. I'll continue to play with the idea of stuffing a 3 ID 27in port in a smallish box, but will probably go with a sealed design. If I need more low-end I'll just have to disguise my old Velodyne somehow...maybe as a plant stand.

    Since music is my primary goal (even though I've set my room up as 2+2, i.e. no center channel hanging over the fireplace / tv, and ceiling surrounds for a bit of back fill) I'd prefer the better quality 'sound' in the 40's than one that goes lower.

    So, it is just a balance of the extra 2dB (which is significant in this lower range) with the extra cone extension for the HO vs what may be a bit cleaner HF. Thinking I'll barely be able to measure difference in distortion much less hear a difference (?), but I would be able to hear the 2dB difference.

  • Since the ported model output is tempting, I've been playing with getting an equivalent 27in 3 ID port in a small box (20ht x 11 wide x what's necessary for depth). It seems like a folded slot port would fit, I'm just concerned about the bend (looks like I'm building a car sub). These will be on short stands I'll build, so bottom porting would be ideal.

    I may just stick with sealed, but heck playing around before making sawdust...

  • edited February 2022

    The PR solution looks interesting here.

    Q: how much spacing should there be between the active W and passive radiator? I understand they work in tandem, but are there back-wave issues? I see subs with forward active W and two side passives - in fairly close proximity- any issues ?

  • edited February 2022

    Not really. Often when two PRs are used they are placed on opposing cabinet sides for "force cancellation" benefits.

    Jeff B wrote about the benefits of PR's for Salk Sound over here:
    https://www.salksound.com/blogtopic.php?id=6

    I'm a big fan of PRs, but they do get expensive, much more so than a tube of ABS plastic anyway.

    I'm not deaf, I'm just not listening.
  • edited February 2022

    great read- ok I’m getting out my ccard…
    I’ll probably go with matching the RSS210HO (per your rec vs the HF) with the DA RSS265-PR (not a fan of foam surrounds CSS).

    While I understand a rear placed PR due to its wavelength is no issue per-se as 4pi radiation, the speakers will be placed alongside my fireplace in the living room- but this is directly open to a small room behind - so the passives would be directly aimed into that other room. While I saw a comment about bottom mounted PR’s (my speakers will be sitting on short stands - open at bottom, and slightly tilted up) I think the surrounds on these units won’t be an issue in this format)

    Looks like Vd will be ~ 1.6x (passive vs active)

  • decibel,
    Lastly (maybe), I see you modeled the 4ohm version of the HO vs the 8ohm. Per Parts Express, looks like the 4ohm version requires a much larger box?

  • CSS APRs don't have foam surrounds FWIW, they're rubber. But overall they are not very "pretty", best suited to be hidden on the backside of the cabinet.

    If it's truly 4pi radiation, then why would it matter which side of the cabinet the PR or port is on? You have a problem of no rear wall behind the speaker regardless of where the port or PR is located on the cabinet.

    I personally would avoid bottom mount of PR or speaker. PR generally has added weight to the cone, often 100+ grams so you have that suspension sag problem limiting the usable excursion as well less force required to push the cone vs pull because gravity, just doesn't sit well with me.

    I'm not deaf, I'm just not listening.
  • edited February 2022

    so which version, 8ohm vs 4Ohm
    I'll have no issues with matching vs the coax, I'll be bi-amping with miniDSP btwn W and coax (coax is passive)

  • Often the 4 ohm variants are happier in a smaller cabinet, however these 2 driver variants model about the same, but you already knew that having your own in-depth comparison ;)

    It sounds like you have plenty of amp power available regardless so...the 8 ohm version claims an extra 1mm xmax so it's a clear winner for that extra 0.5dB of headroom, or use the 4 ohm variant to have more headroom on your amp when you crank it to 11. The choice is yours.

    tajanes
    I'm not deaf, I'm just not listening.
  • edited February 2022

    If you compare the Dayton BassBox auto-tune suggestions, I would conclude that either Dayton has made an error entering values into Bassbox, or they have errors in the datasheet specs, because they're suggestion for the 8 ohm variant I would hardly call optimal given the published parameters.

    Given Dayton's past history of datasheet errors, either situation above could be true. Cms and VAS is exactly the same on both datasheets which is very suspicious. Currently I have more trust in the 4 ohm specs.

    Steve_Leetajanes
    I'm not deaf, I'm just not listening.
  • thanks again! good day to order from PE 10% PREZDAY10

  • I’m still considering the PRs facing downward, as I don’t want the PR to ‘play’ directly into another room if placed on the rear (speakers will be located on either side of fireplace which is shared with a small room behind, i.e. pathways on both sides of fireplace).

    While low frequencies become ~omnidirectional, with a PR (or port) as the frequency nears fs the active driver movement excursion becomes less (and hence sound wave propagation) and the PR becomes the larger source of the sound. I plan on placing the speakers on short stands (10 to 12 inches) tipped up a few degrees (aimed at the seating / listening location) so this may add a bit of bass coupling directed towards the listening area (which can be eq’ed to extent necessary).

    I’ll be taking a look at the surrounds relative to what added weight may be required (modeled at this point from zero, to maybe +50gs) and note that at an amp wattage that would max out the woofer the PR is not even close to its max excursion (so downward facing wouldn’t appear to limit any needed excursion). Or said another way, I see gravity at best adjusting the resting place of the PR, with no net limit on its (for my application) modeled excursion, and I don’t expect gravity over time to have any or at least anywhere near the impact on the surrounds as through its beating it will take with playing loud…

    So, sorry for the longish set-up, I’ll get around to my questions.

    IF I don’t place the PR downward and I don’t want direct firing rearward, what about, as with the attached rough drawings (sorry for the poor quality), vented to the sides? With the wavelengths that the PR will be handling I see little to no issue with horn/port affects?

    In the end, I may just have to remake some additional sawdust. Thoughts?

  • The horror

    UPS just delivered my RSS265PR-10s, and they have been packed, shipped, and apparently stored horizontally- ‘ope there goes gravity…’

    Comp to early versions, these cast aluminum PRs have quite firm surrounds- thinking under fire they will see (and need to handle) multiples of 1G. ‘Course their robustness wouldn’t hold a candle to Bill Dudleston’s (Legacy Audio) PR downward facing beasts in his subs, but sag from G1 horizontal positioning has got to be one of their least concerns.

    So, maybe PRs, and our active drivers sitting in boxes on our shelves, need to be rotated (like bottles of wine) from time-to-time… it’s 4:00 somewhere…

  • @tajanes said:

    IF I don’t place the PR downward and I don’t want direct firing rearward, what about, as with the attached rough drawings (sorry for the poor quality), vented to the sides?

    That looks like a wonky bandpass enclosure, I would avoid this unless you plan for that "vent chamber" to be very large.

    tajanes
    I'm not deaf, I'm just not listening.
  • I think that you can slot load the passive radiator,on the rear, it would be the same as facing it down with a slot formed at the floor. You don't need the deflection dome from you drawing though.

    6thplanet
  • I still don't think it matters where you put it.

    Steve_Lee
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