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Just another subwoofer

edited March 13 in DIY

It's a Dayton RSS390HO-4. It'll be powered by an SVS Sledge STA-1000D with integrated DSP. The subwoofer came new, but second hand at a decent deal. The plate amp also nearly new, got at a deal because the knob to control the DSP, including the volume is broken. It's a rotary encoder with pushbutton, replacement part costs all of $3.50, should arrive next week.

I'm tired of MDF so this one is built from plywood. Not fancy baltic birch stuff though, just one side good pine and fir plywood. I had a quarter panel of pine to use up so the rear panel and port were cut from it, and the rest is fir plywood so all the faces you will see will be the same stuff. Nothing real fancy for this build, just quick and easy and make a lot of bass.

Haven't decided yet if the cabinet will be stained dark espresso or just painted black. You may notice the dado around the top. The top will be my leftover acacia counter top board that I used for this build , will be installed with a gasket and table top clamps:
https://www.leevalley.com/en-ca/shop/hardware/table-hardware/connectors-and-fasteners/40146-tabletop-mounting-clamps?item=13K0101

The big 15" driver needs a hefty countersink to flush mount, so I stuck some blocks on the back side of the baffle to give the screws some meat to hold on to.

Probably a few more braces to be added, as well as round-over of the port and fill any exposed voids, then sand and finish. More to come...



I'm not deaf, I'm just not listening.
kenrhodesSilver1omotajanesrjj45squamishdroc4thtryjoeybutts
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Comments

  • That's looking good. It should pound out some kick drum without breaking a sweat!

  • edited March 13

    Thanks Tom.

    It's being tuned to 30Hz and apparently should take a full 800W without running out of Xmax.

    rjj454thtry
    I'm not deaf, I'm just not listening.
  • Nice job!

    I have to get over my abhorrence/anility of dust slinging router and get back in the shop to catch-up on languishing projects.

  • Yup, that's a big ol bass maker!
    That Acacia is some frickin hard stuff.

  • edited March 13

    Pretty nice day today. Cleaned up the ports, but a bevel on the lid and sanded the crap out of everything. Screwed everything down for a test fit - everything fits :)

    With a dark stain in mind, I really should have cut the front baffle with the grain running vertically.. too late for that now.

    I made the port a fair bit shorter than the simulation specified, due to the fact that the port is the entire width of the cabinet and right at floor level so there is a fair bit of reinforcement at both ends that effectively extends the length.

    Comparing simulation vs reality, I am tuned 1Hz too high, but I think I'm going to call it "close enough". Dashed yellow is real measurement.


    4thtryjoeybutts6thplanetrjj45
    I'm not deaf, I'm just not listening.
  • edited March 13

    @6thplanet said:
    Yup, that's a big ol bass maker!
    That Acacia is some frickin hard stuff.

    It is pretty tough stuff, in line with teak or oak I think for hardness. It's surprisingly light weight given it's hardness. I really like that it cuts cleanly, very easy to work with without worry of chip-out like soft wood.

    The acacia top is really just to make the subwoofer a bit more of a functional table rather than just an ominous black box in the corner of the room, and also to use up a leftover piece of wood that I didn't have a better plan for.

    6thplanetrjj45
    I'm not deaf, I'm just not listening.
  • Real world acoustic measurement of driver + port. The port measurement is a bit dirty since the port is on the front, and I didn't do anything to try and shield it from the driver output.

    Solid bass to 30Hz was the goal, I think it will deliver.

    rjj45
    I'm not deaf, I'm just not listening.
  • edited March 13

    Btw...wow do these drivers ever ring. Full range signal sounds like it's from a tin can, output at 2kHz is much more than the bass down low. I'll be sure to put that DSP amp to good use and make sure the resonance is completely squashed.

    4thtry
    I'm not deaf, I'm just not listening.
  • So that's the aluminum cone singing at 2k. Incredible!

  • Mostly the dust cap based on my fingernail tap test.

    I'm not deaf, I'm just not listening.
  • edited March 16

    Stained plywood.. It's the okayest, g/f seems to think it's nice enough so that's good enough for me. I hit it with some steel wool to bring some character out, otherwise it was going to look pretty boring brown. I might give it a little more in a couple spots, otherwise it'll get a top coat in a few days .

    Unfortunately the SVS plate amp PEQ functions won't be able to address the breakup of this driver. The frequency bands available are only through the bass frequencies to address room modes. My Outlaw 976 however does have full featured EQ at any frequency for the subwoofer so it will be able to handle the task, though with a low pass filter at 100Hz or so it may not be of any concern anyway.

    I'm not deaf, I'm just not listening.
  • edited March 16

    I see they stopped making the 976, nice little preamp. I fortunately picked one up just beforehand, to have an option for a bit of surround backfill (vs a ~Hafler circuit) and I run as a 2+2, no center. I'm still looking for an opportunity to hide my velodyne, somewhere. I like your end table sub- nice. For music the surrounds' level is dropped down from movie settings. As with subwoofers (for music more so than movies) imo if you can notice them its too much...

  • edited March 16

    976 is a decent unit, not many options out there for processors that don’t cost $2000+ and include balanced outputs. I believe due to part shortages Outlaw decided to drop the product altogether rather than string people along for months on end waiting for something that may never arrive.

    I also don't use a centre channel - not yet anyway. My furniture arrangement doesn't make it practical without placing the centre in a poor height or the TV at a poor height so it requires a significant furniture change to make it a good idea.

    I'm not deaf, I'm just not listening.
  • The MX100 McIntosh would be great, but at $5g+, I'll wait for the replay....

  • I wasn't thinking ahead enough, or I would have built it (the sub) into the crawl space to exit on the front sides of my fireplace hearth

  • edited March 16

    Just playing around with the measured near-field response. 2nd order low pass at 100Hz, comparison of just the low pass vs adding a notch filter at 1.9kHz. Certainly won't hurt, I'll do a listening test and see if I can still hear the "tin can" sound with a filter in place.

    I'm not deaf, I'm just not listening.
  • edited March 16

    At that low level, maybe not. But I'd have to think having the notch filter in place, attenuating the breakup of the driver, is the way to go.

    Q: How does the notch filter affect phase- or does it not matter this far away from the sub freq range you will be using?

  • With the high Q filter in place the response is not being affected until nearly 1kHz. Phase is a function of frequency response so the same comment applies to phase.

    tajanes4thtry
    I'm not deaf, I'm just not listening.
  • Got it fully assembled today. Still have a coat or two of tung oil to put on the top. The acacia top doesn't match the rest of the speaker as much as I'd like but it'll do.

    Listening to the sub play by itself, with 100Hz 12dB crossover, the addition of a notch at 1.9kHz is audible, but not by much, I'm sure I wouldn't notice the difference with other speakers playing along. With the crossover at 80Hz is very hard to tell the difference between using the notch filter or not.

    4thtry
    I'm not deaf, I'm just not listening.
  • So a little venting on the feature of the 976 processor or lack thereof. I'm sure a lot of AVRs operate in a similar way, I do recall a Emotiva UMC-200 which did have a lot more control of sub filters and the blend of sub to main speakers.

    In my testing I've determined that the 976 will only include the subwoofer output for audio that doesn't have a dedicated sub channel (such as normal 2 channel stereo) if you set the front left/right speaker to "small". What this means is that you must use a high pass with the main speakers to include the sub, and there is only a single crossover frequency. If you set the front speaker high pass filter to 80Hz, it sets a low pass for the subwoofer at 80Hz as well, and it is a non-adjustable 24dB slope. This is unfortunate, as often adjustment of crossover and slope independently gives a lot better control over the speaker integration. It also means that you should be disabling the crossover on the sub amp to avoid compounding the filters, since the processor will not send unfiltered audio to the sub output.

    The 976 doesn't include any "auto-EQ" which was a selling feature for me as it does include fully manually adjustable parametric EQ instead. The mic included with the unit sets the level and distance only, and for this purpose it does a fairly good job as well...with the exception of the subwoofer.

    For the sub, it decided to set the level a bit strong. Some people might enjoy this for theatre rumbles, and to know they have a sub with everything they listen to. For music, the elevated bass is a bit unnatural.

    This response is taken after auto-level and distance, front left and right speaker with subwoofer, measured at listening location with some smoothing. Nearly 20dB of bass boost... boom boom!

    I'm not deaf, I'm just not listening.
  • I wonder what your cone treatment would do on that dustcap?

  • edited March 19

    Mod podge? That stuff is basically just white/clear pva glue, good treatment for paper, on aluminum cone I think it with both look terrible and also not stick well and end up peeling off.

    Some liquid electrical tape or flex seal stuff would probably be a good treatment for aluminum. I won’t bother, for sub duty the ringing is mostly a non-concern.

    I'm not deaf, I'm just not listening.
  • That acacia would've made a great baffle

  • Yeah, I had considered that. Idea was to make it a functional table, potentially an end table next to the couch so I went with the durable wood on top. If I had enough material I would have wrapped the table top around to the baffle.

    I'm not deaf, I'm just not listening.
  • re the 976, I haven’t yet used it with a sub - and I’ll have to look but the surrounds’ dB relative levels can be set, so surprising that the sub level cannot be set?
    Have you considered sending full front signal to your sub (via a Y) and using the sub’s controls to set Xover and level- and/or could get a miniDSP for the Xover settings (also levels and eq) btwn mains and the sub. Kinda an extra when the a/v processor should handle this.

  • edited March 20

    I didn’t say the level couldn’t be set, that would be ridiculous. I just mentioned the auto-level routine set it way high .

    Sub amp has full left / right input (balanced option too ;))and independent low pass and high pass output so if I really wanted I could bypass the 976 controls completely, run left right to the sub and use it’s crossover features to crossover the main left/right. Then I would have independent control of crossover frequency and choice of 12 or 24dB slope. Downside is that line signal has to run to the sub and back to run the front L/R speakers which could be a fair distance depending on placement.

    I'm not deaf, I'm just not listening.
  • edited March 20

    When using a small DSP sub controller such as this, how do you deal with the DSP signal processing delay relative to your main speakers. The mains would be playing in real time whereas the DSP would be delayed due to DSP signal processing. Is this an inaudible non-issue or is this something that needs to be addressed? I am currently under the impression that DSP is an all or nothing proposition. You need to time delay all drivers by the same amount to make it work properly. Would this be correct?

  • edited March 20

    How do you deal with the fact that the subwoofer is a different distance to listener than the main speakers? Suppose you’d need some delay to account for that.. for HT use, it’s very easy, just adjust the speaker distance accordingly, delay control is built into every AVR. Quick glance of the manual for this product it would appear the intended application is for use with an AVR. Use of a subwoofer without delay/phase control of the tops is just a “you get what you get” approach based on speaker placement. The delay that is inherent to speaker placement is going to be much more than the DSP is adding.

    But how much delay are we really talking about here for a DSP installation? At low frequency it actually takes some significant delay to have meaningful effect on phase interaction. Good news is that it can be easily determined with a simple loopback measurement. I have a miniDSP 2x4 on the shelf, stay tuned and I’ll take some measurements of its delay impact later today.

    rjj45
    I'm not deaf, I'm just not listening.
  • edited March 20

    The results are in..

    For comparison, I started with dual channel loopback on my equipment to show before/after effects. I am measuring at 96kHz, and here you can see a perfect impulse at sample 300, or 3.125ms in time.

    Next, I inserted the miniDSP 2x4 (original model, non-HD) in the loop. I set the DSP to default flat EQ across the board and bypassed the crossover. This will give the best case scenario on delay from input to output on the DSP.

    You can see the impulse is no longer perfect, because the miniDSP is frequency limited by it's 48kHz sampling rate. The peak of the impulse is now at sample 403, or 4.198ms. 4.198 - 3.125 = 1.073ms +/- 104us.

    So we can assume, the basic miniDSP provides about 1ms of injection delay to the signal path.

    This delay makes our subwoofer effectively 35cm further away from the listener than it actually is. That would be huge for a 2kHz crossover to a tweeter, but what does it mean for our subwoofer? Here I took my front left and right and subwoofer response in-room, no gating, at listening location, and smoothed to 1/3 oct.

    Left/right speakers have LR24 high pass filter at 100Hz
    subwoofer has LR24 low pass filter at 100Hz.

    It's a bit ugly, but the focus here is not the specific response itself, but the change in response that 1ms delay of the subwoofer provides when a miniDSP is inserted into the signal path.

    Purple dash - original response
    White solid - with 1ms added delay of subwoofer.

    I think most listeners won't be able to tell the difference .

    kenrhodesSteve_Lee4thtryrjj45tajanes
    I'm not deaf, I'm just not listening.
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