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The Dude

Incorporating second sub with Minidsp

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Hello, getting ready (hopefully within the next 2 weeks) to integrate a second sub into my HT. Previously, I ran a Minidsp with a single sub and an amp in a 2 channelsystem. Doing this with 2 channel yielded great results. Since then I have changed up to an AVR Inegra DTC 40.2 and Crown XLS2505, the sub is a diy TH spud (secondone will be as well). I figured that between the AVR and XLS, I could dial in the sub decently. After reading here and there, I am starting to believe I could do better by incorporating the Minidsp back into the system. Is there a a video that helps explainhow to? Is it absolutely necessary to upgrade to the newer Minidsp HD? Currently i am running the single sub out directly to Crown amp, crown amp is set up to simulate a single input to be split into two outputs ( I may be bridging at this time, but would have to confirm). Is this how I should run it with minidsp or should I run it both sub outs from the avr to individual inputs of the minidsp with individual outs to each channel of the amp? Also how should I set the sensitivity on the crown amp? Thanks

 

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The AVR is a DTR 40.2, after reading the manual, it states that both 2 sub outputs are the same signal, that being said, it doesn't sound like using both are of any benefit to me and only one is needed. 

 

Reading this now.

 

https://www.dropbox.com/s/w7jmpozner6muzw/MiniDSP 2x4 Set-Up Guide Latest Version.pdf

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If you can setup the miniDSP 2x4 (as I assume that you've got on hand) with your A/V preamp/processor (AVP) and subwoofer amplifier without significant subwoofer hiss or saturation distortion, it should work well.  The issue with the 2x4 (non-"HD") is lack of gain and higher noise floor.  I'd set the crossover frequency of the subs as low as you can to eliminate the hiss and to limit the modulation and harmonic distortion of the subwoofer(s). 

 

Here is a video I just found that will likely help you out using REW measurements, and the video is focused on aligning and equalizing multiple subs.  I haven't watched it all, but it seems to have the right topics in it:

 

 

Chris

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My experience with the TH subs (one behind each Jub) is via use of two dedicated Crown XTi-1000s in bridged mode--one amplifier per TH sub.  Note that this will give you too much power (about 1200 w), so you'll need to ensure that you've got the subs sealed up really well to avoid air leaks, and you'll also need to ensure that you're not over-driving your woofers in the TH subs--which can easily unload the cones (as I unfortunately experienced many years ago, and had to replace all four woofers eventually). 

 

The XTi-1000 amplifier has a DSP front end built into the amplifier, so all I had to do was use REW to equalize subwoofer output.  The DSP crossover built-in can also limit the highest voltage drive level that you allow to go the the subs.  I recommend reading up on that feature and using that capability to avoid woofer failures.

 

The AVP that you own will help you with bass management, but I've found that I leave the subs on all the time, crossing at 40 Hz to the Jubs.  I also use the extended LF response of the K-402-MEH in the center front location to extend and fill in the "anti-node" room modes in the room, and this works very effectively to smooth out the subwoofer response at the listening positions.  There is still too much LF response at the walls of the room due to the nature of LF response in-room, but note that this setup is a good compromise for the LP response.

 

Chris

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Chris, I actually watched that video this morning, it was a long video, but explained alot (actually got me thinking that some of these methods can help with the rest of the system). The 2 biggest issue they mention about the standard Minidsp are the delay and amount of PEQ capabilities. I have heard of the issues you mentioned, but never experienced them. If there seems to be a hiss issue, I would consider upgrading to the HD version.

They talk about setting delays based off of the differences from the 2 distances of the 2 subs to the mlp. Mine should be roughly the same, so in theory, I shouldn't need much delay. But I assume this may not always be true. I was hoping that the Crown XLS2505 I have should be enough to power the subs. But always wondered if some more head room wouldn't hurt.

Hopefully I finish the second sub within the next couple weeks, so I am excited to try this all out.





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Yes, at subwoofer frequencies the required delays are pretty large (i.e., a half wave of delay at 40 Hz is 25 ms which also corresponds to 14 feet of physical offset).  So if you're within 10-12 ms of being in perfect time alignment at that frequency, that's close enough.

 

Chris

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Chris, correct me if I am wrong, but if I recall your th spuds are firing in the corner upward. I noticed@rigma is firing his dts-10s into the room (assuming room design is a factor). But why would he not flip them? Is there a trial and error to see what yields best response?

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I use the backs of the Jubilees to form a triangular mouth extension from the SPUDs to the top of the Jub bass bins. 

 

The SPUDS are located with their mouths in the room corners closest to the floor, facing toward the back wall of the room.  The each Jub is placed in front of each SPUD, with each Jub bass bin back forming a duct  that is oriented toward the ceiling, with the horn extension being formed by the side wall, the front face of each SPUD, and the back of the Jub bass bin.  This increases the effective length of the SPUD horns from ~21 feet to about ~24 feet.  I get a -3 dB point low frequency response of about 14 Hz, including the flexibility of the side walls/plywood stiffeners and losses due to the undersized horn mouths. 

 

Below ~80 Hz, there really isn't any directionality of the low frequency response, so the orientation of horn mouths doesn't make any difference if crossing to the subs below that frequency.  The only thing that you'll hear if looking at the horn mouth exit is harmonic distortion at higher frequencies.  Pointing the SPUDs mouths away from the listening position is actually one way to attenuate those harmonics--which is the predominant distortion type with the SPUDs. 

 

Chris

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On 9/28/2020 at 4:24 AM, Chris A said:

I use the backs of the Jubilees to form a triangular mouth extension from the SPUDs to the top of the Jub bass bins. 

 

The SPUDS are located with their mouths in the room corners closest to the floor, facing toward the back wall of the room.  The each Jub is placed in front of each SPUD, with each Jub bass bin back forming a duct  that is oriented toward the ceiling, with the horn extension being formed by the side wall, the front face of each SPUD, and the back of the Jub bass bin.  This increases the effective length of the SPUD horns from ~21 feet to about ~24 feet.  I get a -3 dB point low frequency response of about 14 Hz, including the flexibility of the side walls/plywood stiffeners and losses due to the undersized horn mouths. 

 

Below ~80 Hz, there really isn't any directionality of the low frequency response, so the orientation of horn mouths doesn't make any difference if crossing to the subs below that frequency.  The only thing that you'll hear if looking at the horn mouth exit is harmonic distortion at higher frequencies.  Pointing the SPUDs mouths away from the listening position is actually one way to attenuate those harmonics--which is the predominant distortion type with the SPUDs. 

 

Chris

Interesting use of the Jube backs to extend the SPUD horn.  This thread and especially that video got me off my butt and integrating the 2 DTS 10s I acquired earlier this year.  Because of my room dimensions the left one works best to the outside of the Jube as a corner extension but the right one may be able to have its mouth in the corner and use your extension trick.  It's been fun breaking out REW and the UMIK-1 again this past week and measuring/seeing  how these 2 monsters behave in my room.

Two DTS-10s integrated with Jubes - Left.jpg

Two DTS-10s integrated with Jubes - Right2.jpg

Two DTS-10s integrated with Jubes - Right.jpg

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Being the same model and about the same distance from my PLP they sum nicely with no intervention but the design has that well known 56Hz peak/resonance.

both DTS10s summed PLP.JPG

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I've got a MiniDSP 2x4HD on order to use with them instead of the Xilica soon.  It will allow a high pass lower to keep most of the 15-20Hz subsonic goodness that is a primary strength of this horn. Not that I'll feel that very much but for movie LFE I do like to demo the opening of BladeRunner 2049 and Edge of Tomorrow which pressurize and shake the house nicely!  Current amps driving the DTS-10s?  Hypex NC400 monos (from kits) which may be underpowering them a bit at about 400w/4 ohms.

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