OB SUB build - another one

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  • Jr. Member
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OB SUB build - another one
« on: 27 Nov 2022, 11:03 pm »
Hi Guys,

Thought I'd post my build of two dual OB subs in H frame forward configuration - single ended RCA.  I thought I'd also add some additional information to reflect the information I was looking for prior to and during my build.

I ordered the double trouble kit and flat pack from Danny although there had been some notes about the amplifier plates possibly not being suitable for 220V AC (I'm in Australia) due to mains 'hum'/interference.  I had resolved to use 220VAC to 110VAC step down transformers with US plug outlets to get around this issue.

The kits duly turned up - very fast from UPS - with the usual import tax saddled on top ($900 AUD if anyone is interested).  These where incredibly well packed although showing some signs of 'careful' handling along the way.  The flat packs were incredibly well packed and protected with lots of custom-cut foam to protect the MDF parts.

One item I had wanted to know more about was the plate amp box - so here's a photo:

Yes - it has a base
No - it doesn't have a hole for a cable entry

So, I'd read on the forums that the length of cable on the plate amp should not be extended.  I seem to recall Hobbs saying somewhere that he would usually just cut off of the supplied spade connectors on the plate amp wires and terminate into whatever connector you wanted to use.  In my case, I had ordered the Neutrik plugs with the kit.

I've seen photos on the forums of the female end being mounted on the plate amp box and also with it mounted on the subs themselves.  I decided to mount the female end on the subs and attached the male end to the plate amp wires. 

Of course, this presents the problem of how to securely pass the wires through the side of the plate amp box, provide strain relief and make things look 'pretty'.

I separated the plate amp wires into BIG (driver) and SMALL (servo), twisted them around each other then twisted the two bundles together.  I then sleeved the cables in 20mm black heat shrink.  I then' over sleeved' them in braided mesh and fitted another short sleeve of heat shrink over the 'ragged' braided mesh.

Once I had the cable bundle size, I got hold of some black PVC cable glands which would provide a snug fit on the bundle (20mm in my case), drilled some holes of the right diameter in the plate amp box and put everything together.

Great .... except the wall thickness of the box is too thick for the interior thread width of the PVC gland.  I ended up gluing these in place with polyurethane glue, but I'd be interested in knowing what everyone else has done.  I don't seem to be able to readily get hold of thick wall PVC glands here in Australia - certainly, Bunnings don't carry them as stock.

Here's a photo of what I ended up with.  I think it looks great and provides a strong, secure grip on the cable to the sub.

I Duratex'd the boxes.

Dry fit of a sub frame - these are HEAVY and joints are TIGHT:

Parts laid out and rough sanded.  I had already glued up the 'sandwich' double thickness sections:

OK - so I undercoated the MDF parts (masking off the dado) but forgot to mask off the corresponding sections that fit into the dado - BIG mistake - as the paint meant the parts wouldn't go together without some judicious further sanding.  I had planned to veneer and undercoat all the relevant parts before assembly - whilst veneering made sense, I personally wouldn't waste time again on painting the remaining MDF until it was assembled and glued up. 

My skills are not up to that task without a lot of double handling / duplication of work.  Next time, I'll veneer and finish, then assemble, mask off and paint.

MDF parts and corresponding veneer coated with Titebond II and drying ready for the hot iron (Titebond II is available from most SydneyTools outlets here in Australia and it seems to work well for this job).

I used a Jarrah wood paper-backed veneer from Briggs Veneers here in Australia https://www.briggs.com.au/product-ranges/sustainable-natural-real-wood-veneers

Dusty fun.....

Veneer grain filled and drying (I used Earl's / Timbermate grain filler in a matching colour to the veneer - it's an Australian product and gives great results), waiting sanding:

Glue up:

Finished frames waiting woofers and a polish:

With woofers fitted:

Wiring was straightforward - just reference https://www.audiocircle.com/index.php?topic=149708.0

Now for integrating them into my existing system.... I thought this would be straightforward .....

I have a LR pair of X-Statik and centre X-Voce with a separate LFE sub, 4 overhead speakers and two full size Q-Acoustic rears.  I have a DENON X-4700H amp feeding this lot, with the X-Statiks fed from an AUDIOLAB 6000A (in PRE_POWER MODE) on pre-amp outputs from the DENON.

When in HT 'mode' I intended to use the pre-amp outputs which also feed the AUDIOLAB 6000A to connect to the LINE IN on the Rythmik plate amp.  After messing around with REW, I realised this wouldn't work as I was effectively bypassing the PEQ setting on the plate amp.  I NEED to feed the X-Statiks from the Rythmik plate amp in order to use the PEQ capabilities of the plate amp.  This may be self-evident now, but at the time it took some head-scratching.

I ended up routing the speaker outputs of the AUDIOLAB 6000A to the HIGH LEVEL input on the plate amp (frustrating, as I wanted to use the neater LINE IN connection) then looping out of the plate amp to the speakers:

The speaker wiring is double stacked in this image and PEQ seems to be working.

And final set-up in my music / HT room:

X-Statik are 5 feet off the back wall and OB subs are 4 feet off the back wall.

So, after 24 hours of running, I have the following curves out of REW:



It looks like I have a peak at 80-100Hz in the room - this appears with both the X-Statik on their own AND with the OB subs in play.   There is NO treatment in the room, apart from sofa and rug.

The double roller blinds (privacy and black-out, respectively) across three large, floor to near ceiling picture windows (single-glazed in Australia  :o) seem to provide a measure of room control which has surprised me.

My plan is to give the subs a good 150+ hours of run in before remeasuring and then consider room treatment, although my ears don't notice any particular peaks or dips.  I have already noticed an improvement in the REW curve below around 30Hz, as the woofers break in.

Overall impressions - these things make a big difference.  Before any sort of tweaking the OB subs were very harsh and 'boomy' - they shift a LOT of air.  Lots of complaints from the family.  After integration and tweaking they have 'disappeared' - a smooth blend into the overall sound in the room with better bass extension.  I'm in love with the OB sound - imaging and sound stage is phenomenal.

We've now watched three movies back to back in HT 'mode' - the start of 'Edge of Tomorrow' being a great bass workout and listened to around 10 hours of stereo music with the DENON OFF and AUDIOLABS 6000A in integrated mode, streaming music via ROON / Qobuz on my streamer.  (I use a Zidoo Neo S, if that is of interest).

I'm SO tempted by a pair of NX-Otica now ..... grrr.


Early B.

Re: OB SUB build - another one
« Reply #1 on: 28 Nov 2022, 01:07 am »

And yeah, dude -- you definitely need to build a matching pair of NX-Oticas. :) 

Oh, one more thing -- it will take you months or years to get those subs dialed in precisely, so you haven't heard how good they are yet.


  • Jr. Member
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Re: OB SUB build - another one
« Reply #2 on: 28 Nov 2022, 02:12 am »
Thanks Early B.

hmm... NX Otica as next years 'summer' project possibly.... :)

Danny Richie

Re: OB SUB build - another one
« Reply #3 on: 28 Nov 2022, 02:28 pm »

After you get the room treated I will help you dial in those subs. It will be easy to achieve a flat response.

Think about some type of thick or large diameter corner traps. Then cover that wall with a combination of diffusers and absorbers. 

Vince in TX

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Re: OB SUB build - another one
« Reply #4 on: 28 Nov 2022, 06:42 pm »
Very nice!   That setup looks a bit familiar.    :green:

You can see some big corner bass traps in my setup similar to what Danny was mentioning.   They're 6" deep.   I never measured the response, though.   That's still on the "to do" list.   I already have the calibrated mic.   I just haven't gotten the time to mess with it.   I'm too busy enjoying the sound.    :thumb:

Oh, and I may also make the leap to the NX-Oticas at some point, although these X-Statics are doing exceptionally well.


  • Jr. Member
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Re: OB SUB build - another one
« Reply #5 on: 28 Nov 2022, 08:20 pm »
Thanks Guys,

@Vince - your set up continues to be my inspiration - with the caveat that my listening room is also a sitting room - although, I do have A LOT of control on internal finishes, as long as I don't compromise on the nature light - wife happiness factor is very important.

@Danny - thank you so much for the offer.  Once the OB subs have settled in, I'll remeasure and reach out for recommendations - I can see a need for controlling bass in the 80-100Hz zone (bass absorption, I assume) and smoothing the mids (diffusion, I assume).

I'm torn between building something or buying something like this :  https://soundacoustics.com.au/product/bass-traps/lf70-corner-bass-trap-bear-series/ as they appear to have some credibility behind them.

The usual products promoted in the forums here for acoustic control tend to be $$$$ in Australia as a result of the volume required during overseas shipping.

Anyway, onward with getting these speakers settled - I figure at least another 120 hours to go, although they sounds fantastic already.



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  • Audio - It's all a big fake.
Re: OB SUB build - another one
« Reply #6 on: 28 Nov 2022, 08:30 pm »


  • Jr. Member
  • Posts: 75
Re: OB SUB build - another one
« Reply #7 on: 28 Nov 2022, 10:15 pm »
Thanks Tyson - looks like they have a local distributor as well.  I think I'll 'pop in' for a chat.   :D