Monolith DF Base Panel - Home Theater Forum and Systems -

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post #1 of 6 Old 05-16-06, 06:49 PM Thread Starter
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Monolith DF Base Panel

I posted this on a UK forum. I thought it might be useful for the Monolith owners I've noticed on here and anybody else with a down firing sub with, shall we say, an active floor covering.

I have a laminate wood floor which is foam backed on a suspended concrete floor. Coupled with the relatively hard surface of the rest of the room, leather sofas etc, I thought I'd try and tackle the floor interaction by deflecting some of the acoustic and mechanical output from the Monolith, thereby taming some of the in-room peaks that I suffer.

I have no shame in suggesting that I got the idea from the base panel of the SVS box subs. I don't see why it should'nt work for any down firing sub although, obviously, the panel dimensions would have to be adjusted to suit your sub. All references are to UK suppliers and measurements which are metric, as they should be in this day and age

It should also be noted that I have a BFD which I am prevented from taking possession of until my birthday on June 2nd. I was bored and reckoned that anything that could help wouldn't hurt things once the BFD is up and running.

For this I bought a 450x420x19mm panel of MDF. Hombase supplied this cut to size. They were accurate in the size if not in actually charging me for the wood. The fact that it was amongst about 15 matchpots of paint my wife had chosen may have helped.

Jpeg 1. Turn the DF upside down and align the panel acurately on the upturned spikes. Once you're happy, press down hard. You now have perfectly aligned pilot holes for the drilling that follows. Look carefully and you can just see them.

Jpeg 2. You will need some M8x25mm bolts and some 25mm washers. Now I look at my receipt again, I can't see these on there either - This keeps getting cheaper! All in they were supposed to be about a couple of quid.

Jpeg 3. Using the 25mm wood drill and the pilot holes, drill a hole deep enough to recess the head of the bolt and the 25mm washer. I used the 25mm washer to prevent the bolt crushing the MDF when everything is tightened up when bolting to the DF. The washers in the bolt pack are inadequate. Turning the bolt and washer upside down, as shown, allows you to judge when this is about right. Once happy, drill the center of the hole with an 8mm wood bit. The DF spike holes are 8mm hence the requirement for 8mm bolts.Sand the edges and corners of panel to suit. I did my best to approximate to the radius of the Monoliths edges and upon refection, I could've done a bit more, but I'm no pro.

Jpeg 4. Spray the panel with ordinary grey primer for cars (Mine came from Halfords). MDF absorbs quite a lot of paint and I sprayed 3 coats with light sand papering (240 grade) after each to achieve a smooth finish. The edges in particular need quite a lot of attention to get smooth, as the paint tends to exagerate the particle nature of the board. I sprayed the 2 top coats in Halfords Citroen Arctic Silver - it was the best match to my Atacama stands, from memory. I sanded lightly after the first coat again. It's worth noting that you will never see the bottom of the panel, nor the middle of the top, so pay your attention to the edges. This image is of the primed panel.

Jpeg 5. This image looks like poop. The camera flash is really unforgiving, but I may well apply another can of the silver to get a perfect finish. From my listening position it looks to be a decent match to my Atacama stands and it looks shiny. You can see the panel bolted in place and one of the Focul Polidods which I placed directly over the bolt hole. They are exactly the same diametre as the DF feet which is a happy coincidence and serve to decouple any mechanical energy from the floor. I used a touch of carpet tile spray to hold them in place, but anything from Prit Stik upwards will work. Placing my hand on the floor next to the sub whilst playing shows no vibration from the floor. Plenty of air is moving over the back of my hand however. I used 4 of the large Polipods, one at each corner, plus one small spare Polipod in the center of the panel. The four big ones compress enough under the weight of the DF that the small one also touches the floor. It's a bit 'belt and braces' but by their nature the 'Pods', whilst isolating the DF from the floor, also absorb any resonance within the panel. So no harm there then.

Jpeg 6. DF, right side up fixed to panel. Overall height is about the same as with the spikes fitted. The same arrangement will work with spikes fitted if you are on a carpeted floor, but you would need to source spikes with a longer thread as they first have to pass through about 10mm of MDF plus the 25mm washer before reaching the thread in the feet.

End result, visually you decide. Paint it any colour you like to match your decor, or not at all if you can't be arsed! Aurally, in my room at least, there is a definite tightening of the bass. I assume this is due to the supression of the floors contribution. The once slightly overpowering upper sub bass is now tamed and as a result, I have turned the DF up slightly. This has allowed the lower frequencies to step up a notch, which has increased the perceived depth of the bass response.

All of this was already there, I haven't added anything to the audio chain, but a bit of subtraction has added to the overall effect in a very positive way. God knows what difference the BFD is going to make with active equalisation, if this is the difference £20 of wood, bolts and a little time can make.

Give it a wizz. If it makes no difference, so what? It's the price of a very average interconnect that can make things sound worse.

Edit: For some reason (I'm an idiot?) Jpeg1 is the last image and Jpeg2 is the first.
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Last edited by russ.will; 05-16-06 at 06:56 PM.
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post #2 of 6 Old 05-17-06, 11:25 AM
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Re: Monolith DF Base Panel

So how did you like the end result? Did it achieve what you were looking for?

BTW, nice work. I like the contrasting color scheme you have going.

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post #3 of 6 Old 05-17-06, 03:56 PM Thread Starter
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Re: Monolith DF Base Panel


The base panel has helped with integration into the room. The floor covering is laminate wood which is on a foam underlay. I suspected that it was contributing at certain frequencies due to the amount of vibration I could feel in it. I decided this couldn't help with reproducing clean transients and may be just one factor in a rather peaky in room response I have.

I wanted to isolate the floor from the acoustic and mechanical output from the sub, hence the panel, isolated and damped in turn by the supporting sorbothane feet. I didn't know if it would work, but I was at a loose end with nothing to lose.

I don't think this has improved the sub. It's just prevented the floor from masking it's qualities with added upper bass intereference and slight smearing of transients and detail. It has helped smooth frequency response a touch and the texture of deep bass certainly seems more defined. Not in an earth shattering kind of way, but a small step in the right direction.

The next BIG upgrade, after the BFD that is, will be a carpet. The Sorbothane will be replaced by spikes as I will then, finally, be able to get to the concrete floor.

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post #4 of 6 Old 05-17-06, 04:05 PM
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Re: Monolith DF Base Panel

Am I confused? So generally the sub comes with those extended black feet and still fires down... you just added the base, right? Looks like you did a nice job of it.

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post #5 of 6 Old 05-17-06, 04:31 PM Thread Starter
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Re: Monolith DF Base Panel

Yup, exactly right.

Have a look here for the griff on BK. They sell direct only, so their reputation and customer base is entirely built up on forum feedback. That and the fact that they OEM subs for a number of well known brands including MJ Acoustics, Rel and Ruark.

Bare in mind that UK rooms tend to be smaller, so the PB10 sized Monolith is the biggest in the range. Also note that the PB10 retails for 400 in the UK which at approx $1.90 to the pound makes the PB10 a $760 sub.

The standard solid steel feet are threaded to accept either 8mm spikes or hard rubber inserts for wood floors. Until now, I had been using the spikes with spike cups.

All I have made is the panel, painted it and stuck the Polipods to it and bolted it up.

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post #6 of 6 Old 12-16-08, 07:05 PM
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Thumbs up Re: Monolith DF Base Panel

Old post i no russ, is this only worth doing if you have a laminate flooring and concrete floor? as i have a wood suspended floor and carpet.

nice job by the way could not do it better my self the base panel makes the sub look better, only thing i would of matched it to the sub color.
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