counter-balancing a speaker and enclosure box for soffit mounting / decoupling with minimal tooling low tech

[klem]

So I have some Neumann KH420s that to the best of my memory, are front face heavy vs back side when you remove the amps for a soffit mount. In order to simplify decoupling process, it seems best to counter balance the speaker in its box via additional dummy load rather than determine the different load ratings at a given location. This is not a cheap speaker, so I need to be very careful to ensure no tipping in this process.
Any suggestions on a methodology for adding counterbalancing weight?
I am thinking a small 2x4 block (or better yet curved/domed shaped supports of some sort) centered under speaker and box, observe tipping direction and add weight above box, then progressively reducing the size of the support underneath as I maintain a more equally distributed weight / not tippingcentered load? I don't have access to scales that can determine the weight footprint at any given area for an unbalanced box, though that would certainly be nice to have.
Thanks for any helpful suggestions to help me think this through...

 

[kags]

Are you mounting the speakers at an angle? If so, the are more likely to slide, rather than tip. In my experience soffit mounting is more an issue of vibration isolation than balancing mass. Can you elaborate your problem?

 

[RoadrunnerOZ]

If soffit mounted then they are likely to be angled which could bring COG in front of the leading edge of the box but only once you exceed past the balance point tip angle - however the major weight will be in the magnet(s) behind the front line of the speakers and so for a vertical face they will tend to tip rearwards. If you are angling them then you could make a cardboard triangle template that matches the face angle, with the speaker box on the floor tilt the speaker forward on the front edge to match the angle of mount and see if it wants to fall backwards or forwards. But is all this necessary?
I have soffit mounted many speakers - some heavy like the Urei 813’s - (they weigh 80Kg yours weigh 35Kg) for those I made a rubber isolated clamping frame from 4 x 2 Oregon that used threaded rods to tension the frame and clamp the frame against the rubber and then speaker - then angled runners were built back into the wall that the clamp frame and speaker slid up into the wall on - then with bolts from below through the runners into furniture tee nuts on the back of the clamp frame base timbers the clamping frame was locked into place.
There doesn’t seem to be much need to counterbalance the box - tilting pressures are not really a problem but vibrating out of the wall is!
The likelihood is the box is always going to want to tip backwards anyway unless the angle forward gets fairly extreme and I can’t see an easy way of adding weight to the front of a speaker box to stop it wanting to tip backwards. If your aim is to just stand a tilted box on an angled surface with it counterbalanced to not tip and no clamping, it will slide straight off your angled shelf - counterbalance or no, the tendency will be for the weight to slide down the incline, vibration acts like roller bearings. The required holding force to prevent sliding would be the same whether the box is counterbalanced or not - vibration from the box will make it slide easily - put a speaker box on a flat table, run 50Hz through it and the weight of the speaker wires is enough to slide it to the edge of the table if the volume of signal is sufficient.

 

[klem]

yikes, the assumptions made in absence of evidence to the contrary! i do appreciate the responses. i will post some pictures hopefully later today schedule permitting. in the meantime, to clarify:
i have no interest in mounting the speakers at an angle in the wall. the soffit wall, and front faces of speaker box, and speaker should all be 90 deg perpendicular to floor.
the goal is to even out the unequal weight of the speaker as best as possible without the use of multiple scales. once the weight is re-distributed, i can move onto selecting proper isolating materials/methods for the speaker box.

 

[DFischer]

What kind of decoupling are you planing on using? If you are using discs with different load ratings, you can use higher rated discs under the heavier edge and lower rated discs under the lighter edge, proportional to the load imbalance. I'd suggest putting the monitors on a thin dowel or pipe on top of a large flat surface and rolling it to find the location of a balanced fulcrum. For example, If the center of mass is 2/3rds of the way from the rear edge, then use discs rated for 0.5*0.67*M and rear discs rated at 0.5*0.33*M, where M is the mass of the monitor. If you'd rather balance the speaker mass for a decoupling platform designed for an evenly distributed load, you could place the pipe/dowel fulcrum in the center of the speaker and add counterweights until it balances.

 

[RoadrunnerOZ]

Are the speakers going to be clamped or stand free? As far as a counterweight goes if you’re afraid of the speaker tipping forward you could always use a mic stand weight - these are vinyl bags filled with barium lead (not real lead Pb) - they are very heavy or you could go to a boat keel maker and get some pigs of the metal they use for racing yacht keels. Even though the amp has been removed the weight is all behind the speaker face as there is nothing protruding past the face. The cabinet is front heavy once the amp is removed so you can just weigh the amp assembly on some bathroom scales and insert the equivalent weight inside the box making sure it’s fastened down. Do they provide a blanking plate for amp removed soffit mount as you could bolt a weight to that - the REK-4 remote electronics mounting kit will have one if you’re planning on using that - this comes with the appropriate connectors to connect the speakers to the remote box and they also sell the necessary cable pack available in different lengths to go with this kit.

 

[RoadrunnerOZ]

i have no interest in mounting the speakers at an angle in the wall. the soffit wall, and front faces of speaker box, and speaker should all be 90 deg perpendicular to floor.
the goal is to even out the unequal weight of the speaker as best as possible without the use of multiple scales. once the weight is re-distributed, i can move onto selecting proper isolating materials/methods for the speaker box.

As long as you make sure that the tweeter is pointing directly to the listener’s ears and not shooting over the head (page 10 of the user manual) - this means a fairly low installation height (ear height for the tweeter) which for vertical box orientation will then block the mid range if there is a desk/console/table at the engineers front unless the speakers are mounted on their sides.
These speakers have been designed with the removal and remoting of the electronics in mind. There is no mention in the installation manual of compensating for the amp weight removal, nor are there any weighted plates for replacement so I guess it’s DIY.
If you are trying to achieve F50/R50 weight distribution you’d need a pretty heavy weight at the rear to compensate for the speaker weight at the front. Setting the box on a thin dowel roller, dead centre F/R perpendicular to the sides would be the best way to show/measure balance - you can tape this in position on the bottom of the box with some gaffer or packaging tape, set hook bolts into any available mounting holes on the back of the speaker and hang your weight from there.
Or for another simpler method you could use two flat bathroom scales and add weight to the rear of the box until both scales match - to get pinpoint weight reading on each scale you could tape two dowels to the base of the box, one to the front edge, one to the rear, mounted right at the very edges of the box using tape then setting the box down with each dowel on its own scale with the readout display outside the box edges - this would make a stable bed for measurements - you don’t need four scales to do this and you can buy cheap bathroom scales at places like KMart - I got some digital scales for $19 from Aldi.
There are available speaker isolation disc pucks, rubber bumpers, point contact cones etc. which are designed for any speaker - no commercially made speaker will have a uniform 50/50 front/rear weight distribution yet they use the same isolator for front and rear corners and I think maybe your concern about balancing the box could be largely unwarranted. The same acoustic energy should be delivered to the front isolators as to the rear regardless of the supported mass (depending on the box construction)

 

[Gold]

The first thought that comes to mind is, weigh the amp and fill the hole with something that is a similar weight. Probably non ferrous.

 

[RoadrunnerOZ]

That still wouldn’t completely balance the box - I don’t think the amp is quite that heavy and by the look is externally mounted so there may be a mechanical advantage in the weight distribution when the amp is fitted being as far rearward as possible - the box is still likely front heavy. The remote electronics connect to the existing cables that exit the speaker box and the substitute panel has the fittings for the extension cable - this panel could be a mount point for additional weight.

 

[Gold]

Another thought is that sorbothane is VERY sticky. If you put sorbothane under and around the speaker it might hold the speaker in place as is.

 

[RoadrunnerOZ]

Yeah and it comes in many different profiles

 

[klem]

@DFischer i hadn't considered pipe to help me balance it. If you'd be willing to suggest more specifics with this, especially given you are also in the USA, that would be appreciated. I.e., what diameter pipe to place underneath box? I can't imagine using a single pipe for this, but this sounds a bit better than my idea of a 2x4 length underneath the box. I like the idea of getting progressively smaller with the pipe to help with the balancing.

The cabinet is front heavy once the amp is removed so you can just weigh the amp assembly on some bathroom scales and insert the equivalent weight inside the box making sure it’s fastened down. Do they provide a blanking plate for amp removed soffit mount as you could bolt a weight to that - the REK-4

That assumes that the 420 with amp installed IS distributed evenly.
I won't have access to the speakers until next week, but once I unpack them, of course I'll weigh each part to help in determining dummy load placement.

There is a thread at GS about this very thing, but all the pics are gone and the OP hasn't been logged on for a couple of years, and never gave a final update.

A lot of ideas are floating around, but it is getting away from the primary question of ideas on how to assess and counter-balance without scales. My goal is to have the weight as equally distributed as possible via additional counter-balancing weight so I can use the same isolator. Once that's done, then as mentioned in above post, the speaker will be perpendicular to floor and therefore there shouldn't be any need to worry about preventing the speaker from sliding!

@Gold
Sorbothane was what I used the last time I soffit-mounting these speakers. I was not entirely happy with the excursions it allowed, and was somewhat limited in the choices of products they made in terms of load values and Fn. Maybe that's changed in their standard offerings in the years since then, dunno. I've recently found some other isolating that should perform better than the Sorbothane rings, but that's down the road. I really shouldn't have written decoupling in the title, it's introduced a lot of side-track ideas. Apologies for not being clearer. So here's a pic of what I'm trying to do, keeping it simple.



Box is 2 layers of 3/4" MDF with an inner 1" semi-rigid fiberglass batt on all sides except base where it would just be shorted out. This drawing does not show any additional weight that would be added to the rear face or top face towards rear. But it does show that I want this to be relatively simple right angles / not tilted. The isolators are also not shown, but my eventual plan once I could specify them was to place them underneath the speaker box. The stand of 2x4s will probably be enclosed and filled with dry sand bags or something heavy. Ideally I could forgo fasteners between the stand and the concrete floor.

At any rate, it would be great if the discussion could focused solely on the question posed in the OP. Once that's achieved, I'd welcome the input on decoupling systems. Thanks for your input.

 

[Gold]

That looks good to me. Are you sure this will be a problem? If the box fits tight enough the speaker may not go anywhere.

I wasn’t suggesting using sorbothane strictly for decoupling. I was suggesting that it can function as glue that doesn’t mar the speaker and is acoustically favorable. Like a 1/16” thick sheet as part of a sandwich of materials.

 

[kags]

I installed 420s with remote amps last year and we built platforms, similar to what you drew and the speakers sit flush with a front wall structure- not soffits per se, but a baffle-wall. I never considered the speakers being out of balance with the amps removed. It never even crossed my mind, not is it mentioned by Neumann.

 

[RoadrunnerOZ]

Point to note - for a vertical installation the speakers would possibly need to be installed tweeters down as they (tweeters) need to be at seated ear height and the other drivers having no impedance between the ears and the speaker like a bench or desk - (unless they are being listened to without any furniture/hardware between them and the listener) - any furniture would occlude the midrange and bass drivers and also causing reflections and comb filtering. There must be nothing in the way.

Doing this alters the weight balancing as the woofer then would be at the top of the speaker being the heaviest driver and with the deepest magnet assembly going rearward into the cabinet. Soffit installs are at a height to allow uninterrupted path from all drivers to the engineer and therefore requiring to be tilted down to focus the top end on the ears - they also must point inwards at 30° to focus on the seat position, proper acoustical operation requiring the distance between the speakers to be exactly the same as the distance to the ears - forming an equilateral triangle between Left/Right/ears. See pages 9/10/11/12/13 of the installation manual. These studio monitors are not designed for a flat to the wall 90° install as the response at the ears would end up with major dips.

 

[DFischer]

I think the other posters are making some good points, but sticking strictly to your question about balancing the monitor with counter-weights without using any scales...

The diameter of the pipe doesn't matter much, say 1/2" to 1". Put it in the middle of the speaker front to back, put some tape on it so it can't roll. Think about a see-saw. If it's front heavy, it will tip forward onto the table. Put weight on the back until it starts to tip backwards. Fine tune the weight by holding the monitor level and seeing which way it tips. An remember that the distance of the weight from the fulcrum is as important as the mass. Torque = mass * distance from the fulcrum (projected on to the bottom of the speaker perpendicular to the pipe).

 

[RoadrunnerOZ]

If using the REK-4 remote kit (which is sort of necessary for remoting the electronics) the metal case replacement which bolts to the rear of the speaker can be used as a mounting point for counterweight material. You can buy sheet lead which is available as flashing for roof ridges and guttering - this comes In varying widths in 3 meter rolls and can be cut with heavy scissors. Using spray contact like SikaBond SprayFix the lead could be attached to the cover plate. This use of cut pieces of sheet lead would allow for fairly accurate balancing and a damped weight that would never rattle. To tune the weight a bag could be hung from the mounting screws and adding cut to size pieces to the bag until the box is balanced - then they can be attached to the cover plate. Employing the dowel system as mentioned by DFischer and in my post #7 for finding the balance is the simplest quick way without scales

If you are trying to achieve F50/R50 weight distribution you’d need a pretty heavy weight at the rear to compensate for the speaker weight at the front. Setting the box on a thin dowel roller, dead centre F/R perpendicular to the sides would be the best way to show/measure balance - you can tape this in position on the bottom of the box with some gaffer or packaging tape, set hook bolts into any available mounting holes on the back of the speaker and hang your weight from there.

If inverting the speaker for installation the dowel obviously needs to be taped to the top of the box

 

[ruairioflaherty]

Wow, this thread...

To the OP, I have done this quite a few times with large ATCs, PMCs etc. I suggest biting the bullet and picking up a few scales on Amazon. I have a pair that I bought for something like $35 each that I've used for everything up to PMC BB5-XBD (massive).

And yes, you are 100% correct to consider this. We have done other solutions and I've never been happy.

Edit - these are what I bought - they have worked great for quite a few projects - https://www.amazon.com/gp/product/B0153I0418/

 

[ruairioflaherty]

Decoupling is non trivial. I worked for quite a few years with Thomas at Northward Acoustics and learned some of the ins and outs from him. I am using ATC110 decoupled with his full suspension system.

 

[kags]

Decoupling is non trivial. I worked for quite a few years with Thomas at Northward Acoustics and learned some of the ins and outs from him. I am using ATC110 decoupled with his full suspension system.

I’m very curious about your experiences (audibility-wise) and solutions. I’m not asking for any trade secrets. I’ve installed hundreds of monitor systems and I’ve found decoupling useful sometimes and inconsequential most of the time.

I work directly with a handful of respected speaker manufacturers - at all price points, from home studio applications to mastering to rock-and-roll high-SPL mains - and we have done considerable testing of decoupling devices and methods. We mainly experience that geometry, symmetry, listening axis, and acoustic treatment (of course with proper x-over implementation) all make a noticeable difference. Decoupling, especially with massive speaker cabinets rarely affects the sound quality. Poor construction of the enclosure or mounting will obviously matter.

Would you share some experiences?

BTW, has anyone seen the research being done by Trinnov regarding speaker arrays controlling acoustic problems in small studios? I don’t know enough about it yet, seems expensive, but may be interesting.