Amp Riser Effectiveness

[endorka]

Taking this a little bit further now...

The 1800x1200mm riser above will be sufficient most of the time, but sometimes a bigger one would be useful for drum kits. Some drummers I've recorded here would require 2100x1800mm to be safe, and a bit larger could be useful. But a riser this size in the studio all the time would get in the way, especially when it comes to do some studio upgrades.

Also, sometimes it would be great to have several smaller risers for multiple musicians, amps and percussion. So I wondered if a modular riser approach would be possible? Here's what I have in mind using risers of a variety of dimensions based on the above design. 1 1800x1200mm, 2 1200x600mm and 2 600x600mm.

Imagine they are arranged into a base. The largest 1800x1200mm riser is in the centre to get it under the most loaded part - kick drum, snare drum and drummer. Intuitively I'd space the risers a little bit apart so the edges don't touch and buzz / rattle. The risers have T-nuts placed in them at appropriate positions;

And two 1800x1200 plywood boards placed on top, again a little apart to stop rattles. These are securely attached to the risers with flush fitting furniture bolts going into the T-nuts in the risers below. The seam is down the centre of the 1800x1200mm riser, so they are all held together giving a 2400x1800mm riser. That's 8x6', a good sized riser for sure;

When the drum riser is not required the 1800x1200mm top panels can be moved to another room, or stored on top of the 1800x1200mm riser. It would be interesting to measure the effect of the extra mass.

Another option is to use one of the 1800x1200 top panels to make a second 1800x1200 riser from the small ones;

The trouble is, I'm not even sure it it is valid to combine these risers in this way. Will they be less effective than a proper 2400x1800 riser? Or even worse than nothing at all? I honestly have no idea, so any comments would be most welcome.

Edited to add some more thoughts on this;

Assuming the top bolted on layers (combined 2400x1800mm) is also 18mm plywood, the bolts will make a proper join and the top layer of the riser sandwich becomes a single 2400x1800x36mm mass. If slides 9 and 10 on this Green Glue slide show are an accurate depiction of how the CLD sandwich works, this will be fine, the bolted layers will act as one thicker layer.

However the the link Adhoc posted states that for optimum damping the "wood" layers should be the same thickness, but up to 1:3 difference will still be good. It occurs to me that this might only apply in the case when the total mass is kept constant, i.e. one layer becomes thicker as the other becomes thinner. It might not apply if the proportions change due to mass being added. But it it does, there could be an argument there for making the top bolt on layer a bit thinner than 18mm. On the other hand, doing this will lose some structural strength.

The layers below in separate risers will not be joined directly to each other, but intuition suggests they will bend and flex in a similar way as if they were. The gaps between risers might allow greater overall movement relative to the top layer than a single 2400x1800mm sheet would though. So maybe the damping layer is less constrained, and therefore not quite as effective as a another sandwich of 2400x1800mm sheets? But I can't see it being any worse than having the same mass perched on top of the single 1800x1200mm riser.

On the other hand, green glue still works when applied to multiple overlapping sheets of drywall, so that is encouraging.

Cheers!
Jennifer

[Soundman2020]

I like the concept, Jennifer, but I'm wondering if it wouldn't be easier to just make the modules to fit together, with some type of latches or bolts to joint them, rather than having a single large deck that fits on top. Storing that deck might be problematic in itself, as well as being heavy and cumbersome to move. Just having individual modules that join together would probably be simpler, and more useful. The mechanism to keep them joined could also be simple... I'm sure you can come up with something!

- Stuart -

[endorka]

Good point, thank you. It would also allow more variations e.g. an 1800x1800mm riser, large enough for many drum kits.

Cam locks and dowels as found on many Ikea type flat pack furniture could be a good way of holding the risers together temporarily. There's a double end version that allows the dowel to be removed from both risers when not joined together. Nice!

If the bending moment of the joined risers splits the wood around the dowel, the join could be braced with a couple of steel rods underneath.

dowel and cam lock.PNG (176.02 KiB) Viewed 40547 times

dowel and cam lock.PNG (176.02 KiB) Viewed 40547 times

Cheers,
Jennifer

[endorka]

The 18mm plywood and MDF cuts arrived yesterday afternoon, just in time to prepare a quick test for a rehearsal session in the evening. No screwing or green gluing of the board, just the 3 layers lying loosely on top of each other, on top of 50mm thick Knauf Earthwool RS45 insulation slabs. The camera perspective is a bit skewed, the big riser is 1800x1200mm or 6x4 feet;

The drummer was using a small electric kit that fitted on the single 1800x1200 riser. A few months ago a drummer with a similar kit was here, and you could hear the bass drum beater / pedal / foot impact thumping through the entire house (timber frame). In that respect it was no better than an acoustic kit. The only escape was in the garage!

With the drums on the test riser the impact transmission to other rooms was hugely reduced. I couldn't hear it in the kitchen. In the living room two floors below it was a distant thump. Too loud for study or reading due to the rhythmic clue in, but probably ok for watching television or similar.

The platform is very stable and sturdy, you can walk on it no bother. But watching the motion of it with the drummer playing was fascinating. It was visibly moving left, right, back and forward, I think more so than up and down, and compounds of all those movements. The whole system was working extremely well at damping them. Utterly fascinating to see all this movement that would otherwise be going into the house structure being contained in this way.

Hopefully screwing, green gluing and perhaps bolting will squeeze a little more reduction. Even if not, it is still well worth doing. There will also be the possibility of bolting several risers together to increase the mass.

Cheers,
Jennifer

[Purelythemusic]

Nice one good update! Did the drummer notice any uncomfortable sensation from it? Forgive my ignorance but is the RS45 45kg/m3? And is that ideal density?

I used some Rockwool RW45 to casually ‘float’ some hifi speakers in a built in cabinet which seems to have successfully limited flanking transmission to the cabinet... it was stuffed in tight though so probably ended up being denser... plus I didn’t do any testing... but in the next room (separated by brick wall) you can hardly notice music at 70db which is probably the loudest volume I’d listen in there... upstairs is a different story though as there are two downlights in a lath and plaster ceiling, gap then floorboards and carpet.

[endorka]

Yes, the Knauf RS45 is 45kg/m3, specs below, I think it is very similar to the Rockwool RS45;

https://www.knaufinsulation.co.uk/produ ... -slab-rs45

I think Glenn Stanton used something similar, but may be mistaken. In the Rod Gervais book p.269 it mentions using 3 psf for a similar structure over an entire floor. I assume it's a typo though and he means 3 pcf, which is close to 45 kg/m3.

The drummer loved it, I think there is something psychological about stepping up on a platform to perform. Even if it is only 10cm high, the effect is still real, I know I get it It's actually really cool to walk on, there's a nice give but it is also steady. I imagine if one was a dancer or into aerobics or what have you it would be a good surface for it.

What has occurred to me though is the consequence of micing an acoustic kit with the mics off the riser so they are decoupled. On one hand, it might be good to not have the physical flanking impact arriving at the mic before the sound through the air. Maybe tighten or clean up the sound a bit. On the other, the kit will now be moving a little bit relative to the mics. Although it kindof does that to some extent anyway, especially the membranes.

These downlights are brutal aren't they? Huge acoustic holes. I have to replace about 15 of them with acoustic, fire and insulation rated equivalents in two bathrooms under or sharing the eaves with the studio. Not the end of the world, but it all takes time

Cheers,
Jennifer

[Soundman2020]

Thanks for the update and the testing, Jennifer! That's great to have positive feedback on how the concept works in practice.

If you have a chance, it would be fantastic to see results for the "magical myths" as well: carpet, towels, blankets, bits of rubber, tennis balls ...


- Stuart -

[endorka]

I've made some progress on these risers, there are 5 in total, dimensions in feet for convenience;

1 6x4'
2 4x2'
2 2x2'

I took the modular approach quite far so they can be combined in various ways, e.g;
1 8x6'
2 6x4'
1 6x6', 1 6x2'
1 6x6', 1 4x2', 1 4x2'
1 8x4', 1 4x4'
1 10x4', 1 4x2'
1 12x4'

Very useful for multiple or unusual sized instruments, especially when they are in different rooms. The 8x6' is a total beast; I am really glad I went with this modular approach, moving that would have been a nightmare. The 6x4' is heavy but manageable with two people, like a heavy bit of furniture.

Building so modular took quite a lot of planning and thinking though. Building two 6x4' that could be joined along one edge would be far simpler!

They are joined by the cam lock bolts commonly found on flat pack furniture. I've left a gap for a 9mm edge trim on each riser;

This clever little jig ensures the horizontal and vertical holes required for the bolts are drilled true;

A test fit demonstrated that they all lined up properly;

I was concerned that weight applied near the joins would cause the plywood to split or delaminate where the bolts enter, but I was able to walk about on the riser without this happening.

Next was to screw and green glue the layers together. I did the smallest panels first to figure out a good workflow before the larger ones. Screw schedule was 20cm along the edges and ~40cm in the field, as specified by Rod Gervais book p.269. The riser stack was turned upside down, aligned at the edges, and I pre-drilled holes into the two layers of the MDF. Screws were sized 50mm long so they could be screwed into this upside down assembly with sufficient grip on the plywood layer without the tips protruding through it.

The 6x4' riser was quite an undertaking, I was glad of the practice on its smaller siblings!

With all the layers green glued and screwed, it was time to add the insulation and cover it in fabric. First staple along the bottom of the lowest layer so the weight of the riser helps seal the insulation into the fabric. Leave a bit of slack;

The slack allows the fabric to be brought down along the side of the lowest layer and stapled there too for extra strength and sealing;

Fabric applied all round. Next jobs are to turn it the correct way up again and apply a trim along the edges.

[Purelythemusic]

Nice, good write up! I suppose of you wanted you could put any sort of practical flooring down for whatever footfall is expected.

[endorka]

Thank you!

Yes, the Rod Gervais book used laminate flooring as the top layer. It would look well smart. He also used plywood as the sub layers. I imagine one reason he did this was that MDF does not hold a screw well, and as he was making an entire floor he'd be putting the screws in from above.

Carpet would be a possibility too. I went for plywood as per Glenn's recipe, it's cheaper and I won't be upset if drummers and cellists impale it with their spikes! After a "near miss" of this type on a session a few months ago I'm not taking any chances. The rubber pads the drummer's kick drum had worn though exposing the spikes to the floor. You couldn't see the spikes from above, I only noticed when I mic'd up the kick drum. The spikes would have gone right through the rug and chewed up the wood floor.

Using ply also means I can also record drums placed directly on a hard surface rather than a rug or drum mat. It may add a bit more ambience and snare bottom sound into the oveheads.

Cheers,
Jennifer

[endorka]

Here it is flipped over and roughly arranged in the 6x6' configuration. Next step is to add the trims.

It's a wee shame about the dark mark on the plywood of the large one, it came like that. Scrubbing with white spirit has lightened the mark a bit, and I'm waiting for some potion to arrive that will apparently lighten it further. Fingers crossed, if it doesn't, sanding might do the job.

Cheers,
Jennifer

[endorka]

My band was rehearsing here all weekend, and I bolted together a test of the 6x6' configuration. It just has a wood spacer between each riser component, the proper trim has still to be fitted. There were five of us in total for a "silent" rehearsal using headphones as monitors. The electric kit would have fitted entirely on the 6x4' riser, but the extra side bits were useful for the SPD-SX drum pad.

The individual components fit together securely, there is no lateral movement between the riser components. There is a little bit of up and down flex as you walk close to the edges, but no big deal. The band were wandering over the combined risers without a second thought. If there was some acoustic benefit to be had from making the combined risers more rigid in this way it could perhaps be achieved with some steel rod inserted between components in the bottom layer of MDF.

I still have no quantitative data on the reduction of impact noise, but can offer qualitative data gathered over a weekend of rehearsals;

- During a similar rehearsal some months ago with an electric kit on a rug on the wooden floor, the impact thump of the bass drum pedal was so loud in the living room two floors below that watching television was not possible.
- This time, the impact thump of the bass drum pedal was not audible while watching television. It was also ok for internet browsing on a laptop and similar activities. Still too noticeable during activities demanding quiet and concentration such as paperwork or study though. I still have some way to go with other sound isolation activities but as this is an impact sound in a timber frame house, I accept there is going to be a limit that may well prohibit reducing it much further.
- I have a room mic compressed and piped through to our headphones so we can talk to each other easily. In this, foot stomping from the musicians not on the riser was louder than the kick drum pedal impact. It may be that the foot stomping is also more audible than the kick two floors below as well. More rigorous tests required I think.
- In the kitchen two floors below and on the other side of the house from the studio you couldn't hear anything. Previously you could. Win!
- If I rap my knuckles on the riser you can barely hear it when standing outside the closed studio door. Rapping my knuckles on the wooden floor is clearly audible. I did not expect this, I thought the only benefit in impact reduction would be to floors below.

All in all, a massive reduction in sound transmission and big quality of life improvement. Absolutely worth doing, I doubt there are many improvements in the acoustic world that give such a huge attenuation of bang for the buck!

Cheers,
Jennifer

[Soundman2020]

Thanks for the update, Jennifer. I'm really glad to see that it worked out so well for you! Surprising what a simple bit of plywood and some insulation can accomplish, isn't it? It looks pretty darn good too.

It might just be the photo angle, but are you sure that the rear edge of the riser isn't touching the wall behind it? From the photo, it looks like it might be... Just wondering about that. If it was touching, then you might get another small improvement by sliding it over a bit, so it doesn't touch.


- Stuart -

[endorka]

Cheers Stuart. It's just the camera angle, the riser is about a foot away from the rear wall.

I've still to add a wooden trim along the sides / edges that will cover up most of the fabric without touching the floor. Also some Danish Oil to make the plywood surface look a bit posher.

Indeed, for such a simple and cheap build it is an amazing improvement. I can see how the same technique covering the entire floor surface (structural load and ceiling height permitting) as in Rod Gervais' book would confer substantial benefits for many applications. I'm inclined to lash up some sort of hammer drop test to get some proper measures as well

[Soundman2020]

Cheers Stuart. It's just the camera angle, the riser is about a foot away from the rear wall.

Are you sure? It doesn't look like a foot...

Jennifer--drum-riser-wall-space.gif (120.64 KiB) Viewed 40483 times

Jennifer--drum-riser-wall-space.gif (120.64 KiB) Viewed 40483 times

Indeed, for such a simple and cheap build it is an amazing improvement. I can see how the same technique covering the entire floor surface (structural load and ceiling height permitting) as in Rod Gervais' book would confer substantial benefits for many applications. I'm inclined to lash up some sort of hammer drop test to get some proper measures as well

You could always go the whole nine yards, and buy a proper calibrated tapping machine to do that!

impact-noise-standard-tapping-machine.jpg (31.48 KiB) Viewed 40483 times

impact-noise-standard-tapping-machine.jpg (31.48 KiB) Viewed 40483 times

That's what acoustic test labs use to measure impact noise isolation. Might be a bit expensive for just a a single use, though! I bet those things are damn expensive.... I'm thinking a hammer drop would be a bit cheaper! Just don't drop it so hard that it damages your floor surface.

- Stuart -