Amp Riser Effectiveness

Document your build here: All about your walls, ceilings, doors, windows, HVAC, and (gasp!) floated floors...
User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Fri, 2019-Oct-25, 13:30

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;

Drum riser base.png


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;

Drum riser topped.png


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;

Riser 2 1800x1200 base.png

Riser 2 1800x1200.png


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
You do not have the required permissions to view the files attached to this post.

User avatar
Soundman2020
Site Admin
Posts: 129
Joined: Thu, 2019-Sep-19, 22:58
Location: Santiago, Chile
Contact:

Re: Amp Riser Effectiveness

Postby Soundman2020 » Sat, 2019-Oct-26, 23:36

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 more simpler, and more useful. The mechanism to keep them joined could also be simple... I'm sure you can come up with something!

- Stuart -

User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Sun, 2019-Oct-27, 02:33

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


Cheers,
Jennifer
You do not have the required permissions to view the files attached to this post.

User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Sat, 2019-Nov-09, 16:00

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;

Riser Test.jpg


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
You do not have the required permissions to view the files attached to this post.

Purelythemusic
Active Member
Posts: 38
Joined: Sat, 2019-Oct-12, 18:39
Location: England - Bristol

Re: Amp Riser Effectiveness

Postby Purelythemusic » Sat, 2019-Nov-09, 17:18

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.

31E58BC2-1349-4AB6-A2E6-3A7F7B7DB176.jpeg
You do not have the required permissions to view the files attached to this post.
- Success in music is being able to make music whatever your situation -

User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Sat, 2019-Nov-09, 18:01

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

User avatar
Soundman2020
Site Admin
Posts: 129
Joined: Thu, 2019-Sep-19, 22:58
Location: Santiago, Chile
Contact:

Re: Amp Riser Effectiveness

Postby Soundman2020 » Sun, 2019-Nov-10, 00:13

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 ... :)
:shot:

- Stuart -

User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Mon, 2019-Nov-18, 20:22

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;
2019-11-17 15.08.33.jpg

2019-11-17 14.58.46.jpg


This clever little jig ensures the horizontal and vertical holes required for the bolts are drilled true;
2019-11-17 18.44.56.jpg


A test fit demonstrated that they all lined up properly;
2019-11-17 20.48.30.jpg


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.
2019-11-18 13.37.05.jpg


The 6x4' riser was quite an undertaking, I was glad of the practice on its smaller siblings!
2019-11-18 16.57.21.jpg


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;
2019-11-18 17.46.34.jpg


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;
2019-11-18 18.13.55.jpg


Fabric applied all round. Next jobs are to turn it the correct way up again and apply a trim along the edges.
2019-11-18 19.33.32.jpg
You do not have the required permissions to view the files attached to this post.

Purelythemusic
Active Member
Posts: 38
Joined: Sat, 2019-Oct-12, 18:39
Location: England - Bristol

Re: Amp Riser Effectiveness

Postby Purelythemusic » Tue, 2019-Nov-19, 04:24

Nice, good write up! I suppose of you wanted you could put any sort of practical flooring down for whatever footfall is expected.
- Success in music is being able to make music whatever your situation -

User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Tue, 2019-Nov-19, 05:41

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

User avatar
endorka
Active Member
Posts: 60
Joined: Mon, 2019-Sep-23, 06:36
Location: Scotland
Contact:

Re: Amp Riser Effectiveness

Postby endorka » Tue, 2019-Nov-19, 05:53

Here it is flipped over and roughly arranged in the 6x6' configuration. Next step is to add the trims.
2019-11-19 08.43.24.jpg

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
You do not have the required permissions to view the files attached to this post.


Who is online

Users browsing this forum: No registered users and 0 guests