I've made some speaker stands out of cinder blocks like in this article:

Velvetron

I've epoxied the cinder blocks together and epoxied the cinder blocks to a circular piece of wood. I did not add spikes like in the article. I have a couple of questions:

I have the stands currently on carpet. Do I need to use spikes at the base of the stand to de-couple them from the floor or is that not necessary?

I also need to add a platform to the top of the cinder blocks to rest the monitors on, what material should I be using? I see MDF mentioned in a lot of projects, should I use MDF epoxied to the cinder blocks and then some kind of foam between the MDF and speaker?

Appreciate the help! Let me know if I failed to include any information.

That looks good and I'm interested to know if the design is good sound-wise. Is it heavy? Stable? Does it vibrate a lot?

Maybe the more experienced guys like Andre, Ethan or DanDan could chime in and give some insights on this.

Cheers!

Link broken?

The spikes will couple the speaker (or stands in this case) to the floor. The spikes will penetrate the carpet, thus bypassing any decoupeling action the carpet might provide (probably not very much). This might be good or bad depeinging on the situation:

If solid, heavy concreet slab on ground; it might be a good, easy way to keeping the speakers from moving around and possibly wobbling since any decoupling offerd by a carpet will not be very effective in the lower range (you need dedicated feets that matches the weight of the speaker and this speaker need to be very heavy in order to reach a low resonant frequency needed to provide decent decoupling down low).

If not on ground floor and not very thick/massive concreet floor, but relativly lightweight floor that can easely resonate; a proper decoupeling is the best option (actually, it's the best option in any case if done right if the speakers are heavy enough), but again; spikes does NOT decouple, they do the opposite if anything.

The totalt confusion regarding spikes in the audiophile lala-land is truly fascinating.

Speaker Decoupling

If lightweight speaker, these will probably not decouple all the way to cutoff of the speaker. Any test results for a lightweight speaker to be found anywhere?

Play around with this app and you'll notice that if lightweight speaker, you need to use springs to get satisfying decoupeling all the way down to cutoff:

AMC | Vibration Isolator Pro

https://www.sorbothane.com/Data/Site...properties.pdf

https://www.sorbothane.com/Data/Site...nce-curves.pdf

Their website suggests decoupling is acheived as long as the sorbothane reaches 10-15% compression. So according to them as long as you match weight, you'll acheive decoupling. Ive seen a few designers who recommend them, for what that's worth. The data on their pdfs looks good enough to excite my ignorant side.

Playing with that app i cant match anything that would decouple my speakers below 20hz as is

It´s all about how low the resonant frequency of the system can become. I’m sure that Sorbothane works well to a point, but if you need proper decoupling all the way down to the cutoff of the speaker (if it plays at least somewhat low), you need specialized solutions. If the speaker has a useful response down to 30 Hz, the natural frequency of the system needs to be lower than about 15 Hz to offer decoupling all the way down.

AMC knows their stuff. Have a look and play around with their application (it´s free) and see what happens when trying to decouple a lightweight speaker with good results.

Told you

Ah, i see what you did there. Damn, now im rethinking my flush mount design. I really hate acoustics. I just read theres only a three year shelf life on sorbothane too. Now assuming i set the crossover for my subwoofers to like 100-180hz all these problems go away, right? Except shelf life.

And what about Vibration? A complicated "cousin" to acoustics...

If you place a lightweight speaker on very soft isolators (needed static deflection met) it is very unstable construction. You like it to stand still.
Add inertia. Say 50 kilo or more... Now the whole construction is a bit different.

More on the subject here (LINK)

Best

Yes, if 100 Hz x-over (and assuming normal slopes like 24 dB/oct or steeper) the natural frequency only needs to be about 50 Hz or lower.

I can confirm akebrakes' comment. If soft isolators are used close to their max load (= more efficient isolation down low in frequency), the speaker rocks back and forth like a ship in a storm if you push it gently. For my flush mounted speakers I made a very simple, cheap but effective device to stop any motion. Shown here: find out a good heigth for flush mounting speakers

If there is is place above a flushmounted too light speaker, the idea can be used to put additional load onto the speaker / isolators, instead of putting something heavy on top of it. Check the manufacturers' data on max compression of the isolator and measure with a caliper how much room there is left under the speaker as you screw down the Allen screws from above. (I imagine this may be somewhat similar to Northwards' way of adding enough load on the spring isolators under the speakers).

The installed speaker in the doghouse is shown in bit further up here: find out a good heigth for flush mounting speakers

...but keep in mind that the subs start becoming more directional or, more precisely, you may start getting directional information in the upper range of the subwoofers - hence my recommendation to use only one sub (if possible) and place it on axis in between l/r speakers, with the sub firing sidewards and the speaker as close as possible to the front wall (different story when flush mounted obviously):
this leaves more options for x-over adjustments and coupling of lf sources, having a huge effect on the overall speaker system response and how it's interacting with room geometry (someting somewhat neglected in many places imo), but can cause other problems (and i'm sure jens will remind us with the related link).

3 year shelf life? Really? I have some sheets/pads that are far older than that.., still feels like new...

Directivity is not an issue below 150-200 Hz since most normal subs (unless very large) are more or less omnidirectional at this range and and x-over at 150 Hz is often no problem at all. And I personally always recommend 2 subs for more than one reason:

Add a sub instead of even more bass trapping to even out freq response?

not my experience and not what i recommend, but what i was assuming/expecting - maybe i should start another thread with a couple of examples when and where NOT to use multiple subs (and then keep linking to it everytime the issue of using a sub comes up)?

Lots of good info, thanks. I am using 2 subs with a minidsp ddrc-88a-bm so hopefully ill be ok in that regard.

Im pretty sure vibration wont be an issue, but we will see when im done building my baffle. I designed an enclosure for the speakers with sorbothane hemispheres for decoupling and sorbothane bumpers to stop vibration and sway.

The only part that worries me is the three year shelf life. I might look into swapping out for springs in the future or if the sorbothane doesnt perform well.

Looks good. It looks like you use threaded rubber feet to position the speaker within the wooden frame (?). I see no acoustical use for the ones on the sides though. Practical perhaps yes but also 8 more places which can transfer vibrations to the frame.

If you use cheap solid rubber feet reaching 90% / -20 dB isolation at 20 Hz requires about 7 mm of ”compression” load (deflection actually as elastomers are incompressible.) That is very hard to reach with cylindrical feet, with conical shaped feet it is more easily achievable. You find more info here: https://www.tme.eu/se/Document/fb716...173/DVA-EN.pdf (The feet I used are hollow "rubber balls" with flanges, quite cheap too and don't need that much of a load to reach quite low in frequency isolation.)

The feet on the top and sides are made of sorbothane also and just for recoil

OK. I think ( = don't know for sure really) the manufacturer of Sorbothane has good info on their site about suitable compression and load versus surface area in combination with the thickness and shape of the rubber. If you haven't checked their site already, it might be worth checking up to reach optimum performance, small details can make a difference. (The theories for vibration isolation are identical to those as in the Elesa paper. What changes is that you have a much softer rubber material which also has better internal damping properties than solid rubber like neoprene or EPDM)

One thing with the DDRC-88A to be aware of is the lowest latency (with dirac bypassed) is 6ms before considering group delay from any filters. Not terrible, but it is on the high side if people are tracking through the speakers in the CR or for virtual instruments

Did you consider the OpenDRC-DA8 (~3ms)? Also the 88D is ~2ms according to minidsp.

I already own it so it is what it is

I just want to say, that threads like this blow my mind. They really show me how little I understand about acoustics.

*goes into corner and cries.*

Heh, i feel like that all the time. The good part is we get to learn everyday.