Basstrap: EQ Acoustics or HOFA ..or DIY?

[3ee]

EDIT: went for the DIY corner bass traps, check out pics here: https://drive.google.com/file/d/0B3pYSM ... sp=sharing

Hello,

I'm in the process of upgrading my studio's room acoustics and I have these two choices for a significantly more effective "bass trap" solution to foam (which isn't really doing anything to the low freqs anyway)

HOFA Basstrap
http://hofa-akustik.de/en/modules/basstrap/details/


--- or---

Spectrum Studio Corner Bass Trap L
http://www.eqacoustics.com/products-pag ... ass-trap-l

and here's it's performance data (100mm):
http://www.eqacoustics.com/learn-more/a ... mance-data



One is based on sheer mass and density stuffing (14.5 Kg in wight per piece) and the other on a membrane and I'm not sure which would be more effective for the usual front-side wall corners.

edit: Maybe it's a better idea to go DIY?

[Compyfox]

First and foremost, let me say that KVR is probably not the best place for these kinds of questions. Acoustic experts are over on GearSluts. Among them the really helpful GIK Acoustics members.

That being said - it really, really depends on what application you need, what issue your room has, what space you have in your room, what budget, etc.



Generally, everything around 7kPa as flow resistance and panel thickness between 8cm (3inch) to 10cm (4") already work as moderate broadband absorbers. In some setups, they're also already effective down to a specific freuquency with a coefficient of 0,75 and up (the higher this value, the better the absorption) - example: mounted and then spaced from the wall, etc. All good and fine, if you ignore specific issues in your room (standing waves come to mind) and just want general treatment.


What I see upfront from these two absorbers:

a) the HOFA one is after sheer mass and is just for plain "absorption". Though I've never seen these things upfront. So I can't tell you if behind the fabric is a thin layer of wood, or the absorptive material directly. It's also wasting more space (a diameter of 41cm is not to underestimate in corners).

b) the eqacoustics panel is a 10cm panel with a thin membrane (probably wood) in front of it. What this does is absorbing frequencies down to a specific range, and to not just "dull out the room", it also works like a diffusor (frequency reflector, due to the hard surface, and at a specific frequency due to the thickness of this membrane). Though even here, a bit more details would be fine. Like - is the membrane slotted with a specific pattern, or does it just have holes only to let frequencies through and just reflect/diffuse a certan frequency range. Sure isn't a specific tuned Helmholtz resonator.



What is the right route to go?

Good question.


Right at the start, I'd measure the room to find the most pressing issues. For this, there is Room EQ Wizard, and there is an extensive tutorial over on GIK Acoustics. Then you can start the treatment you need. For example... if you have nulls or peaks in the low frequency range - then broadband absorbers or plain bass traps alone won't probably do the trick (but help reduce the issue first!). It also tells you where you already overdid it in terms of treatments.

If you want to go DIY, there are a sh*tload of posts over on GearSlutz. Though in general, I do recommend rockwool material with a flow resistance higher than 8kPa (Knauf and Rockwool Sonorock/TermaRock comes to mind in the EU area) for broadband absorbers (which also work great angled in corners) up to 10cm, and flow resistance between 5 and 8kPa if we talk panels thicker 15cm due to their different behavior in terms of absobtion coefficients.

See the following screencap.

screenshot-www acousticmodelling com 2016-02-23 21-14-43.png

I know, this doesn't answer your question "what" to go for from these two.

But would it be so easy - like: one absorbs more, the other reflects more... I don't want a more dead room if the front wall corners are treated floor to ceiling - and I also want something that uses less space/profile - so I go with eqacoustics"... sadly, it's not.


Also keep in mind:
Filling your room with absorptive modules does not necessarily get you a flat frequency response of your speakers. But it can definitely reduce room resonance and improve decay times/flutter echo issues.



Just my 2c - again, GearSlutz might be more suited for that type of question.

[3ee]

Compyfox,

many thanks for your response!

The thing is, I'm (almost) sick and tired of studying these stuff... I went to gearslutz back and over again and many other places on the web for about 1-2 years now for acoustics... (I've picked up many good tips from Ethan Winer (Real Traps) and Dennis Foley from Acoustic Fields to name a few)

Short story: I already have a Behringer ECM8000 mic, I know my way well around REW (incl generating stereo fiter IRs and what-not) and concluded that these two examples of products are "best" (whatever that means) AND ship to where I live...
(I also noticed some interesting GIK Acoustics alternatives but unfortunately they don't seem to ship here even though one of their headquarters are on UK)

Recently I moved my monitors and sweet-spot to the most optimal place in the room (which is the first and most important step to good room acoustics, I can confirm that!) so that was a major improvement...

I already have foam "bass-traps" and foam panels and I'm looking to improve my room acoustics even more...

Luckily I'm moved away from any "nulls" (that was the main problem with my previous place space-setup) and now I imagine that if I place some of these two (either HOFA or the EQ Acoustics panel), besides the corner foam (space is not really an issue, I even think to leave an extra little gap of air anyway) that will improve the spectrum a bit...

in other words: reverberation, 1st reflection comb-filtering and other associated side-effects are not concerned here.... only the frequency spectrum "flatness" I wish to tame a bit more (mainly in the low-mid to 70Hz bass area) I think that translates in room modes / standing waves ...

My room is rectangular H L W : 2.50m 5.20m 3.10m if that helps (so it's a "small" room according to acousticians)

So, what do to? ... Being that one is based on high mass (the hofa basstrap doesn't have a wood membrane or anything, it's super stuffed with high density wool as far as it goes and then it's pressed to make room for even more according to the details they gave me via e-mail) and the other EQ Acoustics option has a membrane...

I don't mind some extra reflection or absorption to my setup since it's balanced from what I can tell... I don't have too much of one or the other since I was always conscious not to bring too much absorption to not deaden the room sound... since this is suppose to be a control room for mixing ... and dare I say by a long stretch... mastering

[camsr]

The first and most important step is moving the speakers (as 3ee already found out) to a location that sounds balanced where you listen to it. Do not neglect height of the speakers, do something to raise or lower them also.

[3ee]

^ yeah, the problem with that is that my stands don't go any lower than 90 cm ... and if I were to go any higher I'll reach the half of the height which everyone seems to tell to avoid... probably a good idea to test anyway, thanks for reminding.

[Compyfox]

....and concluded that these two examples of products are "best" (whatever that means) AND ship to where I live...
(I also noticed some interesting GIK Acoustics alternatives but unfortunately they don't seem to ship here even though one of their headquarters are on UK)

The question is - where are you located? Because GIK does pretty much ship everywhere if you contact them as state your issues.

I already have foam "bass-traps" and foam panels and I'm looking to improve my room acoustics even more...

Not too fond of foam.
The flow resistance is higher and they're ideally only efficient in mid to high ranges. Else foam blocks have to be HUGE to cover low frequencies.

Which is why I wrote: low flow resistance for bass traps, high flow resistance for broadband absorber panels.

in other words: reverberation, 1st reflection comb-filtering and other associated side-effects are not concerned here.... only the frequency spectrum "flatness" I wish to tame a bit more (mainly in the low-mid to 70Hz bass area) I think that translates in room modes / standing waves ...

If you have issues in that area, I don't think that bass traps will fix that alone.
You will still see a frequency shift (a certain low or high shelf, peaks and the likes). So a "room EQ" is still mandatory.

So, what do to? ... Being that one is based on high mass (the hofa basstrap doesn't have a wood membrane or anything, it's super stuffed with high density wool as far as it goes and then it's pressed to make room for even more according to the details they gave me via e-mail) and the other EQ Acoustics option has a membrane...

I don't mind some extra reflection or absorption to my setup since it's balanced from what I can tell... I don't have too much of one or the other since I was always conscious not to bring too much absorption to not deaden the room sound... since this is suppose to be a control room for mixing ... and dare I say by a long stretch... mastering

I think this is a matter of taste. And something that you need to try yourself.

I built traps in thickness 8cm, 10cm (mounted at an angle in the corners in my rec room) and I also built a 25cm thick monster bass trap (20cm thick material) that is now behind my PC desk, and a similar concept as room divider in my recording room. And it seems to work for me.

I could always add more - but I don't have infinite space. So for me it would be the angled traps.

[camsr]

^ yeah, the problem with that is that my stands don't go any lower than 90 cm ... and if I were to go any higher I'll reach the half of the height which everyone seems to tell to avoid... probably a good idea to test anyway, thanks for reminding.

Yes it is difficult to adjust height. You will have to be mechanically creative.
The half height can be mitigated by a ceiling cloud.

[3ee]

OK, so it seems that I'll be going DIY... significantly more cheaper than commercial alternatives!

So, I found 2 rockwool products that seem interesting:

Using this table, I deducted either density or air resistance:


both are 10cm thickness.

one is "tube"-like with some fence reinforcement that I think to make a couple tube-traps out of (maybe with included air gap "spiral":
80 Kg / cubic meter (roughly 40 kPA)

ISOVER SC PR 80/100



-----------------
the other is simple a panel-like form: 25 kPA (roughly 60 Kg / cubic meter)

Knauf Insulation EXPERT CFB 035 100mm



so, what do you think?
(the tube one, 80 Kg / cubic meter (roughly 40 kPA) , is probably too dense to experiment with, no? ..which will obviously result in a thick tube-trap, significantly thicker than 10 cm anyway... ) , so best to go with the 60Kg / metric cube "normal" panel ones?

[Compyfox]

Okay - I think you kind of shoot a bit over the goal here. GearSlutz can be a great place, but also very confusing.

If you've read posts by Ethan Winer (RealTraps) and Glenn Kuras (GIK) respectively, you know that they usually shoot for medium dense material like "Owens Cornering". Which is somewhere between 8kPa and 15kPa. That happens to be around 20kg/m3 to 45kg/m3 - but this still doesn't give you the actual flow resistance in kPa as each material is differently handled. So the graph from GS is a bit exaggerating.


Now here is the deal:
Owens Cornering 803 (iirc) uses around 8-9kPa and is semi rigid - it's mineral wool or "glass wool". I don't know the exact values offhand anymore, but I seem to remember that they were usually around 30kg/m3,

GIK acoustics uses "Ecose material", which Knauf Insulation provides. And this is also no secret - GIK Acoustic ships the material, and it's called "Earthwool" (sadly, I did not find an equivalent in Germany - they don't have that "type"), read: "rockwool" basically.


Here is what I did:
For my 20cm thick GOBO (filled with 10+4cm material, plus 1cm "grill frames" on each side), and my 30cm monster trap behind the PC (filled with 2x10cm and left over 4cm panels, plus 2x1cm "grill frames"), not to mention my ceiling clouds and general broadband absorber modules... My corner absorbers are 10cm thick, angled from the wall. My broadband absorbers are either 2x4cm (so 8cm) or 10cm. I used what I have. My ceiling clouds are currently 4cm. All of them wrapped in simple linen (I think 240g/m2).

I used ROCKWOLL "Sonorock" (or was it Termarock - don't know anymore) at about 6-7kPa.

They're easily accessible in Germany/EU. In Berlin for example via specific Insulation and house construction providers.




Now... Owens Cornering is more dense, and therefore "better" in terms of absorption coefficients if you go after mid range and up (so called "broadband"), while using not that much of space. Most of these panel absorbers are no thicker than 4" to 5" (10-13cm). Actually, my wall frames are 12cm in depth... so I could in theory push 5" material in there and be happy. But I do have 3,15-4" material in there due to the 2cm "air gap" adding to the absorption factor. Have rockwool angled to the wall (corner absorbers), and the coefficient is even higher - especially if we look at the center point of this 90degree triangle setup.



So what is the "equivalent" to the Owens Cornering panels in the EU?

You have two options:
- Knauf Insulation
- Sonorock


Sadly, Germany doesn't list the Knauf Insulation "Earthwool", tough I didn't contact these people yet (last time I did that, was in 2013). They come with a weight of about 45kg/m3 and 60kg/m3. But here is the kicker - the UK page does neither list the weight, nor the flow resitance. Also, if you compare this material to GIK Acoustics - it's 10cm shorter in lengths (they're only 90cm x 60cm, GIK ships at 120x60cm). By the graph given above, GIK's 45kg/m3 material should be in the 15kPa range, while the 60kg/m3 material should be in the 20-25kPa range.

The "German" Equivalent is also "Glasswool", I did not find a comparison sheet for Rockwool - and clicking through 100s of products is a pain. So if you want to go with KNAUF in Germany - then it's the "Akustik TP120" or "Akustik TP440". Both have a flow resistance of 11kPa, but only the latter is available in 5cm thick slabs (like GIK ships) at 125x62,5cm. Again - I did not(!) find a Rockwool solution on the German KNAUF page (no comparison system).


If you go with Sonorock, you have a bit more variety.
All of the slabs have a size of 120x62,5cm at various thickness. And a density of 6kPa/m3 up to 43kPa/m3(!!!).
I talk about Sonorock (6kPa) to Termarock 30 (7kPa), Termarock 40 (10kPa), Termarock 50 (16kPa) and Termarock 100 (43kPa)

But hen again, the "weight" is not given on that page... so yeah.



Now... what is the best solution for you?
As mentioned - low kPa for bass traps, medium kPa for broadband absorber. And for tuning specific frequencies, then you definitely(!) need tuned absorber modules.

Most of the GIK absorbers (I've seen them in action at Musikmesse) are fairly light, yet 4" (roughtly 10cm) deep. So my assumption is that they use more resisting material for general broadband absorbers, and less resisting material for bass traps. Or they just mix and match. We will never know their trade secrets - and it's fine really. Either you do DIY and be happy, or you use properly designed modules and therefore support the creators. That simple.



Want to do your own math, maybe this page (which I liked several times in earlier threads like this) might be of help:
http://www.acousticmodelling.com/

Specifically the "multi layer" absorber calculator.


I hacked some values in for you:
Comparison 43kPa and 16kPa general Broadband Absorbers, 2cm airgap
Comparison 7kPa and 16kPa as Bass Traps, 2cm airgap
Comparison 7kPa and 16kPa as Bass Traps, diagionally mounted, center distance to wall corner 32cm (absorber with outer frame = 120x65m 45degree mounted to wall)
Comparison 7kPa and 16kPa as Bass Traps at 20cm thickness, spaced 10cm off the wall


As you can clearly see with the last graphs especially, the "less flow resistant" the material, the better the bass absorption. And a good middle way as broadband absorber is about 15-20kPs with 10cm, spaced about 2-5cm off the wall.

I hope this helps you deciding which material to go for.




SUMMARY - Would I build the same absorbers with the same knowledge I have today?

Yes and no. I'd definitely get different material after I've done my research (I'd also build the corner absorbers a tad different - maybe like the EQacoustic ones - if I had the equipment to do so!). For example for "broadband", "ceiling clouds" and "Gobo's" (standing room dividers); I'd use a bit more rigid material with a tad higher kPa and definitely slim down on frame thickness. For thick (think 20-30cm thick) monster bass traps, I'd still waste 6-7kPa slabs - since they're just better for this kind of task.

I want to rebuild my 20cm thick GOBO at some point to more slim-lined and maybe even foldable gobo's (see GIK's Screen Panel Gobo for FreeStand Gobo). And for this, higher kPa material is better (think 15kPa) to reduce everything in size and weight.

I also want to overhaul the "general design" of my absorbers - as of this moment, I have "open frames" (which makes exhange of material more easy) but I do want to cover them in linen so that they look like commecial products. Not that I don't like the look - it's just a bit more clean. This would also save me of paining the frames (and thefore save like 2 days of work/waiting time).

If size is a non issue, and you're on a budget - go with whatever you want, but keep the limitations in consideration.




I hope this helps.


EDIT:
I'd try to get in touch with GIK acoustics again. Figure out why shipping is an issue. I'm sure they can sort things out for you. They're all about education, satisfied customers and are generally helpful people. Else they wouldn't trust the community so much and certainly not reveal any secrets in that realm.

[3ee]

many thanks Compyfox for another detailed response!

Sounds like a plan with the GIK Acoustics DIY Ecose Earthwool boards as they seem reasonably priced.
Will contact them for shipping info, want them shipped to Romania btw

http://gikacoustics.co.uk/product/diy-b ... ol-45kgm3/

I'm thinking to use all 5 boards / pack (25 cm thickness) for one corner bass trap or if I calculate correctly, for the given density for 45Kg / m3 should 4 boards (20cm thick) be enough?

...off course I'll also leave 5 to 10 cm air gap in the back as well as have an extra gap from the wall VS placement to hopefully increase performance even more.

[3ee]

Oh wow, shipping price is unbelievable, I'm even ashamed to post it here I guess we are spoiled with good shipping prices from big companies like Thomann or what?!

Anyway, I think I found the Knauf Ecose 'NaturBoards' ...it has to be one of the current models in the catalog, I'll contact them and post info here too.

added:
"KNAUF NATURBOARD FIT" density 30Kg/m3
...they come in 5 or 10 cm thickness. I have them available in my country (for about 14 euro per 6 boards pack - 10cm thick) 1000x600x100mm

I also asked for info on the other NaturBoard models, these seem like fairly new products and it seems like we have to ask about density cause the new tech spec sheet won't show them anymore...

[Compyfox]

many thanks Compyfox for another detailed response!

Glad I could help.

I'm thinking to use all 5 boards / pack (25 cm thickness) for one corner bass trap or if I calculate correctly, for the given density for 45Kg / m3 should 4 boards (20cm thick) be enough?

...off course I'll also leave 5 to 10 cm air gap in the back as well as have an extra gap from the wall VS placement to hopefully increase performance even more.

Okay - now it depends on what you want to do.

Do you want´
- broadband absorbers as "corner traps" (read: angled at 45degrees to the corners)
- corner chunks (either as cube, cylinder or triangle)

This declares how much material you really need, and how thick it should be.


If we take a look at the GIK Acoustic material again:
- Soffit Traps (cube "chuncks") // size: 120cm x 41,3cm x 41,3cm (filled to the brim!)
- 244 Bass Traps (panels) // size 120cm x 60cm x 12cm (so 4,5" thick - probably 2cm air gap unless 4cm thick panels were used and then compressed a bit to fill frame to the brim)
- Monster Bass Trap with Flex (panels) // size 120cm x 60cm x 16,7cm (it uses an airgap system - and I think the gap is in-between the panels, or at the back of it)

The designs can vary a bit of course, and this is basically the trade secret of the company that I won't question. As a rule of thumb (that you always read): 2" as general broadband absorber (so 5cm), and 4" to 6" as bass trap (10-15cm). (Super) Monster Traps can be thicker (20cm to 40cm, or 7,8-8" to 15") - but they definitely need less flow resistant material in order to be effective (as I said - I have a monster trap with 30cm deep frames, filled with 24-25cm thick material, being 2x10cm and 1x4cm plus 0,5cm to 1cm thick face-frames per side)

For general Broadband absorbers I created 12cm frames, and stuffed it with 10cm thick material at 7kPa, then mounted diagonally to the wall. The center distance to the corner is therefore 32cm. According to the calculator above, these would be the results:

Comparison "DIY" Monster Trap/Flex System and general 10cm Bass/Broadband Absorbers


This might not look "deep enough" frequency wise, but if all corners are treated, this will definitely add up, reduce standing waves/resonances, etc.

Now it's down to you what you do. My recommendation is to find an insulation supplier in your country and order directly. Worked for me in recent years.


If you're unsure, then go with 15cm deep panels, no air gap in between
See this calculation (again, notice the results with the kPa difference)



EDIT:

"KNAUF NATURBOARD FIT" density 30Kg/m3
...they come in 5 or 10 cm thickness. I have them available in my country (for about 14 euro per 6 boards pack - 10cm thick) 1000x600x100mm

If we look at the chart above (GearSlutz) that's about 6-7kPa.


Just to be sure, contact KNAUF or hit their page and ask/look for the "flow resistance". Then go by the calc sheets I provided. For me - 10cm thick material was enough for corner traps. But it's "more loose" than 5cm panels. Price difference is minimal as well.

[3ee]

On their website, for KNAUF NATURBOARD FIT, tech specs show an approximation but I'll ultimately contact Knauf for more precise info...

air flow resistance: ≥5 kPa.s/m2 ..so that's more or equal to about 5k

I'm thinking to build 4 , 30cm thick panel type "bass-trap" absorbers to be mounted more or less @ 45 degrees in the corner.

I'm playing with the calculator and looks like I'm achieving quite good -theoretical- results with a thickness around 300mm ... but I'll play some more

300mm thick.png

[Compyfox]

One major question you should ask yourself: "do I have the space to do that?"

30cm thick panels at 60cm width sure waste a lot of space.
So I'd actually do three types of builds:
1) angled like the EQacoustics one (so the corners have to be angled as well), ton of work without the right rools
2) block chunks
3) wedge chunks

Here is a Google link that shows various "chunk" designs".

A cool design IMO is something like this: block chunk with open sides
The material is fairly cheap, wrapping is simple as well and you can stack these things on top of each other. For a 30x30 chunk (though I do recommend 40x40 if the space allows it), you can use 120x60cm panels. So... 3 blocks of 40x40 and 3 stripes of 20x40 per rockwool slab. Assuming that you bought 5cm thick ones, and you want to fill 100cm "chunks", you need 5x 5cm slabs per block chunk. If you go with 10cm, you only need 2,5 slabs.

Build a 30x30 panel, and you have a bit more material to work with: 8x 30x30 - so at 100cm height and 5cm thick slabs, you need 2,5 slabs, and for 10cm thick slabs merely 1,5 slabs.

Usually, 10cm packs have 5 slabs. And 5cm packs have 7-8 slabs.

THIS... is down to experimentation!!!

But in general, this is a similar design to the HOFA one. And the more "surface", the more absorption. If you just need to treat the corners in general however, 20x20 to 40x40 should suffice. Whatever room you have at your disposal. I don't have that much - so no real chance for me to go super crazy (maybe in the future with different designs - but I need to find a way how to mount these things to the wall without tipping over or falling down). Actually, my corner absorbers (angled regular panels) to eat some space in the recording room. But it's better than not having any absorptive material at all.



So If you want to go the usual 10-15cm panel diagonally mounted, it won't waste as much space as 30cm thick panels, and you can get 5cm slabs or 10cm slabs. The advantage over the rectangular/block chunks, is that you have air holes "behind" the absorber panel.

Assuming your ceiling is 220cm height, you can use two frames per front corner.
With 5cm slabs at 10cm thick panels - that''s not even half a pack per corner. With 10cm slabs, you can cover both corners easily
With 5cm slabs at 15cm thick panels - that's about 1 pack per corner. And you still have slabs left over to build ceiling clouds


In case of ceiling clouds (leftover slabs):
I built super light ceiling clouds out of aluminum L brackets and two-component adhesive (see this similar concept). Then I wrapped the slabs in linen and simply let them sink into the frame. Easy/Lightweight solution - needs a bit of time until the glue between the aluminum brackets has fully cured however. Though I was happy that my rockwool slabs were fairly rigid - else they would have fallen down by now.

[3ee]

Sorry for the late reply, fell sick (even had nightmares with rockwoll ) and had to catch up with work but now I'm all better!

So, thanks again, change of plans for the better...

Finally, looks that I'm gonna build triangular corner traps... 4 traps of 120cm height
the only thing would be is that one side would be 60cm and the other 50cm but that doesn't bother me at all and have space for that, the longer 60cm length will be parallel to the wall I see in front...

50cm cause if I cut one piece 100cm in half
60cm cause it's the orig. lenght

the thickness is 10cm and there are 6 pieaces per pack

Fabric:

I studied quite a bit about fabrics lately, so in general, "acoustical" textiles are usually made from synthetic fiber (usually polyester cause it's flexible, doesn't change with temperature which can result in saggyness and the fiber types are diverse) , "open-weave" fabric and/or not too dense and the ultimate test would be to simply blow air through the material and feel that most will get through easily...

anyway, found a cool "new" material... and it's interesting cause it's not really open-weave (it's micro-fiber actually) yet claims it's specifically designed to let air pass though "100%" ... anyway, I have a friend that has some samples, so I'm very curious on this "miraculous" microfiber... will post my experiences in this thread.

here's the fiber just in case...
https://cameleontextil.com/coolpass-mes ... p-161.html

Coolpass is a highly advanced material that was designed to keep the body cool and dry at all times. This new type of polyester is a 100% breathable microfiber and ensures a better regulation of moisture. Clothing that uses the COOLPASS-technology will dry much quicker than other workwear and is highly suitable for wearing as bottom layer in the three-layer system.