Auralex Acoustics Lenrd Bass Traps Charcoal 4

Bought a pack of these because of space reasons into an already treated stereo & home cinema environment. I have some very special corners by the ceiling, which should be treated in the bass range but the space is very limited so anything bigger or heavier than the LENRD was out of the question. Anyway, I also measured its performance in places where other bigger products could be placed as well for comparison.

As it is a foam product around 25kg/m3 density with some zig-zag facing the room the biggest issue is that it simply does not have enough depth to reach the low ends. It does not mean that there is no effect below 100Hz, but to have a real impact you should place a lot of them into the room. The effect of 4 pieces (a pack) is measurable down to 50Hz (rather in the time domain and not in the frequency domain and still very subtle - but there it is anyway) but it is not nearly enough to fix low-end modes.

In addition, as this is a foam product without any wooden panels on it, if you put too many into the room, you can easily kill the highs and then the mid-range as well - and still not there in terms of controlling the bass. In my case with unclever placing with just 4 of these, I could easily remove 50ms reverberation time in the 500-2000Hz range, which is a very serious loss for an already treated room.

Pros: small and light, easy to install, official performance is available on the manufacturer's website, so you can plan before buying.

Cons: very expensive for a simple foam, very subtle effect below 100Hz, absorption of mids and highs are not limited in any way, placing too many into a room is not a good idea as there is no balance in low-mid-high absorption.

Verdict: As it is rather expensive product, I would only recommend it if you know what you are doing - and can deal with the consequences. If you do not plan and rather go for the trial and error route, well you had better choose a less expensive foam for that.

I got a pack of 4 placed in my studio and I'm pretty happy with the result overall, however I've got a bunch of other (partially self-made) absorbers placed in the room, so it's hard to tell how much of a difference they make. I'd suggest buying one pack and try them yourself before you buy a second pack, due to the high price.
They were a bit smelly when I got them, so they spent about 3 months in another room - didn't have the studio by that time yet, so I could afford the wait - now I don't smell anything on them anymore.
If you know what you're doing and where to place them, they might be a good addition to the overall audio quality in your room.

One last thing, don't waste your money on double-sided glue tape, I spent about 30 bucks just to get one hanging on the ceiling/wall corner, which as you guess wasn't worth it. There's glue available here at Thomann.de, I haven't tried that one yet since I got another from a friend, but I think glue should be much easier/cheaper for fitting them on the walls.