See www.realtraps.com Lots of data there.
Some get there traps tested at independent third party laboratories - such as GIK. This provides conclusive evidence of their effectiveness - how they work in your specific room is of course highly dependent on your specific issues and placement.
Large thick broadband corner absorbers are the most sensible approach to bass trapping, IMHO. (Fibreglass or rock wool works well but appropriate density foam can be good too....size does matter in acoustic absorption)
Read everything you can on the www.Realtraps.com website. They give you the best information with wonderfully comprehensive details.
FYI: Foam is not all that effective as a bass trap even if the website selling it says so. Compressed fiberglass or bonded acoustical cotton are leagues better down load and across the board.
The ones in the corners.
Depends on the frequencies you want to trap. Although I'm skeptical of their product claims to go as deep as they state, I'm in no position to argue. The methods of measuring sabines for an individual trap have little to do with a typical listening position or overall effectiveness. It might be fun to have a shootout between the brands with a single microphone in the same room. Should the constraints be dollars or square footage? Would it be relevant? Probably not. It wouldn't be your room and your speakers.
The science of these is not complex, often misunderstood and, sometimes, misrepresented. What it comes down to is addressing your unique situation, which is the probably the least understood. However, no matter which brand or type, most who have just taken a stab at it have been impressed with almost everything, which seems to indicate it's all worthwhile.
Thanks for all the responses thus far. I have seen the data on the Real Traps and other websites. It's difficult for me to view the data as objective since I have no direct knowlege of the subject and the results support the product being advertised. Asthetics is important. Interestingly, I just had my room professionally acoustically treated. The focus was on the upper frequencies. The reason for asking this question is just in case this treatment leaves any low frequency issues unresolved.
As an aside, I enjoy your well thought out responses to many questions on this forum. Am I correct to assume that using corner traps, such as ASC tube traps, is virtually always likely to improve bass response? One nearly always sees them in every high end store/room/show/ etc. in all 4 corners. I have some ASC traps already, and aesthetically these will probably be the best fit for my room.
I found this comparison of 3 different traps and a lot of info where I found the link.
The results are so uniform and illogical, it only goes to show the flaw of the test. The microphone was in the room's 100 Hz null. Perhaps, the best trap actually reduced the null and had the least measured absorption. I can't see any conclusion from this test.
I have owned many of the above products.. The Foam factory stuff is IDENTICAL if not making the Lenrd bass traps for Auralex..
However as mentioned, and some contended above.... My verdict is FOAM is crappy for real effect, Don't believe the marketing, because its simple, Foam is more effective than NOTHING AT ALL... But thats the point most will deal with foam traps and believe something worked, they are very good for Echo and bringing down noise floor, and for some hearing this is an "Effect" but Bass if you want to truly effect it the Foam corner traps are about the worst product for it. GIK tri traps are probably the most effective as well as cost effective product, and unfortunately all else are way too much money for the cylinder types etc..., and they should not be.
This is based on listening and going thru many of these products by themselves and in combination, at one point I had as many as like 30, 2 foot lenrd and foam factory bass traps... Got fed up as they would only be semi effective in MANY used, which also starts to kill your soundstage being overdamped...
Then tried the new GIK trip traps, Just 2 of them were 10 times as effetive, and they were no installation needed, and this was with nothing else in the room, I pulled down everything else.
As an aside, I enjoy your well thought out responses to many questions on this forum. Am I correct to assume that using corner traps, such as ASC tube traps, is virtually always likely to improve bass response?
Yes, for sure! Sorry I missed your question. It is extremely rare to have too much bass absorption. These are broadband absorbers and NOT "tuned tube" traps (tuned helmholtz resonators to a specific frequency - like your beer bottle). They appear similar to other broadband absorbers in the way they function - so you can place many of them in a room without fear.