John Sayers' Recording Studio Design Forum Archive

Scott R. Foster wrote:Hi John:

What does a bass trap do?

it absorbs the low frequencies at the high SPLs typically generated in a control room.

John:

I know you design and build some pretty spiffy stuff, but I think you are getting a bit over the top to claim title to a well known and long used generic word for absorption systems that work on low frequencies.

Are you are suggesting a mineral fiber panel wrapped in fabric and mounted in a corner will not serve precisely the function you use to define what a bass trap is? If so, I beg to differ.

What about a mineral fiber panel in a steel frame, or an acoustic foam wedge, or a tuned and ported vessel with a mineral fiber lining of a dimension such that it is tuned to a bass note?

Aren't all these contructs also "bass traps"?

Or, does a "bass trap" in your semantic universe require a "fancy" bit of timber hung on a string in a secret chamber above the ceiling to merit the noble title? [just teasin' ya]

Somehow I thought that's what you'd say Scott .

look, maybe I'm old fashioned but to me for a product to be called a bass trap I should be able to stick it on the wall and it absorb bass, not in the corner specifically. A straight panel absorber will absorb bass, but it's called a panel absorber, not a trap and it's design goes back over 50 years..

The term Bass Trap originated with the dead studio construction of the 70s and it referred to a hanging trap system as invented and utilised by Tom Hidley of Eastlake Audio where he was trying to contain the extreme SPLs reached by the 70s rock bands where existing acoustic treatment of the time, aka BBC, couldn't cut it.

the broadband effect of these traps gives you low end response and reverb times like these pics below

If you compare your absorption peaks to these results you will plainly see the difference between a Bass Trap and a piece of 703 hanging across a corner.

cheers
john

John,

Can you show me comparable threads where you responded comparable against the use of the word "Bass Trap".
Checking Google for "Bass Trap" gives me 75,500 hits.
I haven't checked them, but I assume only extremely tiny fraction will relate to Tom Hidley and the hanger principle. A wild non-checked guess: <= 0.5%?

The notions "Bass Trap" and "bass trapping" has became a generic notion for trapping/absorbing bass.
A Google check about Panel Traps also delivers numerous hits (couldn't split them to correct number of hits since it seems to be used for other things too).

Is this all about semantics?

John Sayers wrote: A straight panel absorber will absorb bass, but it's called a panel absorber

Definition used by the Arizona State University http://www.asu.edu :

http://www.asu.edu/hc/electrics/Sound_Terms/sound_terms.html wrote:diaphragmatic absorber: A flexible panel mounted over an air space that resonates at a frequency (or frequencies) determined by the stiffness of the panel and the size of the air space. Also called bass trap.

You certainly can point to numerous comparable messages of you, where you disputed the same with Ethan where Real Traps covers the whole company under the name Traps.
And his DIY Panel absorbers are referred to as Panel Traps as well.

But I'm really glad you point to this resonant peak in the absorption as indeed one of the strange things related to corner absorption.
That problem or question mark, I discuss alread for 5 years on the net.

But you know yourself VERY well, that you can not relate ANYTHING from your room entered response measurements with this absorption behavior of that device.
The peaks and dips in RT and Room response (which is the result of a complete room, not one single device of series of) point to much larger anomalies than the difference in absorption shown by those measurements.

In a strict diffuse field a difference of - 3 dB should point to a difference in + 100% absorption (a doubling). The anomalies in your room response are larger. And this piek does not increase absorption with 100%, far from.
I know this comparison is nonsense, but so do you.

What I see happening here is that you attack a company on semantics, which delivers a "most to core stripped" piece of acoustic device, giving honest information about the content of the device, meaning that DIYers can compare such a DIY solution with others.

The original post in this very thread starts here with a guy wondering:

• "do I have to replace my simple devices by special designed ones, which people say are much better".

The company who delivered those DIY bags, proves with measurements that this DIY solution is FAR from inferior versus the "SPECIAL DESIGNED TRAPS".

Shouldn't it be nice that the Forum should welcome such information, whether people buy from that company or not?

That company delivers that bag on its own for a low price for semi-DIY purposes, but you even don't need to buy it, and use the info as a 100% DIY solution. NO magic involved, with references to vague mysterious membranes and expensive high densities.

But I repeat, I'm glad you noticed and discussed that resonant absorption peak, which is typical for the principle. I possibly will quote you on that in the future.

Eric - I said - maybe I'm old fashioned. I was just pointing out what I mean by the term Bass Trap - you are welcome to use the term any way you like. I checked the Arizona University chart and they do say a diaphragmatic absorber is a bass trap. Mind you, I clicked on the other links and they don't say much else - it's the only page in their sound area which appears to be part of a lighting project of some kind - I wonder where they copied that list from.

So what we have here is a diaphragmatic absorber is a bass trap, a construction like I refered to is a bass trap and a piece of 703 across a corner is a bass trap.

Doesn't appear very scientific to me, but hey - you are the scientist.

"do I have to replace my simple devices by special designed ones, which people say are much better".
The company who delivered those DIY bags, proves with measurements that this DIY solution is FAR from inferior versus the "SPECIAL DESIGNED TRAPS".

I suppose it's what you call special design traps. I showed what I call a special design trap and I believe it's superior to the DIY version. If you believe you can get a room reverb response like I showed, note the top end verbtime compared to the low end, with DIY cloth bag Traps - go for it.

cheers
john

John,

I don't discuss whether the use of the word Bass Traps is right or wrong,

My related document uploaded here by you shows, that I called those things "diagonal absorption" when I measured them. Is that the correct term? I've no idea. It was just a logical term for me to distinguish the principle from my other measurements.
For me, even "corner absorption" wasn't that evident, since I measured also flat applications in corners, also showing a specific behavior.
But now people seem to understand "corner absorption" almost automatically as this "diagonal absorption" (... straddling the corners).

It's the studio world itself who uses the name "Bass Traps" for anything specifically used to trap or absorb bass. Hence they link it more functionally.
Here (locally in my surroundings) I still refer to "diagonal absorption" and also "corner absorption" (term I also use on the net), since all my old data and docs are using these notions. On the net I also use bass traps, not because the notion should be right or wrong, but because the studio world itself made it a generic term (including here at the Forum), which Google proves beyond any doubt.

I don't refer to SPECIAL DESIGNS with all the magic involved, people do, triggered by commercial interests pushing that through.
My use of the notion here is derived from the related uncertainties expressed by the original poster.
But you knew exactly in which context I used all this.

I humbly admire real developments and designs as the one you showed, but I can't accept your close to systematic degeneration of corner absorption as the logical path to go, known by anyone for ages, knowing the surprise of labs when they see their first related measurements and how Dr. Peter D'Antonio and Prof. Dr. Trevor Cox referred to corner behavior and absorption in the most recent and most extensive $ 175 book designated to diffusion and absorption and related devices (Acoustic Diffusers and Absorbers; Theory, Design and Application - 2004).
I also remember my related discussions with a Prof. specialized in Room and Building acoustics, where an acoustic lab assistant (all graduated academics) was involved trying to find mathematical relations to explain this behavior.
BTW: Also RPG managed by Dr. Peter D'Antonio uses the notion Bass Trap for several types of devices, none related to Hidley and hangers.

And to be honest, if these measurements entered by Ready Acoustics are confirmed by an official report, then it proves that the "ALSO SO LOGICAL" higher density advised anywhere as an axiom is wrong or at least EXTREMELY questionable.
And that advice has cost MANY people lots of money already.

I'm not comparing commercial products here, just the principle.
Because I gladly admit that GIK delivers commercial products with very high density on very interesting prices, compared to other products.

I fought and/or questioned this axiom for years also, but it gives me the bad name, since I'm not a populist.
But I also know that there are people who do read, analyze and see.

I hope I will not help start any flame wars here... But this is as good a place as any to ask this question, since Ethan, Glenn, John and Scott are all here...

I'm looking for some acoustic treatment for a home studio, but it has to be very portable, so any kind of acoustic pannels make sense...

There is a big difference in price betwen the RealTraps, GIK and ReadyTraps... Let's just say i'm a buyer and want to know the difference betwen them... As I'm shure, any potential buyer of absorbers...

With my very limited knowladge in acoustics, as far as I understand, The main difference is that ReadyTraps don't have a membrane. So they absorb higher freqs and could make a room more dead sounding.

Am I correct?

I don't think any of the panels are tuned (or they wouldn't be universally "fitting" to all the rooms)(I could be wrong... please correct me if I am...)

I'm not after any business secrets here, but what do you think makes your product outstanding? If you would just say it in words and not use graphs, since one of the three manufacturers clearly disagrees with the other two when it comes to testing...

Soulfood

Reasonable question, but I'll stay out of it.
I will in the future compare those thing on a site, where I will compare them analytically.
Too much personal things are involved here.

But you'll get your answer here. Hope you can figure it out.

John:

OMG Semantic Debate - I Surrender!

FWIW I'll grant you the right to hold strong beliefs on semantics in this venue - you certainly have earned the juice to have firm opinions on the correct jargon for the field. Also FWIW, I have no aspiration in that regard. You can be in charge of the naming of names as far as I am concerned - to the extent any choices arise.

To that end, IMO, you need to find a different target for fighting the good fight to get the "right" name into common usage. This horse done left the barn.

I would [if I thought it mattered] respectfully disagree with the notion that constructs which are not explicitly designed to use the tuned resonance of a wooden panel to absorb LF shouldn't be called bass traps - as that strikes me as counter intuitive to the simple meaning of the words "bass" and "trap"and the idea that devices that grab bass and don't let it go fit the bill.

But let's face it - it doesn't matter - history and the vox populi have obviously surpassed your view point. Dirty as it may be, the deed is done.

The term "bass trap" covers a broad range in common usage no matter what you or I think. Thus, IMO, to be well understood by a broad audience you need to use a more specific term for that which you hold to be a "real" bass trap - otherwise I fear others are going to assume a larger set of items than you wish to describe.

You have lots of interesting things to say on the topic.. it'd be a shame if so many misunderstood you.

My $0.02

My over-simplified view on this discussion: the term "bass trap" should almost be abolished, because it's been bandied about to the point that it means NOTHING any more. Similar to the term "vehicle" when referring to transportation - if you need to move large quantities or weights of material, a VW Jetta isn't your "vehicle" - but a van or semi-truck might be. Likewise, if you want to get there fast (and the roads are good) then forget the van, go for a Lamborghini or Porsche or similar.

To my mind, "bass trap" SHOULD mean "only traps BASS", not "traps everything". True, a BROADBAND trap such as a corner absorber, or even 4" MW spaced off a wall, will ALSO trap bass; but it will, in the process, further lower the RT in OTHER frequency bands; this may or may NOT be a good thing.

You can build a "low mid trap" using either helmholtz or resonant panel methods, and including enough absorbent inside to broaden the response, or you can build a "surgical" trap by leaving out most or all the inner absorbent (careful about adding resonances BACK to the room though) - this might be necessary if you've NOT been careful about room ratios, etc - when you end up with more than one mode contributing to an excess of one specific frequency needing to be reduced. This is not for the faint of heart, since it would require knowing WHERE to put the trap as well as how to build, tune, etc.

I think we need to address the (mostly ignored) concept of EVEN reverb times more than we do; it seems to me that most posters on these forums either "get there" ACCIDENTALLY, or not at all. And a room with wildly differing reverb times at different frequencies is NOT a room you want to listen to music in; it's ESPECIALLY not one you should MAKE or RECORD music in.

In one of Newell's books (probably more than one) he stresses the point that an unbalanced room isn't a place to make multi-track recordings, because every track you add to the mix from such a room, ALSO adds that IMBALANCE and after a few such tracks you can't even BEGIN to "fix it in the mix" - to me that's a powerful argument for choosing proper dimensions in the first place, and then treating any "leftovers" once the room's built and tested, so you have a NEUTRAL environment to record in/mix in.

Speaking of which, we also don't (usually) stress the differing RT requirements between CR and recording spaces; I know that smaller rooms (including a lot of CR's) can't officially HAVE a real RT60, but a CR should still be deader than almost all recording spaces or you'll think you have enough reverb in the mix when it's really your listening space talking...

As a "responsibility" thing, I'd like to see more reference to BROADBAND trap/absorption when talking about non-resonant traps; it just seems more honest and USEFUL when trying for a balanced RT environment. I think we've ALL been guilty of too much "genericism" here, so that most people who are just "discovering" acoustics call any and ALL acoustic treatments a "bass trap".

My idea of a SIMPLE but USEFUL method of constructing usable recording space (at least partially due to Eric's help in slightly understanding multi-leaf problems) is to

1 - figure out how loud YOU are, and how loud your outside ENVIRONMENT is, and build your containment to be at least a few dB BETTER than you ever think you'll need, at ALL frequencies. This ain't usually cheap, or even possible, but it's the GOAL. One main reason for building BETTER than you think you need, is that virtually ANY acoustic treatment you add inside will WEAKEN the containment due to multi-leaf problems; in a way, even broadband absorption can do this because you will often play LOUDER when the room's more balanced, so more gets OUT.

1a - don't build squares, or cubes - and whether you build a full RFZ environment for Stereo mixes or a more absorbed surround CR, at least splay walls/ceilings enough so that you don't have to use inordinate amounts of broadband absorption just to tame flutter - just because you can't HEAR flutter when you clap in a room, doesn't mean it's GONE - it just means that the components are likely too FAST for your ear to discern between your CLAP and the flutter. Your multi-track recordings, however, WILL add these artifacts and they WILL color your mix.

Choose average dimensions that give as balanced modal responses as possible; not everyone believes in Bonello but I think it's a good start. Messr's Bolt, Sepmeyer, etc, were pioneers but they didn't have computers; I believe there are far more "golden" room ratios than the ones they calculated. In fact, if you use Jeff Szymanski's VERY helpful sheet ModesV2, found in the file section at Studiotips, you can find more balanced combinations of dimensions than some of the well-known (1:1.6:2.33, for example) ratios. Point being, you do NOT want to choose BAD ratios, whether you go with Bolt, Sepmeyer, Louden, Bonello, or whatever.

I equate the above with its electronic counterpart - "The best way to get rid of noise, is to not generate it in the first place" - acoustically, this might translate to "the best way to treat a room, is to size it so it doesn't NEED (as much) treatment"...

Once the room is built (hopefully with enough foresight to make it a bit larger than you think you'll need), it's time for testing; if you've done enough homework in the earlier stages, your main treatment needs might be limited to balancing out the reverb times - and this brings me right back to my objection to the GENERIC term, "bass trap". If we continue to call everything that ALSO traps bass, instead of ONLY traps bass, a "bass trap", we do any who ask for advice a DIS-SERVICE.

Let's say that we have this room, and it's down to only needing a bit of low end at one or two specific frequencies, reduced by a few dB; the top end is already "dull" enough, the mids are at the same/close RT, and we then add 3 or 4 fully absorptive "bass" traps; now, we just helped the bottom (probably) but now the mids and highs are too dead.

If we aren't aware that this (actually BROADBAND) "bass" trap is really absorbing a MUCH WIDER band than we were led to believe, we (meaning the person I referred to earlier, new to acoustics) will probably sit there wondering what happened to our sound, and why "that idiot" told me his products would SOLVE my problems when they really just CHANGED my problems...

At this point, I doubt seriously whether my ramblings could be compared to a logical thought process but I wanted to voice my concerns - I absolutely HATE reading posts from people who've taken the advice on these forums only to be frustrated and unhappy with the results, and I think this "genericism" in terms is largely responsible for that.

Now I gotta go fix the brakes on my van (wife needed the car for some "hippie fair" and I work nights tonight) - there are times when I wish I didn't know shit about anything other than our favorite subject, so I wouldn't even be TEMPTED to do all this other crap; still, I guess it's better to be somewhat versatile in life. (maybe )

Just a "reality" check from one who prefers to keep his $.02 SIMPLE... Steve

SoulFood wrote:I'm looking for some acoustic treatment for a home studio, but it has to be very portable, so any kind of acoustic pannels make sense...

Buy or make something light weight that is easy to hang or place to maximize portability. There are significant differences between products as to these attributes. For example the RT424 weighs less than 10 lbs.

With my very limited knowladge in acoustics, as far as I understand, The main difference is that ReadyTraps don't have a membrane. So they absorb higher freqs and could make a room more dead sounding.

Am I correct?

No!

The whole point of my original post here was to explode the myth purported by Glenn that magical qualities arise in "membraned" panels such as the MiniTrap with the result that HF is not absorbed.

As I demonstrated quite clearly - the HF absorption curves of the RT424 [a fabric wrapped 703 panel an analog of which can readily by be made by a DIY user] and the MiniTrap are stunningly similar - in fact in large part, they are precisely the same!

Don't be misled by attempts to divert the discussion to uncertainties of low frequency measurement... the original false proposition, and your question are about high frequency - and I assure the % uncertain measurements are miniscule from both labs in these frequency bands [less than 3% on average from 500 to 5,000 Hz for the RAL data - you can see these numbers yourself once I get the final reports posted].

I don't think any of the panels are tuned (or they wouldn't be universally "fitting" to all the rooms)(I could be wrong... please correct me if I am...)

I'm not after any business secrets here, but what do you think makes your product outstanding? If you would just say it in words and not use graphs, since one of the three manufacturers clearly disagrees with the other two when it comes to testing.

If you want to modify a panel with a membrane or scrim to fit a need in a particular room - it aint "rocket surgery". Software like Room EQ Wizard or ETF and a measurement microphone will suffice to validate the results you are achieving, and adding a scrim or membrane to a mineral fiber panel is trivial [spray adhesive around the edge of the face and add a sheet of 4 to 6 mil poly for example].

There are no significant secrets to adding scrims and membrane to mineral fiber panels. People have done it for years [often for good reasons - but sometimes for dumb ones]. If you have a particular tuning need, I suggest you explain it in a forum such as this, and perhaps Eric or some other person who has made 100's of such devices and is therefore highly skilled in the art of making srimmed / membraned MF membrane panels for specific uses will offer a suggestion on a material to try for the particular need encountered.

That said, I can't imagine why you would want to tune panels meant to be portaged around to different rooms - but your circumstances may allow that idea to makes sense.

Finally, I doubt you will have more luck getting a consensus with words than you have had with graphs from competitive producers of products intended for the same uses. I have tried to restrain myself to correcting what I feel are false descriptions of our products and there suitability - I didn't come here to run a commercial - but I freely admit a prejudice. FWIW, I like our products [hell I helped design them], I know what they will do, I know they are light weight, sharp looking, an excellent value in the current market, and easy to mount and demount. That is not to say you have no other valid choices, merely that I earnestly believe our products are amongst the categories worthy of your consideration.

I suggest you resolve to develop your own judgments - let your intellect and your wallet be your guide.

Good Luck!

PS: Perhaps direct communication of your needs to the sundry manufacturers would best suit your desire to obtain information versus "start a flame war"?

I will not even try to contribute to this thread... It's mostly way over my head...

But what I thought this thread would be great for is getting opinions of different experts explaining their products under the supervision of moderators and anyone interested in the subject. Its much harder to sell "snake oil cables" if you have alternative opinions... And that's a good thing for consumers...

I don't expect to find "the best product out there" or anything like that. I just feel this is a chance for people to learn more about what they're buying or building so they can make an educated decision about their preferences...

And thank you for your input Knightfly! It's really useful to remind forum leechers that even reverb is what we're after... The question I have right now is, how much high freq absorbtion does a room typically need... Come to think of it... The questions in my head are becoming a little off-topic... I'll save them for later

SF,

> what do you think makes your product outstanding? <

I agree with Scott that this is the stuff that starts flame wars. And I know that's not your intent!

I will be happy to tell you exactly what distinguishes RealTraps from other manufacturers, but a public forum is not the most appropriate place. In fact, all of that information is already all over our web site. It's on the main page, the FAQ page, our extensive list of high-profile customers, as well as made clear by all the tutorial articles and videos on our site.

So if you're seriously considering buying treatment (not just asking hypothetically), you're most welcome to email me from our site and I'll be glad to answer any further questions.

> It's really useful to remind forum leechers that even reverb is what we're after <

Yes, that too. Very much so.

--Ethan

I am 100% with Ethan, if you would like to know more about someones product I would contact them through email.
I edited this to not start a flame war.
Glenn

"but I freely admit a prejudice. FWIW, I like our products [hell I helped design them], "


You did?