Which is it Ben? A myth or not? Hint... it's not a myth, there are dozens of people that have measurements showing it.
That's a good suggestion Ben. When will you be starting to begin your posts with the fact that you have never heard a tapped horn and use an antique woofer with 2 mm xmax in open baffle as a subwoofer, and antique mains with dramatic engineering deficiencies and you don't trust simulation as a useful tool despite literally thousands of measurements that correspond almost exactly to sims when sim'ed and measured properly?
Please explain the measurements shown in the link I posted and the measurement shown by shredhead. The modal region is WAY higher in frequency than these subs are playing down to. There's no way to boost low single digit frequencies in a room without pressurization, which is room gain.
I don't know the guy that measured shredhead's graph so I can't personally vouch for it but I do know that the guy in the link I posted knows what he is doing and his measurement is not fiction.
Ben,
1)Contrasting viewpoints offer one a choice, the "audiophile" view is often uninformed as to the "why" things sound "bad", "good" or "fast" or any other of hundreds of subjective terms.
2) Different opinions again, although I prefer from a "green" standpoint to ride my electric motorcycle, which goes about 35 miles from 25 cents worth of electricity (or "no cost" electricity from my solar panels) the batteries used to provide that remarkable performance are still quite expensive, but the nearly 100% efficient (but very heavy by today's neodymium standards) 45 year old motor used was given to my brother (who gave it to me) for free. Unfortunately, the batteries required to power a car the weight of my Mustang up the mountains I live in and provide the 120 mile round trip that I frequently commute would cost about the same as the gas (at $4 per gallon) used for driving 125,000 miles using an ICE. The tech is there, but it is cost prohibitive for the average person.
I have heard, built, and measured subs with response so close to the original recorded or live sound source as to be virtually indistinguishable, so I differ from your opinion (not fact) that "we have no good technology for subs". That technology is affordable for a person of average income. We already have good alternatives to ICE and bad sounding subs, you not using or having heard or seen either does not change that fact.
3) Sealed or infinite baffle loudspeakers have long been accepted by the audiophile crowd, and (as been already pointed out in several posts) can provide earthquake like SPL down to 5-10 Hz, easily reproducing the sound of the largest and lowest pipe organ notes at considerably louder SPL than those blower driven sound producer devices.
4) The "other criteria" that tell "the rest of the story", such as phase, impulse, and distortion response are now as easy to measure as frequency response, but take considerably more education to understand and interpret.
5) That would be a stupid person, sims can help determine whether a cabinet design will produce a sound that one may like or dislike, but a sim does not make sound, as anyone that has ever used a simulation program would be well aware of.
Although the vast majority of the cabinets I have designed and built over the last 41 years were done without the aid of any simulation program, or even an electronic calculator, I do appreciate that programs like Hornresp and Akabak can provide simulations remarkably close to the measured phase, impulse, and frequency response of cabinets, provided the loudspeakers used and the cabinet "as built" accurately duplicates the parameters inputted to the program.
Art
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At a seminar Geddes was asked about room gain and he said that it doesn't exist. Take from that what you will.
I take that as an out of context quote.
Earl had nothing to contrary to say when I posted screen shots of my (single) home stereo sub, which rolls off at 40 Hz when measured near field, but has response extending flat below 20 Hz in the listening position when the two entrance doors to the room are open.
Contrary to the usual "sealed room cabin gain" thinking, the in room LF level is actually reduced when the doors (which have near soundproof sweeps on the bottom) are shut. That measurement was a surprise to me, I had assumed the opposite would have been the case.
That said, rooms can have such radically different LF response I tend to ignore the concept of "room gain", unless in reference to car or van sized "rooms".
Art
That's interesting. When Earl was asked about room gain at a small seminar he said it doesn't actually exist. Now the thing is I respect Earl's research and knowledge tremendously and know he knows what he's talking about with the way that waves propagate about a small listening room. So I wonder what mechanism one would use to describe what traditional room gain actually is?
Maybe room gain is really just resonances in a very large cabinet outside of the speaker? One could simulate a speaker in akabak and have the output radiator element simply couple into a very large box surrounding the smaller box. Then probe the sound pressure inside the larger box. There is no "gain" if you use the strict sense of the term in time dependent equations of energy transfer - such as those used for energy levels in a microwave traveling wave tube amp or laser. Gain means you will have emission greater than input. Here the room walls etc all absorb or act as sinks. No gain technically. But there is a room enhanced resonance of the pressure spectrum.
Hi Y'all,
Do 12" still count as small speakers?
In case you haven't noticed, in http://www.diyaudio.com/forums/subwoofers/160879-build-your-own-2x12-th-kraken-212-th-36.html Post #357 mordikai shows a link to a great subwoofer driver buy: JBL GTO1214 12" Single 4 ohm Grand Touring 1400W Car Subwoofer .
Take a simple dual driver MLTL, and build 4 of those. You should now have sufficient acoustic power to analyze the performance versus a single large sub. 🙂
And yes, here is the simulation @ 1 x Pi (driver cost $472.--) :
Regards,
Do 12" still count as small speakers?
In case you haven't noticed, in http://www.diyaudio.com/forums/subwoofers/160879-build-your-own-2x12-th-kraken-212-th-36.html Post #357 mordikai shows a link to a great subwoofer driver buy: JBL GTO1214 12" Single 4 ohm Grand Touring 1400W Car Subwoofer .
Take a simple dual driver MLTL, and build 4 of those. You should now have sufficient acoustic power to analyze the performance versus a single large sub. 🙂
And yes, here is the simulation @ 1 x Pi (driver cost $472.--) :
Regards,
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Traditionally, rooms have boundaries, boundaries increase LF output compared to free space or half space.
Modal response of a room is size and shape dependent, depending on where the sub(s) and listener(s) are located there may be gain or loss at varying frequencies
Art.
"Room gain" is one topic that is debated endlessly (and needlesssly) on this forum. Here's my grasp of it.
The problem is that "room gain" isn't a traditional engineering term but a pop description for something real but irrelevant (and I don't know the engineering term if there is one specific to it). Yes, anybody can use any words they please in any way these choose. But if they want to post coherently, they need to recognize common usage*.
In common usage, "room gain" is the phenomenon of pressure boost at low frequencies in a totally tightly sealed space (some small cars with no air vents might quality, if there are such vehicles). I don't think it applies to speakers with ports or OBs. Elsewhere I describe all the NECESSARY conditions for this kind of pressurization. In short, nobody's home has any "room gain" to speak of at any freq except near Baltimore and unless the room is made of concrete on all 6 sides and has no door or window.
There are ALL KINDS of phenomena that make a mic in one position seem to be picking up a surprising amount of bass as compared to that mic and speaker in your backyard.
Here's one that few people ever think of but I don't think anybody could be calling this "room gain." Every domestic room I can imagine absorbs more treble and little bass. So your speaker will sound bassier indoors as compared to your backyard, to a perfect anechoic chamber, or to a perfectly reverberant space.
Lots more acoustic reasons a mic in one location would pick up lots of bass in your room. Pity the loudspeaker forum doesn't include room acoustics sub-forum because good HiFi implementations depend on knowing how to address room acoustics before the glue is dry on your cabinets.
But please don't call it "room gain."
Ben
*I was tempted to say "educated usage" but that just doesn't sound right in the Democratic Republic of the Web. Steven Pinker's 2014 style manual is a valuable read - very flexible points of view. He's also chair of the Usage Panel of a major dictionary.
The problem is that "room gain" isn't a traditional engineering term but a pop description for something real but irrelevant (and I don't know the engineering term if there is one specific to it). Yes, anybody can use any words they please in any way these choose. But if they want to post coherently, they need to recognize common usage*.
In common usage, "room gain" is the phenomenon of pressure boost at low frequencies in a totally tightly sealed space (some small cars with no air vents might quality, if there are such vehicles). I don't think it applies to speakers with ports or OBs. Elsewhere I describe all the NECESSARY conditions for this kind of pressurization. In short, nobody's home has any "room gain" to speak of at any freq except near Baltimore and unless the room is made of concrete on all 6 sides and has no door or window.
There are ALL KINDS of phenomena that make a mic in one position seem to be picking up a surprising amount of bass as compared to that mic and speaker in your backyard.
Here's one that few people ever think of but I don't think anybody could be calling this "room gain." Every domestic room I can imagine absorbs more treble and little bass. So your speaker will sound bassier indoors as compared to your backyard, to a perfect anechoic chamber, or to a perfectly reverberant space.
Lots more acoustic reasons a mic in one location would pick up lots of bass in your room. Pity the loudspeaker forum doesn't include room acoustics sub-forum because good HiFi implementations depend on knowing how to address room acoustics before the glue is dry on your cabinets.
But please don't call it "room gain."
Ben
*I was tempted to say "educated usage" but that just doesn't sound right in the Democratic Republic of the Web. Steven Pinker's 2014 style manual is a valuable read - very flexible points of view. He's also chair of the Usage Panel of a major dictionary.
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Ben, common usage is to call the phenomenon "room gain". You've even called it room gain yourself if I'm not mistaken. Everyone calls it room gain and there's nothing wrong with that term. If you have a more proper scientific term let us know what it is.
While it may be true that a room and it's furnishings may absorb more treble than bass, the measurement I linked to stops at 90 hz. 90 hz is not treble. Even without eq the system is fairly flat at the listening position from 5 - 60 hz.
This is not some kind of measurement problem or room acoustics problem and it's not a high frequency absorbtion issue. I seriously doubt you even clicked my link, so please stop saying everyone is uneducated and has problems with their rooms and systems, or at least try to point out any specific problems that you see. A lot of these guys have a significant time and money investment in their education and equipment and they do know what they are doing.
While it may be true that a room and it's furnishings may absorb more treble than bass, the measurement I linked to stops at 90 hz. 90 hz is not treble. Even without eq the system is fairly flat at the listening position from 5 - 60 hz.
This is not some kind of measurement problem or room acoustics problem and it's not a high frequency absorbtion issue. I seriously doubt you even clicked my link, so please stop saying everyone is uneducated and has problems with their rooms and systems, or at least try to point out any specific problems that you see. A lot of these guys have a significant time and money investment in their education and equipment and they do know what they are doing.
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Hi bentoronto,
Post #111: "There are ALL KINDS of phenomena that make a mic in one position seem to be picking up a surprising amount of bass as compared to that mic and speaker in your backyard.
Here's one that few people ever think of but I don't think anybody could be calling this "room gain." Every domestic room I can imagine absorbs more treble and little bass. So your speaker will sound bassier indoors as compared to your backyard, to a perfect anechoic chamber, or to a perfectly reverberant space"
Low frequency sound waves pass quite readily through walls build with todays 2x4/plaster board construction, and some surfaces become reflective at high frequencies, even if they were absorptive through the midrange. Then there is the subject of the number of sofas in the room. So this could become a very difficult subject real easily.
The reason that outdoors a loudspeaker seems to produce a lot less bass, and a lot more highs (on axis) is probably due to dispersion. And in room you get that bouncing around stuff, that leads to low end reinforcement which some people like to call room gain, and which is very obiously not at all easily quantifiable. But at least it is measurable (even if it is not room gain 🙂 ).
Regards,
Post #111: "There are ALL KINDS of phenomena that make a mic in one position seem to be picking up a surprising amount of bass as compared to that mic and speaker in your backyard.
Here's one that few people ever think of but I don't think anybody could be calling this "room gain." Every domestic room I can imagine absorbs more treble and little bass. So your speaker will sound bassier indoors as compared to your backyard, to a perfect anechoic chamber, or to a perfectly reverberant space"
Low frequency sound waves pass quite readily through walls build with todays 2x4/plaster board construction, and some surfaces become reflective at high frequencies, even if they were absorptive through the midrange. Then there is the subject of the number of sofas in the room. So this could become a very difficult subject real easily.
The reason that outdoors a loudspeaker seems to produce a lot less bass, and a lot more highs (on axis) is probably due to dispersion. And in room you get that bouncing around stuff, that leads to low end reinforcement which some people like to call room gain, and which is very obiously not at all easily quantifiable. But at least it is measurable (even if it is not room gain 🙂 ).
Regards,
If you use WinISD to calculate the box frequency of a room 14'x14'x8' (~50,000 l) room with one 30" x 6'8" door (~1.4 m circular port, 0.1m long), you get 9 Hz. Below that frequency, the room looks like it is open to the rest of the space. Above that frequency, the mass of air in the doorway loads the opening, and you get some pressurization.
Think of the inside of the room as the inside of a bass reflex cabinet. The room does not need to be tightly sealed to have "room gain".
Marc
Think of the inside of the room as the inside of a bass reflex cabinet. The room does not need to be tightly sealed to have "room gain".
Marc
Ben, this is just not true. Like you said, it's a "pop" term not an engineering term but it is most certainly not irrelevant and if you had any experience with a good measurement rig you would know that. Room gain is a broad term that includes pressure vessel gain and boundary gain. At any rate, it usually starts affecting 20-30Hz down boosting at around 8dB/octave.
Refer to my example in this measurement which I just did this afternoon. It shows listening position, listening position with a window open and close mic (1 inch from driver). Notice how at frequencies 6-7Hz and 25Hz with the window open, it actually adds to the gain. I believe welter already brought up a similar point to this in post #106.
When you take a sub from outside and bring it into a roooom... you get ROOM... wait for it..... GAIN! It doesn't have to be any more confusing than that. It is a rising response from 20-30Hz to DC. That's what we are referring to here. I promise you it is not something that we are making up to deceive fellow DIY'ers. Like just a guy already brought up, there have been hundreds of measurements posted online for years now from people with measurement rigs who have established this as fact.
On the other hand I am sure that there are plenty of people with subs out there that have no idea what this means because they have a signal chain that rolls off drastically starting at 20Hz, combined with a measurement rig that does the same thing and by the time their sub reaches 28Hz, it's already down 3-5dB and falling like a sack of potatoes.
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I like simple explanations.
thank you.
What happens in the two octaves from 4.5Hz to 18Hz?
More simple explanations would be appreciated.
I have seen a few papers and many anecdotes stating <<6dB/octave and usually quoting ~3dB/octave.
Is there science on why these very different numbers are so far apart?
Theoretically, "room gain" is simple. First, set some rules.
- The "room" is sealed and rigid.
- All frequencies are assumed to be below the lowest "modal" or resonant frequecy of the room.
Under the above rules, SPL is simply the difference in air pressure in the room between the cone being "in" and the cone being "out". It can be calculated directly as the ratio between the volume of the room and the swept volume of the speaker - the amount of air it displaces. Therefore, a constant cone excursion results in a constant SPL, regardless of frequency. The attached Excel spreadsheet can calculate the theoretical SPL.
So where does the rising SPL as the frequency drops come from? Remember that in free space, to maintain a constant SPL as the frequency drops the cone displacement has to increase: 4x the excursion if the frequency halves. Under the above "in room" rules, 4x the excursion results in 12 dB more SPL. So a speaker with a flat free-air response will exhibit a rising response in a room.
Back to reality... real rooms aren't sealed and rigid. And they often have Helmholtz-style resonances at very low frequencies. So the amount of gain achievable may vary from almost none to quite a lot at some frequencies. There's also no hard and fast rule at what frequency it starts to become noticeable, beyond that in general the larger the room the lower the frequency.
In summary, "room gain" (what I call pressurisation SPL to separate it from above-modal SPL) is real, but don't count on it.
- The "room" is sealed and rigid.
- All frequencies are assumed to be below the lowest "modal" or resonant frequecy of the room.
Under the above rules, SPL is simply the difference in air pressure in the room between the cone being "in" and the cone being "out". It can be calculated directly as the ratio between the volume of the room and the swept volume of the speaker - the amount of air it displaces. Therefore, a constant cone excursion results in a constant SPL, regardless of frequency. The attached Excel spreadsheet can calculate the theoretical SPL.
So where does the rising SPL as the frequency drops come from? Remember that in free space, to maintain a constant SPL as the frequency drops the cone displacement has to increase: 4x the excursion if the frequency halves. Under the above "in room" rules, 4x the excursion results in 12 dB more SPL. So a speaker with a flat free-air response will exhibit a rising response in a room.
Back to reality... real rooms aren't sealed and rigid. And they often have Helmholtz-style resonances at very low frequencies. So the amount of gain achievable may vary from almost none to quite a lot at some frequencies. There's also no hard and fast rule at what frequency it starts to become noticeable, beyond that in general the larger the room the lower the frequency.
In summary, "room gain" (what I call pressurisation SPL to separate it from above-modal SPL) is real, but don't count on it.
It depends mainly on the size of the room, how much transmission loss there is (due to materials in construction) and to a lesser degree, the dimensions and layout of the room. Of course a stick built drywall room is going to have more loss than a concrete bunker so probably it will have less room gain. I learned from Bossobass that for most rooms it is ~8dB/octave. He has years of measurement experience with the highest end sub drivers, signal chains and measurement rigs measuring in room response.
You can predict certain peaks/valleys in frequency response based on room dimensions but there are too many variables to accurately guess exactly what a sub will measure like in a particular room.
I wish I had a simple explanation for you Andrew but like a lot of science, it isn't a simple subject and like I said in my previous post, not everyone has a system even capable of extension into the single digits. There are a lot of people who don't take into account their signal chain's combined rolloffs. You have to add the rolloff of your player (if sending analog out), AVR, EQ (if applicable), amplifier and subwoofer. If your system has a combined low end rolloff starting at -3dB @25Hz falling into a 4th order (or in many cases greater) dive bomb you will not notice there is any room gain at all from your measurements. I believe this is one reason for all of the conflicting information floating around about the effects of room gain.
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Don,
thanks for the excel-sheet, but didn't you make a little mistake in the unit of the speaker-area?
In the spread-sheet is mentioned mm2 but I think it ought to be cm2... It won't affect the formulea in the sheet however... 😎
Cheers,
Edwin