I rather think a degree in Physics would be enough studying of waves and their interactions with boundaries.
The things you're suggesting directly contradict my measurements, experience, and understanding of the underlying mechanics. Forgive me, then, if I'm a little slow to take your word as gospel.
Chris
The things you're suggesting directly contradict my measurements, experience, and understanding of the underlying mechanics. Forgive me, then, if I'm a little slow to take your word as gospel.
Chris
Hi Chris,
Good, you have an understanding.
I have specific experience in the area and studied the interaction with room volume and low frequency response. I'm not wrong. I did practice in this actual field. Very early as a matter of fact.
Yes, you can pressurise any vessel. Headphones work as coupled pistons. Totally different than an open environment. Humans also have a log response to SPL as you well know. But perceiving sound and actually getting it flat with good dynamics is a different experience. The speaker system is a high pass filter at low frequencies. The room a sort of helmholtz resonator. The characteristic of which depends on a lot of factors.
At home I have a large listening room. However the very low bass is apparent in other areas and does not exist in that room. An informal, empirical example of what I'm talking about. WHy would you suggest that is? I know the answer by the way.
I do respect your experience, most here just read junk and parrot it back. However, I am 63 years old and have been teaching / training for decades and I simply have run out of patience repeating the same experience with people. I have university training in Electronics Communications, and a test and measurement background as well. I have no ego invested in this at all. My professions pounded that flat early on!
-Chris
Good, you have an understanding.
I have specific experience in the area and studied the interaction with room volume and low frequency response. I'm not wrong. I did practice in this actual field. Very early as a matter of fact.
Yes, you can pressurise any vessel. Headphones work as coupled pistons. Totally different than an open environment. Humans also have a log response to SPL as you well know. But perceiving sound and actually getting it flat with good dynamics is a different experience. The speaker system is a high pass filter at low frequencies. The room a sort of helmholtz resonator. The characteristic of which depends on a lot of factors.
At home I have a large listening room. However the very low bass is apparent in other areas and does not exist in that room. An informal, empirical example of what I'm talking about. WHy would you suggest that is? I know the answer by the way.
I do respect your experience, most here just read junk and parrot it back. However, I am 63 years old and have been teaching / training for decades and I simply have run out of patience repeating the same experience with people. I have university training in Electronics Communications, and a test and measurement background as well. I have no ego invested in this at all. My professions pounded that flat early on!
-Chris
No sense in beating a deaf horse, Chris.
To further your point, it's when I go outside, that I actually hear the lowest octaves out of my Kef 105s; on the front lawn.
To further your point, it's when I go outside, that I actually hear the lowest octaves out of my Kef 105s; on the front lawn.
Not sure if this helps or hinders, but I use two BMS 18n862 sealed subwoofers and other than one PEQ around 34 Hz, this is the response in room at the seating position. The FS is 20 Hz on these driver with 19mm Xmax. The room is 5.1x5.0m (annoyingly nearly square, 34 Hz resonance) and 2.65m high, I set the low pass at around 38 Hz
The cabinet I designed and made and ensured it was very rigid and a suitable volume
This is a single cabinet, I now have two and with a very mile 2db LS filter at 20 Hz I am pretty flat to 5Hz
The cabinet I designed and made and ensured it was very rigid and a suitable volume
This is a single cabinet, I now have two and with a very mile 2db LS filter at 20 Hz I am pretty flat to 5Hz
I am very surprised to see decent mic response down as low as that indicates, but I do see a 7 dB drop. Low frequency measurements are very fdifficult to do in anicolic chambers, next to impossiible in uncontrolled locations.
I know many mics and speaker systems claim response that low but it is rarely encountered in the real world. I would be highly suspicious of this response curve, not because I don't believe you but more because of the difficulty of getting valid readings that low. I have no doubt that you have thundering low bass response, but I will bet you that you have deeper bass outside the room and in other areas of the house.
Normally the diagonal of the room represents 1/2 the wavelength of the lowest frequency the room will supprt.
I know many mics and speaker systems claim response that low but it is rarely encountered in the real world. I would be highly suspicious of this response curve, not because I don't believe you but more because of the difficulty of getting valid readings that low. I have no doubt that you have thundering low bass response, but I will bet you that you have deeper bass outside the room and in other areas of the house.
Normally the diagonal of the room represents 1/2 the wavelength of the lowest frequency the room will supprt.
Apparently, you don't visit avsforum.com where people have multiple 24" subs in their home theaters. 5hz and below is their goal.
It may be the goal, however I do know the instrumentation aspect only too well. Low frequency measurements are extremely unreliable, just the physics of it. For extremely low frequencies (like yours) an open field is often used. It is a real pain to get anything resembling reality at low frequencies through measurements. The mic may respond down there in a coupled test chamber, but not in free air! Similar to headphones.
So are you saying that if 5hz cannot be measured in 2pi that there is no way a 0.5 or 1pi measurement is possible?
There was a good discussion on the UMIK and Dayton mics at lower frequencies and they were better than you might expect. If I could find it I'd link it, In can say the Edge of tomorrow or 'mother' dig very deep indeed.
Did I say that? No, I did not. You're putting words in my mouth. Please do not do that.
I said it is extremely difficult to get accurate measurements at very low frequencies. I suggest you read some material on that subject. What I will say is that there is so much experiemental error in your readings that you cannot trust them. These are make you feel good measurements, the reality may be significantly different. I worked professionally in a calibration lab as well, certified in fact.
I'm not trying to tell you don't know anything, but you can't grab a "calibrated mic", a laptop and computer program and make accurate measurements. Everything I do is traceable to NIST (look that up). "Calibrated" can mean all kinds of things, you have to check the standards and stated errors in order to understand what numbers you can trust from it.
There is a massive differnce between having tests done properly with little error, and ad-hoc testing done by people not familiar with what factors can influence the outcome of a measurement. There is even math involved. You have to develop an error budget and make sure you have controlled all the variables in your test. Setting up the test is more important than actually doing thte test. The skill is in the setup, not the test.
Very few chambers are actually anechoic much below 100 Hz due to the length of the absorbtive wedges required- roughly 1/4 wavelength long. A chamber would need to be lined on all six walls with absorbtive wedges 14 feet (4.3 meters) in length to be anechoic down to 20Hz, most have 1 meter or less.
The location of the measurement certainly influences the outcome.
Your argument seems to be that low frequencies need a room mode that's low enough to "support" a given frequency.
Room modes cause constructive or destructive interference depending on the location of the source and mic/listener, but room dimensions being multiples or fractions of a wavelength are not required for a wave to propagate within or outside the room.
The low frequency response being different at different locations inside or outside a room does not negate the response measured at a specific location, any more than a low frequency measurement at one location insures consistent room response.
Using a good omni condenser or back electret mic with known response, a laptop and a computer program, knowledgeable people can and do make measurements accurate at specific locations within the room.
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Hi weltersys,
I agree with you. The room does need to support the lowest frequency of interest, and there are plenty of modes in a room. Measurement location will change your results.
Hi BP1Fanatic,
I'm not going to get into a deep discussion because I simply do not have the time to do so. I'm all over this place, I have actual work here to do - and I am working on the bench. Plus I have a social life. Your question is a challenge the way it is worded, one that can open up a long discussion.
Why not instead read some actual industry information. This from the industry and not entusiast sites. Not white papers either. Actual papers on the subject
I agree with you. The room does need to support the lowest frequency of interest, and there are plenty of modes in a room. Measurement location will change your results.
Hi BP1Fanatic,
I'm not going to get into a deep discussion because I simply do not have the time to do so. I'm all over this place, I have actual work here to do - and I am working on the bench. Plus I have a social life. Your question is a challenge the way it is worded, one that can open up a long discussion.
Why not instead read some actual industry information. This from the industry and not entusiast sites. Not white papers either. Actual papers on the subject
No mention in databass about low frequency measurement being particularly hard. They do use different mic's https://data-bass.com/#/articles/5cc09423a75a260004255c87?_k=cr7mm7
You can get the £100 mic's calibrated down to 5Hz by Cross Spectrum, so they obviously believe they are capable. I doubt my graph, given it's consistency is of no use below 18Hz
I'm not having a go by the way, more perhaps appreciating for me I am not proving but have no reason to believe the results are worthless below 18Hz
You can get the £100 mic's calibrated down to 5Hz by Cross Spectrum, so they obviously believe they are capable. I doubt my graph, given it's consistency is of no use below 18Hz
I'm not having a go by the way, more perhaps appreciating for me I am not proving but have no reason to believe the results are worthless below 18Hz
I'd say this is pretty on point. I remember modeling drivers and more magnet strength increased the higher frequency output, and the apparent "f3" moved up but the SPL at the very low frequencies stayed the same. So the changing "f3" is in some sense a mirage, the actual low frequency output remained the same. It seemed the very low end was determined really by the mass, and maybe the suspension unless the box was small and swamped it out (I was working in automotive at the time, small boxes are rather a thing in that field ha ha). This is ignoring ports, and ignoring changes around the in box resonance where sure the magnet/coil affects the Q.
Someday I'll kite a PC from work to get back to running simulations like that. It is project #176 on my list...🤣
@anatech - now we have a problem. I actually HAVE a university degree in sound engineering from a technical university. The whole program - electronics, acoustics, psycho acoustics, signal processing, recording/mix/mastering. Worked as live sound engineer during university time, does mixing and mastering but mainly doing technical acoustics for the industry for over a decade now. Built plenty of speakers from PA to bedroom. I'm pretty sure I know how low frequencies need to sound.
I tell you - you are wrong. As do all the others here and they delivered good reasons.
How to continue, more insulting? Or do you explain what you mean with "room doesn't support low frequencies" cause that's no term in acoustics, physics or psycho acoustics.
And I can proof it without any problems cause I have a proper room and installation right next to me. Measurements are done with an Audio Precision system and class 1 microphones (Earthworks M50 and GRAS 1/4"). The room is 3x4,5x2,5m big. And it's no problem at all to produce, hear, feel and measure 20Hz and lower in there. And yes, it sounds pretty damn good and it's easy to detect mastering mistakes at lowest frequencies others simply don't hear on their systems.
I also built a speaker für measurements in an anechoic chamber from 16Hz to 60kHz. The chamber is 2x2x2m - no problem at all to do measurements at 16Hz with a PRESSURE microphone. (You would run in troubles with a pressure gradient/cardioid microphone, but that's not how our ear works!) And you also HEAR the low frequencies in the chamber (and better as at the outside of the chamber).
And I also built pure pressure chambers to achieve sound pressure levels up to 160dBSpl for technical testing of devices - I would say i understand the differences.
There is a broad transition from sound behaving as a wave to sound in a pressure chamber. In small rooms we are living in this transition zone for very low frequencies. The EAR works as pressure receiver - it doesn't detect sond velocity. So it doesn't care about this transition, hearing is working there without problems.
(Sorry for the harsh tone - but it's a pain that the "no low frequencies in small rooms" myth is still legit and never get's any substential explaination. I'm probably a little sensitive in that regard.)
I tell you - you are wrong. As do all the others here and they delivered good reasons.
How to continue, more insulting? Or do you explain what you mean with "room doesn't support low frequencies" cause that's no term in acoustics, physics or psycho acoustics.
And I can proof it without any problems cause I have a proper room and installation right next to me. Measurements are done with an Audio Precision system and class 1 microphones (Earthworks M50 and GRAS 1/4"). The room is 3x4,5x2,5m big. And it's no problem at all to produce, hear, feel and measure 20Hz and lower in there. And yes, it sounds pretty damn good and it's easy to detect mastering mistakes at lowest frequencies others simply don't hear on their systems.
I also built a speaker für measurements in an anechoic chamber from 16Hz to 60kHz. The chamber is 2x2x2m - no problem at all to do measurements at 16Hz with a PRESSURE microphone. (You would run in troubles with a pressure gradient/cardioid microphone, but that's not how our ear works!) And you also HEAR the low frequencies in the chamber (and better as at the outside of the chamber).
And I also built pure pressure chambers to achieve sound pressure levels up to 160dBSpl for technical testing of devices - I would say i understand the differences.
There is a broad transition from sound behaving as a wave to sound in a pressure chamber. In small rooms we are living in this transition zone for very low frequencies. The EAR works as pressure receiver - it doesn't detect sond velocity. So it doesn't care about this transition, hearing is working there without problems.
(Sorry for the harsh tone - but it's a pain that the "no low frequencies in small rooms" myth is still legit and never get's any substential explaination. I'm probably a little sensitive in that regard.)
Yes, this is certainly a myth. At low frequency the response in a room is the woofer's free field response convolved with the the source to listener room transfer function. That transfer function is determined by the room's modal response. In a rectangular room that transfer function can be calculated as the sum of all modes from DC to infinity. Higher frequency modes don't contribute significantly to low freguency so they can be ignored. The first, and lowest AC mode (axial mode) is determined from the room's longest dimension, front to back, side to side, or of floor to ceiling. All other AC modes, tangential and oblique, are at higher frequency. Lastly, what is typically ignored when speaking of room modes, is the DC mode. The DC mode is what causes room gain. However, even without the DC mode, there would still be reproduction below the 1st AC mode.
As an example, the room to listener transfer function for a rectangular room looks something like this for a specific room size, source and listener position. The plot extends fro 10 Hz to 100 Hz. The blue trace is the response as computed by the summed modal method. The pink trace was calculated for the same conditions using a finite element approach. The First AC mode is at 25 Hz. Below 25 Hz the response drops to a minimum at about 16 Hz then rises again below that. Without the DC mode the response would flatten out at low frequency. The thing about the DC mode is that it's contribution is not dependent on either the source or listener position. Thus at frequencies well below the first AC mode, the SPL is uniform throughout a small, sealed room when the wave length is much greater that any room dimension. Open a window or a door, and that's another issue. Additionally, the room transfer function is not necessarily minimum phase. It can be, but it is not required to be so. This, along with the amplitude response, has a significant effect on low frequency transients in a room.