We should probably be referring to equal loudness contours, rather than Fletcher-Munson. Fletcher and Munson did their research in the 1930s, and it's been superseded. See https://en.wikipedia.org/wiki/Equal-loudness_contour. The difference in the bass area is significant. On the ISO 226:2003 curves, the curves at 20 Hz are approximately 15 dB above their 40 Hz points. (It varies, depending on level.) Which means that if a woofer is generating 20% distortion (i.e. -14dB), the 2nd harmonic at 40 Hz could well sound louder than the fundamental at 20 Hz. That's not going to be good sounding bass.
@anatech You've continued to say that small rooms can't "support" bass, but you haven't clarified what you mean, and you haven't suggested any further reading or references to back up what you've said. I do find your claim implausible. I'm wondering why we're all so familiar with the term room gain (and cabin gain, for cars), but not with the term room cut.
@anatech You've continued to say that small rooms can't "support" bass, but you haven't clarified what you mean, and you haven't suggested any further reading or references to back up what you've said. I do find your claim implausible. I'm wondering why we're all so familiar with the term room gain (and cabin gain, for cars), but not with the term room cut.
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"Support" remains an ambiguous and imprecise word to use in this instance. On the one hand a small room will 'support' bass because we can hear and measure it, but on the other hand it will not 'support' the wavelength of these lower frequencies. I feel that the original statement should be reworded.
What we're talking about here is what's sometimes referred to as the "pressure zone", frequencies below the so-called lowest mode (where the longest room dimension is equal to half the wavelength). If I understand you correctly, you're saying that frequencies in the pressure zone can be reproduced, but they get no "gain" from the room?
I'm really no expert on this (as is probably obvious), but I thought that a sealed source would get "room gain" at these frequencies. Here's a link to an analysis that (I think) supports my naive understanding: https://www.audiosciencereview.com/forum/index.php?threads/analytical-analysis-room-gain.23211/
Have I got it wrong?
I'm really no expert on this (as is probably obvious), but I thought that a sealed source would get "room gain" at these frequencies. Here's a link to an analysis that (I think) supports my naive understanding: https://www.audiosciencereview.com/forum/index.php?threads/analytical-analysis-room-gain.23211/
Have I got it wrong?
Might be of some use https://www.svsound.com/blogs/subwoofer-setup-and-tuning/what-is-subwoofer-room-gain
Thanks. The trouble with trying to read up on somthing like room gain is that you either find academic sources, which give lots of detail, and are probably reliable, but go way over my head, or commercial sources, which make plenty of assertions, but have to be taken with a pinch of salt.
I didn't expect to get a response that low when I built my sub and chose th driver etc, I wanted to reach below 20 Hz in a meaningful way and just embarked and measured and listened this is an interesting place for bass info https://data-bass.com/#/?_k=pux7g6
You're making things confusing at best, and spreading misinformation at worst.
The wavelength you've described would be the (1,1,1) standing wave. That is the lowest frequency that will have a standing wave in the room, and represents the bottom of the modal region.
Frequencies below that one can occur within the room. Those frequencies are in the pressure zone, where the entire room will be at approximately uniform pressure, and that pressure will vary at whatever frequency is being reproduced.
Headphones work in the pressure zone for a substatial bandwidth. After all, they're simply a speaker in a very small room which happens to encompass an ear. Earphones have an even wider bandwidth in the pressure zone: the "room" is the ear canal, a couple of cc in volume.
In all cases, sound can be reproduced perfectly well.
Chris
PS - What happens in a sealed subwoofer? Is there no pressure inside?
Agreed, providing the port is designed and properly - I would suggest that 95% or more are not - but still, to my ear at least, the resultant sound falls far short of a sealed enclosure sensibly driven. Ported enclosures will always remain practically 'something for nothing' but the performance does not come without compromises as does any loading; such is life. One simply has to decide at the design stage where the compromise is to be!
Reading around more on this issue of room gain, I found a really helpful discussion here on diyaudio, dating from 2014, between Gedlee (Earl Geddes) and bolserst. See here, beginning at post #82: https://www.diyaudio.com/community/threads/room-modal-response.248717/page-5
Wow! Returning to this because we got way off topic and nobody answered the original question: What governs a DRIVER'S frequency response?
I ask because I'm playing with my desktop speakers (3" woofers). The 'volume' of the bass audibly falls @ 42Hz. But even at 15hz the drivers are still 'responding' - they're going nuts! I can see the drivers moving. Air movement is present in the port. I can feel the vibration on the desk.
I ask because I'm playing with my desktop speakers (3" woofers). The 'volume' of the bass audibly falls @ 42Hz. But even at 15hz the drivers are still 'responding' - they're going nuts! I can see the drivers moving. Air movement is present in the port. I can feel the vibration on the desk.
Hi Surtsey,
The lowest effective frequency response for a driver is determined by the piston size and by itself (without a baffle or box) sets how much of the output simply travels around the driver to be cancelled. The other determining factors are the electrical and mechanical characteristics called Thiel-Small parameters.
Just because the cone travels back and forth does not mean you will get useful output, and it certainly will not have a flat frequency response. I designed home audio and club loudspeaker systems for over a decade. You simply cannot get around physics. Those small sub-woofers work by treating the speaker as a simple piston, heavily eq the output and hit it with excessive power. that is the cost of fighting physics. This applies to your speakers, they are simply smaller and have lower power handling capacity.
Does that help?
The lowest effective frequency response for a driver is determined by the piston size and by itself (without a baffle or box) sets how much of the output simply travels around the driver to be cancelled. The other determining factors are the electrical and mechanical characteristics called Thiel-Small parameters.
Just because the cone travels back and forth does not mean you will get useful output, and it certainly will not have a flat frequency response. I designed home audio and club loudspeaker systems for over a decade. You simply cannot get around physics. Those small sub-woofers work by treating the speaker as a simple piston, heavily eq the output and hit it with excessive power. that is the cost of fighting physics. This applies to your speakers, they are simply smaller and have lower power handling capacity.
Does that help?
Port air movement below tune is uncontrolled driver movement, effectively very high distortion. All ported and PR boxes need at least a 2nd order HPF just below tune to control this and keep it low distortion.
Just because something is making noise doesn't mean it's useful sound. I've also been designing and building pro and domestic speakers for decades.
As mentioned, your speakers are likely ported and below tune they unload, the slug of air that should stay within it to act as a resonant mass gets pumped out of the port, replaced and pumped out again not constructively contributing to the output. The driver is mostly operating free air at that point with a tiny baffle. What it's producing at those lower frequencies is not anywhere sufficient in level to be audible (to revisit the "Equal Loudness Contours" again). You can calculate about what your driver could ideally be capable of with this tool: http://www.baudline.com/erik/bass/xmaxer.html Choose to solve for dB and you'll see how limited it is in the lower frequencies. This, of course, is idealized. As others have discussed the issues with regards to enclosure, the port unloading, and how the interaction with all depends on the driver's T/S parameters, you'll already appreciate how non-ideal the real speaker is.
I've just read the thread and I don't see a post that answers the initial question by Surtsey; which is about the driver itself and not the interaction of the driver in the box and that box in the room.
I'm probably wrong but I thought it was the combination of the drivers diametre and mass and spider stiffness that determined a drivers frequency response at the low end and in that respect the voice coil size and magnet mass and strength were able to be disregarded.
So my understanding is that one of the reasons bigger woofers have lower a Fs is simply that they are heavier, certainly when I play with old paper woofers and add mass by painting them with diluted PVA the Fs drops a little.
"What governs a driver's lowest frequency response?"
anatech did try tho.I'm probably wrong but I thought it was the combination of the drivers diametre and mass and spider stiffness that determined a drivers frequency response at the low end and in that respect the voice coil size and magnet mass and strength were able to be disregarded.
So my understanding is that one of the reasons bigger woofers have lower a Fs is simply that they are heavier, certainly when I play with old paper woofers and add mass by painting them with diluted PVA the Fs drops a little.
Hi Moondog55,
I designed enclosures and systems back before computers, then used an original IBM PC. I wrote the code for that.
So, your question is pretty broad. The Fs depends on both electrical and mechanical characteristics. The resulting Qt is very important and works with an enclosure to end up with a system Q. A woofer in a box, no matter the box type, is a high pass filter. You can examine it the same way. So the slope and amount of hump (hopefully not ringing) is determined by all the parameters together. There are other things that come into play that affectt he sound apart from pure volume (I should say actualvolume as opposed to what you think the volume is).
When you begin talking about a wide range system employing multiple drivers, you have other factors. Everything is a compromise - like everything else in engineering and life.
I designed enclosures and systems back before computers, then used an original IBM PC. I wrote the code for that.
So, your question is pretty broad. The Fs depends on both electrical and mechanical characteristics. The resulting Qt is very important and works with an enclosure to end up with a system Q. A woofer in a box, no matter the box type, is a high pass filter. You can examine it the same way. So the slope and amount of hump (hopefully not ringing) is determined by all the parameters together. There are other things that come into play that affectt he sound apart from pure volume (I should say actualvolume as opposed to what you think the volume is).
When you begin talking about a wide range system employing multiple drivers, you have other factors. Everything is a compromise - like everything else in engineering and life.
I know that; mostly; but the OPs question wasn't about driver/box interactions but simply for the driver [ woofer] on it own, and it wasn't my question but Surtseys.
Empirically I know that I personally can only get deep satisfying bass with large woofers but isn't that partly an efficiency thing and partly power response?
Empirically I know that I personally can only get deep satisfying bass with large woofers but isn't that partly an efficiency thing and partly power response?
Hi Moondog55,
Yes. I tried to answer that. But a raw driver will never have a flat frequency response. The closest were drivers made through the 40's to 70's designed for free air. However they still needed a baffle.
Yes. I tried to answer that. But a raw driver will never have a flat frequency response. The closest were drivers made through the 40's to 70's designed for free air. However they still needed a baffle.
So only effective piston size is relevant and driver mass has little effect?
Sorry but the physics of that is beyond my knowledge and understanding because I have drivers here with different physical dimensions but equal or very similar free air resonant frequencies, 8" and 10" and 12" and around the 30Hz point.
One of the drivers with an 8" nominal has a lower Fs that the 18" woofer in my last box, so it can't only be the drivers size
Sorry but the physics of that is beyond my knowledge and understanding because I have drivers here with different physical dimensions but equal or very similar free air resonant frequencies, 8" and 10" and 12" and around the 30Hz point.
One of the drivers with an 8" nominal has a lower Fs that the 18" woofer in my last box, so it can't only be the drivers size
You are correct in some ways.
The box size in relation to the piston size combined with the dynamic characteristics. It all matters. Every speaker driver has an ideal box size and type that will give you the flattest response and most extended bass response. This is what you aim for. Each box will be a different size, and the larger woofers need a bigger box. Sometimes much larger, but heir performance can be impressive. Efficiency will depend on the driver of course. Big driver in a small box is unhappy, and a smaller woofer in the same box often will outperform the larger one.
The size and type of box can be calculated using the T/S parameters. Basically ported boxes unload the woofer below the port frequency (not a good thing). So you either have a ported system that responds down way low, or you electrically restrict the frequencies to above that port frequency. Read electronic crossover. So for smaller woofers or full range drivers, a sealed box is often the best choice. Having said that, the Qt of the driver also is more suitable for sealed or ported. The happy Qt for a ported system is around 0.383 for the raw driver. I personally prefer the entire system to have a Q of around 0.71. That is called optimally damped.
My systems always performed as calculated. I measured the drivers myself for one. I also corrected the volume for padding, the speaker(s) and bracing. Some padding adds to the effective volume. Don't forget tot correct for the volume taken by the port in those systems. I even took the air density into account.
The box size in relation to the piston size combined with the dynamic characteristics. It all matters. Every speaker driver has an ideal box size and type that will give you the flattest response and most extended bass response. This is what you aim for. Each box will be a different size, and the larger woofers need a bigger box. Sometimes much larger, but heir performance can be impressive. Efficiency will depend on the driver of course. Big driver in a small box is unhappy, and a smaller woofer in the same box often will outperform the larger one.
The size and type of box can be calculated using the T/S parameters. Basically ported boxes unload the woofer below the port frequency (not a good thing). So you either have a ported system that responds down way low, or you electrically restrict the frequencies to above that port frequency. Read electronic crossover. So for smaller woofers or full range drivers, a sealed box is often the best choice. Having said that, the Qt of the driver also is more suitable for sealed or ported. The happy Qt for a ported system is around 0.383 for the raw driver. I personally prefer the entire system to have a Q of around 0.71. That is called optimally damped.
My systems always performed as calculated. I measured the drivers myself for one. I also corrected the volume for padding, the speaker(s) and bracing. Some padding adds to the effective volume. Don't forget tot correct for the volume taken by the port in those systems. I even took the air density into account.