some questions

[Professor smith]

what causes the plopping sound in a subwoofer? when i overdrive mine it can cause this noise. Either its the amp clipping or the driver mechanically reaching a limit.

And when i think about how much distance subwoofer drivers move, even 18 inch ones i think its simply not enough. Ideally i would like a massive plate the size of a door with the excursion of 12inches at 10hz. Is this currently impossible? I dont believe that 18inch cones are sufficient to be honest. Do you all agree?

[AndrewT]

no.

[jackand08]

It would help if you could describe the sound a bit more. I'm currently thinking that it is the driver reaching its excursion limits and hitting against the back of the loudspeaker magnet. This will happen when a driver is overloaded, just that how much overload a driver can handle and how well it handles it are related to the quality of the driver.

Regarding your question about subwoofers not being big enough, I (and many more) will probably think that there isn't a problem. The larger the woofer's cone area, the more air it can move with less excursion. A small driver will have to have high excursion to reach the amount of air moved by a larger driver (with less excursion). As many others have put it: excursion should not be a substitute for cone area.

It is not impossible to get down to 10Hz but there really is no point in going this low, especially for hi-fi listening. Most music simply does not go this low whilst the ones that do don't have much of this low frequency bass material.

With a larger cone, the laws of physics start to turn against you and you get poor damping and it takes more energy to get the cone moving. Just think, most arena sized systems will achieve the bass levels found at concerts and gigs with many 18 or possibly even 12 inch subwoofer drivers mounted in well designed enclosures and placed strategically around the room.

[Professor smith]

It is not impossible to get down to 10Hz but there really is no point in going this low, especially for hi-fi listening. Most music simply does not go this low whilst the ones that do don't have much of this low frequency bass material.

well one reason is that if you can go down to 10hz you wont have any problems with overexcursion at 20hz.


what does amp clipping on a subwoofer sound like?

when you take these subwoofers with 18inch or more drivers, out into the open, all the bass disappears. In which case the only solution is to have much more excursion. This proves that these box subwoofers are inadequate.

Another question i have is this:What is the point of having a box? isnt it to eliminate the rear wave? We all know how powerful and long soundwaves at 20hz are, so how is a box going to be sufficient?

[AndrewT]

Originally Posted by Professor smith

well one reason is that if you can go down to 10hz you wont have any problems with overexcursion at 20hz.

these tow do not follow. Ability to move at or reproduce 10Hz is absolutely no guarantee that high level 20Hz signals cannot result in over-excursion. I can make any driver cone move at 1Hz. That proves nothing other than I'm a time wasting idiot !

what does amp clipping on a subwoofer sound like?

an almighty Thwack

when you take these subwoofers with 18inch or more drivers, out into the open, all the bass disappears. In which case the only solution is to have much more excursion. This proves that these box subwoofers are inadequate.

no, when you move the speakers from a boundary or two or three to an region where there is no boundary you have changed the loading. The bass has not disappeared, it is simply rolled off at a different frequency due to the different boundary conditions. Most speakers (drivers) are specified for a single boundary, i.e. 2Pi space

Another question i have is this:What is the point of having a box? isnt it to eliminate the rear wave? We all know how powerful and long soundwaves at 20hz are, so how is a box going to be sufficient?

not necessarily. The rear "box" is a form of loading. Different boxes give different loadings.
sealed, vented, infinite baffle, baffle mounted, open back. These are all "boxes" in the loosest use of the term and they all give a different loading which results in a different frequency response.

[revboden]

Originally Posted by Professor smith

well one reason is that if you can go down to 10hz you wont have any problems with overexcursion at 20hz.


what does amp clipping on a subwoofer sound like?

when you take these subwoofers with 18inch or more drivers, out into the open, all the bass disappears. In which case the only solution is to have much more excursion. This proves that these box subwoofers are inadequate.

Another question i have is this:What is the point of having a box? isnt it to eliminate the rear wave? We all know how powerful and long soundwaves at 20hz are, so how is a box going to be sufficient?

You use the word "these" please be more specific.

All the bass disappears? it dosent disappear, you are noticing the lack of reflected energy. There is a reason that when I set up a concert rig outside I use 16-30 "18-2" cabinets (http://www.jblpro.com/catalog/genera...?PId=118&MId=3) that's 32-60 18" speakers depending on the audience size.

The box, if sealed is to absorb the rear wave. It dosen't matter how long the wave is if you are absorbing it into a damping material like fiberglass or polyfil. If the box is ported, it is acting as a resonance chamber and the ports are resonators, the air in the port acts like a passive radiator near the tuning frequency and transmits the VLF pulse energy to the outside of the box.

[revboden]

read this:
Helmholtz resonance - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Loudspeaker_enclosure

[Professor smith]

Originally Posted by AndrewT

these tow do not follow. Ability to move at or reproduce 10Hz is absolutely no guarantee that high level 20Hz signals cannot result in over-excursion. I can make any driver cone move at 1Hz. That proves nothing other than I'm a time wasting idiot !

its all very well refuting my statement but wheres the proof theres no guarantee? Did you know that excursion is inversely proportional to frequency? Supposing that is true, my statement follows from it. I think its generally true.

The bass has not disappeared, it is simply rolled off at a different frequency due to the different boundary conditions. Most speakers (drivers) are specified for a single boundary, i.e. 2Pi spacenot necessarily.

The funny thing about bass is that it does disappear no matter how much air is being displaced; If you happen to be standing in the wrong place, you will hear no bass. Do you agree?

The rear "box" is a form of loading. Different boxes give different loadings.
sealed, vented, infinite baffle, baffle mounted, open back. These are all "boxes" in the loosest use of the term and they all give a different loading which results in a different frequency response.

I dont understanding what you mean by loading. That doesnt explain much.

It dosen't matter how long the wave is if you are absorbing it into a damping material like fiberglass or polyfil.

Studios use thin foam to absorb higher frequencies (shorter waves) whereas the long waves at lower frequencies cannot be absorbed by the same material or thickness so a different method has to be used. Often it is much more difficult. So Your statement above does not make sense to me.

[Professor smith]

Originally Posted by AndrewT

not necessarily. The rear "box" is a form of loading. Different boxes give different loadings.
sealed, vented, infinite baffle, baffle mounted, open back. These are all "boxes" in the loosest use of the term and they all give a different loading which results in a different frequency response.

My original remark was in relation to closed boxes which many subwoofers employ. In this case how can such a small box eliminate this long wave emanating from the rear of the drive unit? Even with a different 'loading' such as a ported enclosure, what effect does the size of the enclosure have?

by the way whats a 2pi space?

[jackand08]

The funny thing about bass is that it does disappear no matter how much air is being displaced; If you happen to be standing in the wrong place, you will hear no bass. Do you agree?

I think I and many other loudspeaker designers will agree that the bass disappears audibly but it it still there, just at much lower levels-this is the function of a box, to enforce that bass that is otherwise lost into the surrounding air if the speaker is used without any kind of enclosure. Try mounting the speaker into a piece of wood (the board will act as a form of baffle-albeit a simple one) but even then you will hear more bass than you do with the speaker in free air facing you. Other forms of box bring the energy radiated from the rear of the speaker and bring it out at the front, so you're not wasting the (quite large) amount of energy that the speaker radiates behind it.

its all very well refuting my statement but wheres the proof theres no guarantee? Did you know that excursion is inversely proportional to frequency? Supposing that is true, my statement follows from it. I think its generally true.

I think many others will be able to provide you with sufficient evidence that:
1) In a perfect world without many other variables, excursion is proportional to frequency-except we are not in a perfect situation so many other things affect this rule.
2) The fact you think it is true doesn't mean it is as you have yet to provide any hard evidence-only (often) flawed observations.

Most music (recorded on CD's, available in downloads etc.) has been compressed and manipulated to remove any low bass material produced in the recording (if there was any anyway). This is to save precious bandwidth when compressing into MP3 files and other compressed formats. Lower bass material takes up more bandwidth and has more energy and affects the compressing process so it is cut off below the level which humans can hear (not feel) and below frequencies that most (except very good) hi-fi systems can reproduce.

By saying what you have, you are basically dismissing over 50 years of R&D done on loudspeakers and enclosures and how they interact with each other. This research has brought about the most simple boxes (ported, sealed etc.) and some of the most complicated (bandpass, folded horn etc.), along with how to calculate the parameters for these enclosures.

I suggest you go and read some books and theory into loudspeaker and cabinet design then come back when you have a bit more knowledge and some evidence for your theories. I needn't provide any evidence here as this forum is full of it (just have a look through the `Loudspeakers` section of the forum and do some searches), re-posting it here would be a waste of time since it is already somewhere else.