xmax and deep bass

[elastic 1]

i was wondering what role xmax plays for a driver.

many people claim the more xmax the louder the low lows are.

what do you experts know about it?

[Drek75633 1]

xmax is the amount of movement of the cone. The more movement of the cone. The more air you move. The deeper the bass. The louder it gets on the low end.

[jrod1050 5]

Fs is a better measurement for low end output

[bigrank916 72]

i was wondering what role xmax plays for a driver.

many people claim the more xmax the louder the low lows are.

what do you experts know about it?

Im no expert by any means but Xmax is the linear excursion of the driver. I dont believe the second part to be true either.

[bigrank916 72]

Fs is a better measurement for low end output

Not always true but usually a safe bet. I believe the SA8s Fs is in the 40s.

[KU40 173]

It plays a part. But so do other factors, including fs and other parameters, and box design.

[elastic 1]

whats more important? cone area or xmax for low end?

[abmoore 8]

Doesn't a driver reach its full xmax at fs? Or is that just the resonant frequency, I would think they correspond. But for lower frequencies, more air needs to be moved to achieve a higher spl, so sd, bl, and other factors also influence spl. A high xmax, bl, low fs, generally high Q, and high power handling seem to be prevalent in low end beasts, what I mean by that is a lot of output below 40 Hz. Just what I have seen, someone on here has a better explaination.

Just saw your post, 4 times the cone area will equal double the xmax? Or it may be proportional, hopefully someone chimes in, I think denim had a good explaination somewhere on here, I could be wrong.

Edited April 20, 2010 by NCSU ECE

[mr.sagat 10]

I don't think xmax helps on a meter too much. I used to run an old school stroker, that thing was only rated at 13mm xmax and got stupid loud on higher spl tones. Xmax and cone area do seem important if maximum air movement and displacement for hitting lows is your agenda. I'm sure others on this forum know a lot more about this subject than I do.... (sits down in front of computer and waits to learn)

[///M5 2,833]

You can NEVER just look at one parameter and gain ANY insight on what a driver will do. Do NOT shop for drivers using one or two of the T/S. Either use them all, or just go by recommendations. All of the theoretical recommendations above are based on assumptions for the rest of the driver which no one knows anything about since you haven't told us what you are comparing.

Always better to state your goals then ask a comparative question.

The ONLY thing you should garner from an Xmax spec is the actual excursion the cone can mechanically deal with and this means nothing on its own for how loud it will be or for how the driver will sound.

[abmoore 8]

Oh I thought he was just discussing the theory behind it. OP, is your goal deep bass? And can someone post an answer explaining the relationship between the t/s parameters and "deep" bass, like how they all correspond, or what the common similarities are in these subwoofers that are used for extended low frequencies. There has been about five questions a day concerning that it seems.

[///M5 2,833]

Oh I thought he was just discussing the theory behind it. OP, is your goal deep bass? And can someone post an answer explaining the relationship between the t/s parameters and "deep" bass, like how they all correspond, or what the common similarities are in these subwoofers that are used for extended low frequencies. There has been about five questions a day concerning that it seems.

It isn't a trivial discussion, nor should it be summarized in one page. Do you some searching and ask questions and you'll get answers.

[elastic 1]

so many companies are showing off their xmaxs on woofers saying more travel = more bass.

alpine does, orion, jbl, etc.

the xxx has over 50mm linear excursion and is known to be a low end monster, and so is the w7 with 32 mm xmax.

therefore i assumed xmax is important for loud low end. on the other hand ive seen videos of l7s doing crazy hairtricks and they only have 16 mm excursion.

[ryan s 12]

Hmmm...I wonder if there's anywhere we could look to find Xmax vs SPL and T/S explanations...

Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

SSA Car Audio Forum -> Technical Info & How To's

[Impious 1,476]

Oh wow.....what a thread

Fs is a better measurement for low end output

False.

As M5 & others have stressed, you can not look at Fs in isolation of the other parameters as well as enclosure design. For example, a low Q low Fs driver will have anemic low frequency response in a sealed enclosure, completely contradictory to your statement.

[Impious 1,476]

Doesn't a driver reach its full xmax at fs?

A driver can reach Xmax at any frequency. Whether or not it will depends on the power at hand and enclosure alignment.

Fs is a better measurement for low end output

Not always true but usually a safe bet. I believe the SA8s Fs is in the 40s.

Not a safe bet.

Much more to it than simply the Fs.

[Impious 1,476]

whats more important? cone area or xmax for low end?

There's much more to it than that.

First, cone area and Xmax are multiplied to arrive at a parameter known as Vd, or volume displacement. This is the amount of linear air displacement the driver is capable of achieving. The higher the Vd, the higher linear output capabilities the driver has as a larger Vd means the driver is capable of displacing more air.

Second, don't confuse Xmax with excursion. They are different. Excursion is how far the cone is physically moving. Xmax is the maximum amount of linear excursion the driver is capable of achieving. Excursion is the amount of movement, Xmax is the limit of how much of that movement is "linear". Generally a driver operating at Xmax will have ~10% THD. This is typically the highest amount of acceptable performance. As you exceed Xmax it's generally considered that the distortion performance would be at an unacceptable level (among other things).

In sealed enclosures, Vd is one of the important factors along with alignment and the driver's parameters in determining output capabilities. All things equal, the driver with the higher Vd will have higher output. In reality, things are never equal. So you have to look at the response of the driver in a given alignment along with your environment and available power. Having a higher Vd isn't any good if you don't have the requisite power to reach Xmax or if the driver is in an alignment that begins to roll off at a high frequency. Having a higher Vd is only a capability of higher output; whether or not you will be able to realize that higher output is dependent upon several other factors.

In terms of low frequency performance, you're required to increase displacement by a factor of 4 in order to maintain a given SPL level one octave lower in frequency. This means that you need to displace 4x the air at 25hz as you do at 50hz to maintain the same SPL level at both frequencies. You can see how having a higher Xmax could be beneficial as displacement requirements increase substantially in lower frequencies. In the low frequencies Vd can be very important as it can very much limit how much linear output your system will be able to achieve. Luckily in car audio we have substantial cabin gain in the low frequencies as well, so we can maintain SPL levels at lower frequencies without having to quadruple our displacement. A 12db gain at 25hz compared to 50hz, for example, is equivalent to quadrupling your displacement. So if you have a 12db gain at 25hz compared to 50hz in your vehicle, you've already accomplished the feat.

Generally you want the most cone area you can reasonably place within your space, environment and enclosure requirements. Why? A driver with a larger cone area will displace a greater amount of air for a given excursion level. This means that it takes less excursion to reach a given SPL level with more cone area. This, in turn, means that the driver(s) would ideally be operating further within it's linear range at that SPL level which, ideally, reduces distortion. This ofcourse assumes the drivers are of similar distortion performance as distortion performance will vary based on driver designs. For example, one driver may still have less distortion at 15mm than another more poorly designed driver (from a distortion perspective) driver operating at 10mm.

The reason Xmax "doesn't matter" for SPL is because 1) the subwoofers are generally "burped" near tuning where excursion is minimized and 2) Xmax is a linear parameter....people competing in SPL don't really care about having higher distortion due to possibly exceeding Xmax. But that doesn't mean Xmax is not important in ported enclosures. Xmax is not a limitation on how far the driver can physically move , only on how much of that movement is linear. Also, going back to what we said about power and alignment; Xmax does not tell you how much excursion you will have in your alignment with your power. And that is what ultimately determines how much output you will have from the enclosure, any enclosure. Vd is still "important" in ported enclosure as it still helps determine which driver has the capability for higher linear output, but you have to look at your power and alignment to determine which will ultimately have higher excursion, and hence output, in use. In a ported enclosure generally enclosure size and tuning are going to have a significant impact on low frequency response and excursion with regards to frequency; but that doesn't make Xmax irrelevant for daily listening. About a half octave above tuning, the enclosure will behave similarly to a sealed enclosure meaning excursion will increase to a point that is similar to that of a sealed enclosure. Xmax may become important in this region where it's possible to reach or exceed the Xmax of the driver.

That post feels like it was one giant ramble.....hopefully it makes sense.

[KU40 173]

so many companies are showing off their xmaxs on woofers saying more travel = more bass.

alpine does, orion, jbl, etc.

the xxx has over 50mm linear excursion and is known to be a low end monster, and so is the w7 with 32 mm xmax.

therefore i assumed xmax is important for loud low end. on the other hand ive seen videos of l7s doing crazy hairtricks and they only have 16 mm excursion.

The XXX drivers also have quite low FS, lower than probably 98% of other car audio drivers. And are also low Q drivers. So which of these individual parameters makes it a low end monster, and why did you choose xmax to represent it as such?

The thing is just that xmax is soooo easy to market because you see a subwoofer move. To 99% of people buying a subwoofer, more movement = better in their eyes.

[abmoore 8]

whats more important? cone area or xmax for low end?

There's much more to it than that.

First, cone area and Xmax are multiplied to arrive at a parameter known as Vd, or volume displacement. This is the amount of linear air displacement the driver is capable of achieving. The higher the Vd, the higher linear output capabilities the driver has as a larger Vd means the driver is capable of displacing more air.

Second, don't confuse Xmax with excursion. They are different. Excursion is how far the cone is physically moving. Xmax is the maximum amount of linear excursion the driver is capable of achieving. Excursion is the amount of movement, Xmax is the limit of how much of that movement is "linear". Generally a driver operating at Xmax will have ~10% THD. This is typically the highest amount of acceptable performance. As you exceed Xmax it's generally considered that the distortion performance would be at an unacceptable level (among other things).

In sealed enclosures, Vd is one of the important factors along with alignment and the driver's parameters in determining output capabilities. All things equal, the driver with the higher Vd will have higher output. In reality, things are never equal. So you have to look at the response of the driver in a given alignment along with your environment and available power. Having a higher Vd isn't any good if you don't have the requisite power to reach Xmax or if the driver is in an alignment that begins to roll off at a high frequency. Having a higher Vd is only a capability of higher output; whether or not you will be able to realize that higher output is dependent upon several other factors.

In terms of low frequency performance, you're required to increase displacement by a factor of 4 in order to maintain a given SPL level one octave lower in frequency. This means that you need to displace 4x the air at 25hz as you do at 50hz to maintain the same SPL level at both frequencies. You can see how having a higher Xmax could be beneficial as displacement requirements increase substantially in lower frequencies. In the low frequencies Vd can be very important as it can very much limit how much linear output your system will be able to achieve. Luckily in car audio we have substantial cabin gain in the low frequencies as well, so we can maintain SPL levels at lower frequencies without having to quadruple our displacement. A 12db gain at 25hz compared to 50hz, for example, is equivalent to doubling your displacement. So if you have a 12db gain at 25hz compared to 50hz in your vehicle, you've already accomplished half of the feat.

Generally you want the most cone area you can reasonably place within your space, environment and enclosure requirements. Why? A driver with a larger cone area will displace a greater amount of air for a given excursion level. This means that it takes less excursion to reach a given SPL level with more cone area. This, in turn, means that the driver(s) would ideally be operating further within it's linear range at that SPL level which, ideally, reduces distortion. This ofcourse assumes the drivers are of similar distortion performance as distortion performance will vary based on driver designs. For example, one driver may still have less distortion at 15mm than another more poorly designed driver (from a distortion perspective) driver operating at 10mm.

The reason Xmax "doesn't matter" for SPL is because 1) the subwoofers are generally "burped" near tuning where excursion is minimized and 2) Xmax is a linear parameter....people competing in SPL don't really care about having higher distortion due to possibly exceeding Xmax. But that doesn't mean Xmax is not important in ported enclosures. Xmax is not a limitation on how far the driver can physically move , only on how much of that movement is linear. Also, going back to what we said about power and alignment; Xmax does not tell you how much excursion you will have in your alignment with your power. And that is what ultimately determines how much output you will have from the enclosure, any enclosure. Vd is still "important" in ported enclosure as it still helps determine which driver has the capability for higher linear output, but you have to look at your power and alignment to determine which will ultimately have higher excursion, and hence output, in use. In a ported enclosure generally enclosure size and tuning are going to have a significant impact on low frequency response and excursion with regards to frequency; but that doesn't make Xmax irrelevant for daily listening. About a half octave above tuning, the enclosure will behave similarly to a sealed enclosure meaning excursion will increase to a point that is similar to that of a sealed enclosure. Xmax may become important in this region where it's possible to reach or exceed the Xmax of the driver.

That post feels like it was one giant ramble.....hopefully it makes sense.

You say ramble, I say point made. Thanks for the explaination in further detail. I was forgetting it was a linear measurement for some reason. Isn't xsus, or xmec, the max excursion. And how does Vas relate to excursion? Is that the box size needed to reach full excursion at tuning, resonance, or something like that? I might start another thread about bl, that also seems to be a big advertising technique.

[Impious 1,476]

Isn't xsus, or xmec, the max excursion.

Xsus = suspension limited linear excursion

Xmag = motor limited linear excursion

Xmax = lesser of Xsus and Xmag

Xmech = mechanically limited excursion (without regard to linearity).

Generally if you exceed Xmech, shit starts breaking

And how does Vas relate to excursion?

It doesn't, really.

Vas is the volume of air that when compressed to 1m^3 exhibits the same compliance as the suspension of the driver. Otherwise described as "equivalent air compliance".

It's basically just another way of expressing the compliance of the driver's suspension. Larger Vas = looser suspension, smaller Vas = tighter suspension. It's most useful in determining enclosure volumes.

For example, the formula for determining the enclosure size for a given sealed enclosure alignment is;

Vb = Vas/([Qtc/Qts]^2-1)

Basic mathematics.....since Vas is the numerator, as Vas increases the required enclosure volume (Vb) for a given alignment (Qtc) will also increase (assuming Qts stays the same).

[abmoore 8]

Isn't xsus, or xmec, the max excursion.

Xsus = suspension limited linear excursion

Xmag = motor limited linear excursion

Xmax = lesser of Xsus and Xmag

Xmech = mechanically limited excursion (without regard to linearity).

Generally if you exceed Xmech, shit starts breaking

And how does Vas relate to excursion?

It doesn't, really.

Vas is the volume of air that when compressed to 1m^3 exhibits the same compliance as the suspension of the driver. Otherwise described as "equivalent air compliance".

It's basically just another way of expressing the compliance of the driver's suspension. Larger Vas = looser suspension, smaller Vas = tighter suspension. It's most useful in determining enclosure volumes.

For example, the formula for determining the enclosure size for a given sealed enclosure alignment is;

Vb = Vas/([Qtc/Qts]^2-1)

Basic mathematics.....since Vas is the numerator, as Vas increases the required enclosure volume (Vb) for a given alignment (Qtc) will also increase (assuming Qts stays the same).

The Vas explaination makes everything fit together now. Thanks, was like one of those lightbulbs going off in my head. Seeing the correspondance in a lot of different subs and the higher Vas numbers they have. Generally speaking, will larger drivers with low Fs have a higher Vas?

[Impious 1,476]

That's the calculation for Vas.

Should be pretty easy to figure out from there what will cause an increase in Vas

(p is the density of air & c is the speed of sound, both of which are constants, only really need to worry about Sd & Cms)

Oh, and Fs;

So what happens to Fs and Vas when Cms and Sd increases? Or decreases?

[Duran 387]

*facepalm*

[ryan s 12]

so many companies are showing off their xmaxs on woofers saying more travel = more bass.

alpine does, orion, jbl, etc.

the xxx has over 50mm linear excursion and is known to be a low end monster, and so is the w7 with 32 mm xmax.

therefore i assumed xmax is important for loud low end. on the other hand ive seen videos of l7s doing crazy hairtricks and they only have 16 mm excursion.

The XXX drivers also have quite low FS, lower than probably 98% of other car audio drivers. And are also low Q drivers. So which of these individual parameters makes it a low end monster, and why did you choose xmax to represent it as such?

The thing is just that xmax is soooo easy to market because you see a subwoofer move. To 99% of people buying a subwoofer, more movement = better in their eyes.

JBL's in the game like everyone else...they have to sell things. Truth is, I trust JBL probably more than any "mass marketed" company since you can actually contact them and they will tell you what you want to know. They publish full T/S specs. Even the global product manager (Andy Wehmeyer) posts on DIYMA, and he know his stuff. I mean...he knows his audio, not just the products

I don't want to see my drivers move at all Multiple drivers = increased SPL = decreased Xmax = decreased distortion...so many wins in one!

Basic mathematics.....since Vas is the numerator, as Vas increases the required enclosure volume (Vb) for a given alignment (Qtc) will also increase (assuming Qts stays the same).

And then there is the situation where the box Qtc will equal the driver's Qts, further complicating things...except for infinite baffle when that's ideal 2x IB15s in a 14 cu ft trunk, for example.

[elastic 1]

very good answers! thanks.

did i catch it up right: xmax becomes more important in sealed boxes than in ported ones?