WinISD closed box alignment question

[boywonder]

I've inputted 2 very similar drivers into WinISD...

The Faitalpro 4FE35 (ceramic magnet version) and 4FE32 (neo magnet version) to determine a closed box alignment.


FaitalPRO | LF Loudspeakers | 4FE32


FaitalPRO | LF Loudspeakers | 4FE35


*yes I'm evaluating 16R drivers..two per box parallel.....



The T-S parameters for both of these drivers are very close (as expected) with the exception of Qts, Qes and BL product.

When I input the 4FE32 (neo mag version) I get multiple choices for system Qtc ranging from .9 equal ripple resp to 1.5 equal ripple.

Inputting the 4FE35 (std magnet) the only alignments offered are 1.2 and 1.5 equal ripple.....I've faked the Qts, Qes and BL T-S values for the 4FE35, but WinISD still only allows two alignments Qtc 1.2 and 1.5.....


I thought that driver Qts was a big factor in possible alignments, but now I'm confused.....

 

[boywonder]

I think I've figured this out......although sometimes WinISD acts a little wonky....


The very high Qts of the 4FE35 (1.18) vs the Qts of the 4FE32 (.8) seems to be the variable that makes all the difference. It appears that with a very high Qts sometimes you cannot get a flat (or even close to flat) response in the box at any box volume.

 

[GM]

Correct; once Qts' is > 0.707, none can be flat, just increasingly more 'humpbacked' [under damped] with increasing Qts'.

Qts' = Qts + any added series resistance [Rs]: HiFi Loudspeaker Design

GM

 

[badman]

"The T-S parameters for both of these drivers are very close (as expected) with the exception of Qts, Qes and BL product."

Those are the result of a change in motor strength- the most important parameters for a box. Consider the Qts as the lowest possible alignment- it's what Qtc would be in an infinite baffle. The box can only add to it. Those motors are relatively weak leading to the underdamped alignment and "humps". All things being equal, the stronger the magnet, the lower the Qes and accordingly Qts. Most people like a Qtc of .7 to 1 for sealed.

 

[boywonder]

Consider the Qts as the lowest possible alignment- it's what Qtc would be in an infinite baffle. The box can only add to it.

Excellent way to look at Qts..never really occurred to me that way....


..so Qts above .707 even in infinite baffle will still has a resultant system Q greater than .707 without a box.....interesting....and that makes sense since you can make the box infinitely large and still not get flat response...are there downsides to doing this? like power handling. etc? I know the upside is no rear wave reflection issues.


So instead of putting the 4FE35-16 (Qts=1.18) in a 20L enclosure or some other large enclosure..just leave the back of a small enclosure open....same response for all practical purposes.



In the past I've generally aimed for a system Q around 1.0....for a little bass bump. I understand that this results in some "ringing" since it's under damped.

 

[boywonder]

Can I assume that if I construct an open back enclosure for either of these drivers that I get their rated SPL (91db)? ......and if I make a large/wide baffle I get additional gain due to 2pi radiation instead of 4pi?....


.....or there is no free lunch and the large baffle is needed to get rated SPL?

 

[GM]

..so Qts above .707 even in infinite baffle will still has a resultant system Q greater than .707 without a box.....interesting....and that makes sense since you can make the box infinitely large and still not get flat response...are there downsides to doing this? like power handling. etc? I know the upside is no rear wave reflection issues.


So instead of putting the 4FE35-16 (Qts=1.18) in a 20L enclosure or some other large enclosure..just leave the back of a small enclosure open....same response for all practical purposes.



In the past I've generally aimed for a system Q around 1.0....for a little bass bump. I understand that this results in some "ringing" since it's under damped.

Not quite, the air mass in the box has some weight and at some point its resistance will mass load the driver to a lower Fs, though not enough to justify the size unless it's a sealed basement or similar.

Yes, good to squeeze it some if high power is desired, with 4x Vas the pioneer's choice.

From this we see that if we couple it to a significant air mass such as a 4x Vas stuffed pipe [TL] it will push Fs lower, flatten impedance. An Fs/Qts' alignment works well for damping > 0.707 Qt TLs down to transient perfect ~0.5 Qt using FG or wool insulation, polyfil not so much unless a bigger pipe is used.

Well, it will cancel out below its dipole corner frequency.
Correct, a common tuning back when recordings didn't have much below 50-60 Hz, but much more obvious as recordings, cab tunings dropped much below 40 Hz.

GM

 

[GM]

Can I assume that if I construct an open back enclosure for either of these drivers that I get their rated SPL (91db)? ......and if I make a large/wide baffle I get additional gain due to 2pi radiation instead of 4pi?....


.....or there is no free lunch and the large baffle is needed to get rated SPL?

Well, the higher the Qt, the smaller the baffle can be till the driver alone IS the baffle [2.0 Qt?] and its dipole Qt is 0.707 'max flat' in theory [as I understand it], but have never proved it nor recall any write up/measurements, but have yet to read all of the info available.

In short, if you want to get the high Q boost, then yes, you'll need a big, wide baffle setting on and perpendicular to the floor.

GM

 

[boywonder]

Well, the higher the Qt, the smaller the baffle can be till the driver alone IS the baffle [2.0 Qt?] and its dipole Qt is 0.707 'max flat' in theory [as I understand it], but have never proved it nor recall any write up/measurements, but have yet to read all of the info available.

In short, if you want to get the high Q boost, then yes, you'll need a big, wide baffle setting on and perpendicular to the floor.

GM

Aren't the manufacturers specs measured with the driver mounted in some standard IEC baffle? If that's the case wouldn't the SPL numbers reflect half-space/2pi radiation?.....and a skinny baffle would be less forward facing SPL..baffle step loss etc.

 

[boywonder]

..... though not enough to justify the size unless it's a sealed basement or similar.

sealed basement?.....you lost me there....

Yes, good to squeeze it some if high power is desired, with 4x Vas the pioneer's choice.

same here....lost again....?? What's the rationale for 4X Vas? that's the point where the air behind the driver doesn't have much effect on overall Q? ....anything 4X or larger?

From this we see that if we couple it to a significant air mass such as a 4x Vas stuffed pipe [TL] it will push Fs lower, flatten impedance. An Fs/Qts' alignment works well for damping > 0.707 Qt TLs down to transient perfect ~0.5 Qt using FG or wool insulation, polyfil not so much unless a bigger pipe is used.

Ok....I understand this one.....if I stuff wool/polyfil in an open back enclosure I'll also get some damping...although the more I think about this a pipe/TL arrangement gets a lot more damping material behind the driver than a tall skinny tower.

Well, it will cancel out below its dipole corner frequency.
Correct, a common tuning back when recordings didn't have much below 50-60 Hz, but much more obvious as recordings, cab tunings dropped much below 40 Hz.
GM

Is this essentially baffle step loss...or more precisely the loss by just holding the naked driver in your hand?

 

[GM]

..so Qts above .707 even in infinite baffle will still has a resultant system Q greater than .707 without a box.....interesting....and that makes sense since you can make the box infinitely large and still not get flat response...are there downsides to doing this? like power handling. etc? I know the upside is no rear wave reflection issues.

So instead of putting the 4FE35-16 (Qts=1.18) in a 20L enclosure or some other large enclosure..just leave the back of a small enclosure open....same response for all practical purposes.

In the past I've generally aimed for a system Q around 1.0....for a little bass bump. I understand that this results in some "ringing" since it's under damped.

Not quite, the air mass in the box has some weight and at some point its resistance will mass load the driver to a lower Fs, though not enough to justify the size unless it's a sealed basement or similar.

Yes, good to squeeze it some if high power is desired, with 4x Vas the pioneer's choice.

From this we see that if we couple it to a significant air mass such as a 4x Vas stuffed pipe [TL] it will push Fs lower, flatten impedance. An Fs/Qts' alignment works well for damping > 0.707 Qt TLs down to transient perfect ~0.5 Qt using FG or wool insulation, polyfil not so much unless a bigger pipe is used.

Well, it will cancel out below its dipole corner frequency.

Correct, a common tuning back when recordings didn't have much below 50-60 Hz, but much more obvious as recordings, cab tunings dropped much below 40 Hz.

GM

 

[GM]

Aren't the manufacturers specs measured with the driver mounted in some standard IEC baffle? If that's the case wouldn't the SPL numbers reflect half-space/2pi radiation?.....and a skinny baffle would be less forward facing SPL..baffle step loss etc.

Only for sure if it says so.

No, dipole; half space literally means buried flush in an acoustically large, flat field and measured from up in the air on axis.

Correct.

GM

 

[GM]

sealed basement?.....you lost me there....

same here....lost again....?? What's the rationale for 4X Vas? that's the point where the air behind the driver doesn't have much effect on overall Q? ....anything 4X or larger?

Ok....I understand this one.....if I stuff wool/polyfil in an open back enclosure I'll also get some damping...although the more I think about this a pipe/TL arrangement gets a lot more damping material behind the driver than a tall skinny tower.

Is this essentially baffle step loss...or more precisely the loss by just holding the naked driver in your hand?

Some homes have [partial] below grade crawl spaces or basements which make good IBs, though ideally need to be sealed up airtight.

Just a rule-of-thumb where there's enough air mass loading to begin shifting Fs, Qts, with 10x the point of diminishing returns. You'll have to do the math to fine tune it.

Correct.

Right, plus helped protect the driver from turntable [TT] 'rumble'.

GM