I'm trying to design my first ported enclosure of a little 6.5" sub. It's a JL Audio 6W3v3-4.
I've used WinISD to model a 10L enclosure tuned to 32.03Hz with 100w input power, which is basically the parameters for a vented enclosure listed on the JL Audio website.
I'm a bit worried about the spike in excursion below the tuning frequency. Is there any thing I can do about this? Do I need to run a high pass filter to avoid damage?
I've used WinISD to model a 10L enclosure tuned to 32.03Hz with 100w input power, which is basically the parameters for a vented enclosure listed on the JL Audio website.
I'm a bit worried about the spike in excursion below the tuning frequency. Is there any thing I can do about this? Do I need to run a high pass filter to avoid damage?
Yep, if you're going to be hitting this sub with any real power, a HPF is mandatory.
If you'll always be careful, and turn it down if the sub makes any unhappy sounds, you can probably get away without it.
It's worth noting that you'll only see those large excursions if you hit the cabinet with 100W@20Hz. Very little music contains high-level content below 30Hz, so it's possible you'll get away without needing a HPF.
For security, though, I'd always recommend using one.
Finally, subwoofers often need some EQ to sound their best in any given room, so the HPF could be done there as well.
Chris
If you'll always be careful, and turn it down if the sub makes any unhappy sounds, you can probably get away without it.
It's worth noting that you'll only see those large excursions if you hit the cabinet with 100W@20Hz. Very little music contains high-level content below 30Hz, so it's possible you'll get away without needing a HPF.
For security, though, I'd always recommend using one.
Finally, subwoofers often need some EQ to sound their best in any given room, so the HPF could be done there as well.
Chris
It's also worth noting that Xmax is basically an indication of where driver linearity starts suffering. It's not a hard limit in most cases. Xmech (AKA Xdamage) is typically used for the mechanical limit of the driver, and that can be just a little over Xmax or multiples of Xmax depending on the driver. If the suspension is strong enough and the limiting factor, this may protect the driver from actual damage caused by use at full excursion. Unfortunately, Xmech isn't specified as often as Xmax, and you may not know if it's a limit caused by the voice coil crashing into the back plate or if it's a softer limit caused by the surround and/or spider. Since that's a car woofer, I would expect it to suffer abuse more gracefully than one designed for audiophile purist use, but I don't have direct experience with it, so I'm just speculating based on the intended market.
Mainly listening to '94 era Jungle and early 2000's UK dubstep on vinyl. It's all very deep bass heavy, I'm sure plenty between 20-30hz. This sub will be playing lossless vinyl rips in my work van. I'm struggling to find a 20Hz HPF that I could just pop inside the enclosure like a crossover. Do you have any suggestions? I think a DSP or full range equaliser might be out of my current budget.
Some amps have built-in high pass/infrasonic/sub bass filters, but I assume yours doesn't?
https://jlaudio.zendesk.com/hc/en-us/articles/212932558-Understanding-Infrasonic-Filters
This is another low-cost option
https://www.parts-express.com/FMOD-Crossover-Pair-30-Hz-High-Pass-266-248?quantity=1
https://jlaudio.zendesk.com/hc/en-us/articles/212932558-Understanding-Infrasonic-Filters
This is another low-cost option
https://www.parts-express.com/FMOD-Crossover-Pair-30-Hz-High-Pass-266-248?quantity=1
The amp is an Alpine BBX-T600. 130w bridged into 4ohm. HPF starts at 80Hz which doesn't help.
These inline thingies look like they could be perfect though! Is there a draw back to them? Edit: the reviews aren't great. Eek! 😬
These inline thingies look like they could be perfect though! Is there a draw back to them? Edit: the reviews aren't great. Eek! 😬
Do you already have the rips?
It is usually very easy to run digital files through a filter and save the filtered version or include a filter while ripping.
Yes, but I'm not sure I want to have to edit them all. There's nearly 2000 already with more to come, so would take ages. The subs on my other setups have no issues below 30hz so would mean maintaining a second library just for van? Maybe I need to learn to solder together my own HPF? It can't be too different from a crossover. I'd need to find a schematic as I'm definatley at a 'monkey see, monkey do' level of comprehension with this stuff.
Looks like if I replace the amp with a JL Audio Hx/300 I'll get an infrasonic filter built in! Sorted! Thanks for the advice everyone!
Just for the sake of thoroughness . . .
https://www.hlabs.com/products/crossovers/index_files/Page446.htm
I used 500 Hz ones years ago for testing and found them acceptable. I have an active crossover in my test rack now, so haven't messed with them lately. It's a little odd that the reviews are so polarized. Makes you wonder if some people got bad ones or if they picked the wrong model for their application. As with any new component, it's best to get them from a source that allows easy returns so trying them is low risk.
Doing it at speaker level is a little dicey if you don't have experience since the impedance will be varying significantly around your tuning frequency. It's not impossible, but also not something that's easy to just throw some generic components at and get good results. With large component values caused by the low frequencies, passive speaker level crossovers can sometimes cost more than a budget line level crossover/DSP these days.
There's some interaction between the FMOD and input impedance of the amplifier they're connected to, but it's typically pretty minor for average modern amps.
https://www.hlabs.com/products/crossovers/index_files/Page446.htm
I used 500 Hz ones years ago for testing and found them acceptable. I have an active crossover in my test rack now, so haven't messed with them lately. It's a little odd that the reviews are so polarized. Makes you wonder if some people got bad ones or if they picked the wrong model for their application. As with any new component, it's best to get them from a source that allows easy returns so trying them is low risk.
If you're talking about doing that at line level, it would basically be the same thing as an FMOD.
Doing it at speaker level is a little dicey if you don't have experience since the impedance will be varying significantly around your tuning frequency. It's not impossible, but also not something that's easy to just throw some generic components at and get good results. With large component values caused by the low frequencies, passive speaker level crossovers can sometimes cost more than a budget line level crossover/DSP these days.
Yes, the drawback is the crossover frequency is dependent on the amplifier input impedance.
In your case, the stated crossover frequency should be close to right on, since the Harrison Labs FMOD is designed to feed a 22k ohms input impedance and your Alpine BBX-T600 is 20k ohms.
The difference between 10k and 47K input impedance is ~2/3 octave, quite a lot, like the difference between the notes C# and G, seven keys on a piano.
RCA inputs for home stereo amps are commonly 100k ohms, some as high as 800k ohms.
At such high impedance, the FMOD might be octaves off, insertion loss huge, reviews are not likely to be good...
The average of 10k and 800k is 405k 😉
Art
Hmm, ln(47000/10000)/ln(2) = 2.2327 octaves, so really quite a lot! 
, though don't know how to equate it to this piano's tuning. 🙁
, though don't know how to equate it to this piano's tuning. 🙁
A smattering of amps from the first page of Stereophile's reviews.
(12k+50k+14k+47k+20k+34k+47k)/7=32k
https://www.stereophile.com/content/burmester-218-power-amplifier-specifications
Input resistance . . . unbalanced: 12k ohms
https://www.stereophile.com/content...bute-monoblock-power-amplifier-specifications
Input impedance: 50k ohms (unbalanced)
https://www.stereophile.com/content/krell-kma-i800-monoblock-power-amplifier-specifications
Input impedance: . . . 14k ohms single-ended
https://www.stereophile.com/content/plinius-reference-150-power-amplifier-specifications
Input impedance: 47k ohms
https://www.stereophile.com/content/accuphase-300-monoblock-power-amplifier-specifications
Input impedance: . . . 20k ohms single-ended
https://www.stereophile.com/content/naim-classic-200-series-nap-250-power-amplifier-specifications
Input impedance: . . . 34k ohms single-ended.
https://www.stereophile.com/content/schiit-audio-tyr-monoblock-power-amplifier-specifications
Input impedance: 47k ohms (unbalanced)
(12k+50k+14k+47k+20k+34k+47k)/7=32k
https://www.stereophile.com/content/burmester-218-power-amplifier-specifications
Input resistance . . . unbalanced: 12k ohms
https://www.stereophile.com/content...bute-monoblock-power-amplifier-specifications
Input impedance: 50k ohms (unbalanced)
https://www.stereophile.com/content/krell-kma-i800-monoblock-power-amplifier-specifications
Input impedance: . . . 14k ohms single-ended
https://www.stereophile.com/content/plinius-reference-150-power-amplifier-specifications
Input impedance: 47k ohms
https://www.stereophile.com/content/accuphase-300-monoblock-power-amplifier-specifications
Input impedance: . . . 20k ohms single-ended
https://www.stereophile.com/content/naim-classic-200-series-nap-250-power-amplifier-specifications
Input impedance: . . . 34k ohms single-ended.
https://www.stereophile.com/content/schiit-audio-tyr-monoblock-power-amplifier-specifications
Input impedance: 47k ohms (unbalanced)
I was referring to the difference in filter response with different input impedance, not the ratio between those input impedances:
The difference between 25 and 17Hz, is ~ two thirds of an octave, or the difference between the notes C# and G, seven notes on a piano in "Octave 0":
I chose notes closest to the frequencies Harrison Labs listed for their FMOD HP filters using the two different impedance terminations they listed.
The difference between 37Hz (near D in "octave 1") and 26Hz (near G#, "octave 0") is also about 2/3 octave.
Each octave is a doubling of frequency, there are 12 notes (half steps or semitones) in an octave.
I didn't do any math, can't say what frequencies would result using 100k ohms or 800k ohms termination, but would expect it would be off by a lot more than 2/3 of an octave.
Art