Hi, I am in the process of experimenting with some subwoofers in a Lexus LS430. These vehicles are not exactly bass-friendly as the rear seats are quite robust and do not fold down. The only direct provision to get bass into the cabin is via a ski-pass. I've removed the storage box here to open up a void that measures roughly 8"x10".
The vehicle came with the typical 2cf ~42Hz pre-fab fart box which was quickly junked and immediately replaced with a quick design that I whipped up in WinISD. Currently, I am running two Alpine SWR-1223D's in two boxes grossing 6cf after displacements tuned to roughly 38Hz. For amplification I have an Alpine PDX-M12 (1200W RMS @ 2/4ohms) with SSF turned off and high-pass set at ~80Hz.
I am essentially after very strong output in the 35Hz-50Hz region (primarily centered around 40Hz). Soon after installing the box I noticed severe trunk rattle which I reduced substantially by stuffing pillows around the aperture of trunk walls and the enclosure. Pictures of the configuration are below:
I am quite used to this type of sound profile and upon listening I feel something is off in the expected response. I am noting that the system is abnormally bone-shaking between 27-37Hz. Even with the windows down, trying to negate cabin gain it's loudest in this region. Not exaggerating; with these two twelves at full bore I would have to say that it's almost comparable to my 3000W, two Sundown 15Zv3s in a 7cf box @ 35Hz, on two Fosgate T1500BDCPs that I have in another vehicle). From 39Hz-43Hz the output is respectable and from then on falls flat on its face down to 50Hz. I understand that box is a bit peaky however even at full bore it sounds likes it's down to a third of the volume at 50Hz (by my ear-o-meter I'd guess easily -12dB). Typically I expect output in this 43-50Hz region to be absolutely skull-cracking, which it is not.
I'm going back to modelling to see what exactly is going on. I just recently started using Hornresp as I believe it to be a more complete model.
To begin, I modeled the existing 6cf enclosure and responses are below (grey is nominal, black is the lossy inductance model). As expected, the box peaks but judging by ear its down a lot more than what it looks like on paper (sounds a lot more than -6dB down (between 43-50Hz). I'd have to say, 32-33Hz is the loudest to ear. I tried to verify this with a smartphone RTA app and I cannot get an accurate read on the dB as the microphone inside is definitely not linear (even at extremely low volumes).
Next, I am thinking that the vented enclosure firing through the ski-pass is acting like some sort of pseudo-6th-order. So, for this I modeled another enclosure in front of the vented enclosure. With subs moved as close to the back seats as possible the void between the back seats and subs was approximated as about 2cf with the ski-pass acting like a 3 inch long port of ~80sqin. It's not exactly peaking at the right frequency, then again the box isn't perfectly sealed to the front chamber. However I can attribute the peaking and null characteristic in the profile to something similar to what I could be hearing.
From this, I think potentially the way forward may be to design a fourth order. For this I made two chamber (60L/90L ratio with the front section coming out to about ~43Hz tune). Again, the profile using lossy inductance is in black with the nominal profile in grey. I am really liking the lossy inductance profile but the question I have is whether this will be closer to the truth than the nominal profile (which I would prefer to have more low-end).
I've always built ported boxes and I'm a firm believer in never wasting the back wave of the driver so I have not built any 4th order bandpasses. Despite my hesitation, in my heart I feel that this may be the way to go for a couple of compelling reasons:
- Even with the pillows stuffed in the aperture I am still getting some nasty trunk rattle at full bore (albeit substantially less than before).
- With that seemingly insignicant ski-pass armrest up the bass is attenuated greatly. With such as small seemingly insignificant change I can only image how much output I am losing due to trunk vibration.
- The response of the enclosure should be more predicable and I think potentially louder than the ported due to minimization of cancellations/unpredicable loading effects.
The questions I have are:
1) Is my modelling and conjecture correct?
2) Should I be using the leaky inductance model for this subwoofer? From what I researched the model is mostly valid when the Le/Re ratio close to 1:1. The Type-R using shorting rings so the inductance is somewhat more controlled (2.41mH @ 1kHz / 3.70ohm parallel).
The only thing stopping me from proceeding is seeing how peaky the nominal 4th order model looks. To me the leaky inductance model profile looks gorgeous but I am not sure if that will reality. The 4th BP enclosure is a 1:1.5 ratio which I think is fairly reasonable compared to some of the crazy 1:3, even 1:4 designs I've seen. I've also looked at some 6th order series enclosure but I think there is way more unpredictability there, not to mention the front chamber needs to be unfeasibly large with a very short port to get the where I want (in which case the ski-pass is nominally 3" long, not including seat cushion depth either).
I tried to be as detailed as possible so apologies for the long post. I would be quite appreciative of any advice. Thanks.
The vehicle came with the typical 2cf ~42Hz pre-fab fart box which was quickly junked and immediately replaced with a quick design that I whipped up in WinISD. Currently, I am running two Alpine SWR-1223D's in two boxes grossing 6cf after displacements tuned to roughly 38Hz. For amplification I have an Alpine PDX-M12 (1200W RMS @ 2/4ohms) with SSF turned off and high-pass set at ~80Hz.
I am essentially after very strong output in the 35Hz-50Hz region (primarily centered around 40Hz). Soon after installing the box I noticed severe trunk rattle which I reduced substantially by stuffing pillows around the aperture of trunk walls and the enclosure. Pictures of the configuration are below:
I am quite used to this type of sound profile and upon listening I feel something is off in the expected response. I am noting that the system is abnormally bone-shaking between 27-37Hz. Even with the windows down, trying to negate cabin gain it's loudest in this region. Not exaggerating; with these two twelves at full bore I would have to say that it's almost comparable to my 3000W, two Sundown 15Zv3s in a 7cf box @ 35Hz, on two Fosgate T1500BDCPs that I have in another vehicle). From 39Hz-43Hz the output is respectable and from then on falls flat on its face down to 50Hz. I understand that box is a bit peaky however even at full bore it sounds likes it's down to a third of the volume at 50Hz (by my ear-o-meter I'd guess easily -12dB). Typically I expect output in this 43-50Hz region to be absolutely skull-cracking, which it is not.
I'm going back to modelling to see what exactly is going on. I just recently started using Hornresp as I believe it to be a more complete model.
To begin, I modeled the existing 6cf enclosure and responses are below (grey is nominal, black is the lossy inductance model). As expected, the box peaks but judging by ear its down a lot more than what it looks like on paper (sounds a lot more than -6dB down (between 43-50Hz). I'd have to say, 32-33Hz is the loudest to ear. I tried to verify this with a smartphone RTA app and I cannot get an accurate read on the dB as the microphone inside is definitely not linear (even at extremely low volumes).
Next, I am thinking that the vented enclosure firing through the ski-pass is acting like some sort of pseudo-6th-order. So, for this I modeled another enclosure in front of the vented enclosure. With subs moved as close to the back seats as possible the void between the back seats and subs was approximated as about 2cf with the ski-pass acting like a 3 inch long port of ~80sqin. It's not exactly peaking at the right frequency, then again the box isn't perfectly sealed to the front chamber. However I can attribute the peaking and null characteristic in the profile to something similar to what I could be hearing.
From this, I think potentially the way forward may be to design a fourth order. For this I made two chamber (60L/90L ratio with the front section coming out to about ~43Hz tune). Again, the profile using lossy inductance is in black with the nominal profile in grey. I am really liking the lossy inductance profile but the question I have is whether this will be closer to the truth than the nominal profile (which I would prefer to have more low-end).
I've always built ported boxes and I'm a firm believer in never wasting the back wave of the driver so I have not built any 4th order bandpasses. Despite my hesitation, in my heart I feel that this may be the way to go for a couple of compelling reasons:
- Even with the pillows stuffed in the aperture I am still getting some nasty trunk rattle at full bore (albeit substantially less than before).
- With that seemingly insignicant ski-pass armrest up the bass is attenuated greatly. With such as small seemingly insignificant change I can only image how much output I am losing due to trunk vibration.
- The response of the enclosure should be more predicable and I think potentially louder than the ported due to minimization of cancellations/unpredicable loading effects.
The questions I have are:
1) Is my modelling and conjecture correct?
2) Should I be using the leaky inductance model for this subwoofer? From what I researched the model is mostly valid when the Le/Re ratio close to 1:1. The Type-R using shorting rings so the inductance is somewhat more controlled (2.41mH @ 1kHz / 3.70ohm parallel).
The only thing stopping me from proceeding is seeing how peaky the nominal 4th order model looks. To me the leaky inductance model profile looks gorgeous but I am not sure if that will reality. The 4th BP enclosure is a 1:1.5 ratio which I think is fairly reasonable compared to some of the crazy 1:3, even 1:4 designs I've seen. I've also looked at some 6th order series enclosure but I think there is way more unpredictability there, not to mention the front chamber needs to be unfeasibly large with a very short port to get the where I want (in which case the ski-pass is nominally 3" long, not including seat cushion depth either).
I tried to be as detailed as possible so apologies for the long post. I would be quite appreciative of any advice. Thanks.
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With so much cabin gain, seems like stuffing the vents is a quick way to flatten it out somewhat since it's already a crude 6th order, then tweak it if necessary with vent design/ damping.
GM
GM
Do you mean stuffing the vents (as in lining them), or plugging them parttially? Either way, am I correct in thinking that it would lower the fs even more? I'll try that tomorrow night and see what happens (as $3 Walmart pillows are very plentiful 😉) Another option could be to put something inside to the box to lower the gross volume to see if that raises the Fs and see what that does.
On the topic of pillows, just tonight, I added two more pillows between the trunk liner and parcel shelf. The output increased a little more however and trunk rattle was further reduced but still obnoxious in my view. I'm not sure how much further I could seal it, and this is one of the key attractors for me going to a 4th.
Being a bit OCD, the fact that MDF is cheap, and that I like woodworking I'm not opposed to building an entirely new box as well. 🙂
On the topic of pillows, just tonight, I added two more pillows between the trunk liner and parcel shelf. The output increased a little more however and trunk rattle was further reduced but still obnoxious in my view. I'm not sure how much further I could seal it, and this is one of the key attractors for me going to a 4th.
Being a bit OCD, the fact that MDF is cheap, and that I like woodworking I'm not opposed to building an entirely new box as well. 🙂
I use two Alpine Type R drivers in my car. I opted for a sealed design though. While going vented will give appreciably more output, the result could be an appreciable non-flat in-car response, depending on the cabin gain characteristics of the car. The best option all depends on what your goal actually is here.
Given what you've done so far, the first thing I'd probably try doing (after getting better measuring equipment, LOL) is to turn the boxes around so they face the rear of the vehicle, to see if that makes any appreciable improvement in performance, as mounting the subs do that the driver are nearer the center can result in a drop in midband performance. If that doesn't work, I'd consider going sealed and making a small coupling chamber to couple the output of the sealed box to that ski pass.
Given what you've done so far, the first thing I'd probably try doing (after getting better measuring equipment, LOL) is to turn the boxes around so they face the rear of the vehicle, to see if that makes any appreciable improvement in performance, as mounting the subs do that the driver are nearer the center can result in a drop in midband performance. If that doesn't work, I'd consider going sealed and making a small coupling chamber to couple the output of the sealed box to that ski pass.
Hmm, didn't get a notice till Brian's post..... anyway, I meant blocking them off as in sealed up tight, but 'ran the [published] numbers' for a max flat BP4 to get a baseline, EQ to 'taste' 😉.
GM
Ive built a number of enclosures. you could essentially build 2 small sealed boxes and determine the vent length for the skihole area to reach the desired tuning frequency. then mount the boxes and vent to a bottom and top plate. then cut a 3/4" trim panel to cover the back and seal the output into the cabin.
hint. mount the drivers magnet side in thr vented front chamber to aid cooling of the motors and if you want to get fancy you can double the rear panel and add a 3/4" lexan window.
i wouldnt reccomend facing the current boxes i to the teunk if the rattle bothers you.
Also...some of the rattle is the rear speakers bottomong out. remove them or build back boxes.
hint. mount the drivers magnet side in thr vented front chamber to aid cooling of the motors and if you want to get fancy you can double the rear panel and add a 3/4" lexan window.
i wouldnt reccomend facing the current boxes i to the teunk if the rattle bothers you.
Also...some of the rattle is the rear speakers bottomong out. remove them or build back boxes.
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