Hi guys thought I would get some feedback on a budget passive subwoofer project I am working on. The sub I am using for this is a Polk MM2154DVC. I will be using it in the recommended 1.5cu ft sealed box.
I will be building it into a cube shaped end table. The table is 3/4 particleboard but made well and then I will add an internal MDF with the inner and outer box glued together. Should make a nice stiff box. And it works out exactly right for two of these subwoofers. So after adding the internal devider I will have an easy upgrade to a second subwoofer if needed.
For basic testing I will be using my NHT mono ma-1a amp. This will be underpowered but will do for a while if I am careful. I will be wiring the coils in series so it will be 8ohm. The amp is only rated down to 6ohm so I dont think it would like the 2ohm load if I ran the voice coils in parallel. And of course looking for a great deal on a higher power amp.
And I do have a couple of questions. Since the internal volume will be exactly what the recommend I would think there is no reason to stuff the enclosure. But should I line the inside with something?
I will be building it into a cube shaped end table. The table is 3/4 particleboard but made well and then I will add an internal MDF with the inner and outer box glued together. Should make a nice stiff box. And it works out exactly right for two of these subwoofers. So after adding the internal devider I will have an easy upgrade to a second subwoofer if needed.
For basic testing I will be using my NHT mono ma-1a amp. This will be underpowered but will do for a while if I am careful. I will be wiring the coils in series so it will be 8ohm. The amp is only rated down to 6ohm so I dont think it would like the 2ohm load if I ran the voice coils in parallel. And of course looking for a great deal on a higher power amp.
And I do have a couple of questions. Since the internal volume will be exactly what the recommend I would think there is no reason to stuff the enclosure. But should I line the inside with something?
Hmm, this cab alignment appears to be designed for a car audio app, so a poor choice for a HIFI/HT one even if heavily stuffed as it should be since it's acoustically too small (~60 Hz F3). Another 'problem' WRT SQ is that with the coils wired in series it has a published (high) inductance of 4.4 mH, so will in theory require a lower than normal XO point to make it ~flat in-room, especially if nearby as you're planning. This lowers its effective efficiency, though may not be an issue due to it being close to the LP.
Based solely on the measured specs then, a minimally damped sealed cab of at least 150 L (and preferably larger) to get F3, Fb down into the mid 30s makes more sense to me.
GM
Based solely on the measured specs then, a minimally damped sealed cab of at least 150 L (and preferably larger) to get F3, Fb down into the mid 30s makes more sense to me.
GM
Ahh OK thanks for the help. Just opening up the entire volume in this one would make it 87.7700L - cross bracing. I could also pretty easly change the height up to about double what it is now. That would give me 191.029 L - bracing. Or of course I would build an enclosure from a fresh start hmm. 
Last edited:
Attachments
It makes the driver 'feel' a larger/weaker air spring, so Fb drops and since a 0.707 Qtc alignment has the lowest F3, all others will raise it: Sub Box Polyester Fiberfill
GM
Depends on the performance goals and how accurate the published specs are. Many require a larger cab, though it's not as big a deal with sealed as it is with vented; plus, ~36 Hz is low enough for most music, but way too high for some recordings and especially for watching movies released after ~1993.
GM
Thanks for the info GM. And I have another question. Since it is a sealed enclosure with smoother drop off than a ported sub it should have a little more useful low end below 36Hz when you factor in boundary gain and room gain correct?
I will see soon how it sounds with this enclosure. I got it about 90% done today. Just need to cut the hole for the subwoofer and wrap the botton third where it is indented. Look like a mid century moderm cube type design. Something like a Bose 501 but hopefully better haha. Anyway when the subwoofer comes in I will let you know how it sounds.
Any way hopefully this will perform really well for most music and good for home theater. As a side note I watch a lot more old movies than I do new ones.
I will see soon how it sounds with this enclosure. I got it about 90% done today. Just need to cut the hole for the subwoofer and wrap the botton third where it is indented. Look like a mid century moderm cube type design. Something like a Bose 501 but hopefully better haha. Anyway when the subwoofer comes in I will let you know how it sounds.
Any way hopefully this will perform really well for most music and good for home theater. As a side note I watch a lot more old movies than I do new ones.
You're welcome!
In theory, but being located at LP normally means not near any boundary or where room gain is high other than the floor (2pi space) and at the current size it will have to be heavily stuffed to lower Qtc enough to maybe extend the audible BW a bit lower enough to take at least a little advantage of any room gain, though it will improve SQ if you're one of those relatively few folks that are sensitive to LF damping.
Auditioning it damped with one side, back and top or bottom wall covered with 1" acoustic fiberglass insulation or similar and then with it heavily stuffed will 'tell the tale' the range of performance tuning options and whether or not it will please.
GM
In theory, but being located at LP normally means not near any boundary or where room gain is high other than the floor (2pi space) and at the current size it will have to be heavily stuffed to lower Qtc enough to maybe extend the audible BW a bit lower enough to take at least a little advantage of any room gain, though it will improve SQ if you're one of those relatively few folks that are sensitive to LF damping.
Auditioning it damped with one side, back and top or bottom wall covered with 1" acoustic fiberglass insulation or similar and then with it heavily stuffed will 'tell the tale' the range of performance tuning options and whether or not it will please.
GM
Yes the extra boundary will increase acoustic efficiency up to +3 dB and even more if near a hard corner.
For best coupling/mirror imaging we want the driver as close as practical, but the WLs are so long in the LF that it's not real critical.
The damping is mostly for quelling eigenmodes somewhat and keep them from reflecting back through the driver which can give the box a hollow sound, but try it without to see if it's acceptable to you. Still, all things considered, heavily damping it to get a lower tuning to take max advantage of that room loading seems the solution, but only one way to know for sure........
GM
For best coupling/mirror imaging we want the driver as close as practical, but the WLs are so long in the LF that it's not real critical.
The damping is mostly for quelling eigenmodes somewhat and keep them from reflecting back through the driver which can give the box a hollow sound, but try it without to see if it's acceptable to you. Still, all things considered, heavily damping it to get a lower tuning to take max advantage of that room loading seems the solution, but only one way to know for sure........
GM
OK that is what I was thinking. The box is now setup with the woofer next to the floor and really is more stable this way anyway.
For damping my plan is now to try it without any damping or stuffing when the woofer gets here. Then after a few days take it apart and try it with the full dampening. Then make a choice from there.
For damping my plan is now to try it without any damping or stuffing when the woofer gets here. Then after a few days take it apart and try it with the full dampening. Then make a choice from there.
Finally got the subwoofer in and got everything together. It sounds good. Much less sloppy than my Cerwin Vega home theater sub I was using. Also really fills in the bass when pared with my Polk SDA 1 main speakers.
Next thing to do is make a cover to hide the subwoofer.
Attached is a very low quality image but it gives you an idea.
Next thing to do is make a cover to hide the subwoofer.
Attached is a very low quality image but it gives you an idea.
Attachments
Good! Yeah, my 'loud is beautiful........' sig line was CV's mantra decades ago, but they lost their way........
I love a happy ending.
GM
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.