New Budget Home Subwoofer Project

[Sulla]

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?

[Sulla]

Also would there be any benefit to having more internal volume inside the enclosure past the recommended 1.5?

[GM]

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

[Sulla]

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.

[Sulla]

Also how does internal stuffing effect F3, Fb ?

[Sulla]

Well from the box design programs I have been playing with and the room I have for the enclosure in my house that about 152 liters will be the goal. That shows an FB of about 36HZ and an F3 of 36Hz. And if I am doing this right you start to run into diminishing returns over this size.

[bjorno]

Originally Posted by Sulla

..that about 152 liters will be the goal. That shows an FB of about 36HZ and an F3 of 36Hz. And if I am doing this right you start to run into diminishing returns over this size..

Hi Sulla,FYI

You are IMO pretty close with your estimation, See my investigations:

b

[Sulla]

Thanks bjorne I have not built a box since probably the mid 1980s some time so I was really not sure if I was doing it right haha. Hopefully I can get it built this week. With the woofer and amp together only costing $100 I am curios to see how it performs in the real world.

[GM]

Originally Posted by Sulla

Also how does internal stuffing effect F3, Fb ?

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

[GM]

Originally Posted by Sulla

And if I am doing this right you start to run into diminishing returns over this size.

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