[Bsmooth]

I have my AudioEngine a5+ in my bedroom now, and I must say I'm pretty impressed with the sound, but there lacking just a tad on the low end. I tried looking for a small sub, because space is very limited(Thanks to all for suggestions for the small sub BTW).
 The best I could find was a Jamo S 808
 ahttps://www.amazon.com/Jamo-808-Sub-WH-White-Subwoofer/dp/B07JJFVVB2/ref=pd_lpo_sbs_23_t_1?_encoding=UTF8&psc=1&refRID=4V9NNFNT9EZGT123YZ7B sub
Its about the right size to fit under a cabinet we have, but it is a bit tall. I was wondering If I got a plate amp and a speaker , could I make the enclosure maybe 6 inces tall instead of the 7 and about the same dimensions, what sort of bass response would I get?

[JLM]

Just adjust the exterior dimensions to keep the internal volume unchanged (and still fit the plate amp/driver/possible port).

Of course you'd need to use the same plate amp/driver to get the same response.  Have you heard it yet?  In most, the term "tiny sub" is an oxymoron as they can't go deep at any reasonable volume.  In fact most tiny subs have worse bass performance than 2-way monitors like your Audioengines.

[Mark Korda]

(https://www.avsforum.com/forum/155-diy-speakers-subs/1690890-just-finished-my-home-depot-5-gallon-bucket-subwoofer-large-pictures.html)     Bsmooth, I made one of these and it's fun. I don't have mine hooked up yet because I'm still shuffling stuff around....Mark Korda

[Doublej]

I would just buy something like a PSB 100 "subwoofer".

6 3/8 x 6 3/8 x 7 7/8”

[srb]

(https://www.avsforum.com/forum/155-diy-speakers-subs/1690890-just-finished-my-home-depot-5-gallon-bucket-subwoofer-large-pictures.html)     Bsmooth, I made one of these and it's fun. I don't have mine hooked up yet because I'm still shuffling stuff around...

A 5-gallon bucket won't fit into the 6" under-cabinet space. 

[Mark Korda]

Sorry, I didn't catch the size requirements...Mark K

[Bsmooth]

maybe not the right size but I appreciate the idea. That is one different sub. Even If it didn't turn out like you wanted you had some fun and learned something, I would say that would be a success. I've built quite a few different speakers through the years, and tried quite a few ideas. Most of them were flops, but I must admit in a strange way they were fun. Frustrating at times, but I learned a lot about crossovers, especially microhenries, and winding coils.
 So thanks for relaying your experiences !

[WGH]

Yes, it is possible to build a small subwoofer although I never did, but I thought about it. The articles below and software spread sheets get into the weeds real quick, but you asked so here is one answer:

Back in May 1996, Matthew S. Polk (Polk Audio, Inc.) wrote an article in Audio Magazine about his HVCD Sub-Woofer (High Velocity Compression Drive). For a small fee, Matthew also supplied the spread sheet for calculating band pass box and driver parameters along with power port dimensions. The files and calculations are for personal use only.

First read the original Audio Magazine article - More Bass In Less Space by Matthew Polk
http://wghwoodworking.com/audio/Audio_1996-HVCD-Subwoofer.pdf

Second, if you are still interested read the information and instructions supplied with the HVCD Sub-Woofer spreadsheet
http://wghwoodworking.com/audio/PolkHVCD.pdf

Third, if you have Microsoft Excel or Quattro Pro download the spreadsheets I copied from the original 3.5" floppy disks and start calculating
http://wghwoodworking.com/audio/POLK-HVCD-SUB-WOOFER.zip

You will be able to extend the bass even lower with a Marchand Bassis, a parametric equalizer that will extend the bass response of a small box and is a DIY alternative to the Behringer.
The April 1990 Audio magazine has a detailed article about the construction, adjustment and use of the Bassis by Ralph E. Gonzalez.
Here is a copy of the article in a pdf file for anyone wanting to build one of these units:
http://wghwoodworking.com/audio/bassis.pdf



Bare boards used to be available, assembled Bassis are still listed on their website
http://www.marchandelec.com/wm8.html

Have fun!

[srb]

Here's a small economy 8" subwoofer that's 6.2"H from budget/value leader Monoprice .....

https://www.monoprice.com/product?p_id=33829&gclid=EAIaIQobChMIqYfYqtvJ4AIVUUwNCh2gtwu1EAQYASABEgKKh_D_BwE