Overnight Sensations MTM Bass Question

[JJanzen]

Ok, I have verified/clarified a couple of items. 1) Paul's design for 3/4" MDF cabinets is by my calculations 3.85 cu. ft. My cabinets are 4.17 cu. ft......a bit of a difference (7.5%). The specs for the (2) ports on my drawings are incorrect. The actual port size that comes with the Meniscus kit is 1 3/8" I.D. x 5 1/2" long. Other than the cubic footage difference, the only other cabinet issue is the width of the front baffle and the cabinet configuration. Reducing the size of the interior of the prototype cabinet down to 3.85 cu. ft. will be easy to do but reducing the baffle width won't be.

Chris, I don't understand the tuning portion that you mentioned above. Could you further explain?

I will also take them apart this week and check the polarity of the wiring to make sure I got that correct.

Thanks again for everybody's thoughts and comments....I really appreciate it!

Joel

[djg]

Actually, the volume of the stock OSMTM cab is .32 cu. ft. 9 liters.

[Kornbread]

Going over the crossover and rechecking driver connections would be my first step. You could cut up some cheap $1.50 extension cords, run that from each driver out the port, pull the crossover out and lay it on the floor, and recheck everything. Even if the connections are correct, moving them around would give you an idea of what it sounds like when one or more drivers are out of phase. ~4ft³ is sub woofer territory.

[davidroberts]

Ok, I have verified/clarified a couple of items. 1) Paul's design for 3/4" MDF cabinets is by my calculations 3.85 cu. ft. My cabinets are 4.17 cu. ft......a bit of a difference (7.5%). The specs for the (2) ports on my drawings are incorrect. The actual port size that comes with the Meniscus kit is 1 3/8" I.D. x 5 1/2" long. l

I am not sure what design you are looking at but Paul's website shows the cabinets are 21l or 0.75 cu ft. If your cabinets are 4.17 cu ft (it doesn't look like it from the posted drawing) they are about 5.5 times the designed cabinet size.

https://sites.google.com/site/undefi...htsensationtmm

Using your volume and port sizes in Unibox your design results into a tuning of ~15hz. The blue line is the enclosure design per Paul's website, the Red is your current cabinet size and ports.

[djg]

Again, the stock OSMTM cab is .32 cu. ft. 9 liters volume. You're looking at the TMM tower. Similar but different. Probably get more bass from the TMM.

[Kornbread]

I didn't even realize there was an mtm version of the os.

[davidroberts]

djg, sorry that was my oversight on the TMM and MTM version. It still doesnt change the fact that the enclosure volume the OP sighted are way too large for this design.

Here is the frequency response for the MTM (blue), TMM (pink) and OP's posted volume and port size.

[djg]

Yes, OP misplaced a decimal point at the very least.

[djg]

If I wanted a pair of skinny mini towers with more than adequate bass, and I had $500 sitting around, I think I would go for Paul C.'s Speedster TMM. I need a pair of those like I need another hole in my head.

https://sites.google.com/site/undefi.../speedster-tmm

[JJanzen]

Ok, so I my calculations are all screwed up...I deal in square footage all day long in my regular job and divided my cubic inches by the incorrect number. Guys, thanks for bringing that to my attention! I do agree with djg that Paul's design is .32 cu. ft. My cabinets are .35 cu ft. with the corrected calculations. David, would you be kind enough to re-run the frequency response again with the OS MTM shown as well? Just to be clear, my port size is 1 3/8" I.D. x 5 1/2" long. Thanks again!

Joel

[Prana Ferox]

JJanzen, does your cabinet have any kind of stuffing, liner or fill?

Paul tends to recommend a fistful or two of Polyfill for his builds to add a bit of damping, seemingly to cure exactly what you're complaining about . A big bag is cheap as heck in your local Wal-Mart sewing section.

From the OSMTM write-up: "The enclosure could be lined with convoluted foam, which is pretty standard for a vented design such as this. In my case, to keep things simple, I did not line the enclosure at all. Instead, I used a few light handfuls of polyfil behind the woofers (the internal braces sort of held it in place). As I told many people who built the original Overnight Sensations, getting the right amount of stuffing takes a bit of experimentation. I find the best results when I over-stuff a bit, then gradually take some out, listening each time. I know when I get the right sound; the speaker suddenly just sounds "huge.""

[Millstonemike]

djg, sorry that was my oversight on the TMM and MTM version. It still doesnt change the fact that the enclosure volume the OP sighted are way too large

DJG nailed the issue. Dave, I suspect a comparison pic of the excursion graphs at power would show the the OP what he's hearing.

[djg]

You might want to build a "stock" enclosure including interior treatment to see how that sounds. It's possible you just don't like this design.

[Chris Roemer]

Your vol. and tuning are VERY close to Paul's - it's your (stepped) baffle and driver placement that could color things.

[JJanzen]

JJanzen, does your cabinet have any kind of stuffing, liner or fill?

Paul tends to recommend a fistful or two of Polyfill for his builds to add a bit of damping, seemingly to cure exactly what you're complaining about . A big bag is cheap as heck in your local Wal-Mart sewing section.

From the OSMTM write-up: "The enclosure could be lined with convoluted foam, which is pretty standard for a vented design such as this. In my case, to keep things simple, I did not line the enclosure at all. Instead, I used a few light handfuls of polyfil behind the woofers (the internal braces sort of held it in place). As I told many people who built the original Overnight Sensations, getting the right amount of stuffing takes a bit of experimentation. I find the best results when I over-stuff a bit, then gradually take some out, listening each time. I know when I get the right sound; the speaker suddenly just sounds "huge.""

Yes, there is poly in the cabinets. The complete kit that Meniscus sell comes with everything.

[JJanzen]

Your vol. and tuning are VERY close to Paul's - it's your (stepped) baffle and driver placement that could color things.

Chris, I had no idea that would effect the sound quality. I think I will build a couple of cabinets identical to Paul's original specs and see if I can do an audible comparison.

Thanks everyone for your thoughts on this....I learned a lot and really appreciate it.

Joel