Overnight Sensations MTM Bass Question

[JJanzen]

Newbie on the forum here. I purchased an OS MTM kit back in 2015 and finally got around to building some prototype cabinets and such. I am quite pleased with the outcome but the bass seems to be "rolling" and not tight like I expected it to be. I am a hobbyist woodworker with an interest in speaker cabinet design but don't know much about the technical side of things. I was wondering what might make sense here (if anything). I have attached a pic for reference. Both ports come out of the bottom. I had hoped this design would allow the speakers to be mounted on the wall with a "french cleat" but my initial trial of that concept did not sound well at all. I then threw together some quick stands and pulling them out away from the wall about 18" and pointed at the listener seems to give the best results. Any ideas on how to tighten up the bass? Thanks.

Joel

[Millstonemike]

What type of programming are you playing? Lower frequencies in Home theater may be overdriving the OSs beyond their capabilities. If it is a HT receiver, try invoking the receiver's HP filter on the front mains.

Also, when you say "Both ports come out the bottom." I presume you mean one ort for each speaker cabinet; correct?

[djg]

The DIYSG OSMTM kit has two ports.

[Millstonemike]

My bad. I didn't read the "fine print".

[Kornbread]

Two ports? IIRC, the ot are generous with the bass so mounting them on the wall are probably not the best placement. I had them out about 4' from the wall.

[djg]

OSMTMs need a subwoofer for bass, regardless of whatever comments and reviews you may have read.

Should I assume you made your cabinets to the specifications in the kit and Paul C.'s website? Oh wait, your picture shows a cabinet much different than the specified cabinet. It has a wide stepped baffle. That will change bass response, as will a different cabinet volume still using the kit supplied ports.

Give us some details on the cabs. Please.

[LOUT]

If the test-box internal space is different than the suggested 10L-11L, you'll end up with different bass-behavior....a smaller box will limit how low/deep the bass can reach and usually gives a louder spike of high-bass right before the low-end falls off a cliff...a box that's too large can let the speaker reach lower/deeper bass which can often get flubby and distorted even at modest volumes.
The proper internal box-space (and port tuning) should help the speaker reach a decent balance of bass depth and volume before getting messy, though most smaller speakers will still get flubby if given really deep bass and cranked too loud...so limiting the deepest lows they're sent (usually by letting the reciever or player know they're smaller speakers, or telling it to send deep bass to a subwoofer instead) can still help.


A speaker being placed a few feet forward from the wall behind it will lose up to 5-6db of bass (and often low mids) compared to the same speaker being placed with its back right up against the wall. This is usually balanced out in the crossover design (called BaffleStepCompensation, I think) but it means speakers that are designed to sound best a few feet foward from the wall will end up sounding noticeably bass-heavy if you put them right against the wall or very close to it.
Speakers being wall-mounted will usually need a crossover that's designed for that placement....or you might EQ the bass down with software or your reciever to get a similar effect if you don't want to change the design physically.


The height and width of the box-face ("baffle") the speakers are mounted to can affect the frequency response as well, usually in the high-bass up to the mids. The crossover will be designed to work together with a particular "baffle" size and shape, and moving to a larger-than-ideal baffle can give you louder mids and high-bass.


It sounds like you might be suffering all three of these right now, but most/all of it can probably be fixed when you change over to the recommended box-size/tuning and front-baffle shape, make sure the reciever isn't sending subwoofer bass to them, and probably add a bit of EQ to tame the 80-500hz range since you'll be wall-mounting.

Reasonable expectations might be to limit them under around 15-30watts and assume they'll get flubby with bass under 45hz unless you're playing them at modest volumes under 2-3watts (which can still reach about 85db....maybe 90db against a wall, I think).

[Birchmen]

Not really anything new to add, but
Whats the box volume?
Whats the port tune?
How is your room?
How have other speakers performed in the same place?

Any significant changes to the baffle can have a big impact. Also, wall mounting/close wall placement can have a big impact.

[davidroberts]

Pretty sure your issues are due to the modifications to the box volume and the baffle. As others have mentioned put them in the correctly sized box that Paul designed with the ports on the back as designed and I promise you will see much better results.

Most people who have built them correctly are amazed at the amount of bass from such a small speaker. That is one of the reasons they are so popular and Paul continued to due multiple different designs.

From Paul's conclusion on his website: "These are fairly small speakers, and to most ears they will put out a sound that defies their size. This is one speaker that will keep you wondering, "Is the sub still on?"

[Millstonemike]

The internal box volume is critical. If your test boxes are oversized, you can reduce the internal volume by adding some "wood" inside. Port location doesn't really matter much.

[djg]

Note: OP hasn't been back since his first post. Why do we even bother?

[JJanzen]

Sorry guys, been away for a few days! I really appreciate all the comments.

Back in 2015 when I designed these cabinets, I followed the cubic inch requirements of the cabinet exactly as Paul had originally specified. I purchased the kits with crossovers and ports from Meniscus and sent them the plans for review and comments. As I recall, they indicated both ports could come out of the bottom, the back or the front and felt like, even the cabinet shape, design and config was different from the original design, those issues would not effect the performance of the speaker. I reached out to them this week and they thought it sounded like one of the drivers might be wired incorrectly (+-). I haven't had time to check that out yet.

I have messed around with placement and have found they sound the best about 18-22" out from the wall. I built the temporary stands so I could move them around. They are currently hooked up in the basement of a rental house I own with a carpeted floor. I have a 70 watt per channel Denon 5.1 receiver powering them.

I have attached the original design drawings as a multiple page pdf. As you can see, these prototypes are built out of 3/4" particle board with the intention of building the final cabinets out of 3/4" MDF that I can either paint or veneer. Any and all thoughts are much appreciated and welcomed! Thanks.

Joel

[djg]

Why not try a "stock"cabinet and see how it sounds? If the speakers are wired right. Some people don't like some speakers, even very popular ones.

[JJanzen]

More files

OS MTM Speaker 020819 Pg1.pdf
OS MTM Speaker 020819 Pg2.pdf
OS MTM Speaker 020819 Pg3.pdf
OS MTM Speaker 020819 Pg4.pdf
OS MTM Speaker 020819 Pg5.pdf

[JJanzen]

Note: OP hasn't been back since his first post. Why do we even bother?

No wifi or computers on a hunting trip

[djg]

I jumped to a conclusion, sorry..

[Kornbread]

No wifi or computers on a hunting trip

I will admit to being a little confused about having two ports. Wall placement will make a noticeable difference in their sound as you have already noted by moving them out 18"-22". Baffle size and shape also play a role as well as changing things from a TMM to an MTM. How much of a role, well, that is a question for the ears of the listener. If it sounds good to you that is all that matters.
Having one woofer polarity reversed will nearly cancel each other out.
You shouldn't have to build new cabinets from mdf just to paint or veneer them.
Most of the time, I will run the wires out the port, lay the crossover on the floor beside the speaker, and temporarily connect it there until I know everything is ok. I am the world's worst with missing a connection or mixing up polarity. Put the crossover in the pedestal of these OS towers.

[Chris Roemer]

From what I can tell, Paul's cabs were 9L (0.32cf) tuned near 60Hz, whereas yours appear to be more like 10L (+?) (0.36-0.40?) tuned to 50Hz.
You might want to try shortening your vents from 4" down to 2-1/2" to 3"?
Also, the 1" dia. seems a bit small to me.

As has been stated, your baffle (esp. the width) should definitely have an "effect" on Paul's design (can't say if it's "adverse" or not, but most likely it will be different).
To maintain the design (better), most would keep the width the same (and driver placement - esp. w/regards to the cab top) and, if a shallower cab was needed, would have added height below the driver array.

[djg]

Here's the DIYSG S2000 MTM cab, same as their OSMTM cab with a different baffle. 1/2" Baltic Birch. Two 1 3/8" dia. x 4 1/2" L ports. These.

https://www.parts-express.com/parts-...table--260-388








You know, the S2000 series, also by Paul Carmody, is a big improvement over the OS series, IMHO. If you're calculating volume, note the back panel has a 1/4" rabbet.