MBM DIY Design Concepts...

Early B.

GV#27 and I thought we'd kick around some ideas for potentially building a mid-bass module. This idea was inspired by the MBM-12 from Hsu Research: http://www.hsuresearch.com/products/mbm-12.html

Let's get it going.

First thing we ought to do is consider the differences in design between actual subwoofer and an MBM. First, since the MBM driver is only handling frequencies from 50 Hz - 80 Hz, we'll need to choose an appropriate driver. According to the Hsu website, the driver should have these traits:

"...a very light cone, low inductance voice coil, and a strong magnet yields extremely quick response with high efficiency."

OK, so where can we find the driver?

If anyone can find some links to DIY MBM's, please post them.

Thanks.

Systems

It appears the driver that HSU uses for the MBM has a rather higher than normal resonant frequency allow them to use a vented design tuned to around 50hz.
It might be hard to source such a beast that can be used in a vented box with that high of a tuning.However there are many 12" drivers that are suitable for use in small sealed enclosures with the roll off starting around 50hz or so.I plan to try an Infinity 12" car driver that seems to fit the bill with high efficiency,high power handling ,a light poly cone and can work in a tiny 1 cubic ft sealed box. Although a sealed designs response will overlap the main sub more than a ported design because it has a more gradual roll off below its tuning.This may or may not be a problem it will be system dependant.

Early B.

GV--

Will the Infinity car driver be "musical" enough for ya or too boomy? I dunno. Maybe it doesn't matter too much for 50-80 Hz. I guess I should have mentioned that my intent is to use the MBM for HT only.

I really like the sealed sub idea. That should make the MBM easier to build, especially if it is only 1 or 2 c.f. Will a sealed sub require a more powerful amp?

My budget for this project is $250 or less. Here's the breakdown:

driver - $75
amp - $125
MDF, supplies, etc. - $50

beardog03

are my polk momo 12`s usable for this project ?
They ar ethe older models...I have had them fro awhile now (got them here)
They were about three months old , gently used when I got them, and they haven`t left the box they came in since I got them...

I`m dieing to use them for something..!!

Early B.

Is there any reason why a used Hsu sub (or other brand) wouldn't work well for this application?

Can someone with an extra sub or dual sub setup try this and report back?

Based on the MBM-12 manual, here's how you hook up the MBM to your receiver:

Use a Y adapter to split the signal from the sub out to feed both the true subwoofer and the MBM-12. Set the crossover frequency on the subwoofer to 50 Hz, and crossover switch to ‘in’. The MBM-12 will then reproduce the range from 50 Hz up to the crossover frequency set on your controller. Your true subwoofer will reproduce the range from 50 Hz down.

VR3

This sounds soooo pointless...

I'm all for weird configurations (I I have alot of ideas that are weird)

But this seems to be over-thinking it.

Why not just get some speakers that are real good in that 50hz and above region and just cross a real sub at 50hz instead of having an extra piece?

Maybe I'm just missing it, try it - maybe it does make a difference. But I dunno, sounds kind of BSish to me.

Early B.

Vr3MxStyler2k3 wrote: »

This sounds soooo pointless...

...Maybe I'm just missing it, try it - maybe it does make a difference. But I dunno, sounds kind of BSish to me.

Most concepts in audio sound "kind of BSish" to me. I dunno if it works or not, but I think it's worth exploring.

Early B.

Vr3MxStyler2k3 wrote: »

Why not just get some speakers that are real good in that 50hz and above region and just cross a real sub at 50hz instead of having an extra piece?

Allow me to extend your logic -- why have a sub at all? Just get some speakers that are real good down to 20Hz instead of having an extra piece...

See where I'm going here? It may seem logical, but not necessarily true. A dedicated subwoofer is used because it can play lower frequencies better than your main speakers, no matter how deep they dig. So let's take it a bit farther. It may be possible for a dedicated mid-bass module to play mid-bass frequencies better than the main speakers. That's what I want to find out.

Systems

Vr3MxStyler2k3 wrote: »

This sounds soooo pointless...

I'm all for weird configurations (I I have alot of ideas that are weird)

But this seems to be over-thinking it.

Why not just get some speakers that are real good in that 50hz and above region and just cross a real sub at 50hz instead of having an extra piece?

Maybe I'm just missing it, try it - maybe it does make a difference. But I dunno, sounds kind of BSish to me.

OK here is my take on this mid bass thing.I will be using it on the LFE channel only as my main speakers have extension down to 25hz therefore need no help.For the LFE I am currently using a pair of DIY 12" subs in opposing corners of my listening room.(They are large so my only placement option for them is in the corners)
The plus side of the corner placement is that it gives me maximum output from them because of the several db of room gain that they recieve from the corners.
The down side of corner placement is that room modes rear their ugly heads which can lead to some bass boom.To try and minimize the severity of the peaks created by the room modes I have set the LFE crossover point at 45hz which I find sounds much better than the usual 80hz setting.

Unfortunately that means that Im missing some info in the 45-80hz range that can add a goodly amount of impact to movie sound tracks.Therefore If I could add a small unobtrusive enclosure close to my couch it would give me the missing info back.And the fact that it is in the nearfield would not be as affected by room modes.:)

Systems

Early B. wrote: »

GV--

Will the Infinity car driver be "musical" enough for ya or too boomy?

Yes I believe it will sound musical in a small sealed box.The boominess usually associated with car woofers is more a fault of using improperly designed boxes (usually ported)and the envirement in which they are used.

Systems

beardog03 wrote: »

are my polk momo 12`s usable for this project ?
They ar ethe older models...I have had them fro awhile now (got them here)
They were about three months old , gently used when I got them, and they haven`t left the box they came in since I got them...

I`m dieing to use them for something..!!

Maybe,do you have info on those such as FS,Vas ,and Qts?

beardog03

any thoughts on my 12" momo`s ?!!

Systems

beardog03 wrote: »

any thoughts on my 12" momo`s ?!!

See post above.:)

beardog03

oops !
my bad !

I will have to look up the info on them

Systems

beardog,are these your drivers?http://www.polkaudio.com/caraudio/specs/mm2124/ If so they ll should work fine for mid bass duties above 50hz in a 1.25 cu ft sealed box.

beardog03

No they are the ones with the yellow momo

http://www.polkaudio.com/caraudio/products/mm124/

Systems

beardog03 wrote: »

No they are the ones with the yellow momo

http://www.polkaudio.com/caraudio/products/mm124/

Yes they should work also but in a slightly smaller box of 1cu ft.(per driver)

beardog03

kool !
:cool:

I didn`t know that you could use car subs for home use !

Systems

beardog03 wrote: »

kool !
:cool:

I didn`t know that you could use car subs for home use !

Some are not suited but many can be adapted to home use it depends on their actual parameters.Many car woofers are designed for use in small sealed boxes but have limited low frequency extension usually 40-50hz range.
But this works in a car because there is a ton of low frequency gain (cabin gain) which works to extend the response to a much lower frequency. These same drivers should work well (for DIY mid bass modules) for use in a large space because we only want response down to 50hz.

I use a pair of 12" car woofers in sealed boxes for my main LFE subs.But to get the deep extension into the 20hz region I had to add a special EQ circuit.

beardog03

So now I should get a plate amp?
about what, 350w ? (per speak)

Systems

beardog03 wrote: »

So now I should get a plate amp?
about what, 350w ? (per speak)

If you were going to try this I would built just one to see if you actually like the results.If you set it up close to the listening position then power requirements will be less, so I doubt you will need a full 350w'. but having more power than needed is a good thing.It must also be happy with a 4ohm load.

If you use a plate amp it must have at the very least a phase switch but it would be a BIG bonus if it had a continuosly variable phase control instead.This will be necessary to achieve a good blend between the mid bass unit and the sub or sub's.Of course it will also need a built in crossover which virtually all of them have.

Early B.

GV -- what optimal specs should we seek in a woofer? I'm interested in scouring ebay and partsexpress for the woofer, but I'm not sure what to look for.

Thanks.

Systems

Early B. wrote: »

GV -- what optimal specs should we seek in a woofer?

Here is a general guideline of what I would look for.Drivers with parameters different than these might still be usable.If you find something of interest post the specs and I will run them in a box calculator program for you.

Sensitivity=90-93db or higher

Fs= 25-30 hz

Qts= .3-.5

Vas =under 100litres

xmax=12mm or greater

Early B.

What about this one:

http://cgi.ebay.com/12-Eosone-Woofer-250-W-RMS-Division-of-Polk-Audio_W0QQitemZ230170734211QQihZ013QQcategoryZ3276QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

dudeinaroom

hmmm.. mid bass driver...ported...strong magnet.....bass guitar speaker? 4-6" midbass drivers(same cone area as a 12") just a couple thoughts.

Early B.

Or this one?:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=299-674

Systems

Early B. wrote: »

What about this one:

http://cgi.ebay.com/12-Eosone-Woofer-250-W-RMS-Division-of-Polk-Audio_W0QQitemZ230170734211QQihZ013QQcategoryZ3276QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

The price is certainly right.It looks usable but because of it's large Vas spec you would need a 1.6 cu ft box.

I should add that I don't know how this concept will work as I have yet to try it.While I believe It does hold promise if setup correctly I make no claims for its performance.So if someone builds it and is dissatisfied please don't shoot me.:D Build at your own risk.:)

Systems

Early B. wrote: »

Or this one?:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=299-674

That one looks real good except the Xmax is only6.6mm which is less than I would want.That means it excursion capability is limited.Otherwise it looks good in a 1 cu ft box.

Im not sure of the Xmax on the Polk you linked to as they did'nt state it in the specs.

Systems

dudeinaroom wrote: »

hmmm.. mid bass driver...ported...strong magnet.....bass guitar speaker? 4-6" midbass drivers(same cone area as a 12") just a couple thoughts.

Certainly possible with the right drivers.

Early B.

OK, one more:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-444

Systems

Early B. wrote: »

OK, one more:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-444

As you would expect for the price that is the best of the three.The only thing is it's sensitivity is on the low side but should be fine.