Unusual approach to 2.1 bedroom system?

[engr_dave]

My 16-yo son is due for an upgrade from the awful $20 computer speakers in his bedroom. And this is a good excuse for me to build more speakers and dabble in computer audio.

It turns out I have a bunch of RS180 woofers and RS28A tweeters - I considered Modula MTMs, but MTs fit better on his desk - so you'll be seeing another Modula MT build here shortly.

Here's where it gets interesting: A Yamaha 6.1 receiver (RX-V2200) is collecting dust in my closet. Not high end, but decent, and has 24/96 SPDIF inputs. (I think MSRP was $1.2K back in 2003). I don't need surround channels (100wpc, 20Hz-20KHz, 0.04% THD, 8 ohms - manual says 6 ohm min). What I DO need is an amp for a sub. With a few cuts and jumpers, I can disconnect the C, LR, CR, & RR amplifiers and connect them to the sub signal - and still be able to use the setup level controls. Voila! Free 400W (4-channel) sub amp.

Here's the problem: A sub design with four 8-ohm drivers (or two 8 ohm DVC drivers), Vb around 2 cu ft or less, and $200 or less in drivers is elusive. Dayton's SD-270 and SD-315 DVC drivers have 8 ohm coils but don't model well in that size (1 cuft per driver). I also haven't run across four 6-1/2" or 8" subs that seem to work either.

Am I wasting my time hacking a receiver when I can buy a 500w plate amp for $200 and drive, say, RSS315HF sealed or HO ported?

[cjd]

Is the time wasted? Only you can say.

Given the new rackable sub amps PE is selling that even include what (on the surface) seems like a decent line-level crossover capability, I'd say it's very much sinking time just for the fun of it.

C

[HeatMiser]

I can't help with drivers for the type of sub you're talking about, but if you'd be willing to consider a very different approach... have you seen the little 25 Hz tapped horn that was worked up over at AVS for the Exodus Anarchy driver?

http://www.avsforum.com/avs-vb/showthread.php?t=1238398

Of course strictly speaking it's a much bigger box than you specified, but with a footprint of around 7" x 20" and 30" tall perhaps it would be a workable solution - and you might very well only need one, and one ~100W channel of amplification is just about right IIRC.

Just thought I'd toss that out there and see if it interests you at all.

[engr_dave]

That little horn is interesting, Paul. Thanks for the link. Form factor doesn't work real well (wanted to use the sub as a nightstand next to his bed). But you're right... I probably don't need to use all four amps... for a bedroom sub. That Exodus driver is indeed 8 ohm. Tempting. Are there 8" or 10" versions of that?

Chris, you're right, PE's SA230 looks really nice (the SA1000 is overkill). Unfortunately, ONLY the SA1000 has "real" high-pass outputs. The "out" RCA jacks on the SA230 are just "pass thru". No high pass - PE confirmed this. WTF? Apparently, RCA jacks on plate amps are just pass-thru, also

Makes me wonder what everyone with high end computer audio (outboard DAC, separate pre and power amp) does for 2.1. Pricey crossover like Bryston 10B or Marchand Bassis? I believe Outlaw discontinued their ICBM. Fortunately, I still have some of Bob Ellis' "Active Filter Four" boards. I guess I can build my own!

Maybe modding the receiver is not such a bad option after all...

[JonP]

Makes me wonder what everyone with high end computer audio (outboard DAC, separate pre and power amp) does for 2.1. Pricey crossover like Bryston 10B or Marchand Bassis? I believe Outlaw discontinued their ICBM. Fortunately, I still have some of Bob Ellis' "Active Filter Four" boards. I guess I can build my own!

Maybe modding the receiver is not such a bad option after all...

Ahhh... still have a few of Bob's boards myself. That would more than do it for you. Extra features on those, but you don't have to stuff the whole thing.

There used to be this: http://www.hometheatershack.com/foru...fications.html but it's discontinued and apparently no longer available. Bob (another one) at CSS used to import them for NA, but I don't see them on his site anymore.

I have one that's been heavily modified into a test bed... IC pin sockets everywhere so I can change filter parts, added stereo or mono sub capability, better opamps, etc. Needed some work to make it right, but it works well with my small 2.1 setup for work.

If you are up to fully building from scratch, there's a few designs I've been looking at. I've been getting the bug again, spare time permitting, I might get to building a few and possibly developing a simple 2.1 crossover.

There's also the miniDSP, but a simple active circuit would be cheaper, if somewhat less flexible.

On the amp issue, I'd fall in the camp of using some kind of plate amp with its crossover turned all the way up or bypassed, and the active board doing the work... if only for permitting the sub to be standalone flexible. It is another chunk of money saved to use the HT amp. Small 2.1's typically don't need big, power hungry subs anyway.

[engr_dave]

Back on task - I finally made some progress. 'Decided to build a conventional powered sub and not mess with modding the receiver. I picked up a BASH 300 amp and an RSS265HF.

I actually cut all of the pieces for 0.82 cu ft vented Modula MTs but when I mocked one up, it was HUGE! Way too big to put on a computer desk. Then I built a pair of 0.38 cu ft "Karma Indignia's" (see other thread). Even those were imposing size.

So "round three" = 0.25 cu ft sealed Modula. It modeled fairly well with F3 of 85 Hz and Qtc in the 0.6 range. I know Jon suggested keeping the 0.82 size when going sealed "to absorb the back wave" but I just don't have that much room. As it was, I decided to get the speakers completely off of the desk and turn them into in-walls. Building 0.82 cu ft into a wall cavity would have meant cutting up a lot of wall!

With 1" baffles, the RS180 still came dangerously close to the back wall of the enclosure. So I "extended" the baffles go give a little more breathing room behind the woofers.

The sub is 1.85 cu ft net tuned to 23 Hz with a 3" flared port. I had to put an elbow in the port to get it to fit - learning, in the process, that the thinwall port tubes don't fit standard PVC fittings. I had to grind out the inner diameter of the male end of the elbow to accept the flare.

[JonP]

Wow... now that'll be a cool dedicated system! Good to see progress...

Couple of things...

I forget if there was a in wall Modula crossover version, you might want to check with Jon about that. Ideally, you would want to reduce or eliminate the baffle step compensation when doing a in wall speaker, not sure how much crossover modification that would take in this case.

A Modula MT and sub combination in a bedroom will be MIGHTY... :B possibly in other parts of the house too, hope your son is good with suggestions on volume knob use... 8O

Your son is going to be a bit upset in a few years, when he realizes his awesome speaker setup won't be removable when he moves out!! :M

Oh well, another opportunity for a new project!! :T

[engr_dave]

I forget if there was a in wall Modula crossover version

I did use Jon's "non-BSC" version of the Modula MT crossover. I was a little concerned because I believe the impedance dips pretty low with this design. But in extended listening sessions over the weekend (before installing in wall) the Yamaha receiver never complained. When pushing it hard, though, it's fan became audible.

hope your son is good with suggestions on volume knob use

Yes, I'm sure we'll have a little father-son talk about that. :naughty: He hasn't blown up the family room system, which includes a JBL 2235-based sub (rated at 300W) driven by a bridged Adcom 555 (600 watts) so there is hope.

setup won't be removable when he moves out!!

I considered that in the design. The "two-piece" approach allows me to remove the baffle, replace the drywall, and just leave the empty cabs buried in the wall (crossovers are external). Then I would just need to build new boxes for the baffles to attach to.

I'll post some pics and listening impressions tomorrow.

[engr_dave]

More build pics. The first is sub in veneering process. Note that the 1" baffle edge is darker than the 3/4" MDF. I think this must have been HDF; it's super hard and heavy. Leftover from my RSS390HO subs a couple of years ago.

I had some unfaced oak veneer left over from a project long ago which will match my son's desk perfectly (which I built in solid oak and toned to a purplish mahogany color). The two pictures of the sub without driver are stained (Minwax "Sedona Red") before shooting toner and topcoat.

I set these up temporarily in my media room for listening tests. Even though inwall cabs are not optimal for absorbing the back wave, they sound surprisingly good. I lined interior with 3/4" foam and loosely filled the side chambers and behind the tweeters with polyfill. Overall, they sounded a bit lean and dry, as you would expect away from walls with no BSC, but otherwise very natural and open-sounding. I was particularly impressed with their imaging. Amazing focus and depth - particularly considering I was only driving them with a mid-fi receiver. Terry Evans (Audioquest CD) was there in the room!

You can see the finished sub next to the media room CC. It also sounds fantastic. Deep and articulate. John Clayton (Diana Krall's acoustic bassist) sounded perfect. Low notes from the electric bass on Lyle Lovett's "Step Inside This House" CD came through with authority. This sub won't rip plaster off of the walls, but plays plenty loud in my media room. Should be more than enough for a bedroom.

Time to start cutting up some walls!