How Do I Build A Pair of OB Subs Inexpensively?

bprice2 · « **on:** 17 Mar 2010, 12:11 am »

I've looked around here a bit and have found a couple of threads on building OB subs. It appears most are going for the offerings of GR Research and Hawthorne Audio. While it sounds like either would be a great way to go, I'd prefer to not spend that much money.

So, I was thinking that maybe I could utilize the 120 wpc Class D Audio amp I recently purchased and bridge it for 240 wpc (into 4 ohms) and purchase another amp board (bridged) and run a pair of OB subs from it.

Of course, I would also need to purchase at least a pair of suitable drivers for this project. I guess I'd also need to purchase some kind of crossover.

What do y'all think? Is there an inexpensive way of doing this? I'm thinking in the $300 range tops.

Here's how I'm visualizing this working: from my RWA Signature 30 amp's line level outs, run the signal to a crossover and then to the Class D amp and then to the drivers set up in OB. Will this work?

Thanks,

Brett

mcgsxr · « **Reply #1 on:** 17 Mar 2010, 01:04 am »

For an affordable Xover, I would choose either the B1 or B2 Reckhorn from this site - http://www.creativesound.ca/products.php?make=Reckhorn&category=

For affordable OB woofers, I have found that car subs (used) are the best bet. Look for something with a dual voice coil. By using only one VC, you double the effective QTS, often bringing it up to the desirable 0.6-0.8 range. Car subs tend to have lots of XMAX, and low FS, other desirable traits.

I use 2 MAW-12 woofers in this config, using an old pro audio amp for the power, and using a Reckhorn Xover - have done so for closing on 3 years now.

Mariusz · « **Reply #2 on:** 17 Mar 2010, 01:54 am »

Did you see this http://www.audiocircle.com/index.php?topic=77435.0

You can get the parts yourself too. Just not sure how much would you save?

Cheers
Mariusz

neobop · « **Reply #3 on:** 17 Mar 2010, 02:34 am »

I'm kind of new to the world of open baffle speakers, but not to speaker building. Seems to me that large woofers with a high Qts are best for open baffle. Carver, commenting on his amazing speakers, suggested a Qts greater than 1.0. Anyway, Parts express sells a Goldwood 15" driver, with a Qts of 1.03, the Fs is 29Hz, but apparently it will play below its resonant frequency. Response is listed as 20Hz to 2.5KHz. Power handling = 150 watts RMS/240 max - 8 ohms. (#290-346) $42.92

Many sub amps have built in EQ for lower frequencies. Although the drivers are 8 ohms, eff is 90dB.

mcgsxr · « **Reply #4 on:** 17 Mar 2010, 03:35 pm »

Having built a few OB woofers, I would say that there is a combination of XMAX, FS and QTS that deliver the goods optimally - many many find the pro 15's to be inexpensive and work well, though their XMAX tend to be lower than car subs.

The Eminence Alpha 15 has a long history around here, and at around $60 each are tough to beat it would seem. Perfect match for a Reckhorn Xover and your proposed Class D amps I would say, for your target budget.

http://www.usspeaker.com/ALPHA15-1.htm

bprice2 · « **Reply #5 on:** 17 Mar 2010, 04:07 pm »

You guys have given me a lot to think about...thanks.

What if after my original post, someone offered me a pair of used 15" Augies for a good price? Would the combo of the Reckhorn B2 (the B1 is sold out) and the Class D amp at 240 watts into 4ohm or 120 watts into 8 ohm be a good combo? It sounds like it to me, but it puts me a little over budget. It is, however, tempting.

mcgsxr · « **Reply #6 on:** 17 Mar 2010, 04:29 pm »

I have never heard either the Augies, nor the Eminence Alpha's, I have always used car subs myself.

As for your dilemma - both are proven options, and both have vocal supporters.

Don't think you can go wrong with either. If the price were close, I would go with the used Augies myself...

Nick77 · « **Reply #7 on:** 17 Mar 2010, 05:31 pm »

Brett i was going to reccomend diy cable but it looks like there has been a price increase on his ob subs.

http://www.diycable.com/main/product_info.php?products_id=684&Cid=3ebb745181f1562502848ef5684fea1d

bprice2 · « **Reply #8 on:** 17 Mar 2010, 05:44 pm »

Thanks, KN. I think I now have everything set up, except the drivers. I just purchased the B-2 Reckhorn Bass Management System and have worked out what I need with Tom at Class D Audio. I guess I'll also need to sell my current subwoofer and try and recoup some of my expenditures.

dvenardos · « **Reply #9 on:** 27 Mar 2010, 09:47 pm »

GR is now offering the OB subs that are designed for the GR V2 kit. A pair of the 12" subs and amp are $279 + shipping. I just picked up a set for my first OB sub.
http://www.audiocircle.com/index.php?topic=78931.msg751367#msg751367

neobop · « **Reply #10 on:** 28 Mar 2010, 02:24 pm »

Quote from: dvenardos on 27 Mar 2010, 09:47 pm

GR is now offering the OB subs that are designed for the GR V2 kit. A pair of the 12" subs and amp are $279 + shipping. I just picked up a set for my first OB sub.
http://www.audiocircle.com/index.php?topic=78931.msg751367#msg751367

Are you making the subs OB? Doesn't look like appropriate specs for OB. Low eff and normal Qts, will that work?

bprice2 · « **Reply #11 on:** 28 Mar 2010, 07:09 pm »

Six hundred dollars later and now I have completed (sort of) my OB bass system...not inexpensive, but it totally rocks.

Here's what went into it:

-2 Hawthorne Audio Silver Iris OB 15" Augies (used).

-Class D Audio 120 wpc amplifier. Actually, the amp consists of two 120 wpc amp boards bridged. So, each bass driver is receiving 240 watts.

-Reckhorn B-2 bass management system.

The system now looks like this:

Bolder modded Squeezebox III -> Burson Buffer -> Mapletree Preamp -> Red Wine Audio Signature 30 -> Omega Bipoles: RWA Sig 30's line level outs -> Reckhorn B-2 -> Class D Audio amplifier -> Augies in open baffle.

I used 1/4 inch mdf panels cut in 22" squares for the baffles, per Bob in St. Louis' suggestion in another thread. I used bookshelf brackets to stand the baffles up in an L configuration.

While my wife isn't particularly thrilled with the look or the size of the new speakers, I think they sound incredible. They are replacing a Martin Logan Dynamo subwoofer, which has an 10" driver in a sealed box. While the ML sub is pretty good for what it is, it doesn't compare to the new bass system. Articulate, musical, and punchy are all adequate descriptors for the OB subs. I'm not only amazed that I was able to put all this together, but am equally amazed at how it sounds.

Come to think of it, I have a pretty weird speaker set up. The mains are single drivers firing front and and back in a bipole configuration and are now backed up by two 15" OB dipole subs. The combo sounds very, very good to me.

The next challenge will be to put the amp in a wife acceptable enclosure and try and do something with the OBs that she will also find acceptable...maybe make stands for the Omegas out of them.

mcgsxr · « **Reply #12 on:** 28 Mar 2010, 07:41 pm »

Nice job, great way to get your feet wet in OB - the bass.

Glad that some of the input we were able to lend have manifested in happy ears - that is the end goal!

Take your time with the OB woofers, and find a creative way to integrate them into your system cosmetically - lots of shapes out there that will allow integration without messing with the sound you have found - W, C H shaped baffles etc.

bprice2 · « **Reply #13 on:** 8 Apr 2010, 07:16 pm »

I'm not sure what is going on with the OB bass system I built. It now sounds like crap...no bass and what sounds to me like very weak and muddied mids with vocals and other artifacts that should be filtered out with the Reckhorn B-1.

Just out of curiosity's sake, does anybody know what a blown Augie might sound like?

fergs1 · « **Reply #14 on:** 9 Apr 2010, 01:39 pm »

maybe the missus sabotaged it

bprice2 · « **Reply #15 on:** 9 Apr 2010, 03:37 pm »

Quote from: fergs1 on 9 Apr 2010, 01:39 pm

maybe the missus sabotaged it

I kind of doubt it. I don't think she'd do anything to depreciate the value of what she will eventually ask me to sell off.

It turns out the Augies are fine. I plugged them into a subwoofer plate amp and they most definitely produce bass...good bass at that. Something must be wrong with the Class D Amp/Reckhorn B-2 combo. My guess right now is that the B-2 is defective.

ebag4 · « **Reply #16 on:** 9 Apr 2010, 03:43 pm »

Brett,
Glad you got the Augies working and that no digits were lost in the process

Best,
Ed

bprice2 · « **Reply #17 on:** 9 Apr 2010, 03:51 pm »

Quote from: ebag4 on 9 Apr 2010, 03:43 pm

Brett,
Glad you got the Augies working and that no digits were lost in the process

Best,
Ed

Today is a new day!

tubesguy2 · « **Reply #18 on:** 9 Apr 2010, 04:21 pm »

Quote from: bprice2 on 28 Mar 2010, 07:09 pm

I used 1/4 inch mdf panels cut in 22" squares for the baffles, per Bob in St. Louis' suggestion in another thread. I used bookshelf brackets to stand the baffles up in an L configuration.

Hmm ... that doesn't sound like Bob. Are they really 1/4" or are they a stack of, like, 6 or 9 1/4" panels glued together?

bprice2 · « **Reply #19 on:** 9 Apr 2010, 06:15 pm »

This is apparently the second thread in which I referred to the panels as 1/4". Not sure how I got that in my head. They are 3/4" MDF panels. Sorry.