Need help with OB design - cheap, cheap, cheap

Hi All, I never had much interest in OB speakers, but to be fair, I never really listened to them. Well, this past weekend was the AK fest and I sat and listened to the Salk Audio OBs for a couple hours. Now I want to build a pair with stuff I have laying about. So, what are the critical specs I need to look for in the drivers? I have a lot of drivers and would rather go about this with some clarity of thought vs. just trying everything I have to see what works.

Here is what I have so far.

TWEETER:

The old but wonderful Philips tweeter. The back is enclosed so not really OB. Here is 1. the spec sheet and 2. a crossover designed for them.

http://www.troelsgravesen.dk/WWDT_files/ad0160.pdf

WWDT (at the bottom of the page)


MIDS:

The Parts Express PA130 5" midrange driver.... here is the spec sheet

http://www.parts-express.com/pdf/295-010s.pdf


WOOFERS:

And this might work for the woof - I have 4 of them. - CERWIN VEGA S-10.8 10" 8 OHM 400W STEALTH WOOFER

This is all I could find on them

• Woofer Size: 10".
• Frequency Response: 40Hz -500Hz.
• Power Handling: 200 watts RMS (400 watts Maximum).
• Sensitivity (2.83V @ 1 meter): 93dB.
• Impedance: 8 ohm.
• Mounting Diameter: 9.0" (22.86 cm.).

I posted this in the Fun OB thread but then realized that I was highjacking the thread and so I am starting this thread.

Panomaniac posted a number of posts about the RROW and that makes a lot of sense. But, I don't know enough about crossover design to figure a crossover out.

P.S., this is all stuff I have laying around for years if you are wondering why I would chose these componants.

Cheers.
 

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woody

Member
Paid Member
2002-01-15 12:57 am
Tyrone Ga. U.S.A.
You might look at Martin King's OB projects they cover a little of the theory
behind a good OB. One of the things to look for in a woffer is a high QTS this is
one of the things Martin discusses in his article. Both Martin King and Nelson Pass
both like the Emminence Alpha 15A for use on an open baffel and it's cheap!
I built Martin's 2 way OB and am verry verry pleased with the results.
 
If you're resigned to using what you have on hand, then I say "go for it" using what you have on hand. I would be sure open baffle is what you want if you really don't have a lot of room for these. They really need ~3 to 4 feet behind them to work well and give that wonderful open sound.

I agree with Panomaniac's advice to read up on what Martin King has posted on his website. That's how I came up with my 2-way open baffles. I would also take some time to read through Panomaniac's OB thread as well. You may not be using the same components, but getting different ideas/perspectives/opinions is not a waste of time- IMHO.

Since you're looking at using 10" woofers, I would definitely recommend spending time on the MJK papers regarding H-Frames. 10" woofers are what come with the Linkwitz ORION speaker, so it can definitely work if implemented right. If you can afford the fee for Martin's worksheets, I think that would be a better investment than buying different drivers.

If you can't afford MJK's sheets/fees then spend as much time as you can researching different ideas/implementations as possible and build what you want with what you've got. Start with cheap scrap wood and once you've got something you're happy with, then worry about a "finished" product.

A really long reply, but you shouldn't feel discouraged by not having exactly the same things as everyone else has. Work with what you've got if that's what you want.

Good luck!
 
Yep, wood is something I do not lack around here. I will start reading tomorrow. I printed out MLKs articles on OB design and H and U frames. I most likely have all the crossover components needed as well. Should be fun. P.S., I do have three feet behind the OBs. I don't know if this will hurt the sound, but they will be in front of a wall of plate glass windows....floor to ceiling, wall to wall. Cheers.
 
Yep, wood is something I do not lack around here. I will start reading tomorrow. I printed out MLKs articles on OB design and H and U frames. I most likely have all the crossover components needed as well. Should be fun. P.S., I do have three feet behind the OBs. I don't know if this will hurt the sound, but they will be in front of a wall of plate glass windows....floor to ceiling, wall to wall. Cheers.

Use heavy drapes then
 

jerome69

Member
2008-02-18 11:33 am
Lyon
OB is very difficult although you are an experiment designer. I recommend to have some measurement tools. You should measure T/S parameters. Better will be the response.
I think you can use your drivers, as you must start with something and you have them. It is important to learn something from this first design.

The gainphile's architecture is very interested because the H frame deliver a lot of bass. I think active is better and easier. I think it could be done passive but hard to do.

For a starting point you can also use my architecture of baffle. You can also use my simple crossover (replace rear tweeter by a 4omhs resistor) for my project BOB.

But if you want more simple crossover, you can use the OB1 argos crossover calculation, inverse the midrange. You can use this crossover topology from lampizator. The midrange must be also inverted.

Have fun :)
 
Well, there is more to this than sticking a driver on a board. Much reading to do. I do have a couple questions.

I read that the baffle should be less then 2.2x the midrange diamiter. So how does that work if I am using a 5" midrange driver and a 10" woofer. OR, does that apply for the diamiter of which ever driver at it's positioin in the board?

I read last night about the H frame and that might be a good option for my 4 10" woofers. The ones I saw one line had one woof facing forward and the other facing backward. Wouldn't you get the same effect by facing them both the same way and reversing polarity? Acctually I don't know how to wire them in that situation.
 
I read that the baffle should be less then 2.2x the midrange diamiter.
This is only a recommendation, if you want the maximum flat response from the baffle. But it will cost you some driver efficiency. Since your midrange driver is limited in size and excursion, you better put it on a larger baffle.
So how does that work if I am using a 5" midrange driver and a 10" woofer. OR, does that apply for the diamiter of which ever driver at it's positioin in the board?
It would apply for the width of the board at the position of the driver. For the most part you try to get things right in the horizontal plane - where stereo happens.
 
Well, there is more to this than sticking a driver on a board. Much reading to do. I do have a couple questions.
Yes and no. :)

I read that the baffle should be less then 2.2x the midrange diamiter. So how does that work if I am using a 5" midrange driver and a 10" woofer. OR, does that apply for the diamiter of which ever driver at it's positioin in the board?
If you go to H cab woofers, the midrange baffle can be whatever you feel is appropriate. I personally prefer the wider baffle.

I read last night about the H frame and that might be a good option for my 4 10" woofers. The ones I saw one line had one woof facing forward and the other facing backward. Wouldn't you get the same effect by facing them both the same way and reversing polarity? Acctually I don't know how to wire them in that situation.
The Idea is the basket creates an asymmetrical front and back wave if both face forward. By reversing one and changing polarity, the front and back waves are more symmetrical. I personally think its a very low order effect and I chose not to do it on my designs. YMMV. What you suggested would just kill the base.

HTH

Doug
 
Keeping in mind your design parameters of cheap, utilizing your current speaker inventory and for use in a small room, I might suggest something along the lines of what I did about 6 years ago.

I built a Orion/Phoenix type speaker just to see what DR dipoles were like. I used a RS 1197 (Fostex 103ish) fullranger and added a $3 Infinity tweeter as a supertweeter.
The bass was handled by four $6 Pioneer 10" from PE on closeout. There were mounted in Phoenix W enclosures. To make the whole thing work, I simply put a cap on the 4" and tweeter and used a Pyle electronic HiPass XO on the woofers. They are $20 and can be crossed at 180hz with 12db boost. Just throw a reasonable amp on the woofers and another on rest. I also used an old Pioneer eq to adjust the woofers with slightly better results than just using the boost on the XO.

Parts-Express.com:pyle Wave PLXR2 Electronic Subwoofer Crossover | electronic crossover automotive crossover car audio crossover car crossover subwoofer crossover

In my small room, the crappy 10" Pioneers were really amazing. The whole system system was less than $100 (excluding amps of course) and sounded far better than than I could of imagined.

Ive dismantled it but might put it back together for fun.

amt
 
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djn, you can use any driver you like, on any baffle. It really is that easy.

The part where it gets trick it twofold: first, how to do the crossover/eq for each driver. Like was said earlier, passive crossovers and OB mix like oil and water. MJK does have a spreadsheet that can help, if you have to go that way. OB's require a lot of EQ.

The other tricky part is making sure you have enough volume displacement in the bass. You will probably do fine working with what you've got, but before too long, this concern might move up to the top of your list.

Either way, give it a try - you'll probably enjoy it!

I might add that measurements can really help you out here - box simulations to do not apply to OBs.
 
Ok, I do have testing equiptment so I might as well put something together and see how it goes. I just got this from CV for the woofers. Not too high a Qts. They might be better suited for a box below the OB mids. I'll have to play with it.

THIELE/SMALL PARAMETERS
PHYSICAL DIMENSIONS
Parameter (unit)
SPL (dB) 86.633
Re (Ω) 4.1
Qms 2.811
Qes 0.448
Qts 0.387
Fs (Hz) 31.35
Vas (L) 43.53
Cms (mm/N) 0.139
Mms (g) 184.97
Sd (m2) 0.047
BL (T*M) 18.25
Xmax (mm) one way 12.9
Pwr (W) NOM/MAX 400/800
E