OB 3 Woofers?

[NurEinTier]

Decided on OB speakers.
Am thinking
1x1" tweeter
2x6" mids
2x15" woofers.

Is there any advatage going to 3 woofers (3x12" or 3x15")?
Or is this going towards TL sound?

[Cal Weldon]

Three woofers makes it difficult to get an impedance you like. If you use 1, 2, 4 or 8, things get easier.

[mashaffer]

Just a thought but if you went with only one midrange per side (wide range?) you would not have to worry about lobing. Unless your room is very large a good 6 or 8" mid should have plenty of output. I have single 8s per side in my 14' square room and my ears are overstressed long before the drivers are and my drivers are just old console units.

mike

[NurEinTier]

The room is 3.7m x 5m (12 ft x 16 ft), minimal furniture.
The test OB I've built has 1x1" 1x6" 1x8"
Listen position quite near the speakers.
I love the sound so much I gave away my commercial speakers.

The 6" mid sounds great already,
bas is super tight but to light for hardrock.
The highs are way too sharp.
Now I want the real thing.
Quality drivers should give me:
Perfect female voice, Kate Bush, K's choice.
Hart hitting bass, Metallica, Rammstein.
Sharp guitars, Hendrix, Led Z.

I like my 1 x 6" mid but 2 mids would give me higher output and less distortion.
Lobbing doesn't worry me because I see lots of 2 mids speakers so I know it can be done.

Bass is a bit of a problem.
My 1 x 8" is very tight, very good for normal music at normal levels but it doesn't do Sepultura in "The Neighbours Are Not Home" mode.

2 x 15" for this room should be overkill even for an OB.
Was thinking possibly 3 x 12" but 3 drivers would give me impedance troubles.

So now I'm thinking 4 x 10" per side or even 4 x 12".
Extra costs are no problem.

But wouldn't 4 woofers per side change the OB sound to a TL sound?
Is there an advantage using 4 x 10" over 2 x 15"?

[Cal Weldon]

When I build, I like use as few drivers as possible to get the job done. More does not mean better.

[Kensai]

How about a WMTMW arrangement?

I'm a minimalist for speaker (and pretty much anything else) design, though I love OBs and line arrays. I would do a simple cap cross on the tweeter (B&G Neo3 PDR would be my recommendation; my fave in OB from personal experience).

Then do a simple inductor cross (high gauge air core with a high DRC) in front of the mid drivers and then hook the woofers in series with their respective mids. This would add the inductance of the mid drivers voice coils to that of the inductor already on the + line, causing the cross lower than the mid. All you're looking to do is to get the woofers to cross low enough that the highest effective frequency they're putting out is safely lower than the wavelength of the mid and woofers' center to center spacing. Something you can do to if that doesn't result in a low enough cross for the woofers would be to hook 2 or more woofers in parallel off the - of the mid. This will lower their effective impedance which will increase the effective crossover frequency (if you put 2 8ohm drivers in parallel there, that will result in 4 ohm load which will cut the effective crossover frequency for the woofers in half; if you put 4 the effective load will be 2 ohms causing the crossover frequency to be only 1/4th which should certaily be more than low enough). This will also increase you SPL capability in the low frequencies and also increase your line length, which is always desirable (as long as your ceiling is high enough).

For the mids, you could really pick anything from 3"ers to some 8"ers. HiVi B3S are cheap, sound good, and will really drop your center to center spacing. Possibly some Dayton RS series drivers of whatever size you deem appropriate, or even some nice Fostex drivers (pretty much any of their full/wide rangers will work here).

For the woofers, I like the cheap Dayton 8" DVC (did I also mention I like to keep costs down?). You can just wire up one voice coil and leave the other open which will leave you with an 8ohm load but effectively double Qts which will put it righ in the optimal range for OB use. Putting 4 of these on there will make up for the efficiency decrease of only running 1 voice coil.

An extension of this design would be to make a SWMTMWS line (where S is a larger "subwoofer"). Keeping with my cheapness, you could use a Dayton 12" DVC (same rules apply as above) or something like Pyle 12" "Blue". You would simply put those in series with the woofer which will increase the inductance before the subwoofer and lower its crossover frequency, hopefully dropping it below the frequency of the center to center spacing with the woofer.

I know, I'm crazy. I also know I'm likely to get shredded for this, too, but I have put together some convincing things using this sort of design.

Let us know what you end up with and how that turns out for you

Kensai

[NurEinTier]

"More does not mean better."
Wouldn't 2 drivers give you more output and less distortion?

"Then do a simple inductor cross (high gauge air core with a high DRC) in front of the mid drivers and then hook the woofers in series with their respective mids. This would add the inductance of the mid drivers voice coils to that of the inductor already on the + line, causing the cross lower than the mid. All you're looking to do is to get the woofers to cross low enough that the highest effective frequency they're putting out is safely lower than the wavelength of the mid and woofers' center to center spacing. Something you can do to if that doesn't result in a low enough cross for the woofers would be to hook 2 or more woofers in parallel off the - of the mid. This will lower their effective impedance which will increase the effective crossover frequency (if you put 2 8ohm drivers in parallel there, that will result in 4 ohm load which will cut the effective crossover frequency for the woofers in half; if you put 4 the effective load will be 2 ohms causing the crossover frequency to be only 1/4th which should certaily be more than low enough). This will also increase you SPL capability in the low frequencies and also increase your line length, which is always desirable (as long as your ceiling is high enough)"

Well didn't understand too much of that.
I still have a lot to learn and will need lots of help with the connections and crossovers.
In fact I hope a local DIY builder will take me under his wings.

"tweeter (B&G Neo3 PDR would be my recommendation"
Never heard a ribbon.
Did some googeling seems it has many fans, I'll keep it in mind.
Really had paper in mind for all drivers though.

"HiVi B3S are cheap, sound good"
They are very cheap but also small and alu.

"Possibly some Dayton RS series"
Alu again and Dayton are very hard to come by in Europe.

"or even some nice Fostex drivers (pretty much any of their full/wide rangers will work here)"
I'm prejudice against full range.
There must be some trade off with a normal mid.

"For the woofers, I like the cheap Dayton 8" DVC"
Would love to use Dayton woofers but sadly very limited choice and availability in Europe.

"You can just wire up one voice coil and leave the other open which will leave you with an 8ohm load but effectively double Qts which will put it righ in the optimal range for OB use. Putting 4 of these on there will make up for the efficiency decrease of only running 1 voice coil"
Lost me again for the most part.
Being a newbie is not easy.

"make a SWMTMWS line (where S is a larger "subwoofer"). You would simply put those in series with the woofer which will increase the inductance before the subwoofer and lower its crossover frequency, hopefully dropping it below the frequency of the center to center spacing with the woofer."
Wouldn't this be a 4 way setup (and crossover)?
I think 3 way should be enough.

"Let us know what you end up with"
I will.
This was just my first question on OB.
Ther's no hurry, already have a nice sounding set.
You can expect some more questions from me.
It's clear I need a lot more learning to do.

In the meanime I think I'll go with 2 mids and 2 woofers per side.
4 woofers seems a lot more complex than 2 woofers.

[Kensai]

Sorry, didn't mean to overwhelm . . . I was just in a rush and felt compelled to address all of that. No worries about being new. We're all new at something all the time, and I consider myself to be pretty new at all this anyway. I just have some very strong opinions (like I hate all stand alone subwoofers, and anything in a standard ported enclosure; most folk won't jive with stuff like that, as I'm sure you can understand).

I'm also usually more of a denizen of the full-range page down the block from here, but even there, you get alot of stuff revolving around the fact that there's no such thing as a perfectly full range driver, and that "full rangers" might more appropriately be termed "wide range" drivers. I'm going to have to say that any full ranger worth its salt is going to do a better job at midrange than any driver that is designed/designated specifically as a "midrange", especially anything with a closed back (and we're talking OB here, so close back drivers are right out, anyway). There are plenty of more "standard" woofers of smaller dimension that would work great in the midrange capacity, for your application, too. The main thing to look for (and the main reason I suggest using a full range driver here) is the driver's ability to cover the "critical range" successfully, generally from 100-200Hz up to around 5-7khz so you can keep any crossovers out of that range.

Which brings me to something else I'm not fond of . . . crossovers. This is one of those areas where I know just enough to really screw things up if I try to be ambitious. I've heard way to many cheap and/or poorly designed crossovers in my day, pretty much anything sold at retail, it seems, just totally gets in its own way, sometimes even when the drivers themselves are decent, all in the name of shaving the cost. What I was proposing for crossover above is simply 1st order high and low pass designs.

The fact that using so many drivers as you propose will make the vertical area covered by drivers easily tall enough to be a short line array. Coupled with the fact that you say your listening position is fairly close, the line doesn't need to be very long to be effective, as long as your tweeter is at approximately ear height when seated. Assuming a line array, your crossover doesn't need to be absolute, where your tweet and mid both roll off toward a common point where the joint output of the 2 drivers keeps the overall system response fairly flat. With an array, its assumed that drivers will be covering much of the same frequency spectrum as each other, and if you look at the work of Jim Griffin on line arrays, you'll see that power tapering and frequency shaping in the vertical plane (from driver to driver) is a proven and acceptible method for designing a line.

The main thing I was proposing, and the thing that most will object to is using the inductance that a standard dynamic driver's voice coil produces as a first order lowpass for drivers run in series with it. So technically, I was suggesting 3-4 way systems above, but very plausibly without any more crossover components than a single capacitor on your tweeter.

The whole bit about running multiple woofers or subwoofers in parallel off the - pole of the driver above it is an attempt to lower the load of that particular segment of the speaker which will increase the effectiveness of the crossover value before it. Say the inductance of your mid would give an 8ohm driver a low pass value of 4khz. If you were to run 4 of those drivers in parallel off the - pole of your mid, you would have an effective load of 2ohms, and that same amount of inductance provided by your mid's voice coil would create a low pass of 1khz, a frequency which is well below the wavelength of the center to center distance of 2 8" drivers.

And the reason I recommend the planar tweeter (other than the fact that I own and use a pair in my normal livingroom rig and love them) is the fact that they will actually give you dipole HF. No cone driver is going to give you much over 1khz from the back of the driver, and even that may be muddied by the basket and magnet structure as the higher the frequency, the easier it is to disrupt it with physical material. Again there will be some here who will debate the utility of this (or just flame me outright), but the difference of having all cones in OB or (gasp) having some sort of closed back tweeter handling my HF and using these planars is night and day.

Anyway this is a journey that never ends, so enjoy it like a pleasure cruise instead of some barefoot trudge through the desert.

Kensai

[Cal Weldon]

Originally posted by NurEinTier
"More does not mean better."
Wouldn't 2 drivers give you more output and less distortion?

Yes and yes. Two woofers are required for volume, not quality. The fewer the drivers the better, provided they are capable of your requirements. If not, use different drivers or multiples of the same.

KISS

[Cloth Ears]

NurEinTier,

Did you see that Tony Gee had 4 Ciare 15.75Ndw2 woofers for sale, ideal for OB?

I'd love to, but I've got a garage already full of different drivers, amplifiers and half-built boxes - and a lovely lass who puts up with it "as long as you don't use any more shelves".

Back on topic, personally, I'd look for a single mid that would do the job if you can find one. The advantages of it in the vocal range (I think) override any disadvantages. Maybe even a "full-range" (anything without a whizzer), as this would allow you create a crossover with not very many parts.

Then again, Cloth Ears prefers closed boxes anyway - so you may wish to ignore this post...