Nelson Pass: The Slot Loaded Open Baffle Project

[vdi_nenna]

make sure you fully disconnect the amp so it can't make a path

Disconnecting them is one of the reason I haven't tested yet. Been too busy listening.
The FR driver really started to open up. They are doing some amazing things. Treble is still rough and may need something to take away some of the edge around 10k to 12k or higher.

There is this weird drop out if I tilt my head to one side, kind of like cancellation, but it's in the higher range. Never happened before until the Parts-Express RS180-8 FR drives were used. Moving the speaker back closer to the back wall helped reduce this effect.
I have to really lock my head in position to not lose the image. I heard this is common with FR drivers.

Any ideas why?

 

[mightym]

I believe what you refer to is the phenomenon called "beaming".

I counteract both the rising response and the beaming of my Fostex FE206E's by toeing in the speakers to a focus point in front of the listening position.

Hope this helps.

John

 

[freddi]

fullrange can beam at high frequecies where there's only a few degrees of latitude off axis before a significant drop occurs (and often, a "hole") The only graph I have handy is the old Eminence B102 - look at how it measures on-axis vs ~ 20 degrees off

An externally hosted image should be here but it was not working when we last tested it.

Nirvana's Super 8 has on-axis amplitude exceeding a Selenium ST324 slot loaded tweeter around 17KHz.
-here's FE206EN (stock) vs a stamped frame Nirvana Super 8 ~on-axis/in-room
http://imageshack.us/a/img100/1599/fe206envsansuper8indrui.gif

 

[vdi_nenna]

Thanks guys. I've been mainly focusing the drivers behind my head.

 

[vdi_nenna]

First is the slotted 6 driver sweep. Second is the full-range driver.
Not sure it's correct. I calibrated the WT3, but the results are always the same.

 

[vdi_nenna]

I re-calibrated and got a more realistic result.
This is the bass unit.

 

[freddi]

cool - looks like a significant shift in resonance from ~41 down to 30 - if you hit "measure parameters" it will give the impedance curve and display system Q (~like a sealed box) -

could one dispense with the curved plenum innards like this for 10 drivers per side? (manifold might be too deep)

An externally hosted image should be here but it was not working when we last tested it.

 

[mightym]

I think that one of the reasons the 8" woofers were used is the Dipole peak is going to be much higher than a larger woofer. Making the plenum too deep would have the same effect AFAIK, lowering the peak.

I'm looking about for a suitable 10" driver to mount below some 12" Co & Tri-Axials I've picked up to try on OB. I have some aprox 40" X 3?" X 1" ply (off cuts I pick up really cheep ) to use as motorboards. with the single pair of 10" subs on a plate amp under each driver ( possibly 2 pr on different plenums if needed ).

I'm also considering a Tractrix front horn with Open Back for one pair of the vintage drivers. I'm keeping the details on that under my hat until I find out whether it works/integrates or not.... Think homage to WE theater bass horns....

John

 

[hajj]

cool - looks like a significant shift in resonance from ~41 down to 30 - if you hit "measure parameters" it will give the impedance curve and display system Q (~like a sealed box) -

could one dispense with the curved plenum innards like this for 10 drivers per side? (manifold might be too deep)

Unless you're crossing over very low to the woofers, I think you'll run into resonance problems at the frequency where 1/4 of the wavelength is equal to manifold depth.

 

[bernard991]

another SLOB variation ?

I am wanting to try the SLOB too but I don't have any 8" drivers , however I can get some fairly good 6" woofers that will work in OB config ....is it possible that I could get some feasibly good results using 8 per side giving me the same 24" slot that NP had ?
...also the size of the baffle is a challenge ..WAF so I would like to try a bit smaller
any thoughts opinions very appreciated !
thanks

 

[vdi_nenna]

This project is scalable. Can use smaller or large woofers
Doesn't have to be 3 pairs of drivers. You can use 1 pair, if you want.
Your results will vary depending on how low the drivers can go.

 

[bernard991]

thanks for that VDI
if I was to use 8 - 6" per side @8 ohms each any idea how to wire them up for driving them reasonably efficiently ?

 

[vdi_nenna]

There is a paragraph in the article that better explains wiring for parallel or series.

 

[Russell Dawkins]

I'd wire two sets of four in parallel. Each set of four would be series parallel wired (two pairs of two) for 8 ohms per set. Parallel these for ~4 ohms final impedance.

 

[noSmoking]

how I wired them.....

hi,
I tried a few combinations and some speakers were louder or got over driven,Yes I am a POWER driver,lol.Sometimes I push them to see how much they will suffer before they distort or blow,but ,I found two ways to try ,That I liked.
1st I figured since you have 2 speakers facing each other and in one slot, they should work together so I have read this article about push pull ,well I think if it pushes and the other speaker pulls that only moves that volume of air,what does that do? I think not much,So I think instead if you wire them to both push,then you got 2 times push coming out the slot ,opposite when it pulls in.....So I have wired each 2 together and connected all of them for the impedance,

 

[puppet]

I think that there are other advantages to the push pull arrangement. The thread posted in the subwoofer section has a nice explanation of those advantages ... distortion cancellation being one of them.

I don't recall the author of that individual post within that thread but check it out. It's a good explanation and one that isn't intuitive ... until you read it at least

 

[noSmoking]

Hi Puppet!

I think that there are other advantages to the push pull arrangement. The thread posted in the subwoofer section has a nice explanation of those advantages ... distortion cancellation being one of them.

I don't recall the author of that individual post within that thread but check it out. It's a good explanation and one that isn't intuitive ... until you read it at least

I'll take a look, I think I read about alot of different combo's of wiring them and my last way of using them in a positive pushes in and neg pulls out seems to sound the best,but I am always willing to try out Idea's from other members
I used the speakers that Nelson Pass recommended and I have 12 speakers per side,Have you tried any mods to these ,How did you make yours?
Thanks for the input

 

[puppet]

noSmoking .. I haven't built one myself. I'm working on something else right now with OB.

I had thought about doing this or the other push/pull deal ... got it in my head that big woofers (for me) are "right". What I'm stuck on is the scaling of the enclosure in that regard. The slots get big (long). So I'm wondering if there is a "perfect" ratio for this or not. I'm not that smart so I'd have to experiment .. when I have more free time I guess.

Your project sounds nice. Hope it works out for you!

 

[bernard991]

thanks lads for many great ideas to sort through ...DIY !
I am ordering the 6" Aura's from PE , cheap ~ 9 ea
seems like a good place to start my experiments
...the other challenge I alluded to was the downsized baffles ...I have no doubt that it will not be easy to find the optimum balance of performance and the acceptance thing .

 

[noSmoking]

Hi Bernard,

thanks lads for many great ideas to sort through ...DIY !
I am ordering the 6" Aura's from PE , cheap ~ 9 ea
seems like a good place to start my experiments
...the other challenge I alluded to was the downsized baffles ...I have no doubt that it will not be easy to find the optimum balance of performance and the acceptance thing .

I changed the slot just a little from the original drawings ,The lines out from the speaker were parallel out the slot ,I tapered them just a little ,
I have understood that any standing waves are not a good thing,So to scale any size is a ez thing to do,I placed a speaker about 12 " from the front and drew the tapers from there,I don't have a formula but I get plenty low bass out of them ,so I'm happy with their out come,I also rounded the sides of the slot to the front,I built one speaker with rounded slots to the face panel and one not ,I didn't hear a difference .
I don't have the stuff to measure them yet,I like the sound so to me that's ok!