[dewar]

I'm treating myself to a bunch of new drivers to keep myself busy for the new year, and thought I'd run my idea past y'all for hopefully a bit of constructive criticism.

Got a Feastrex D5NF on the way, plus 4 Eminence Beta 15A's which I've scooped up for a pittance. Wanting to go OB.

What I'm left wondering is what size to make the baffle (would like to get the D5NF down to 200hz), thinking of Dick Olsher's Feastrex/Augie baffle as a starting point.

I'll run 2 15" Beta per side, driven with a 120W NAD amp, low passed and room corrected with Behringer DEQ2496. I'm wondering if I should go with a W baffle, or an H baffle one driver above the other in the same plane, but facing different directions and wired out of phase (like Linkwitz Orion). Whatever configuration, bass drivers will be in their own baffle that will sit inside but not touch the main baffle that holds the Feastrex.

My last nagging doubt is whether I can run the 5" Feastrex full range. I dont listen over 80db. If a first order high pass might be recommended, can anyone suggest cap values for say 200hz high pass?

Appreciate any input before I get going. Will start out with MDF as I suspect there might be a bit of experimenting ahead. Likely end up with marine ply.

cheers

B.

[DaveC113]

No offense, but that sounds like a really bad idea. An OB isn't going to do anything to control the very large excursion capabilities of the d5nf, plus you'll get to x-over in a super annoying frequency range. Just my opinion, fwiw....

[dewar]

thanks for the input.

The excursion issue and XO point for the subs seem to be the only drawback in going OB, but I really like the sound of open baffles so would like to give it a go. 

Would have thought 200hz would be acceptable if I do high pass them, it seems to be the in the ballpark of the few folks using the D5NF in OB, and the Sonic Purity commercial design which is a Watt/Puppy type setup. Or are you thinking that the Beta 15-A's wont sound good playing that high up? (I'm currently running Augies up to 200hz with some Bastanis speakers and hear no problems).

Cheers
B

[Angaria]

The betas will sound fine in an OB setup up to 200Hz.  I would definitely take the bass off of the feastrex if possible - midrange will clear up.  Since you've got the 2496, the best thing to do would be to experiment with different XO points.

[dewar]

Cheers Angaria

The 2496 is the DEQ, not the DCX, so XO will have to be passive. Ive got no experience with XO, but looking at an online calculator now and putting in the published 14.5ohm figure, I get about 50uf. Does this sound about right?

Dick Olsher said he had no luck with a first order XO and ended up with a 2nd order Ox on his OB design, but I cant think why I couldnt get a 1st order high pass to integrate with the bass drivers if I have the flexibility of DEQ on them? Taking opinions here.

I'll likely build a box for them one day, but dont have the means for it ow, and would like to wait till theres a bit more consensus on what is the ideal enclosure for these guys.

B.

[Angaria]

Let me ask - is there a particular reason you want a 1st order XO, or is it the simplicity of the implementation?

[dewar]

My thinking is just that the less I have in the signal path the better, and with a 1st order slope having -18db @25hz I figure it's all I need as far at attenuation goes, given my listening levels.

Any advantage to 2nd order over 1st you reckon?

[richidoo]

dewar, congrats on your new project.

I built an OB D5nf last year. It was fun and I learned a lot.  Here is the FR plot as simulated with Martin King's quarter-wave.com mathcad sheet. No hi pass filter.

I spent a lot of time optimizing the size and location of the driver, feel free to try it for yourself. I thought that the sound was excellent with the Feastrex alone (except for no bass.) It does not have enough vibration to excite the baffle to vibrate audibly. I made it from 3/4 MDF with no side walls. 20 x 48 overal bafle, with driver 5 inches lateral and 39 up from floor. Each side mirror image.

Then I added some Peerless 12" drivers for bass. Their resonance is 20Hz and Qts was pretty good .6 maybe? I was thinking about the Olsher article like you. I used DCX for xo. The finished speaker sounded horrible, mostly because the bass driver was vibrating the MDF baffle which colored and smeared the midrange. So those Vifa baffle side brackets are critical to the Olsher OB design - I did not use them to my detriment. I can't remember what my settings were but I think about 180 was the freq of xo. The Feastrex is so fast and plays so low, you want to use as much of that as possible, but lower you go, the steeper must be the co slope.

A digital xo is nice because you can steepen the slope without phase penalty, but higher order passive filters will be audible in the Feastrex, in comparison to nothing. That's why 1st order passive is desirable, no phase error.

The driver's resonance is 115Hz, so maybe that's why Dick chose to rolloff faster to avoid it. In email he said he was aiming for about 250Hz. Any normal woofer will be slower than the Feastrex in the xo region, so this is probably the main reason he didn't want to let Augie run up into 600Hz with 1st order. Dick is a great guy, very gracious and helpful. He is also a very serious scientist.

The imaging of this large baffle was OK but not great. Experiment with toe angle distance from front wall and maybe even absorption on the front and rear to help.

You will need to EQ boost the Alphas to get <40Hz low bass from them. They will resonate at ~40Hz iirc, and you may have to pad them down a little to match the less sensitive Feastrex.

I ran the D5nf full range with powerful amps, open baffle to fairly high volumes (not head banging) and never heard them bottom out. You will hear them bottom out before any damage is done. I have never bottomed them out in other designs either. They play very loudly. I never heard the resonance at 115Hz, in fact, the FR in a small planet10 horn was within 1dB from 300Hz down to 70Hz with no filter. As a single driver in a bass aligned cabinet it can handle a lot of bass without upsetting the midrange due to very low moving mass. Bass drum thumps do interrupt the midrange though 

You can find a nice plan for 2 driver W on GR research website. Face one driver fwd and the other rearward to cancel non linearities front and back.

The Eminence will play plenty high for you, they are intended for electric bass and guitar amps. They are not Feastrex kind of resolution tho, so a low crossover freq and steep low pass filter are in order.
Good luck!
Rich

[dewar]

Excellent stuff, thanks richidoo.

So I think I'll try run them fullrange in a decoupled baffle, at least while I've still got my Bastanis speakers for Friday night sessions. XO on the subs can be done >30db with the DEQ if need be. Will front the baffles with 3/8" wool felt, have had a lot of joy with this before with regard to imaging.

I'll eventually try a box for them as I say, and could still use the w baffles. Havent heard of anyone using dipole subs with monopole speakers, but I dont see why not - dipole bass sounds best to my ears.

many thanks
B.

can I ask what you got them in now, and how does it compare to OB?

[Angaria]

If the shallow attenuation of first order works in your system, sure, enjoy your phase response:)  You might try the GR OB servo subs - extremely clean bass, and they'll hit 200Hz fine.

[richidoo]

Sounds like you have a good plan. Unfiltered the Alphas will play up into the midrange, so -30dB might not be enough. You can't believe the resolution of the Feastrex in the midrange, so everything matters. A cheap passive 4th order low-pass at 150-180Hz ala Parts Express might be something to try.

I always wondered if absorbent on the baffles would help imaging. Thanks for the tip!

I built some sealed boxes for mine this week (Qtc=.7.)  I'll post the plans once I see if they sound any good. They should make -6dB @130Hz with Qtc .7 should make a good match for the servo subs. I agree with Angaria the GR paper servo drivers are the WTG because they are designed specifically for OB. Monopole Feastrex with dipole bass is what I want to try. Maybe you'll beat me to it and save me the experiment? haha   I heard a few spheres at RMAF and that really excited me.

I have made a few cabinets designed by planet-10. One called Freddie Chang, and the other called Maiko, both are horn/reflex designs typical of planet-10. The Freddie makes 70Hz flat. The Maiko is larger with two horns, flat to 50Hz. In a small room to boost the low bass a little and some good bass trapping Maiko really fulfills the promise of full range single driver. Maiko is undergoing a revision now, I intend to build the Maiko 2 as soon as it is released. Feastrex driver seems to like cabinets made of pine. I use Finnish white pine at Home Depot. I think the pine vibes jibe with the paper driver better than other harder woods normally used for speaker cabs.

Here's a pic of my "Maiko 1" per plan (before mods:)

Rich

[Christopher Witmer]

I built some sealed boxes for mine this week (Qtc=.7.)  I'll post the plans once I see if they sound any good. They should make -6dB @130Hz with Qtc .7 should make a good match for the servo subs.

Mind if I ask just the external dimensions? Just curious . . .

-- Chris

P.S. I'm finally getting ready to cut wood for a pair of Rythmik servo subs myself (sealed) . . . mine have been sitting around here unassembled for a few years, so they are a bit different from any of the current models. I'm having 5mm aluminum cut to size to form a subcompartment for the plate amps; that should be here in about a week. (I'm not even sure if the latest Rythmik amps need such a thing; for all I know they may be fully enclosed.) Then I'll be all set to get down to building. I'm going to be recycling a stack of 20mm thick lauan plywood desk tops for the material.

[dewar]

Thanks guys,

By 30db I meant 30db/oct, i.e at least a 4th order, so I'm with you on that. The DEQ2496 has a 12db/octave high/low pass filter in the GEQ menu which some people dont know about, and then I'd simple use a couple of the PEQ's to pull it down further after 200hz. I've done this on my Bastanis and to my ear there doesnt seem to be a problem combining the natural 6db/octave roll off of the unfiltered widebander with a much steeper slope on the bass drivers.

Nearly went with the GR servo OB drivers myself, but the Beta 15-A's were on offer for AU$100 and money was tight. Also, I want to keep the DEQ on the bass drivers and thought it might not be a good idea to have to use the plate amps filters as well, i.e doubling up the filters and processing might introduce added latency or phasyness or something. Lets compare notes when we're done. I'm grateful for the guys pioneering the D5NF cabs, looking forward to hearing about the Maiko 2 and maybe dipping my toes there as well, if the cabinetry isnt beyond my meager woodworking skills.

cheers
B

[Christopher Witmer]

You may be able to modify your woofers for deeper response without too much difficulty. I know a fellow -- someone who knows what he's doing -- who picked up a large quantity of inexpensive (Eastern European mfr.) 8-inch woofers upon which he promptly performed some simple surgery, removing sections from the woven cloth spider behind the cones until their F0 dropped to where he wanted it. He put them in an open baffle and was extremely pleased with the results. I believe he was using Lowthers for his main speakers at the time, but he may well have kept that setup when he switched over to Feastrex . . .

-- Chris

[dewar]

Interesting that, but I wouldnt nearly be so brave

Also, if I put them in an enclosure bass extension wont be an issue as I'll mate them with dipole subs - in fact I would prefer the D5NF get down to 100z than 50hz as I've got some room issues between 50 and 100hz and would prefer the subs to be playing this region as I have DEQ control over them, if that makes sense. I'm also guessing that 50hz electronic bass lines might better be handles by the 200 solid state watts on the subs than by the 2w SET amp driving the D5NF's....?

[richidoo]

dewar The alphas are ideal for open baffle with high Q and sensitivity, they'll sounds great. Especially if you can boost bass a little with the DEQ. I didn't know it had a low pass function, that's cool.

Chris, the box is small - Vb = .42ft^3 per online loudspeaker calculator. Nothing fancy.

[Christopher Witmer]

I would prefer the D5NF get down to 100z than 50hz

Sorry if I wasn't clear in how I expressed myself . . . I was attempting to describe modification of the Beta 15-A units to make them play lower, not the D5nf.

-- Chris

[panomaniac]

Will front the baffles with 3/8" wool felt, have had a lot of joy with this before with regard to imaging.

Ditto that.  It has worked well for me, too.

I think some folks have missed the fact that you have the BETA 15s, not the Alphas.  Not the same driver.

Please keep us up to date on how this works.  X-over points and all.  My guess is that you'll end up with 1st order electrical on the fullrange.  I've heard the Feastrex drivers, they are fan-freaking-tastic.  $$, but damn nice.

[Christopher Witmer]

The parameters of the Alpha and the Beta suggest the Alpha is much better suited to OB than the Beta . . . that's part of the reason why I suggested that modding the spiders might be worth considering. With EQ they may still be fine as-is, however.

[milen007]

hi guys

i am planning to do OB on this 5" feastrex. any success on using the alpha woofer with passive crossover?

thanks
erwin