[Bob in St. Louis]

Hey there. 

A local buddy of mine is asking me to poke some holes in some plywood for a pair of Lowther DX2's he has. He does not have the wood working tools needed to accomplish this, so I volunteered to help him out. This is his first venture into OB. He's already got two pieces of plywood that measure 2' X 4'.
I've done many baffles, but not for Lowthers, so naturally, I've got a few questions.

- Where do I put the hole. You know, that whole "closer to the top, offset, front/rear mount, more to one side" argument.
- What's the ideal baffle size? Should I just use his 2' X 4' pieces, or trim them to....???
- What kind of bass output should he expect for a pair of DX2's on an open baffle?

To the best of my knowledge, he's not a radical basshead, Home Theater guy, or anything like that. He just wants his first venture into OB to be the best it can be. Anything else I'd need to know about DX2's on OB?

Thanks in advance folks! 

Bob

EDIT: Here's a couple pics of the DX2:
{Image removed}

[MJK]

Bob,

Those are not DX2 drivers. They look more like PM6A or PM2A drivers. Do they have a sticker on the back or was the box labeled with a model number? I have DX2 drivers and they have a very small magnet. Both of my alnico A series have bigger magnets shaped like the ones in your picture.

You will not get much bass from only the Lowthers. If you run them full range you may have problems with excessive motion at low frequencies. If you match those with two Alpha 15A drivers per side in a 2' x 4' baffle with a 2nd order low pass at 200 Hz and 2nd order high pass at 400 Hz (passive or active) you will have an excellent system. It will produce 96 dB/W/m and be -3dB at 40 Hz.

Simulation here ---> http://www.quarter-wave.com/OB.pdf

Martin

[Bob in St. Louis]

Sorry about the photos Martin. I've not seen his drivers, that was a Google search for "Lowther DX2". I pulled those pictures from the Lowther site. I've removed the images so there's no confusion.

These drivers are an experiment into OB for him. He's currently happy with his existing rig, but has had these drivers sitting idle for a while and thought they'd be suitable. OB has peaked his interest and if these happen to 'knock his socks off', he might be willing to step into the wonderful world of open baffle. THEN we might talk about bass augmentation.

That being said, his main two channel focus does not seem to be very bass heavy. I can't remember every type of music he likes, but as he was listing his favorites, I recall thinking "these are not bass intense genres". There was a lot of vocals in there, and nothing too strenuous for a driver.

I do not believe he's interested in crossovers, additional amps, or purchasing addition bass augmentation drivers, so the DX2's will be as true to a single driver pair as it gets.

In your estimation Martin, have you an idea of the expected bass output based on a couple watt input? Off the top of your head?

I apologize for being lazy and not doing the math or research on my own. I'm simply trying to get a guy hooked up. 

Bob

[Bob in St. Louis]

Received this via PM:
---------------------
The qts is .25 so I would guess not much output below 300hz.
Voice coil travel is +/- 1mm so if you don't high pass @ 400hz (or maybe higher with a 6 dB slope) it would be real easy to destroy on an OB.

[MJK]

Received this via PM:
---------------------
The qts is .25 so I would guess not much output below 300hz.
Voice coil travel is +/- 1mm so if you don't high pass @ 400hz (or maybe higher with a 6 dB slope) it would be real easy to destroy on an OB.

That matches my simulation results. I don't think it would be a good idea to run the DX2's full range.

Martin

[Mr Content]

Bob your friend would find it a very unpleasing introductin to OB. The Dx2 would sound very unbalanced, and peaky without the proper bass augmentation. You will have to talk him into some SI's if he only wants a single driver solution.

Mr C

[Bob in St. Louis]

Alright folks, thanks for the good information. I'll talk to him and see what he wants to do.

You will have to talk him into some SI's if he only wants a single driver solution.

  I agree Mr. C......I agree.  Maybe I'll have him over one of these days. 

I take it that no amount of wings would help the lower octaves? Short of making his baffles an entire sheet of plywood, there is no way a pair of DX2's are going to go much lower than ~300? It doesn't sound like it, but I just wanted to be sure there's no way in your opinions this driver can handle a resonable spectrum on it's own.

Thanks again fellas!
Bob

[MJK]

I take it that no amount of wings would help the lower octaves? Short of making his baffles an entire sheet of plywood, there is no way a pair of DX2's are going to go much lower than ~300? It doesn't sound like it, but I just wanted to be sure there's no way in your opinions this driver can handle a resonable spectrum on it's own.

Even in an infinite baffle, the Lowther DX2 is not going to produce bass all by itself. You either need to add a helper woofer(s) or some form of enclosure to produce the bass.

I still maintain that with a pair of Alpha 15A woofers it would make a killer OB system.

Martin

[TerryO]

I take it that no amount of wings would help the lower octaves? Short of making his baffles an entire sheet of plywood, there is no way a pair of DX2's are going to go much lower than ~300? It doesn't sound like it, but I just wanted to be sure there's no way in your opinions this driver can handle a resonable spectrum on it's own.

Even in an infinite baffle, the Lowther DX2 is not going to produce bass all by itself. You either need to add a helper woofer(s) or some form of enclosure to produce the bass.

I still maintain that with a pair of Alpha 15A woofers it would make a killer OB system.

Martin

I wouldn't be surprised that Martin's suggestion of using two Alpha 15A woofers for a "Killer System" is right on the money.The Alphas aren't that expensive to achieve what might be the best system your friend will ever own. I listened to Jon Ver Halen's Lowther/Tone Tubby system at VSAC and it was probably the best sounding, or one of the best sounding, speaker systems there.

See Jeff Poth's coverage of VSAC: http://www.enjoythemusic.com/vsac_2008/

Best Regards,
TerryO

[Scott F.]

Short of making his baffles an entire sheet of plywood, there is no way a pair of DX2's are going to go much lower than ~300?

I wouldn't say that. I'm taking mine down to 150Hz then augmenting with my vintage woofers. At 150Hz, the xmax is still very reasonable unless you are trying to get concert level SPL's out of them. My panels are 17" wide and 53" tall. I offset the driver to knock down some of the peaky mid/treble buildups. Overall, and Bob you've listened to them many times, they sound pretty decent when implemented like this. Granted, the DX series sounds night and day different from the PM that I use but something like this might work.

Honest to goodness the best way to implement Lowthers into an open baffle is to do an vented enclosure for a 15" (similar to mine). Although the thought of an OB 15" might seem cool, you need to EQ the hell out of it to get a decent FR.

Think Dick Olsher's Basszilla. It works extremely well.

If you want to do some calculations on the baffle size, do a search for Edge, the baffle diffraction calculator. It does a reasonable job simulating the frequency response on a baffle. If you can't find it, drop me a PM and I'll send you a copy.

[opnly bafld]

Although the thought of an OB 15" might seem cool, you need to EQ the hell out of it to get a decent FR.

 
Think again.

Lin

[MJK]

Honest to goodness the best way to implement Lowthers into an open baffle is to do an vented enclosure for a 15" (similar to mine). Although the thought of an OB 15" might seem cool, you need to EQ the hell out of it to get a decent FR.

I am not sure I agree. How do you defined decent FR?

Without any EQ the Alpha 15A gets to 40Hz in an OB. If you want more low frequency output use the Alpha 15A in a H frame and apply a few dB of boost. Personally, I would rather use a higher Qts driver and acoustics then applying a lot of EQ trying to force a solution with the wrong driver. Typically higher Qts drivers are also cheaper and more efficient down low compared to the bigger magnet lower Qts drivers.

Martin

[tubesguy2]

Martin, you've talked me into it, albeit with PM6As rather than DX2s.  I already had one pair of Alphas, and they're available for $60 each, with free shipping, right now from PE.  Any crossover tips?  Thanks - Pat

[alexstl]

Hi everyone,  I am the guy with the Lowthers that Bob and Scott are helping.  For the record, bass is not that important to me but it also easy/cheap to order a pair of Alpha 15" speakers to compliment the lowthers.  I already looked them up on PE.  What else do I need to make it work?  thanks for all of your help, Alex

[panomaniac]

You'll need a crossover.   Martin can give you an idea of what.

[Bob in St. Louis]

Hey Alex,
I didn't ask what amp you planned on running for the DX2's since just about anything would work for a pair of these drivers in OB.
But now that we're talking about a couple bass augmenting drivers, things get a *little* more complicated.
Do you plan on using one amp to drive all four drivers, or were you going to have two amps?
Either way, you'll need a crossover or some other form of splitting up the signal either passive (after the amp), or active (before the amp).

Sounds like I'll be poking four holes in the plywood instead of two.  aa
Speaking of which, If we're going to mount a 15" bass augmenter to the same piece of 3/4" plywood the DX2's are on, I'd recommend to have four total pieces of plywood. I can laminate the pieces together to give us a total thickness of 1.5".
That will help with baffle vibrations to put it simply. We can get as fancy as you want with constrained layers of dissimilar material, bracing, etc....
I CAN get fancy if you want.    Or....we can just use the 3/4" you've already got.

Bob

[Bob in St. Louis]

............Oh, and by the way......

Although the thought of an OB 15" might seem cool, you need to EQ the hell out of it to get a decent FR.

............. ..........Scott, now you KNOW I can't let THAT comment slide by. 
If you believe the 15 on OB as being "bad", think of it as having a fling with a "bad" girl....
Even though you know it goes against what you were taught, It just feels so darn good. You have to go back for more.  aa

Bob

[MJK]

OK, here are my recommended crossover options.

Each channel is a Lowther PM6A or DX2 full range driver with two Eminence Alpha 15A woofers wired in parallel.


Active Crossover Settings

Low Pass - 200 Hz 2nd order Linkwitz-Riley
Hig Pass - 400 Hz 2nd order Linkwitz-Riley


Passive Crossover Sizing (classic 2nd order circuit configuration)

Zobel circuit across the woofers
  Mills 4 ohm resistor
  Solen 30 uF

Low Pass
  ERSE 14 ga Super Q 4.7 mH in series with the drivers
  Solen 130 uF in parallel with the drivers

High Pass
  Solen 27 uF in series with the drivers
  ERSE 14 ga Super Q 5.6 mH in parallel with the drivers


http://www.erseaudio.com/Products/14-AWG-1-63mm
http://www.partsexpress.com/solen-metallized-polypropylene-capacitors.cfm


These would be my starting crossover values and I would tweak them by ear.

Hope that helps,

Martin

[alexstl]

I have a few amps to choose from including a prima luna prologue integrated model two currently running mullard el34s but I also have a quad of kt88s.  I also run a fisher 500c that has been modernized.  I use both of these amps with Cain and Cain Abbeys with no sub augmentation.  If we need real power I have a musical design signature 150 with an audio research sp9 pre.  I have other amps also like a classic decware or a vintage sansui.  I think the prologue two would be the most flexible to roll tubes to experiment but I am open to suggestions.  thanks for all the help, Alex     

[MJK]

I recommend a powerful SS amp for the woofers. You do not want a low damping factor tube amp driving these woofers. I would also recommend a good SS amp for the Lowthers.