The DIY Near-Field Monitor Project, Round Two

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Consul

Well-known member
Joined
Jun 3, 2004
Messages
1,653
Location
Port Huron, Michigan, USA
Well, after hours of looking at useless spec sheets and analyzing many designs without being able to listen to any of them, I'm moving forward with the idea of presenting a complete near-field monitor project.

Talk about the blind leading the blind.

Design Idea One: Fostex Full-Range with Supertweeter

At this point, I have three ideas, one of which is not mine, but belongs instead to one Robert W., who goes by neustation on PSW and rfenergy on DIYAudio. He told me about a monitor he designed and built around the Fostex FE167E full-ranger driver, and the Fostex FT17H supertweeter, crossed over at 15khz 1st-order, just to fill in the upper octave, which can be done passively since bi-amping this setup would be silly. It all sits in a 24L reflex cabinet tuned to 51hz. According to my simulations, the -3dB point for the bass is around 50hz, which is doing pretty good, I think. There is also baffle-step compensation required, which could be done actively or passively.

The only possible issue I have with this design is that the FE167E has an xmax of .6mm, which is extremely limited. In this kind of bass-reflex cabinet, about 1 watt of power is all it takes to hit maximum excursion. Granted, the FE167E is a pretty efficient driver (94dB at 1 watt/1 meter), but this is still not loud enough for anything other than a small room.

Still, Robert insists that this design has served him so well over the past couple of years that he has sold off all of his other monitoring systems. That's at least one ringing endorsement, and one I hope to put to the test, as Robert lives in the Detroit area and seems willing to let me stop by for a listen. I'll let you know what I find.

On the plus side, it's an inexpensive and relatively easy build, using readily-available parts.

Design Idea Two: Smaller Fostex Full-Ranger with Subwoofer

For this one, I would move to the Fostex FE127E full-range driver, which covers the upper range just fine, but lacks in the bass. For that, I'm looking at the Dayton RS270S 10" woofer. Inexpensive, and it has gotten a lot of good press from many speaker builders. This would be an active bi-amp design, with the crossover around 200 to 300 hz. The higher the better, actually, as the FE127E also has a limited .67mm xmax, but that's less of an issue here as we're not asking it to do much in the bass. I would go with an all-sealed design for this one, aiming for a Qtc of .707, although I still need to determine how big of a cabinet that Dayton would like for that. It has a Qts of .35, which is sitting right on the line of "seal or no seal". :green: I'm also still considering the idea of making it a side-firing sub.

This is one of my own ideas, which means there is no proven track record, other than people who have built small cabinets for this particular Fostex driver and then mated it to a subwoofer. That's basically what this design idea is, only it's all in one cabinet instead.

I have yet to simulate this one, so it may yet prove to be a wash, but at least I have it documented here for review.

Design Idea Three: The Most Radical of Them All

The Seas 27TAFNC/G is a nice little neodymium tweeter that has gotten good ratings from Zaph on his Tweeter Mishmash page. According to him, it can cross over as low as 2khz 4th-order and still have good harmonic distortion specs. I'll have to take him at his word.

Why a neo tweeter? Well, the total diameter is important with coaxially-mounted tweeters.

Okay, let me explain that one.

One of the issues with near-field design is imaging: how good the stereo field sounds between each speaker. In order for imaging to be good, you need the sound from all of the speaker drivers to hit your ears simultaneously. This can be an issue with two-way designs where the tweeter sits above the woofer, especially in, shall we say, intimate environments.

So, let's mount the tweeter coaxially with the woofer instead. I was taking a look at the Seas CA18RNX for a vented enclosure, or its higher-Qts cousin, the CA18RLY for a sealed version. I would design this with active bi-amping, crossing over at 2khz to 2.5khz. Based upon only the factory sheets, it looks like both of these mid-woofers could handle that fine.

Again, I have yet to simulate this idea, but, again, it's now documented here for further review.

I'm still running into issues with time and phase alignment of the tweeter to the woofer, and I continue to kick around how to solve that problem, assuming it's enough of one to begin with. (As a side note, if you remember my thread in the Lab about time-delaying a signal? Well, this is why I was asking.) I'm also looking into what diffraction issues might be caused by coaxial-mounting, and I'm hoping to corner one of the physics profs at school later to help me find out.

Conclusions

All of this quackery has finally brought me to the end of this post. I am no engineer, I'm pretty good at physics, I have no speaker design or building experience, and yet I think I can put together a near-field solution. I'm a total moron for thinking so, and I know that, and admit that. I'm still trying to figure out why I haven't stopped. Maybe it's because this is the first true challenge I've had in years that I've actually been enjoying for a change.

Either way, after some community review, I would like to pick, and then refine, one of the above designs, and then go for broke and see if I can make it work. If I can, I would like to present it as a complete A-Z project to the community.

Go Team! :wink:
 
Speaker building is fun and can range from very simple to simply absurd!

>>>Qtc of .707

I doubt you will be happy with the resulting response. I would suggest you aim for 1 to 1.5. Especially if the woofer enclosure will be anywhere near a corner or a wall.

There is a simple formula for determining the maximum allowable distance between the acoustic centers of two adjacent drivers based on their x-over frequency. I forget that at the moment.

Coax mounting can introduce significant time smear. DSP is about the only way to fix that...

HTH!
 
[quote author="SonsOfThunder"]>>>Qtc of .707

I doubt you will be happy with the resulting response. I would suggest you aim for 1 to 1.5. Especially if the woofer enclosure will be anywhere near a corner or a wall.[/quote]

That's really odd, because so far, you are the only person going against everything I've learned everywhere, including from Vance Dickason, who recommends against a Qtc (total cabinet Q) over 1.0 for all applications. Raising the Qtc increases the bass levels of the speaker in exchange of transient accuracy. Putting a speaker near walls and corners also increases their bass response, so I'm afraid your logic is not making any sense to me, unless of course you know something I don't, which is entirely possible. :wink:

Heck, one other designer recommended a Qtc of 0.5, so called "transient perfect" alignment. Thomas Barefoot's MiniMain 27 is a sealed-box tuned to .707 (according to info on his web site), which is one of the reasons I decided to aim for that.

That is, of course, assuming a closed box. If I decide on one of the ported designs, this conversation is pretty much gravy. :wink:
 
Hey Darren,

My instinct, don't go with Fostex. What you want from monitors is a ruler flat and transparent sound. I never heard either of those from Fostex. Also, their bass sucks. They can have some other pleasurable to ears qualities and can be "musical", but don't expect them to have those.

If you insist on wide range drivers, then save on a few six packs and go with Zaph's 3 incher and a sub. Cheap and effective. You don't like it, use as your media speakers.
If you are on a budget, take either Zaphs L18 or L15 all aluminum designs. I just don't see anything in that price range to beat the quality.
If you have some dough, then it is another matter.

Best, Mark
 
It's not a matter of just building something someone else already designed. So far, on the web, there is no "A to Z" all-active bi-amped near-field monitor project, and I want to rectify that. The ultimate for me would be to be able to put together PCB sets for the active electronics needed, including the amps. I think that would be keen.

So far, there are two basic approaches to the big picture:

1) Pick a current proven project and adapt it. (Option One above)
2) Really be an idiot and start from scratch. (Options Two and Three above)

Now, of course, we could take Zaph's L18 design and adapt it for active bi-amping. It would need a notch filter added into the crossover, but that's not a big deal, really. Time alignment would still be an issue, but that can be solved with cabinet design more readily than any other method.

Indeed, there are other, some say better, full-range drivers out there. At this point, anything is an option. The idea of this thread was to narrow the options, though, rather than widen them.

I'm also pretty well set on active multi-amping as well (except in option one above, for reasons already given). Everything Rod Elliot wrote about it, plus my own experiences, have pretty much sold me.
 
My instinct, don't go with Fostex. What you want from monitors is a ruler flat and transparent sound. I never heard either of those from Fostex. Also, their bass sucks. They can have some other pleasurable to ears qualities and can be "musical", but don't expect them to have those.
I agree. I was obsessed with similar idea, but decided to go with more classic project at the end. BTW, I stopped few months before because of lot of work in my studio but I have few more days to finish the job. Just to remind you, I'm talking about this http://www.groupdiy.com/index.php?topic=12511&start=0
Consul, I see you appreciate T.B. work. Did you checked his comments about my past idea?
Also, Fostex fullrangers can be interesting, but only in area of "cloning" auratones... :sad:
 
[quote author="Consul"]
Now, of course, we could take Zaph's L18 design and adapt it for active bi-amping. It would need a notch filter added into the crossover, but that's not a big deal, really. Time alignment would still be an issue, but that can be solved with cabinet design more readily than any other method...

...I'm also pretty well set on active multi-amping as well (except in option one above, for reasons already given). Everything Rod Elliot wrote about it, plus my own experiences, have pretty much sold me.[/quote]

That's what I'd do.
 
Hrm... That definitely gives me a few things to think about. I'll come back tomorrow, hopefully, with some sort of prelim design. Right now, I'm re-plowing through moby's thread. :grin:

Thanks for the help, everyone!
 
Darren,

If you are quoting VD, then I assume you have read some edition of the LDC which has from the very first, shown a family of curves similar to this:

thiele%20-%20small%20graph.gif


And you also have read about boundary-loading effects. But boundary loading generally only increases the apparent output at the lowest freqs, not the whole band. Most people I know will say that a .707 cabinet sounds tubby and dull. (of course this is all subjective and certainly depends on the woofer and a kajillion other factors).

But its easy enough to experiment with this to hear the difference for yourself! Build the box for .707, then calculate the volume for Qtc = 1.2 let's say. Now find the difference in size and make a block of wood the same size as this difference (make sure to dimension it so that it won't interfere with anything inside the cab :thumb:). Listen to your woofer with and without the block and you decide which you like better.

HTH!
Charlie
 
If you are too add the subwoofer then the .707 is a good idea and can control cone excursion.

When you can do this with a non-ported enclosure, it will make things even easier for the Mid/Woof
and the Sub handles 100-ish down.
Use your electronics for the Sub crossover point and EQ curve and phase shift etc (not just polarity but delay/phase).

This all leaves the Mid as a near passive straight forward system.
...
this is a typical approach - see Thomas' stuff as pointed out above.

err
add the Tweet or super tweet with either passive or active electronics.

That B DSP active crossover (or similar) is cool for quick checking of drivers and combinations.

JLM SAMs can't be far away ???
 
Yeah, I've noticed that the tweeter/midwoofer/subwoofer combination is popular in the studio monitoring world. I have to think there's a reason for this.

What I like most about Thomas' design is the way he designed the subwoofer: he locked the magnets together back-to-back, and then runs them in a push/push (also called a bipole) configuration. I don't know what kind of time-smear side-firing subs might cause, though, or how to correct for it if it does. Those 10" Daytons I linked to earlier would be a possibly good candidate for this configuration, I think.

He also mentions the two 5-inch midwoofers have a waveguide chamber in the rear, which sounds very reminiscent of Lynn Olson's Ariel ME2 design here: http://nutshellhifi.com/ME2txt.html#me2 and http://nutshellhifi.com/ME2.gif

I'm just thinking out loud...

EDIT: You mean these, Kev? http://www.jlmaudio.com/BAM1.htm

After seeing that page on the JLM Audio site, I was thinking about the picture down below (the tubular ones) and I found it interestingly close to this design on the Parts Express site:

http://www.partsexpress.com/projectshowcase/tubular/index.html

Again, just thinking out loud...
 
http://www.jlmaudio.com/BAM1.htm
Also , don't forget about this project. http://www.humblehomemadehifi.com/Proteus.html
Tony, author of Proteus was from big, big help for my project. :thumb:
 
[quote author="Moby"]
http://www.jlmaudio.com/BAM1.htm
Also , don't forget about this project. http://www.humblehomemadehifi.com/Proteus.html
Tony, author of Proteus was from big, big help for my project. :thumb:[/quote]

Not sure if D'Appolito would be good for near fields. Do you have an experience with that?
 
The Proteus - To D' Appolito or not to D' Appolito, that is the question

and if you don't want to answer the question
... go for the single woofer


SAM
Small Active Monitor - yes, a single woofer

BAM
as said above
Big Active Monitor - dual woofer
and I'll let Joe explain his crossover and whether it is D' Appolito or NON D' Appolito
:roll:
then he may want to keep the Maths of his crossover to himself.
:cool:


Thomas' design ... he locked the magnets together back-to-back, ...
others have joined two woofers front to front.
so
I cone with two voice coils and double the weight.
...
lowers the resonance and so a lower note
lower efficiency
higher power handling - two voice coils - usually in parrallel and so draws more current from the amp. Can be a problem if the woofers are 4 ohms.
..
you still have the same maximum cone excursion
this is always a limiting factor for the low and loud.

I'll let Thomas explain his dual sub method
as I haven't look closely and it's his baby anyway.
 
Not sure if D'Appolito would be good for near fields. Do you have an experience with that?
Sorry, I missed a point about nearfield. Yes, I use them as midfield. My MTM is configured with separate sealed woofers, unlike Proteus (one chamber for two woofers) so there will be no problem for rearranging to MT. Just skip one bass enclosure and that works. BTW, Scanspeak 18W8545K-00 sounds pretty impressive , with tight , controlled and fast low end :wink:
Also http://www.humblehomemadehifi.com/dd8.html mk2 is interesting small speaker and I remember Tony suggested that to me as bookshelf nearfields.
 
Well, just three people in and already I have three wildly different sets of opinions and possible approaches. I guess I'm just going to have to make a decision and go with it.

So far, I think Marik's idea of adapting Zaph's L18 design to active use is the best bet. It's a proven combination of drivers in a proven design. That's a great platform to build on. It would not be too expensive, and the parts should be readily available. I think I like it.

Zaph won't offer support to people who mess with his designs, but maybe this is in an interesting enough direction for him to at least keep an eye on it. I think he's mentioned in his blog about wanting to play with active bi-amping, and not having yet had the chance to dive in and do so.
 

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