Consul
Well-known member
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:
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:
. Listen to your woofer with and without the block and you decide which you like better.
