Steve,
Too bad you're all the way across the pond. I'd be happy to demo them for you! And the FE108eS Mets, so you could get a direct comparison to what you have.
Martin,
I'm looking forward to having you check out the F120a Mets. At the rate I'm going, they should be up & running in only another 2 months or so.
And after they are completed, I have a pair of FF85K waiting for a micro-Fonken build. I am thinking that those might pay you a visit to see how they sound w/ really good upstream gear and a little help on the bottom end from, say, an 18" Goldwood.
Bluegti,
I tried a saw board--didn't like it. As for biscuits, I don't know their advantages over dowel pins, but a dry fit up works just fine w/ dowel pins. And the clamp/jig cost $50, compared w/ about twice that for the cheap biscuit cutter. Anyway, this is a big step up for me over using screws.
Cheers,
Jim
Too bad you're all the way across the pond. I'd be happy to demo them for you! And the FE108eS Mets, so you could get a direct comparison to what you have.
Martin,
I'm looking forward to having you check out the F120a Mets. At the rate I'm going, they should be up & running in only another 2 months or so.
And after they are completed, I have a pair of FF85K waiting for a micro-Fonken build. I am thinking that those might pay you a visit to see how they sound w/ really good upstream gear and a little help on the bottom end from, say, an 18" Goldwood.Bluegti,
I tried a saw board--didn't like it. As for biscuits, I don't know their advantages over dowel pins, but a dry fit up works just fine w/ dowel pins. And the clamp/jig cost $50, compared w/ about twice that for the cheap biscuit cutter. Anyway, this is a big step up for me over using screws.
Cheers,
Jim
Finished drilling holes for dowel pins and began applying finish to exterior surfaces. I really enjoy applying that first coat of finish, watching the wood come to life.
As some doubt has been cast about the ability to do a dry fit-up when using dowel pins, see photo below. I don’t think I would want to crack open the glue without a dry fit-up to be sure everything is right. Despite some small errors, it’s starting to look good. You can see the sides have a coat of polyurethane.
Red oak veneer has been ordered and should be here tomorrow. I haven’t decided yet how much to veneer. Certainly the front baffles need to be covered, so that they have a more similar pattern than the plywood provides. The backs can probably be left as is. Sides remain open to discussion.
As some doubt has been cast about the ability to do a dry fit-up when using dowel pins, see photo below. I don’t think I would want to crack open the glue without a dry fit-up to be sure everything is right. Despite some small errors, it’s starting to look good. You can see the sides have a coat of polyurethane.
Red oak veneer has been ordered and should be here tomorrow. I haven’t decided yet how much to veneer. Certainly the front baffles need to be covered, so that they have a more similar pattern than the plywood provides. The backs can probably be left as is. Sides remain open to discussion.
Attachments
I made a couple of changes from the FE108eSigma Mets. First, I did claim at the end of the 108 Met build that I would make the next Mets with a removable port baffle. That after a total fiasco with lining ALL sides with foam, then having to cut open the port baffles to strip out foam from three of the sides. The F120a Mets use a 3 inch diameter port, which is a large enough hole to enable access. All I had to do was make the port press fit, which is easy to do thanks to the Parts Express Router Buddy. I will, however, make certain that the ports stay put and are well sealed by using a thin bead of PE speaker gasket material (soft, sticky polymer that doesn’t harden.)
As to the lining: having learned the hard way, I put 0.5 inch PE acoustic barrier foam on only the back panel from just above the driver down to the bottom. In the peak, I put a modest amount of Accousta-Stuff fiber fill. That can easily be modified via the driver hole.
The next change is that I used the router with a round-over bit to trim the vertical edges of the front baffles. Then I veneered the baffles with red oak. This may have sonic benefits by reducing diffraction, but there are other intangible benefits: The original Mets had a high WAF. These are even better!
Finally, I decided to put the binding posts on the port baffle rather than on the back panel. Time will tell if this was a good choice.
As to the lining: having learned the hard way, I put 0.5 inch PE acoustic barrier foam on only the back panel from just above the driver down to the bottom. In the peak, I put a modest amount of Accousta-Stuff fiber fill. That can easily be modified via the driver hole.
The next change is that I used the router with a round-over bit to trim the vertical edges of the front baffles. Then I veneered the baffles with red oak. This may have sonic benefits by reducing diffraction, but there are other intangible benefits: The original Mets had a high WAF. These are even better!
Finally, I decided to put the binding posts on the port baffle rather than on the back panel. Time will tell if this was a good choice.
Attachments
Jim Shearer said:
We like doing that on our floorstanders... works well as long as you aren't switching them in and out a lot or using firehose cables.
dave
planet10 said:
I had to laugh at the thought of someone running 12 ga. cables to these speakers.
With a max rating of 10 watts rms, you can get along just fine with the fine (tiny gauge) wire!
Has anyone thought of using a Markaudio CHR-70 driver for a Metronome? And if so, what would the dimensions be for the "box"?
They’re finished!
Photo below shows one of the F120a Mets next to one of the FE108eSigma Mets (which were my first SFRD build two years ago.) You can see that I have learned a bit about veneering and improving appearance. And, yes, they are significantly larger than the 108 Mets. These look almost as good as they sound. Next post has a close-up of the driver, so you can see the round-over on the vertical edges where the veneer wraps around.
When I installed the drivers, I put washers between the driver and the baffle (a la Bob Brines.) This keeps the gasket from compressing too much; and with a stamped steel basket, it prevents distortion of the frame by the mounting screws. I have previously used steel washers and Nylon washers, both worked well. This time I thought I would try neoprene washers. Long story short: bad idea!
With neoprene washers there was a muffling in the mid-range. Lara Fabian, Diana Krall, and Natalie Maines all sounded like they had cotton in their mouths. Swapped out neoprene for steel and, Voila! all is now good.
I tried them first without BSC: highs were too hot. The I put in the BSC I use with the 108 Mets; 1 mH inductor and 4.5 ohms: highs were too dull. I looked back at the BSC calculator: 1 mH and 4.5 ohms would be about 4 dB of correction; I think I want about 2 dB. So I tried 0.7 mH and 2 ohms: highs were just right.
I have about 150 hours on the drivers now, and they’re sounding very good. I haven’t measured yet, but I think the bass is reaching down into the high 30’s. For me, I want a system to get down to 30 Hz, so I may still use a sub with these Mets.
These are very revealing drivers, but not hyper-detailed. On classical CDs, edit points that are evident on other speakers are rather jarring on the F120a’s--perhaps because they are so involving that the disruption in the flow of the music is heightened. Moving on to jazz (where SFRDs really shine,) Jacintha’s performance of “And the Angels Sing” (from Autumn Leaves, the songs of Johnny Mercer) was fabulous. The opening bass line is well reproduced and doesn’t seem to need any help from a sub. I had intended to get a quick listen to “Lilly Was Here” from Candy Dulfer’s album SAXuality, but I couldn’t stop at just one track--I couldn’t turn it off. When you get drawn into the music like that, you know you have a winner.
It may be a bit early to make final judgements, but I think I like the new F120a Mets about as well as the FE108eSigmas in the mids; the F120a may be a bit better in the highs, and the F120a’s are a clear winner on the low end. If you add in a sub to fill out the low end, then I see it as a close contest. Not that they sound exactly the same--they are certainly different. As I listen more (and perhaps the drivers break in more,) I find myself leaning toward the F120a’s. As always: YMMV.
Photo below shows one of the F120a Mets next to one of the FE108eSigma Mets (which were my first SFRD build two years ago.) You can see that I have learned a bit about veneering and improving appearance. And, yes, they are significantly larger than the 108 Mets. These look almost as good as they sound. Next post has a close-up of the driver, so you can see the round-over on the vertical edges where the veneer wraps around.
When I installed the drivers, I put washers between the driver and the baffle (a la Bob Brines.) This keeps the gasket from compressing too much; and with a stamped steel basket, it prevents distortion of the frame by the mounting screws. I have previously used steel washers and Nylon washers, both worked well. This time I thought I would try neoprene washers. Long story short: bad idea!
With neoprene washers there was a muffling in the mid-range. Lara Fabian, Diana Krall, and Natalie Maines all sounded like they had cotton in their mouths. Swapped out neoprene for steel and, Voila! all is now good.I tried them first without BSC: highs were too hot. The I put in the BSC I use with the 108 Mets; 1 mH inductor and 4.5 ohms: highs were too dull. I looked back at the BSC calculator: 1 mH and 4.5 ohms would be about 4 dB of correction; I think I want about 2 dB. So I tried 0.7 mH and 2 ohms: highs were just right.
I have about 150 hours on the drivers now, and they’re sounding very good. I haven’t measured yet, but I think the bass is reaching down into the high 30’s. For me, I want a system to get down to 30 Hz, so I may still use a sub with these Mets.
These are very revealing drivers, but not hyper-detailed. On classical CDs, edit points that are evident on other speakers are rather jarring on the F120a’s--perhaps because they are so involving that the disruption in the flow of the music is heightened. Moving on to jazz (where SFRDs really shine,) Jacintha’s performance of “And the Angels Sing” (from Autumn Leaves, the songs of Johnny Mercer) was fabulous. The opening bass line is well reproduced and doesn’t seem to need any help from a sub. I had intended to get a quick listen to “Lilly Was Here” from Candy Dulfer’s album SAXuality, but I couldn’t stop at just one track--I couldn’t turn it off. When you get drawn into the music like that, you know you have a winner.
It may be a bit early to make final judgements, but I think I like the new F120a Mets about as well as the FE108eSigmas in the mids; the F120a may be a bit better in the highs, and the F120a’s are a clear winner on the low end. If you add in a sub to fill out the low end, then I see it as a close contest. Not that they sound exactly the same--they are certainly different. As I listen more (and perhaps the drivers break in more,) I find myself leaning toward the F120a’s. As always: YMMV.
Attachments
Was it ever agreed as to which of MJK's spreadsheets would give a close approximation to this build. I would like to work some designs for some bigger units. The link to the original plan does not seem to work now. Is it still available?
jamikl
jamikl
jamikl,
I used the ML TQWT sheet to model the Met. If you don't already have the MathCAD sheets, it's too late. MJK has discontinued licensing them. And for others who have have them (legally) time is running out, as they will not be re-licensed.
Dave,
Thanks. Tension was running high around here, as this is my first attempt to alter a known (and very successful) cabinet for a different driver. I would have been devastated if it didn't work well.
I used the ML TQWT sheet to model the Met. If you don't already have the MathCAD sheets, it's too late. MJK has discontinued licensing them. And for others who have have them (legally) time is running out, as they will not be re-licensed.
Dave,
Thanks. Tension was running high around here, as this is my first attempt to alter a known (and very successful) cabinet for a different driver. I would have been devastated if it didn't work well.
OK, time for a wrap-up.
With 500 hrs. on the drivers and some serious listening, I dropped the BSC altogether. I had thought that there was something in the highs that was bothering me, but now I think I was experiencing some allergy related problems which affected my hearing--and perhaps the drivers weren’t fully run in. When I got past that and began comparing the F120a Mets to the FE108eSigma Mets, it was clear that the BSC was not needed.
Yesterday MJK came over with his PRAXIS system to have a listen and to measure the F120a Mets. The measurements show that their performance matches the MathCAD simulation. The image below shows the SPL plot with 1/6 octave smoothing. As you can see, there is no evidence of baffle step, so there is nothing to correct. At frequencies above those affected by the cabinet, this plot matches (within error limits) Martin’s measurement of his F120a's in his OB system. The Met cabinet design is an unqualified success. 😎
However... comparing the F120a’s to the Fe108eSigma’s, I prefer the FE108’s. Even though the FE108’s can’t match the low end of the F120a’s,there is something more lively in the FE108’s presentation. The best driver I have heard is the Lowther PM2a (approximately $2,100 per pair) in Martin’s MLTL cabinet and in his large OB system. I don’t know how to characterize the presentation of that driver other than holographic (and scary real!) I bought the F120a drivers with the hope that they would be a step beyond the other Fostex drivers I have. These other drivers now include: Fe108eSigma, FE206e, FE127e, and FF85k. The F120a is cost almost as much as all these other drivers put together, and is the first one to fall short of expectations. I didn’t expect it to reach the level of the PM2a, but I had hoped it would be a step closer than the cheaper Fostex. 🙁 For what ever reason, the F120a just isn't my cup of tea.
After I make some cosmetic improvements to the FE108 Mets, the F120a’s are probably headed for storage; until such time as I figure out their ultimate disposition.
With 500 hrs. on the drivers and some serious listening, I dropped the BSC altogether. I had thought that there was something in the highs that was bothering me, but now I think I was experiencing some allergy related problems which affected my hearing--and perhaps the drivers weren’t fully run in. When I got past that and began comparing the F120a Mets to the FE108eSigma Mets, it was clear that the BSC was not needed.
Yesterday MJK came over with his PRAXIS system to have a listen and to measure the F120a Mets. The measurements show that their performance matches the MathCAD simulation. The image below shows the SPL plot with 1/6 octave smoothing. As you can see, there is no evidence of baffle step, so there is nothing to correct. At frequencies above those affected by the cabinet, this plot matches (within error limits) Martin’s measurement of his F120a's in his OB system. The Met cabinet design is an unqualified success. 😎
However... comparing the F120a’s to the Fe108eSigma’s, I prefer the FE108’s. Even though the FE108’s can’t match the low end of the F120a’s,there is something more lively in the FE108’s presentation. The best driver I have heard is the Lowther PM2a (approximately $2,100 per pair) in Martin’s MLTL cabinet and in his large OB system. I don’t know how to characterize the presentation of that driver other than holographic (and scary real!) I bought the F120a drivers with the hope that they would be a step beyond the other Fostex drivers I have. These other drivers now include: Fe108eSigma, FE206e, FE127e, and FF85k. The F120a is cost almost as much as all these other drivers put together, and is the first one to fall short of expectations. I didn’t expect it to reach the level of the PM2a, but I had hoped it would be a step closer than the cheaper Fostex. 🙁 For what ever reason, the F120a just isn't my cup of tea.
After I make some cosmetic improvements to the FE108 Mets, the F120a’s are probably headed for storage; until such time as I figure out their ultimate disposition.
I'd like to increase the tuning frequency. I remember Scottmoose saying he'd designed these to be flat which made me think it was not the only valid tuning. I am running the stock FE108es mets.
My purpose is to add warmth through the upper bass. I accept that I'll need some augmentation. What I'd like to know is whether shortening the port is the right way to do it...will it still sound right or will it be a mis-alignment?
My purpose is to add warmth through the upper bass. I accept that I'll need some augmentation. What I'd like to know is whether shortening the port is the right way to do it...will it still sound right or will it be a mis-alignment?
Allen,
When I got home from vacationing with the grandkids, I ran a quick model of the FE108eSigma Met to confirm my initial thought: shorten the port and you will indeed increase the tuning frequency; but the effect is to just put a bump at the bottom of the response. Changing from a 3" long port to 2.5" will push the tuning freq up by about 4-5 Hz and make a bump of about +3 dB that is about 8 dB wide. In other words, you would be moving toward boomy, one-note bass. Not what I would want.
Cheers, Jim
When I got home from vacationing with the grandkids, I ran a quick model of the FE108eSigma Met to confirm my initial thought: shorten the port and you will indeed increase the tuning frequency; but the effect is to just put a bump at the bottom of the response. Changing from a 3" long port to 2.5" will push the tuning freq up by about 4-5 Hz and make a bump of about +3 dB that is about 8 dB wide. In other words, you would be moving toward boomy, one-note bass. Not what I would want.
Cheers, Jim
Thanks Jim, I'll leave the frequency alone. My first thoughts (well, the negative ones...it was mostly positive 🙂 ) of this speaker were that it was thin sounding and went harsh when I turned them up. I wanted to pump the bass using the tuning and then cross them over, but this seems to be changing now that I have some hours up on the Fostexes. Not sure whether it's them or me but the bass seems to be filling and warming and they can seem to play louder than before without stress.
I still need to go through the recommended mods like the floor coupling and internal damping but if I still want to try crossing them over I might use the damping factor tweak instead of the tuning, but in fact I'll probably play with it on its own first.
Q: Has anyone considered removing a square from the back panel directly behind the driver and just larger than it and replacing it with a longer piece glued to the back of the back panel so that there would be an extra 18mm of air space behind the driver so it isn't as cramped?
I still need to go through the recommended mods like the floor coupling and internal damping but if I still want to try crossing them over I might use the damping factor tweak instead of the tuning, but in fact I'll probably play with it on its own first.
Q: Has anyone considered removing a square from the back panel directly behind the driver and just larger than it and replacing it with a longer piece glued to the back of the back panel so that there would be an extra 18mm of air space behind the driver so it isn't as cramped?
Allen,
A couple of comments spring to mind as I read you post.
The 108's need an extended break-in period. In the first 100 hrs, mine made some awful sounds. By 400 hrs they were doing pretty well.
I had to fix mistakes in damping material--I had put 0.5" acoustic foam (from Parts Express) on ALL of the inside.
What was needed was foam on only the back panel. I also placed the Mets on marble tiles so the ports fire into a hard surface rather than carpet.
Then the final touch was MJK's recommendation of baffle step correction.
Please keep us posted on how it's working for you.
Cheers, Jim
A couple of comments spring to mind as I read you post.
The 108's need an extended break-in period. In the first 100 hrs, mine made some awful sounds. By 400 hrs they were doing pretty well.
I had to fix mistakes in damping material--I had put 0.5" acoustic foam (from Parts Express) on ALL of the inside.
What was needed was foam on only the back panel. I also placed the Mets on marble tiles so the ports fire into a hard surface rather than carpet.Then the final touch was MJK's recommendation of baffle step correction.
Please keep us posted on how it's working for you.
Cheers, Jim
As the metronomes got my attention and MJK made his worksheets available again i tried to simulate the FE206E for a metronome style enclosure.
I don't know if i really made it right as it's the first time i used MJKs worksheets, but simulation looks good to me.
For simulation i used factory defined specs for FE206E (don't know how accurate they are, but couldn't find measured specs) and 4 Ohms of serial resistance. I tuned a bit higher than the FE207E for lower excursion between 50 and 90 Hz.
Here is the pdf of my simulation.
For a better simulation (and therefor further learning for working with the mathcad worksheets) i would appreciate if someone could send me measured specs or hints on how to simulate better. 🙂
/Cathul
I don't know if i really made it right as it's the first time i used MJKs worksheets, but simulation looks good to me.
For simulation i used factory defined specs for FE206E (don't know how accurate they are, but couldn't find measured specs) and 4 Ohms of serial resistance. I tuned a bit higher than the FE207E for lower excursion between 50 and 90 Hz.
Here is the pdf of my simulation.
For a better simulation (and therefor further learning for working with the mathcad worksheets) i would appreciate if someone could send me measured specs or hints on how to simulate better. 🙂
/Cathul
I not sure if it makes any difference, as I am too lazy to do it right, but your simulation is technically incorrect. You appear to have used the MLTL worksheet. This produces a linear taper as if the box has a constant width and the depth increases from one end to the other. The main feature of the Metronome is that it increases in both width and depth from one end to the other -- a quadratic taper.
To correctly model a Metronome, you need to calculate the area at various point down the pipe and enter those into the TL-Sections worksheet. Again, I don't know if it makes any difference. Perhaps you will take the time to do it?
My measurements on a single pair of 206's:
Fs 39
Re 6.69
Qe 0.28
Qm 3.86
Qt 0.26
Vs 56.3
BL 9.4
SPL 96
Bob
To correctly model a Metronome, you need to calculate the area at various point down the pipe and enter those into the TL-Sections worksheet. Again, I don't know if it makes any difference. Perhaps you will take the time to do it?
My measurements on a single pair of 206's:
Fs 39
Re 6.69
Qe 0.28
Qm 3.86
Qt 0.26
Vs 56.3
BL 9.4
SPL 96
Bob