I have rediscovered a pair of old radio shack speakers that I've had since before I knew about Fostex drivers. They contain the Foster 10F3 (with the alnico magnet, I am pretty sure, based on reading done here). No hole in dust-cap, no migrating glue, kinda stiff suspension. Guessing that these are from the late 1960's.?
I posted about this on an existing thread a couple weeks ago, but got no response, so thought I would try again with a new thread. I understand the need to manage the number of threads, but I do have a few questions.
I listened to one of these Solo 103 speakers, on music and test tones. The general sound is a little more real or natural than the Fostex fe126e, that I like, and have listened to a lot.* The Solo 103 seems to start to roll off on the low end at about 300 hz, but is still pretty strong at 250hz or so. In overall tone it is quite similar to the fe126e (built about 35 years apart). At the top end, the RS Solo 103/Foster10F3 seems to start to roll off somewhere below 10k hz. On a tone sweep it sounds very smooth from 300 to 8k.
I earlier posted about wanting to build a 2 or 3 way with a Fostex full range speaker(as mid or mid/high) covering as much of the range as possible. I think that these Foster 10F3's must be about 90 db efficient above 300hz, guessing from how loud they sound next to my existing speakers. Planet 10 said (in another thread) that a 20 watt amp would work with these drivers (full range?), but I am wanting to find out if they would handle power well enough to work with the 1960's JBL LE10a woofers.
1)Here is the main question: If the lower crossover point was 500hz with 12db/octave roll-off, how much power could the system handle, if it was being limited by the power handling of the Foster 10F3? (I plan on using an 8ohm JBL LE10a from the mid 1960's, and I think it is rated for 75 watts and about 89db efficient). I want to be able to play the system fairly loud when I get the itch.
2)Baffle step question: Would a resistor on the Foster 10F3 help with woofer baffle step, and thus also with power handling? How much reduction in output does a 10ohm resistor in series make? Would it be worth whatever noise/distortion the resistor added?
3) Alternate woofer question: What currently available woofers- in what alignments-are preferred by folks out there to work with these vintage Foster 10F3 drivers?
THANKS, Howard
I posted about this on an existing thread a couple weeks ago, but got no response, so thought I would try again with a new thread. I understand the need to manage the number of threads, but I do have a few questions.
I listened to one of these Solo 103 speakers, on music and test tones. The general sound is a little more real or natural than the Fostex fe126e, that I like, and have listened to a lot.* The Solo 103 seems to start to roll off on the low end at about 300 hz, but is still pretty strong at 250hz or so. In overall tone it is quite similar to the fe126e (built about 35 years apart). At the top end, the RS Solo 103/Foster10F3 seems to start to roll off somewhere below 10k hz. On a tone sweep it sounds very smooth from 300 to 8k.
I earlier posted about wanting to build a 2 or 3 way with a Fostex full range speaker(as mid or mid/high) covering as much of the range as possible. I think that these Foster 10F3's must be about 90 db efficient above 300hz, guessing from how loud they sound next to my existing speakers. Planet 10 said (in another thread) that a 20 watt amp would work with these drivers (full range?), but I am wanting to find out if they would handle power well enough to work with the 1960's JBL LE10a woofers.
1)Here is the main question: If the lower crossover point was 500hz with 12db/octave roll-off, how much power could the system handle, if it was being limited by the power handling of the Foster 10F3? (I plan on using an 8ohm JBL LE10a from the mid 1960's, and I think it is rated for 75 watts and about 89db efficient). I want to be able to play the system fairly loud when I get the itch.
2)Baffle step question: Would a resistor on the Foster 10F3 help with woofer baffle step, and thus also with power handling? How much reduction in output does a 10ohm resistor in series make? Would it be worth whatever noise/distortion the resistor added?
3) Alternate woofer question: What currently available woofers- in what alignments-are preferred by folks out there to work with these vintage Foster 10F3 drivers?
THANKS, Howard
I have the 10F3 and other similar drivers and I use them in a similar manner as you want to but I also have the more robust speakers right next to them for 'as the evening wears on'. They sound very good but the coils are lightweight, the formers are paper and they were made in a time when sound came from tubes and high power was not an issue. If you are asking how much they will take at what XO point, you might want to reconsider your approach. Seriously, they are a great little driver and it would be a shame to jeopardize that. Put the system together with the LE10, which is another really good driver [but too expensive to fix if you blow it] and make yourself a separate party type system. I have never regretted doing that. 
EDIT: What Dave says is true if you are somewhat reasonable but I'm not like that.
EDIT: What Dave says is true if you are somewhat reasonable but I'm not like that.
Cal, I can see from your photos that you understand party-capable speakers. I did picture my 10F3/LE10 speakers in my bedroom-so I guess they don't need to go all that loud.
If I do bring down the level of 10F3 with a resistor, will it adversely effect the sound? Having it too loud with respect to the woofer would not be great. Thought it might help with baffle step.
Any ideas about crossover point/cabinet width with respect to baffle step for this combination?
If I do bring down the level of 10F3 with a resistor, will it adversely effect the sound? Having it too loud with respect to the woofer would not be great. Thought it might help with baffle step.
Any ideas about crossover point/cabinet width with respect to baffle step for this combination?
It's really up to you. If you have a good supply of caps coils and resistors, you can keep busy for hours just farting around and seeing what works best for you. Word of caution though: Stop after an hour or so and walk away for a few minutes. Information overload can happen and throw off your results to the point where you come back the next morning and wonder what the heck were you thinking.
I understand that there is a real art to crossover design, especially series. Have any idea where to look on the web for especially insightful, not too scientific approaches? I have seen a tutorial on no-measure crossover design, but others say if you don't measure your really shooting in the dark. I would like to get the equipment/skills to measure, but I am not there yet.
A super duper thing would be to build ( or find) a big shallow horn - a wave guide .
Since the speaker in question has an inverted surround, so it doesn't produce much interference ( produced by a regular pronounced roll )
So the blending between the two might find its right way acoustically.
That's the function and purpose of any crossover design, to fit the project.
It may happen , virtually never but it's actually how it works, even without any crossover -just the natural mechanical one ...as the speakers are still pass band devices that exhibit max efficiency on narrow spectrum band.
Since the speaker in question has an inverted surround, so it doesn't produce much interference ( produced by a regular pronounced roll )
So the blending between the two might find its right way acoustically.
That's the function and purpose of any crossover design, to fit the project.
It may happen , virtually never but it's actually how it works, even without any crossover -just the natural mechanical one ...as the speakers are still pass band devices that exhibit max efficiency on narrow spectrum band.
In the past I made a wave guide that was about 1.5" (37.5mm?) deep to fit around a Fostex fe126e. It seemed to noticeably boost the output, on axis, around 1000hz or so, which that speaker didn't need.
One of the main things I want to do is to keep the low frequency energy out of the little foster 10F3.
I think one of the main reasons there are low pass filters used on woofers is that the woofer's response gets really ragged above a certain point. But I do believe that JBL used the LE10a, like the one I want to use, without a low pass in their L77 system.
One of the main things I want to do is to keep the low frequency energy out of the little foster 10F3.
I think one of the main reasons there are low pass filters used on woofers is that the woofer's response gets really ragged above a certain point. But I do believe that JBL used the LE10a, like the one I want to use, without a low pass in their L77 system.
What characterizes the low frequency cut of a Wg or horn is the mouth aperture.
Having a boost at the crossover frequency may help if the design allows for it.
Usually passive filters introduce a boost at stop band ( ripple )..only Butterworth is flat.
One reason to use a coil or LC is to determine precisely the band assigned to the woofer.
Then, a WG with a driver bigger than 3" may be outraugeosly resonant due to the
multiple sources that happen to exist, due to the geometry of the cone, so it was just an idea .
I'm listening actually with a pair of speakers composed by a 10 '' and a 2", with series
crossover and a 7'' WG (old speaker cones, new duty) . Indeed , the 2'' mid-tweeter is the only thing 'new' that I bought for this project .
Having a boost at the crossover frequency may help if the design allows for it.
Usually passive filters introduce a boost at stop band ( ripple )..only Butterworth is flat.
One reason to use a coil or LC is to determine precisely the band assigned to the woofer.
Then, a WG with a driver bigger than 3" may be outraugeosly resonant due to the
multiple sources that happen to exist, due to the geometry of the cone, so it was just an idea .
I'm listening actually with a pair of speakers composed by a 10 '' and a 2", with series
crossover and a 7'' WG (old speaker cones, new duty) . Indeed , the 2'' mid-tweeter is the only thing 'new' that I bought for this project .
I'm listening actually with a pair of speakers composed by a 10 '' and a 2", with series
crossover and a 7'' WG (old speaker cones, new duty) . Indeed , the 2'' mid-tweeter is the only thing 'new' that I bought for this project .
Hi Picowall, Do you mean that you have somehow used old cones to construct wave guides?
Have you seen this Martin King design paper(which is enlightening to me with respect to full-range + helper woofer designs)?-it is an open baffle design with passive crossover using a Fostex FE103 and Eminence 15" pro woofer http://www.quarter-wave.com/OBs/OB_Design.pdf
Driver update: I had a disappointing moment a couple hours ago when I opened the second Solo 103, that I had been listening to, and the driver was really trashed- migrated glue, loose, distorted surround. But since it had sounded good, I started repairing it. Also it turns out that this "pair" is likely not from the same production run, because there are slight differences in the drivers and cabinets.
It's a sport seldom praticated, but gives good results. Vetust ellipticals from Tvs are the best
Yes, I recommended it to a member, Roushon, some 2-3 years ago. Better than going out alone in the dark...
But keeping in mind that if he wan't satisfied by the project, they could be repurposed, like bass for PA or little Pc speakers .
Too bad ! But they can eventually turn out to be good Wgs
Primer Primer primer
Picowall:
When you use old cones as waveguides, do you make them thicker and heavier somehow?
Regarding: “What characterizes the low frequency cut off a Wg or horn is the mouth aperture”:
Seems like the aperture of the horn mouth would determine the cutoff frequency if the other dimensions of the horn were intact-which must depend on expansion rate and thus overall shape. If it is too shallow, like mine at 1.5”with a 5” diameter, it seems like it would not function as a horn-but I don't really know enough about it to really say.
Regarding: “One reason to use a coil or LC is to determine precisely the band assigned to the woofer”:
I wasn't sure what you meant by LC, so I looked and found this about resonant circuits (as filters): LC circuit - Wikipedia, the free encyclopedia
Hey! I haven't given up on the thrashed 10F3 yet(see how it went from trashed to thrashed?!) I haven't played the damaged 10F3 since I started refurbishing it, but I see no reason why it shouldn't still play well. It was producing sweet sound, even in it's trashed condition.
The project:
I am getting intrigued by the idea of using the original RS Solo 103 boxes; I do really like vintage stuff. I am thinking about replacing the Solo 103 backs, which could be penetrated by the initial section of a rear loaded horn. The initial horn section and mouth would fold inside the cabinet somewhat, the remaining volume of which would become the compression chamber for the horn. The horn structure would continue in the form of a stand, the upright section of which would be behind the plane of the back of the Solo 103. The horn mouth would be at floor level and be integrated into the base. So there would be a 18-24”space between the flat spreading horn mouth at floor level and the Solo 103, that could accommodate various woofer options, or the Solos could be used “solo”. With the helper woofer enclosure in place, the overall look would be one box stacked on the other, on a 3” tall base. I know this is all way harder than building a “normal” BLH, but I am up to it----I just have to find the time. I have strived in the past to create horn designs that were simple and easily reproducible---this would rather be a one(pair) of a kind creation.
I want to build a little waveguide into the existing cutout space between where the driver rear-mounts in the enclosure, and the existing grill cloth. It would be 1/2” deep (baffle thickness), with an outside diameter of 4” and an inside diameter of 2.75”, which is the diameter of the cone itself. I think/hope that the cone would not bump it on forward excursions.
The option to switch out woofers/enclosures is attractive to me for various reasons; among them is the fact that our local PNWAS(Seattle) speaker contest does not allow powered/bi-amped speakers. So I could use one version at home, and compete with another version.
When you use old cones as waveguides, do you make them thicker and heavier somehow?
Regarding: “What characterizes the low frequency cut off a Wg or horn is the mouth aperture”:
Seems like the aperture of the horn mouth would determine the cutoff frequency if the other dimensions of the horn were intact-which must depend on expansion rate and thus overall shape. If it is too shallow, like mine at 1.5”with a 5” diameter, it seems like it would not function as a horn-but I don't really know enough about it to really say.
Regarding: “One reason to use a coil or LC is to determine precisely the band assigned to the woofer”:
I wasn't sure what you meant by LC, so I looked and found this about resonant circuits (as filters): LC circuit - Wikipedia, the free encyclopedia
Hey! I haven't given up on the thrashed 10F3 yet(see how it went from trashed to thrashed?!) I haven't played the damaged 10F3 since I started refurbishing it, but I see no reason why it shouldn't still play well. It was producing sweet sound, even in it's trashed condition.
The project:
I am getting intrigued by the idea of using the original RS Solo 103 boxes; I do really like vintage stuff. I am thinking about replacing the Solo 103 backs, which could be penetrated by the initial section of a rear loaded horn. The initial horn section and mouth would fold inside the cabinet somewhat, the remaining volume of which would become the compression chamber for the horn. The horn structure would continue in the form of a stand, the upright section of which would be behind the plane of the back of the Solo 103. The horn mouth would be at floor level and be integrated into the base. So there would be a 18-24”space between the flat spreading horn mouth at floor level and the Solo 103, that could accommodate various woofer options, or the Solos could be used “solo”. With the helper woofer enclosure in place, the overall look would be one box stacked on the other, on a 3” tall base. I know this is all way harder than building a “normal” BLH, but I am up to it----I just have to find the time. I have strived in the past to create horn designs that were simple and easily reproducible---this would rather be a one(pair) of a kind creation.
I want to build a little waveguide into the existing cutout space between where the driver rear-mounts in the enclosure, and the existing grill cloth. It would be 1/2” deep (baffle thickness), with an outside diameter of 4” and an inside diameter of 2.75”, which is the diameter of the cone itself. I think/hope that the cone would not bump it on forward excursions.
The option to switch out woofers/enclosures is attractive to me for various reasons; among them is the fact that our local PNWAS(Seattle) speaker contest does not allow powered/bi-amped speakers. So I could use one version at home, and compete with another version.
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