Following on from a thread in Full Range - I recently accidentally ended up buying some Fostex FF85wk full range drivers, and ended up making some cardboard open baffle bodge-ups to mount them in...
They sound WAY better than I would have ever expected, and I'm now fancying a trip down the OB rabbit hole.
I'm using a powered sub to do proper low end stuff, but the '85's don't really reach quite low enough, and for night time listening (when the sub goes off to reduce neighbor annoyance), I'm lacking in bottom end.
My ideal situation would be to have the 85's doing their thing from maybe 200hz upwards, then having something going down to maybe 60-70hz, so effectively the sort of bass I'd get from something like a LS3a type 2-way stand mounter. This then gives a nice point to bring the sub in when suitable.
I know NOTHING about OB, so I'm reading a lot, and it's yet to really sink in. I don't mind having a sealed/ported box for the mid/bass component, but would love to try open first.
Would something like this work for my 60-70hz - 200ish hz requirement?
MONACOR - Products - SP-202PA
Only thing I thought was that the free air resonance might be too high?
Any help would be hugely appreciated
I'll be back re x-overs, but I'm hoping to actively manage that end of things ideally.
They sound WAY better than I would have ever expected, and I'm now fancying a trip down the OB rabbit hole.
I'm using a powered sub to do proper low end stuff, but the '85's don't really reach quite low enough, and for night time listening (when the sub goes off to reduce neighbor annoyance), I'm lacking in bottom end.
My ideal situation would be to have the 85's doing their thing from maybe 200hz upwards, then having something going down to maybe 60-70hz, so effectively the sort of bass I'd get from something like a LS3a type 2-way stand mounter. This then gives a nice point to bring the sub in when suitable.
I know NOTHING about OB, so I'm reading a lot, and it's yet to really sink in. I don't mind having a sealed/ported box for the mid/bass component, but would love to try open first.
Would something like this work for my 60-70hz - 200ish hz requirement?
MONACOR - Products - SP-202PA
Only thing I thought was that the free air resonance might be too high?
Any help would be hugely appreciated
I'll be back re x-overs, but I'm hoping to actively manage that end of things ideally.
Welcome to the Open Baffle Club! We have a lot of fun here, but there is a lot to learn.
That Monacor isn't really suited to OB bass, unless you use 4 per side. And 8" woofer is too small on its own to give satisfaction on OB. Its Qts of 1.1 would give it a fat low end, but the 68Hz fs will limit your bass extension, even with 4.
Using a single woofer per side, I'd never go smaller than a 12".
We have a lot of fun here, but there is a lot to learn.That Monacor isn't really suited to OB bass, unless you use 4 per side. And 8" woofer is too small on its own to give satisfaction on OB. Its Qts of 1.1 would give it a fat low end, but the 68Hz fs will limit your bass extension, even with 4.
Using a single woofer per side, I'd never go smaller than a 12".
When someone says OB multiway I think of this LX521 Description
Of course one should start by reading the whole of the Linkwitz Lab site............
However, what you are thinking of is an OB WAW, so you could (but really shouldn't) skip some of it
Of course one should start by reading the whole of the Linkwitz Lab site............
However, what you are thinking of is an OB WAW, so you could (but really shouldn't) skip some of it
offwego, will you still be getting a miniDSP?
If so, having a very high Qts woofer isn't so important, as you could get a mid Qts woofer, with a low Fs, and EQ the bottom end a bit to get it flat.
Also, consider crossing the 85 a bit higher than 200Hz... on an open baffle, I doubt you will reach 200Hz easily, so, I would go up to 300, or even 500Hz, with the WAW setup.
I don't know if GRS drivers are easy to get in the UK, but at Parts-Express, they are quite cheap and a highish Qts usually. They have been used in many OB setups, due to their low price and reasonable performance.
If so, having a very high Qts woofer isn't so important, as you could get a mid Qts woofer, with a low Fs, and EQ the bottom end a bit to get it flat.
Also, consider crossing the 85 a bit higher than 200Hz... on an open baffle, I doubt you will reach 200Hz easily, so, I would go up to 300, or even 500Hz, with the WAW setup.
I don't know if GRS drivers are easy to get in the UK, but at Parts-Express, they are quite cheap and a highish Qts usually. They have been used in many OB setups, due to their low price and reasonable performance.
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I think the FF85WK should be crossed more at ~400Hz, effectively its upper mass-corner.
With a first-order slope, you're good for 1W below Xmax (0.35mm) and even full rated power (5W) only takes it to 0.7mm, which it can likely handle. A second-order slope keeps it below 0.35mm at rated power.
I suggest reading MJK's excellent paper on his 2-way OB design with a small fullrange.
http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf
http://www.quarter-wave.com/OBs/OB_Design_Part_2.pdf
With a first-order slope, you're good for 1W below Xmax (0.35mm) and even full rated power (5W) only takes it to 0.7mm, which it can likely handle. A second-order slope keeps it below 0.35mm at rated power.
I suggest reading MJK's excellent paper on his 2-way OB design with a small fullrange.
http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf
http://www.quarter-wave.com/OBs/OB_Design_Part_2.pdf
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Something like MiniDSP eventually yes (although, can I do 3-way with them?), TBH though, for the sake of saving outlay now, plus gaining the opportunity to play with my first cross-overs, I'll go passive to start with
Did you look at Scott's signature?
I have now
What about SWAWAW...Sub woofer assisted woofer assisted wide-band?
I only want to about 60-70hz from the woofer, so does that change things much?
I've been experimenting with open baffle and 'frame type speakers over the past few years. Here are some tidbits that might be helpful for someone who is embarking on a new design and wants to get the best sound possible.
1. Less is More (*except see #2)
When it comes to baffles, less is more. That is to say that you will get the best off-axis response when you use minimal or no baffle. This is one reason why SL's LX521 is shaped like it is - minimal baffle. He showed in a recent presentation why large baffles with a small driver mounted more or less centrally is bad, acoustically speaking.
Make the baffle dimensions as close to the diameter of the driver as possible for even off-axis response. You can even use no baffle at all, the "nude driver" system. It's most useful for frequencies above 800-1k Hz where even "minimal baffle" is still too much baffle.
The downside of little to no baffle is a 6dB per octave loss at lower frequencies, below the "dipole peak" (the first peak in a dipole's response). The peak is at about +6dB WRT the inifinite baffle SPL, and below this it will drop off a 6dB/oct. When the driver is small this peak can be above 1kHz - for a 4" driver this might be as high as 2.5kHz if the driver is used "nude". This causes so much loss at lower frequencies (e.g. by 200Hz) that the driver's maximum power input or driver excursion cannot sustain output relative to the SPL near the dipole peak. There is just way too much dipole cancellation! But the best way to solve this is NOT to make the baffle larger.
A better solution to this problem is to use more and different sized drivers. Each driver can then operate in a band that is closer to the dipole peak and not too far above and below it. Again, this is one reason why SL's LX521 is 4-way. When you try to construct a system from a small full-ranger and a woofer, you have to make the baffle large so that the fullranger dipole losses are not too large at low frequencies. This leads to the off-axis response issues I mentioned above, which many builders don't seem to know about or care about but if you want your system to sound good, it's important to not go overboard with a huge (planar) baffle. Thus we are back to small baffles, large dipole losses, and the need for some kind of driver to fill in the hole between the (sub) woofer and the fullranger. This "hole" is often spanning frequencies from 150Hz to 500-750Hz. A large (e.g. 15" or 18") low Xmax, high sensitivity pro driver is perfect for this application. Because of the size of the driver cone, just put it in a planar baffle not much wider than the driver frame and you are done. Most 18" pro driver that are not designed to be a dedicated subwoofer can reach 500Hz.
2. Load that BASS!
The exception to the rule of "less is more" comes at the lowest frequencies, that is below 150Hz. Remember, we are designing a DIPOLE system so we need a dipole (sub) woofer. Otherwise the radiation pattern will change from (mid) driver to (sub) driver and it will be difficult to blend them properly. At the lowest frequencies you want a LONG front-to-back pathlength to reduce dipole cancellation as much as possible. But because the frequencies are low and wavelengths are long, the problems with large baffles do not apply here like they do for high frequencies. You can even get away with folding the baffle info a U- M- or H-frame if you know how the internal resonances of these structures will influence the response. When you fold the baffle into these shapes you are forming a short transmission line, which has a 1/4 wave resonance. You can only use the 'frame BELOW about half this resonance frequency. The resonance causes a null in the response, and the response starts falling off into this null at about half this frequency below a peak that will also form. Useful depths (one side depth) of a 'frame are from 8-16 inches, which corresponds to bandwidth up to a max of about 275Hz and 125Hz respectively.
We want to make the losses for our subwoofer as low as possible, so we might as well make the 'frame as deep as possible so that where the response is rolling off into the TL resonance null is about where we want to cross over to the next (e.g. mid) driver. This determines the "depth" dimension of our 'frame.
There will still be dipole losses at the lowest frequencies. These add on top of the driver's own high pass response (around its resonance frequency). The size of the 'frame also influences this end of the subwoofer response. It turns out that the deeper you make the 'frame the more the mass of air within the frame couples to the moving mass of the driver. When you add mass to a driver, Qts goes up and Fs goes down. Any increase in Qts is useful in a dipole woofer system because by and large the driver's own Q is relatively low (e.g. 0.5 or less) with the exceptions being "high Q" OB specific drivers. With an OB even a Qts of 1.5 is not "too high", so in this case higher is always going to be better in terms of the amount of bass energy that the 'frame can generate per Watt of input power. In fact, I find that using an H-frame maximizes this effect because there is air loading on BOTH sides of the driver. Thus I suggest that you use an H-frame type system for your subwoofer.
The last piece of the puzzle for a 'frame is how WIDE to make it. The width influences the Q of the peak in the response just below where the response is falling off into the TL resonance null I mentioned above. It also has some influence on the overall efficiency of the 'frame system and the amount of airload. When the H-frame is wide, the Q will be low. This makes it relatively easy to employ simple filtering to create the crossover and accommodating the peak is not a problem. The classic example of this is Martin King's Eminence Alpha-15 subwoofer that he describes in his 2008 (?) paper comparing planar, U-, and H-frames with this woofer. He could simply use a second order low-pass filter to both flatten the response and, along with the natural rolloff into the TL null, cross over to the mid driver. He used a ratio of about 2-to-1 of WIDTH-to-DEPTH and this worked well with only slight peaking at the crossover point to the mid for the H-frame. I suggest this ratio, or even a bit more if/when possible and when the size can be accommodated in your listening space.
So, in summary, load that subwoofer with an H-frame. The crossover point to the mid should determine the depth of the frame. Note that the depth (in inches) of 8-16 inches is on EACH SIDE of the H-frame, e.g. the total depth dimension is 16-32 inches, front-to back, plus the thickness of the baffle supporting the driver. Make the width about twice the one-side depth, or a little more (more is better here), so if you use a one-side depth of 8 inches the H-frame will be 16x16 inches internal height and width. In this case you would get roughly a cube measuring around 18-20 inches (external dims) on a side (accounting for thickness of material used to construct it.
3. In Conclusion...
From the above lines of reasoning we can conclude that at least a 3-way system is required. This is comprised of an H-frame subwoofer, a large format pro driver "midrange" from 200-700Hz in a minimal baffle, and other driver(s) covering higher frequencies. A fullranger can be used, however, better would be to sue a small (e.g. 4-6") driver nude plus a dipole tweeter such as the B&G neo 3PDR crossed over around 3.5kHz or as low as the tweeter can support the output requirement. This results in a 4-way design, however, the added complexity does improve the response and the tradeoff is worth it if you are striving for the highest sound quality in your loudspeaker designs.
These design criteria are what I currently use to design my own OB/dipole systems.
1. Less is More (*except see #2)
When it comes to baffles, less is more. That is to say that you will get the best off-axis response when you use minimal or no baffle. This is one reason why SL's LX521 is shaped like it is - minimal baffle. He showed in a recent presentation why large baffles with a small driver mounted more or less centrally is bad, acoustically speaking.
Make the baffle dimensions as close to the diameter of the driver as possible for even off-axis response. You can even use no baffle at all, the "nude driver" system. It's most useful for frequencies above 800-1k Hz where even "minimal baffle" is still too much baffle.
The downside of little to no baffle is a 6dB per octave loss at lower frequencies, below the "dipole peak" (the first peak in a dipole's response). The peak is at about +6dB WRT the inifinite baffle SPL, and below this it will drop off a 6dB/oct. When the driver is small this peak can be above 1kHz - for a 4" driver this might be as high as 2.5kHz if the driver is used "nude". This causes so much loss at lower frequencies (e.g. by 200Hz) that the driver's maximum power input or driver excursion cannot sustain output relative to the SPL near the dipole peak. There is just way too much dipole cancellation! But the best way to solve this is NOT to make the baffle larger.
A better solution to this problem is to use more and different sized drivers. Each driver can then operate in a band that is closer to the dipole peak and not too far above and below it. Again, this is one reason why SL's LX521 is 4-way. When you try to construct a system from a small full-ranger and a woofer, you have to make the baffle large so that the fullranger dipole losses are not too large at low frequencies. This leads to the off-axis response issues I mentioned above, which many builders don't seem to know about or care about but if you want your system to sound good, it's important to not go overboard with a huge (planar) baffle. Thus we are back to small baffles, large dipole losses, and the need for some kind of driver to fill in the hole between the (sub) woofer and the fullranger. This "hole" is often spanning frequencies from 150Hz to 500-750Hz. A large (e.g. 15" or 18") low Xmax, high sensitivity pro driver is perfect for this application. Because of the size of the driver cone, just put it in a planar baffle not much wider than the driver frame and you are done. Most 18" pro driver that are not designed to be a dedicated subwoofer can reach 500Hz.
2. Load that BASS!
The exception to the rule of "less is more" comes at the lowest frequencies, that is below 150Hz. Remember, we are designing a DIPOLE system so we need a dipole (sub) woofer. Otherwise the radiation pattern will change from (mid) driver to (sub) driver and it will be difficult to blend them properly. At the lowest frequencies you want a LONG front-to-back pathlength to reduce dipole cancellation as much as possible. But because the frequencies are low and wavelengths are long, the problems with large baffles do not apply here like they do for high frequencies. You can even get away with folding the baffle info a U- M- or H-frame if you know how the internal resonances of these structures will influence the response. When you fold the baffle into these shapes you are forming a short transmission line, which has a 1/4 wave resonance. You can only use the 'frame BELOW about half this resonance frequency. The resonance causes a null in the response, and the response starts falling off into this null at about half this frequency below a peak that will also form. Useful depths (one side depth) of a 'frame are from 8-16 inches, which corresponds to bandwidth up to a max of about 275Hz and 125Hz respectively.
We want to make the losses for our subwoofer as low as possible, so we might as well make the 'frame as deep as possible so that where the response is rolling off into the TL resonance null is about where we want to cross over to the next (e.g. mid) driver. This determines the "depth" dimension of our 'frame.
There will still be dipole losses at the lowest frequencies. These add on top of the driver's own high pass response (around its resonance frequency). The size of the 'frame also influences this end of the subwoofer response. It turns out that the deeper you make the 'frame the more the mass of air within the frame couples to the moving mass of the driver. When you add mass to a driver, Qts goes up and Fs goes down. Any increase in Qts is useful in a dipole woofer system because by and large the driver's own Q is relatively low (e.g. 0.5 or less) with the exceptions being "high Q" OB specific drivers. With an OB even a Qts of 1.5 is not "too high", so in this case higher is always going to be better in terms of the amount of bass energy that the 'frame can generate per Watt of input power. In fact, I find that using an H-frame maximizes this effect because there is air loading on BOTH sides of the driver. Thus I suggest that you use an H-frame type system for your subwoofer.
The last piece of the puzzle for a 'frame is how WIDE to make it. The width influences the Q of the peak in the response just below where the response is falling off into the TL resonance null I mentioned above. It also has some influence on the overall efficiency of the 'frame system and the amount of airload. When the H-frame is wide, the Q will be low. This makes it relatively easy to employ simple filtering to create the crossover and accommodating the peak is not a problem. The classic example of this is Martin King's Eminence Alpha-15 subwoofer that he describes in his 2008 (?) paper comparing planar, U-, and H-frames with this woofer. He could simply use a second order low-pass filter to both flatten the response and, along with the natural rolloff into the TL null, cross over to the mid driver. He used a ratio of about 2-to-1 of WIDTH-to-DEPTH and this worked well with only slight peaking at the crossover point to the mid for the H-frame. I suggest this ratio, or even a bit more if/when possible and when the size can be accommodated in your listening space.
So, in summary, load that subwoofer with an H-frame. The crossover point to the mid should determine the depth of the frame. Note that the depth (in inches) of 8-16 inches is on EACH SIDE of the H-frame, e.g. the total depth dimension is 16-32 inches, front-to back, plus the thickness of the baffle supporting the driver. Make the width about twice the one-side depth, or a little more (more is better here), so if you use a one-side depth of 8 inches the H-frame will be 16x16 inches internal height and width. In this case you would get roughly a cube measuring around 18-20 inches (external dims) on a side (accounting for thickness of material used to construct it.
3. In Conclusion...
From the above lines of reasoning we can conclude that at least a 3-way system is required. This is comprised of an H-frame subwoofer, a large format pro driver "midrange" from 200-700Hz in a minimal baffle, and other driver(s) covering higher frequencies. A fullranger can be used, however, better would be to sue a small (e.g. 4-6") driver nude plus a dipole tweeter such as the B&G neo 3PDR crossed over around 3.5kHz or as low as the tweeter can support the output requirement. This results in a 4-way design, however, the added complexity does improve the response and the tradeoff is worth it if you are striving for the highest sound quality in your loudspeaker designs.
These design criteria are what I currently use to design my own OB/dipole systems.
Something like MiniDSP eventually yes (although, can I do 3-way with them?), TBH though, for the sake of saving outlay now, plus gaining the opportunity to play with my first cross-overs, I'll go passive to start with
Just thought - I'd need to be able to switch on/off a high pass for the woofer to choose between it naturally not making too much bass for night time listening, and it being cut off in a known place to integrate the active sub for full listening...
thanks! - I'm going to be drinking a lot of tea whilst making notes today by the look of it!
We found in our WAW that 240-250 Hz was near optimum (but the same one we use active at 240 Hz ended up with a 450 Hz passive XO) and in an OB i would consider that too low. When we used its predecessor in an MJK-style OB with the Eminence Alpha 15 we used his passive XO scheme, woofer at something like 250 Hz, midTweeter at about 450 Hz (the article is a must read) with OB artifacts filling in the hole. I’m not a big fan of the woofer, but love the FF85.
More info here: 7th Annual Vancouver Island diyFEST 2010. Hard to believe that was just over 10 years ago.
WAW = Woofer Assisted Widerange, a term we hope replaces the afore used FAST term which no one seemed to like (and which never seemed to have an aggreed upon acronym expansion).
dave
Possibly. With many OBs behind us, i have not caught the bug… in every case something just sounded wrong. I will have one more try, i have an OB plan hatched, 8 10” OB woofers ready…
dave
Looks like bass is hard work relative to the top end - is it worth the effort to stay OB below the 85's crossover point, or should I just go for a standard mid/bass is a reflex port stand mount box?
If your design breif was to go OB down to 80hz fairly flat, would you them be able to go smaller than the 15" type things, or is that still 'low'?
If your design breif was to go OB down to 80hz fairly flat, would you them be able to go smaller than the 15" type things, or is that still 'low'?
I just want Linn Kan range really - as i mentioned, I listen a lot at night, and at that point a speaker that suggests bass, but rolls it all off in reality, is useful. If I can then select it to actually have a known roll-off when I want to turn my sub/s on, then I can have it both ways as it were.
" In Conclusion...
From the above lines of reasoning we can conclude that at least a 3-way system is required. This is comprised of an H-frame subwoofer, a large format pro driver "midrange" from 200-700Hz in a minimal baffle, and other driver(s) covering higher frequencies. A fullranger can be used, however, better would be to sue a small (e.g. 4-6") driver nude plus a dipole tweeter such as the B&G neo 3PDR crossed over around 3.5kHz or as low as the tweeter can support the output requirement. This results in a 4-way design, however, the added complexity does improve the response and the tradeoff is worth it if you are striving for the highest sound quality in your loudspeaker designs"
Ok, very very useful post (thanks Charlie!)...if I wanted to push that 'midrange' driver about 100-120hz lower, could an open backed box (as I understand it you describe this as a 'U' frame) make this happen, whilst still going with keeping the baffle down to the minimal width you're looking for re off axis performance?
From the above lines of reasoning we can conclude that at least a 3-way system is required. This is comprised of an H-frame subwoofer, a large format pro driver "midrange" from 200-700Hz in a minimal baffle, and other driver(s) covering higher frequencies. A fullranger can be used, however, better would be to sue a small (e.g. 4-6") driver nude plus a dipole tweeter such as the B&G neo 3PDR crossed over around 3.5kHz or as low as the tweeter can support the output requirement. This results in a 4-way design, however, the added complexity does improve the response and the tradeoff is worth it if you are striving for the highest sound quality in your loudspeaker designs"
Ok, very very useful post (thanks Charlie!)...if I wanted to push that 'midrange' driver about 100-120hz lower, could an open backed box (as I understand it you describe this as a 'U' frame) make this happen, whilst still going with keeping the baffle down to the minimal width you're looking for re off axis performance?
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