For your enjoyment, here is another open baffle woofer I recently threw together. I say 'another', because this design evolved out my use of a popular OB woofer, MJK's Alpha 15a in an H-frame. See here for the background on MJK's design: http://www.diyaudio.com/forums/showthread.php?t=118282&highlight=alpha+15a
My issues with the Alpha 15 were pretty simple: using a 15" driver in a 17" by 17" by 17" enclosure, its too big to pass as 'elegant'. Also, although it rolls off at about 30Hz, it's nonlinear distortion (NLD) below 45-50Hz is relatively high. Related, some people have concerns about the drivers Xmax being reached easily at lower frequencies. This may be a realistic worry considering how high the NLD is below 45Hz. IMO, NLD is overrated - in the bass region, psychoacoustic masking limits our dynamic range to about 40dB, up to at least the 5th harmonic (see Floyd Toole's latest book, and references therein). Also, just as important, any actual musical instrument (as opposed to synthesized tones), has harmonics that are barely lower in level than the fundamental - and subsequently are much louder than the NLD harmonics produced by the driver itself. If in doubt, put an instrument in front of a fft. There are two reasons I'm concerned with NLD here - first, it shows that the driver is reaching its volume displacement limit, and hence SPL limit. Second, IMD creates a 'dynamic noise floor', which may or may not be an issue, depending on the recording. I'm also just a sucker for 'cleanliness', so lowering NLD is nice if it is easy.
I might add that I have never found issue with how the Alphas sound, even at loud volumes.
So here are a few pictures of the design - nothing revolutionary, just simple and useful, and I hadn't seen something like this around here yet.
My issues with the Alpha 15 were pretty simple: using a 15" driver in a 17" by 17" by 17" enclosure, its too big to pass as 'elegant'. Also, although it rolls off at about 30Hz, it's nonlinear distortion (NLD) below 45-50Hz is relatively high. Related, some people have concerns about the drivers Xmax being reached easily at lower frequencies. This may be a realistic worry considering how high the NLD is below 45Hz. IMO, NLD is overrated - in the bass region, psychoacoustic masking limits our dynamic range to about 40dB, up to at least the 5th harmonic (see Floyd Toole's latest book, and references therein). Also, just as important, any actual musical instrument (as opposed to synthesized tones), has harmonics that are barely lower in level than the fundamental - and subsequently are much louder than the NLD harmonics produced by the driver itself. If in doubt, put an instrument in front of a fft. There are two reasons I'm concerned with NLD here - first, it shows that the driver is reaching its volume displacement limit, and hence SPL limit. Second, IMD creates a 'dynamic noise floor', which may or may not be an issue, depending on the recording. I'm also just a sucker for 'cleanliness', so lowering NLD is nice if it is easy.
I might add that I have never found issue with how the Alphas sound, even at loud volumes.
So here are a few pictures of the design - nothing revolutionary, just simple and useful, and I hadn't seen something like this around here yet.
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Above, you can see MJK's H-frame next to my recent 'pet'. I don't know if it deserves a name, so lets just call it GWx4 for now - the drivers are four Goldwood GW-210 10" drivers, available from PE for $18 each. The Alpha driver is $60, while the Goldwoods are $72 (per side). So we are talking $12 more (but there's more to that). The drivers are high Qts types, so need little EQ in their lower end.
The footprint of the GWx4 is about 13" by 11", and stands about 23" tall. I more or less fixed how big I wanted the enclosure to be, and then worked with it. A larger enclosure would make the whole thing more sensitive, but one of the primary goals of this design was to not be 'big'. As you can see, the enclosure is somewhere between an H-frame, and an OB with wings. Using one set of drivers behind a front set is something I've only seen in an Emerald Physics design, and of course only works in the bass range. Of course, there is no free lunch - above 400Hz, one sees interference patterns, depending on where the mic is. But 400Hz is high enough.
So lets talk goals:
1) Smaller size - particularly footprint
2) Greater SPL output
3) Bandwidth of 45Hz to 200Hz
4) High Sensitivity
5) Low Cost
to be continued after lunch...
The footprint of the GWx4 is about 13" by 11", and stands about 23" tall. I more or less fixed how big I wanted the enclosure to be, and then worked with it. A larger enclosure would make the whole thing more sensitive, but one of the primary goals of this design was to not be 'big'. As you can see, the enclosure is somewhere between an H-frame, and an OB with wings. Using one set of drivers behind a front set is something I've only seen in an Emerald Physics design, and of course only works in the bass range. Of course, there is no free lunch - above 400Hz, one sees interference patterns, depending on where the mic is. But 400Hz is high enough.
So lets talk goals:
1) Smaller size - particularly footprint
2) Greater SPL output
3) Bandwidth of 45Hz to 200Hz
4) High Sensitivity
5) Low Cost
to be continued after lunch...
cuibono,
I don't get the complete picture from your pictures. Are both volumes behind the driver baffles open to the outside? Since you've already got a central cavity, why don't you go full circle - ending with a W-frame? If the pictures tell the full truth, I see a vast mismatch between the impedance on either side of the cone. Wouldn't that be a severe source of NLD?
I don't get the complete picture from your pictures. Are both volumes behind the driver baffles open to the outside? Since you've already got a central cavity, why don't you go full circle - ending with a W-frame? If the pictures tell the full truth, I see a vast mismatch between the impedance on either side of the cone. Wouldn't that be a severe source of NLD?
Interesting cuibono. It looks like a 'compound woofer' as described by SL. According to him, it won't play any louder than 2 drivers in an H-frame the same size but the cavity resonance should be higher. Seems like it works if it plays well up to 400.
http://www.linkwitzlab.com/models.htm#B1
http://www.linkwitzlab.com/models.htm#B1
Goals:
1) Small size: 13" by 11" versus 17" by 16" footprint. I adjusted the final dimensions to be able to use 12" wide pine board, and a height of 23" is a good base for the mid/tweeter.
2) SPL output: the 4 10" drivers have 60% greater surface area (Sd) than the Alpha, which means less linear movement (and NLD) for a given SPL. The volume product (Sd times Xmax) is 483cm cubed for the GWx4, and 325cm cubed for the Alpha. So greater total dBSPL, by about 2dB, with less distortion. Also having the drivers facing different directions reduces some orders of NLD harmonics, a good thing. Power handling is also increased, which is important - less VC heating, less NLD, less chance of melting something. Another possibility for more output is using the GW-212, a 12" driver with probably the same motor as the GW-210, but that would increase the footprint of the speaker more than I'd like. Later, I'll show the drivers NLD measurements.
3) Bandwidth of 45-200Hz: I set the lower limit to avoid having to use larger or more expensive drivers. 45Hz is also good place to have subs take over, which is something I'll add sooner or later. In my current OB design, I found the woofer was much more capable of handling the 100-200Hz region compared to the mid driver - which was dealing with needing a lot of EQ (aka, low sensitivity due to OB roll off), and a lot of room interference. The woofer had neither of these problems, so I've been crossing them at about 180Hz. I'm still not sure if this skews the soundstage downwards, but seems okay for now. Anyway, the multiple drivers don't develop interference patterns till above 400Hz, which is plenty of bandwidth. In the future, I'll use a different setup where the woofers will be crossed at about 115Hz, so everyone will be happy. Adding chokes to a couple of the woofer is an option to prevent midrange cancellations, particularly with mid's crossed high.
Something to note is that SL's Orions use a pair of 10" drivers, but they are way more expensive, have way more Xmax, and are used down to 20Hz. Cutting off OB woofers at 45Hz makes things a lot easier to do, including dealing with room modes.
4) High Sensitivity - 'high sensitivity' designs have a couple of benefits - the most obvious is less thermal heating through the voice coil. Another is the purported improvement in musical 'transients'. This is still a grey area to me, particularly as it applies to either the bass, mids or treble, and the inability to subjectively quantify music's 'transient' character. But I'll give it a go, considering the reputation horns have as being 'dynamic'.
Particularly for OB use, woofers are usually less sensitive than mids or tweeters. The main way to get around this is by using multiple drivers, but size matters too. As it turns out, the GWx4 and MJK H frame end up being just about the same sensitivity (within .5dB, depending how you measure it), although there is a major caveat to this - the GW woofers are 8ohm, and I'm using them in parallel - but I'm not trying to drive a 2ohm load - I'm using 2 amps, each driving 4ohm loads. This makes a bit of a difference to the cost and actual sensitivity. I decided to do this because amps are cheap these days, and GC or Class D amps would be a good match to these. 50W per channel should give plenty of head room.
So, remembering I'm using one amp with the Alphas, and two with the GWx4, they are both approximately 87.5dBSPL/2.83V/1m sensitive at 50Hz, measured 33" above the floor, outdoors. (Moving closer to the floor greatly inflates the SPL; I recently made the mistake of using that number in another thread...) They are about doing 90.5dBSPL at 100Hz, under the same conditions (and with no LP filtering). I was actually hoping the design would be closer to mid-90's, as it looked that way simulated, but didn't work out that way in real life.
So far, that has been the only disappointment in this design. But that's okay, 90dB at 100Hz on OB is better than a lot designs are doing.
5) Low Cost: the GWx4 drivers are $12 more than the Alpha, but then add about $50 for another channel of amplification. For me, the improvement in size, output and distortion character are worth it. Amps are cheap. Particularly relative to other high-output OB designs, I think this design qualifies as a budget/low cost/high value design. Actually, I haven't listened to the design yet, and I don't expect it to sound particularly different to the Alpha 15a - but I do know it is more aesthetic and more capable, which makes me happy.
ACTUAL DATA COMING UP NEXT
1) Small size: 13" by 11" versus 17" by 16" footprint. I adjusted the final dimensions to be able to use 12" wide pine board, and a height of 23" is a good base for the mid/tweeter.
2) SPL output: the 4 10" drivers have 60% greater surface area (Sd) than the Alpha, which means less linear movement (and NLD) for a given SPL. The volume product (Sd times Xmax) is 483cm cubed for the GWx4, and 325cm cubed for the Alpha. So greater total dBSPL, by about 2dB, with less distortion. Also having the drivers facing different directions reduces some orders of NLD harmonics, a good thing. Power handling is also increased, which is important - less VC heating, less NLD, less chance of melting something. Another possibility for more output is using the GW-212, a 12" driver with probably the same motor as the GW-210, but that would increase the footprint of the speaker more than I'd like. Later, I'll show the drivers NLD measurements.
3) Bandwidth of 45-200Hz: I set the lower limit to avoid having to use larger or more expensive drivers. 45Hz is also good place to have subs take over, which is something I'll add sooner or later. In my current OB design, I found the woofer was much more capable of handling the 100-200Hz region compared to the mid driver - which was dealing with needing a lot of EQ (aka, low sensitivity due to OB roll off), and a lot of room interference. The woofer had neither of these problems, so I've been crossing them at about 180Hz. I'm still not sure if this skews the soundstage downwards, but seems okay for now. Anyway, the multiple drivers don't develop interference patterns till above 400Hz, which is plenty of bandwidth. In the future, I'll use a different setup where the woofers will be crossed at about 115Hz, so everyone will be happy. Adding chokes to a couple of the woofer is an option to prevent midrange cancellations, particularly with mid's crossed high.
Something to note is that SL's Orions use a pair of 10" drivers, but they are way more expensive, have way more Xmax, and are used down to 20Hz. Cutting off OB woofers at 45Hz makes things a lot easier to do, including dealing with room modes.
4) High Sensitivity - 'high sensitivity' designs have a couple of benefits - the most obvious is less thermal heating through the voice coil. Another is the purported improvement in musical 'transients'. This is still a grey area to me, particularly as it applies to either the bass, mids or treble, and the inability to subjectively quantify music's 'transient' character. But I'll give it a go, considering the reputation horns have as being 'dynamic'.
Particularly for OB use, woofers are usually less sensitive than mids or tweeters. The main way to get around this is by using multiple drivers, but size matters too. As it turns out, the GWx4 and MJK H frame end up being just about the same sensitivity (within .5dB, depending how you measure it), although there is a major caveat to this - the GW woofers are 8ohm, and I'm using them in parallel - but I'm not trying to drive a 2ohm load - I'm using 2 amps, each driving 4ohm loads. This makes a bit of a difference to the cost and actual sensitivity. I decided to do this because amps are cheap these days, and GC or Class D amps would be a good match to these. 50W per channel should give plenty of head room.
So, remembering I'm using one amp with the Alphas, and two with the GWx4, they are both approximately 87.5dBSPL/2.83V/1m sensitive at 50Hz, measured 33" above the floor, outdoors. (Moving closer to the floor greatly inflates the SPL; I recently made the mistake of using that number in another thread...) They are about doing 90.5dBSPL at 100Hz, under the same conditions (and with no LP filtering). I was actually hoping the design would be closer to mid-90's, as it looked that way simulated, but didn't work out that way in real life.
So far, that has been the only disappointment in this design. But that's okay, 90dB at 100Hz on OB is better than a lot designs are doing.
5) Low Cost: the GWx4 drivers are $12 more than the Alpha, but then add about $50 for another channel of amplification. For me, the improvement in size, output and distortion character are worth it. Amps are cheap. Particularly relative to other high-output OB designs, I think this design qualifies as a budget/low cost/high value design. Actually, I haven't listened to the design yet, and I don't expect it to sound particularly different to the Alpha 15a - but I do know it is more aesthetic and more capable, which makes me happy.
ACTUAL DATA COMING UP NEXT
I've actually done several days of measuring, but I'm fairly tired of looking at all the data, so I'm only going to post the most concise.
First is an overlay of the FR of each woofer design, measured under the same conditions: 2.83V at the drivers terminals (but remember there are two amps driving the GWx4), mic at a distance of 2m, .84m off the ground (which would approximate the listeners ears), all done outdoors with long MLS signals.
As you can see, between 45 and 100Hz, the are doing just about the same thing. Remember, at a distance of 2m and outdoors, there are some environmental effects on the data - so lets call these close approximations. 1m data had more similar results.
Green is the MJK H frame with the Alpha 15a, Brown is the GWx4. Note the nasty FR above 400Hz... Also, the GWx4 has less of a peak at 200Hz - the GWx4 baffles are less than 4" deep, as opposed to 7.5" for the Alpha 15.
First is an overlay of the FR of each woofer design, measured under the same conditions: 2.83V at the drivers terminals (but remember there are two amps driving the GWx4), mic at a distance of 2m, .84m off the ground (which would approximate the listeners ears), all done outdoors with long MLS signals.
As you can see, between 45 and 100Hz, the are doing just about the same thing. Remember, at a distance of 2m and outdoors, there are some environmental effects on the data - so lets call these close approximations. 1m data had more similar results.
Green is the MJK H frame with the Alpha 15a, Brown is the GWx4. Note the nasty FR above 400Hz... Also, the GWx4 has less of a peak at 200Hz - the GWx4 baffles are less than 4" deep, as opposed to 7.5" for the Alpha 15.
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Here is the nonlinear distortion data, done using sweeps. These two graphs were measured the same way, but differently than above. The driving signal was 6dB higher, at 5.66Vrms at the terminals, and measured at the opening of the H-frames indoors. I would have rather measured at a greater distance, outdoors, but there is way too much noise and environmental effects. Indoors, I barely had enough noise free dynamic range.
5.66V represents about 93.5dB at 50Hz and 96.5dB at 100Hz at 1m, so decently loud, but not insane.
The first graph is the Alpha 15a, the second is the GWx4. What you can see, in both of them, is they really loose control of things between 40 and 50Hz. The GWx4 maintains control lower. The other thing I see is that at 50Hz, the GWx4 tall order NLD is 20dB lower than the Alpha. This makes me happy. At -75dB, 4th and 5th order distortion is 'clean' and I'd postulate inaudible, and indicates that the woofers have plenty of headroom till distortion becomes an issue. I need to redo the simulations, but when considering both sets of speakers, I would guess the GWx4 should be able to hit 108dBSPL in the mid bass without problems - which is a lot of output, and comparable to some of the more high end designs. Just not below 50Hz unfiltered. Again, due to masking, instruments natural harmonic content and recording lack of dynamic range, I wouldn't worry about NLD till its around -45dB compared to the fundamental.
Oh - my computer makes these annoying glitches during the sweeps that cause spikes in the graphs below - so ignore the tall sharp spikes.
5.66V represents about 93.5dB at 50Hz and 96.5dB at 100Hz at 1m, so decently loud, but not insane.
The first graph is the Alpha 15a, the second is the GWx4. What you can see, in both of them, is they really loose control of things between 40 and 50Hz. The GWx4 maintains control lower. The other thing I see is that at 50Hz, the GWx4 tall order NLD is 20dB lower than the Alpha. This makes me happy. At -75dB, 4th and 5th order distortion is 'clean' and I'd postulate inaudible, and indicates that the woofers have plenty of headroom till distortion becomes an issue. I need to redo the simulations, but when considering both sets of speakers, I would guess the GWx4 should be able to hit 108dBSPL in the mid bass without problems - which is a lot of output, and comparable to some of the more high end designs. Just not below 50Hz unfiltered. Again, due to masking, instruments natural harmonic content and recording lack of dynamic range, I wouldn't worry about NLD till its around -45dB compared to the fundamental.
Oh - my computer makes these annoying glitches during the sweeps that cause spikes in the graphs below - so ignore the tall sharp spikes.
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Hi all, thanks for the questions.
Yes, the thing is all open. As I was working this design up, I tried using the drivers in the H-frame 'isobarically', ie, connected face to face in the middle of the baffle, and wired out of phase. This didn't work, in fact it worked a bit worse! I'm not sure what an W frame is, but I was considering doing a ripole - but decided not to because of the increased build complexity. I don't know enough to guess what the degree of impedance mismatch is, but the NLD looks decent to me. Let me know what you think. I haven't tried it, but I'd guess sealing the middle of the enclose would be unhelpful, similar to using them isobarically.
I think an important part of the design is that the woofers are all open to the air on each side. When I disconnect the back drivers, the output falls by about 4.5dB between 25 and 200Hz (it should drop 6dB, which indicates there is some inefficiency in the design, but 1.5dB isn't a big deal to me.) See above about 'isobaric' use. One of the questions in my mind is how does distance between the front and back drivers effect output. But the current setup works decently, so I probably won't look into it more - I like the current size.
Yes, the thing is all open. As I was working this design up, I tried using the drivers in the H-frame 'isobarically', ie, connected face to face in the middle of the baffle, and wired out of phase. This didn't work, in fact it worked a bit worse! I'm not sure what an W frame is, but I was considering doing a ripole - but decided not to because of the increased build complexity. I don't know enough to guess what the degree of impedance mismatch is, but the NLD looks decent to me. Let me know what you think. I haven't tried it, but I'd guess sealing the middle of the enclose would be unhelpful, similar to using them isobarically.
I think an important part of the design is that the woofers are all open to the air on each side. When I disconnect the back drivers, the output falls by about 4.5dB between 25 and 200Hz (it should drop 6dB, which indicates there is some inefficiency in the design, but 1.5dB isn't a big deal to me.) See above about 'isobaric' use. One of the questions in my mind is how does distance between the front and back drivers effect output. But the current setup works decently, so I probably won't look into it more - I like the current size.
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Cuibono,
That is a very interesting design. Goldwood offers quite a few drivers with Qts values that are ideal for OB. The prices are also very attractive. You are definitely thinking outside of the box.
If I understood you correctly, you measured higher NLD using the Alpha 15A compared to the Goldwood drivers but at these low frequencies you did not think it was audible. Is that correct? How loud are you playing these driver so that they are approaching Xmax?
Neat design,
That is a very interesting design. Goldwood offers quite a few drivers with Qts values that are ideal for OB. The prices are also very attractive. You are definitely thinking outside of the box.
If I understood you correctly, you measured higher NLD using the Alpha 15A compared to the Goldwood drivers but at these low frequencies you did not think it was audible. Is that correct? How loud are you playing these driver so that they are approaching Xmax?
Neat design,
Very intriguing. I'm always interested in "small but more SPL" dipoles (and cheap).
How does your 4x woofer work, and what is the function of the opening on the side? Any pics right from the side to show how the woofers are aligned?
Is this a smaller version of CS1's 4xalpha setup?
Very interesting.
How does your 4x woofer work, and what is the function of the opening on the side? Any pics right from the side to show how the woofers are aligned?
Is this a smaller version of CS1's 4xalpha setup?
Very interesting.
Thanks CLS and MJK for the comments!
MJK - At 30Hz, I could hear beating of the sine wave with the Alpha - and I think it shows in the NLD. I'm can't recall hearing it with the GWx4, but there was clearly large cone movement. Voltage was 5.66Vrms. Unfortunately, I can't measure displacement (although I could try it with a wedge micrometer), and I'm not sure I am driving them to Xmax - but considering the high NLD below 40Hz for both woofers, I consider them at their limit. But, like you've pointed out before, music isn't pure sine waves, and likely the limit for max spl is somewhere higher with music. In the past, I used to impress my room mates by playing very loud rock music - like really really loud, probably close to live levels - but at these levels, especially with rock, I just couldn't hear distortion - I don't know how to explain it really, but I assume my ears were probably being heavily distorted, preventing me from being able to judge stuff like that. All I can say is that they impressed all my rocker room-mates - and they didn't sound bass shy.
There has been some interesting research lately that has given rise to my opinion that below 45Hz, sealed subs work the same as OB - so the obvious choice for this area would be a couple of subs.
MJK - At 30Hz, I could hear beating of the sine wave with the Alpha - and I think it shows in the NLD. I'm can't recall hearing it with the GWx4, but there was clearly large cone movement. Voltage was 5.66Vrms. Unfortunately, I can't measure displacement (although I could try it with a wedge micrometer), and I'm not sure I am driving them to Xmax - but considering the high NLD below 40Hz for both woofers, I consider them at their limit. But, like you've pointed out before, music isn't pure sine waves, and likely the limit for max spl is somewhere higher with music. In the past, I used to impress my room mates by playing very loud rock music - like really really loud, probably close to live levels - but at these levels, especially with rock, I just couldn't hear distortion - I don't know how to explain it really, but I assume my ears were probably being heavily distorted, preventing me from being able to judge stuff like that. All I can say is that they impressed all my rocker room-mates - and they didn't sound bass shy.
There has been some interesting research lately that has given rise to my opinion that below 45Hz, sealed subs work the same as OB - so the obvious choice for this area would be a couple of subs.
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Magic! No, actually... Yes, the inspiration for the second back set of drivers was from seeing the CS1. The (kind of obvious) idea of using multiple amp I got from SL. I had recently been trying to do room treatments and find ways to diffuse/reflect/absorb things below 200Hz, and ultimately found nothing affected sound that low - so I had a good idea that having one baffle in front of another would not be a problem. I also initially tried mounting the woofers face to face (isobarically), but that didn't work at all. Keeping the midsection open is essential (it looks like). Essentially, the front baffle is transparent up to about 200-400Hz (except for about a 1.5dB loss). There is no special alignment of the woofers - they are basically two H-frames one in front of the other, just missing the inner wings. I'll take some more pictures when the sun returns to this part of the earth
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That was why I was a little curious. I have run my Goldwood 18" H frame system and before that my Alpha 15A OB system at very loud listening levels (even the Telarc 1812 CD) without seeing much deflection. So if you are seeing distortion at volume levels approaching Xmax, I started wondering how loud the system was playing. My listening is all acoustic music so electronic music and HT might place different demands on a speaker then my favorite jazz CDs.
You have an interesting concept that definitely warrants a little MathCad work to see what is possible.
I'm going to build my OB system soon. But I'm wondering how loud you need to play to need 4 woofers. I'm currently not unsatisfied with my full range driver in a folded voight pipe. Granted, I don't play very loud, it still gives me enough clean bass to be happy. Of course, it is by no means thundering, loud, scary. I've heard that. But wouldn't one of those big 15" thingies be enough for a home environment?
Also, what trade-offs do you have to make when you go to something like 4 woofers? More power, more amps maybe (you mention that). Does that not add to the quality (or lack thereof) of the sound?
I'm intrigued by your design and can only thank your and many others' efforts here for helping us understand better how these things work (not to mention saving us time and money).
Also, what trade-offs do you have to make when you go to something like 4 woofers? More power, more amps maybe (you mention that). Does that not add to the quality (or lack thereof) of the sound?
I'm intrigued by your design and can only thank your and many others' efforts here for helping us understand better how these things work (not to mention saving us time and money).
Hi ra, thanks for your comments! Sharing is a big part of all this.
Either of these designs can play loudly, although that is opinion ultimately. It depends on what kind of stuff you're listening to and how loudly. They will definitely play a good bit more loudly than a single full range driver.
I guess the only compromise I feel with the GWx4 is having to use a extra amp per side. More drivers usually means more complicated frequency response, crossover and enclosure build, but the above design doesn't really have these - in fact, building the baffles was pretty simple.
Either of these designs can play loudly, although that is opinion ultimately. It depends on what kind of stuff you're listening to and how loudly. They will definitely play a good bit more loudly than a single full range driver.
I guess the only compromise I feel with the GWx4 is having to use a extra amp per side. More drivers usually means more complicated frequency response, crossover and enclosure build, but the above design doesn't really have these - in fact, building the baffles was pretty simple.
Dammit, somebody always beats me to it!
I bought a pair of the GW-210/8 a few years ago and messed around with a W frame with mixed but acceptable results. For a long time I figured that this arrangement was probably the best for low-end extension with these drivers, short of a very wide standard OB, and lost interest, finding it kinda a novelty.
I revisited these drivers armed with a little more knowledge, an inspiration from the ultra-exclusive "Whisper" (or the newer Helix http://legacyaudio.com/index.php?option=com_content&task=view&id=65&Itemid=195), and 8 of the 4 ohm versions. The results are surprising in the amount of output and extension (within reasonable expectations), and un-surprising insofar that the claims of the Whisper's arrangement and it's effect on bass are probably true. The sound is quite good and the low cost makes it very attractive for me to look deeper into this configuration.
I'm not the first to the plate, but I'll never be armed with hard numbers, either...
I bought a pair of the GW-210/8 a few years ago and messed around with a W frame with mixed but acceptable results. For a long time I figured that this arrangement was probably the best for low-end extension with these drivers, short of a very wide standard OB, and lost interest, finding it kinda a novelty.
I revisited these drivers armed with a little more knowledge, an inspiration from the ultra-exclusive "Whisper" (or the newer Helix http://legacyaudio.com/index.php?option=com_content&task=view&id=65&Itemid=195), and 8 of the 4 ohm versions. The results are surprising in the amount of output and extension (within reasonable expectations), and un-surprising insofar that the claims of the Whisper's arrangement and it's effect on bass are probably true. The sound is quite good and the low cost makes it very attractive for me to look deeper into this configuration.
I'm not the first to the plate, but I'll never be armed with hard numbers, either...
From the pics what I see is 3 drivers facing in one direction and one driver facing in the other. Now unless the drivers are wired to compensate for this I am not sure how this works.
Maybe the angle the pictures are taken does not provide a complete view.
Any idea on what specs should the drivers be for this application? How does this system compare in Max SPL and F3 to a system using the same driver in a sealed/ported box? I would assume that a single driver in a sealed box would produce as much Max SPL as this combination of 4 right? What we are gaining is better quality of bass.
Also is the radiation pattern similar to that of an H frame? Can such a woofer be placed in the middle of a room or in a corner?
So many quyestions!
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