johninCR said:
I sorta followed the thread on Hawthorne about these, but the pics really put the size into perspective...
dave
planet10 said:
I think I'm on to something different with both what I'm doing with the UBaffle to eliminate the need for rear wave damping to avoid the 1/4 wave resonances and using the Helmholtz slot to load the expanding pathway. No one has shown much interest though, and I don't know enough about what is actually happening to try to optimize it.
The B200 with only 2mm of excursion and the too uptilted response isn't the ideal driver, but if Dan would build me a coax 10 or 12 with a Qts of .7, an Fs of 35hz, using an XBL2 motor, then I know I could build an OB cab similar in size to those I have for the B200 and get real 30hz extension without corners.
Dan,
http://www.quarter-wave.com/OB_Wings_Out.jpg
These OB speakers are approximately 100 dB efficient and start to roll-off at about 50 Hz. I applied 3 dB boost (worked with no boost but I like it better now, fuller sound) to the woofers and crossed over the the Lowthers at 200 Hz. Loud, great dynamics, very small cone motions. You just need four high efficiency 15" woofers to compensate for the rolling off of the OB, a high efficiency Lowther, and a good sized baffle. When not in use the wings fold back to make the whole thing smaller, but still not small by most definitions. Without the wings, or with the wings folded back, the bass does not go quite as deep but is still acceptable.
I am not sure if this is chasing my tail, but it was easy to build and not to difficult to simulate and design. Only down side is I needed to buy four reasonably priced high efficiency woofers. By having four lower Qts woofers to boost efficiency, I think that the bass is tighter then if I had used a higher Qts driver typical of OB applications.
http://www.quarter-wave.com/OB_Wings_Out.jpg
These OB speakers are approximately 100 dB efficient and start to roll-off at about 50 Hz. I applied 3 dB boost (worked with no boost but I like it better now, fuller sound) to the woofers and crossed over the the Lowthers at 200 Hz. Loud, great dynamics, very small cone motions. You just need four high efficiency 15" woofers to compensate for the rolling off of the OB, a high efficiency Lowther, and a good sized baffle. When not in use the wings fold back to make the whole thing smaller, but still not small by most definitions. Without the wings, or with the wings folded back, the bass does not go quite as deep but is still acceptable.
I am not sure if this is chasing my tail, but it was easy to build and not to difficult to simulate and design. Only down side is I needed to buy four reasonably priced high efficiency woofers. By having four lower Qts woofers to boost efficiency, I think that the bass is tighter then if I had used a higher Qts driver typical of OB applications.
johninCR said:
johninCR,
Would you mind elaborating on the two way with the 108? No crossover on the 108? I've tried several different two-way configurations with the 108, none of which worked to my ears without at least a capacitor on the 108. The 108 simply lacks the excursion to be run fullrange except horn loaded where the horn can control the excursion. I even had trouble getting the 108 to perform well on open baffle with a crossover due to overexcursion. I've now found a happy home for it in a small sealed enclosure crossed over to a pro-sound 12" woofer.
Curious as to what you've found with this driver.
thanks
Joe
Does anyone here have a 1m FR graph @ 1watt (or 2.83v) input for their OB speaker systems so we can confirm where these average sensitivity estimates are coming from?
Dan, can you post the same for the 100db 20mm xmax driver you mentioned without revealing the source?
Hate to put anyone through too much trouble, but I'm very curious about all this. Plus I have a fascination with graphs 🙂 .
BTW, Dan I agree with what you have said, but if you read these forums, you are saying the exact opposite of what many want to hear or believe. The ones who swear that high Q , high sensitivity (at 1k of course 😉 ) woofers are the absolute best for OB. You know, so that some 1.5 watt wunderamp can be used. Or at least just a single cherished stereo amp.
Active amplification/eq of just the (dipole) bass frequencies would be considered heresy or just sheer madness. Even when MCM is selling plate amps for 50 bucks.
Cheers,
AJ
p.s. Martin, I don't doubt your claims, it's just that those things look like my refrigerator with both doors open😀
Dan, can you post the same for the 100db 20mm xmax driver you mentioned without revealing the source?
Hate to put anyone through too much trouble, but I'm very curious about all this. Plus I have a fascination with graphs 🙂 .
BTW, Dan I agree with what you have said, but if you read these forums, you are saying the exact opposite of what many want to hear or believe. The ones who swear that high Q , high sensitivity (at 1k of course 😉 ) woofers are the absolute best for OB. You know, so that some 1.5 watt wunderamp can be used. Or at least just a single cherished stereo amp.
Active amplification/eq of just the (dipole) bass frequencies would be considered heresy or just sheer madness. Even when MCM is selling plate amps for 50 bucks.
Cheers,
AJ
p.s. Martin, I don't doubt your claims, it's just that those things look like my refrigerator with both doors open😀
Martin,
It's great to see one of you math guys "chasing tails" with the rest of us OBers and trying to be as minimalist as possible. My advice would be to forget trying to stay pure dipole, since a real figure 8 isn't possible in a typical room setup and cardoid can work to your advantage.
Joseph,
I don't have an excursion problem unless I go loud (more than a few watts) and for loud I cut the 108 and switch to the Iris tweet, so I have 2 speakers in one with the flip of a switch. If I could find a cap that I couldn't readily hear to protect my 108's, I'd be more than happy to use it. You're drivers must be different than mine, because none of them are happy couped up inside any box. 🙂
AJ,
I used to like graphs too, until my ears became well enough trained to realize that I could hear lots of stuff that a graph couldn't tell me. Throw a tone generator and spl meter into to ear training, since our ears don't have a flat sensitivity. After that all you need is some known constants for your control reference and a tone sweep is all you need to understand the frequency response. I can freehand a graph for you, if you still want it.
It's great to see one of you math guys "chasing tails" with the rest of us OBers and trying to be as minimalist as possible. My advice would be to forget trying to stay pure dipole, since a real figure 8 isn't possible in a typical room setup and cardoid can work to your advantage.
Joseph,
I don't have an excursion problem unless I go loud (more than a few watts) and for loud I cut the 108 and switch to the Iris tweet, so I have 2 speakers in one with the flip of a switch. If I could find a cap that I couldn't readily hear to protect my 108's, I'd be more than happy to use it. You're drivers must be different than mine, because none of them are happy couped up inside any box. 🙂
AJ,
I used to like graphs too, until my ears became well enough trained to realize that I could hear lots of stuff that a graph couldn't tell me. Throw a tone generator and spl meter into to ear training, since our ears don't have a flat sensitivity. After that all you need is some known constants for your control reference and a tone sweep is all you need to understand the frequency response. I can freehand a graph for you, if you still want it.
I really don't think we're saying anything in disagreement; in fact, the presented examples of lower F3, high efficiency dipole designs confirms my statements. The effective panel widths are huge - 50" or more. The original OB poster was looking for 12" to 24" wide flat panels. I think all would agree you're not going to get extension into the sub 200 Hz range with high efficiency and a simple 24" wide flat board!
Get the baffle width to 60", and you'll start rolling off in the bass around 200 Hz; you'll be ~6 dB down around 80 Hz, low enough that many people would feel fine not using a subwoofer. Use several drivers and you can get the efficiency up; however, I thought the idea was a full range, single driver? I've been adressing the issue from that viewpoint - what we can do with a single wideband driver.
If you want to make the baffle just 24" wide, though, you're not going to get strong output down to the 150 Hz and lower range. John's solution of a U-Baffle is good, but it will take careful consideration to avoid pipe resonances. And if you do have a pipe resonance, you'll need a thicker cone to avoid reflections coming through, meaning more mass...
A good theoretical treatise on open baffles/dipoles is available at Seigfried Linkwitz's site, http://www.linkwitzlab.com . He's got a lot of good information about dipoles there...
About driver efficiency; assuming a really strong motor with a gap flux level of ~1.3T, and no saturation issues in the pole or backplate, an 8" driver would need to have a total moving mass around 13 grams to get an efficiency of 100 Hz.
Setting the Fs to 80 Hz means we need a compliance around 0.25mm/N; the resulting Qes will be 0.189, for a Qts of right around 0.18.
What about a high Q design? Well, we'll go with a really weak motor, and a really light moving mass, and a really soft suspension. Here's what we "want" as a goal, for example:
Fs: 60 Hz
Qts: 0.71
Vas: 155L
Re: 6 Ohms
SPL: 98 dB @1W, 1m
To achieve this, we'd need to following:
Cms: 2 mm/N (about as soft as you can get)
BL: 3.1 N/A (really weak!)
Mms: 3.4g (not possible; the voice coil will weigh in at 25% more than that on its own)
Basically, we can't get there...
For a 4" driver, we may be able to the efficiency up to the 88-89 dB range, and still have an Fs in the 70 Hz range. But not any higher. Just not enough cone area to get the efficiency really cranked up.
Dan Wiggins
Adire Audio®
Get the baffle width to 60", and you'll start rolling off in the bass around 200 Hz; you'll be ~6 dB down around 80 Hz, low enough that many people would feel fine not using a subwoofer. Use several drivers and you can get the efficiency up; however, I thought the idea was a full range, single driver? I've been adressing the issue from that viewpoint - what we can do with a single wideband driver.
If you want to make the baffle just 24" wide, though, you're not going to get strong output down to the 150 Hz and lower range. John's solution of a U-Baffle is good, but it will take careful consideration to avoid pipe resonances. And if you do have a pipe resonance, you'll need a thicker cone to avoid reflections coming through, meaning more mass...
A good theoretical treatise on open baffles/dipoles is available at Seigfried Linkwitz's site, http://www.linkwitzlab.com . He's got a lot of good information about dipoles there...
About driver efficiency; assuming a really strong motor with a gap flux level of ~1.3T, and no saturation issues in the pole or backplate, an 8" driver would need to have a total moving mass around 13 grams to get an efficiency of 100 Hz.
Setting the Fs to 80 Hz means we need a compliance around 0.25mm/N; the resulting Qes will be 0.189, for a Qts of right around 0.18.
What about a high Q design? Well, we'll go with a really weak motor, and a really light moving mass, and a really soft suspension. Here's what we "want" as a goal, for example:
Fs: 60 Hz
Qts: 0.71
Vas: 155L
Re: 6 Ohms
SPL: 98 dB @1W, 1m
To achieve this, we'd need to following:
Cms: 2 mm/N (about as soft as you can get)
BL: 3.1 N/A (really weak!)
Mms: 3.4g (not possible; the voice coil will weigh in at 25% more than that on its own)
Basically, we can't get there...
For a 4" driver, we may be able to the efficiency up to the 88-89 dB range, and still have an Fs in the 70 Hz range. But not any higher. Just not enough cone area to get the efficiency really cranked up.
Dan Wiggins
Adire Audio®
I too am interested in open baffle possibilities. There are a number of interesting ideas here. There are also a number of interesting threads on O.B.'s. But, we've got a driver designer here asking us what we want in a driver. How often does that happen? Dan knows his physics and loudspeaker design. If he says something won't work, he's likely right. How about a discussion re: his four questions for us?
To recap my perspective, I'd like a driver similar to the current 8" with more excursion (40L sealed enclosure, not bigger, -3db at 80hz, I like the 94.5 db efficiency, but it could be lower in the name of excursion and suit me fine). I also want an 8" or a 6" that works in more moderately sized TL variations (than the current driver does.) Finally, something for a BassZilla or FAST (or MJK's if I could afford the woofers) type open baffle might be neat too, but lets not argue the enclosure merits.
To recap my perspective, I'd like a driver similar to the current 8" with more excursion (40L sealed enclosure, not bigger, -3db at 80hz, I like the 94.5 db efficiency, but it could be lower in the name of excursion and suit me fine). I also want an 8" or a 6" that works in more moderately sized TL variations (than the current driver does.) Finally, something for a BassZilla or FAST (or MJK's if I could afford the woofers) type open baffle might be neat too, but lets not argue the enclosure merits.
johninCR said:
No probably not different drivers, just different tastes and priorities. The 108 did sound quite nice on open baffle, but fell apart with anything more than background music SPLs. Since these are the only speakers I owned I didn't want to limit my listening to background music levels. A compromise, but not one that I regret. I'm working on getting an active system together to remove all of the passive components between the amp and driver, but for now I'm fairly happy with what I have.
Joe
Dan,
What the OB crowd really needs is a quality coax (most just won't admit it), because you've shown us that a full ranger isn't possible if we want the efficiency. Whizzers just don't cut it. Some type of different mechanical XO would be ideal, but since that's probably not possible, stay minimalist on the XO for transparency. Forget max flat because that just isn't going to happen with OB anyway.
I think the Hawthorne driver is a great first step in the right direction for OB, but 15's just aren't room friendly for most. I can probably pull rabbits out of the hat and make a 10" work and still get to 30hz. With a 12" I know I could, and if you give me decent excursion I can make it go loud too.
I understand that OB is still somewhat on the fringes and what I'm doing is out on the fringe of the fringes, but as people are exposed to good OB setups, they won't want to give it up despite the lack of driver selection. Give people a single drive unit sound, the open naturalness of OB, and real bass, then it will gain favor rapidly.
I have been using the Audax PR170M0
FS 117 Hz
Qts .5
Sensitivity 100dB, its more like 96dB
In a sealed enclosure F3 is about 160 Hz
This is a nice sounding driver. Though not full range by any means. A similiar driver with extended high frequency out past 10 KHz with at least a smooth roll off and an F3 that could reach down to 100 Hz would be on my wish list. This would make X-over to a tweeter, if needed, easily accomplished.
My preference for the bottom end is to use a bass driver. Most full rangers that can go to the 40Hz range can't be played loud enough if called upon, unless you backload them like the Klein horns Nelson Pass built. Wish I had that kind of room. By reaching to 100 Hz you have more options. You could integrate with a subwoofer or a bass driver. The benefit of using a bass driver is freeing up the midrange of the fullranger from the modulation that takes place trying to produce bass frequencies.
I like fullrangers because it makes crossovers easier to implement. Similiar to the Basszilla approach. I know that this defeats the purpose of having a single driver, but this is how I would implement any full or single range driver.
BDP
PS- I posted some measurement of the PR170M0 on an open baffle a while back. Do a search for PR170M0
FS 117 Hz
Qts .5
Sensitivity 100dB, its more like 96dB
In a sealed enclosure F3 is about 160 Hz
This is a nice sounding driver. Though not full range by any means. A similiar driver with extended high frequency out past 10 KHz with at least a smooth roll off and an F3 that could reach down to 100 Hz would be on my wish list. This would make X-over to a tweeter, if needed, easily accomplished.
My preference for the bottom end is to use a bass driver. Most full rangers that can go to the 40Hz range can't be played loud enough if called upon, unless you backload them like the Klein horns Nelson Pass built. Wish I had that kind of room. By reaching to 100 Hz you have more options. You could integrate with a subwoofer or a bass driver. The benefit of using a bass driver is freeing up the midrange of the fullranger from the modulation that takes place trying to produce bass frequencies.
I like fullrangers because it makes crossovers easier to implement. Similiar to the Basszilla approach. I know that this defeats the purpose of having a single driver, but this is how I would implement any full or single range driver.
BDP
PS- I posted some measurement of the PR170M0 on an open baffle a while back. Do a search for PR170M0
Hi John,
I was simply interested in how you arrrived at your 96db sensitivity average. That would be rather high for an open baffle (single)woofer system. It's not that I don't trust your ears (or that of the majority of DIYers, who seem to use this very method for design),
it's just that whereas I can't hear your system, I could certainly look at a graph to see how you arrived at your avg. sensitivity estimate.
I'm sure you've seen dipole and cardioid FR before, I just wonder how closely your trained hearing based FR graph would match that of a microphone derived graph of an in room scenario
when compared. It would be interesting to see.
Dan, would you agree that the 6" diameter cone of an 8" driver would need a tweeter (preferably coaxial)? Or are there methods outside of physics to avoid cone breakup/beaming treble issues?
cheers,
AJ
I was simply interested in how you arrrived at your 96db sensitivity average. That would be rather high for an open baffle (single)woofer system. It's not that I don't trust your ears (or that of the majority of DIYers, who seem to use this very method for design),
it's just that whereas I can't hear your system, I could certainly look at a graph to see how you arrived at your avg. sensitivity estimate.
I'm sure you've seen dipole and cardioid FR before, I just wonder how closely your trained hearing based FR graph would match that of a microphone derived graph of an in room scenario
An externally hosted image should be here but it was not working when we last tested it.
when compared. It would be interesting to see.
Dan, would you agree that the 6" diameter cone of an 8" driver would need a tweeter (preferably coaxial)? Or are there methods outside of physics to avoid cone breakup/beaming treble issues?
cheers,
AJ
My SPL values are calculated using my MathCad worksheets. No measurements yet, but I would expect them to show the same result.
AJ,
I'm just going by the manufacturers sensitivity which is based on their IB response. The straight Iris's actually are a couple of dbs more sensitive than B200 cabs because I have to use a lot of rear wave attenuation to flatten them out. The 108's are 91db and the B200's are significantly more sensitive and the Iris's are perceptively more sensitive than the B200's.
You're right that the comparison would be interesting, but I listen to too wide a variety of music to be satisfied with the rolled off bass that many OB guys are satisfied with. I'm not building to sell, so all I need is loud enough with my flea power amp, of course, I'd love 100db or better, but I'm realistic.
Keep in mind that I'm being conservative because going OB is definitely a gain in overall output, which I just reverified with a comparison of my 108's in OB to the Fostex horn I'm just finishing. BTW, in terms of SQ of the first couple of watts, it's simply no contest. The open natural sound wins hands down. I still need to see how much the horns handle power better, but I think my little journey into RLH's is a dead end, unless someone tells me what's wrong with the Fostex 108 horn. I never heard a good horn before, so I needed to satisfy my curiosity.
It also helped confirm that my Helmholtz loaded thing isn't just creating some bloated resonance, because the bass is much cleaner than what is coming out of the Fostex cab. I'm not quite getting the purity of straight dipole, but I think that's because I'm ending up with some percentage of monopole output down very low (bringing more reflections into play and my prototypes needed more bracing.
I'm just going by the manufacturers sensitivity which is based on their IB response. The straight Iris's actually are a couple of dbs more sensitive than B200 cabs because I have to use a lot of rear wave attenuation to flatten them out. The 108's are 91db and the B200's are significantly more sensitive and the Iris's are perceptively more sensitive than the B200's.
You're right that the comparison would be interesting, but I listen to too wide a variety of music to be satisfied with the rolled off bass that many OB guys are satisfied with. I'm not building to sell, so all I need is loud enough with my flea power amp, of course, I'd love 100db or better, but I'm realistic.
Keep in mind that I'm being conservative because going OB is definitely a gain in overall output, which I just reverified with a comparison of my 108's in OB to the Fostex horn I'm just finishing. BTW, in terms of SQ of the first couple of watts, it's simply no contest. The open natural sound wins hands down. I still need to see how much the horns handle power better, but I think my little journey into RLH's is a dead end, unless someone tells me what's wrong with the Fostex 108 horn. I never heard a good horn before, so I needed to satisfy my curiosity.
It also helped confirm that my Helmholtz loaded thing isn't just creating some bloated resonance, because the bass is much cleaner than what is coming out of the Fostex cab. I'm not quite getting the purity of straight dipole, but I think that's because I'm ending up with some percentage of monopole output down very low (bringing more reflections into play and my prototypes needed more bracing.
Thanks both.
The way I see it is, the more options to go OB, the better. HE drivers being one of those options. That was my suggestion the last time someone on DIY querried about what DIYer's would want in a driver.
I have a gut feeling we will start to see more drivers designed/built specifically for OB use, although the vast majority of people will still feel the irresistible urge to listen to boxes.
cheers,
AJ
The way I see it is, the more options to go OB, the better. HE drivers being one of those options. That was my suggestion the last time someone on DIY querried about what DIYer's would want in a driver.
I have a gut feeling we will start to see more drivers designed/built specifically for OB use, although the vast majority of people will still feel the irresistible urge to listen to boxes.
cheers,
AJ
AJinFLA said:
Only those who are inconsiderate or don't know any better. Even bass heads would love the sweet spot of my compact W+U baffle OB bass aumenters that have 4 12's per side. Plenty of bass in the "cone of non-silence" without disturbing parents or neighbors. Plus bass without most of the reflections is so much more clean and natural that I could never go back.
A coaxial solution would be great, if the tweeter could keep up with the wideband mid. Low and low-Q Fs, high excursion capabilities would be the order of the day. The driver could then be used in a tall sealed floorstander of 3-4 ft^3, which is about visual critical mass in many households. So a mid-Qts (.5?) wideband, 6.5" with 95dB and *possibly* a coaxially mounted tweeter, would pretty much be the driver for everyone I think. Oh and some of that XBL^2 good stuff, that motor rocks.
A wideband coaxial 6.5 with a hemp cone, good SPL, a tweet that can hang, mid-Q, XBL^2 motorwerks, upon reflection, kinda sounds like the ultimate driver, and ultimate compromise. I believe something like that might actually set some kind of new benchmark.
The TONE of the 8" V 1 cone is extraordinary, monstrous, almost addictive, to me at least, and a 6.5 would be so much the better. Lose the whiz, better still. The whiz just cannot hang with the quality of what is coming forth from the cone, another league completely, though they are working on a hemp whiz, the sonic quality of the hemp cone is such that ANY whiz is just out of place.
Again thanks to DW for listening, and for genuine interest and curiosity, the pulse of this madness, in the first place.
The TONE of the 8" V 1 cone is extraordinary, monstrous, almost addictive, to me at least, and a 6.5 would be so much the better. Lose the whiz, better still. The whiz just cannot hang with the quality of what is coming forth from the cone, another league completely, though they are working on a hemp whiz, the sonic quality of the hemp cone is such that ANY whiz is just out of place.
Again thanks to DW for listening, and for genuine interest and curiosity, the pulse of this madness, in the first place.
I'm with Dmason, let the woofer do what it does best (maybe better than any other w/xbl2?). I'm surprised that none of the major companies have come up with a Braxial design ala car audio. With a consumer shift towards "smaller is better", comounting the tweeter to save space and possibily making a more coherent presentation, would be more developed I'm thinking.
Dan,
I thought you were an OB minimalist convert. It's the OB market that needs a premium driver. There are plenty of quality wide band drivers for boxes and almost nothing available for OB. People rave about the B200 on OB and it's almost a joke, because that sloped response only sounds good on a very limited amount of music. I jumped through a lot of hoops to mechanically flatten the response of the B200 and it's still quite forward in the mids. As it stands right now, there is no reasonable sized drive unit that can go full range on OB. I don't want to knock the Hawthorne driver, but the lower resolution, compression tweet, and pro-type XO prevent it from being a high end driver.
Most will say full range is not possible, but I've already done it with a coax 15" and I know I could do it with a 12" and I think I can get there with even an 8" or 10" if I get at least 6-8mm of Xmax.
I believe in this so much that I'll help fund the R&D with a firm commitment to buy 3-5 or more pairs of a custom run. We just need the help of an expert like Dan to achieve a high end result. A goup deal could work to everyone's benefit cost wise. If I have to go it alone I will, but then it turns into a commercial venture and prices go up.
I thought you were an OB minimalist convert. It's the OB market that needs a premium driver. There are plenty of quality wide band drivers for boxes and almost nothing available for OB. People rave about the B200 on OB and it's almost a joke, because that sloped response only sounds good on a very limited amount of music. I jumped through a lot of hoops to mechanically flatten the response of the B200 and it's still quite forward in the mids. As it stands right now, there is no reasonable sized drive unit that can go full range on OB. I don't want to knock the Hawthorne driver, but the lower resolution, compression tweet, and pro-type XO prevent it from being a high end driver.
Most will say full range is not possible, but I've already done it with a coax 15" and I know I could do it with a 12" and I think I can get there with even an 8" or 10" if I get at least 6-8mm of Xmax.
I believe in this so much that I'll help fund the R&D with a firm commitment to buy 3-5 or more pairs of a custom run. We just need the help of an expert like Dan to achieve a high end result. A goup deal could work to everyone's benefit cost wise. If I have to go it alone I will, but then it turns into a commercial venture and prices go up.
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