Very often the major problem with cheap drivers in OB, is that they make to much mechanical noise, when they move a lot. If you go for 8 woofers, you will already pay an amount, where you can get decent 15" and half decent 18" woofers.
Right now I have 8 pcs 10" OEM VIfa woofers. They do a good job, but make mechanical noise when pushed to the limits. My new project is with very good 15" woofers (Gladen RS15 FA). And they have no noise, no matter how much the cone moves.
Right now I have 8 pcs 10" OEM VIfa woofers. They do a good job, but make mechanical noise when pushed to the limits. My new project is with very good 15" woofers (Gladen RS15 FA). And they have no noise, no matter how much the cone moves.
FYI: I just got a flyer from Parts Express. Their PA465 18" "subwoofer" is on sale for $155. This would be a pretty good driver for use in an open baffle (or my favorite, the H-frame). It doesn't have any fancy construction or motor, but should fit the bill nicely.
Dayton Audio PA465S-8 18" Pro Subwoofer 4" VC 8 Ohm
Product Specifications:
Nominal Diameter: 18"
Power Handling (RMS): 1,000 Watts
Impedance: 8 ohms
Sensitivity: 93.9 dB 2.83V/1m
Voice Coil Diameter: 4"
Thiele-Small Parameters:
Resonant Frequency (Fs): 32.3 Hz
DC Resistance (Re): 5.4 ohms
Voice Coil Inductance (Le): 4.98 mH
Mechanical Q (Qms): 6.92
Electromagnetic Q (Qes): 0.62
Total Q (Qts):0.57
Compliance Equivalent Volume (Vas): 6.81 ft.³
Mechanical Compliance of Suspension (Cms): 0.09 mm/N
BL Product (BL): 21.9 Tm
Diaphragm Mass Inc. Airload (Mms): 271g
Maximum Linear Excursion (Xmax): 10 mm
Surface Area of Cone (Sd): 1,225 cm²
Dayton Audio PA465S-8 18" Pro Subwoofer 4" VC 8 Ohm
Product Specifications:
Nominal Diameter: 18"
Power Handling (RMS): 1,000 Watts
Impedance: 8 ohms
Sensitivity: 93.9 dB 2.83V/1m
Voice Coil Diameter: 4"
Thiele-Small Parameters:
Resonant Frequency (Fs): 32.3 Hz
DC Resistance (Re): 5.4 ohms
Voice Coil Inductance (Le): 4.98 mH
Mechanical Q (Qms): 6.92
Electromagnetic Q (Qes): 0.62
Total Q (Qts):0.57
Compliance Equivalent Volume (Vas): 6.81 ft.³
Mechanical Compliance of Suspension (Cms): 0.09 mm/N
BL Product (BL): 21.9 Tm
Diaphragm Mass Inc. Airload (Mms): 271g
Maximum Linear Excursion (Xmax): 10 mm
Surface Area of Cone (Sd): 1,225 cm²
sismik11 raised this question in Post #60
"These speakers have very small magnets. Normally I consider this a problem, but many seem to apply that this is not the case when dealing with open baffle speaker design. Can anyone explain why this is so?"
A smaller magnet structure is an advantage for a woofer operated as a dipole. You will typically find that woofers with more powerful neodymium magnets have a significantly smaller (and lighter) magnet structure. Also reduced basket webbing improves air flow from the rear of the driver. Hence, the emitted sound from the forward and rear directions of the woofer is more symmetrical thus better emulates a true dipole.
"These speakers have very small magnets. Normally I consider this a problem, but many seem to apply that this is not the case when dealing with open baffle speaker design. Can anyone explain why this is so?"
A smaller magnet structure is an advantage for a woofer operated as a dipole. You will typically find that woofers with more powerful neodymium magnets have a significantly smaller (and lighter) magnet structure. Also reduced basket webbing improves air flow from the rear of the driver. Hence, the emitted sound from the forward and rear directions of the woofer is more symmetrical thus better emulates a true dipole.
Mr Griffin had explained in the previous post from yours.
It's the difference of monopole and dipole. And velocity vs pressure.
Talking about SPL and how it is related to cone movement.
So the pressure is related to velocity and resistance of air, or better, impedance Z. p=Z * v
As you have a "low coupling" from membrane to fluid (air ) in OB since the wavelenghts involved are much bigger than the phisical elements.
The solution is to send more voltage to the speaker and this results in higher excursion. But for a double lenght in excursion the price rises a lot, I see.
Four of us went to visit Jim at his house during the following month of July (I believe, since it's been over 4 years ago), and were treated with the greatest of hospitably from Jim and his wife.
After finishing a fabulous lunch, we auditioned 5 or 6 different systems. I liked the line source arrays he had downstairs, and the triple (almost) full range ribbons he had upstairs, the best.
In return, I have invited Jim to come listen to my system, which utilizes the much maligned mono-pole bass system, but at this point he refuses to communicate with me, entirely. Strange, to say the least.
Scott L,
I'm not ignoring you but I have been busy today so I did not have a chance to reply.
Of course I would love to hear your system. We can work out a plan for a listening session.
You will have to visit me again to hear my later (2015 version) version of an open backed system. I'm working on a Constant Beamwidth Transducer line array/system which should be finished this winter. The CBT system will have a monopole bass setup that you will like but it will not rival your infinite baffle bass setup.
Jim
I'm not ignoring you but I have been busy today so I did not have a chance to reply.
Of course I would love to hear your system. We can work out a plan for a listening session.
You will have to visit me again to hear my later (2015 version) version of an open backed system. I'm working on a Constant Beamwidth Transducer line array/system which should be finished this winter. The CBT system will have a monopole bass setup that you will like but it will not rival your infinite baffle bass setup.
Jim
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The 88 db sens. rating on this driver, is actually a bit mis-leading. It refers to the average mid-band sensitivity which should not be substituted for a sensitivity rating for bass, which appears to be 80 db +/- 1 db, from 30Hz up to 280Hz. Sensitivity and relative system efficiency are often confused for one another. They are related, but certainly NOT the same thing. Ultimately, system efficiency depends upon the type/and/size of the enclosure. For an open-baffle (di-pole) bass attempt, some aspect of the design must be substituted for the lack of the enclosure. The exact conditions for the response sweep are not given, such that we can only assume it was done on an IEC baffle, and reveals the effect of the high Qts, as witnessed by the rise in response near it's low end, relative to what is typically shown for normal-Q-range drivers. This, along with a few other revealing specification indicators, does confirm you suspicion that this driver is a prime candidate for a di-pole bass configuration. Yes, probably best realized using multiple drivers, on a baffle at least as large as an IEC (65x53 inches). Also, if a woofer has to chuff and puff to produce bass, it's not being used in an ideal situation. Having stated that, I have no idea if the driver's construction techniques would be prone to producing mechanical noise, but again, if your woofers are flopping around in extreme fashion, then you have the wrong design.
About a year ago, I was invited to listen to the Linkwitz LX-521 speaker system. As far as it's bass production, all was fine as long as it was not asked to do something it simply could not do, and that was to play back Bella Fleck's flight of the Cosmic Hippo. I don't think they are made for that type of music, but more for small scale acoustics.
I would have thought cone surface area (sd) was more important than the available Xmax of a driver in low frequency reproduction of an OB design. Xmax is so easily used up in OB design without it effectively contributing anything to the output.
Personally, I use 8 Peerless SLS 10 inch drivers (830688) in series/parallel with 4 in each branch. Each branch equates to a nominal impedance of 32 ohms and when in parallel with the other branch produces a load impedance to the amplifier of 16 ohms. This is a large OB subwoofer for my home theatre which is all OB in design. The reason for the high load impedance (16 ohms) is that it improves the dynamic range of the subwoofer at low frequencies so that it is not easily overloaded by big thumps that sometimes occur in movies like 'Jurassic Park' etc. It may be less efficient than using it as a 4 ohm arrangement but hey it saves those driver cones from pumping wildly. The amplifier has plently of power even with a 16 ohm load so there is no problem with volume.
C.M
Personally, I use 8 Peerless SLS 10 inch drivers (830688) in series/parallel with 4 in each branch. Each branch equates to a nominal impedance of 32 ohms and when in parallel with the other branch produces a load impedance to the amplifier of 16 ohms. This is a large OB subwoofer for my home theatre which is all OB in design. The reason for the high load impedance (16 ohms) is that it improves the dynamic range of the subwoofer at low frequencies so that it is not easily overloaded by big thumps that sometimes occur in movies like 'Jurassic Park' etc. It may be less efficient than using it as a 4 ohm arrangement but hey it saves those driver cones from pumping wildly. The amplifier has plently of power even with a 16 ohm load so there is no problem with volume.
C.M
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This is also what I have found in practice, and, importantly, keeps the distortion to a minimum. OB bass has very low distortion so increasing Xmax should be something to be avoided. Size of baffle is equally important, folded is no problem if crossed low enough to avoid resonances
I must say that your continuing efforts are quite impressive ! I spoke to James yesterday, and he was surprised/shocked/saddened that it had been over 4 years since our last visit with each other. Grainger also said he remembered you from back when you were in the previous home. The guys here in Knoxville LOVE audio, and we certainly do welcome your visit to our area ! p.s. I am working on a 34 cubic foot push-pull, slot loaded bass array, to add into my system.
Hey Scott and Jim,
Love what you guys do.... Keeping the DIY speaker journey alive and fun and sharing ideas and systems over lunch (& beer!) ... Great day out in my book!
All the very best
Derek.
Hi Derek, so nice to hear from you ! Thanks for chiming in ! The region we live in has a high density of audiophiles, and DIY'ers. Perhaps the highest density in all of the nation. I try to keep up the interest by having "audio gatherings" at my place. It's centrally located to most off the gang, and since it's a bachelor's pad, I don't need to ask permission to have the guys over. Sure, beer and food sometimes, but we almost always have coffee ! Some of the guys call it the "audio laboratory", but in truth I just have one large/devoted audio room, and a small living room system. I just wish I had more space ! ( I came back in an edited this, just to announce that the female folks are also more than welcome, and they actually do show up from time-to-time)
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Small magnets imply high Qts, which is handy for OB bass!
Regarding suitable drivers, I can recommend these as being very decent :
SKYTRONIC 12" PP CONE RUBBER EDGE SPEAKER 150Wrms, 300 WATTS MAX | eBay
Also available here:
Qtx, Loudspeaker 12" 30 Cm - 902.222
And you'll find the Thiele-Small data for the 902.222 (and others) here:
http://www.avsl.com/assets/downloads/thielesmall_902127.pdf
Qts is a tad low (see the big magnet?) at 0.49, but all other important parameters are good, and they work well in practice.
It's a great pity: they used to make the 902.184, a 15 inch version. Sadly, no longer in production, though I think you'd agree that the specification was pretty impressive for OB applications...
Regarding suitable drivers, I can recommend these as being very decent :
SKYTRONIC 12" PP CONE RUBBER EDGE SPEAKER 150Wrms, 300 WATTS MAX | eBay
Also available here:
Qtx, Loudspeaker 12" 30 Cm - 902.222
And you'll find the Thiele-Small data for the 902.222 (and others) here:
http://www.avsl.com/assets/downloads/thielesmall_902127.pdf
Qts is a tad low (see the big magnet?) at 0.49, but all other important parameters are good, and they work well in practice.
It's a great pity: they used to make the 902.184, a 15 inch version. Sadly, no longer in production, though I think you'd agree that the specification was pretty impressive for OB applications...
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