Given adequate motor strength, there is no difference in transient reproduction between a single larger unit compared to multiple smaller units that equal the Sd (effective cone area).
Small drivers can have adequate cone stiffness and control with lighter weight cones and magnets, but it takes about four 6" cones to equal the cone area of a single 12" speaker.
I'd've thought that being able to wire series-parallel means more flexibility on impedances than a single driver.
However, taking Sd to be equal for 4x6.5" drivers and 1x10" driver, each of the 4 6.5" drivers will have to move as far as the 10" driver to give equal output.
For a decent 10" subwoofer, 1" p/p of travel is reasonable enough to do. But even for the most specialised 6.5" driver, this is a lot of excursion, and distortion will have increased considerably.
The excursion to driver size ratios mean the 10" driver ought to win in this respect.
Chris
However, taking Sd to be equal for 4x6.5" drivers and 1x10" driver, each of the 4 6.5" drivers will have to move as far as the 10" driver to give equal output.
For a decent 10" subwoofer, 1" p/p of travel is reasonable enough to do. But even for the most specialised 6.5" driver, this is a lot of excursion, and distortion will have increased considerably.
The excursion to driver size ratios mean the 10" driver ought to win in this respect.
Chris
Good point Chris,
It all depends on the frequencies you're using with your woofers. If it's below 500Hz, all is well--if you are trying to cross to a tweeter at 3KHz, I'd go for four 6.5's and use two of them with an inductor for baffle step correction.
If it is for below 200Hz, I'd go with larger woofers personally--either two 8's, one 10" or whatever you can handle as far as size goes.
It all depends on the frequencies you're using with your woofers. If it's below 500Hz, all is well--if you are trying to cross to a tweeter at 3KHz, I'd go for four 6.5's and use two of them with an inductor for baffle step correction.
If it is for below 200Hz, I'd go with larger woofers personally--either two 8's, one 10" or whatever you can handle as far as size goes.
Impedance with work, yes, but you'll lose out on the sensitivity boost.
You really shouldn't be using 4 x 6.5 for the sake of deep extension. The goal of such an alignment would IMO be to get lots of dynamic range in the midbass. You'll still want some real woofers (12" + 20mm xmax) to handle the deep bass with aplomb.
FWIW, I too want to do a speaker with four 6.5" woofers. What I want to attempt is something similar to this, using some nice woofers IE Exodus Anarchy and some Dayton RS28s.
It depends on what you are coupling them too, room size is another. The single ten will have better low end , the 4 , 6.5's, better attack.
Choose your poison ...
B&W has an excellent white paper on the 800 Nautilas speaker which covers the selection of one 15" paper cone woofer over multiple smaller Al cone woofers. B&W engineers may believe that one 15" woofer has the best bass, but their later production 800 series Nautilus with two 10" woofers is a much more popular product.
Personally, I have been using two 8-ohm, 15" woofers wired in parallel for a 4-ohm load with ~100 db/watt SPL before baffle step compensation. This allows me to build a 94-95 db/watt 25-25Khz speaker. To my ears, something special happens with high'ish effciency speakers ... details... transients ... subtle vocal harmonics ...
"The New 15 inch Bass Unit
The rationale of using a single large pulp-coned driver for the bass of the Nautilus™801 was not immediately apparent. Early attempts at producing prodigious bass from domestically acceptable enclosures, utilized multiple drivers in slim Matrix™ cabinets. The use of light alloy cones was also propounded at this stage; on paper they seemed to be the superior choice for a bass driver, working well within its piston region as on the Nautilus™. While the measured results looked very promising, subjective assessment failed to excite; the speed and timing of multiples were always inferior to a single driver of equivalent area, but aluminum cones larger than 8” sounded distinctly metallic and muddled when mounted in Matrix™ cabinets. Parallel work on subwoofers involved the evaluation of various bass drivers for possible future use, the majority of these were pulp coned.
Drivers with light, rigid piston cones regularly won the listening tests for “slam” and timing but would often provide insufficient subjective depth because they were too light. Drivers with the best low frequency performance would often have a denser, more heavily doped pulp cone that was actually no stiffer than it’s lighter counterparts.
In collaboration with our cone /surround suppliers, we developed a low density kapok cone pulp with a very high stiffness /mass ratio. It has a large proportion of Kevlar® and stiffening resin, and the required mass is obtained through slow deposition rather than high compression. This means that while the resulting cones have a fairly poor surface finish and take a long time to cure, their internal structure is an open network of long, undeformed fibers. This composition is enhanced by a surface impregnation of hard thermosetting resin, meaning that the overall structure is effectively a thick laminate, with a very high resistance to the static bending stresses caused by cabinet pressure over the whole cone, and the local variations of radiation impedance that can encourage the formation of audible bell modes and localized flexure."
Personally, I have been using two 8-ohm, 15" woofers wired in parallel for a 4-ohm load with ~100 db/watt SPL before baffle step compensation. This allows me to build a 94-95 db/watt 25-25Khz speaker. To my ears, something special happens with high'ish effciency speakers ... details... transients ... subtle vocal harmonics ...
"The New 15 inch Bass Unit
The rationale of using a single large pulp-coned driver for the bass of the Nautilus™801 was not immediately apparent. Early attempts at producing prodigious bass from domestically acceptable enclosures, utilized multiple drivers in slim Matrix™ cabinets. The use of light alloy cones was also propounded at this stage; on paper they seemed to be the superior choice for a bass driver, working well within its piston region as on the Nautilus™. While the measured results looked very promising, subjective assessment failed to excite; the speed and timing of multiples were always inferior to a single driver of equivalent area, but aluminum cones larger than 8” sounded distinctly metallic and muddled when mounted in Matrix™ cabinets. Parallel work on subwoofers involved the evaluation of various bass drivers for possible future use, the majority of these were pulp coned.
Drivers with light, rigid piston cones regularly won the listening tests for “slam” and timing but would often provide insufficient subjective depth because they were too light. Drivers with the best low frequency performance would often have a denser, more heavily doped pulp cone that was actually no stiffer than it’s lighter counterparts.
In collaboration with our cone /surround suppliers, we developed a low density kapok cone pulp with a very high stiffness /mass ratio. It has a large proportion of Kevlar® and stiffening resin, and the required mass is obtained through slow deposition rather than high compression. This means that while the resulting cones have a fairly poor surface finish and take a long time to cure, their internal structure is an open network of long, undeformed fibers. This composition is enhanced by a surface impregnation of hard thermosetting resin, meaning that the overall structure is effectively a thick laminate, with a very high resistance to the static bending stresses caused by cabinet pressure over the whole cone, and the local variations of radiation impedance that can encourage the formation of audible bell modes and localized flexure."
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6" is mostly what you would call a midwoofer
to the best of knowledge you need to double the amount of drivers, fore every step down in size
15" = 2x12"
12" = 2x10"
10" = 2x8"
8" = 2x6"
try calculating 'backwards' to see how many 6" you need
my number is 16 drivers
whatever it is, theres still more to it than just the size
btw, I like my 12" woofers in closed box
but then, I never play very loud
woofers are not visibly moving
but still, I can feel the bass in my feet
to the best of knowledge you need to double the amount of drivers, fore every step down in size
15" = 2x12"
12" = 2x10"
10" = 2x8"
8" = 2x6"
try calculating 'backwards' to see how many 6" you need
my number is 16 driverswhatever it is, theres still more to it than just the size
btw, I like my 12" woofers in closed box
but then, I never play very loud
woofers are not visibly moving
but still, I can feel the bass in my feet
one problem with this could be that you may know what you want, but doesnt know exactly what it takes to get there
and members who knows how to do it, may not know exactly what it is you imagine
another problem could be that once you get what you have imagined, you may actually not like it at all
the reason fore me saying this is that you cannot 'isolate' a certain sound' aspect, without compromising other areas
and you may not like those 'compromises', or didnt expect them
its a bit like when they say, know your 'enemy'
and members who knows how to do it, may not know exactly what it is you imagine
another problem could be that once you get what you have imagined, you may actually not like it at all
the reason fore me saying this is that you cannot 'isolate' a certain sound' aspect, without compromising other areas
and you may not like those 'compromises', or didnt expect them
its a bit like when they say, know your 'enemy'
One can do a whole lot of generalization, selection of real drivers could well change things.
In general a 10" will go lower giving deeper bass, 6s will extend higher and likely be easier to integrate with what comes above.
Personally i like to use pairs in push-push so as to get active vibration cancelation, and reduce the load going into the box.
Push-pull also uses 2 opposed woofers, but is harder to mechanically. It does indeed reduce 2nd order distortion but at the expense of 3rd order (but only if you are using "cheap" woofers out of their linear range. If the balance is tipped such that 3rd is larger than 2nd then it likely willsound worse.
dave
In general a 10" will go lower giving deeper bass, 6s will extend higher and likely be easier to integrate with what comes above.
Personally i like to use pairs in push-push so as to get active vibration cancelation, and reduce the load going into the box.
Push-pull also uses 2 opposed woofers, but is harder to mechanically. It does indeed reduce 2nd order distortion but at the expense of 3rd order (but only if you are using "cheap" woofers out of their linear range. If the balance is tipped such that 3rd is larger than 2nd then it likely willsound worse.
dave
4x6.5" woofers will have over 500cm^2 of Sd in most cases.
1x10" woofer will have around or under ~350cm^2 of Sd.
I don't think they can be compared very fairly.
A single 12" woofer is a much better comparison, as they tend to have ~500cm^2 Sd.
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If the question really is 1x10" vs 4x6.5", Assuming typical average characteristics, I would lean towards the 4x6.5" for reasons of efficiency. However; If we go with the fair comparison of a 12" driver. I would lean towards the 12" unless I needed higher frequency reproduction from it.
1x10" woofer will have around or under ~350cm^2 of Sd.
I don't think they can be compared very fairly.
A single 12" woofer is a much better comparison, as they tend to have ~500cm^2 Sd.
------------------
If the question really is 1x10" vs 4x6.5", Assuming typical average characteristics, I would lean towards the 4x6.5" for reasons of efficiency. However; If we go with the fair comparison of a 12" driver. I would lean towards the 12" unless I needed higher frequency reproduction from it.
In the old days (80's) 6.5 inch drivers, for all their attributes, lacked voice coil overhang, or x-max. So even with decent, though often optimistic, fs, the little guys just couldn't get down there with a good 10 inch. It's about volume displaced. Not quantum physics. It doesn't take 16 though.
I had a 6 X 6.5" open backed cabinet back in a 2 X 3 pattern in the 90's that performed incredibly well.
They sounded very clean and went very low.
I had once lost one driver rendering its adjacent driver non operational and I didn't even notice it for the longest time.
I was using the 6.5" poly's from Radio shack and I think that they were made by pioneer.
They were very under rated power wise.
I used them fullrange on my Bass guitar rig,But when I played music through them they were loud an clean with a good 300 watt power amp on them.
Although they would start to lobe above 2Khz to 3Khz but this is expected for this type of configuration.
I had a pair of 1" dome tweeters to solve that issue but I never installed them.
Later that box got stolen and I still miss it today.
I have this same story documented elsewere ,But I thought I would give you my honest opinion on this.
They went very low and were very punchy and held their own very well on outside gigs as well.
I used to run them on a Ampeg V4-B tube bass amp and a Radio Shack 18" for the sub running off of a Sunn Concert slave amp for the lows.
Many of my Professional Bass player friends really liked that setup more so than their own at times.
jer
They sounded very clean and went very low.
I had once lost one driver rendering its adjacent driver non operational and I didn't even notice it for the longest time.
I was using the 6.5" poly's from Radio shack and I think that they were made by pioneer.
They were very under rated power wise.
I used them fullrange on my Bass guitar rig,But when I played music through them they were loud an clean with a good 300 watt power amp on them.
Although they would start to lobe above 2Khz to 3Khz but this is expected for this type of configuration.
I had a pair of 1" dome tweeters to solve that issue but I never installed them.
Later that box got stolen and I still miss it today.
I have this same story documented elsewere ,But I thought I would give you my honest opinion on this.
They went very low and were very punchy and held their own very well on outside gigs as well.
I used to run them on a Ampeg V4-B tube bass amp and a Radio Shack 18" for the sub running off of a Sunn Concert slave amp for the lows.
Many of my Professional Bass player friends really liked that setup more so than their own at times.
jer
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B&W White Paper on Bass
"Advantages of Producing a Coherent Wavefront:
One remarkable fact was consistently noticed during the development of the new 380mm bass unit for the Nautilus™801, and that was that a single large and stiff bass cone always sounded better than a number of smaller cones, even though they may well have had the same aggregated properties. One possible explanation for this is the concept of the production of a “coherent wave front”. This will be produced by a single large very stiff cone, which can couple with the air in a uniform manner over the whole of its surface area unaffected by differences in loading over that area. This behavior is to be compared with that of several cones which, even though they may be closely spaced, will still leave gaps of “uncoupled air” between them. The very stiff cone material of the large single driver, which is a thick sandwich of Kevlar® reinforced paper fibers with a very stiff skin, makes it less responsive to local changes of acoustic impedance or unbalanced modal pressures either behind or in front of the cone.
A “coherent wavefront” simply means there is either a constant or a smoothly changing phase relationship between neighbouring parts of the wavefront. So even if two drivers are relatively close together compared to a wavelength. Also, even if their contributions are equivalent to a single large driver, their different acoustic environments will mean that their outputs are slightly different, in terms of both amplitude and phase. Furthermore, the air between the drive units is not being driven at all and this will translate into a change in phase across the resulting wavefront as the air tries to “fill in” the lost contribution. One can postulate that, at low frequencies, air can “spill off the edges” of the individual cones more easily in an array of small cones, which obviously have more edges for it to spill off, than from a single large one. For instance, two 12 inch drivers have a combined circumference of 1630mm whereas one 15 inch cone has a circumference of only 1037 mm. It is also interesting to note in this context that the radiation resistance and reactance at low frequencies of one 15 inch cone, is actually larger than that of two 12 inch cones, even though the area of the 15 inch cone is 0.02m2 smaller than two 12 inch cones. This is because the change from a steadily rising radiation resistance characteristic at low frequencies, to a horizontal one at high frequencies, occurs at a lower frequency with one large driver than with two smaller. Mutual radiation impedance effects will redress this imbalance to some extent, provided that the two individual drivers are close enough together for one driver to acoustically load the other, though it will only be totally redressed if the array of small drivers produces a totally contiguous surface in all directions. With a less stiff cone, localized changes in rear (or front) pressure due to modes, or the presence of obstructions which prevent the free flow of air, will mean that the cone will flex in response to this differential loading during each vibration cycle. This flexure, quite apart from upsetting the resulting wavefront, may well ultimately cause the demise of the drive unit itself which may eventually even fall apart due to the repeated stresses. This is especially true of light cones trying to compress the air in very small boxes, but the principle can obviously be extended to large boxes having rear obstructions – such as a Matrix™ indeed – which inevitably impede the free flow of large volumes of air which occur at low frequencies.
All these effects are, of course, highly audible and conspire to remove the “punch” or timing effects which are often used to describe “fast” bass."
The beautiful Avalon Isis design matches what I have learned about speakers.
3-way design with wide bandwidth midbass and high efficiency bass from either one very large diameter woofer (18") or paralleling two large diameter woofers (12" or 15"). Isis uses 7" midbass and two 12" woofers.
STYLE IS IMPORTANT.
"Advantages of Producing a Coherent Wavefront:
One remarkable fact was consistently noticed during the development of the new 380mm bass unit for the Nautilus™801, and that was that a single large and stiff bass cone always sounded better than a number of smaller cones, even though they may well have had the same aggregated properties. One possible explanation for this is the concept of the production of a “coherent wave front”. This will be produced by a single large very stiff cone, which can couple with the air in a uniform manner over the whole of its surface area unaffected by differences in loading over that area. This behavior is to be compared with that of several cones which, even though they may be closely spaced, will still leave gaps of “uncoupled air” between them. The very stiff cone material of the large single driver, which is a thick sandwich of Kevlar® reinforced paper fibers with a very stiff skin, makes it less responsive to local changes of acoustic impedance or unbalanced modal pressures either behind or in front of the cone.
A “coherent wavefront” simply means there is either a constant or a smoothly changing phase relationship between neighbouring parts of the wavefront. So even if two drivers are relatively close together compared to a wavelength. Also, even if their contributions are equivalent to a single large driver, their different acoustic environments will mean that their outputs are slightly different, in terms of both amplitude and phase. Furthermore, the air between the drive units is not being driven at all and this will translate into a change in phase across the resulting wavefront as the air tries to “fill in” the lost contribution. One can postulate that, at low frequencies, air can “spill off the edges” of the individual cones more easily in an array of small cones, which obviously have more edges for it to spill off, than from a single large one. For instance, two 12 inch drivers have a combined circumference of 1630mm whereas one 15 inch cone has a circumference of only 1037 mm. It is also interesting to note in this context that the radiation resistance and reactance at low frequencies of one 15 inch cone, is actually larger than that of two 12 inch cones, even though the area of the 15 inch cone is 0.02m2 smaller than two 12 inch cones. This is because the change from a steadily rising radiation resistance characteristic at low frequencies, to a horizontal one at high frequencies, occurs at a lower frequency with one large driver than with two smaller. Mutual radiation impedance effects will redress this imbalance to some extent, provided that the two individual drivers are close enough together for one driver to acoustically load the other, though it will only be totally redressed if the array of small drivers produces a totally contiguous surface in all directions. With a less stiff cone, localized changes in rear (or front) pressure due to modes, or the presence of obstructions which prevent the free flow of air, will mean that the cone will flex in response to this differential loading during each vibration cycle. This flexure, quite apart from upsetting the resulting wavefront, may well ultimately cause the demise of the drive unit itself which may eventually even fall apart due to the repeated stresses. This is especially true of light cones trying to compress the air in very small boxes, but the principle can obviously be extended to large boxes having rear obstructions – such as a Matrix™ indeed – which inevitably impede the free flow of large volumes of air which occur at low frequencies.
All these effects are, of course, highly audible and conspire to remove the “punch” or timing effects which are often used to describe “fast” bass."
The beautiful Avalon Isis design matches what I have learned about speakers.
3-way design with wide bandwidth midbass and high efficiency bass from either one very large diameter woofer (18") or paralleling two large diameter woofers (12" or 15"). Isis uses 7" midbass and two 12" woofers.
STYLE IS IMPORTANT.
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