Relative Size of Drivers = how many of these to equal one of those?

BlueWizard

Distinguished Member
I've touched on this before, but I thought it might be nice to have this information all in one spot, and since I addressed this in another forum, I thought it would be worthwhile to cut and paste it here.

The question was asked, more or less, how many 4" speakers does it take to equal an 8" speaker-
- - - - - - - - - - - - - - - - - - - - - - - -

Find the Piston area of the speakers using the area of a circle. If you do this, you will get a chart that looks something like this -

4.5" - 1
5.0 - 1.3
6.5 - 2.6
8.0 - 4.3
10 - 6.8
12 - 9.9
15 - 16.0


This was actually given to me when I asked a similar question in another forum.

Area of a Circle equals PI times the Radius Squared.

A = (PI) R²

So, let's work this out.

A = (pi) R² = (3.14159) x 2² = 3.14159 x 4 = 12.566 square inches (4" driver)

A = (pi) R² = (3.14159) x 4² = 3.14159 x 16 = 50.265 square inches (8" driver)

So, if we divide the two 50.265 / 12.566 = 4.00

So, one 8" speakers equal FOUR 4" speakers.

Here is another chart that I calculated myself -

4.00" = 12.57 sq.in. = 1.00
5.00" = 19.64 sq.in. = 1.56
5.25" = 21.65 sq.in. = 1.72
6.00" = 28.27 sq.in. = 2.49
6.50" = 33.18 sq.in. = 2.64
7.00" = 38.49 sq.in. = 3.06
8.00" = 50.27 sq.in. = 3.999 = 4.0
10.0" = 78.54 sq.in. = 6.25
12.0" = 113.1 sq.in. = 8.997 = 9.0
15.0" = 176.7 sq.in. = 14.06

Using this chart, we divide 4 (for an 8" speaker) by 1 (for a 4" speaker) and we get the same result; FOUR 4" speakers equals ONE 8" speaker.

Also notice that a 6.5" speaker using this last chart, is 70% larger than a 5" speaker. (2.64/1.56 = 1.70)

A 12" speaker is 125% larger than a 8" speaker. (9/4 =2.25)

And so on...

Steve/bluewizard
 
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BlueWizard

Distinguished Member
Adding some additional points -
- - - - - - - - - - - - - - - - - - - - - - - - -
If you want the difference between two specific speakers rather than a generalization, look up the full specs on the speakers, and look at the Sd specification, which is the surface area of the actual cone.

Here is a chart I makes using the Sd of Dayton speakers. Keeping in mind that the cones could be very different. One could be shallow and flat, another very deep. Some could be curved, other very straight.

Using Dayton woofers as an example, and using their Sd spec, we determine the relative effective size of various speakers.

4.00" = 37.4 cm² = 1.00
5.00" = 52.8 cm² = 1.41
5.25" = 93.3 cm² = 2.49
6.00" = 84.9 cm² = 2.27
6.50" = 134.8cm² = 3.60
7.00" = 132.7cm² = 3.55 (more typical 125cm²)
8.00" = 211.2cm² = 5.65
10.0" = 343.1cm² = 9.17
12.0" = 498.8cm² = 13.3
15.0" = 843.7cm² = 22.6

Further because the surround is not part of the Pistonic action of the driver, we have to subtract the surrounds. Now a typical surround is about 0.75". But part, about half of the surround, does have some pistonic action; about half.

To allow for this, we subtract 0.75" from the rated dimension of the speakers.

So, an 8" speaker minus 0.75" is now 7.25". To find the area we still use the same formula (7.25/2 = 3.626) -

A = (pi) R² = 3.14159 x 3.625² = 41.28 square inches.

Now a 4" driver, which would now be 3.25" (3.25/2 = 1.625) -

A = (pi) R² = 3.14159 x 1.625² =8.296 square inches
So, we divide the value for the 8" by the value for the 4" and we have -

41.28 / 8.296 = 4.96

Using this method, it takes 4.96 FOUR inch drivers to equal ONE 8" driver.

This is probably the most accurate as a general estimation for all drivers, as it uses the actual cone diameter plus half the Surround, and assumes Pistonic action.

Sorry haven't worked this chart out yet.

The corrected formula, though more confusing, would be - where "D" is diameter -

A = (pi) ((D - 0.75) / 2)²

A = (pi) ((8" - 0.75) / 2)²

A = (pi) ((7.25) / 2)²

A = (pi) (3.625)² = 3.14159 (3.625)² = 41.28

Which is exactly what we had before.


This last method, is the most accurate, but simply comparing the area of a circle of the rated size of the driver, is probably sufficient to make an estimation.

Steve/bluewizard
 
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BlueWizard

Distinguished Member
One last point from the previous post -

I made a reference to how much larger a given driver was than another. That's not really the way to look at it and it created some confusion, so this was my response -

"I think you meant to say "225% larger".

Yeah, that is confusing. If you divide one by the other, the first 100% they are the same, it is only the addition 125% that it is larger.

For example, if the answer were 1.25, that would only be 25% larger.

Another example, we can clearly see that 625 is only 25% larger than 500.

But if you divide 625 / 500 you get 1.25. Clearly it is not 125% larger, just 25% LARGER.

Look at it this way, I think it is less confusing -

Also notice that a 6.5" speaker using this last chart, is 70% larger than a 5" speaker. (2.64/1.56 = 1.70)

A 12" speaker is 125% larger than a 8" speaker. (9/4 =2.25)


Restated, and the way we would commonly look at it -

It takes 1.7 FIVE inch divers to equal ONE 6.5" driver.

It takes 2.25 EIGHT inch drivers to equal ONE 12" driver.


What we functionally want to know is NOT how much bigger is this than that, but rather how many of these does it take to equal one of those.

Steve/bluewizard
 
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BlueWizard

Distinguished Member
So, what is the value of all this rambling? Like I said, this came up recently in a discussion about Focal 936 vs Focal 948.

The 936 has THREE 6.5" bass drivers.

The Focal 948 has TWO 8" bass drivers.

Which is really bigger?

Turns out the 948 only has 10% more cone area than the 936. (Using the numbers I used then)

Using the second chart in Post #1, one 8" driver has a relative value of 4.

A 6.5" bass drive has a relative value of 2.64.

4 x 2 = 8

2.64 x 3 = 7.92

8 / 7.92 = 1.01

Using these new figures, TWO 8" are really only 1% larger than THREE 6.5".

Again, to get the most accurate comparison assuming pistonic motion of the driver, this formula will give the closest approximation.

A = (pi) ((D - 0.75) / 2)²

Where "D" is the rated Diameter of the speaker. The "0.75" is the correction for the surround ring on the driver. This accounts for the true pistonic size of a given driver.

I will finish the chart that uses this formula and post the results. That way you can avoid the math and just use the chart.

Hopefully someone will get some value out of this information.

Steve/bluewizard
 
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Paul Smith

Well-known Member
Don't forget to take account of X-max.
Probably the most important factor (other than diameter) to say if one driver is equal to another.

Paul.
 

BlueWizard

Distinguished Member
Yes, when comparing speakers, there are other factors like Xmax, sensitivity and other factors, but the sole point of this post is to compare size.

How many of these equal one of those?

Also, in the last formula I discovered I made a bit of a mistake. I subtracted 0.75 inches to allow for the surrounds, but that was only on one side, I should have considered both sides.

To do this on specific speakers, measure from the outer edge of the speaker frame to the center of the surround. In this case surround means that soft black ring that attaches the actual cone to the frame of the driver. Then DOUBLE it.

So, the formula should really be more like -

A = (pi) ((D - 1.5) / 2)²

For that general purpose, this chart is probably fine.

4.00" = 12.57 sq.in. = 1.00
5.00" = 19.64 sq.in. = 1.56
5.25" = 21.65 sq.in. = 1.72
6.00" = 28.27 sq.in. = 2.49
6.50" = 33.18 sq.in. = 2.64
7.00" = 38.49 sq.in. = 3.06
8.00" = 50.27 sq.in. = 3.999 = 4.0
10.0" = 78.54 sq.in. = 6.25
12.0" = 113.1 sq.in. = 8.997 = 9.0
15.0" = 176.7 sq.in. = 14.06

On my 5" bookshelf speakers, from the outer edge of the frame to the center of the surround is about 0.5".

On my 8" speakers and my 12" speakers, from the outer edge of the frame to the center of the surround is about 1".

So using this last example, the formula that adjusts for the true pistonic size of the driver would be -

A = (pi) ((D - 2.0) / 2)²

But over all, this is just a way to get a general idea of the relative size of speakers.

If you want to be more precise, you can use the formula that subtracts the surround from the rated size.

As an average between small drivers and large drivers, this is probably the best compromise -

A = (pi) ((D - 1.5) / 2)²

Steve/bluewizard
 
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MemX

Well-known Member
Yes, when comparing speakers, there are other factors like Xmax, sensitivity and other factors, but the sole point of this post is to compare size.

How many of these equal one of those?
Without wishing to dismiss your work, there is no point doing this ^^^ without doing this:
Don't forget to take account of X-max.

For example, a 15" driver may have 1.55 times the amount of surface area of a 12" driver (14/9, using your calculations), but if the 12" driver has 1" (25mm) of one-way XMax and the 15" driver has only 8mm (1/3") of one-way Xmax, which might be the key difference between a modern driver designed for in-car use versus an older design designed for pro-audio use in some sort of horn cabinet, the swept area (Vd, IIRC?) of each cone moving at Xmax is (using your figures above):

12" driver = 113.1 square inches x 1" XMax = 113.1 cubic inches of swept area
15" driver = 176.7 square inches x 0.333" XMax = 58.89 cubic inches of swept area.

So, although the 15" has a larger area of cone, the 12" has 1.92 times the swept area of the 15" - in which case the one 12" driver in question actually equals two of the 15" drivers in question.
 

KelvinS1965

Distinguished Member
Bottom line is you've still got to listen to them to decide which one suits you anyway.

All the maths in the world counts for nothing if you don't like the result and we (hopefully) all agree that speaker choice is a personal one rather than an absolute.

Just my few thoughts.
 

BlueWizard

Distinguished Member
I've had this come up before, which is why I created these charts. The information can come in handy to a lot of people.

For example, if you are building speakers, you might want to weigh various driver combinations. Should I use three 6.5", two 8", or one 10"?

Another is when comparing speakers in the same brand and series. The thread that enticed me to post this was comparing the Focal 936 with 3x6.5" against the Focal 948 with 2x8". One might assume 2x8" is bigger, but as I have shown, using the numbers I have, they are within 1% of being the same size.

One could just as easily apply it to the Wharfedale Diamond 157 which has 2x6.5" bass drivers and the Diamond 159 which has 2x8" bass drivers. How much bigger is the 159 than the 157? Using the number from the chart the 157 is a relative 5.28 and the 159 is a relative 8. Dividing the two we find the 159 is 52% larger, it takes 1.52x 157s to equal a single 159. That does give you some sense of the relative size of those two speakers.

While what MemX said about the 12" long throw vs the 15" short throw driver is technically true, I can't envision a situation where anyone would ever be considering those two drivers for the same project. That is still valuable context to illustrate the limits of what these charts and formulas can do. But just because they can't do everything, doesn't mean they can't do something.

As to KelvinS1965's comment, this is about the size of the speakers, and nothing more. Knowing the relative size of two speakers is worthwhile, but as he points out, it does nothing to tell you how they will sound, beyond perhaps some sense of how well they will work in a given room.

The sole purpose is to help you compare the relative size of speakers, and in that limited context, it does what it is suppose to do.

In another thread in another forum, I guy was considering rebuilding a guitar practice amp, and he was wondering if 2x4" driver equaled 1x8" driver. The answer is, of course, NO. It take 4 or 5 Four inch drivers to equal one 8" driver.

Even drivers that appear pretty close, can be very divergent. The best example is that a 6.5" bass driver is nearly TWICE as large as a 5" bass driver. That is not intuitively obvious from a simple statement of the driver size. (1.7x 5" = 1x6.5")

However, part of the problem is how do we compare the relative size of drivers? Especially when the very parameters we need are not available to us? Answer, we make a fair guess. The last chart I posted uses the Rated Size of the speakers. The last formula I posted, for which I haven't made the chart yet, tries to get a more accurate sense of the actual piston size of the driver.

Another method is to use the Sd specification, which is the actual rated cone area. This is difficult to find on raw drivers, and near impossible on commercial speakers. And it is questionable as to whether the surface area determines the amount of air moved, or if it merely determines the shape of the air moved. Most treat drivers as pistons, consequently, most would take the pistonic dimension rather than the actual cone surface area. Which is what my charts reflect, the piston size of a given driver.

You are free to use which ever method you think is best. But as a generalization, the charts I made give a fair approximation of the relatives size.

This is of limited use, applies to a limited context, but it is still worthwhile information. You just have to temper any conclusion you reach with a dose of good judgement.

Steve/bluewizard
 

BlueWizard

Distinguished Member
OK, I recalculated using this formula -

A = (pi) ((D - 1.5) / 2)²

I used 1.5 as the adjustment factor, based on the fact that my 5" speakers would be 1 and my 12" speaker would be 2, and this was half-way between. The only way to get more accurate, would be to measure actual specific drivers between the outer edge of the frame and the center of the surround, then double that number and use it in the calculations. Alternately simply measure from the center of the surround to the center of the surround to get the true piston diameter of the driver.

I also performed the calculations in an EXCEL spreadsheet, and verified the first calculations using a calculator to make sure I had entered the formula correctly in the spreadsheet.

Here are the results. This is a closer approximation of the true piston size of a range of drivers -

4.00" = 4.91 sq.in. = 1.00
5.00" = 9.62 sq.in. = 1.96
5.25" = 11.05 sq.in. = 2.25
6.00" = 15.90 sq.in. = 3.24
6.50" = 19.64 sq.in. = 4.00
7.00" = 23.76 sq.in. = 4.48
8.00" = 33.18 sq.in. = 6.76
10.0" = 56.75 sq.in. = 11.56
12.0" = 86.59 sq.in. = 17.64
15.0" = 143.14 sq.in. = 29.16

If we compare a 6.5" and a 5" using this new chart, we have 4/1.96 = 2.04. So, a 6.5" is 2.04 times bigger than a 5" driver.

If we use the previous chart that simply used the Rated Dimension and made no adjustment, then compare the two same two drivers, we have 2.64/1.56 = 1.69 or 1.7. Implying that a 6.5" is is 1.7 times bigger than a 5".

If we compare 3x6.5" against 2x8" we now have -

three 6.5" -
3 x 4 = 12

two 8" -
2 x 6.76 = 13.53

13.53 / 12 = 1.1275 = 1.13

So, using these new numbers, TWO 8" drivers are about 13% larger than THREE 6.5" drivers.

Using the original Rated Size unadjusted chart we have 8 / 7.92 = 1.01, or the 2x8" is 1% larger.

I think either way, you can get a rough idea of the relative difference between two different driver configurations.

Which you use is up to you.

Steve/bluewizard
 

BlueWizard

Distinguished Member
Yes, I know I rambled on, which is precisely why I'm going to summarize in this last post -

Relative Speaker Size by the Rated Size of the Speakers
-
Using A = (pi) R²

4.00" = 12.57 sq.in. = 1.00
5.00" = 19.64 sq.in. = 1.56
5.25" = 21.65 sq.in. = 1.72
6.00" = 28.27 sq.in. = 2.49
6.50" = 33.18 sq.in. = 2.64
7.00" = 38.49 sq.in. = 3.06
8.00" = 50.27 sq.in. = 3.999 = 4.0
10.0" = 78.54 sq.in. = 6.25
12.0" = 113.1 sq.in. = 8.997 = 9.0
15.0" = 176.7 sq.in. = 14.06

Relative Speaker Size Adjusted for True Piston Size -
Using A = (pi) ((D - 1.5) / 2)² -

4.00" = 4.91 sq.in. = 1.00
5.00" = 9.62 sq.in. = 1.96
5.25" = 11.05 sq.in. = 2.25
6.00" = 15.90 sq.in. = 3.24
6.50" = 19.64 sq.in. = 4.00
7.00" = 23.76 sq.in. = 4.48
8.00" = 33.18 sq.in. = 6.76
10.0" = 56.75 sq.in. = 11.56
12.0" = 86.59 sq.in. = 17.64
15.0" = 143.14 sq.in. = 29.16

Either one is workable to give you a rough idea of the relative size of one combination of speaker drivers compared to another combination.

Also, since these are just calculations that anyone can do, feel free to save a copy on your computer, if you think it might be a handy reference.

Steve/bluewizard
 
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Cribbster

Active Member
All very interesting but what we would like to know is what was the difference when you actually went to hear them? Was there a 1% difference between them or did it transpire to be largely an academic exercise because the effect of physics meant that the 8" drivers by virtue of moving more air provide a sound of greater depth than lost of smaller drivers? :)
 

BlueWizard

Distinguished Member
I never claimed that by looking at these charts you could know everything there is to know about a speaker. All it gives you is a fair approximation of the relative size of the drivers.

The person weighing the Focal 936 against the 948 was concerned that the 948 would be too much for his room, based in the assumption that 8 is bigger than 6.5. But when you use the chart to determine the actually approximated difference between the speakers, under the worst case estimate, there is a 13% difference. Is 13% really that significant?

Now if he were comparing two 6.5" against two 8", the result would have been different. That represents a 69% difference in size, the 2x8" is 69% larger than the 2x6.5".

This person already picked his speaker FOCAL ARIA, it was down to whether it should be the 936 or the 948. So, the underlying question wasn't about sound quality, he had already made that determination, it was about size.

The 948 has these specs -

Sensitivity = 92.5dB
Low Response = 31hz at -6dB


The 936 has these specs -

Sensitivity = 92dB
Low Response = 32hz at -6dB


So they are very very similar. The 13% cone advantage of the 948 is probably enough to account for the extra 0.5dB in output. Or it could simply be the slightly larger cabinet size. But 0.5 dB is very small, below perception.

Again, no one claimed that comparing the relative size told you everything you needed to know about a speaker. It simply provides one more bit of information, should you need to know that information.

Steve/bluewizard
 

Matyam

Active Member
So steve im using some cerwin vega e 715 s for my home cinema duties 15" ,.102 db sensitivity, 26-20khz .But in room I have measured flat at 21hz -6 at 17 hz equed .To be WAF I would need 7 X6.5 drivers per side to match? Is there a guide of driver size to rated output hz which seems more logical or not and has speaker design in your opinion moved on much as has been hinted at ?
 

BlueWizard

Distinguished Member
I would take 7.29x 6.5" to equal a 15", but equal to does not mean being the equal of. You last question brings home the reason why nicely.

If you look at the specs on Datyon bass drivers, you will generally find as the bass driver gets larger, the bass response gets lower. However, as the bass moves lower so does the Midrange. Rarely do you ever see large bass drivers in a 2-way system because they simply don't have the Midrange. They simply can not reach high enough to join with the tweeter.

But, you can find the same thing within a give size of speaker. If you compare a cross section of 6.5" drivers, you will find some have pretty deep bass. But those with deep bass have no midrange. Others of the same size, have less bass an more midrange.

It is common today to find 3-way speakers that are NOT Bass, Midrange, Treble, but rather Low-Bass, Mid-Bass, Treble. The Low-Bas/Mid-Bass take a 6.5" woofer (as an example) one of which is designed and tuned to have very low bass, which make it weak in the Mids, then combine that with a very similar driver, that is a bit weak in the bass, but reaches higher in the midrange, high enough to merge with a tweeter. The bookshelf version of that same speaker would have the Mid-Bass, and Tweeter, and would, as bookshelf tend to do, compromise low bass.

So, there are specific drivers specifically design to serve a specific purpose. You can not really compare a common 15" woofer to a common 15" Subwoofer. A Subwoofer is a driver very specifically designed to cover an EXTREMELY narrow range of sound. In some cases, it is barely functional across 500hz. More often, it doesn't function outside of a 300hz range. Where as a typical 15" woofer, will probably, best case, function across a 2000hz range.

By the same token, you do not compare a row boat to a cargo ship. 500 row boats might be equal to a small cargo ship, but they are not the equal of a cargo ship.

Generally, Raw Drivers are the wrong context for this, though in DIY speaker building applications, it has some value. Rather, this is for comparing speakers, full complete speakers systems, of similar characteristics, to determine there relative size.

Which I illustrated in this question -

How much bigger is the Focal 948 than the Focal 936? (3x6.5" vs 2x8")

Answer: About 13% bigger.

How much bigger is the Diamond 159 than the Diamond 157? (2x6.5" vs 2x8")


Answer: About 69% bigger.

In a modest room, the difference between the 948 and the 936 is not that significant. However, the difference between the Diamond 159 and the Diamond 157 is pretty significant.

If you are dealing with Raw Drivers, and you are, perhaps, building your own speakers, this chart still has some value, but you simply weigh it against the many other parameters you are considering.

For example, if you are building common Towers (floorstanding) and you want to keep the front profile narrow, but you would like as much kick as a 12" bass driver, how many drivers to you need?

To equal 1x 12" bass driver, you need -

4.41 x 6.5" bass drivers

2.61 x 8" bass drivers

Of course, you have to consider many other parameters including rated frequency response of the bass drivers, Vas - which is an indication of the needed Cabinet volume, Fs - Resonance Frequency, and many other factors. This one bit of information derived from the charts doesn't tell you everything, but it does tell you something. You just have to understand how it can realistically be used.

For what it is worth.

Steve/bluewizard
 
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Matyam

Active Member
I would take 7.29x 6.5" to equal a 15", but equal to does not mean being the equal of. You last question brings home the reason why nicely.

If you look at the specs on Datyon bass drivers, you will generally find as the bass driver gets larger, the bass response gets lower. However, as the bass moves lower so does the Midrange. Rarely do you ever see large bass drivers in a 2-way system because they simply don't have the Midrange. They simply can not reach high enough to join with the tweeter.

But, you can find the same thing within a give size of speaker. If you compare a cross section of 6.5" drivers, you will find some have pretty deep bass. But those with deep bass have no midrange. Others of the same size, have less bass an more midrange.

It is common today to find 3-way speakers that are NOT Bass, Midrange, Treble, but rather Low-Bass, Mid-Bass, Treble. The Low-Bas/Mid-Bass take a 6.5" woofer (as an example) one of which is designed and tuned to have very low bass, which make it weak in the Mids, then combine that with a very similar driver, that is a bit weak in the bass, but reaches higher in the midrange, high enough to merge with a tweeter. The bookshelf version of that same speaker would have the Mid-Bass, and Tweeter, and would, as bookshelf tend to do, compromise low bass.

So, there are specific drivers specifically design to serve a specific purpose. You can not really compare a common 15" woofer to a common 15" Subwoofer. A Subwoofer is a driver very specifically designed to cover an EXTREMELY narrow range of sound. In some cases, it is barely functional across 500hz. More often, it doesn't function outside of a 300hz range. Where as a typical 15" woofer, will probably, best case, function across a 2000hz range.

By the same token, you do not compare a row boat to a cargo ship. 500 row boats might be equal to a small cargo ship, but they are not the equal of a cargo ship.

Generally, Raw Drivers are the wrong context for this, though in DIY speaker building applications, it has some value. Rather, this is for comparing speakers, full complete speakers systems, of similar characteristics, to determine there relative size.

Which I illustrated in this question -

How much bigger is the Focal 948 than the Focal 936? (3x6.5" vs 2x8")

Answer: About 13% bigger.

How much bigger is the Diamond 159 than the Diamond 157? (2x6.5" cs 2x8")


Answer: About 69% bigger.

In a modest room, the difference between the 948 and the 936 is not that significant. However, the difference between the Diamond 159 and the Diamond 157 is pretty significant.

If you are dealing with Raw Drivers, and you are, perhaps, building your own speakers, this chart still has some value, but you simply weigh it against the many other parameters you are considering.

For example, if you are building common Towers (floorstanding) and you want to keep the front profile narrow, but you would like as much kick as a 12" bass driver, how many drivers to you need?

To equal 1x 12" bass driver, you need -

4.41 x 6.5" bass drivers

2.61 x 8" bass drivers

Of course, you have to consider many other parameters including rated frequency response of the bass drivers, Vas - which is an indication of the needed Cabinet volume, Fs - Resonance Frequency, and many other factors. This one bit of information derived from the charts doesn't tell you everything, but it does tell you something. You just have to understand how it can realistically be used.

For what it is worth.

Steve/bluewizard
On another slight tangent a old friend of mine has a pair of linn keltiks now these sound sublime and where ever you stand in that room the sound field is so even.Now these are rated flat from 20-20khz with relatively small kef bass drivers arranged isobarikly like the sub diyers copy mks but he still needs a sub for films why is that?My cv speakers whilst no match higher up the audio range I still prefer at bottom end just need the best of both but how ?
 

MemX

Well-known Member
There is no replacement for displacement, as the Yanks like to say ;)

You need to shift a lot of air to reach the required levels of movie bass, hance the need for big drivers with decent excursion. Smaller drivers in multiples may move similar amounts of air in total, but would you rather have a 1" driver moving 143" peak to peak or a 15" driver moving 1" peak to peak, to use figures stated above and extrapolate them to extremes? :)

with relatively small kef bass drivers arranged isobarikly like the sub diyers copy mks
I think you meam Push Pull? Isobaric designs uses two drivers, one hidden in the box and usually face-to-face or face-to-magnet with the outside driver, to half box size but only have the output of one driver. Push Pull reduces distortion but has the output of both drivers.
 

BlueWizard

Distinguished Member
Here is an example of speakers in a Push-Pull arrangement. This is from another discussion, the original poster proposed hanging the rear driver off the back of the cabinet directly behind the front facing driver. My intent with the graphic was to show him he could accomplish the same thing by placing the driver inside the cabinet.

In the MK Subs, one of the bass drivers faces forward like a normal driver, the other is inside the Port area and face upward into the cabinet. If you look closely at the MK subs, you can see a bit of the magnet of the second driver in the port area.


PushPullSpkrMod.jpg


Also shown is the original speaker as he planned it.

PushPullSpeaker.jpg


Again, with an MK Sub, one driver faces forward, and the other in on the bottom in the port facing upward.

Also notice that in this design the speaker drivers are time aligned. The high, mid, and front woofer magnets, and as such the voice coils, are all in a straight vertical line.

Here is more info on Isobarik speakers which come in many configurations -

Linn Isobarik - Wikipedia, the free encyclopedia

Photo -

File:Linn Isobarik DMS loudspeaker enclosure.png - Wikipedia, the free encyclopedia

Notice in this last type, both drivers are sealed in the same cabinet, with only one driver feeding the outside world.This is the method that the LINN speakers use.

Just adding this for reference.

Steve/bluewizard
 
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MemX

Well-known Member
Here is an example of speakers in a Push-Pull arrangement. This is from another discussion, the original poster proposed hanging the rear driver off the back of the cabinet directly behind the front facing driver. My intent with the graphic was to show him he could accomplish the same thing by placing the driver inside the cabinet.

In the MK Subs, one of the bass drivers faces forward like a normal driver, the other is inside the Port area and face upward into the cabinet. If you look closely at the MK subs, you can see a bit of the magnet of the second driver in the port area.


View attachment 506615

Also shown is the original speaker as he planned it.

View attachment 506616

Again, with an MK Sub, one driver faces forward, and the other in on the bottom in the port facing upward.
I am confused.

The original design was indeed push-pull, with one cone pushing away from its basket at the same time as the other pulls towards its basket. This reduces harmonic distortion by cancelling out driver non-linearities between the inward and outward stroke effects on the chassis components.

The re-design you proposed has both cones pushing away from their baskets at the same time (and therefore both pulling towards their baskets at the same time) - a push-push design.

There doesn't seem to be any similarities between the two because the force-cancelling, opposed layout of the initial design has changed, and now when the bottom and top drivers both pull in at the same time, they will try to rotate the entire box around a middle central point.
 
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BlueWizard

Distinguished Member
In the initial design, I assumed that when the front cone went forward, the second driver cone also went forward. Since the drivers are not sealed within the same box, this makes the arrangement a DiPole.

If you look at the colored arrows, that is also true in the modified design. When the upper cone move forward (to the left), the lower cone moves in the same direction (to the left), though relative to itself, that is backward, yet in absolute direction, it is in sync with the upper cone.

In short, the upper driver pushes out of the box, and the lower driver pulls into the box. Same physical movement in space. They either both go to the left (blue arrow), or they both go to the right (red arrow).

I don't know whether the guy ever built the design or not.

Steve/bluewizard
 
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Matyam

Active Member
So in a ideal world but only for performance sakes not aesthetically with a blank sheet what sort of speaker design would you have built money no object to cover the audio spectum 20-20khz and why ie size drivers, number off ? When my cv s go pop I would like a project.
 

stevos

Distinguished Member
This has to be worth a sticky. A bit technical for these forums but a really interesting read neither the less.
 

Jameskatie

Distinguished Member
I don't think it should be stickyd it's not really very helpful to anyone :-s sorry Steve, and if those speakers were wired up how you say in "dipole" there would be next to no output and having them in two seperate chambers defeats the point in push-pull.
 

MIKEVO

Well-known Member
So in a ideal world but only for performance sakes not aesthetically with a blank sheet what sort of speaker design would you have built money no object to cover the audio spectum 20-20khz and why ie size drivers, number off ? When my cv s go pop I would like a project.
Well, my Sub1 has 6 x 8 inch drive units and to date, I have never heard a Sub that plays Louder or Deeper, so its not all about size. :cool:

Steve's guide is very helpful to get a general idea of how much air would be shifted for a given size drive unit compared to another, but he is only quoting total area's as a guide and should save people a lot of hassle in having to work it out for themselves, so thanks Steve. :smashin:

How people implement the drive units is a totally different subject.
 

BlueWizard

Distinguished Member
As I have repeatedly said, this information isn't meant to tell you everything about a speaker, it is just a generalized best guess as to the relative size of various drivers. Given that you very likely can NOT get the Sd specification (surface area) of commercial speaker system, this is the next best thing.

Once you go beyond what I have given here, you need to have specific drivers in your hands so you can make more detailed calculation that would give you are more close estimate of the actual surface area of the driver. But that is a lot of measuring and calculating when likely all you want to know is ROUGHLY how many of these speaker equals this many of those speakers.

Within the context of what I have said, this is valuable information, and I have no control of people taking this information beyond the intended context. People have assumed that this is the end point of evaluating speakers, no ... it is the starting point. How much time and effort you want to put in between the starting point and end point is purely up to you.

In the context, I have illustrated two perfect examples of how this information can be used. Actually 3 illustrations, if we consider the 5" vs 6.5" example. When you are buying or evaluating speakers, it could be well worth knowing that a 6.5" is nearly twice as big as a 5".

Again, this the RELATIVE difference, not the Absolute difference between speaker drivers, and that is the context in which you have to take it. To get the absolute difference, you have to have absolute knowledge of the drivers, which you virtually never will have.

In the Focal 948 vs the Focal 936, we would naturally assume that 8" is bigger than 6.5". But when we figure it out using the information provided, we discover that 3x6.5" is very nearly identical to 2x8". If you are trying to determine which speaker best fits a give space, then it is clear, it really doesn't matter. In which case, it is down to budget. Are you willing to pay the extra money to get the 948?

When used in context, this is worthwhile information, but - NO - I never claimed it was the end-all be-all of speaker knowledge. It is simply one more handy bit of information that you can use or not use are you choose.

Steve/bluewizard
 

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