Do three 6.5" woofers really take the place of a 12" or 15" woofer? - AVS Forum
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post #1 of 57 Old 06-12-2012, 01:04 PM - Thread Starter
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Hi:

I remember my very first pair of speakers - AAL (American Acoustic Laboratories).

They were supposedly the best speakers the "higher-end" store sold at the time.

I don't remember the size of the other components - but the woofer was 15"

They were great sounding speakers.

Today, they don't make speakers like that anymore.

Everything is thin and usually have either a number of 6.5" woofers, or some have 8" woofers (Salon2).

Do more very small (in comparission to 15") woofers really take the place of one larger (12" or 15") woofer confused.gif
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post #2 of 57 Old 06-12-2012, 01:35 PM
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If you get enough then yes they can, but most don't. With that being said where you place your mains is usually not the best and sometimes is a terrible place for bass. Thus today you usually have a sub to go along with your mains, this allows placement in the room that will give you quality bass.

Plus these new sub's go lower than most of the old 15's would in main speakers.
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post #3 of 57 Old 06-12-2012, 03:53 PM
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With woofers, it's all about how much air you move.
The area of a circle is pi r^2 so...
5.5" ~ 24 sq in
6.5" ~ 33 sq in
7" ~ 38 sq in
8" ~ 50 sq in
10" ~ 78 sq in
12" ~ 113 sq in
15" ~ 176 sq in
18" ~ 254 sq in

So, two 12" and three 10" woofers would be about equal.
To push as much air as your old 15", you'd need about FIVE 7" woofers.
Plus, there's no way they would hit the low your speaker did and, if you're talking subs, today's new boxes go even lower.
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post #4 of 57 Old 06-12-2012, 03:54 PM
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Different sized (and shaped/depth) drivers also have different dispersion/off axis characteristics. It isn't always about output.

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post #5 of 57 Old 06-12-2012, 08:27 PM
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Don't forget about different technologies like XBL2. Increases output while lowering distortion which can really help a smaller driver keep up or outperform larger drivers. While the high excursion, XBL2/splitgap the Arx woofers 5.25" can easily outperform some 6.5"s and maybe even some 7" drivers.
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post #6 of 57 Old 06-15-2012, 04:30 PM
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Quote:
Originally Posted by cschang View Post

Different sized (and shaped/depth) drivers also have different dispersion/off axis characteristics. It isn't always about output.

+1

A proper design is about mating the coverage pattern of the two sections, at the crossover frequency. There's something to be said about a superbly designed 15", or 12" two way. Some of the finest, best imaging loudspeakers available anywhere are constructed in such a manner.


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post #7 of 57 Old 06-15-2012, 07:34 PM
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Quote:
Originally Posted by joshua.jones View Post

With woofers, it's all about how much air you move.
The area of a circle is pi r^2 so...
5.5" ~ 24 sq in
6.5" ~ 33 sq in
7" ~ 38 sq in
8" ~ 50 sq in
10" ~ 78 sq in
12" ~ 113 sq in
15" ~ 176 sq in
18" ~ 254 sq in
So, two 12" and three 10" woofers would be about equal.
To push as much air as your old 15", you'd need about FIVE 7" woofers.
Plus, there's no way they would hit the low your speaker did and, if you're talking subs, today's new boxes go even lower.
Driver cone area only considers two dimensions. How much air is moved is a three dimensional measurement, displacement, quantified as T/S spec Vd. Some eights have more Vd than some fifteens, and the rest of the driver specs that determine response also allow some eights to go not only louder but lower than some fifteens, so one can't take a simplistic 'bigger is better' approach.
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Different sized (and shaped/depth) drivers also have different dispersion/off axis characteristics. It isn't always about output
Dispersion is the only factor purely determined by cone size. The main reason for using multiple smaller drivers rather than one larger driver is the wider dispersion that the smaller drivers give. But multiple smaller drivers are more expensive than one larger driver with equal Vd, so where dispersion isn't an issue the one larger driver makes more sense.
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post #8 of 57 Old 06-15-2012, 11:44 PM
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post #9 of 57 Old 06-16-2012, 05:36 AM
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Quote:
Originally Posted by HomeTheaterGuy74 View Post

Hi:

I don't remember the size of the other components - but the woofer was 15"
They were great sounding speakers.
Today, they don't make speakers like that anymore.

If you mean they don't make speakers like that (brand) anymore then that might be. If you mean they (the industry) doesn't make larger sized speakers with 15" woofers, then you simply haven't looked hard enough.

Just to make a side comment on the woofer size...

My old speakers had a 15" horn loaded woofer. It's improved replacement uses two 12" horn loaded drivers. At first I presumed there would be a diminishment in performance. Turns out that the two 12" drivers have more ability than the single 15" (so the depth of the sound is improved and distortion was lowered). The two 12" drivers also cross HIGHER than the single 15" so they were able to raise the crossover point at the same time and take the speaker to a 2-way format instead of the traditional 3 way format.

It was an interesting ear-opening experience for me to hear & learn about the differences. There are certainly a multitude of reasons why I'm not a speaker engineer!! wink.gif
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post #10 of 57 Old 06-16-2012, 08:55 AM
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Quote:
Originally Posted by HomeTheaterGuy74 View Post

Hi:
I remember my very first pair of speakers - AAL (American Acoustic Laboratories).
They were supposedly the best speakers the "higher-end" store sold at the time.
I don't remember the size of the other components - but the woofer was 15"
They were great sounding speakers.
Today, they don't make speakers like that anymore.
Everything is thin and usually have either a number of 6.5" woofers, or some have 8" woofers (Salon2).
Do more very small (in comparission to 15") woofers really take the place of one larger (12" or 15") woofer confused.gif

There is no replacement for displacement.
To drive large & heavy 15" woofers would be a huge task for the home avr. Which is why it makes sense to have a 10" active subwoofer in it's place. This allows listening down low even without cranking up the volume across all frequencies.

I actually did this setup. I took 2 def tech CLR 2002 and using it as L/R speakers each with a velodyne VX-11 powered subwoofer. The sub does 2 things for me.
1. Clean low frequency
2. Speaker stand for the L/R speaker
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post #11 of 57 Old 06-16-2012, 09:57 AM
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When you talk about low bass capability, it is how much air you can move.

This depends on two factors; the total cone area and the maximum cone travel of each speaker (and amplifier power).

The lowest I have ever heard a subwoofer go was the Vandersteen 2W sub, which uses three 8" drivers that are designed for VERY long excursion (cone travel). I have heard them do organ notes at 14 HZ very powerfully. This design allows the same cone area as a 14-inch driver, but with three times the voice-coil power and more rigid cone structures than a larger single driver.

The problem with 15-inch and larger cones is that they tend to flex too much as the center is driven by the voice coil, rather than move as a rigid piston. Making them stiff enough to resist this increases mass, which is not desirable. One solution is a carbon-fiber composite cone, but that is extremely expensive.




Quote:
Originally Posted by HomeTheaterGuy74 View Post

Hi:
I remember my very first pair of speakers - AAL (American Acoustic Laboratories).
They were supposedly the best speakers the "higher-end" store sold at the time.
I don't remember the size of the other components - but the woofer was 15"
They were great sounding speakers.
Today, they don't make speakers like that anymore.
Everything is thin and usually have either a number of 6.5" woofers, or some have 8" woofers (Salon2).
Do more very small (in comparission to 15") woofers really take the place of one larger (12" or 15") woofer confused.gif
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post #12 of 57 Old 06-16-2012, 12:55 PM
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No one has done the basic math, which is interesting. For simple 2 dimensional area, 4 circles of equal diameter have an area equal to one circle of twice the diameter. So, the total area of four 8" circles is equal to one 16". If you know that, then you can see that adding just one circle increases the total area by 1/3. So two 12" circles are equal in area to one 16".

I keep saying circles to avoid the depth dimension of a cone, but I think it's a reasonable assumption that it would be relative to the diameter as you go up and down in driver diameter, so as a simple, do the math in your head rule of thumb, the above works for me.

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post #13 of 57 Old 06-16-2012, 05:54 PM
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Quote:
Originally Posted by HomeTheaterGuy74 View Post

Hi:
the woofer was 15"
They were great sounding speakers.
Today, they don't make speakers like that anymore.
Everything is thin and usually have either a number of 6.5" woofers, or some have 8" woofers (Salon2).
The reason for the lack of larger drivers is WAF as the box needs to be wider, and slimmer speakers are more domestically acceptable to most.

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Originally Posted by fjames View Post

No one has done the basic math, which is interesting
Yes it has in post 3 and then Bill expands on it in post 7, explaining that volume displacement (Vd) determines SPL not just cone area (Sd). The best place to get Sd is from the manufacturers T/S specs. The numbers given in post 3 look like they are calculated from the nominal diameter of the driver, which is usually the frame size and the cone area is smaller. 176 in² / 1135 cm² for the 15" is in reality more like 137 in² / 880 cm² for a JBL 2226 for example.
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post #14 of 57 Old 06-16-2012, 07:01 PM
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Originally Posted by A9X-308 View Post

Yes it has in post 3 and then Bill expands on it in post 7, explaining that volume displacement (Vd) determines SPL not just cone area (Sd). The best place to get Sd is from the manufacturers T/S specs. The numbers given in post 3 look like they are calculated from the nominal diameter of the driver, which is usually the frame size and the cone area is smaller. 176 in² / 1135 cm² for the 15" is in reality more like 137 in² / 880 cm² for a JBL 2226 for example.

Post #3 doesn't say what I did at all. Post #7 is why I said my way was a good way to ballpark it. Now I have to add yours to the "relative so irrelevant" idea for ballparking - i.e. frame size vs. diaphragm size is probably close enough for most to ignore, since you're usually only concerned with the relative difference between two (or more) arrangements.

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post #15 of 57 Old 06-16-2012, 07:53 PM
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Originally Posted by fjames View Post

Post #3 doesn't say what I did at all. Post #7 is why I said my way was a good way to ballpark it.
There's no need to ballpark anything. Look up Vd on the manufacturer's driver data sheet. As for Sd, in and of itself it's almost meaningless.

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post #16 of 57 Old 06-16-2012, 08:20 PM
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Originally Posted by Bill Fitzmaurice View Post

There's no need to ballpark anything. Look up Vd on the manufacturer's driver data sheet. As for Sd, in and of itself it's almost meaningless.
That's what ballpark means - doing it in your head instead of looking stuff up in data sheets that you probably don't have handy at the time. I presented a simple way to conceptualize the difference between similar speakers with different woofer arrangements, which is what I interpreted the OP to be asking. Something you can do on a showroom floor, or while cruising some site with a gazillion speakers.

As for Sd not meaning anything, in and of itself I suppose you're right. But I thought I made the point that I was assuming a similar Vd for the same Sd within a comparable speaker price range. If you can provide numbers that show commonly used drivers of the same nominal diamteer, as used in similar price point end products have relevantly different Vd, that would be interesting.

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post #17 of 57 Old 06-17-2012, 06:21 AM
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Originally Posted by fjames View Post

If you can provide numbers that show commonly used drivers of the same nominal diamteer, as used in similar price point end products have relevantly different Vd, that would be interesting.
I'll do better than that. Here's a $200 eight inch driver with 5mm xmax;
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-894

And from the same manufacturer a $90 eight inch driver with 12mm xmax:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-920

Excursion is not directly related to either driver size or price. It took me all of two minutes to find these two drivers, and these aren't isolated examples by any means.

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post #18 of 57 Old 06-17-2012, 08:06 AM
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Thanks for explaining all this, Bill. I found it very insightful smile.gif

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post #19 of 57 Old 06-17-2012, 09:28 AM
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Originally Posted by cel4145 View Post

Thanks for explaining all this, Bill. I found it very insightful smile.gif
I didn't yet explain all. One of the most common dual woofer alignments is the MTM, or D'Appolito. It has wider horizontal dispersion than a single woofer speaker with the same cone area. It also has less vertical dispersion, the product of the two woofers being vertically aligned, which reduces early reflections off the ceiling and floor. Well engineered MTMs use the 6dB higher voltage sensitivity of two woofers compared to one to offset the 6dB loss in sensitivity created by the baffle step. Another dual woofer alignment is the x.5, which low passes one woofer to get 6dB additional sensitivity in the lows while only one woofer runs full range, so that there's no reduction in dispersion, lobing or combing. That's usually a moot point with vertically aligned woofers, but it can be critical to get a good result with horizontally aligned woofers, as in center channel cabs.

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post #20 of 57 Old 06-17-2012, 09:35 AM
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Quote:
Originally Posted by HomeTheaterGuy74 View Post

Hi:
I remember my very first pair of speakers - AAL (American Acoustic Laboratories).
They were supposedly the best speakers the "higher-end" store sold at the time.
I don't remember the size of the other components - but the woofer was 15"
They were great sounding speakers.
Today, they don't make speakers like that anymore.
Everything is thin and usually have either a number of 6.5" woofers, or some have 8" woofers (Salon2).
Do more very small (in comparission to 15") woofers really take the place of one larger (12" or 15") woofer confused.gif

No.

Maximum excursion limited SPL from a monopole operating into free space at 1 meter is

102.4dB + 20log(displacement) + 40 log(f) with displacement in m^3

or

102.4dB + 20log(travel) + 20 log(area) with travel in meters an area in meters^2 if you prefer.

Output at the maximum linear excursion into full space for various representative drivers one meter away is as follows at 120, 80, 40, and 20Hz. Many drivers have less excursion and lower output. Subtract 3-5dB getting to your listening position in a typical living and more for a larger space.

You can add 6dB for a floor mounted woofer (as in many 3-ways), 6dB if there are a pair of bass drivers, 10dB for three, and 6dB at the cross-over point to a sub-woofer.

Size Driver Sd (cm^2) x xmax (mm) 120Hz 80Hz 40Hz 20Hz
4 1/2" Seas W12CY001 50 x 3 89dB 82dB 70dB 58dB
5 1/4" Peerless 830873 88 x 3.5 95dB 88dB 76dB 64dB
6 1/4" Seas L16RN-SL 104 x 6 101dB 94dB 82dB 70dB
7" Seas W18EX001 126 x 5 102dB 95dB 83dB 71dB
8.5" Seas W22EX001 220 x 5 106dB 99dB 87dB 75dB
10" Peerless 830452 352 x 12.5 118dB 111dB 99dB 87dB
12" Peerless 830500 483 x 12.5 121dB 114dB 102dB 90dB

Where jazz sounds great at 85dBC average and good recordings have 20dB of dynamic range peaks are hitting 105-107dB a meter from each speaker. Feeding _Take Five_ through 60Hz second order Butterworth IIR low-pass filters I noted right channel low frequency peaks 10dB down from that; although that's still 30 times the acoustic power you can squeeze out of a 6" driver at 40Hz.

In this case it'll take about ten of the 6" Seas to equal one of the 12" Peerless drivers.
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post #21 of 57 Old 06-17-2012, 09:53 AM
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Quote:
Originally Posted by joshua.jones View Post

With woofers, it's all about how much air you move.

Right.
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So, two 12" and three 10" woofers would be about equal.
To push as much air as your old 15", you'd need about FIVE 7" woofers.

No.

1. Driver sizes generally come from the basket dimensions, with the frame taking up a larger fraction of the area on smaller units. You might get 830 cm^2 Sd out of a 15" driver (AE15) and 126 cm^2 Sd out of a 7" driver (Seas W18) with is a 6.6:1 ratio.

2. Geometry allows larger drivers to have more excursion. You might have 18.5mm of xmax out of the AE IB15 versus 5-8 out of a typical mid-woofer like the saes. This isn't quite an apples-to-apples comparision although the difference is 24:1.

This comes partiall from design trade-offs- - sub-woofers and woofers can be built with more excursion than mid-woofers because the high-frequency roll-off from voice coil inductance is beyond their pass-band, although ultimately geometry still limits you. I'm not aware of any 6" drivers which go beyond 12.5mm (Adire Extremesis), although there are 15" drivers that make it past 35mm (Adire Tumult).
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post #22 of 57 Old 06-17-2012, 10:03 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The main reason for using multiple smaller drivers rather than one larger driver is the wider dispersion that the smaller drivers give.

At low frequencies it doesn't matter. A 15" driver is still acoustically small compared to an 11' 100Hz sound wave and isn't costing you anything compared to a couple dozen 6" drivers.

Once you're building 3-way speakers the main reason is to keep the cabinet thinner and easier to sell to a market looking for contemporary aesthetics.
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post #23 of 57 Old 06-17-2012, 10:16 AM
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Originally Posted by chikoo View Post

There is no replacement for displacement.
To drive large & heavy 15" woofers would be a huge task for the home avr.

Not at all. A 4 cubic foot speaker built with a 15" woofer can take 1/10th the power to run at a given SPL as a .5 cubic stand mounted monitor with a 6" bass driver and the same bass extension. That's _much_ easier. You could even get more than ample volume out of the bigger speaker with a 16 Ohm impedance.

It's often much harder to drive a couple of 5-6" drivers where the speaker maker has allowed the impedence to drop so they don't loose sensitivity. I've owned "8 Ohm compatible" speakers which dropped into the 3 Ohm range.

This ignores the dynamic nature of music and home theater (where you're likely to have listening levels that produce avereage power requirements that are a smaller fraction of a Watt than music) that keep average power dissipation low and "too hard for a receiver to drive" more of a marketing mantra.

I've built amplifiers with match-box sized heat sinks and power transformers that fit in the palm of your hand that peak somewhere past 250W but should manage manage only 10-20W in FTC tests. I've never driven one to thermal shutdown.
Quote:
Which is why it makes sense to have a 10" active subwoofer in it's place. This allows listening down low even without cranking up the volume across all frequencies.

Electronics providing a bass boost are trivial to implement and have been around for decades in the form of loudness controls. Lexicon was putting SPL dependent implementations in their pre-amps 20 years ago and such schemes have become mainstream in AV receivers.

The benefits there over trying to do the same thing with a sub-woofer are that you can have the required boost beyond the sub-woofer cross-over and have the process automated so that it's there at low levels and automatically gone at higher listening levels.beyond the sub-woofer cross-over and have the process automated so that it's there at low levels and automatically gone at higher listening levels.
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post #24 of 57 Old 06-17-2012, 10:52 AM
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Originally Posted by Drew Eckhardt View Post

At low frequencies it doesn't matter.
Who said anything about low frequencies?
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Once you're building 3-way speakers the main reason is to keep the cabinet thinner and easier to sell to a market looking for contemporary aesthetics.
The reason for the move to narrower cabs is the same as that for the move to smaller drivers, dispersion.
For those interested in delving deeper into the hows and whys of speaker design this is a very good place to start:
http://techtalk.parts-express.com/showthread.php?t=219617

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post #25 of 57 Old 06-17-2012, 12:29 PM
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Originally Posted by fjames View Post

Post #3 doesn't say what I did at all. Post #7 is why I said my way was a good way to ballpark it. Now I have to add yours to the "relative so irrelevant" idea for ballparking - i.e. frame size vs. diaphragm size is probably close enough for most to ignore, since you're usually only concerned with the relative difference between two (or more) arrangements.
I expect anyone older than about 10 to be able to determine the relative area of two circles of different diameter.

The Sd varies considerably between drivers of even the same 'nominal' frame size, so two 18" units may not have anywhere near the same Sd, let alone Vd, which is the important part.
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post #26 of 57 Old 06-17-2012, 02:17 PM
 
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[/QUOTE]The reason for the move to narrower cabs is the same as that for the move to smaller drivers, dispersion. [/quote]

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post #27 of 57 Old 06-17-2012, 04:02 PM
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Quote:
Originally Posted by A9X-308 View Post

I expect anyone older than about 10 to be able to determine the relative area of two circles of different diameter.
The Sd varies considerably between drivers of even the same 'nominal' frame size, so two 18" units may not have anywhere near the same Sd, let alone Vd, which is the important part.

Is everyone from The Outback so RUDE? It's Ok to have a different opinion but you sir have poor manners. On another thread you TOLD me You don't care what Paul Kipsch had to say... like you were schooling me and you were smarter then him and Me. Most of us here are grown Men and act like it. Do try to express your self in a more polite manner and some of your comments will be taken better. You come as a KNOW IT ALL on about every post I have seen from you.

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post #28 of 57 Old 06-17-2012, 06:50 PM
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Long ago I wanted large woofers, big, big, bigger. Finally I found myself with a Definitive Technology PF18TL subwoofer my brother had the PF15TL subwoofer. I ran the sub with Paradigm Studio 20s. He ran his system with Definitive Techs BP10s. I wanted to compare are speakers because we were thinking of a trade. After some time I found the Paradigm Studio 20s a tad bright and fatiguing. Now don't get me wrong those are accurate first rate speakers. It may have been me (long story about how the mind....). A little back ground. I was running Paradigm 7se speakers when I saw the Sub on sale at Pecars Audio of Rochester Michigan. I called, had them hold one and drove fast to the store, I bagged one a $1000 18" sub for $500! That PF18TL sub could play much louder and cleaner than the PF15TL in the 20-30hz range. There was a night and day difference. Both had the same amp but the 18" woofer was more efficient and went about 10Hz deeper versus the 15". On paper Definitive Technology's PF15TL and PF18TL subs looked close. But the PF18TL is a sleeper and now rare to find. It measures flat to 23Hz in my living room, still usable at 20Hz about -5dB down and shaking the whole house, knocking pictures of shelves! The PF15TL was flat to about 33Hz.

Anyways I wanted to hear his BP10s so I took my Paradigm Studio 20s to his house and hooked it up next to the BP10s and with his PF15TL sub. The BP10 had a more natural high end IMO, not as fatiguing. The midrange of both were smooth, smooth, smooth. The main difference was the sound stage. The BP10s had a more open bigger sound, but accurate.

And now the shocker. The BP10s could play deeper and cleaner than the 15" PF15TL sub. I was really surprised and impressed with the BP10s. I did not expect them to dive into the 20-30Hz range so clean and strong. Now of course my PF18TL was better than the BP10s but for music you do not need a sub with the BP10s. I did trade with him.

Lets look at it this way. Lets pretend two BP10s are two mini monitors with one sub, the sub has four 6.5" woofer in a well designed enclosure. This is equal to subwoofer with a 13" woofer in well tuned enclosure. The bass port on the ground augments output as does the double drivers in each speaker. This is why the BP10s easily cleaned the floor in the sub bass region versus the PF15TL, however the PF15TL could play just a good bit louder in the 40-120Hz range.

So this is why many Paradigm speakers, Definitive Technology, and others use multiple smaller drivers like two 8" drivers per speaker, that's equal to a sub with a woofer bigger than 15"s. This is also why the bass is clean and tight in such configurations. The dual drivers just keep clean and fast with help from the well tuned cabinets. Done right there is no need for a large driver for most people, except for rock concert volume, very large rooms, and yes for superior deep bass (lower than 25Hz). So yes DT power towers with larger woofers will blow you out the room! But don't think smaller drivers can't go deep, clean and shake a moderate sized room.
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post #29 of 57 Old 06-18-2012, 05:52 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

One of the most common dual woofer alignments is the MTM, or D'Appolito. It has wider horizontal dispersion than a single woofer speaker with the same cone area. It also has less vertical dispersion, the product of the two woofers being vertically aligned, which reduces early reflections off the ceiling and floor

This somewhat of a tangent question. How is it possible having two woofers in a symmetrical configuration can widen horizontal dispersion over a single woofer? I can understand that destructive interference will reduce the vertical dispersion while the horizontal remains the same thus "squeezing" down the listening window. I don't understand how the window can be stretched horizontally just by adding another woofer. Could you please explain? Thanks.
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post #30 of 57 Old 06-18-2012, 06:59 AM
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Quote:
Originally Posted by Ron Alcasid View Post

This somewhat of a tangent question. How is it possible having two woofers in a symmetrical configuration can widen horizontal dispersion over a single woofer? I can understand that destructive interference will reduce the vertical dispersion while the horizontal remains the same thus "squeezing" down the listening window. I don't understand how the window can be stretched horizontally just by adding another woofer. Could you please explain? Thanks.
Ron, it's two smaller woofer vs a single larger woofer. The sum of the cone area of the two smaller equaling the single larger woofer.

The smaller woofers will have better dispersion than the larger woofer.

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