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Quad 8" sealed sub...

post #1 of 44
8/21/12 at 12:04pm
Thread Starter 
Hi all, I just wanted to let you guys know about the new project I am starting. I have read and learned so much on here that I thought you might like to know that your efforts in education and information sharing have not gone to waste.

I am slowly building up my first real HT system Started by scoring a deal on a new Pioneer VSX-1022 receiver. Next I am upgrading my crappy RCA 32" LCD tv to a Samsung 51" plasma. Front stage is currently a pair of JBL Control 25s for the L+R and a pair of Klipsch Quintet sats that I have wired in parallel for the center channel. They are placed one on each side of my receiver for now until the new display gets here. No rear surround as of yet but I will probably go with the Monoprice 4929 8" 2way in ceiling for budget reasons. Only doing 5.1 at this time.

So on to the subwoofer. What I have is 4 CDT Audio MS-80 8" subwoofers that were intended for car audio. You may be familiar with these but they were high end SQ subs about 10 years ago. Made for a small sealed enclosure with .25-.45 ft^3 airspace and very efficient (90db). Here are all of the specs I have on them, which isn't much.

MS-80
8" Minibox Subwoofer
Power handling: 100/200
Frequency response: 30Hz-500Hz
Sensitivity: 90dB
Box volume:Sealed Airspace .25-.45 cubic feet

That's it. I even email CDT for the T/S parameters and they don't have them. So I have all intentions of measuring these myself when I get a chance but CDT support forwarded my email to someone internally who suggested that for HT use I should use 4 of the 8" MS-80 subs in a single enclosure with 2.0 cu ft airspace. They are 4 ohm drivers so I can do a series/parallel to present 4Ohms to my amp which is rated at 300 watts RMS into 4 Ohms.

For spousal approval I need to buld a shallow downfiring enclosure that will fit UNDER the coffee table that we are using as an AV stand. See pic. I have 10" clearance under the table, so an enclosure that is 8" high x 28.75" wide x 21" deep (exterior dimesions, 3/4" MDF) gives me 1.999 cu ft volume with enough clearance for 1.5" feet.

Attached pic shows one 8" in a test box I had laying around and the table that the new enclosure will go under. You can also see one of the Klipsch Quintet sats and the Pioneer. (Please ignore the 10" Alpine sub that came out of my Jeep, I was just curious smile.gif I'm fairly impressed with just a single 8" in a non optimum box (it's too big by 2x) so have decided to go forward with the real deal. Also ignore the hanging wires, we just moved back into the house last week after a complete renovation and I haven't gotten around to snaking the cables into the walls yet.

I'll try to update as I go along with build pics.

Any suggestions about anything feel free to chime in.

TIA, K subsmall.jpg 31k .jpg file
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post #2 of 44
8/22/12 at 8:24pm
Years back I read an interview article where Jim Fosgate had been working on improving his bass in the listening room. Now for those who say Jim who, well he was the inventor of Prologic II which Dolby was happy to purchase. Anyway, Jim had his subs running with 15 inch drivers. He was unhappy with the sound. He felt that the drivers were distorting the bass due to the wight of the speakers not being able to come to rest before the next note hit them. The drivers were still moving from the last note when the new one hit it. He replaced the 15s with 12s. Better but not perfect. Tried 10s. Better but not to his liking. Each time he increased the number of drivers to have the same amount of surface driving bass into the room but he still did not like that the mass of the drivers were causing the bass to not be to his liking. Flabby was his description if I remember right. WIth his experience with sound quality I would say he has the ears to decide this.

Then he went with multiple 8 inch drivers. Finally he had the sound he wanted. The drivers were of low enough mass to recover or stop moving from previous signals and deliver the next signal with better clarity. Flabbiness was gone. His theory was smaller drivers can deliver good bass, you just have to have enough drivers. Back in the day when I first started looking into the hobby of speaker building a book I had bought equated that five 8 inch drivers had the same surface area of 2 15 inch drivers. I never did the math on that but I do believe the idea it was trying to put across is smaller can deliver the same results if you have enough of them.

Now I know there has been some discussion over the years of 8 inch drivers just not delivering what 15s or even 18s can deliver. But I kind of lean toward what Jim Fosgate has said. To me he is the expert when it comes to sound. His work has led to what we all enjoy today in our personal theater rooms. We enjoy the fruits of his experiments and inventions. If he says multiple 8 inch drivers can sound better than single 15 inch drivers, I believe him.

Presently I have two DIY 12 inch ported drivers in my theater room. I think they sound great. I have days though, I want to buy a bunch of 8 inch drivers and get to work on new sub-woofers. I figure 6 in each enclosure would be pretty good bass.
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post #3 of 44
8/22/12 at 8:49pm
The myth of smaller drivers reacting faster than large.... sigh... the myth lives on. rolleyes.gif
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post #4 of 44
8/22/12 at 11:22pm
Quote:
Originally Posted by awblackmon View Post

Years back I read an interview article where Jim Fosgate had been working on improving his bass in the listening room. Now for those who say Jim who, well he was the inventor of Prologic II which Dolby was happy to purchase. Anyway, Jim had his subs running with 15 inch drivers. He was unhappy with the sound. He felt that the drivers were distorting the bass due to the wight of the speakers not being able to come to rest before the next note hit them. The drivers were still moving from the last note when the new one hit it. He replaced the 15s with 12s. Better but not perfect. Tried 10s. Better but not to his liking. Each time he increased the number of drivers to have the same amount of surface driving bass into the room but he still did not like that the mass of the drivers were causing the bass to not be to his liking. Flabby was his description if I remember right. WIth his experience with sound quality I would say he has the ears to decide this.
Then he went with multiple 8 inch drivers. Finally he had the sound he wanted. The drivers were of low enough mass to recover or stop moving from previous signals and deliver the next signal with better clarity. Flabbiness was gone. His theory was smaller drivers can deliver good bass, you just have to have enough drivers. Back in the day when I first started looking into the hobby of speaker building a book I had bought equated that five 8 inch drivers had the same surface area of 2 15 inch drivers. I never did the math on that but I do believe the idea it was trying to put across is smaller can deliver the same results if you have enough of them.
Now I know there has been some discussion over the years of 8 inch drivers just not delivering what 15s or even 18s can deliver. But I kind of lean toward what Jim Fosgate has said. To me he is the expert when it comes to sound. His work has led to what we all enjoy today in our personal theater rooms. We enjoy the fruits of his experiments and inventions. If he says multiple 8 inch drivers can sound better than single 15 inch drivers, I believe him.
Presently I have two DIY 12 inch ported drivers in my theater room. I think they sound great. I have days though, I want to buy a bunch of 8 inch drivers and get to work on new sub-woofers. I figure 6 in each enclosure would be pretty good bass.

Mr. Fosgate was smart enough to know better rolleyes.gif Fast drivers are called tweeters. When will this myth go away?
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post #5 of 44
8/23/12 at 12:21am
awb, very interesting post.

i suspect that there are many things getting mixed up though.
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post #6 of 44
8/23/12 at 10:18am
Perhaps it is a myth but he isn't the only source of this myth that uses multiple drivers and claims better bass due to it. Say or do what you will, but I grew up with the name Jim Fosgate at every turn of my life. So I kind of have a soft place for him. Especially he and I being somewhat the same age. I suspect there may be a lot of changes in the capabilities of newer equiptment, but I know more about older equiptment. I know it was a lot easier to install a stereo system then than a computerized AV system now. Analog had more information than mp3 carries. Sound changes. Ideas change, equipment changes. What may have worked years ago with older stuff, may be a new game today. Still, I have the temptation to try it out for myself. I suspect I may well like what I hear, myth or not.smile.gif

I wil be really interested in your project KBlair. Keep us posted.
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post #7 of 44
8/23/12 at 10:30am
Hey, most of us know the name Fosgate and I'm well familar with his work.

However, multiple drivers equally better bass? Absolutely! I doubt anyone around here would argue against that. But.... larger drivers = sluggish bass and smaller drivers = fast bass is just plainly false. I'm sorry but there is WAY more to it that smaller, lighter cones being "faster". It's pretty laughable.
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post #8 of 44
8/23/12 at 12:00pm
Thread Starter 
I did the math and the four 8" drivers I have is equivalent to a single 16" driver (which no one makes), so 5 8" drivers might be close to 2 15" drivers.

I'm not schooled on all the theory but from personal experience I know that I like multiple smaller drivers as opposed to one large driver. Back in the day when I was playing in the 12 volt arena I always has multiple 8s or 10s where as most of the other guys had 12s or 15s. They were going for SPL and I was more interested in sound quality.

But I do have a question. Say you have two 4 Ohm drivers in parallel vs one 8 Ohm driver. The amp still sees an 8 Ohm load, still delivers the same amount of power, but it is split across the 2 drivers. How do the drivers physically react to this? If each driver only has to move half as much (because there are two), then physics dictates that they will react faster than a single driver moving twice as much. I don't know if that is true but logically it makes sense. I do know that I started playing bass on a 2x15 rig and once I heard a 8x8 rig I immediately sold my 2x15 cabinet. I guess I like tighter and more accurate bass because that's the way multiple small drivers sound to my ears.

I'm hoping that this project will produce a more musical sub than is normal for an off the shelf ported HT 12" ported sub and I believe it will but we will find out.

I'll post some more pics of the individual drivers in a bit and maybe someone can give me some pointers as to how to go about measuing the T/S specs. I've read up on the voltmeter method and the software method but have yet to try it.
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post #9 of 44
8/23/12 at 1:23pm
Quote:
Originally Posted by KBlair1701 View Post

I'm not schooled on all the theory but from personal experience I know that I like multiple smaller drivers as opposed to one large driver.

You're mistaken associating your preference for what you've experienced with driver size.

If you did prefer it, and it was because of the driver size, it's what's called expectation bias. Or, if you preferred it, it was due to other factors affecting performance. Or, most likely, both reasons.

One thing is certain, a smaller cone size only benefited the scenario psychologically.

Quote:
Originally Posted by KBlair1701 View Post

Say you have two 4 Ohm drivers in parallel vs one 8 Ohm driver. The amp still sees an 8 Ohm load, still delivers the same amount of power, but it is split across the 2 drivers. How do the drivers physically react to this?

Two 4 ohm drivers in parallel is 2 ohms. In series, they'd result in 8 ohms.

Now, you're getting to the meat of things. Splitting the drive across two woofers, given the same power level, you'd increase the SPL by 3dB. That would be two four ohm drivers in series, compared to an 8 ohm driver alone. Now, if the amp has the stability and overall capability, if you parallel two drivers across it you can yield up to 6dB increase, due to the manner in which power is derived (beyond this discussion really).

Keep in mind, double the power = 3dB increase, double the drivers w/same power =3dB increase, double power and double speakers 6dB increase.

Quote:
Originally Posted by KBlair1701 View Post

If each driver only has to move half as much (because there are two), then physics dictates that they will react faster than a single driver moving twice as much. I don't know if that is true but logically it makes sense.

Nope, actually they slow down. Any increase in driver area for a given SPL, given frequency, lowers speed. If a driver has to complete a 20hz cycle, and it's load is halved thus it must displace half as much air, it slows down. Conversely, as you put a 41hz tone thru your rig, turning the volume up, the driver speeds up to maintain freq, yet increase displacement (SPL).
Quote:
Originally Posted by KBlair1701 View Post

I do know that I started playing bass on a 2x15 rig and once I heard a 8x8 rig I immediately sold my 2x15 cabinet. I guess I like tighter and more accurate bass because that's the way multiple small drivers sound to my ears.

That's cool, but understand the entirety of the factors influencing things.





Welcome to AVS, slow down a bit and enjoy the wealth of info that abounds.

Good luck
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post #10 of 44
8/23/12 at 1:50pm
Quote:
Originally Posted by KBlair1701 View Post

I did the math and the four 8" drivers I have is equivalent to a single 16" driver (which no one makes), so 5 8" drivers might be close to 2 15" drivers.

No. No way. Not even close. A single 15" maybe. Not two.

Like FOH said, if you half the excursion (woofer travel) it actual is slowing down. If you want to speed up the driver, simply make it produce more SPL or increase the frequency or both.

I'm sorry but comparing a 2x15" setup to 8x8" setup is not apples to apples. There are MANY factors that would contribute to a percieved SQ difference. One of them, as FOH mentioned, is a kind of expectation of SQ. The rest has to do with so many things your head will spin. I won't get into it now but maybe someone else will for me. smile.gif Welcome to AVS. You have much to learn and this is a very advanced area of the forum. Good luck!
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post #11 of 44
8/23/12 at 2:10pm
Gosh, I've been away from this stuff for so long I don't even remember all the verbiage. Anyhow the MMS/bl/cms relationship to bass quality is known and it just so happens that lots of smaller drivers usually get you on the happy side of that relationship. But big drivers can also get you there just fine. Either way, keeping travel down might be the best idea due to the increase in distortion with increased travel. Nothing new here.
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post #12 of 44
8/23/12 at 6:12pm
Quote:
Originally Posted by Looneybomber View Post

Either way, keeping travel down might be the best idea due to the increase in distortion with increased travel. Nothing new here.

That's worthy of a +1

That's the entire point. The linear envelope of travel that exists in any driver. Both magnetically, and suspension wise, the linear aspect is associated with less travel.
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post #13 of 44
8/23/12 at 8:09pm
Spreading the bass duties across more and more motors is almost an unqualified great idea. No need to reduce cone area per driver in the process though. People may like the result of doing the former and confound it with the latter.
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post #14 of 44
8/24/12 at 6:28am
Thread Starter 
Thanks all, some great discussion here. Sorry I had a brain fart on the series/parallel math. Had just gotten off an 18 hour shift when I wrote that.

I'm just working with what I have due to budget reasons, but if I have four 8" drivers then why not, right?

Driver pics coming soon, maybe I can find time to measure the T/S this weekend. It's been years since I've done any box modeling but I have already downloaded all the free software I can find. Once I get the T/S and my room measurements does someone want to help me with that? I can't go much larger than 2.0 ft^3 but I can go smaller or possibly go ported (though the manufacturer says these are for sealed). If I could I would do 4 separate enclosures and spread them out, but I'm not the only one with a vote on what gets built IYKWIM.
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post #15 of 44
8/24/12 at 7:13am
Thread Starter 
Driver pics as promised




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post #16 of 44
8/24/12 at 8:33am

Multiple lower excursion, lower diameter woofers may cost significantly less however, which would be a benefit.

 

Not sure how different transient response would be between lots of smaller woofs v/s one larger woof so long as both were well within x-max.  Linear range is relative and no driver is perfectly linear, so it really should be boiled down to two direct comparisons for any real conclusion to be made.

 

BL an Le are bigger factors than Mms, however Mms can dictate BL requirements which in turn drives(indirectly) Le(typically) kinda cyclical.

 

This is makes sense to me.

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post #17 of 44
8/24/12 at 7:21pm
smile.gif

OK, the whole fast/slow bass thing was coined by idiots (audio reviewers) who were grasping for a reason why dynamic woofers with high mass didn't mate well with low mass electrostatic speakers. Mostly, the fault lay with ESL's that needed to crossover too high and woofers that had too shallow a slope on their low pass filters.

I have a portable sub design that uses eight 8" Dayton subs and is the size of a large suitcase (hence, the suitcase sub). Dimensions are approx. 13"h x 17"w x 24"d. It's a sealed, bipolar design with 4 woofers on each side in a push/pull config. The design is really for bass/keyboard/PA use, but several of these could be quite potent in an audio system. The system is sealed and would weigh in around a 100lbs. and be easy attach to a luggage style dolly.

My concept was to get true, high fidelity bass from a small sub. It needs to have high output down to 31hz (low B on a 5 string bass), but no lower. Due to its small size, efficiency isn't astounding at 31hz, but with the massed, high excursion drivers, it should be able to very cleanly reproduce that low B at 105db (or a little more). The downside is that you need to EQ this baby and have a lot of power to drive it. A Digmoda plate amp with two 500 watt amps would be perfect. Efficiency is sacrificed for low distortion and low bass response.

A couple of these and a Mackie SRM-450 would make for an awesome bass or keyboard rig.

So why am I on about this here? Using massed small sub drivers has several advantages over a single, large driver such as:

• Drastically lower driver mass - this means much less stored energy in the diaphragm which means that the driver starts & stops much more easily - use of a servo system to damp the cone is less necessary (low stored energy is as important as steady state harmonic distortion in how a speaker driver sounds)

• The composite magnet strength can be much greater

• There's greater flexibility in cabinet design

• Greater linear excursion

But, hey, don't take it from me. One of the most powerful, high fidelity subs available is Paradigm's Sub 2 which uses six 10" woofers.

The 8 drivers in the suitcase sub would be equivalent in driver area to two 15"ers while having 1/4 the moving mass and and 50lbs. of magnets. A 15" woofer with only 66 grams of moving mass, an Xmax of 36mm and a 25 lb. magnet structure doesn't exist but does with four 8"ers.

So what's the big down side? Cost. The cabinet is more complex and costly to build and the drivers will run you a lot more. An active suitcase sub would run about $2500 to produce.

jeff
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post #18 of 44
8/24/12 at 9:00pm
Jeff, moving mass doesn't impact the perfomance in the manner in which you think.

The performance of the Paradigm isn't becuse it used mutiple small drives.
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post #19 of 44
8/24/12 at 9:06pm
Quote:
Originally Posted by jeffhenning 
The 8 drivers in the suitcase sub would be equivalent in driver area to two 15"ers while having 1/4 the moving mass and and 50lbs. of magnets. A 15" woofer with only 66 grams of moving mass, an Xmax of 36mm and a 25 lb. magnet structure doesn't exist but does with four 8"ers.
Your math is a bit puzzling, especially concerning this 8" sub with 36mm xmax you speak of.

I love all the oversimplifications that never cease re driver design. A bit like insisting the Toyota tercel is the best race car because it is light, thus can stop and start quicker. smile.gif
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post #20 of 44
8/24/12 at 11:51pm
i suspect that he didn't compensate for the difference in sd. to a first order approximation, 4x8 is about equal to a 1x15 in cone area, so 4x8" with 8mm xmax will be roughly the same as 1x15" with 8mm xmax...not to say that there are not other effects that make the 8" array better or worse...there can be.

op, the smallish drives that you have there aren't going to perform nearly as well in your home theater room as they would in your car. car cabins are very small and bass loading is very high. the bass won't be anywhere near as much bass in your home as in your car.
Edited by LTD02 - 8/25/12 at 12:04am
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post #21 of 44
8/25/12 at 4:06pm
Thanks for all of your lack of understanding.

True story:
I ran this design and 2 other speaker designs past Don Keele (inventor of the CBT and constant directivity horn, to name a few patents he holds). He told me to quit my job as a web developer and become a loudspeaker designer.

No BS.

#1: Moving mass is a huge consideration in any loudspeaker driver when it comes to it's design. Yes, you can alter the suspension design a fair bit to idealize the performance for a given design/size/type, but the bottom line is this: the lower the moving mass the less energy it takes to to start the drive moving and the less it takes to stop it. Of the designs you can actually fit in a normal room, the best and cleanest overwhelmingly use servo systems to damp the voice coil movement so that it more closely duplicates the input signal and relies less on the air spring effect of the cabinet and suspension to control the woofer. The downside of using only the cabinet/suspension to control the woofer is that there are limits to what they can do to control the cone motion. No matter how great the design is in its ability to cope with controlling and damping the cone's various movements, it's a passive, physical system. What is input to it will never closely resemble it's output at high volume. If it was possible to make an 18" woofer that had close to infinite stiffness and a mass lower than the air it was moving, subs would be drastically cleaner than they are now. Until then, we have servo systems from Paradigm, Velodyne and Rythmik to lead the way.

#2: The Paradigm sub I mentioned lends a small part of it's performance to its use of smaller, massed drivers, but the other consideration that you missed when I was talking about the benefits of massed smaller drivers is the form factor. The Sub 2 has six 10" woofers which is equivalent in radiating surface to about three 15"ers, but in a drastically smaller package. Those drivers are custom made for the task and, even then, a digital/servo system is used improve performance. My sub is smaller, lighter and designed only to perform to 31hz, not 7hz. At that, it will kick ass.... not like the Sub 2, but for less money and with much less back strain when you need to move it (remember, this is for portable music systems).

#3: For the slow people in the crowd, comparing one 15" to the equivalent, composite specs of four 8" woofers is quite valid. Bass reproduction is all about moving air. The more you can move, the greater the efficiency. The composite Xmax of the 4 drivers I mentioned is 36mm. That's a hell of a stroke and greater than what can be attained by any single 15". Basically, no woofer can do that (and you probably wouldn't want it to). The moving mass isn't additive like Xmax is so it's not a factor and stored energy in each driver is much lower. The force of the magnets probably doesn't sum like the Xmax, but, given that most woofer lines use the same magnet regardless of the size of the cone, there will be some summation of the magnet's effect on the drivers efficiency and control. How much, I don't know.

So, in closing, all of this made a whole lot of sense to genius who has a bunch of loudspeaker patents to his credit, has designed the most radically new speaker design in decades (the CBT-36) and has about 50 years in the field. You'll have to excuse me if your criticisms don't phase me.

All the best,
jeff
Edited by jeffhenning - 8/25/12 at 4:17pm
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post #22 of 44
8/25/12 at 7:19pm
"The composite Xmax of the 4 drivers I mentioned is 36mm. That's a hell of a stroke and greater than what can be attained by any single 15"."

you are confusing excursion with swept volume. swept volume is what sets the spl. volume is total radiating area multiplied by point to point excursion.

one 8" driver has to move about 4 times as far in order to produce the same spl as a 15" driver, because it has 1/4 the radiating area.

four 8" drivers have about the same cone area, so have to move about the same excursion as a 15" driver.
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post #23 of 44
8/25/12 at 7:32pm
"Moving mass is a huge consideration in any loudspeaker driver when it comes to it's design. Yes, you can alter the suspension design a fair bit to idealize the performance for a given design/size/type, but the bottom line is this: the lower the moving mass the less energy it takes to to start the drive moving and the less it takes to stop it."

that is how i used to think about it, but it appears to have been incomplete. one must also consider the electro-magnetic domain. there are some effects that "resist" the change in the electro-magnetic field that is trying to "start and stop" the cone, just as mass does in your physical inertia-only theory.
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post #24 of 44
8/25/12 at 7:41pm
Quote:
Originally Posted by jeffhenning 
Thanks for all of your lack of understanding.

Don Keele… told me to quit my job as a web developer and become a loudspeaker designer.

#3: For the slow people in the crowd...

So, in closing, all of this made a whole lot of sense to genius who has a bunch of loudspeaker patents to his credit, has designed the most radically new speaker design in decades (the CBT-36) and has about 50 years in the field. You'll have to excuse me if your criticisms don't phase me.

You botched basic arithmetic and are at best acknowledging half the physics at play in a driver, so you'll have to excuse me if your snippy word play and being knighted by a genius don't impress me.
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post #25 of 44
8/25/12 at 8:36pm
Quote:
Originally Posted by jeffhenning View Post

The composite Xmax of the 4 drivers I mentioned is 36mm. That's a hell of a stroke and greater than what can be attained by any single 15"
That's not how it works. You don't add the xmax of the four drivers to get a 36mm total. You add the displacement (Vd) of the four drivers to get a system total. The Vd of an eight with 9mm xmax is about 200cc, making the Vd of four of them 800cc. That's equalled by a single fifteen with 9mm xmax.
Quote:
#1: Moving mass is a huge consideration in any loudspeaker driver when it comes to it's design.
Only with respect to high frequencies, and then only as it applies to transient response. In the lows, not so much. For instance, a fifteen using the same motor as an eight will have higher sensitivity than the eight, even though the Mms of the fifteen may be four times that of the eight. That's due to the inherent low electrical to acoustical conversion efficiency resulting from the very low impedance of air versus that of a voice coil. A larger cone improves the impedance match, increasing low frequency sensitivity despite the higher cone mass.
Quote:
Multiple lower excursion, lower diameter woofers may cost significantly less however, which would be a benefit.
For equal system Vd multiple drivers cost more, not less, as most of the cost of the driver is in the motor. That's the number one reason why fewer larger drivers are used as opposed to more smaller drivers.
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post #26 of 44
8/25/12 at 8:49pm
Quote:
Originally Posted by jeffhenning View Post

Thanks for all of your lack of understanding.
True story:
I ran this design and 2 other speaker designs past Don Keele (inventor of the CBT and constant directivity horn, to name a few patents he holds). He told me to quit my job as a web developer and become a loudspeaker designer.
No BS.
#1: Moving mass is a huge consideration in any loudspeaker driver when it comes to it's design. Yes, you can alter the suspension design a fair bit to idealize the performance for a given design/size/type, but the bottom line is this: the lower the moving mass the less energy it takes to to start the drive moving and the less it takes to stop it. Of the designs you can actually fit in a normal room, the best and cleanest overwhelmingly use servo systems to damp the voice coil movement so that it more closely duplicates the input signal and relies less on the air spring effect of the cabinet and suspension to control the woofer. The downside of using only the cabinet/suspension to control the woofer is that there are limits to what they can do to control the cone motion. No matter how great the design is in its ability to cope with controlling and damping the cone's various movements, it's a passive, physical system. What is input to it will never closely resemble it's output at high volume. If it was possible to make an 18" woofer that had close to infinite stiffness and a mass lower than the air it was moving, subs would be drastically cleaner than they are now. Until then, we have servo systems from Paradigm, Velodyne and Rythmik to lead the way.
#2: The Paradigm sub I mentioned lends a small part of it's performance to its use of smaller, massed drivers, but the other consideration that you missed when I was talking about the benefits of massed smaller drivers is the form factor. The Sub 2 has six 10" woofers which is equivalent in radiating surface to about three 15"ers, but in a drastically smaller package. Those drivers are custom made for the task and, even then, a digital/servo system is used improve performance. My sub is smaller, lighter and designed only to perform to 31hz, not 7hz. At that, it will kick ass.... not like the Sub 2, but for less money and with much less back strain when you need to move it (remember, this is for portable music systems).
#3: For the slow people in the crowd, comparing one 15" to the equivalent, composite specs of four 8" woofers is quite valid. Bass reproduction is all about moving air. The more you can move, the greater the efficiency. The composite Xmax of the 4 drivers I mentioned is 36mm. That's a hell of a stroke and greater than what can be attained by any single 15". Basically, no woofer can do that (and you probably wouldn't want it to). The moving mass isn't additive like Xmax is so it's not a factor and stored energy in each driver is much lower. The force of the magnets probably doesn't sum like the Xmax, but, given that most woofer lines use the same magnet regardless of the size of the cone, there will be some summation of the magnet's effect on the drivers efficiency and control. How much, I don't know.
So, in closing, all of this made a whole lot of sense to genius who has a bunch of loudspeaker patents to his credit, has designed the most radically new speaker design in decades (the CBT-36) and has about 50 years in the field. You'll have to excuse me if your criticisms don't phase me.
All the best,
jeff

gumbel.bmp
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post #27 of 44
8/25/12 at 9:00pm
The myth is strong with this one...
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post #28 of 44
8/26/12 at 4:43am
Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Multiple lower excursion, lower diameter woofers may cost significantly less however, which would be a benefit.
For equal system Vd multiple drivers cost more, not less, as most of the cost of the driver is in the motor. That's the number one reason why fewer larger drivers are used as opposed to more smaller drivers.

 

 

Only Sithes deal in absolutes, youll kindly notice I used the word may.  For example, the TC Ultra is a great driver and 18" but real estate not at play I'll take The Dayton DVCs 15s and quickly out perform the 18 with smaller drivers and cheaper, especially considering power cost.

 

So, multiple smaller woofers may cost less and outperform larger ones, now whether you allow it in your universe or not, it is possible in ours, apparently.

 

OP, looks like you've got the woofers already, so technically they cost nothing, build it, measure it, and post your results.  It might be possible for you to get to 30Hz flat with room gain, I'd be surprised if you didn't.

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post #29 of 44
8/29/12 at 6:24pm
I risk showing how very little i know by commenting in this thread, but I love how humble pie tastes and I'm quite used to it so here goes...

I think there's a bit of room for truth in each side's arguments.


To state dogmatically that an 8" driver is faster/more accurate than a 15" driver is clearly not true as, for example, there are many 15" subs out there that are audibly more accurate than certain 8" subs. However...

To state dogmatically that smaller does NOT = faster is also not an all-encompassing truth, because the laws of physics when it comes to stopping an object in motion relative to its mass can not be argued.



So I believe the truth lies somewhere in between. And so this is what I think (albeit with no fancy references or charts or quantum physics formulas to back it up) to be the best way to describe the relationship between driver size/cone mass and accuracy:

Regarding two drivers of different size but constructed of the exact same materials, the smaller of the two will be more accurate while the larger will produce more SPLs when alternating between frequencies, given the same amount of driver travel. Adding multiples of the smaller driver will add SPL while retaining the advantage of accuracy.



To put that into real world application, two 13" drivers will most likely give you the same SPLs but better accuracy as an 18" from the same manufacturer and same product line. However, assuming those same two 13" drivers would be more accurate than an 18" driver from a different manufacturer would not be wise.
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post #30 of 44
8/29/12 at 7:46pm
Quote:
Originally Posted by below90hz View Post

To state dogmatically that smaller does NOT = faster is also not an all-encompassing truth, because the laws of physics when it comes to stopping an object in motion relative to its mass can not be argued.
In this case the cone mass is moot. The force exerted by the magnet/voice coil is immense relative to the mass of the cone, so much so that it totally dwarfs and renders insignificant cone inertia forces, no matter how large the cone is. By comparison consider a 10,000 lb thrust rocket engine pushing a 10 pound payload. Even quadrupling the payload weight isn't going to significantly alter the acceleration of the rocket.
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