Woofer technology - isn't it surprising...

[Gruuve]

...that there's really been no revolutionary technology introduced over the years? Think about it for a minute...for highs, the revolutionary introduction was the tweeter...essentially a piece of material that vibrates at high frequencies. Luckily some out-of-the-box thinking individual made the connection between this vibrating crystal and a small speaker cone! Hook a vibrating material directly to a speaker cone rather than using a magnetic field to move the cone...brilliant in a very simple way.

 

Midrange drivers are pretty much fine as they are...mids are easy for speakers to reproduce. Lows are a different story...to get accurate low frequency response, you have to either have a large enclosure OR a comparatively inefficient driver...physics doesn't allow you to have all three things simultaneously. Really, the only improvements in woofer technology over the years have been incremental...materials with better properties (like the surrounds), stronger magnets, coil wire with lower resistance, etc. No major revolutionary change.

 

I just find that conceptually surprising, given how technology for just about everything moves along so quickly. Doesn't anyone know of a material that vibrates at low frequencies when it sees a sine wave signal?

 

And while I'm on this subject and musing...wouldn't it be possible to use a second coil winding on a driver rather than a permanent magnet? Replace the permanent magnet with another electromagnet (like the voice coil) plus a circuit to rectify the signal (make the electromagnet always have the same pole direction rather than switching back and forth like the voice-coil does) and you've drastically reduced the weight of the driver. Plus, you've changed it's properties (electro-magnet would only "pull" when there's a current versus a permanent magnet which "pulls" all the time) which might be for the better, or might not. Do driver mfg's use permanent magnets simply because that's the way it's always been done? I think we need more innovation in this area!

 

Dave

[Rocky McDougall]

Dave, I am certainly no expert in this field but as I see it, the only thing that controls the output of driven air is the distance of the travel of the cone. If your design could effectivly increase travel of the cone it should work. I have noticed the subs in automobile systems and they seem to be ahead of the instrument systems. They seem to be making woofers that have a tremendous amount of travel and they are using massive amount of power, sometimes 3,000 watts or more to accomplish this.

Your idea would probably quicken the refersal of travel from one direction to the other. But I think you should pursue this. I think it's a wonderul idea. Keep on going.

Rocky

[TimR]

From memory, without looking at any references, I think you need a dense iron core to concentrate the magnetic flux. This way you can get round using less power. Of course I may be wrong.

 

Worth looking at. There is also back emf and things like that to consider.

 

[alexclaber]

Originally posted by Dave Sisk:

...that there's really been no revolutionary technology introduced over the years?

Not really. It all comes down to the medium involved and the wavelengths required.

 

Originally posted by Dave Sisk:

Think about it for a minute...for highs, the revolutionary introduction was the tweeter...essentially a piece of material that vibrates at high frequencies.

That's not technically correct. Tweeters do not have to be driven by piezo crystals - in fact most decent ones aren't. The only pro-audio cabs I've seen with piezo tweeters are budget bass offerings (like SWR Workingmans) and the Bill Fitzmaurice horn cabs. The problem with piezo tweeters is a lack of power handling, sensitivity and peaky response. The line arrays used in the BF design elegantly solve that problem and get amazing sound that costs hardly anything, but used individually piezo tweeters are pretty rubbish.

 

Typical tweeters use the same voice coil and magnet system as woofers and midrange drivers. The nice thing about tweeters in pro-audio is that the small wavelengths involved allow full horn loading from a very small horn, which gives big sensivity and reduces the power handling requirement.

 

 

Originally posted by Dave Sisk:

...Midrange drivers are pretty much fine as they are...mids are easy for speakers to reproduce.

They may be easy to produce but they're very hard to disperse evenly so polar response is the big issue here. Large midrange drivers go loud but are very directional, small midrange drivers disperse well but don't go loud. Horn midrange systems achieve both but are rather big.

 

Originally posted by Dave Sisk:

Really, the only improvements in woofer technology over the years have been incremental...materials with better properties (like the surrounds), stronger magnets, coil wire with lower resistance, etc. No major revolutionary change.

 

I just find that conceptually surprising, given how technology for just about everything moves along so quickly.

Just like the internal combustion engine. In fact few mechanical systems have exhibited revolutionary development over the last century - the big progress has all been in electronics.

 

Originally posted by Dave Sisk:

Doesn't anyone know of a material that vibrates at low frequencies when it sees a sine wave signal?

The problem is not getting the material to vibrate at low frequencies, the problem is getting that material to transfer its energy to the air. If we were dolphins this would be really easy, as speakers couple efficiently with water (because it's dense and uncompressible) but air is so low density and so easily compressed that most of the energy stays in the diaphragm and goes to waste as heat.

 

 

Originally posted by Dave Sisk:

And while I'm on this subject and musing...wouldn't it be possible to use a second coil winding on a driver rather than a permanent magnet?

Some of the earliest speakers were like this, due to the lack of powerful permanent magnets. I believe it fell out of favour due to cost, noise and (I think this would be the big problem now) power handling issues.

 

Originally posted by Dave Sisk:

Plus, you've changed it's properties (electro-magnet would only "pull" when there's a current versus a permanent magnet which "pulls" all the time) which might be for the better, or might not.

Not. Because the speaker needs that centreing force to damp its movement.

 

Every now and then I email a bright idea to Andy Lewis on some speaker related subject. And generally he responds with, "yes, but..." Unfortunately the more you learn about speaker design, the more you realise that there's no such thing as a free lunch!

 

But there are some nice new ideas coming onto the market. I think we'll see most progress coming from electronic systems which take advantage of powerful processing and powerful lightweight amps to compensate for the imperfections of electromechanical speaker systems. Also neo speaker magnets are still in their infancy so there's progress to be made there. And composite cabinet construction could provide some neat weight savings.

 

And finally, for those of you that are willing to carry 4x10" sized cabs, there are some fantastic new horn-loaded designs that will blow convential large cabs away - more bass, more efficiency, more clarity, lower weight, lower cost (if you can self-build).

 

If you can find a way of coupling a high mass low area diaphragm creating a high pressure low velocity wave with the low mass large area room wavefront which is made of a low pressure high velocity wave, without using a rather large horn, then you'll revolutionise woofer technology. But how?!!

 

Alex

[alexclaber]

Originally posted by TimR:

There is also back emf and things like that to consider.

Indeed. Increase magnet strength and you increase midrange sensitivity but you also increase back EMF which decreases bass sensitivity.

 

Originally posted by Rocky3840:

Dave, I am certainly no expert in this field but as I see it, the only thing that controls the output of driven air is the distance of the travel of the cone..

In a sealed cab that's it. In a ported cab you also have the port output to consider which adds another 3dB of output in the tuning region. But, as you say, essentially the Vmax (cone area x cone travel) defines the maximum LF output.

 

Originally posted by Rocky3840:

If your design could effectivly increase travel of the cone it should work. I have noticed the subs in automobile systems and they seem to be ahead of the instrument systems. They seem to be making woofers that have a tremendous amount of travel and they are using massive amount of power, sometimes 3,000 watts or more to accomplish this.

As you increase the travel of the cone so you have to increase the voice coil overhang. Doing this decreases the efficiency (because the overhung part of the coil uses up power but does no work whilst outside the magnetic gap) and also decreases power handling (because the overhung coil cannot transfer heat as easily to the magnet structure). Increasing travel also increases the mass of the surround and spiders, which further lowers the efficiency. And as power handling can only go so high, you eventually hit a limit of practicality for live audio. Acme speakers take this approach, with far greater Xmax than most bass cabs and consequently demand huge power to go as loud. But they will move more air than any other comparably sized cabs.

 

It's easy to get excellent bass in a car. The woofer has such a small volume of air to pressurise that the sensitivity can be very low and the system still go loud. I have a 100W 8" sub in my car that puts out well over 100dB down to 25Hz. It sounds great. But I think it would struggle in my house and be utterly inaudible in a live sound environment.

 

Alex

[moot]

I can't get near as technical but, as a novice I would say that althought the technology/process hasn't changed all that much when it comes to woofers in general, the important part has - efficiency. Remember the old addage "the bigger the box, the bigger the boom" ? Thank all that is holy that addage is no longer true.

While todays drivers may take a bit more power to hit their sweet spot, the improvements in design make it possible to dump them into smaller boxes thus making the bass player smile when he has a cabinet that weighs 40 lbs rather than 200.

Neo seems to be getting big even though it is reasonably old technology but from what I gather, and I don't know from personal experience, it takes a few extra watts to make these babies sound good and the jury seems to be out on lifespan.

Of course, there is always the LFG (low frequency generator) which I would love to be able to afford and then there is the whole amplification debate.

BTW, I blew my power amp yesterday in my car and have a quandry. In shopping I noticed a lot of MOSFET amps and was wondering if they are capable of producing the tight, defined, deafening sound that I am used to? Anyone? Alex?

[Rocky McDougall]

Alex, If you were not concerned with wide dispersion of the sound wave, could you set the driver back inside a tube of the same diameter of the driver ane increase the impact not unlike a short barrel gun compared to a long barrel. In the US there is a car sub called the "Bozzuka" (spelling?) it uses this technology. How would this work on a 15" sub. ?????

Rocky

[Big Daddy from Motown]

I have to take issue with the claim that bass cabinets are smaller than they were in the past. A typical 410 cab is a huge box compared to a 2-12 fender bassman or a b-15 of the olden days. The classic Sunn 200S cab inet was 24x42x15 compared to a swr 410 @23x25.25x18.375 not any easier to lug around by yourself. Personally i don't think they sound all that much better either.

 

However there has been lots of improvement in speakers over the last 40 years , mostly in the materials used.

 

As far as tweeters go once you've heard a true ribbon tweeter you'll appreciate how good the high end can sound.

[TimR]

You can buy the bazooka here as well. It has an inbuilt amp but is only 8inch.

There is a distinct difference in that these are near Field speakers not far Field. In a car the sound doesn't have to be projected outwards.

The sub woofer for my cinema surround sound works on a similar basis it is amazing in my front room but would just be lost in a theatre setting.

[alexclaber]

Originally posted by mattulator:

...the important part has - efficiency. Remember the old addage "the bigger the box, the bigger the boom" ? Thank all that is holy that addage is no longer true.

While todays drivers may take a bit more power to hit their sweet spot, the improvements in design make it possible to dump them into smaller boxes...

If anything efficiency has dropped but power handling has sky rocketed - but the reason for the drop in efficiency is that bass speakers used to be just like guitar speakers with very low Xmax, very little bottom, and lots of midrange. But as you say, the big improvement is that you can get a lot more bass from a smaller box, as long you give it enough power.

 

Originally posted by mattulator:

...Neo seems to be getting big even though it is reasonably old technology but from what I gather, and I don't know from personal experience, it takes a few extra watts to make these babies sound good and the jury seems to be out on lifespan.

I think the lifespan thing isn't really an issue. Either you overheat the magnets and they die or you don't and they last. And I suspect you'd short out the voice coils before managing the latter.

 

Originally posted by mattulator:

In shopping I noticed a lot of MOSFET amps and was wondering if they are capable of producing the tight, defined, deafening sound that I am used to? Anyone? Alex?

Depends if they're implemented well - if you're not clipping the amp I think it makes little difference whether the power transistors are bi-poloar or MOSFET. But amps are amps really - it's the speakers and cabs that make the big difference. (Are you sure you want deafening sound?!!)

 

Originally posted by Rocky3840:

Alex, If you were not concerned with wide dispersion of the sound wave, could you set the driver back inside a tube of the same diameter of the driver ane increase the impact not unlike a short barrel gun compared to a long barrel. In the US there is a car sub called the "Bozzuka" (spelling?) it uses this technology. How would this work on a 15" sub. ?????

Rocky

Those 'bazooka' tube subs are more of a marketing idea than anything. Also, I imagine it's pretty cheap to get a rigid plastic tube and bolt a woofer to one end and either port or seal the other, or you could add another woofer firing outwards (louder) or another woofer firing inwards (deeper). But they're nothing different from a regular cab. Having the speaker firing down the tube wouldn't be good, you'd get a big response peak at 1/4 wavelength equals tube length.

 

Originally posted by Big Daddy from Motown:

I have to take issue with the claim that bass cabinets are smaller than they were in the past. A typical 410 cab is a huge box compared to a 2-12 fender bassman or a b-15 of the olden days. The classic Sunn 200S cab inet was 24x42x15 compared to a swr 410 @23x25.25x18.375 not any easier to lug around by yourself.

But how much louder can a modern 4x10" go?

 

Originally posted by Big Daddy from Motown:

Personally i don't think they sound all that much better either.

Depends what sound you want. A lot of modern speaker cabs are still too many speakers crammed in a small box, with a dodgy crossover and cheap tweeter, and a nice brand name on the front... But a well designed cab with quality modern components does for me what a '60s or '70s design could never achieve (at least in portable form).

 

Originally posted by Big Daddy from Motown:

As far as tweeters go once you've heard a true ribbon tweeter you'll appreciate how good the high end can sound.

They're meant to be really nice. They work by the current flowing through the ribbon and the ribbon then moving between the magnetic poles and acting as the speaker diaphragm itself. The moving mass is tiny, hence very fast response with extremely high frequency response and accurate dynamics.

 

Alex

[moot]

Originally posted by C. Alexander Claber:

Depends if they're implemented well - if you're not clipping the amp I think it makes little difference whether the power transistors are bi-poloar or MOSFET. But amps are amps really - it's the speakers and cabs that make the big difference. (Are you sure you want deafening sound?!!)

 

[Alex

Thanks for the advice Alex - much appreciated.

 

The application is my hobby car. As you may deduce from the photo below it takes a bit to get over the roar of the engine but, I have always enjoyed high volume levels whenever and wherever I listen.

 

The signal chain is Pioneer CD player line out to power amp to Pioneer 6x9 speakers. The 3.2 cf space behind the rear seat makes a dandy enclosure and gets wonderful bass response without the use of subs.

 

Thanks Again Alex.

 

http://i20.photobucket.com/albums/b203/Mattulator/bug7-11-1.jpg

[alexclaber]

Cool car! I have one of these in my car:

 

http://www.mac-audio.de/recoimages/img_1310220_Detail_Modell_col_0_pv300.jpg

 

"Principle: active 8" bassreflex subwoofer

side-fire principle

lower cut-off frequency: 25 Hz

upper cut-off frequency: 150 Hz

rated power output: 100 Watt

max. power output: 200 Watt

adjustable phase: +

measurements: 245 x 265 x 290 mm

Specials: Compact cabinet size, movement control servoloop (MCS), class D amplifier with variable gain, bass boost, variable lowpass filter, variable phase"

 

It's transformed the quality of the sound in the car by adding loads of tight deep bass but also by taking the strain of the midbass drivers in the doors so they're running much cleaner and sound far clearer and sweeter. Sits rather neatly in the middle of the rear footwell where the 'transmission' tunnel would be if my Civic Type-S didn't have a flat floor.

 

Alex

[Gruuve]

So, on another line of thought...do you think the increasing popularity of lighter-weight NEO drivers might make Isobaric cabinet designs a practical possibility for our little bass guitar playing world?

 

Just for reference for those who might not know what I mean...an Isobaric system has two drivers either facing each other and bolted together, or facing the same direction but bolted to opposite ends of a tube...this whole fixture is then inside the enclosure, and the drivers are wired in parallel (in-phase if they are in a tube, or out-of-phase if they are face to face). The benefits are that by doubling the...is it Qts?...of the driver system, you can essentially cut the volume of the enclosure in half. As with most things, there's a few drawbacks...two drivers = heavy (although with Neo drivers, two drivers *might* be lighter weight than the extra wood involved in making an enclosure that is twice the size...it all depends), two drivers = expensive (this would still be true, but then some of the boutique cabs aren't exactly cheap), two drivers isobarically coupled and wired in parallel has half as much input impedance, but there's no sensitivity increase from using two drivers (generally, if you replace one 8-ohm driver with two 8-ohm drivers in parallel, you have twice as much cone surface area plus two drivers in parallel will use theoretically twice as much amplifier power since the total load is now 4-ohms, so you get a theoretical 6db SPL in a normal two driver system...this isn't the case when they are isobarically couple however, the pair uses more power but the SPL output at that power is the same as one driver on half as much power).

 

So, in our little bass playing world, isobaric would mean really small cab with extended LF response, traded off for heavier weight (versus a single driver) and similar sensitivity. Thoughts?

 

Dave

[getz out]

Ampeg IsoVent for sale at Bass Northwest... only $499...

 

http://www.bassnw.com/images/Used%20Amps%20and%20Cabs/Ampeg%20SVT50PRO%20IsoVent_499.jpg

[moot]

Bitchin' cab.

 

Maybe someone will talk a bit about how a rear firing woofer works?

[Big Red 67]

Originally posted by Dave Sisk:

And while I'm on this subject and musing...wouldn't it be possible to use a second coil winding on a driver rather than a permanent magnet? Replace the permanent magnet with another electromagnet (like the voice coil) plus a circuit to rectify the signal (make the electromagnet always have the same pole direction rather than switching back and forth like the voice-coil does) and you've drastically reduced the weight of the driver. Plus, you've changed it's properties (electro-magnet would only "pull" when there's a current versus a permanent magnet which "pulls" all the time) which might be for the better, or might not. Do driver mfg's use permanent magnets simply because that's the way it's always been done? I think we need more innovation in this area!

 

Dave

I think that the fixed magnetic force has to be there for the coil to push against.

[Gruuve]

Well, I'd assume this Ampig has another woofer face-to-face with the one you see in the bottom on the pic. Assuming that's in a cab section sealed from the two 10's, then that's essentially an isobaric design. Presumably the 10's handle mids only, and the isobaric woofer config and the horn are on a 3-way crossover. How old is this, just out of curiosity? (I thought AccuGroove "invented" the cab-within-a-cab design... )

 

Dave

[Gruuve]

Originally posted by Big Red 67:

Originally posted by Dave Sisk:

...wouldn't it be possible to use a second coil winding on a driver rather than a permanent magnet? Dave

I think that the fixed magnetic force has to be there for the coil to push against.

The voicecoil only pushes against the permanent magnet during half of the sine wave signal...during the other half it pulls toward it, and when the sine wave crosses the 0 axis it's neither pushing nor pulling. If you think about it, wouldn't crossing at the 0 axis be the only time that two electromagnets weren't pushing/pulling against each other also? I'm not sure how back EMF and some of the other properties figure into this though...that would definitely change the T/S parameters for a two electromagnet versus electromagnet + permanent magnet deal...just not sure whether it would be for better or worse...

 

Dave

[Big Red 67]

Originally posted by Dave Sisk:

Well, I'd assume this Ampig has another woofer face-to-face with the one you see in the bottom on the pic. Assuming that's in a cab section sealed from the two 10's, then that's essentially an isobaric design. Presumably the 10's handle mids only, and the isobaric woofer config and the horn are on a 3-way crossover. How old is this, just out of curiosity? (I thought AccuGroove "invented" the cab-within-a-cab design... )

 

Dave

As long as the polarity was right it would work. It may just be that the driver is backwards to increase the cab volume.

[getz out]

That Ampeg IsoVent is an isobaric configuration. It is a great sounding cabinet, but unfortunately it is butt heavy.

 

Ampeg stopped making these years ago.

[lug]

Originally posted by getz76:

That Ampeg IsoVent is an isobaric configuration. It is a great sounding cabinet, but unfortunately it is butt heavy.

 

Ampeg stopped making these years ago.

I'm thinking neo's might ressurect Isobaric technology. The problem is still having to use 2 speakers for the same amount of output, an expensive proposition in speaker building.

[Rocky McDougall]

Question: If you had two cabinets, one had a single speaker and the other had 4 smaller speakers yet they both were equal in square inchs of cone surface, the same cone travel and the same power amp. Would there be a tone and/or volume difference. Just curious.

Rocky

[TimR]

I think we all need to go back to school.

A wire carrying a current perpendicular to a magnet Field will move in a direction perpendicular to the direction of the current and the direction of the magnetic force.

If you change the direction of the current, the wire will move back. If you change both the magnetic Field direction and the current at the same time, the wire will continue to travel in the same direction.

Not much use in our application.

An electromagnet is made using D.C. and they get very hot in operation!

 

Elecromagnets

Magnetic Fields

[TimR]

Originally posted by Rocky3840:

Question: If you had two cabinets, one had a single speaker and the other had 4 smaller speakers yet they both were equal in square inchs of cone surface, the same cone travel and the same power amp. Would there be a tone and/or volume difference. Just curious.

Rocky

The waves from each individual speaker interfere with each other, this causes quiet and loud spots depending on where you are standing. Think of it as throwing several stones into a pond and watch the ripples. Much better to throw a large rock in. Nice big ripples, but hard work.

[alexclaber]

Originally posted by Dave Sisk:

that would definitely change the T/S parameters for a two electromagnet versus electromagnet + permanent magnet deal...just not sure whether it would be for better or worse...

The thing is I can't see any advantage to an electromagnet vs a neo magnet. The size of the magnetic coils to maintain as strong field as a neo magnet would make them too heavy to be practical. You'd need extra power to supply the electromagnet. The magnetic field is less likely to be as constant as from a permanent magnet. And finally, the biggest problem - the fixed magnet structure acts as a heatsink for the voice coil: How would the already hot electromagnet act in this role?

 

I gather the IsoVent is the densest cab know to man. 2x10" + 2x15" in a 4x10" sized cab, and made by Ampeg so you know it'll weigh a ton anyway. Ampeg have made some wicked cabs over the years, really groundbreaking designs. And all anyone wants to buy is (two) 8x10"s.

 

Euphonic Audio made a few isobaric cabs - the il-110 featured a tweeter, 5" mid, 10" woofer and 8" internal woofer (to the the isobaric thang). And, of course, Tom Bowlus owns one...

 

I don't quite get how isobaric designs work - obviously the name means constant internal pressure, which the second woofer provides - but surely the external wave from the second woofer moving out of phase cancels out the omnidirectional bass from the front wave of the first woofer. Hmmm...

 

Alex

[Gruuve]

Originally posted by TimR:

If you change both the magnetic Field direction and the current at the same time, the wire will continue to travel in the same direction.

Not much use in our application.

 

Actually, read my original post again...you'd have to to use a (fairly simple?) circuit to rectify the sine wave going to the electromagnet coil that replaced the permanent magnet...ie, make it always swing up on the positive axis (or always swing down, whichever). And you're right, that would generate heat in a component that previously helped dissipate heat (the permanent magnet). However, that coil would be on the outside of the driver, so it seems like there might be opportunity for some cooling considerations? Again, just musing...

 

Dave

[lug]

Originally posted by C. Alexander Claber:

I gather the IsoVent is the densest cab know to man. 2x10" + 2x15" in a 4x10" sized cab, and made by Ampeg so you know it'll weigh a ton anyway. Ampeg have made some wicked cabs over the years, really groundbreaking designs. And all anyone wants to buy is (two) 8x10"s.

 

Euphonic Audio made a few isobaric cabs - the il-110 featured a tweeter, 5" mid, 10" woofer and 8" internal woofer (to the the isobaric thang). And, of course, Tom Bowlus owns one...

 

I don't quite get how isobaric designs work - obviously the name means constant internal pressure, which the second woofer provides - but surely the external wave from the second woofer moving out of phase cancels out the omnidirectional bass from the front wave of the first woofer. Hmmm...

 

Alex

In a nutshell, an isobaric design allows you to halve your interior cab space at the cost of adding an extra speaker. The second speaker results in no dB gain, so is considered prohibitively expensive to produce. The extra weight due to the second speaker is a problem but new neo technology would help in this regard. The easiest way to achieve an isobaric design is to mount two speakers facing each other but wired 180 degrees out of phase. In theory, the resulting cab will have the same frequency response whilst taking up only half the room.

[TimR]

Originally posted by Dave Sisk:

you'd have to to use a (fairly simple?) circuit to rectify the sine wave going to the electromagnet coil that replaced the permanent magnet

I can see where you're trying to get to, but the principle of the electromagnet means that the magnetic force is proportional to the current so you will loose a lot of magnetic force. Exactly what you are trying to avoid.

 

Now if you could scale down this baby.

 

Super cooled magnet

[Gruuve]

Originally posted by Rocky3840:

Question: If you had two cabinets, one had a single speaker and the other had 4 smaller speakers yet they both were equal in square inchs of cone surface, the same cone travel and the same power amp. Would there be a tone and/or volume difference. Just curious.

Rocky

Probably. In theory, the large single driver and the collection of smaller drivers considered together would have to have the exact same frequency response and Thiele-Small parameters. Or put more succintly, they'd have to have the exact same frequency response and each cab's system-level T/S parameters would have to be the exact same with their respective enclosures considered. I think that's very unlikely in practice.

 

In general, I think we can safely say that no two cabs that have different size drivers or difference numbers of the same driver sound exactly the same. I think the one exception to that is probably the Acme's...Andy designed the LowB1, LowB2, and LowB4 to sound exactly the same (within a margin of course) but have different sensitivities (traded off for difference sizes/weights).

 

As I think Getz (?) has said before...there's essentially 3 characteristics and you only get to choose two of them: size (and weight), frequency response (specifically LF extension), and sensitivity (ie. efficiency). Choose two...the third one is dependent on the other two. You can have a small cab with extended LF response, but it'll have low efficiency (the Acme's)...you can have a cab with extended LF response and high efficiency, but it'll be large and heavy...or you can have a small cab with high efficiency, but it'll have limited LF response (most smaller cabs). Physics dictates all this.

 

But you know...you do have to consider...how much 31Hz output do you really need to have? You can activate a 40-Hz highpass filter and most 5-string basses sound almost the same. Make it a 50-Hz highpass filter and you can start to tell a little difference, but it's really not as much as you'd expect (unless you have a bass and strings combination that REALLY produces a lot of fundamental and very little overtones...you probably don't because that wouldn't sound particularly good through any cab or SR system!)

 

Dave

[alexclaber]

Thanks lug, I get that, but how does it actually work? What happens when the compression wave from the first driver hits the rarefaction wave from the second driver? Will it not cancel out the lows like an open back guitar cab?

 

Alex