What's the difference between a true SPL sub and a true SQ sub?

[btdickey99 5,000+ posts]

There are many different ideologies in respect to what makes a SQ or SPL sub. There have even been companies that have experimented with different parameters (one in particular made a sub with a low Fs as a goal because they peak higher in enclosure simulation programs) trying to come up with what exactly defines an SQ and a SPL sub. For demonstration purposes, lets explore the different ideologies of an SPL sub:
High BL = SPL sub. This can be true. Higher BL means the motor has more force and control over the moving assembly at a certain point (there are high BL subs that have a very non-linear BL curve so the BL is focused within a few mm of travel and beyond that range the BL drops drastically). The main goal is to have enough BL to reach full excursion at a given frequency with a given amount of power. But high BL doesn't mean it will get louder instantly compared to lower BL subwoofers (take the older Brahma's - Scotty Johnson used them and whipped arse...BL was ~14 I believe).

A lot of the time higher BL subwoofers have lower Qts's, which lend them to like ported enclosures (once again, more SPL oriented). However, this doesn't mean that they can't sound good in the proper alignment (enclosure type and size).

Low Fs, high Qts = SQ sub. Not necessarily always, but can be true in some instances. Low Fs subwoofers can be coined as sealed-box woofers, which can be true dependent upon other T/S's. Same goes for High Qts. High Qts's vs low Qts's can tilt the tables significantly either way. A lot of the time lower Qts drivers are more driven towards ported enclosures (as stated above) so they're louder than their sealed counterparts (3 dB gain when porting). Hence the "SPL" label.

It's all about the goal of the subwoofer though. Target enclosure volumes with a target F3 in those specified volumes and power handling are the three biggies when designing a subwoofer. There are a lot of other factors too (I am very anal - yes I said anal //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif - about soft part selection and how it affects the overall sound of the woofer along with how the motor is designed for linearity, BL, size, etc).

But anyway...instead of de-railing massively, which I've just done, if you have two woofers: woofer A has a BL of 30 and a Qts of .19 with an Fs of 35 Hz and woofer B has a BL of 19 and a Qts of .40 with an Fs of 28 Hz, woofer A will be your SPL option and woofer B will be your SQ option. But keep in mind that was a HUGE generalization. HUGE generalization.

^^^^^= Smarter than a 5th grader //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[btdickey99 5,000+ posts]

sorry for the noob question, but what is BL?

 

[Papermaker85 5,000+ posts]

B is the density of the magnetic field...

l is simply the length of the coil in that field...

flux density*length of coil will tell you how much "power" the motor has in very simple terms...

power handling, suspensions the box needed/used and enviroment are equally as important in both output and SQ..efficiency is also very important, but not the 1w1m spec youf often see..

The higher/lower B/l means with a given input will determine its electrical dampning or how the woofers reacts to the signal(measured @ resonance)...

i really won't add much to what has been said because it covers a good spread of information but if more questions arise ill be glad to help..

i will state the main differences of SPL woofers and SQ woofers...

SPL first then SQ

Suspension... many high output woofers have very stiff suspensions... this allows you to lower the Q of your port causing its efficiency to be very high and it to be VERY peaky.. its also many times they are not very linear becasue suspension failure from over excursion becomes very easy at high output levels, and cone control is CRUTICAL to efficiency(output)..

in SQ woofers you often see much "softer" suspension simpy because of back pressure.. this corrlates to a higher QMS and lower FS.. don't get confused though having a high FS or low QMS doesn't mean the woofer will sound bad, its simply a matter of what you want to accomplish. But many cases it does help to have such traits, as its proven that a shallower roll off and lower FS have lower group delay.

motors... many motors are very large and have huge top/back plates... this serves a few purposes...

1 absorb heat from the coil

2 provide the proper motor strength for the excursion levels and compression levels(Bl)...

3 provide the proper dampning for the aligment(QES)

is SQ woofers BL isn't as high because higher BL woofers suffer by increasing the affects of inductance/back EMF and the cone is much more controlled by the sealed box. output isn't much of a concern as 12-16mm xmax is enought to reach 120 DB in most applications this helps keep mass lower(shorter gap height/coil height).

high BL isn't bad and it doesn't directly corrulate to a "poor sounding" woofer. it needs to be noted that higher B/L woofers have more weight(MMS MMD) or can have more output potential.. fact of the matter is though the higer the B/l the more potential output, bare none and SQ woofers aren't designed for output...

now when your designing a woofer that sounds good and gets loud things bomce alot more difficult, but that information is gonna cost you a leg....

 

[BringDaBoom 10+ year member]

Stickayyy

Holy God, yeah this needs to be stickied like ASAP. Awesome post John

 

[dragnix 5,000+ posts]

great post and all, but he needs to explain some of those terms abbreviated terms in there also for me to comprehend all that he said

 

[JohnEJanowitz 10+ year member]

B is the density of the magnetic field...l is simply the length of the coil in that field...

flux density*length of coil will tell you how much "power" the motor has in very simple terms...

Keep in mind that looking at BL alone is meaningless. We need to look at BL with respect to the DCR of the coil. The most generalized method for comparing motor strength is Bl^2/Re. The higher the number, the stronger the motor.

Suspension... many high output woofers have very stiff suspensions... this allows you to lower the Q of your port causing its efficiency to be very high and it to be VERY peaky.. its also many times they are not very linear becasue suspension failure from over excursion becomes very easy at high output levels, and cone control is CRUTICAL to efficiency(output)..

This would actually be creating a higher Q resonance. The higher the Q, the more narrow the bandwidth, but more peaky. The lower the Q, the more broad it becomes. You can create more of a peak, but the magnitude of the peak doesn't change all that much. The system is really dominated by the enclosure, mass, Sd and motor strength and the compliance of the driver itself has a minimal effect.

is SQ woofers BL isn't as high because higher BL woofers suffer by increasing the affects of inductance/back EMF and the cone is much more controlled by the sealed box. output isn't much of a concern as 12-16mm xmax is enought to reach 120 DB in most applications this helps keep mass lower(shorter gap height/coil height).

Higher Bl doesn't necessarily mean higher effects of inductance and back EMF. If you have a higher Bl because you put more turns on the coil and increase the L, then your inductance would rise. However, I can take the same woofer, machine the pole down to two different OD's to change the amount of flux in the gap and have two different BL's, but the inductance stays the same in both cases. In this case, effects of back EMF would be greater with the lower Bl driver as there is more air gap. It is much easier for the flux field to modulate in the air gap than in the steel. A similar situation could be seen without changing the gap, but more flux put into the system with larger magnets. This would create more flux in the gap, higher Bl and again inductance woudln't change. If you can actually saturate the top plate and pole, or come close to doing so, the effects of back EMF are nearly eliminated.

Also the cone is much more controlled in a sealed box only below the tuning frequency of the comparable vented enclosure. At and around tuning, the cone is much more controlled as is evident by the excursion minimum at the tuning frequency. There is much more pressure inside a vented enclosure than there is in a sealed enclosure. You are exciting the resonance of the port that can pressurize the air in the enclosure much more than the woofer alone.

high BL isn't bad and it doesn't directly corrulate to a "poor sounding" woofer. it needs to be noted that higher B/L woofers have more weight(MMS MMD) or can have more output potential.. fact of the matter is though the higer the B/l the more potential output, bare none and SQ woofers aren't designed for output...

Higher Bl woofers don't always have more weight. We have 2 different size motors we use with a 2" coil. One is higher Bl than the other due to more flux in the gap. The coil is the same in both cases though and Mms is identical between the two. The lower Bl driver has a higher Q and is more suited to a sealed enclosure. The higher Bl driver is more suited to a vented box.

now when your designing a woofer that sounds good and gets loud things bomce alot more difficult, but that information is gonna cost you a leg....

It's really not so difficult as most of the things you want the same in both cases. Either way you want these properties:

(1) Linear magnetic flux levels across the entire VC movement range.

(2) The flux should be fixed permanently and not move, this is however not the case in 99% of speakers.

(3) High heat absorption properties as close to the VC as possible. The VC if allowed to heat significantly will lower the speaker output Spl very quickly.

(4) Linear inductance as the VC moves through its entire range if the driver has to contribute ANY output above the impedance minima above the Fs of the driver. The only way to accomplish this is to keep the CORE of the VC the same at all excursions. The VC is after all an inductor, however this is the only inductor in the whole audio system that varies it's value with low bass excursion. The low bass creates massive excursions that at the same time changes the parameters of the driver at higher frequencies with every deep in and out stroke.

I'm still working on getting the old Lambda white paper edited to get it on my forum. It discusses the ultimate design for low distortion and talks about all 4 of these aspects. You can find it here from the old site on the web archive for now:

http://web.archive.org/web/20020220130103/www.lambdacoustics.com/library/whitepapers/lambda001.htm

In general though, most people think of SQ woofers as sealed box and SPL as vented. An SQ woofer can play in a vented box just as well, but the key is tuning low so the effects of group delay aren't audible. In a properly done vented box, a woofer needs much less input power and much less excursion to produce equal output to a similar woofer in a sealed enclosure. Less power means less heat and less excursion means the driver operates in a more linear range for any given output. Both of these translate to the vented enclosure being lower distortion.

John

 

[dragnix 5,000+ posts]

**** 08er's trying to be smart //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

 

[dragnix 5,000+ posts]

btw, is AE officially making subs again or no?

 

[JohnEJanowitz 10+ year member]

btw, is AE officially making subs again or no?

We are making some things, just not to the level I had hoped yet. It's been a long time coming with everything I had to get in line. It's been a nightmare getting all the parts the way I want them. That's been the holdup for over a year. I moved a lot of production of things back to the US to gain more control over everything. Cones, spiders, surrounds, edge gaskets, magnet boots, and coils are all sourced in the US with the exception of the aluminum cones. Even those we will be finishing in house so we can make sure the finish quality is good. It also gives us the option of doing custom painted cones and frames. We can do literally any kind of finish on the cone and frame that you could put on a car. We have a direct to aluminum clear that we can then put a candy coat over or any traditional base/clear. All the final machining for T-yoke and top plates is done in house. Every piece is checked so we can hold +/- .002" tolerances. Our production room is all setup. Our QC area is setup where we run a quick breakin tone and measure parameters on every driver before it gets packaged. I designed and sourced the packaging boxes and inner packaging material.

Everything is finally all done and we're ready to start knocking out woofers. The final parts I'm waiting on are cones and spiders. I had to put out the money for tooling to make sure things are exactly as we need them. Sample cones FINALLY arrived and were approved last week. Production cones should be arriving soon. We'll have full parameters and pics coming very shortly of all the new drivers though.

John

 

[munchies 10+ year member]

I've gained IQ points after reading through this thread, thank you.

 

[munchies 10+ year member]

great post and all, but he needs to explain some of those terms abbreviated terms in there also for me to comprehend all that he said

http://en.wikipedia.org/wiki/Thiele/Small

 

[dragnix 5,000+ posts]

We are making some things, just not to the level I had hoped yet. It's been a long time coming with everything I had to get in line. It's been a nightmare getting all the parts the way I want them. That's been the holdup for over a year. I moved a lot of production of things back to the US to gain more control over everything. Cones, spiders, surrounds, edge gaskets, magnet boots, and coils are all sourced in the US with the exception of the aluminum cones. Even those we will be finishing in house so we can make sure the finish quality is good. It also gives us the option of doing custom painted cones and frames. We can do literally any kind of finish on the cone and frame that you could put on a car. We have a direct to aluminum clear that we can then put a candy coat over or any traditional base/clear. All the final machining for T-yoke and top plates is done in house. Every piece is checked so we can hold +/- .002" tolerances. Our production room is all setup. Our QC area is setup where we run a quick breakin tone and measure parameters on every driver before it gets packaged. I designed and sourced the packaging boxes and inner packaging material.
Everything is finally all done and we're ready to start knocking out woofers. The final parts I'm waiting on are cones and spiders. I had to put out the money for tooling to make sure things are exactly as we need them. Sample cones FINALLY arrived and were approved last week. Production cones should be arriving soon. We'll have full parameters and pics coming very shortly of all the new drivers though.

John

wow, sounds great, you definitely need to keep the forum updated //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

I've gained IQ points after reading through this thread, thank you.

Which is huge since this is ca.com

http://en.wikipedia.org/wiki/Thiele/Small

Sorry, i don't allow Wikipedia to fill my head with "knowledge"

 

[Audio Master 10+ year member]

FINALLY SOMEONE WHO IS AS INTELLLYYGENT Amyself and can be herd for tha tru persun thay r its nise to c thta sum pepl actully no wat thay r tawking abot please enlighten these pages more with your wisdom my master

but for realz gnarly posts man love it when i dont know what dudes are saying but know its the truth yo stcky for shore mang

 

[sundownz Pro Seller]

I think John and Nick handled that pretty well //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Electrodynamic 10+ year member]

Yep, John handled the further in-depth explanation really well. John is a smart cookie. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I tried generalizing a lot so the highest amount of readers could understand.