One big subwoofer or two weaker subwoofers?


Do you think that, for stereo, is better to have a bigger subwoofer or a pair of weaker ones?

For example, should it better to have a pair of Rel Strata III (or the new Strata 5) or a single Stadium III?

Thank you
Size is not the issue. It is the quality of the subwoofer.
Two (stereo) subwoofers is generally better; however two mediocre subwoofers is not better than one excellent one.

Since all REL's perform well, two Strata will work very very well. However, if you think someday you'd like to have two Stadium, then get one now and save up for the second one..

Second part is how good are your main speakers?? If two (or even one) Stadium outclasses your main speakers, then don't waste your money; get the two Strata..
ask your rel dealer ,or better yet.. rel north american distributor......rel stentor 3 ,will smoke 2 stratas,or 2stadiums it will even beat studio ii(old model)...just no contest .You read alot of threads, yes 2 should be better than 1 is usually for same size or similar make.BUT when you say bigger (hope better)like stentor 3,this thing is fast, deep ,DEEP,moves air big time can't compare even 4 small subs..Besides stereo doesn't exsist for deep bass . YES i do have one,SEAMLESS
Sugarbrie's first paragraph makes an important about quality. Cheap subwoofers are worse than none, as a rule, since they tend to degrade the sound from the main speakers.

When it comes to subwoofer design, however, one large powerful subwoofer isn't necessarily the best approach. Subwoofers with several smaller drivers (in the 8-10" range) have the virtue of being able to move a lot of air, while the smaller drivers have less mass and thus can respond more quickly than a large driver in the 15-18" range. Multiple drivers in a subwoofer (assuming it is well designed) also offer the advantage of averaging out the resonance points, thereby yielding a smoother frequency response (Vandersteen subwoofers, for example, use three 8" drivers).

The primary advantage of using a stereo pair of subs is that they load the room more evenly, thereby reducing the resonant nodes in the room. A stereo pair of subs also presents a much more realistic sonic image, since deep frequencies may be coming more from one speaker than the other. (When I bought my first Vandersteen subwoofer, I was very pleased with it, and bought the second one expecting it to just add a bit more "oomph" to the deep bass. What I experienced was a MUCH better overall sound reproduction that provided spatial clues.)

Assuming your budget allows you to buy a good quality of stereo subs, I would personally recommend that approach to having a somewhat more expensive single sub.
There are so many issues to consider here. What is the cross-over point? What are the room modes like (2 subs make cancellation of problematic modes much easier)? Is it 2 channel or multi-channel? Here is a link to a paper we wrote on loudspeaker placement. Loudspeaker Placement on Audioholics It may answer a few of your questions--may raise a few more.
When I trying to decide which way to go, I called Sumiko, the US distributor for REL. They stated without a doubt, that one Stadium III was better than two Storm or Strata III's. I purchased a Stadium III and couldn't be happier. I'd go with a sub that has flexible cross over points. REL's go down to 22hz. I never thought I'd have my sub set as low as 23hz, but that's were it ended up. Like a previous post stated, a lot does depend on your main speakers.
One better sub is allways allways better than two of anything else equalling the same price! Assuming you do not buy too big of a sub for the room and that the one sub in it's best position in the room, provides the correct amount of bass at the listening position! This sometimes is not possable no matter how big the sub is in which case two (in mono!) will smooth out the room nodes. Stereo subs is an absolute joke and shows no knowledge of how bass loads a room. Stereo bass with evenly placed subs will just cancel out the bass at the listening position period. TAS covered this topic perfectly a few issues back so the statements I make can be proven by those who should know.
How about two big subs instead of two small subs or one big sub? If you want low frequencies with authority, you can't do that with a small box and keep things "tight" with good transient response : ) Sean
i would agree with Sdcampbell and Sugarbrie, it's the quality that counts. I have had a REL subwoofer in the past and they are very good, and imo, one of the best out there. For audio, i never heard a subwoofer that I liked with a bigger than a 10" woofer (some had multiple woofers). imo, the best speakers that i have heard had 10" or less woofers (most have multiple smaller (10" or less) woofers).
Size matters. Of course so does quality, but 20 Hz sound at any reasonable volume is an uphill battle for an 8-10 inch driver.

It is possible to make a small cone vibrate at subwoofer frequencies, but what happens when the sound goes out into the room? It spreads out and becomes less loud. And with a small driver, the SPL falls off rapidly. If you have a small room, and listen close up, a small subwoofer is OK. In the extreme case, tiny earphone diaphrams can reproduce LF very well, but require immediate proximity to the ear.

Take a look at what the cone of a small subwoofer is doing...long excursion is necessary. For any dynamic loudspeaker, (good ones and bad ones alike) performance deteriorates as cone excursion increases. A large cone will need much less excursion to move the same volume of air.

In keeping with rules of full disclosure, I state that my SW system consists of three 15" plus three 12" drivers mounted in large sealed enclosures embedded (for cosmetic reasons) in the wall of my room. These systems "drive" the entire room, so that the sound is very uniform throughout, and there is an effortless quality that I miss with even excellent smaller subwoofers. Ideally, I would have the entire wall consist of drivers, and it would not matter if it was 20 15" cones, or 120 8" cones. My subwoofer design philosopy is consistent with the nature of my main speakers...three planar MG1.6.
Eldatford: interesting! But if your drivers are IN the wall, why have you sealed them?? Why not IB? Or am I missing s/thing?

BTW, is that 6 low frequency drivers per channel - or is it ONE s/woof (with 6 drivers)?
Pls excuse my confusion.
if you really beleive 8-10 inch is faster than 15 -18inch..your wrong....8-10 quality is better than 15-18 crap' but 15 18 sota, come on !!!!If your room is big enough...if you are using monitors than 8-10 is better
The SW systems are in the wall because I like the characteristics of a sealed (acoustic suspension) system. There are many drivers suitable for sealed box alignment, but few designed for infinite baffle operation. Also, it is an outside wall.

It is three separate SW systems, each having 15" and 12" drivers. Each driver has it's own amp. This is necessary because the 4 ohm driver impedance discourages parallel operation. Each 15" driver is powered by half of a CarverPro ZR1600 digital amp, 600 watts. The 12" drivers are powered by 250 watt SW "Plate amps" and their signals are equalized for phase and frequency response. I intend to use the 12" drivers to tweek the overall system performance, but in practice little or no equalization is needed. The enclosures are about 7.5 cubic feet each. The front baffle of each enclosure (which resemble coffins standing on end) is covered with acoustic foam to absorb some of the back radiation from the Magneplanars. The whole SW system is concealed behind fabric wall covering. In spite of its massive size, it is nearly invisible. (WAF you know). At present I am using 80 Hz 24 dB/octive for crossover. This makes life easy for the Maggies.

Because I designed and constructed the whole thing it didn't cost too much. I reckon it was about $3200, including 2550 watts of power amps, and sheetrock, plaster and paint to remodel the living room. Besides, the project was interesting. Better than dropping $3200 in a one hour visit to an audio shop.
Mavilla, are you really considering different subwoofers or did you start this thread just to see the blood? :-)
I agree with Rives, depends on a lot of other things. There is no "one size fits all" answer. His link along with other usefull info. should help you decide on which may work best for your system and room.

This thread has some great info. on bass and speaker design along with what can happen as you try to blend the wrong sub with your speakers. While the thread is not about subwoofers..the principals apply for a smooth blend.

Fast bass Slow bass is another good read...

You may also want to do some reading at this AA forum,

"Faster". What does this mean? Here is what I think.

Frequency response is part of the story. A subwoofer that is flat to 400 Hz will handle 80 Hz better than one that is flat to 200 Hz.

However, a loudspeaker that reproduces the LF waveform perfectly can still be "slow" in the sense that the amplitude of the sound builds up slowly, and perhaps persists after the electrical signal is cut off. This characteristic does depend partly on the size of the driver, with large ones tending to be slower. However, apart from the enclosure, the full story involves not only the size of the driver (actually the moving mass of the cone) but also the strength of the motor that drives the cone: the voice coil, magnet, and amplifier. My 15inch drivers, for example, have 4 inch voice coils, massive magnets, and are driven by powerful amps. They are not slow. The characteristic of a driver that would correlate with slowness is a ratio of motor force/volt to the moving mass.

Also, I must mention my view that most very low frequency sound sources are, by nature, slow. A large organ pipe, for example, does not sound forth at full volume when activated, and it continues to emit sound after it is turned off, not to mention the hall resonance that can be strong for several seconds. I think that what many people take to be "slowness" in subwoofers is really the nature of the sounds they reproduce.

Finally, aren't subwoofers fun! How often do you see similar debates about tweeters?
Ive used the same single subwoofer for over 20 years. It is a 17 inch Altec Lansing Driver. I am unsure of the model but was designed for large venue sound. I built the vented enclosure (3/4" ply oak veneir) exactly as called for by the tested driver's specifications (optimum curve).
It is powered by a mono bridged hafler 220 (450 watts)via monster cable. I use a crown fx2 crossover set @ 80 Hz. The stereo speakers are smallish Energy's powered by a Crown 300A.

Clearly there are many variables in all this but over the years my experience with this system has been nothing but intense pleasure. It can rock with the best of them and yet is smooth and delicate when required. Certainly over 2 decades my music tastes have varied but remain partial to the blues.

The only downside is the size of the enclosure; about 3' X 3' X 16". And I must admit to a few late night visits from the local constabulary but Ill blame that on the beer, good tunes and friends.

Good luck
Thank you very much for all responses.

The main speakers are Kef Q5. They are not very good speakers, but I wish I could exchange it. If so, I would like to use high quality monitors, or maybe electrostatic panels.

The sub-bass system would help anyway. And it is quite cheaper to build a system this way than buy (reallly) full rang speakers, which are out of my budget (now, and probably always).

Now I use a Kenwood subwoofer. It is slow in the sense that it can not follow the rhythm of the music. It sounds delayed. And of course it can not produce musical notes. Just boom-boom.

My system is 7.1 Kef Q series home theater, but it is mainly used for music DVDs. While my actual boom-boom subwoofer is fine for films, it is not right for music. Therefore I can expand the bass of my main speakers.

I know that neither my actual main speakers (which are said to go down up to 40Hz, but I am sure that it is not true), nor any future speakers will sound very deep, so I am afraid that a bit of low-midrange frequencies should be present from the subwoofers always.

Thanks again. I am going to begin a new thread just to know the differences you feel (not only the specs) when listening to different Rels.

Thanks a lot once again.
Mavilla: Try filling the interior volume of the sub with a varied density of foam ( or polyester fiberfil as a second choice ) and turning the crossover point as low or almost as low as it will go. This should get you a lot closer to something musical rather than something that goes "boom boom". You can fine-tune the quantity i.e. how "tight" or "loose" you want the bass by varying the amount of stuffing in the box. This shouldn't cost you more than about $10 or so to try and will probably make you a whole lot happier. Don't forget to try various placements for the sub once you get things dialed in reasonably close to where you want them with the stuffing.

El: As far as motor structure and mass goes, my Brother's 5" mids and 9" woofers both have 3" voice coils. The 9's have less than 30 grams of moving mass. How's that for "transient response capability"? From what i can tell, this is equivalent to having a fully massaged "big block" bolted into a shopping cart : )

Even with this much "motor structure" and lack of reciprocating weight, these drivers don't demonstrate the high "force factor" aka "slam" that many larger and heavier drivers are capable of. The bass is very tight and punchy, but it just doesn't have the "weight" or "impact" that one can achieve by using a larger driver. Even though my Brother is using two 9" woofers per side, he knows that he's missing bottom end. That's why he's also running two larger sub-woofers per side : ) Sean

PS... Many folks confuse large quantities of bass and / or bass over-hang with deep bass extension. Since it is easier to obtain greater output at higher frequencies than it is to go deep and maintain high levels of linearity, many manufacturers substitute "bloom" for bottom end. Once one gets rid of the "artificial boost", you can really hear the lack of extension. I am going through this right now with my Father and his system. After rebuilding / modifying his system, he thinks he's missing deep bass. Since we effectively made his cabinets larger, which extends bass response, there is NO way that this is possible. What he's doing is confusing the lack of upper bass "bloat" for deep bass extension. While he's VERY happy with the improvements in bass definition and tonality, the lack of 80 Hz bass makes him think that the system is "lean". That's why i'm working on a 15" sub-woofer for him now : )
Sean, don't you think that TWO 15"ers in stereo (i.e. one per channel) would do the trick for yr Dad?
- You would still have definition (not the single-note pulsating muddiness)
- There would be better spl so, bass will be more perceptible
Sean...Those small drivers with big voice coils wouldn't be Dynaudio by any chance. I have a set of Dynaudio MTM boxes with 5inch "woofers" that have 3inch voice coils. They bark furiously, but no bite. Very nice close up in a small room.

Size matters.
My next direction is going to be in a really good subwoofer. I am beginning to think that this is one area where i will probably try a number of home auditions before deciding.

Long live the local brick-and-mortar shops!
Greg: My Dad's system is actually quite solid down to 35 Hz and rolls off below that. Given that he doesn't listen to pipe organ music or electronica, he'll simply have to get used to "natural" sounding bass. It may take some time, but after living with stupendously bloated "thud" for years on end, and thinking it was both "good" and "extended", it may be tough for him to deal with initially. As i've already commented though, he is well aware of the phenomenal increase in bass resolution and transient response, so i'm thinking that there is hope : )

As far as the sub goes, that will be used for HT purposes only. This specific model was rated as being -1.5 dB down at 25 Hz and is quite large. Due to using this strictly for special effects on movies, placement of the sub becomes less critical. This is in comparison to if the sub was used for stereo purposes, which would require some semblance of low frequency imaging. The speakers that he's running for mains are actually too large for the given installation in my opinion. Adding two large sub-woofers with the requisite box size required for good performance would be too much for this room and there just isn't enough space to do so. Given that his mains already have an 8" and 10" per cabinet that share the low frequency load, he's not "hurting" in this regard.

Besides all of that, i'm paying for the sub, amp and cabling, so he can't complain about "only having one sub" : )

El: The mids, tweeters and woofers that my Brother is using are Morel drivers. Given that Morel purchased technology from Dynaudio, one can see the similarities in driver design.

Having said that, i agree with your assessment. That is, even with minimal mass and big motors, these drivers just don't move air / respond like a "big boy" can. This is why i've got six 12's, four 10's, six 8's in my HT system and eight 12's in my main two channel system. Even with all of that, i can hear others saying "What ?!?!?! NO 15's, 18's or 21's ????" : )

UncleJeff: If you do some research, i think that you'll find that you'll have better luck building a sub from a kit than anything that you can buy at a brick and mortar shop for anywhere near the same amount of money. Having said that, most sub kits are PHENOMENALLY easy to put together, so don't let a lack of mechanical / electrical aptitude scare you away from attempting such a project. Sean

PS... The pair of subs that i've got lined up for my next "project" make use of a single 12" and two 15's in large, low Q sealed cabinets. I may use these with my Ohm F's, which should help increase max spl and clean up their transient response a bit. Obviously, active crossovers would be used since passive's do horrible things to the amplifier / speaker interphase : )
Sean..What no 30 inch EV30W? Back in the old days one would install one of these monsters in the ceiling, vented to the attic. Hartley 18 inchers were second best.

If you are looking for 15" subwoofers, check out the JBL SUB 1500 drivers that Parts Express is selling at a good price. I just got three to replace the JBL LE15 that I have been using (which are good, but not really designed for the SW application). I am impressed.
El: First of all, i'm shooting for the 64" drivers that EV used to make. Who wants those "puny" 30 inch EV's when you can have the "BIG boy" : )

The JBL's at Parts Express are designed to be used in a vented system. If i was going to spend that much money on a driver, i would use one that was more optimally suited for a sealed design.

Funny that you should mention them though as the 15" that i'm using actually is a JBL. Some folks consider it the best ( or one of the best ) "audiophile type" woofers that JBL ever made. It is a model 2235 and both the driver and the cabinet that it came in are in great shape.

For those that might remember these, it is a good sized Sumo Samson subwoofer that i purchased for $40 ( yes, FOURTY ) locally. Factory specs showed a response of 25 Hz to 125 Hz +/- .5 dB ( yes, HALF a dB ), but i don't believe that one bit. This is a vented design using TWO huge ( 4" x 18.5" ) ports. Obviously, this thing was designed to move a LOT of air at low frequencies and was optimized for high spl's. Due to that tuning though, i'm quite certain that it would lack "finesse", both at lower volumes and for music use. Given that this will be strictly used for the LFE channel when watching movies, it should work out quite well. Either way, it will be FAR from stock when i'm done with it.

Given the price and the driver involved, there was NO way that i was going to pass up a deal like this. The only bad part about the whole transaction was trying to get this behemoth into a hatchback by myself. The cabinet is appr 30" x 24" x 19" and weighs 150 lbs. Needless to say, i DID break a sweat :( Sean
You guys have to check out the Adire Tumult.I currently use two,each in a 2.5 cu.ft. cabinet.Since the F3 is about 27hz in that small of a cabinet I am going to buy two more and run a Marchand bassis to reshape the curve flat down to about F3 of 16hz.850 watt mono adcoms on each and .....oh boy I gotta go to bed.
Sean...Those JBL 1500 seem to work well in my sealed enclosures, but then they are 7.5 cubic feet. How would I know that these drivers are designed for vented use, other than the FS = 24 which is higher than some but still well below the typical 15" Prosound driver?

The only thing I can cite to match your EV 64" thing is the vibration machine that we use to test our missile GS. This machine really is a huge loudspeaker, and has a "voice coil" four feet (yes feet) in diameter, and shakes two hundred pound objects at awesome levels. Interestingly, its frequency response goes a lot higher than most subwoofers. We use it up to 1000 Hz or so (but not with flat response). I don't know what the power amp's old enough to be some kind of tubes. Maybe amplidyne. I will find out. The drive is a closed-loop servo using accelerometers mounted on the test fixture (a la Velodyne).
If one can do the math using the Thiel-Small parameters, it is not hard to figure out if the woofer will work optimally in a sealed or vented design. Having said that, there are quite a few woofers on the market today that are designed as kinda-sorta "universal" woofers. That is, they'll work in either type of enclosure but not as well as a woofer specifically designed for one or the other. This JBL works optimally in a vented enclosure, hence Revel's use of a vent.

Here's some info that i found on the web for those that are interested in such things. It was written by an individual by the name of Dave Edwards from what i can gather. I don't know who he is, if he is an "industry professional" or "diy'er", etc... Obviously, some of this is going to be up to interpretation and is based on his own experience. I didn't read through all of this, but what i did looked to be of good quality and pretty factual. Like anything else though, some of this may be a "judgment call".

When trying to work these equations, just bare in mind that many "spec's" from various manufacturers of raw drivers are VERY wishful at best. As such, one almost has to have the drivers in hand, break them in thoroughly and then test them to obtain usable spec's. Obviously, if you have spec's from someone that has done all of the above that you feel that you can trust, that will save a LOT of time and money.

As a side note, some of these figures WILL change as the temperature of the motor structure ( voice coil ) on the driver varies. There are also quite a few other very important factors that aren't discussed here that go into making a "world class" speaker design. Having said that, knowing and using some of these simple "guidelines" can net you a very decent speaker without spending a million dollars. Then again, a million dollars could surely get you a VERY fine speaker if you put your mind to it : )


Prior to 1970, there were no easy or affordable methods accepted as standard in the industry for obtaining comparative data about loudspeaker performance. Recognized laboratory tests were expensive and unrealistic for the thousands of individuals needing performance information. Standard measurement criteria were required to enable manufacturers to publish consistent data for customers to make comparisons between various loudspeakers.

Thiele-Small Parameters

In the early seventies, several technical papers were presented to the AES (Audio Engineering Society) that resulted in the development of what we know today as 'Thiele-Small Parameters'. These papers were authored by A.N.Thiele and Richard H. Small. Thiele was the senior engineer of design and development for the Australian Broadcasting Commission and was responsible at the time for the Federal Engineering Laboratory, as well as for analyzing the design of equipment and systems for sound and vision broadcasting. Small was, at the time, a Commonwealth Post-graduate Research Student in the School of Electrical Engineering at the University of Sydney.
Thiele and Small devoted considerable effort to show how the following parameters define the relationship between a speaker and a particular enclosure. However, they can be invaluable in making choices because they tell you far more about the transducer's real performance than the basic benchmarks of size, maximum power rating or average sensitivity.

Fs------This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well.

Re--------This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load.

Le--------This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs.

Q Parameters---------Qms, Qes, and Qts are measurements related to the control of a transducer's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the loudspeaker). The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs. Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock. Qts is called the 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same.
As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If you are in any doubt, contact your Eminence representative for technical assistance

Vas/Cms--------Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker. Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature — a precisely controlled lab environment is essential. Cms is measured in meters per Newton. Cms is the force exerted by the mechanical suspension of the speaker. It is simply a measurement of its stiffness. Considering stiffness (Cms), in conjunction with the Q parameters gives rise to the kind of subjective decisions made by car manufacturers when tuning cars between comfort to carry the president and precision to go racing. Think of the peaks and valleys of audio signals like a road surface then consider that the ideal speaker suspension is like car suspension that can traverse the rockiest terrain with race-car precision and sensitivity at the speed of a fighter plane. It’s quite a challenge because focusing on any one discipline tends to have a detrimental effect on the others

Vd------This parameter is the Peak Diaphragm Displacement Volume — in other words the volume of air the cone will move. It is calculated by doubling Xmax (Voice Coil Overhang of the driver) then multiplying the result by Sd (Surface area of the cone). Vd is noted in cc. The highest Vd figure is desirable for a sub-bass transducer

BL------Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!

Mms------This parameter is the combination of the weight of the cone assembly plus the ‘driver radiation mass load’. The weight of the cone assembly is easy: it’s just the sum of the weight of the cone assembly components. The driver radiation mass load is the confusing part. In simple terminology, it is the weight of the air (the amount calculated in Vd) that the cone will have to push

Rms------This parameter represents the mechanical resistance of a driver’s suspension losses. It is a measurement of the absorption qualities of the speaker suspension and is stated in N*sec/m.

EBP-----This measurement is calculated by dividing Fs by Qes. The EBP figure is used in many enclosure design formulas to determine if a speaker is more suitable for a closed or vented design. An EBP close to 100 usually indicates a speaker that is best suited for a vented enclosure. On the contrary, an EBP closer to 50 usually indicates a speaker best suited for a closed box design. This is merely a starting point. Many well-designed systems have violated this rule of thumb! Qts should also be considered.

Xmax/Xmech--------Short for Maximum Linear Excursion. Speaker output becomes non-linear when the voice coil begins to leave the magnetic gap. Although suspensions can create non-linearity in output, the point at which the number of turns in the gap (see BL) begins to decrease is when distortion starts to increase. Eminence has historically been very conservative with this measurement and indicated only the voice coil overhang (Xmax: Voice coil height minus top plate thickness, divided by 2). Xmech is expressed by Eminence as the lowest of four potential failure condition measurements times 2: Spider crashing on top plate; Voice coil bottoming on back plate; Voice coil coming out of gap above core; Physical limitation of cone. Take the lowest of these measurements then multiply it by two. This gives a distance that describes the maximum mechanical movement of the cone.

Sd------This is the actual surface area of the cone, normally given in square cm.

Zmax-----This parameter represents the speaker’s impedance at resonance.

Usable frequency range---------This is the frequency range for which Eminence feels the transducer will prove useful. Manufacturers use different techniques for determining ‘Usable Frequency Range’. Most methods are recognized as acceptable in the industry, but can arrive at different results. Technically, many loudspeakers are used to produce frequencies in ranges where they would theoretically be of little use. As frequencies increase, the off-axis coverage of a transducer decreases relative to its diameter. At a certain point, the coverage becomes ‘beamy’ or narrow like the beam of a flashlight. Following is a chart that demonstrates at what frequency this phenomenon occurs relative to the size of the transducer. If you’ve ever stood in front of a guitar amplifier or speaker cabinet, then moved slightly to one side or the other and noticed a different sound, you have experienced this phenomenon and are now aware of why it occurs. Clearly, most two-way enclosures ignore the theory and still perform quite well. The same is true for many guitar amplifiers, but it is useful to know at what point you can expect a compromise in coverage.

Power handling-------------This specification is very important to transducer selection. Obviously, you need to choose a loudspeaker that is capable of handling the input power you are going to provide. By the same token, you can destroy a loudspeaker by using too little power. The ideal situation is to choose a loudspeaker that has the capability of handling more power than you can provide lending some headroom and insurance against thermal failure. To use an automobile as an analogy; you would not buy a car that could only go 55mph if that were the speed you always intended to drive. Generally speaking, the number one contributor to a transducer’s power rating is its ability to release thermal energy. This is affected by several design choices, but most notably voice coil size, magnet size, venting, and the adhesives used in voice coil construction. Larger coil and magnet sizes provide more area for heat to dissipate, while venting allows thermal energy to escape and cooler air to enter the motor structure. Equally important is the ability of the voice coil to handle thermal energy. Eminence is renowned for its use of proprietary adhesives and components that maximize the voice coil’s ability to handle extreme temperatures. Mechanical factors must also be considered when determining power handling. A transducer might be able to handle 1,000W from a thermal perspective, but would fail long before that level was reached from a mechanical issue such as the coil hitting the back plate, the coil coming out of the gap, the cone buckling from too much outward movement, or the spider bottoming on the top plate. The most common cause of such a failure would be asking the speaker to produce more low frequencies than it could mechanically produce at the rated power. Be sure to consider the suggested usable frequency range and the Xmech parameter in conjunction with the power rating to avoid such failures


Hope this helps..... Sean
Thanks Sean....I have copied the info so I can read it at leisure. This appears to be the best definition of TS parameters that I have ever seen. What I am looking for is some kind of single dimensionless number (like Bernoulli's number that relates to fluid dynamics) that would describe where a driver falls on the optimization spectrum between vented and sealed. Maybe I will invent such a parameter.
Sean...I guess that QTS is the parameter I had in mind, although as the writup suggests, it does not reliably describe vented/sealed suitability . The JBL 1500 QTS is 0.32, not far from the 0.4 suggested as the boundry between vented and sealed. I am sure that enclosure size, shape, and stuffing has a lot to do with it.

I could easily put a vent in my enclosures, but mice would probably take up residence. (Deaf mice).
El: Here's the "generic" figure that you're looking for.
EBP-----This measurement is calculated by dividing Fs by Qes. The EBP figure is used in many enclosure design formulas to determine if a speaker is more suitable for a closed or vented design. An EBP close to 100 usually indicates a speaker that is best suited for a vented enclosure. On the contrary, an EBP closer to 50 usually indicates a speaker best suited for a closed box design. This is merely a starting point. Many well-designed systems have violated this rule of thumb! Qts should also be considered.

The JBL driver that you refer to has an Fs of 25 and a Qes of .34 according to factory specs. The Fs ( 25 ) divided by Qes ( .34 ) equals the EBP ( 73.5 ). This figure is "kinda-sorta" in-between the "basic guidelines" of 50 for a sealed design and 100 of a vented design. Given the lower Qts and higher Fs of the driver, it definitely leans towards the vented side in my opinion. Having said that, it will also work in a sealed design. Playing with box volume along with the type and density of stuffing will have major effects on the resonant frequency and amplitude of the impedance peak.

As a side note, larger box size can allow increased extension, but it does so at the expense of power handling and transient response. There is an optimally sized box / stuffing combo for any given driver. You can fudge the figures up or down to achieve specific goals, but there are trade-offs involved. Sean

PS... I'm off to work on my Father's sub. Drop me an email if you want to chat further.
Damn, Sean, that's really cool having a father that owns a sub. All I ever got to drive in high school was my Dad's 1953 Buick Special (yes, the one with the 130-horsepower straight six and Dynaslush transmission). I remember taking dates to SEE the submarine races, but having a Dad with a sub would have been a Hell of an improvement!!!
Scott: Thanks for the laugh. Too bad my Dad didn't have a "sub" like that. Taking a date out for a ride in the "sub" and "running out of gas" or having "engine trouble" would have probably been FAR more effective going that route : ) Sean