Subwoofer Driver choice?

[bodcaw boy]

i'm a little confused shawn,

isn't reducing the amplitude of a resonance just pouring less energy into that resonance. and so you haven't changed it's decay but just diminished it?

also wouldn't that effect the "sonic signature" of the passage of the first arrival and now you rely on the room resonance to compensate? just thinking aloud and of course using a horn!

have a blessed day,

roy delgado

[DrWho]

"I know we've had some discussion on this before, but isn't measuring the final response with an RTA and pink noise a bit misleading since it gives the room a lot of time to get excited and build on itself?"

Room gain kicks in on the initial cycle of the wave. That is basically why you get the room gain... the reflections within the room are inphase with what is basically the same cycle of the wave. The more inphase the wave gets the more room gain gain you get... that is why it kicks in below the longest resonant point in the room and increases as you go lower in frequency as the wave gets longer and longer and therefor couples more with itself.

Just because it is "in phase" doesn't mean it is "on time"...

"- but it's going to be a ramping effect and not as dynamic as an "instant" build up."

That is not my experience at all. In fact I'd say my sealed subs that utilize room gain sound more dynamic then the ported sub. Remember... at the top end of a subs bandwidth you aren't using room gain, just down deep. To really take advantage of room gain you need subs with a classic second order rolloff... so a Q around 0.5... that results in a punch/dynamic sounding subwoofer.

can't argue with your experiences, but that doesn't sit right with my experiences...I'd love to hear your setup sometime.

"...if anything, you're just going to have a room that holds onto the notes a bit longer. "

Nope, room gain is below the rooms resonance points.

Hmmm...that's not what my measurements are showing. Maybe resonance isn't the right term - "reverb" or decay time is what I'm talking about...

"Also, the few rooms I've measured indicate that the gains don't start happening until you start cranking the SPL - probably has something to do with the walls' ability to damp lower level signals?"

Possibly, and also leaking bass out reduces room gain. That is why I asked about how solid his room is. If it is a very lossy room then room gain isn't as effective.

Agreed - rolling the windows up and down in the car is a perfect example too.

"Wouldn't it be better to design a system to be flat to 10Hz or whatever the desired cutoff is and then use EQ to back off any extra room gain?"

If you are worried about the time it takes for room gain to build up why wouldn't you be concerned about the exact same thing here? If you think this is an issue then in this case your initial response would be cut by the EQ until room gain kicks in and be no different then a system that utilizes room gain.

Because designing a system to rely on room gain limits one from being able to ignore room gain effects. In other words, there's no reason a system that can go flat anechoic can't sound the same after EQ.

"? In the process you're going to be reducing the distortion of the system - something you can't do when relying on room gain in the first place."

How do you figure? If you EQ out some of the output of the driver to account for room gain how is that different from having the woofer play at a lower level without EQ and ending up at the same SPL?

Shawn

I figure a sytem capable of displacing the air required for the extreme low end is going to have less effects from nonlinear behavior. Using the same drivers, the more capable system is going to have a larger cabinet so it will effectively be more efficient - thus not working as hard. Less losses usually means less distortion. But really, you're not going to be able to use the same driver since it can't be optomized for two different applications...which makes the general "rule" hard to claim as there are bound to be many exceptions.

[DrWho]

"Using EQ does not change the behavior of the decay at all....it just makes the tail hit the noise floor sooner"

Sorry, but it does. I've seen the before and after waterfalls. Again, the Lexicon and Meridian systems are both built specifically to target frequencies in the room with unnaturally long decay times. They do not try and get 'flat' response, in fact the designer of the Lexicon setup said just trying for 'flat' response in an EQ system like this is the wrong way to go.

And I've seen waterfalls that show the exact opposite [] Assuming that both cases are true and not the result of user error (ie, perfect EQ practices), then there must be other factors at play making the EQ effective some of the time???

Thanks for the links...I'll take my time reading them [Y] Poor efzauner....we should probably start another thread. I have a feeling this could open a few more cans of worms.

[bodcaw boy]

Hi everyone

I am trying to decide what drivers to use for a subwoofer for audio and HT. I would like your thoughts on the design process. My HT room is 16x12x8ft. That means a room gain frequency of about 565/16=35 Hz. I plan on using 2 or 4 subs driven by a Pro Audio amp (Mackie, Beringer, Crown etc) so I do not need a single ultra sub in the range of JL12W7 or other really high Xmax sub. I think that several subs working at medium levels in each room corner would be bether than one big sub running at high power with associated power compression and distortion. My mains are LaScalas with Heresy surrounds and center.

With the 35Hz room gain +3dB frequency should I design a sub that has a -3dB point also at 35Hz and try to minimize any low frequency hump? Or should I simply try to make a sub that has the lowest -3db point?

Attached are 2 WinISD design trial with 4 different subs. The first are sealed designs and the second are vented Designs. 2 of the subs are commonly used for home DIY subs, the other 2 are car audio subs. These are subs in the $100 to $200 range.

If I go with a closed design, the Madisound driver gives great low end response, but with a large cabinet. The others have -3dB points in the 35-40Hz range. The Infinity car sub is actually the cheapest of the lot and no slouch!

If I go with a vented design, the Madisound seems out of place, seeming to prefer a sealed design. The others all dig quite low with -3dB points at 18-22Hz.

I hear about many DIY going for the Dayton Titanic in a sealed cabinet but I dont understand why the performance is so great. I also see that most commercial subs are vented designs and they all seem to go very low.

All else being equal (sensitivity, xmax, max power etc) should I go with a sealed Madsound or a vented design with one of the other subs. Should I go for a vented design and pick the sub that gives the highest output given its Xmax, sensitivity and max power?

i don't know but i would go with a k-472.....just happens to be the driver used in the kpt-884-sw.........just happens to be a cinema sub.........just happens to be vented..........just happens to go pretty low.........i don't know.

have a blessed day,

roy delgado

[DrWho]

guys,

is room gain more associated with the "air load" the driver has to couple to?

have a blessed day,

roy delgado

Are you elluding to the differences between 1/2, 1/4, 1/8 space loading - where the gains are the same at every frequency (as long as the dispersion doesn't narrow)? Or the volume and dimensions of the room that correlate to gains that change with frequency (at 12dB/octave rise below the lowest resonance)? I think I worded that right? I'm not sure if they're the correct terms, but I've always referred to the former as boundary gain and the latter as room gain.

[bodcaw boy]

guys,

is room gain more associated with the "air load" the driver has to couple to?

have a blessed day,

roy delgado

Are you elluding to the differences between 1/2, 1/4, 1/8 space loading - where the gains are the same at every frequency (as long as the dispersion doesn't narrow)? Or the volume and dimensions of the room that correlate to gains that change with frequency (at 12dB/octave rise below the lowest resonance)? I think I worded that right? I'm not sure if they're the correct terms, but I've always referred to the former as boundary gain and the latter as room gain.

uh both....doesn't all come down to how much air the driver has to push? kinda of like going from velocity to pressure.....

have a blessed day,

roy delgado

by the way, for the comment in the forte ii thread, another finger please....

[sfogg]

Roy,

"isn't reducing the amplitude of a resonance just pouring less energy into that resonance. and so you haven't changed it's decay but just diminished it?"

Somewhere in those posts I think Jim explained how the decay changes. Basially I think it was along the lines of exciting the resonance less results in a quicker decay. Sort of like hitting a bell lightly compared to hitting one harder. With a light hit the bell decays quickly, the harder you hit it the longer it holds on to the note.

"also wouldn't that effect the "sonic signature" of the passage of the first arrival and now you rely on the room resonance to compensate?"

Actually it doesn't rely on the rooms resonance to compensate since they would only compensate at specific points in the room. The system isn't aiming for flat amplitude response, it is targeting frequencies that have far too long a decay time. Remember too that before the EQ you could have narrow band peaks of 10 or even 20dB. This gets into the question of which is a bigger audio problem... the potential for a *very* narrow dip (the Lexicon filters can be set to a half power bandwidth of something like 0.7hz) in the response or a frequency that is playing for longer then it should everywhere in the room and obscuring detail that follows the note?

From my experience I'd say the room holding onto notes is a much bigger problem. YMMV.

Shawn

[DrWho]

i don't know but i would go with a k-472.....just happens to be the driver used in the kpt-884-sw.........just happens to be a cinema sub.........just happens to be vented..........just happens to go pretty low.........i don't know.

have a blessed day,

roy delgado

Are you able to share its T/S params? The sensitivity on that thing is impressive. 10dB down at 18Hz isn't very impressive, but that should come close to 119dB at 18Hz if the ports don't get overloaded. I bet a little EQ and a little cabinet redesign could fix that though.

[bodcaw boy]

i don't know but i would go with a k-472.....just happens to be the driver used in the kpt-884-sw.........just happens to be a cinema sub.........just happens to be vented..........just happens to go pretty low.........i don't know.

have a blessed day,

roy delgado

Are you able to share its T/S params? The sensitivity on that thing is impressive. 10dB down at 18Hz isn't very impressive, but that should come close to 119dB at 18Hz if the ports don't get overloaded. I bet a little EQ and a little cabinet redesign could fix that though.

oh doc,

you sometimes remind of a bose speaker; first right on and getting it like a nice spl peak and then you dive into a dip, about 20 db down (making you +/- 10 db).....tsk, tsk.

-10db down in half space.........put in a cinema, where it more like quasi 1/4 space and then what happens?

have a blessed day,'

roy delgado

[sfogg]

Mike,

"Just because it is "in phase" doesn't mean it is "on time"..."

Again... same cycle in phase. Think of a 75 foot wave (15hz) in a 20 foot room... the first reflection off the back wall is going to bounce back and hit the speaker while it is still reproducing the same cycle of the wave.

"I'd love to hear your setup sometime."

If you are ever over my way let me know.

"Because designing a system to rely on room gain limits one from being able to ignore room gain effects. "

If you did a good job matching the subs to the room why would you want to ignore the room gain effects? Tom Danley (great grand poobaa of all things bass) calls room gain 'one of the only free lunches in audio.' Why not take advantage of that?

"I figure a sytem capable of displacing the air required for the extreme low end is going to have less effects from nonlinear behavior."

Why? By tuning the system lower your can end up trading output ability on the top end of the subwoofer. Or introduce other problems such as more IMD from the required greater xmax and the potential for more nonlinear behavior all the time from the larger suspensions/spiders and so on for the greater xmax requirements?

Just so we are clear I'm not talking about using a whimpy little driver and hoping room gain will do the rest. I'm talking using great drivers and trying to match them to the room. I have 4 JBL Sub1500s in my L/R subs which are what take advantage of room gain.

Shawn

[bodcaw boy]

Roy,

"isn't reducing the amplitude of a resonance just pouring less energy into that resonance. and so you haven't changed it's decay but just diminished it?"

Somewhere in those posts I think Jim explained how the decay changes. Basially I think it was along the lines of exciting the resonance less results in a quicker decay. Sort of like hitting a bell lightly compared to hitting one harder. With a light hit the bell decays quickly, the harder you hit it the longer it holds on to the note.

i guess that is what i was saying....less energy in the resonance depresses the decay....but it still decays in the same fashion or am i missing something?

"also wouldn't that effect the "sonic signature" of the passage of the first arrival and now you rely on the room resonance to compensate?"

Actually it doesn't rely on the rooms resonance to compensate since they would only compensate at specific points in the room. The system isn't aiming for flat amplitude response, it is targeting frequencies that have far too long a decay time. Remember too that before the EQ you could have narrow band peaks of 10 or even 20dB. This gets into the question of which is a bigger audio problem... the potential for a *very* narrow dip (the Lexicon filters can be set to a half power bandwidth of something like 0.7hz) in the response or a frequency that is playing for longer then it should everywhere in the room and obscuring detail that follows the note?

but we are suppressing a band and if were able to etc the response we would see a notch and then rely on the resonance to flatten out the power response.....although you bring up an interesting point, which is worse?

From my experience I'd say the room holding onto notes is a much bigger problem. YMMV.

Shawn

don't know shawn,

as docs tagline used to say, something about compromise,

have a blessed day,

roy delgado

[sfogg]

Roy,

"uh both....doesn't all come down to how much air the driver has to push? kinda of like going from velocity to pressure....."

OK... you are hinting at something big time here I think.

(possible light going on....)

Is room gain nothing more then better loading the driver in the pressure region and therefor increasing its coupling to the air to make the driver more efficient? Kinda like a horn... but without a horn?

Shawn

[bodcaw boy]

hey shawn,

that's is what i have always thought and i have played with that for quite a bit now. after all, we use a horn to couple the diaphragm better to the air load but if the air load becomes easier to push then doesn't that also start to alleviate how much horn loading we need to do? and so since we are relying less on air load, maybe that leaves the duty of the horn now to just directivity?

have a blessed day,

roy delgado

[DrWho]

i don't know but i would go with a k-472.....just happens to be the driver used in the kpt-884-sw.........just happens to be a cinema sub.........just happens to be vented..........just happens to go pretty low.........i don't know.

have a blessed day,

roy delgado

Are you able to share its T/S params? The sensitivity on that thing is impressive. 10dB down at 18Hz isn't very impressive, but that should come close to 119dB at 18Hz if the ports don't get overloaded. I bet a little EQ and a little cabinet redesign could fix that though.

oh doc,

you sometimes remind of a bose speaker; first right on and getting it like a nice spl peak and then you dive into a dip, about 20 db down (making you +/- 10 db).....tsk, tsk.

-10db down in half space.........put in a cinema, where it more like quasi 1/4 space and then what happens?

have a blessed day,'

roy delgado

lol - I guess that means I must look pretty too....[]

Yes I know...you get an increase in low frequency response (about 3dB actually) - but isn't it going to be the same at 20Hz as at 80Hz since the speaker is essentially omnidirectional at both frequencies? [^o)]

I suppose a better question to ask would be "got some 1/8 space measurements?" []

[bodcaw boy]

doc,

what happened to your 12 db slope gain?

have a blessed day,

roy delgado

[DrWho]

Mike,

"Just because it is "in phase" doesn't mean it is "on time"..."

Again...
same cycle in phase. Think of a 75 foot wave (15hz) in a 20 foot
room... the first reflection off the back wall is going to bounce back
and hit the speaker while it is still reproducing the same cycle of the
wave.

Right, but the reflection is still delayed in time.
You don't need to hear a full cycle to hear the full note....or are you
proposing that because it is within the same cycle that you can't hear
a difference? I suppose an easy test would be to have two woofers
playing the same thing and then shifting one of them back and forth in
time - staying within the bounds of a cycle?

"I'd love to hear your setup sometime."

If you are ever over my way let me know.

Whereabouts do you live? I might need to take a special trip []

"Because designing a system to rely on room gain limits one from being able to ignore room gain effects. "

If
you did a good job matching the subs to the room why would you want to
ignore the room gain effects? Tom Danley (great grand poobaa of all
things bass) calls room gain 'one of the only free lunches in audio.'
Why not take advantage of that?

Well I guess if you want a system that is flat after room gain that makes sense []

Another
thing I see in various places on the internet is the concept of a
"house curve" - a slightly rising low frequency response to account for
equal loudness and the tendency for studios to roll off the low end a
bit to be suitable for playback in cars...but that's all a subjective
argument and there's no need to go there - apart from mentioning that
its easier to bring down the response of a system than trying to boost
it.

I think something inbetween flat 1/8 space anechoic and flat with room gain is the ideal...

I'd hate to argue with Danley though....but doesn't Nousaine design with no regard to room gain?

"I figure a sytem capable of displacing the air required
for the extreme low end is going to have less effects from nonlinear
behavior."

Why? By tuning the system lower your can end up
trading output ability on the top end of the subwoofer. Or introduce
other problems such as more IMD from the required greater xmax and the
potential for more nonlinear behavior all the time from the larger
suspensions/spiders and so on for the greater xmax requirements?

Just
so we are clear I'm not talking about using a whimpy little driver and
hoping room gain will do the rest. I'm talking using great drivers and
trying to match them to the room. I have 4 JBL Sub1500s in my L/R subs
which are what take advantage of room gain.

Shawn

Trading
output ability at the top end? Are you thinking of port resonances or
standing waves in the cabinet? I suppose an easy answer to that is the
passive radiator (can I have my pinky back?). Or is there something
else at play that doesn't show up in the models?

Porting a
cabinet always reduces the cone excursion - until you get below the
tuning point...but that's what the highpass filters are for. You can
also port a system such that it doesn't change the characteristic
transient behavior of the sealed system....so you could basically take
your ideal room matched sealed configuration and then use a port to
extend the LF corner a little bit where the room gain rolls off. Is it
worth the extra expense? I dunno....I see guys doing it all the time
though. They had some acronym for it....something about large and low
tuning or something like that.

[DrWho]

doc,

what happened to your 12 db slope gain?

have a blessed day,

roy delgado

I thought that was the result of reflections from within the room always being in phase. Thems gonna be delayed some - especially in a large cinema, no?

[sfogg]

Roy,

"i guess that is what i was saying....less energy in the resonance depresses the decay....but it still decays in the same fashion or am i missing something?"

I'll see if I can find the post from Jim where he explained this better then I have done as I can't recall the exact specifics of this discussion as it was several years ago. I think it was something along the lines of how a room absorbs/looses/dissapates power. Sort of like consider an electrical circuit that looses 1v of a power every ms. If you start out at 10v your initial power dissipation is slower the first ms compared to if you only start out at 5v. In the first ms starting at 10v and dropping to 9v you only dropped 0.9dB. But the system that started out initially at a lower voltage level of 5v and dropped to 4v dropped 1.9dB. In the second MS the first system has dropped 1.9dB while the second has dropped 4.4dB

Or I might be totally screwing that up....

"but we are suppressing a band and if were able to etc the response we would see a notch and then rely on the resonance to flatten out the power response.....although you bring up an interesting point, which is worse?"

The system actually doesn't really care about using the resonance to flatten out response from the EQ dip. That would only work at very specific points in the room where you see peaks from the resonance itself. There are many points in the room where you won't see that peak, yet are still effected by the resonance.

The amplitude peaks/nulls from the resonances are basically a symptom of the problem, they aren't the problem itself. The problem is certain frequencies in the room 'ring' and basically play for much longer then they should... a wave bouncing back and forth in the room for longer then it is supposed to be there. Literally a note playing that isn't in the music. This sets up standing waves which results in specific points in the room that have the peaks/nulls in the response. However every location between the two walls, excepting nulls, is hit by that wave bouncing back and forth within the room. Meaning every location between those walls, excepting nulls, is hearing the note for longer then they should.

Both the Lexicon and Meridian systems seek to improve the sound over a wide area. They do that by focusing on the decay time of the system which is more constant over area (excepting nulls), not the power response as power response corrections are much more limited to where you measure from.

"as docs tagline used to say, something about compromise,"

Yup, in this case the FR is potentially compromised to try to improve the time domain behavior of the system as both (edit: Both being Lexicon and Meridian) feel that is the better tradeoff for sound quality.

Shawn

[sfogg]

Mike,

"You don't need to hear a full cycle to hear the full note....or are you proposing that because it is within the same cycle that you can't hear a difference? "

There is an amplitude difference from the room gain as compared to not having it so you would hear that difference. And again room gain is on the bottom end, not the top end of a subs performance.

"Trading output ability at the top end? Are you thinking of port resonances or standing waves in the cabinet?"

I think it is simple xmax. To go lower/flatter (without room gain) you need more displacement. You basically use up the xmax at a lower SPL with an extended bandwidth compared to a design with a higher f3 which can then use the xmax for more output. Simple example would be the SVS cylinder subs. The models tuned higher have more SPL ability then the models tuned lower.

"Porting a cabinet always reduces the cone excursion - "

Only at the bottom end of the response. On the other end of the scale there is little difference. Get below the system tuning and the ported system is going to have way more cone excursion.

"until you get below the tuning point...but that's what the highpass filters are for. "

High pass filters are for wimps! (Saying that knowing my subwoofer amps have a high pass at 7hz... and that they might be limiting my response

"..so you could basically take your ideal room matched sealed configuration and then use a port to extend the LF corner a little bit where the room gain rolls off."

Do you have a link for that? Most of the ported system I've seen roll off too fast below resonance to couple with the room like one can sealed. Wouldn't you still run into the potential problem of woofers flapping (no high pass) in that setup?

Shawn

[DrWho]

A link for one of the designs? Or the design concept theory stuff? (I can't think of any for the latter...just a bunch of forum posts - I'll see what I can find though). As far as the flapping driver - won't that be fixed by your amp's filter? []

One other concept I've come across is the psychoacoustics of having a say a kick drum in your living room. It is going to experience the same room gain effects as the sub. In the studio, you basically end up with the "anechoic" sound of the instruments (I say that loosely) - so upon playback, you need your room's rise in the bass response for it to sound like there is a real kick in your living room...I'm probably butchering the concept, but it seems to make sense. Of course - I make this analogy and then compare to my listening to music in the car....I always plug the port in the cabinet to help undo the effects of the cabin gain.

Maybe I'm just a bass freak and enjoy a little boost at the lower frequencies? [^o)]