where have all the acoustic suspension subs gone?

[Jay481985]

I have to disagree with you drwho.

Most high end subwoofers do make the enclosure based on the woofer but for the rest of the non uber subwoofers out there, They make the subwoofer enclosure first and then get a subwoofer to work best in it. If you think I am wrong, look at all those simply way too small enclosures out there touting their the next best thing after sliced bread. I mean really I believe 90% of the market makes the enclosure first to first asthetic and design aspects over any how it sounds terms.

[sfogg]

"And there are also a few more tricks that can be taken advantage of with ported systems..."

There are of course tricks that can be taken advantage of with sealed systems too.

A big one is room gain. If a sealed sub is sized to take advantage of

room gain and the room is fairly well sealed this can extend response

much deeper and in effect be free bass extension.

There is also the additional driver protection in a sealed woofer system compared to ported.

Shawn

[blake_mooney]

Velodyne Servo's!

Acoustic suspension means a sealed, and not ported or bandpassed enclosure.

I use my Orion 10" NT2's in an acoustic suspension HDF box with ultra-linear bass panels the bass is clean, low, precise, and hits like a sledgehammer with my Orion XTR-2150 feeding them.

Most of the kids car's I hear sound like ten men beating on the side of an inflated rubber raft, "boing, boing, boing."

You sacrifice sheer output with this design but the trade-off is high quality bass response

Man I hear that, I hate those kids that role down the street with "loud" or "boomy" bass and they as well as other people think it's quality bass, heh, what a joke.

[chops]

What's the deal with TheWOOFER? That kid hasn't said anything decent yet.

Anywhoo...

[TheEAR]

Sealed subwoofers done right will have the edge over ported,no port noise,no port(s) to deal with.Ports are almost never free from port noise at high SPL.

This is why all servo subwoofers are sealed,and with room gain they can both reach deep and play loud.The extra output a ported will have over a sealed design is in 99% of cases not needed and the better bass quality with a servo sealed subs more than makes up in bass quality for the loss in output.

[DrWho]

Re room gain:

A subwoofer that achieves a flat response after the effects of room

gain does not ensure the most realistic reproduction of the source

material. If a real instrument were in your room, it would also be

affected by the room gain. So to make it sound like it is actually in

the room, then in some way shape or form that room gain needs to be

accounted for at the listening position. I don't know how to explain it

very well, but I know quite a few engineers that belabor the

point...room gain is just a way of making something seem better than it

is.

Btw, room gain is not to be confused with boundary gain...which I suppose in a way are very similar concepts.

Re driver protection:

It's rather a mute point that the woofer becomes "unloaded" below the

tuning frequency because no serious subwoofer is going to be implmented

without EQ - which in all cases effectly controls the excursion of the

driver (unless the engineer is an idiot...)

gosh im tired...I'll wrote me later

[sfogg]

Read your first two sentences in reverse order.

" If a real instrument were in your room, it would also be affected by the room gain."

So if you want to argue this position (I don't) you need to have a

device reproducing it that will similarly be effected by room gain.

"A subwoofer that achieves a flat response after the effects of room

gain does not ensure the most realistic reproduction of the source

material."

You just said the device needs to be effected by room gain just like

the instrument would be. A sealed sub could do that, a ported one

wouldn't.

But like I said... I'm not taking that position. The instrument has

already been recorded in whatever room/hall it was played in. The

effects of that room/hall have already happened and are in the

recording. Therefor flat response is what I want to be able to

reproduce what is on the recording.

"but I know quite a few engineers that belabor the point"

I know quite a few engineers, like Thomas Danley for instance, who

consider room gain to be one of the only free lunches in audio.

"...room gain is just a way of making something seem better than it is.""

If a sub in the room your are using it is basically flat into single

digits how is that not better then a subwoofer that rolls off sooner in

the same room?

"It's rather a mute point that the woofer becomes "unloaded" below the

tuning frequency because no serious subwoofer is going to be implmented

without EQ - which in all cases effectly controls the excursion of the

driver (unless the engineer is an idiot...)"

Yet plenty of ported subs don't have effective enough protection. Every

time the next blockbuster movie comes out with crazy bass spend time

online on a few forums and you will read plenty of posts of 'XYZ killed

my QRS....'

And of course the limiters and or high pass filter (or sliding filters)

in the ported subs will make it even less possible to take advantage of

room gain because if will rolloff the sub even quicker. And those

DIYers may or may not be able to effectively implement protection

circuits.

Hardly a moot point.

Shawn

[DrWho]

Imagine a room with 20dB of gain at 20Hz. Everything that happens in

that room is going to have that 20dB of gain...your breathing,

footsteps, whatever...there is a sonic image of the room when you close

your eyes and have nothing playing. Now take your recording that is

expecting a flat frequency response playback system...sure, with room

gain all the frequencies are the "same volume", but it won't sound like

it is coming from inside your room. It will sound like it is coming

from another sonic space - but since you are still recieving sonic cues

of the actual room you are in you end up with a "confusing" sound stage

- wanting more low frequency extension. It is a psychoacoustical

problem that has nothing to do with "flat frequency response"

We can talk theory all we want, but there is no way in the world

someone is going to claim a subwoofer system that rolls off at 30Hz to

match the boost of the room is going to sound better than a subwoofer

system that is flat to 10Hz anechoic (all other things being equal).

And again, the concept is not my own...I too know quite a few engineers

that feel the same way.

Another comment about room gain...it's fine and dandy to talk about

things in the frequency domain, but room gain is the result of effects

that occur in the time domain. Room gain is essentially reverberation

of the room that is in phase with the original signal...a pressurizing

of the room if you will. It takes a lot of subwoofer to control this

pressurization and when you've got a sub rolling off early you

essentially have a sub that is dropping off in control. The pressure

the driver sees in front of it is also going to change how the driver

behaves - causing the rise time and decay times of the driver itself to

be different resulting in wierd waveform action in the room. When you

pump out the math you essentially come to the conclusion that these

non-linearities are a result of total radiating surface area. I need to

find a way to do some 3D models...it's really an interesting concept.

But anyways, it all comes back down to the enjoyment of the system and

I can't imagine anyone with anechoic extension down to 10Hz would trade

it for room gain extension to 10Hz. Though nobody here has ever

experienced it so it's kinda hard to address the concept. I just have

to take the word of those that have.

As far as protection goes...seems to me people a lot of people are

freaken idiots. It is entirely possible to make ported and sealed subs

completely dummy proof and impossible to overdrive and apparently

manufacturers aren't doing enough dummy proofing....probably because it

costs money. Somebody that is overdriving a ported sub is more than

likely to overdrive a sealed sub too. Heck, if I wanted to I could blow

up any driver I wanted - doesn't mean the design concepts of the system

are flawed.

For a drastic example, go listen to a sealed sub in your car that

achieves a flat response after cabin-gain and then tell me it sounds

better than the bass in your living room. And then go throw in a sub

with flat response down to 20Hz in your car and tell me what you think

[] You'll probably need to EQ it down a bit, but you'll find that you

EQ down to a point that results in more bass than flat after cabin

gain. And in such a situation the reduction EQ is going to make the

system behave more linear because it won't be pushing as hard.

Psychology and non-linearities...I'm not talking low signal level ideal world.

[sfogg]

"but it won't sound like it is coming from inside your room. "

Good!

I have no desire to hear my room.

My goal is not the 'they are here' experience. My goal is the 'I am there' experience.

"- wanting more low frequency extension."

I assure you, that is not the case. Anytime you are in my neck of the woods I can demonstrate this to you.

"but there is no way in the world someone is going to claim a subwoofer system that rolls off at 30Hz to match the boost of the room is going to sound better than a subwoofer system that is flat to 10Hz anechoic "

You speak for everyone in the world now?

"Another comment about room gain...it's fine and dandy to talk about things in the frequency domain, but room gain is the result of effects that occur in the time domain. "

So is a ported system. That is why the impulse reponse and group delay of a ported system isn't as good as a sealed system.

Room gain is the reflection from the long wall bouncing back and still being in phase with the sound the woofer is still reproducing. That is why room gain basically starts kicking in at 1/2 the wavelengh of the rooms longest dimension. The longer the wavelengths get the more in phase the reflections are.... the more you get constructive interference.

"when you've got a sub rolling off early you essentially have a sub that is dropping off in control."

No, you have a woofer that is loosing efficiency due to the air spring inside the box. The air spring is in effect increasing the damping of the system, not lowering it.

Ported systems are the ones that loose control below their tuning point.

"For a drastic example, go listen to a sealed sub in your car that achieves a flat response after cabin-gain and then tell me it sounds better than the bass in your living room. And then go throw in a sub with flat response down to 20Hz in your car and tell me what you think Wink [] You'll probably need to EQ it down a bit, but you'll find that you EQ down to a point that results in more bass than flat after cabin gain. And in such a situation the reduction EQ is going to make the system behave more linear because it won't be pushing as hard."

I don't need to do this in my car.

I have a pair of L/R sealed subs with a f3 of about 33hz. In room I'm within a dB or two of flat to at least 10hz, and likely lower... 10hz is as low as my RTA goes. My real limit is probably the 7hz high pass filter in the K2 that is driving them.

In that same room I have a ported sub (Quantum Sound ContraBass) that has an f3 of 14hz.

In pretty much every way I prefer the sealed subs. They subjectively go deeper with more power. In comparison the CB sounds sort of like a lightweight. A CB is not at all a lightweight subwoofer. And this is even without EQing down the ported sub as your suggested above.

" Though nobody here has ever experienced it so it's kinda hard to address the concept. "

Wrong, I have experienced it.

"...I'm not talking low signal level ideal world."

I'm talking real world experience, not theory.

Shawn

[DrWho]

"My goal is not the 'they are here' experience. My goal is the 'I am there' experience. "

A goal that is IMPOSSIBLE (both mathematically and psychoacoustically). If you want the "I am there experience" then go model your listening room after the studio the recording was produced in and use the exact same playback system. And anyone that has ever spent any time in a recording studio will know that it is a most lifeless and boring musical experience. I'd much rather enjoy the music.

"So is a ported system. That is why the impulse reponse and group delay of a ported system isn't as good as a sealed system. "

You need to define the passband that you're talking about. A ported system will have the same group delay and impulse response of a sealed system over the shared passband. In other words, the only place a ported system will sacrifice this is in the lower octaves of extension provided by the port.

"Room gain is the reflection from the long wall bouncing back and still being in phase with the sound the woofer is still reproducing."

Just because it is in phase doesn't mean that it is time-aligned.

"No, you have a woofer that is loosing efficiency due to the air spring inside the box. The air spring is in effect increasing the damping of the system, not lowering it."

I am not talking about the control of the motor on the driver...I am talking about the control of the driver on the air in the room. Basically it's ability to ignore the changing air pressure outside of the cabinet. Essentially it comes down to an iron-fist approach. A system that can go flat to 10Hz anechoic will control the air inside the room better than a driver that is relying on the air inside the room to get that extension. Heck, take a sealed driver that can do 10Hz anechoic - it doesn't matter...it is going to have better control (all other things being equal).

"I have a pair of L/R sealed subs with a f3 of about 33hz. In room I'm within a dB or two of flat to at least 10hz, and likely lower... 10hz is as low as my RTA goes. My real limit is probably the 7hz high pass filter in the K2 that is driving them.

In that same room I have a ported sub (Quantum Sound ContraBass) that has an f3 of 14hz. "

Hardly an apples to apples comparison.

[sfogg]

"A goal that is IMPOSSIBLE (both mathematically and psychoacoustically). If you want the "I am there experience"

Impossible???

I'm doing it. Others are as well.

If you want to talk about the psychoacoustics of spatial impression, envelopment and the like I'm game.

"And anyone that has ever spent any time in a recording studio will know that it is a most lifeless and boring musical experience."

And if you think my system sounds like a two channel system in a very dry studio you *really* have no clue what my system sounds like.

" I'd much rather enjoy the music."

And you think I don't???

The reason I chose the path I did is because it has brought me more enjoyment from listening to the music then other paths I tried.

Hearing my own rooms signature and 'looking through the window' screams artificial and fake to me compared to what live music sounds like in a hall.

So I am taking the approach of limiting the rooms sound as much as possible and reproducing the ambiance that is already in the recording itself. I don't want or need the room to add its own artificial ambiance/reverb on top of what is already there. The rooms influence is quite simply distortion and it tends to homogenize any and all music played back in it.

"Just because it is in phase doesn't mean that it is time-aligned."

Yes, it does. Room gain happens below the 1/2 wavelength point. The reflection is adding during the same half of the same cycle of the wave. That is why the room gain effects the entire room.

It is not the same as a random modal peak at only specific points in the room. Those occur from constructive interference of two different peaks of the wave and are therefor not time aligned.

"Essentially it comes down to an iron-fist approach."

An iron fist that is trying to control a fluid.....

"I am not talking about the control of the motor on the driver..."

If the motor of the driver has no control over the cone it certainly has no control over anything else either.

" A system that can go flat to 10Hz anechoic will control the air inside the room better than a driver that is relying on the air inside the room to get that extension."

Prove it. Show any sort of measurement that quantifies this.

The system that is using the room gain is working *with the room* to have the output. A system without room gain trying to have the same amount of output is going to be working much harder. The room gain is in effect free output.

"Hardly an apples to apples comparison."

It was the theoretical comparison you suggested I try between a ported sub with extension to 20hz and a sealed sub that uses room gain to get lower then its free air f3. Now you don't like it because I have actual done it, with a ported sub that goes even lower. That makes sense.

Shawn

[DrWho]

"Impossible???

I'm doing it. Others are as well."

What you are experiencing is an approximation - it is not the real

deal. You are essentially claiming that your listening room sounds

identical to the symphony hall the symphony was recorded in and I don't

have to hear your room to disregard the claim.

Why aren't you listening inside an anechoic chamber? That is the best

environment for getting rid of the room's sonic signature and leaving

all of the acoustical cues up to the recording. Again, it all comes

back down to psychoacoustics...you are in room A and the recording is

from room B - when you've got both at the same time your mind gets

confused. Sure, our minds are also cool in that they can easily focus

in on one of the rooms, but there is still that confusion...especially

when the music stops.

You mention ambience in the recording and I wanted to bring up the

point that you are also getting insanely specific to recording

techniques. Anything that is close mic'ed is minimizing the effects of

the room that the instrument is playing in...which means your approach

doesn't work for close mic'ed music because there are no spatial cues

in the recording...apart from what the engineer chose to add...but I

can guarantee they aren't fiddling with anything below 40Hz.

I have no doubt that you enjoy your system and that it sounds fricken

great...but there is nothing "more natural" or "more ideal" about

compensating for or not compensating for room gain. I personally

would rather have a system that doesn't have to rely on a wierd trick

which in my situation (close mic'ed music) does not add to the

"realism". I'm really not after realism either though...more "realism"

should result in less enjoyment. More "revealing" anything should

result in less enjoyment because it brings out more flaws...and flaws

by definition do not enhance enjoyment...

"Prove it. Show any sort of measurement that quantifies this."

That is just an easy application of the mathematics...lower notes

require more displacement for the same SPL. In order to achieve more

displacement for the same SPL you need a more powerful motor. A driver

that can do 10Hz anechoic is going to be able to displace more air than

a driver that is 30dB down at 10Hz anechoic.

"Room gain happens below the 1/2 wavelength point. The reflection is

adding during the same half of the same cycle of the wave. That is why

the room gain effects the entire room."

Again, classical application of the frequency domain...you still have

time domain issues. I guess the best short way to describe it is your

impulse response becomes stretched. But I guess in a small room these

time differences aren't that big...but I wouldn't call a small room an

ideal listening space either...

"It was the theoretical comparison you suggested I try between a ported

sub with extension to 20hz and a sealed sub that uses room gain to get

lower then its free air f3. Now you don't like it because I have actual

done it, with a ported sub that goes even lower. That makes sense."

It's not apples to apples because you're comparing four 15" drivers in

a stereo configuration to a single 18" driver. The mere fact that a

system that is supposedly flat to 14Hz has percievably less bass than a

system that is dropping at 30Hz is a clear indication that something is

screwed up in the comparison. I also don't think one situation is

enough to support making general claims about anything...I don't have

much personal experience either, but I'll divert to the engineers that

do.

Allow me to throw another concept out there...the mastering engineer in

the studio is listening in a dry room at about 90dB when he adds the

finishing touches because our ears are most linear in that range. From

the F-M loudness curves we see that we need a lot more low frequency

energy for it to be percieved just as loud when listening at 70dB. In

such a situation, the extra room gain added onto an anechoically flat

subwoofer system will result in the same tonal balance that the

recording engineer dialed in when listening at 90dB.

Or another way to look at it: show me one person that has ever

complained about having too much 20Hz material and has had to implement

an EQ to tame it...

An engineer once told me "start with the assumptions" - I agree with

everything you say except the assumptions you start with, which seem to

be very specific to your listening habits, source material, and

listening environment. It's all about compromise.

[sfogg]

"What you are experiencing is an approximation - it is not the real deal"

Your kidding??? Duhh... we are talking about music reproduction here....

"You are essentially claiming that your listening room sounds identical to the symphony hall the symphony was recorded in"

No, I'm claiming the playback is closer in sound to what I hear from

live music in a hall then if I let the room add its own

ambiance/reverb/distortion to the playback.

"Why aren't you listening inside an anechoic chamber?"

I wish I were. Not exactly practical to build that in your basement though now is it?

"...you are in room A and the recording is from room B - when you've

got both at the same time your mind gets confused. Sure, our minds are

also cool in that they can easily focus in on one of the rooms, but

there is still that confusion..."

You are arguing my point now, not yours. The original acoustic space is

in the recording. So if you play that back and add the rooms sound on

top of the original acoustic space you get the conflicting queues just

like you said.

"...which means your approach doesn't work for close mic'ed music

because there are no spatial cues in the recording...apart from what

the engineer chose to add.."

And since the engineer in much of such music added the ambiance with

the same type of gear I'm using to extract the ambiance (and it in fact

looks for queues from the addition in the studio) it works very well.

Again, I have lived with it in action for about 8 years now. Have you ever even heard it?

" But I guess in a small room these time differences aren't that

big...but I wouldn't call a small room an ideal listening space

either..."

Neither would I. Psychoacoustically 'small' rooms have all sorts of

problems if you let the rooms 'sound' dominate the playback. Those

problems effect a large part of the frequency range. The problem is for

the room size to get big enough to naturally avoid some of those

problems (such as the lack of interaural time differences in the bass)

the rooms really are bordering on hall size. Of course if you have

stereo bass reproduction and generate ITDs.......

"That is just an easy application of the mathematics...lower notes

require more displacement for the same SPL. In order to achieve more

displacement for the same SPL you need a more powerful motor. A driver

that can do 10Hz anechoic is going to be able to displace more air than

a driver that is 30dB down at 10Hz anechoic."

That is no way shape or form proves your claim that a driver has more

control over the air in the room if it isn't using room gain. You are

now talking simple output ability... not the same thing.

"It's not apples to apples because you're comparing four 15" drivers in a stereo configuration to a single 18" driver. "

No, I'm comparing four 15" drivers to (2) 15" actives driven by a

rotary servo motor and two 18" passives. And again, I'm not talking

about just maximum output ability but talking about extension and

overall sound quality. I've also compared it with just one of my L/R

subs... same result.

"The mere fact that a system that is supposedly flat to 14Hz has percievably less bass than a system that is dropping at 30Hz"

The sealed system is not dropping at 30hz *in room*.... that is the whole point.......

" is a clear indication that something is screwed up in the comparison."

Or that you simply misunderstand how effective room gain can be.

BTW an engineer that worked for ServoDrive (who now makes the

ContraBass) didn't doubt for a second the sealed subs in my room could

have more extension then the CB in room. He is no longer with

ServoDrive though... he has his own company working on sealed designs

that are designed to exploit room gain.

"From the F-M loudness curves we see that we need a lot more low

frequency energy for it to be percieved just as loud when listening at

70dB. In such a situation, the extra room gain added onto an

anechoically flat subwoofer system will result in the same tonal

balance that the recording engineer dialed in when listening at 90dB."

You are reaching..... then that system would have far too much

bass at higher levels and sound like a typical 'boom boom' car system.

Whop-die do...

There are far better ways to deal with F-M loudness curves.... EQ

that automatically adapts to the SPL in room is a better path to take.

Shawn

[keepinitcool]

I got a Carver Dominator, and it has no ports or passives, so I guess it's acoustic suspension. It is tight and fast. Haven't really tested it, but not as boomy as the Klipsh sub I have.

[TheEAR]

DrWho,

No matter how hard you argue,room gain is real.And instruments or performers will NEVER be in your or my room,so your point is PIONTLESS.

IF IF and ...no performance has to be recreated.If it is close to the real thing and distortion is kept in check its A ok. No matter how flat you sub will be in a test chamber it will not perform the same in regular rooms we listen to our music in.

What counts is how it performs in the room its set up.End of story