"Aside from greatly reducing sensitivity, ported designs just won't be able to provide too much below 10hz."
There's no reason you can't tune below 10 Hz, with the same efficiency and output advantages over sealed as before.
The formula for sag only accounts for suspension stiffness, not creep.
The driver mfgr would have to answer that.
There's no reason you can't tune below 10 Hz, with the same efficiency and output advantages over sealed as before.
The formula for sag only accounts for suspension stiffness, not creep.
The driver mfgr would have to answer that.
I've simmed with multiples of drivers in very large enclosures and I find that you just aren't going to get much or gain much tuning below 10hz - in fact, performance seems to suffer. Vas and Fs seem to be limiting factors in how much performance you're going to get tuning so low.
Now if we were to get a driver with Fs of 7hz, Vas of 900 liters, Mms of 500g, and Xmax of 35mm, then we'd be in business, but the sensitivity hit you take really isn't worth it.
I still don't understand why their aren't more giant drivers on the market.
You brought up something else. You have damping materials on the inside of your port tube? I've never heard of that before.
Does your speaker have some adjustability in the port tunning? Doesn't the damping material create some indeterminancy.
Do you have a telescoping section on your port tube?
Did you measure the T/S parameters yourself? What kind of a setup did you have to do that? You have to have a box to attach the driver to, right?
What kind of setup did you use to measure the response of the finished unit?
You brought up something else. You have damping materials on the inside of your port tube? I've never heard of that before.
Does your speaker have some adjustability in the port tunning? Doesn't the damping material create some indeterminancy.
Do you have a telescoping section on your port tube?
Did you measure the T/S parameters yourself? What kind of a setup did you have to do that? You have to have a box to attach the driver to, right?
What kind of setup did you use to measure the response of the finished unit?
It's common practice.
Does your speaker have some adjustability in the port tunning?Not unless I chop off some of the port.
No.
No. Got them from Ascendant Audio, the manufacturer.
RoomEQ Wizard, Soundblaster sound card, Radio Shack digital spl meter.
WinISD Pro and Unibox.
Not to sound rude, but what do you think it is?
Subwoofer
If you really want to get down past 20 Hz - and depending on the average listening level (which you have not specified), the most cost effective method would be either a horn or transmission line. I would suggest reading Pass article:
http://www.passdiy.com/projects/el-pipe-o-1.htm
This is relatively inexpensive project, and you could use multiple tubes to increase output if needed.
If you really want to get down past 20 Hz - and depending on the average listening level (which you have not specified), the most cost effective method would be either a horn or transmission line. I would suggest reading Pass article:
http://www.passdiy.com/projects/el-pipe-o-1.htm
This is relatively inexpensive project, and you could use multiple tubes to increase output if needed.
"I've simmed with multiples of drivers in very large enclosures and I find that you just aren't going to get much or gain much tuning below 10hz - in fact, performance seems to suffer. Vas and Fs seem to be limiting factors in how much performance you're going to get tuning so low."
My findings with WinISD differ from yours.
2 Av18's in 20 cf vented and closed boxes, with 1200 W input:
Tuned to 8 Hz, vented advantage peaks at + 6dB over closed at 6.5 Hz
Tuned to 6 Hz, vented advantage peaks at + 6dB over closed at 5 Hz
"I still don't understand why their aren't more giant drivers on the market."
The answer is still that there isn't a market to support them.
A few zealots are dazzled by the size, but functionally there's nothing a huge driver does that can't be done cheaper with multiple smaller drivers.
And there are disadvantages to the larger ones, like cone brewakup modes at lower freq.
My findings with WinISD differ from yours.
2 Av18's in 20 cf vented and closed boxes, with 1200 W input:
Tuned to 8 Hz, vented advantage peaks at + 6dB over closed at 6.5 Hz
Tuned to 6 Hz, vented advantage peaks at + 6dB over closed at 5 Hz
"I still don't understand why their aren't more giant drivers on the market."
The answer is still that there isn't a market to support them.
A few zealots are dazzled by the size, but functionally there's nothing a huge driver does that can't be done cheaper with multiple smaller drivers.
And there are disadvantages to the larger ones, like cone brewakup modes at lower freq.
I see. I wasn't comparing it to a sealed design, I was comparing it to another ported design, just tuned a bit higher.
By the way, why only 20 cubic feet for dual drivers? My single driver LLT is just over 24 cubes. If you want to get "crazy", look at two Avalanche 18s in 1800 liters with a 7hz tune and 600 watts
zlast, I looked at your link. I also remember those 21" drivers in the MCM catalog. Thats part of what made me think over the years that there must be some market offering of giant drivers.
I think maybe what is shown in your link is a design which places asymetrical loading on the drivers? Maybe?
I think it does reinforce Steve's postion, that it takes quite a bit to do a good job with bass down to 20hz.
I am still not clear what the real trade offs are in enclosure design. I feel that I understand Sealed Box, IsoBaric, and BR. But TR is something else. I don't feel that I've really ever fully understood it. It seems to depend on lots and lots of damping. This is only one of the concerns I've always had about it.
Steve, Does the AVS Forum show something of yours? Thats what I didn't understand. Does it show your set up?
One thing I was wondering was about Left and Right speaker placement. Seems you need them much father appart for music listening than for feature films.
About downwards firing? Is damping material shedding and piling up on the driver a concern? I would think so. What damping do you use? Do you have some barrier protecting the driver back side?
How do you calculate volume and port diameter? Front of the damping, 1/2 way, all the way through it?
Your project is impressive. Thats why I'm so interested.
You mentioned a 600Watt Carver amp? Is that made one channel, 600Watts, or is it two channels hooked up in a bridge?
I think maybe what is shown in your link is a design which places asymetrical loading on the drivers? Maybe?
I think it does reinforce Steve's postion, that it takes quite a bit to do a good job with bass down to 20hz.
I am still not clear what the real trade offs are in enclosure design. I feel that I understand Sealed Box, IsoBaric, and BR. But TR is something else. I don't feel that I've really ever fully understood it. It seems to depend on lots and lots of damping. This is only one of the concerns I've always had about it.
Steve, Does the AVS Forum show something of yours? Thats what I didn't understand. Does it show your set up?
One thing I was wondering was about Left and Right speaker placement. Seems you need them much father appart for music listening than for feature films.
About downwards firing? Is damping material shedding and piling up on the driver a concern? I would think so. What damping do you use? Do you have some barrier protecting the driver back side?
How do you calculate volume and port diameter? Front of the damping, 1/2 way, all the way through it?
Your project is impressive. Thats why I'm so interested.
You mentioned a 600Watt Carver amp? Is that made one channel, 600Watts, or is it two channels hooked up in a bridge?
Steve, certainly you have caused me to reevaluate my postion that you can't go below fs.
But I am still skeptical that it works as simply as you make it sound.
Looks like Elliot Sound Products, and BagEnd both have special circuit approaches to doing this.
Also, there is Velodyne which uses feedback. This last approach I was aware of.
I suspect that a Current Source or a Transconductance Amp is a good way to go about it.
I'm skeptical that you can go thru fs without somehow accounting for it in either the electronics or the enclosure design.
Above fs, voltage across speaker terminals corresponds to cone acceleration. Well below fs, such voltage corresponds to cone position, or tension being exerted on the suspension. Speaker distortion will be very high under such conditions. It depends on suspension linearity like it does not above fs.
Around fs, voltage across the speaker terminals will roughly correspond to cone velocity.
The idea that you can just slew through this second order resonance is counter intuitive to me.
I need to understand all the aspects of this better.
I wonder if around fs might be where your room effects start to come in.
Thanks.
Anybody else know about very large drivers, or those with very low fs?
But I am still skeptical that it works as simply as you make it sound.
Looks like Elliot Sound Products, and BagEnd both have special circuit approaches to doing this.
Also, there is Velodyne which uses feedback. This last approach I was aware of.
I suspect that a Current Source or a Transconductance Amp is a good way to go about it.
I'm skeptical that you can go thru fs without somehow accounting for it in either the electronics or the enclosure design.
Above fs, voltage across speaker terminals corresponds to cone acceleration. Well below fs, such voltage corresponds to cone position, or tension being exerted on the suspension. Speaker distortion will be very high under such conditions. It depends on suspension linearity like it does not above fs.
Around fs, voltage across the speaker terminals will roughly correspond to cone velocity.
The idea that you can just slew through this second order resonance is counter intuitive to me.
I need to understand all the aspects of this better.
I wonder if around fs might be where your room effects start to come in.
Thanks.
Anybody else know about very large drivers, or those with very low fs?
Not my full setup. I borrowed a digital camera to take pictures of the sub when I first finished it last year. Shortly after, I got Boston Acoustics VR3 for my mains, a VR1 for my center, and Ascend Acoustics 340's for my surrounds. Also, the sub doesn't just stand out in the middle of the room like that
it has a spot in the corner, which is where it was placed when I took my measurements.Why would you say that? My speakers are a little over 6' apart and my seat is about 8' back - I have a very very slight toe in with my speakers.
No, not a concern, I have nothing protecting the back of the driver. The enclosure is not stuffed with a ported sub, just lined. This is not a picture of my sub, but a good picture to give you an idea of how it should be done:
Not sure what you are asking.
per channel, see here
Well all I'll tell you is that there have been quite a few people to go this route after me at AVS and htguide.com, many of whom use the SoundSplinter RLp15 driver which has an Fs of 23hz, and get similar great results with tunings in the 14-16.5hz range. Check out some other forums to "see the light" so to speak.
TL
WEll I would not claim to understand Transmission lines entirely either...however you do not have to have a complete understanding to copy someone elses work. The Pipe oragns you are attempting to emulate ARE tranmission lines...carefully examine the average output level between the vented design and el pipe-o...if the weighting and calibration are the same there is a 12DB difference...that means you would need multiple vented enclosures to equal one TL. If you have a suitable low frequency driver, all you need is some sonotube and a jigsaw to try it out...you could also use the same parts to try the large vented enclosure...
WEll I would not claim to understand Transmission lines entirely either...however you do not have to have a complete understanding to copy someone elses work. The Pipe oragns you are attempting to emulate ARE tranmission lines...carefully examine the average output level between the vented design and el pipe-o...if the weighting and calibration are the same there is a 12DB difference...that means you would need multiple vented enclosures to equal one TL. If you have a suitable low frequency driver, all you need is some sonotube and a jigsaw to try it out...you could also use the same parts to try the large vented enclosure...
All I mean is, what is the damping made of, and how do you calculate dimensions. Is it 28" including damping, or excluding it. Most of all, that 18" port tube. 18" inside the damping?
Do you calculate using measurements from inside the damping, or including the damping thickness?
I take it you specifically selected your 18" driver for this appication. 23hz fs is lower than most. Like it could do the 27.5 hz lowest piano note without going below fs.
You didn't get this big driver by salavage.
Do you calculate using measurements from inside the damping, or including the damping thickness?
I take it you specifically selected your 18" driver for this appication. 23hz fs is lower than most. Like it could do the 27.5 hz lowest piano note without going below fs.
You didn't get this big driver by salavage.
Steve,
<< Why would you say that? My speakers are a little over 6' apart and my seat is about 8' back - I have a very very slight toe in with my speakers. >>
The conventional wisdom is: TV viewing distance should be about 3 to 4x the screen height.
Home theater speakers should be on opposite sides of the screen, in close. This is so that acoustic motion across the screen seems continuous.
So with a standard 3:4 TV, say it was 3 feet high, 4 feet wide.
I would sit 9 to 12 feet back. The speakers wouldn't be much more than 4 feet apart.
If instead I had 9:16 wide screen, then my screen would be 3 feet high and 5.3 feet wide.
I think this still places speakers too close for seating distance.
Maybe this is just a picky point. Robert Harley has written about this in his Home Theater book. He says that the music listening speaker placement and the home theater speaker placement are usually irreconcilable. YMMV.
<< Why would you say that? My speakers are a little over 6' apart and my seat is about 8' back - I have a very very slight toe in with my speakers. >>
The conventional wisdom is: TV viewing distance should be about 3 to 4x the screen height.
Home theater speakers should be on opposite sides of the screen, in close. This is so that acoustic motion across the screen seems continuous.
So with a standard 3:4 TV, say it was 3 feet high, 4 feet wide.
I would sit 9 to 12 feet back. The speakers wouldn't be much more than 4 feet apart.
If instead I had 9:16 wide screen, then my screen would be 3 feet high and 5.3 feet wide.
I think this still places speakers too close for seating distance.
Maybe this is just a picky point. Robert Harley has written about this in his Home Theater book. He says that the music listening speaker placement and the home theater speaker placement are usually irreconcilable. YMMV.
zlast, cannot design something well unless you understand why things work and what the trade offs are.
In design review meetings, I've totally destroyed people who have designed something by computer simulations, but clearly don't understand why and how it works.
There have been people flown across the US for an entire day of interviewing, starting with a presentation. I have exposed that they didn't really understand how the things worked that they were talking about. What usually happened then is someone would baby sit while someone else would get them set up with the earliest possible flight back.
I don't understand why TL would be 12dB higher. I feel that I do understand how Steve's beautiful BR enclosure works.
Organ pipes run at their lowest resonance.
When a large BR box starts to resonate like this you have a problem. That is why some have opted to not use large BR. But it is also the reason for damping materials.
The TL's that I have seen are very heavily damped. Otherwise they would be similar to a BR, just with an elongated circuitous design.
The BR's helmholtz resonance defines its lower freq limit. After that its 24db/octave!
TL, as I know it, is not designed this way. The exact length of the "line" is not really a critical parameter.
Steve, conventional wisdom is that putting at subwoofer in a corner is highly likely to produce unflat response.
Some people even put bass absorbers, often cylinders, in the corners to solve this room unflatness problem.
I suspect that your corner placement is compensating for complexities with slewing through fs.
In design review meetings, I've totally destroyed people who have designed something by computer simulations, but clearly don't understand why and how it works.
There have been people flown across the US for an entire day of interviewing, starting with a presentation. I have exposed that they didn't really understand how the things worked that they were talking about. What usually happened then is someone would baby sit while someone else would get them set up with the earliest possible flight back.
I don't understand why TL would be 12dB higher. I feel that I do understand how Steve's beautiful BR enclosure works.
Organ pipes run at their lowest resonance.
When a large BR box starts to resonate like this you have a problem. That is why some have opted to not use large BR. But it is also the reason for damping materials.
The TL's that I have seen are very heavily damped. Otherwise they would be similar to a BR, just with an elongated circuitous design.
The BR's helmholtz resonance defines its lower freq limit. After that its 24db/octave!
TL, as I know it, is not designed this way. The exact length of the "line" is not really a critical parameter.
Steve, conventional wisdom is that putting at subwoofer in a corner is highly likely to produce unflat response.
Some people even put bass absorbers, often cylinders, in the corners to solve this room unflatness problem.
I suspect that your corner placement is compensating for complexities with slewing through fs.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.