# Bose Acoustimass For The Car



## Patrick Bateman (Sep 11, 2006)

There were a couple threads on here where people were asking about transmission lines. Here's a couple of designs that people might be interested in.

I'm starting to think that transmission lines might be a good idea for a car. Here's why:
I've messed around with front loaded horns in the car, and tapped horns. Front loaded horns (generally) deliver the most output of any enclosure type. The downside of FLHs isn't just the size, it's also that they don't go deep. For instance, the most famous horn sub for a car uses a driver with an FS of 30hz, but it's F3 is just 60hz(!) So you get a really impressive amount of output, but it really doesn't play much lower than a midbass.
Tapped horns play WAY low; in fact tapped horns are probably the ultimate solution for infrabass. But it actually becomes a bit of a problem in a car, because we don't NEED a sub that plays to ten hertz!
The most famouns horn car subwoofer has an 8" woofer with an F3 of 60hz; in a tapped horn you can get that exact same woofer to play down to 19hz.

Which brings us to transmission lines.

Transmission lines aren't as efficient as tapped horns or front loaded horns. They don't play as low as tapped horns. *But they're more efficient than vented boxes, and WAY more efficient than sealed boxes.* And they don't have the annoying 180 degree phase flip that affects vented boxes.


TLDR: Front loaded horns get way loud, but you probably won't be happy with a 'sub box' that only gets down to 60hz.
Tapped horns go low and loud, but who needs a car sub with an F3 of 15hz?
Transmission lines are a nice compromise between size and low cutoff.


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## Lycancatt (Apr 11, 2010)

I've never seen a flh for the car? who made one? I know it was limited, but I'd sure like to know what it was and by which brand.

I've always liked the idea of tapped horns, and when this van project comes together, I might just have to give one a try.


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## Patrick Bateman (Sep 11, 2006)

The Bose Acoustimass folding seems to work pretty well. In a thread at diyaudio I explored a bunch of alternatives*, and couldn't find any that worked better.









User "Joemon" was looking for a tiline for a TC Sounds Epic 8*. Unfortunately, it's just not a good candidate. *The qts is too low and the FS is too low.* It would be a great candidate for a front loaded horn.

* An Improved Transmission Line Alignment. - diyAudio

** http://www.diymobileaudio.com/forum...audio-discussion/235426-tc-epic-8-t-line.html


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## Patrick Bateman (Sep 11, 2006)

Lycancatt said:


> I've never seen a flh for the car? who made one? I know it was limited, but I'd sure like to know what it was and by which brand.
> 
> I've always liked the idea of tapped horns, and when this van project comes together, I might just have to give one a try.


I don't want to call him out. The designer does good work and I think it's a really nice box. It's better than most of the boxes I've made. But it doesn't play low. Actually, with cabin gain it's almost flat to 20hz. (It starts to fall off at 60hz, and cabin gain brings that back up.) But subwoofers that measure "flat" in car sound "thin." You really need about ten or twenty dB of boost, starting at 20hz, to make a sub sound right in the car.


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## Patrick Bateman (Sep 11, 2006)

I have a fairly decent idea of what drivers work well in tapped horns, back loaded horns, and transmission lines. *You want something with a lot of displacement, a fairly high Qts, and and a fairly high FS.*

The Alpine SWS-10D2 fits the bill. I have four of these, love 'em. I paid $100 for mine.









This thing is a MONSTER in a transmission line. Look at that response! I'm willing to bet this thing sounds like a fifteen or an eighteen in a sealed box. Ruler flat response curve, but with an F3 in the high twenties. Gorgeous!









The folding is super simple. *It's just like the Acoustimass.* The woofer is offset by one-third of the line length. The box is under two cubic feet!









Here's the response with five hundred watts into four ohms. That's 250 watts for each voice coil. We're *just* hitting the maximum power handling of the voice coil, and we're still not exceeding xmax. A hundred and fifteen dB from a single 10" woofer isn't too shabby. The fact that the box is under two cubic feet is a bonus too. And it's a $99 woofer.









You absolutely MUST have a highpass if you want to get the most out of these boxes. Like a ventex box, tlines unload. So a highpass filter will triple or quadruple your power handling.









Here's the frequency response with the highpass in place. It's basically the same, the filter is just there to protect the woofer.









Here's the group delay. The "neat" thing about tlines and tapped horns is that the group delay is really well behaved, because the rear wave is only delayed by a quarter of wavelength. In a vented box, the rear wave is half-a-wavelength out of phase.


Very very cool box. I'd probably build one of these if I didn't have a JL Audio bandpass already.


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## Patrick Bateman (Sep 11, 2006)

Here's the frequency response of the box recommended by Alpine (black) versus my tline proposal. (grey.) They're pretty darn similar. The tline is a little flatter and plays a little lower. In the real world, I find that tlines sound a lot like sealed boxes. They definitely sound different than vented boxes, likely because the phase doesn't rotate 180degrees, like it does in a vented box.


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## Patrick Bateman (Sep 11, 2006)

By the way, all those crazy 'squiggles' in the tline chart don't show up in real life. Hornresp simulates the woofer as if it was infinitely small. In the real world, the fact that the woofer is 10" in diameter makes those squiggles disappear.


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## thehatedguy (May 4, 2007)

So the small recommended box from Alpine has nearly the same output as a t-line? If so, why worry about the extra complications of building one?


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## Patrick Bateman (Sep 11, 2006)

If you want to get REALLY freaken loud and you have some money to burn, consider this one. 18 Sound 18NLW9600. Seven hundred bucks.

To reach it's full potential, you're going to need four thousand watts at four ohms. That's 126 volts. Yep, that's as much power as a wall outlet 

I have no idea where you're going to find a 4000 watt amp. The amps on Amazon that are advertised as "4000 watts" are more like 1000 watts. This one gets us about halway there and it sells for $1500 : SCV-6000D









Here's the response with 4000 watts into four ohms. The extra 3,500 watts gets you to 130 decibels, fifteen more than the Alpine.

I know that "130 decibels" doesn't sound like a lot these days - the SPL dudes exceed that all day long. But this is in a box that has six octaves of bandwidth and can eat four thousand watts of power all day long.









Here's the excursion - the high pass filter gets us under the 14mm xmax

If anyone wants to take a try at this box, here are the details:
1) The box is 5.4 cubic feet
2) The mouth is 113"^2
3) The throat is 155"^2
4) The line is six feet long, and the woofer is off set by 1/3rd. (Exact same lay out as the Acoustimass sub.)


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> So the small recommended box from Alpine has nearly the same output as a t-line? If so, why worry about the extra complications of building one?


Over at diyaudio you'll see a lot of people having really good results with tapped horns. And *I think the reason they're so successful is because tapped horns and transmission lines are WAY more forgiving than vented boxes.* For instance, I have a couple of TC Sounds woofers that are twelve years old. Due to their age, their parameters have shifted a lot. In a vented box that's a HUGE issue; the vent resonates over an incredibly narrow bandwidth, a fraction of an octave. But transmission lines, back loaded horns, and tapped horns are resonant over a much wider bandwidth.

That's a really convoluted way of saying "it's harder to **** up a transmission line than a vented box."

The other advantage of a tline, th, FLH, and BLH are that they only have ninety degrees of phase rotation.

It's pretty compelling. I'm starting to think I should've been building more tlines and fewer horns. I avoided tlines for the better part of a decade because I built one and it didn't sound any different than a sealed box. *In hindsight I realize I didn't know what I was doing.* At the time I built it like a B&W Nautilus. And in that configuration, you're not going to get any more output than a sealed box. If you want more output from a tline, you need to make it big. And if you make it big you're going to get ripples in the response. Which is why Bose offsets the woofer.


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## edouble101 (Dec 9, 2010)

Didnt Bose use TL in RX-7's back in the day?


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## Lycancatt (Apr 11, 2010)

well, I'm considering the flh for midbass because I have a van and I'm whacky, so if I don't need the response below 60 anyways, its not calling someone out is it? you could just pm me if you wish


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## Patrick Bateman (Sep 11, 2006)

I just realized I contradicted myself. I said that tlines are harder to **** up than vented boxes. And then I said that I avoided tlines for a decade because I made one that didn't work.

I should have clarified that - *tlines are hard to screw up if you start with a good design.* The Bose tline is a good design. It works with a huge variety of woofers. Just copy the folding, put the woofer 33% down the line, and make the throat about 66-133% the size of the woofer. Easy!

Back when I built my tline, in 2001, we had ZERO software to model this stuff. Martin King's worksheets didn't appear until 2004 or 2005. I was doing things by pure faith.

Times have changed - we can model all of this easily and predictably with Hornresp.


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## Patrick Bateman (Sep 11, 2006)

Lycancatt said:


> well, I'm considering the flh for midbass because I have a van and I'm whacky, so if I don't need the response below 60 anyways, its not calling someone out is it? you could just pm me if you wish


The windshield gives you so much gain, you might as well use that as a 'substitute' for a FLH

I've been tinkering with the idea of doing some transmission lines for midbass. I'd planned on using bandpass boxes, and I've already built them. But my CUV has a ton of room under the dash and I think I could squeeze a tline under there. Another neat thing about tlines is that you can put them in weird locations by spreading them out, like Mazda did with the RX7 tline. That one was famously boomy, but I'm guessing that may have a lot to do with the fact that Bose uses really ****ty drivers


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> So the small recommended box from Alpine has nearly the same output as a t-line? If so, why worry about the extra complications of building one?











Jason got me wondering what would happen if I shrunk the transmission line down to the size of the vented box. It's pretty interesting - *the response curve is virtually indistinguishable.* There are two curves on this pic. The black curve is the tline and the grey is the vented. But you can barely tell, they're so tightly matched.









Displacement is always dependent on output, so displacement is identical for the two boxes.









The vented box is 25 liters (as Alpine recommends) with three liters of vent. A total of 38 liters.









Here's the 36 liter transmission line box

















If you want to model it yourself, here's the input screens


Even at this reduced size, I still think the tline is going to have the edge. The mouth of the tline is over fifty percent larger than the mouth of the vented box's vent. And that big mouth will lead to reduced distortion. And tlines will always have an advantage in the time domain, because their phase only rotates ninety degrees.


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## Lycancatt (Apr 11, 2010)

I want to touch a tline..I'm having real trouble picturing this while blind lol..who makes home audio ones? might want to hear/fondole a pair.


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## Patrick Bateman (Sep 11, 2006)

Lycancatt said:


> I want to touch a tline..I'm having real trouble picturing this while blind lol..who makes home audio ones? might want to hear/fondole a pair.











This design is shamelessly copied off of Bose.
Their "acoustimass" subs.









But not the old ones - the old ones were an insanely complicated triple-reflex bandpass design. I'm guessing they figured out the added complexity of a three-chamber bandpass design was more trouble than it's worth.


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## Patrick Bateman (Sep 11, 2006)

In the third post in this thread, I said that the Epic eight wasn't a good candidate for a TL.

It looks like I was wrong! Thanks to Jason, I've realized that you can basically turn any ol' vented box into a tline. And if you do THAT with the Epic 8, you wind up with a rather neat box.









Here's a tline with the Epic 8.
This is a very VERY strange box. It's TEN liters. And it's getting a THOUSAND watts.

That's a really weird combination - I can't recall seeing a sub box that's under half a cubic foot that can handle that much power. But this woofer can do it. (That's assuming you don't blow up the voice coils.)

To give you an idea of how small that is, 10 liters is a cube of air that measures 8.5" x 8.5" x 8.5" (!!!)









Here's the original design I made, which was something like four times as big. This sim is with one watt. I didn't realize the Epic 8 wants such a tiny box.

I guess if you were REALLY clever you could probably figure out some way to fold a tline into that. You'd probably want to mount the woofer outside of the box. I have an Epic 8 and the driver itself is bigger than ten liters!

If any of you want to try this out, just use an online calculator to simulate a vented box. And then take those figures and pop them into hornresp as a tline. The tuning frequency is the same, the box volume is the same, etc. Just juggle the length of the line until you get the tuning frequency to match the vented box.

The crazy thing is that I could've made this box even smaller; my calculator recommended a vented box of just five liters! That's about as big as a couple phone books.


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## Lycancatt (Apr 11, 2010)

I really liked the sound of those old triple chamber bandpass/reflex/whatever they were design, low power, very tight..back when the bose engineers could go nuts and it was usable.


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## thehatedguy (May 4, 2007)

Bose is pumping out patent after patent application for t-lines and tapped horns. They had a recent application using multiple drivers on a tapped horn- lining them a long the central divider to smooth out the HF response. It works in the patent...but may not ever see day since there is still a lot of infringement on Danley's patent.

I have a link to a triple chamber enclosure designer like used in an above post. I think you can do more than 3 chambers too.

But I think PB has stumbled on a little of what PWK was calling horns and such on his webpage...but they looked like big ported enclosures.


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## Patrick Bateman (Sep 11, 2006)

I think I accidentally invented a new box type:

A few posts back, Jason inspired me to figure out what a tline had to offer over a vented box. And by doing that, *I proved to myself that you can make a tline with the same response shape as a vented box.*

While the tline would have less phase shift, you end up with a box that's the same size as a vented box with no efficiency advantage.

I'm a big fan of efficiency, so I started to wonder :

*What if I stuck a chamber in FRONT of the transmission line?*









Barely anyone has made these things, but this is a "series tuned bandpass box." I've never seen one in real life, but I know they can be made.

So it occurred to me, *what if we take the series tuned bandpass concept, and combine it with a transmission line?*

It seems to work! It's a real strange box. Super narrow bandwidth, but ridiculous efficiency. I'm actually kinda shocked by the efficiency, it seems to approach or maybe even exceed the efficiency of a horn. I double checked my work; for a sec there I thought maybe I was off by a digit somewhere.

I'd draw a pretty diagram of what the box looks like, but it's pretty simple: Picture a series tuned bandpass, but replace the side of the box that has a port in it with a transmission line instead. So it's a transmission line feeding a box with a port in it.

Anyways, onto the data:









First, we start out with our transmission line. This is the TL from post #5 in this thread. It's just under two cubic feet. It uses a $99 Alpine 10".









Here's the exact same box as post #5, but simulated in Akabak. I have to use Akabak because what I'm about to show here is a new box type (I think) and I'm not aware of any other program that can model this.









Aaand here's the box I've proposed. It's the same tline as post #5, but I've added a ported box in front of it. A transmission line feeding a ported box. Similar to a series tuned bandpass box.

We see a humongous efficiency gain - something like ten decibels. I guess this is because the bandwidth is so narrow. It doesn't even cover an entire octave.


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## sqshoestring (Jun 19, 2007)

I have a new car and may have to build a box instead of my wonderful IB setup. This looks great but I really like to see a sub flat to 30Hz minimum better yet a little peak around 30. But that is healthy for little 10!

I always figured they would give up complex boxes these days, because it is easier to change the FR with electronics. Back in the day they ran BP so they didn't need electronics to cover it. Still my installs are always nicer to me when the install is tuned and I do not need a lot of EQ.

That TL could be a cool install, having a sub on a line with a little ported box on the other side of the trunk at the end! I love the full trunk room my IB gives me over a square box. You have potential to get some of it back. Can you flatten the line some without affecting flow?


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## Patrick Bateman (Sep 11, 2006)

IB is pretty hard to beat.
I'm thinking the transmission line would be a good way to have a home subwoofer that could play up to 200hz or so, without being as big as a refrigerator.

There's no replacement for displacement and a couple of twelves in an IB sound damn good.


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## T3mpest (Dec 25, 2005)

Taramp's Products - DJ Stage Gear Store

This was in response to "how the hell do we get 4000 watts at 4ohms into a car". The 2 ohm hd8000 would do exactly that. I powered a B&C21sw152 off a taramps hd4000.

I'd love to mess around with a transmission line, but I can't find anyone willing to come up with a design. All I have is 15's and there is barely enough room to do a workable design from what I've been told even for a single 15.

Also, in the SPL and "loud demo car" world, 6th order series bandpasses are WAY more common than parallel ones are, I've actually never seen a parallel design in person, but hasve seen 5+ series bandpass. How does the phase response look on the 6th order tranmsission line look? Honestly the response in the vehicle would be over an octave due to cabin gain and for 150+db demo guys, it would be more than adequate. There frequencies of interest are almost always 30-50hz.


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## sqshoestring (Jun 19, 2007)

Patrick Bateman said:


> IB is pretty hard to beat.
> I'm thinking the transmission line would be a good way to have a home subwoofer that could play up to 200hz or so, without being as big as a refrigerator.
> 
> There's no replacement for displacement and a couple of twelves in an IB sound damn good.


This new car has a flip down seat and likely I would want to use it. Unless I make the sub baffle removable somehow, and not sure how to do that really. I had thought of some removable IB designs but they seem too complex. However a box that can be flatter and long would be better than a square one.

Yes my pair of 15s IB have done everything I wanted. It has been so nice to have effortless bass down to <30Hz and use the trunk. Even with a full trunk they still work ok. If I did it again I would make a temp baffle and try a giant folded (to keep trunk noise out) port with 12s/15s and see if it worked. I can't fit a port in with these 15s in this current car. It may not work, but the FR model is so tempting me to try it.


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## Focused4door (Aug 15, 2015)

sqshoestring said:


> I have a new car and may have to build a box instead of my wonderful IB setup. This looks great but I really like to see a sub flat to 30Hz minimum better yet a little peak around 30. But that is healthy for little 10!
> 
> I always figured they would give up complex boxes these days, because it is easier to change the FR with electronics. Back in the day they ran BP so they didn't need electronics to cover it. Still my installs are always nicer to me when the install is tuned and I do not need a lot of EQ.
> 
> That TL could be a cool install, having a sub on a line with a little ported box on the other side of the trunk at the end! I love the full trunk room my IB gives me over a square box. You have potential to get some of it back.* Can you flatten the line some without affecting flow?*


Would be interesting if you could flatten it enough to make it a false floor for the trunk.


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## Regus (Feb 1, 2011)

Focused4door said:


> Would be interesting if you could flatten it enough to make it a false floor for the trunk.


This sounds like a promising idea - it should be possible to build a box as wide as the trunk, as high as the false floor and of appropriate depth to achieve the required cross-sectional area (I'm not an expert on transmission lines though so it might not be that simple).

Patrick, any thoughts on the smallest driver that would be of use for the height dimension to achieve respectable output? I've seen at least one 8" with a very similar Fs, Qts and Xmax to the 10" Alpine but the power handling is greatly reduced compared to the Alpine (something like 150W RMS) and clearly it will have less displacement at Xmax than the 10" sub would, but it's more likely to be able to fit into a false floor compartment than a larger sub would.


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## knever3 (Mar 9, 2009)

edouble101 said:


> Didnt Bose use TL in RX-7's back in the day?



They sure did!! The best looking OEM stereo on display that I can remember!

My favorite car as well, I have all the dealer brochures for the years they were made for the U.S. and the local dealership pretty much knew me by name!


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## Patrick Bateman (Sep 11, 2006)

Regus said:


> This sounds like a promising idea - it should be possible to build a box as wide as the trunk, as high as the false floor and of appropriate depth to achieve the required cross-sectional area (I'm not an expert on transmission lines though so it might not be that simple).
> 
> Patrick, any thoughts on the smallest driver that would be of use for the height dimension to achieve respectable output? I've seen at least one 8" with a very similar Fs, Qts and Xmax to the 10" Alpine but the power handling is greatly reduced compared to the Alpine (something like 150W RMS) and clearly it will have less displacement at Xmax than the 10" sub would, but it's more likely to be able to fit into a false floor compartment than a larger sub would.


That's the weird thing about transmission lines. *You can really tune them for a wide range of options.* You can make them small, and they'll basically behave like a sealed box. You can make them huge to maximize output. Or somewhere in between.

So the answer to that question has a lot to do with what you're going for.

Horns are different in that respect; the output of a horn has a lot do with the horn. I've seen horns that worked with half a dozen different drivers. The choice of driver wasn't quite "incidental", but pretty close.


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