# How to Generate More SPL Without Spending a Penny



## Patrick Bateman (Sep 11, 2006)

In this thread, I want to demonstrate a free way to get extra SPL out of your speakers. This 'trick' is particularly applicable to subwoofers, but it can also be used for midbasses too.

The trick is very simple; we flare the port. *But in a very specific way.*









Basically, the port ends up being bowtie-shaped.

Towards the end of this post, I will explain why this works. But first, I'd like to show you a real world example.










In the simulation above, I've modeled the same subwoofer in three different boxes. The ported box is one half a cubic foot, or 14.16 liters. 5.3 liters of the box is the back chamber; the other nine liters of the box is the port. The port is straight. *This is your traditional ported box, using straight PVC tubing or a 'shelf' port.*

For comparison's sake, I've also simmed it in a sealed box. The sealed box is 5.3 liters, which is a bit large. *But I wanted to demonstrate how much output the port is adding.*

The simulation at the top right, above, shows the sealed versus the ported box. We see a few things:
1) Due to the very large port, we're getting a LOT of extra output. At the tuning frequency of 50hz, the ported box is over ten decibels louder! That's like going from a 100 watt amp to a 1000 watt amp. HUGE difference.
2) By 30hz, the sealed and the ported have the same amount of output.


In order to show the advantages of a 'kidney shaped' port, I simmed the exact same woofer in a vented box with a kidney shaped port. I tweaked all the variables so that it's a fair fight. The back chamber is the same volume, the ports are the same volume, the overall box size is the same, the tuning is the same.
*The only difference between the two boxes is that one has a straight port, and one has a kidney shaped port.*

That's the sim at the bottom. In that sim, we see a few things:

1) The response curve of the box with the kidney shaped port is much smoother. In fact, it's smoother than the sealed box.
2) The straight port offers a bit more output, but it has a nasty peak and dip at 180 and 270hz. This is likely due to resonances along the length of the port. (All ducts have resonances, but they're particularly severe when the dimensions don't change. IE, expansion or contraction makes resonances less severe.)
3) The most important thing to observe is that the F3 of both boxes is exactly the same. This is Hoffman's Iron Law in full effect; with an identical tuning frequency we're going to get an identical cutoff.



At this point, you're probably thinking, "well that was a whole lot of trouble for nothing. Why would I use a kidney shaped port?"


Here's the interesting thing:
Though the *volume* of the two ports is identical, the EXIT and the INLET of the kidney shaped port is MASSIVELY larger. And when you're moving a lot of air, you want as little turbulence as possible at the entrance and the exit. What happens in the center is less important; turbulence will occur at that transition point.









It's similar to what happens in a jet engine. Big inlet, big exit, tapers down in the center.

What this means In The Real World is that a kidne shaped port will generally offer lower distortion, and it will offer higher output. The difference isn't subtle; when you're putting five hundred or a thousand watts into a loudspeaker, the port is moving A LOT of air. As power increases, the mass of air in a port becomes resistive, and as the air 'pushes' back on the cone, the ported tuning frequency changes. What this all means is that the frequency response of the loudspeaker actually changes as the power goes up. A low turbulence port combats that, so you get a response curve that doesn't vary as you ratchet up the power.

It's interesting that this is actually a bigger problem NOW than it was just five or ten years ago. This is because amplifiers keep getting bigger, and speakers keep requiring smaller and smaller boxes. In 1993 no one would've imagined that we'd have 12" woofers that fit in half cubic foot boxes that can handle five hundred watts of power.

In summary:
1) You can make two boxes that are exactly the same size, and with the same cutoff. Each box has a port that has the same volume, but different shape. Varying the shape of the port can significantly flatten the response.
2) A 'kidney' shaped port allocates more area to the inlet and the exit of the port. This reduces turbulence, like in a jet engine. Reduced turbulence means that when you crank up the power, the response curve won't vary as much as it would with a more turbulent port. It also tends to reduce distortion across all power levels.

If anyone has questions, let me know.


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## legend94 (Mar 15, 2006)

thank you, very cool information!


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## rawdawg (Apr 27, 2007)

I wonder if JBL's Slipstream tech works in a similar fashion?


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## Patrick Bateman (Sep 11, 2006)

I just noticed something. I'd noted that the kidney shaped port has a 'massive' inlet and exit, but my drawings aren't to scale. (It would take all afternoon to make them 100% exact.)

To be exact, the ported box with a straight port uses a 4" circular port. Or 81 square centimers.
The ported box with the kidney shaped port uses an inlet of 440 square centimeters, and an exit of 220 square centimeters. The easiest way to do a kidney port is using a shelf. But if you want to compare that to a circular port, it's like having an inlet that's 9.3" in diameter and circular, and an exit port that's 6.6" in diameter and circular.










The pic above is drawn to scale. I did it using the wireframes from Danley's 'Invisible Bandpass' sub. It uses the same kidney shape; very very wide on the inlet, and wide at the exit. Very narrow at the center.


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## Fricasseekid (Apr 19, 2011)

Scribed for later reading in the bathroom.


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## avanti1960 (Sep 24, 2011)

very interesting. the same principal is used on the water fountain rings at Chicago's McCormick place-
The Dancing Waters of McCormick Place - YouTube
the water flow is expanded into a chamber and then refocused to maintain laminar, turbulent free flow as it exits. 
in person the water "ring" looks just like a smooth solid tube of water. it's pretty impressive. 
right or wrong it seems like a similar port on a subwoofer enclosure may be difficult to calculate based on the driver's T/S parameters and enclosure volume- and that lots of build experimenting would be needed to finely tune. 
might be worth a try though- the SQ of a sealed enclosure with the efficiency of a ported box sounds appealing.
i would also assume that you would want a driver with T/S parameters suitable for a ported enclosure or both ported and sealed, but not a driver with T/S parameters that are unquestionably suited for a sealed enclosure.


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## Patrick Bateman (Sep 11, 2006)

avanti1960 said:


> very interesting. the same principal is used on the water fountain rings at Chicago's McCormick place-
> The Dancing Waters of McCormick Place - YouTube
> the water flow is expanded into a chamber and then refocused to maintain laminar, turbulent free flow as it exits.
> in person the water "ring" looks just like a smooth solid tube of water. it's pretty impressive.
> ...


There's a couple ways to figure out the tuning:

*1) the hard/accurate way*
Put your driver parameters into hornresp. Instead of a horn in front of the driver, there's a port in front of the driver. The volume of air in the box is the 'throat chamber' in Hornresp. This is basically the same way you simulate a back loaded horn in Hornresp, and in a lot of respects, the box design is identical. Check out the guides on avsforum or diyaudio

*2) the easy/sloppy way*
The tuning frequency of a port is determined by the volume of air in a port. So you can use the 'usual' tables for a straight port. The trick is to move the volumes of air around. For instance, a 3" port has an average area of 7.07". But a port that starts out at an area of 6", necks down to 2", then expands to 4" has an average area of 14.66". So you can basically use the same tables as you would for a box with dual ports with a diameter of 3". (7.07" + 7.07" = 14.14")


The usual caveats apply. I'd STRONGLY recommend using a Dayton Woofer Tester to get the impedance curve right.

I actually built one of these boxes for my girlfriends car. It didn't work at first; the Woofer Tester showed me that there was a leak. It turned out there was some small leaks causing issues. (I ended up using some rope caulk between the woofer and the box, and then I really went crazy and wrapped the whole enclosure in fiberglass, just to be sure nothing leaked.)




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## Offroader5 (Apr 8, 2011)

Isn't this the same as putting inner & outer flared ends on a round port? In this kidney shape, the flare just extends further into the port. My question would be at what point is the flare deep enough to affect performance like you've shown? The point at which the flare is deep enough to give the results but not shallow enough to just be another flared port end.


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## Fricasseekid (Apr 19, 2011)

Offroader5 said:


> Isn't this the same as putting inner & outer flared ends on a round port? In this kidney shape, the flare just extends further into the port. My question would be at what point is the flare deep enough to affect performance like you've shown? The point at which the flare is deep enough to give the results but not shallow enough to just be another flared port end.


Keep in mind that on this design the port does not have any parallel sides. The port area is always either increasing or decreasing. That makes a big difference in how port turbulence accumulates.


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## Brian Steele (Jun 1, 2007)

Fricasseekid said:


> Keep in mind that on this design the port does not have any parallel sides. The port area is always either increasing or decreasing. That makes a big difference in how port turbulence accumulates.


It's a bowtie-shaped cross-section, which in turn is an approximation to the ideal "nozzle" shape. There can be central section with parallel sides - it all depends on what you're trying to achieve and the length of the vent required to achieve it.

For an interesting implementation of "nozzle" vents, see this link: 6moons audio reviews: Haliaetus Firebird

Bear in mind that this is from six years ago. Nothing new to see here, folks .


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## Fricasseekid (Apr 19, 2011)

Brian Steele said:


> It's a bowtie-shaped cross-section, which in turn is an approximation to the ideal "nozzle" shape. There can be central section with parallel sides - it all depends on what you're trying to achieve and the length of the vent required to achieve it.
> 
> For an interesting implementation of "nozzle" vents, see this link: 6moons audio reviews: Haliaetus Firebird
> 
> Bear in mind that this is from six years ago. Nothing new to see here, folks .


The larger the section with parallel sides then the larger the section that accumulates turbulence. Are you implying that I think this is new technology? If so, would you show me were I insinuated such a thought?


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## Patrick Bateman (Sep 11, 2006)

Offroader5 said:


> Isn't this the same as putting inner & outer flared ends on a round port? In this kidney shape, the flare just extends further into the port. My question would be at what point is the flare deep enough to affect performance like you've shown? The point at which the flare is deep enough to give the results but not shallow enough to just be another flared port end.


JBL did a whole paper on this, and they found the ideal shapes. There were some shapes that were better at high power, and some shapes that were better at moderate power. And there was one that was a balance of both. (I'm guessing that's what they're using now.)

I'm too lazy to google it; I'll post it later. It's over on harman.com and it's on my thread at diyaudio



















The comparison to laminar flow water jets is an awesome one! I intend to re-use that one a lot 

It's a great point, because you can see the difference between a firehose and a water jet. You can see how the water jet is almost perfectly UNturbulent.

Based on some stuff that I've read from Danley, when wavelengths are very large and the duct is very small, the air molecules 'squirt' through a duct similar to the way that water shoots through a pipe.

So we may be able to utilize some of the same things here.

As for the differences between a plain ol' flared port and one of these 'kidney' ports, the kidney port basically just saves you some space and performs better. For instance, if you have a 'kidney' port that goes from 6" in diameter to 1.5" in diameter then back up to 6" in diameter, it's going to take up less space than a 4" port that flares to 6" in the very last inch. (because the majority of the 4" flared port is 4", while the kidney port 'necks down' to 1.5" )


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## chad (Jun 30, 2005)

Makes one want to investigate bandpass again.


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## Patrick Bateman (Sep 11, 2006)

Brian Steele said:


> It's a bowtie-shaped cross-section, which in turn is an approximation to the ideal "nozzle" shape. There can be central section with parallel sides - it all depends on what you're trying to achieve and the length of the vent required to achieve it.
> 
> For an interesting implementation of "nozzle" vents, see this link: 6moons audio reviews: Haliaetus Firebird
> 
> Bear in mind that this is from six years ago. Nothing new to see here, folks .


neat!


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## Brian Steele (Jun 1, 2007)

Fricasseekid said:


> The larger the section with parallel sides then the larger the section that accumulates turbulence.


The majority of the turbulence actually happens at or near the ends of the vent. See image below.










My comment wasn't addressed at you specifically but at this thread in general. The information being presented here is not really new (though it might be "new" to some readers) and has been in circulation for some time. 

The main "problem" IMO with these special vents is that they are more difficult to realise than your basic shelf vent (both in design and construction). It's easier just to opt for a bigger vent.


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## Offroader5 (Apr 8, 2011)

Patrick Bateman said:


> neat!


Ahh, that answers that I was wondering. The difference between the typical flared port vs. a more funnel or "wine glass" shape.

I may have to experiment with the port on my new enclosure. I'm sure I can find some plastic wine glasses with that shape...question is can I find some with a large enough diameter


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## Patrick Bateman (Sep 11, 2006)

chad said:


> Makes one want to investigate bandpass again.












Here's how the same box from my sims looks like if you seal off one side of the woofer. You can see a few things:

1) F3 is basically the same, but there's more output down low because the front and rear wave aren't interfering

2) output is really narrow, because the volume of the air chambers isn't optimized. (IE when you juggle the air volumes you could widen the bandwidth at the expense of efficiency.)


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## sqshoestring (Jun 19, 2007)

If I could ever get around to _trying_ to port my IB subs into the cabin, this could be an interesting way to do it. One reason is a 'folded' port may be ideal to block trunk noises. I even thought of lining it with thin foam. But thinking pair of 15s would need a big port I can't fit, maybe two ports would work better.


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## Fricasseekid (Apr 19, 2011)

sqshoestring said:


> If I could ever get around to _trying_ to port my IB subs into the cabin, this could be an interesting way to do it. One reason is a 'folded' port may be ideal to block trunk noises. I even thought of lining it with thin foam. But thinking pair of 15s would need a big port I can't fit, maybe two ports would work better.


I've thought about two big flare ports that would fit the factory 6x9 holes in my back dash. A heat gun, the proper size PVC, and lots of trial and error!


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## chad (Jun 30, 2005)

Patrick Bateman said:


> 2) output is really narrow, because the volume of the air chambers isn't optimized. (IE when you juggle the air volumes you could widen the bandwidth at the expense of efficiency.)


One reason I have not messed with it much is that widening the bandwidth loses efficiency, this is why I'm more interested now.....

Once I normally get it where I Like it then I have a bigass enclosure that has the same output in a smaller vented enclosure.


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## trevordj (Feb 22, 2009)

Patrick Bateman said:


> The usual caveats apply. I'd STRONGLY recommend using a Dayton Woofer Tester to get the impedance curve right.
> 
> 
> 
> [/font]


Do you have a good resource I can read about how to do this? I just purchased a Dayton DATS (the new version of WT3) and would definitely like to learn how to do this properly.


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## chad (Jun 30, 2005)

The impedance will peak at the tuning frequency. But it's best to know the Fs of the driver also


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## Brian Steele (Jun 1, 2007)

chad said:


> The impedance will peak at the tuning frequency.


Not for the vented alignments being discussed here. The impedance will be at or near a minimum at Fb.


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## chad (Jun 30, 2005)

Brian Steele said:


> Not for the vented alignments being discussed here. The impedance will be at or near a minimum at Fb.


Due to? The constriction?


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## trevordj (Feb 22, 2009)

That's kinda what I was wondering, do you just shoot for your impedance peak to shift to your desired tuning frequency?


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## trevordj (Feb 22, 2009)

Also, if your desired tuning frequency happens to be at or near the driver Fs, couldn't you mistake a leaky box for a properly tuned one?


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## Brian Steele (Jun 1, 2007)

chad said:


> Due to? The constriction?


For a vented alignment, cone excursion is at a minimum at Fb. Impedance should therefore be approximately Re plus whatever the driver's inductance contributes at that frequency. It's best to model the design first in something like HornResp, check where the Impedance minimum actually is, and then use DATS to confirm that the built system has a minimum at the same point. 

Checking the impedance via DATS is also useful for other things, like ensuring that you've minimized any cable + termination impedances for your subwoofer and also checking for leaks and losses (both of which will affect the measured impedance curve).

What DATS CANNOT do unfortunately is drive the subwoofer at increasing power levels, which will be useful to show how the vents efficiency changes with power level, or how the vent's shape affects this efficiency.


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## Brian Steele (Jun 1, 2007)

trevordj said:


> That's kinda what I was wondering, do you just shoot for your impedance peak to shift to your desired tuning frequency?


Only for SEALED alignments.

For VENTED alignments (including 4th order bandpass), impedance is at or near a minimum at Fb.


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## Brian Steele (Jun 1, 2007)

trevordj said:


> Also, if your desired tuning frequency happens to be at or near the driver Fs, couldn't you mistake a leaky box for a properly tuned one?


Nope. The impedance curve will be very different once that driver is mounted in a box. 

An example: Here's the impedance response of one of my "Blastoramas", measured with DATS. The measurement shows a few things: (1) this is a vented alignment, characterized by the two peaks in the low frequency region, (2) Fb for this vented alignment is around 60 Hz, (3) the alignment is a bit lossy, as the impedance at Fb is noticeably higher than the lowest impedance measured (not surprising, considering that the box is half-stuffed with polyster fiberfill).


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## chad (Jun 30, 2005)

Many thanks!

It all boils down to the fact that I need to spend an evening or 5 with HornResp.


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## Brian Steele (Jun 1, 2007)

chad said:


> Many thanks!
> 
> It all boils down to the fact that I need to spend an evening or 5 with HornResp.


Impedance testing is the very first thing I do after any speaker build. It's very quick and easy to do, and it tells me all I need to know about how close I came to the modeled alignment before doing actual FR measurements (and if the measured impedance response is a good match for the model, chances are that the frequency response will also be a good match as well, at least at low levels). 

It also spares me the pain of having to go through the trouble of setting up all of the cr*p to do an FR measurement, only to discover that there's a leak in the enclosure or the vent's too long / short or additional bracing is required to get the best results.


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## trevordj (Feb 22, 2009)

Brian Steele said:


> Nope. The impedance curve will be very different once that driver is mounted in a box.
> 
> An example: Here's the impedance response of one of my "Blastoramas", measured with DATS. The measurement shows a few things: (1) this is a vented alignment, characterized by the two peaks in the low frequency region, (2) Fb for this vented alignment is around 60 Hz, (3) the alignment is a bit lossy, as the impedance at Fb is noticeably higher than the lowest impedance measured (not surprising, considering that the box is half-stuffed with polyster fiberfill).


That is awesome, thank you for that information. I have a tutorial for hornresp bookmarked on my computer and I definitely need to spend some time with it as well. 

So, just to make sure I am understanding, for the impedance sweep example in your above post, when you say Fb for the vented alignment was 60 Hz, that is your intended tuning frequency. The impedance minimum lies around 70hz in the graph which would be your actual, impedance sweep determined tuning frequency. 

Ported enclosures and DATS are very new to me so I appreciate this info.


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## Brian Steele (Jun 1, 2007)

trevordj said:


> So, just to make sure I am understanding, for the impedance sweep example in your above post, when you say Fb for the vented alignment was 60 Hz, that is your intended tuning frequency. The impedance minimum lies around 70hz in the graph which would be your actual, impedance sweep determined tuning frequency.


Nope, the minimum (between the two peaks) is around 60 Hz. Have a closer look. You'll also note that the phase response curve (in red) crosses the zero axis around this frequency as well.

My *intended* Fb for this design was actually a bit higher. The measured impedance curve is basically suggesting that the vent is too long, or I've got too much stuffing in the box, both of which will shift Fb downwards. I like the resulting sound of the system, so I've left it as is. 

I think most box design programs suggest vent lengths that are a bit longer than actually required to hit a target Fb, particularly when the size of the vent itself is large. I suspect that there are a lot of car audio boomers who think that their subs are tuned to 40 Hz when they're actually tuned a lot lower . Using a tool like DATS allows you to use impedance measurements to confirm if you actually hit the target Fb, or if adjustments to the build are required.


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## hurrication (Dec 19, 2011)

I've studied engine induction systems for a long time and have a lot of flowbench experience at pressure differentials up to 28" and speeds up to .55 mach.. and when I have enough free time I want to try to implement some induction tricks on the bends of a long port to improve its efficiency with better velocity distribution and a higher discharge coefficient for a given cross section. It would be neat to try a short/wide D-shaped bend and maybe a venturi at the inlet/exit with compound angles and maybe a cone in each end with enough curtain area to maintain flow and help the air stay laminar as it exits.

Even though the ideal velocity for a subwoofer port is lower than 20 meters/sec, I can't help but think that an efficient port with a high discharge coefficient would still yield an improvement.


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## trevordj (Feb 22, 2009)

Thanks Brian. In addition to Hornresp it appears I need to invest in a pair of reading glasses .


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## Oscar (Jun 20, 2010)

this "concept" is exactly what I was touting in Fricassekid's thread about a week or two ago. The port profile that JBLs Slipstream port and the one Bose used in their Acoustimass 8th order bandpass is of an elliptical profile as it is the least lossy from an overall standpoint and will generally produce less distortion than a standard cylindrical port with standard radiused bellmouths. 

Here is my Mediafire link to the paper

11094.pdf

Interestingly, the elliptical profile also provides the best overall performance in tapered intake manifold runners as evidenced by this other paper.

http://www.mediafire.com/view/?flnj8lbyr7yd5zb

Funny how Mother Nature has a liking to mathematical structures...makes ya wonder what else she is hiding from us.


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## Patrick Bateman (Sep 11, 2006)

Oscar said:


> this "concept" is exactly what I was touting in Fricassekid's thread about a week or two ago. The port profile that JBLs Slipstream port and the one Bose used in their Acoustimass 8th order bandpass is of an elliptical profile as it is the least lossy from an overall standpoint and will generally produce less distortion than a standard cylindrical port with standard radiused bellmouths.
> 
> Here is my Mediafire link to the paper
> 
> ...


Yes, I started this thread because I wanted to publish a concise set of best practices for ports, and was inspired by the thread you reference. 

The JBL paper you linked is the one that helped me figure out the Danley vented boxes. Basically I was trying to figure out why danley was using these oddly shaped ports. 

The asymmetry of the Danley ports was the thing that really caught my eye. (If you look at the Danley bowtie ports, they're larger on the inlet than the exit)

What's interesting about this is that it adheres closely to JBLs own recommendations, while JBLs own boxes don't! (And neither do Bose). In the JBL paper, they recommend a larger taper on the inlet NOT the outlet!

So it looks like we've been radiusing the wrong side of our ports all these years. Oddly enough, that will make our ports look like the most famous Helmholtz resonator of all:

A wine bottle.


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## Fricasseekid (Apr 19, 2011)

So if we're to want a poor mans way of designing one of these...

Could I assume that if I design a box with a port of 4" wide and 20" long I could then manipulate the port width however I wanted and as long as the overall avg. of the width remains 4" then the tuning frequency would remain relatively the same? Assume the length is kept at 20" as well. 

Also? If the vertex is closer to the outlet end of the port then can one make the guesstimate that the ratio between lengths of the inlet and outlet should the same ratio as between the widths of the port opening? 
What should that ratio be? The drawings look close to a 1:2 ratio of the outlet:inlet.


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## SaturnSL1 (Jun 27, 2011)

I'm already one of the loudest in the neighborhood and now you're throwing MORE valuable information at us?

I thought this forum didn't like concrete shakers


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## nervewrecker (Oct 5, 2009)

Fricasseekid said:


> Also? If the vertex is closer to the outlet end of the port then can one make the guesstimate that the ratio between lengths of the inlet and outlet should the same ratio as between the widths of the port opening?
> *What should that ratio be?* The drawings look close to a 1:2 ratio of the outlet:inlet.


I myself wondering.

Btw, how did Patrick arrive at 81 square cm for a 4" port in his second post? I got 78.5


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## Patrick Bateman (Sep 11, 2006)

avanti1960 said:


> very interesting. the same principal is used on the water fountain rings at Chicago's McCormick place-
> The Dancing Waters of McCormick Place - YouTube
> the water flow is expanded into a chamber and then refocused to maintain laminar, turbulent free flow as it exits.
> in person the water "ring" looks just like a smooth solid tube of water. it's pretty impressive.
> ...












I really think you're onto something, as far as the water jets go. If you think about how loudspeakers work, it's a lot like what a wine bottle does. A big woofer can move a liter of air twenty times in one second (20hz tone played at a volume that displaces a liter of air.)

So if it works for wine bottles, maybe it works for sub boxes? (The recommended port shape in the JBL paper is basically like a wine bottle.)

Before I show you my wine bottle sims, I want to show how a ported box performs versus a sealed box. *This time around, I'm going to use TWO sealed subs versus one ported box.* The reason that I'm doing this is that we all know that sealed subs don't need a lot of space. So I'm using two sealed subs in this sim, so that we can focus on what box performs the best in a given space.










The pic above shows two of the MCMs in sealed boxes, versus one of the MCMs in a ported box. All woofers are getting one watt, so the sealed is drawing twice as much power (since they're wired in parallel.)

I think this sims show why ported is so popular in the SPL scene - it's dramatically louder for the same amount of power.









Here's the same sim, *but the entire ported box is shaped like a wine bottle.*

It doesn't look a lot different than the traditional ported box, right? It's a little bit smoother, but the F3 isn't much different than a conventional ported box, and the efficiency is about the same.


















Now here's the interesting graph 

This is the phase response of all three.
The first graph is the sealed box versus the 'conventional' ported box with a straight port.
The second graph is the sealed box versus my 'wine bottle box'.

In the second graph, we see a DRAMATIC improvement in phase response. In fact, the wine bottle subwoofer has better phase than the sealed sub! (WOW)



Maybe I just had too much coffee this morning, but these are REALLY exciting results for me. Over in the corner of my living room I have a tapped horn with a twelve in it, and for YEARS it's bugged me that I couldn't make a sub that sounded 'tighter' than the tapped horn. And I think a lot of the reason that transients on the tapped horn sound so 'tight' is because the tapped horn has excellent phase response.

And it looks like you may be able to get something similar in a vented box, by juggling the length and the tuning of the port.










If anyone wants to model this in Hornresp, here's what it looks like.
There is no back chamber at all; *the entire enclosure is a port, a port that's shaped like a wine bottle.*

According to the JBL paper you want a LARGE reduction on the inlet, and a SMALL expansion on the outlet, so that's what I did. I was able to attain flatter response using some other shapes, but this box is basically designed to move air. I know that this might look like a tapped horn, but it's not, there's only one deep impedance dip, not the multiple dips you see in a TH


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## Woosey (Feb 2, 2011)

Brian Steele said:


> Nope. The impedance curve will be very different once that driver is mounted in a box.
> 
> An example: Here's the impedance response of one of my "Blastoramas", measured with DATS. The measurement shows a few things: (1) this is a vented alignment, characterized by the two peaks in the low frequency region, (2) Fb for this vented alignment is around 60 Hz, (3) the alignment is a bit lossy, as the impedance at Fb is noticeably higher than the lowest impedance measured (not surprising, considering that the box is half-stuffed with polyster fiberfill).


Is the tuning frequency @ 0 degree phase shift?

I made a sort of same thing like the DATS with a resistor and some jack/line cables to connect to my computer.. Which can be calibrated with accurate measured resistance..

Pretty nice to use and check for leaks and crossoverdesign with LIMP

It also can measure coils and caps fwiw


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## Fricasseekid (Apr 19, 2011)

Mind responding to my question Dr. Bateman?

So if we're to want a poor mans way of designing one of these...

Could I assume that if I design a box with a port of 4" wide and 20" long I could then manipulate the port width however I wanted and as long as the overall avg. of the width remains 4" then the tuning frequency would remain relatively the same? Assume the length is kept at 20" as well. 

Also? If the vertex is closer to the outlet end of the port then can one make the guesstimate that the ratio between lengths of the inlet and outlet should the same ratio as between the widths of the port opening? 
What should that ratio be? The drawings look close to a 1:2 ratio of the outlet:inlet.


----------



## SkizeR (Apr 19, 2011)

how do you even design/figure out the tuning frequency of a port of that shape?


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## Fricasseekid (Apr 19, 2011)

SkizeR said:


> how do you even design/figure out the tuning frequency of a port of that shape?


He doesn't know without his software.


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## Fricasseekid (Apr 19, 2011)

cajunner said:


> it looks like it's easier to produce with straight slot panels than a variable cylinder.
> 
> the flow through a variable cylinder would be better overall, but creating that port dimensionally with available technology would be cost-prohibitive.
> 
> ...


A heat gun with some PVC pipe slowly worked over a large wine bottle could do the trick. Or a slot port with angled shelving would be easy to build.

BAM!!
Lol


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## Patrick Bateman (Sep 11, 2006)

SkizeR said:


> how do you even design/figure out the tuning frequency of a port of that shape?


The same way you find the tuning frequency of any box with a vent.
You find the 'trough' between the impedance peaks.

I built one here that wasn't adjustable in any way, and the 'trough' came out higher than I expected.

So if you build one of these you're going to want a way to measure the impedance. (Get a woofer tester, they're cheap, they're the one tool that every speaker builder can't live without.)


The big question is the SHAPE.

JBL recommends a very specific shape in their paper, and that shape appears to be optimized for the least turbulence.

But the bummer about that shape is that it *doesn't* appear to give the smoothest response.

I can only guess why the JBL paper recommends one shape (wine bottle)
and JBL sells another (bowtie shaped)

If I had to hazard a guess, it's either easier to manufacture a bowtie, or the bowtie has flatter response at the expense of sub optimum turbulence.



I really wouldn't obsess about a decibel here or there though. You guys gotta understand, I use the moniker 'Patrick Bateman' for a reason, I'm completely OCD when it comes to my hobbies.

In the real world, you could probably use a simple elliptical bowtie shape, use the woofer tester to get the impedance trough where you want it, and call it a day.


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## Patrick Bateman (Sep 11, 2006)

Fricasseekid said:


> A heat gun with some PVC pipe slowly worked over a large wine bottle could do the trick. Or a slot port with angled shelving would be easy to build.
> 
> BAM!!
> Lol


Slot port definitely gives you the most control over the volume in the port.
And if you know your way around hornresp, you can do some tricks to change the frequency response and phase by varying the ratio of the bowtie center to the bowtie inlet and exit.









But if you just want to screw around with this, I'd try cutting up one of those 'big mouth' soda bottles, like a three liter of Faygo or Shasta. The trick is that the mouth has to be BIG because the center of the port still needs to be beefy

Some fiberglass wrapped around the PVC would go a long way too.

If you have a woofer tester, you could probably do it like this:

1) Make a circular baffle out of wood, glue it to the Faygo bottle with gorilla glue or any good polyurethane glue
2) Glue a substantial piece of PVC to the mouth of the Faygo bottle. Use your vented box calculator, and then double the length
3) Let everything dry. Wrap it in fiberglass if you're good with fabrication
4) measure the impedance with the woofer tester
5) If the peak is too low, chop some of the PVC off
6) Go back to step four until you have the impedance trough where it needs to be

That's it!


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## Fricasseekid (Apr 19, 2011)

Yet here I am still wondering about the relationship between the port area on a traditional straight port and the port area on ports like these with a varying area. 

This is the 3rd or 4th technical thread where Dr. Bateman had ignored my particular queries. 

Mind responding to my question Dr. Bateman?

So if we're to want a poor mans way of designing one of these...

Could I assume that if I design a box with a port of 4" wide and 20" long I could then manipulate the port width however I wanted and as long as the overall avg. of the width remains 4" then the tuning frequency would remain relatively the same? Assume the length is kept at 20" as well. 

Also? If the vertex is closer to the outlet end of the port then can one make the guesstimate that the ratio between lengths of the inlet and outlet should the same ratio as between the widths of the port opening? 
What should that ratio be? The drawings look close to a 1:2 ratio of the outlet:inlet.


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## req (Aug 4, 2007)

i guess i am not sure what you are trying to construct in the end pat.

could you draw this thing in MS paint? i am picturing a sonotube with a sub on one end and a "wine bottle" shape at the other.

i am not really sure though...


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## Fricasseekid (Apr 19, 2011)

req said:


> i guess i am not sure what you are trying to construct in the end pat.
> 
> could you draw this thing in MS paint? i am picturing a sonotube with a sub on one end and a "wine bottle" shape at the other.
> 
> i am not really sure though...


I think he is designing a sub port that dispenses Faygo when Insane Clown Posse is played.


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## Patrick Bateman (Sep 11, 2006)

req said:


> i guess i am not sure what you are trying to construct in the end pat.
> 
> could you draw this thing in MS paint? i am picturing a sonotube with a sub on one end and a "wine bottle" shape at the other.
> 
> i am not really sure though...


By far the best way to do this is with a slot port.

Like this:










^^ That's a Danley vented sub. See how the port is bowtie shaped?


If you want to do it with a sonotube, it would basically look as you described. The sonotube would be uglier, but would come together quickly if you just want to 'throw something together' and see how it works.

Both options will require a woofer tester to figure out the impedance trough (and the tuning that goes with it.)


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## Patrick Bateman (Sep 11, 2006)

Fricasseekid said:


> Yet here I am still wondering about the relationship between the port area on a traditional straight port and the port area on ports like these with a varying area.
> 
> This is the 3rd or 4th technical thread where Dr. Bateman had ignored my particular queries.
> 
> ...


1) yes, I think your method of getting the port area should work. The trick is to be sure that the volume of the port stays constant, even though the shape changes. For instance, a port that goes from 4" to 2" to 4" has an area that's the same as three 2" ports of the same length.

2) In the JBL paper, they only studied vertices that were in the center. So I can't comment on what happens when you move the center of the bowtie.


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## Fricasseekid (Apr 19, 2011)

Patrick Bateman said:


> 1) yes, I think your method of getting the port area should work. The trick is to be sure that the volume of the port stays constant, even though the shape changes. For instance, a port that goes from 4" to 2" to 4" has an area that's the same as three 2" ports of the same length.
> 
> 2) In the JBL paper, they only studied vertices that were in the center. So I can't comment on what happens when you move the center of the bowtie.


Thank you! You must be a busy man.


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## Patrick Bateman (Sep 11, 2006)

Fricasseekid said:


> Thank you! You must be a busy man.


If the ATMs stop working today, it's your fault


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## Fricasseekid (Apr 19, 2011)

Lol!


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## onebadmonte (Sep 4, 2008)

Cool thread. I just built a ported box for a ten that I modeled in Hornresp. I measured the impedance curve with the DATS thingie and it did not match the predicted impedance curve from Hornresp. The box sounds good, but I'd like to get more out of it. 

You think a test box with an external slot port with a bowtie cross section will be just as good?


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## Oscar (Jun 20, 2010)

I have to disagree with the winebottle analogy. It has some merit, yet the "best balance" as suggested by the JBL paper does indeed have radiused ends where as the winebottle opening to the atmostphere has walls that are 90° to the cabinet walls.

Here is a picture courtesty of the JBL paper on ports:












Same picture, I just copied/flipped the port profile, outlined their "best balance" port and copied the curves as best as I could to the right of it











Couple corrections of things you mentioned about the paper:


> In the JBL paper, they only studied vertices that were in the center


The air vortices that separate from the flow were not in the center of the port---they were at the exits, where all this flaring makes the most difference. (fig 7)



> What's interesting about this is that it adheres closely to JBLs own recommendations, while JBLs own boxes don't! (And neither do Bose). In the JBL paper, they recommend a larger taper on the inlet NOT the outlet!


Not quite. They _specifically_ mention that the "inlet" geometry is the least lossy when NFR=1 where the radius of the bellmouth is equal to the half the length of the port. "Outlet" conditions are different, where they favor NFR=0, which is basically a straight port The problem with this description is that in ports, there is _no_ one inlet and one outlet, as it is not a water hose where the fluid in question only flows one-way. _Both openings of the ports are inlets and they are outlets because the airmass is vibrating back and forth, not one-way._ Since you can't make both openings straight and fully radiused at the same time, a compromise between the two (NFR=0.5) is suggested as a "best balance".

Section 4 General conclusions, Part (2):



> When designing a port for maximum acoustical output,
> both the inlet and the exit fluid dynamics should be
> balanced. The geometry for best exit flow is different from
> that for inlet flow. Inlet flow is best with a very large taper
> ...


This is what I was referring to when I said that there is "no one inlet and one outlet". When the airmass is retreating back into the enclosure as it is moving, the opening to the atmosphere _now_ becomes the inlet, and the inside opening in the enclosure _now_ becomes the outlet. Of course, they keep switching roles between inlet/outlet each and every single time the port airmass changes direction.


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## Patrick Bateman (Sep 11, 2006)

Oscar said:


> I have to disagree with the winebottle analogy. It has some merit, yet the "best balance" as suggested by the JBL paper does indeed have radiused ends where as the winebottle opening to the atmostphere has walls that are 90° to the cabinet walls.
> 
> Here is a picture courtesty of the JBL paper on ports:
> 
> ...




Ah, that's an excellent explanation. JBL had me scratching my head why their doc recommends an asymmentrical flare, and then they use a *symmetrical* flare for their subs.

I figured their engineers mis-interpreted the paper, or it was just easier to manufacture.

But you make an excellent point - the port isn't just PUSHING air out, it's also PULLING air in.

Here's the quote from JBL which didn't make sense until you pointed this out:

"When designing a port for maximum acoustical output, both the inlet and the exit fluid dynamics should be balanced. *The geometry for best exit flow is different from that for inlet flow.* Inlet flow is best with a very large taper
(NFR close to 1.0). For exit flow a very slow taper is best (NFR closer to 0). This points to an NFR of 0.5 as the optimum."


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## Brian Steele (Jun 1, 2007)

Patrick Bateman said:


> "When designing a port for maximum acoustical output, both the inlet and the exit fluid dynamics should be balanced. *The geometry for best exit flow is different from that for inlet flow.* Inlet flow is best with a very large taper
> (NFR close to 1.0). For exit flow a very slow taper is best (NFR closer to 0). This points to an NFR of 0.5 as the optimum."


FWIW, I think the study that suggests the "nozzle" type vent is better was done after that JBL study. In fact, I don't think the JBL study looked at nozzle-type vents at all, and the study of nozzle-type vents points out the turbulence issues that still occur with flared vents (see images earlier in this thread). 

Now here's the part that might be of interest - the Danley sub picture earlier in this thread has this type of "nozzle" flared vent, even though the cross-section shows no curved panels are used in the build. Do you know why?


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## Fricasseekid (Apr 19, 2011)

The suspense is killing me!


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## Patrick Bateman (Sep 11, 2006)

Here's the formula for figuring out the outer diameter of the port, the diameter of the center, and the length:

"Using this simplification we can define a normalized flare rate (NFR) as the ratio of overall port length to flare radius,

NFR = port length / 2 * (flare radius), 
0 < NFR < 1 . (10)

Thus a straight port would have an NFR of 0.0, and a very extreme port with a full radius would have an NFR of 1.0 (Fig. 28). Most port profiles can be approximated with an NFR in this range. This normalization of scale allows the
results to be generalized to any port size.


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## Fricasseekid (Apr 19, 2011)

cajunner said:


> okay, simple devices used to fabricate center vertex porting...
> 
> 
> and no Faygo 3 liter this time...
> ...


Draw us a picture!


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## Fricasseekid (Apr 19, 2011)

cajunner said:


> exactly!
> 
> 
> I'm not the engineer here, though.
> ...


LOL
I say this often, perhaps you've read it before. 
Some people talk about it and some people be about it! 
It takes all kinds I guess.


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## Oscar (Jun 20, 2010)

Brian Steele said:


> FWIW, I think the study that suggests the "nozzle" type vent is better was done after that JBL study. In fact, I don't think the JBL study looked at nozzle-type vents at all, and the study of nozzle-type vents points out the turbulence issues that still occur with flared vents (see images earlier in this thread).
> 
> Now here's the part that might be of interest - the Danley sub picture earlier in this thread has this type of "nozzle" flared vent, even though the cross-section shows no curved panels are used in the build. Do you know why?


Because Bose has (had?) a patent that depicts an elliptical port profile that was used in their Acoustimass 8th Order bandpass and JBLs port had a very similar profile that was a kind of mathematical curve that very closely resembled Bose's port, varying only a few thousandths of an inch in certain places. Court favored with Bose and JBL lost millions in damages. Danley doesn't want to be in the same situation hence no curved panels to even remotely resemble the Bose port, and no chance to lose an impossible lawsuit.


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## sqshoestring (Jun 19, 2007)

Fricasseekid said:


> I've thought about two big flare ports that would fit the factory 6x9 holes in my back dash. A heat gun, the proper size PVC, and lots of trial and error!


Me too but 6.5 in my deck and no holes, it would be a fabrication build. Ideal would be a folded/elbow vent between the subs. Maybe get sub output but not trunk road noise, not going to treatment the trunk for this, not in this car. A model tells me I can get flat to 20hz ported if I cut 30hz. Will have to measure and see what room I have there its something like 6", so maybe 4" wide and foot tall opening would be ok and could still have a solid baffle. Not that big for pair of 15s, but I don't thrash them either.


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## Brian Steele (Jun 1, 2007)

Brian Steele said:


> Now here's the part that might be of interest - the Danley sub picture earlier in this thread has this type of "nozzle" flared vent, even though the cross-section shows no curved panels are used in the build. Do you know why?


Lots of guesses, but no correct answer so far.

The answer is actually quite simple - a rectangular flared vent as pictured in the cross-section of the Danley sub is basically equivalent to a circular vent with a parabolic flare. If you examine the cross-sectional area at points along the vent and work out the equivalent diameter of a circular vent with the same cross-section, you'd see that the changes to this equivalent diameter follow a parabolic curve. The curve is not an extreme one, but it is present.


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## Brian Steele (Jun 1, 2007)

cajunner said:


> does this curve follow the same specs as those listed in the patents?


Which patents? 

The JBL paper referenced earlier in this thread refers to a different type of curve. IMO the research in that paper is superseded by the later research showing nozzle-type vents as being better at reducing turbulence. The actual paper is here: AES E-Library » Sound Source Design in the Very Low Frequency Domain. You can see a few references to it around the 'net, including the site that I linked to earlier in this thread. 

If you design a vent like what's used on the Danley sub, the equivalent profile will be closer to a nozzle profile than the standard "flared vent" profile that's more familiar. Maybe it's close enough so there's no need to resort to curved panels.


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## Don Hills (Sep 23, 2009)

Patrick Bateman said:


> ... I know that this might look like a tapped horn, but it's not, there's only one deep impedance dip, not the multiple dips you see in a TH ...


You may want to take a look at Mark Kravchenko's "Unhorn" work over on DIYAudio. A hybrid between ported and tapped horn, and with a port that tapered like the ones under discussion here. He intended it for car use, and the respose curve followed cabin gain quite well. It was also quite small. I used AkAbak to design a ported enclosure of the same overall dimensions as his enclosure that had an almost identical response curve, but the kicker was that the ported version ended up much larger once you allowed for the volume taken up by the impractically large vent tube.


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## Oscar (Jun 20, 2010)

Brian Steele said:


> Which patents?
> 
> The JBL paper referenced earlier in this thread refers to a different type of curve. IMO the research in that paper is superseded by the later research showing nozzle-type vents as being better at reducing turbulence. The actual paper is here: AES E-Library » Sound Source Design in the Very Low Frequency Domain. You can see a few references to it around the 'net, including the site that I linked to earlier in this thread.
> 
> If you design a vent like what's used on the Danley sub, the equivalent profile will be closer to a nozzle profile than the standard "flared vent" profile that's more familiar. Maybe it's close enough so there's no need to resort to curved panels.


Anyone got a copy of that paper?? I'd love to see the scientific data behind it.


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## sqshoestring (Jun 19, 2007)

I give, so anyone have a general idea of the size needed for 16cf trunk with pair of 15s tuned to 20hz? Will it be ginourmous? Can I make it 15" tall roughly and not that wide, like a sort of slot? I can hack any shape out of wood, but limited room between my 15s. Figure full output roughly <1" total xmax, at that point I would not care if it made noises/etc.


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## Fricasseekid (Apr 19, 2011)

Let me know when you figure it out.


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## Patrick Bateman (Sep 11, 2006)

sqshoestring said:


> I give, so anyone have a general idea of the size needed for 16cf trunk with pair of 15s tuned to 20hz? Will it be ginourmous? Can I make it 15" tall roughly and not that wide, like a sort of slot? I can hack any shape out of wood, but limited room between my 15s. Figure full output roughly <1" total xmax, at that point I would not care if it made noises/etc.


Won't work.

It's counter intuitive, but *vented boxes must be airtight.* Even the tiniest leak will screw up your tuning.

And there's simply no way to make a car trunk airtight, unless you're willing to seal it off completely. And even then there would probably be a leak *somewhere*.


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## Fricasseekid (Apr 19, 2011)

Patrick Bateman said:


> Won't work.
> 
> It's counter intuitive, but *vented boxes must be airtight.* Even the tiniest leak will screw up your tuning.
> 
> And there's simply no way to make a car trunk airtight, unless you're willing to seal it off completely. And even then there would probably be a leak *somewhere*.


Screw up the tuning or just changes the tuning frequency?


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## Patrick Bateman (Sep 11, 2006)

Fricasseekid said:


> Screw up the tuning or just changes the tuning frequency?


Neither; it just doesn't work.

In a properly built vented box (one that's airtight, except for the vent) there's a deep deep null in the impedance at the tuning frequency. This indicates that the vent is doing all the work. When you achieve this, the vent is basically radiating 100% of the energy at that frequency.

When you *don't* achieve this, you'll see that the dip isn't deep, or basically nonexistent. In this condition, the output at the tuning frequency will be reduced by somewhere between zero and six decibels, depending on how 'lossy' the port is. The Holdaways are super smart, and I think they 'got' this, and I think it's one of the reasons that they were doing aperiodic boxes over twenty years ago. A car trunk is basically aperiodic.

This is one of the reasons that my woofer tester is my favorite tool; you can quickly find leaks and rattles. They ALL take away from your output, and in a hurry. The last box that I built, I literally spent HOURS chasing down leaks. IIRC, it turned out that air was escaping through the holes I'd drilled for the screws for the woofer, and also a bit of air through the gap between woofer and box.

It's CRAZY how a tiny tiny pinhole will screw up a vented box.

BTW, this is way less of a problem back in the day, when vented boxes were three or four cubic feet, and woofers had an xmax of 4mm. But with modern woofers with 10 or 20mm of xmax in less than a cubic foot, those motors will squeez air through the box via any route possible.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> linky:
> 
> PASMAG | PERFORMANCE AUTO AND SOUND - JL Audio introduces insanely powerful high output enclosed subwoofer system
> 
> I like.











Nice catch!

This is indeed *exactly* what this thread is talking about. Basically making a vented box, but one that uses a bowtie shaped port*, and a port volume that's so big that the vent is nearly the entire box.

It takes a lot of the technologies behind the tapped horn, but instead of being a quarter wave resonator it's a Helmholtz resonator.




* in the JL box, the end of the port inside of the enclose doesn't flare. Then again, the air in the box doesn't really 'know' where the port ends and the volume of air behind the woofer begins. So the shelf port kind of 'blurs' that line. This is Yet Another Reason to buy a woofer tester, as you'd need one to figure out the tuning, since the termination of the port isn't 'cut and dry.'


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## sqshoestring (Jun 19, 2007)

If my 'trunk port' produced half the boost the model shows it would be worth doing. I would assume I have to fine tune it somehow, I don't even know the real volume of the trunk that is just a factory rating plus a little. For a normal port its most active frequency would be tuning, that might be a way to tune it by hand. But I would need to start someplace and yes I don't see the point of starting that project if someone knows it will not work at all.


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## hurrication (Dec 19, 2011)

I don't understand the allure of porting a trunk IB install. Going by my current understanding of ported boxes, I would think a ported IB trunk (assuming the trunk was 100% sealed) would yield: an absolutely massive peak at the port tuning, and an incredibly high group delay (40+ ms) at tuning.


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## Randyman... (Oct 7, 2012)

Patrick Bateman said:


> Nice catch!
> 
> This is indeed *exactly* what this thread is talking about. Basically making a vented box, but one that uses a bowtie shaped port*, and a port volume that's so big that the vent is nearly the entire box.
> 
> ...


Too cool! It's like a horn-loaded sub's "Mouth" Siamesed with with a standard direct-radiating ported design. Designing something like this from-scratch to fit in a pre-allocated space is probably a lot of fun (*NOT!*)...

I wonder if we will see anything like this in the pro-audio realm? I'd love to see a single or dual 18" pro-audio sub built with this concept  Too bad I'm currently wrapping up my quad of standard 18" slot-ported sub enclosures - I won't be screwing with those for another 4-5 years!


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## Brian Steele (Jun 1, 2007)

Randyman... said:


> Too cool! It's like a horn-loaded sub's "Mouth" Siamesed with with a standard direct-radiating ported design. Designing something like this from-scratch to fit in a pre-allocated space is probably a lot of fun (*NOT!*)...


It's an interesting design, but not a TH, as the length of the vent is too short. I'd like to see what the measured results look like compared to a simple vented box with a shelf vent that size. My concern is that there appears to be no internal flare on the vent, which could lead to increased distortion at higher power levels.

From the image posted earlier in this thread, the design of the Danley vented sub seems to hit all the right spots. In fact, I might be building two subs like that very shortly - for home use


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## Patrick Bateman (Sep 11, 2006)

Randyman... said:


> Too cool! It's like a horn-loaded sub's "Mouth" Siamesed with with a standard direct-radiating ported design. Designing something like this from-scratch to fit in a pre-allocated space is probably a lot of fun (*NOT!*)...
> 
> I wonder if we will see anything like this in the pro-audio realm? I'd love to see a single or dual 18" pro-audio sub built with this concept  Too bad I'm currently wrapping up my quad of standard 18" slot-ported sub enclosures - I won't be screwing with those for another 4-5 years!


well I think JL ripped off Danley, but hey I've ripped off plenty of his stuff so...









This is basically what the TH-Mini looks like inside. (this is a clone.) The original tapped horns came out about six or seven years ago

Loudspeaker Handbook - John Eargle - Google Books
^^^ Jensen Transflex. Documented in Dickason's Loudspeaker Cookbook. Original design is from 61(!) years ago.









JL Audio "high output" box. I think they patented these about two or three years ago?


The thing that's funny about all these designs is that their efficiency is all about the same, for their footprint. This is because you can't escape Hoffman's Iron Law.

Due to Hoffman's Iron Law, I think the 'final frontier' is figuring how to combat power compression and port turbulence, because those will take a toll on your maximum output and dynamics. And all of these designs tackle this to one extent or another.


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## Patrick Bateman (Sep 11, 2006)

Brian Steele said:


> It's an interesting design, but not a TH, as the length of the vent is too short. I'd like to see what the measured results look like compared to a simple vented box with a shelf vent that size. My concern is that there appears to be no internal flare on the vent, which could lead to increased distortion at higher power levels.
> 
> From the image posted earlier in this thread, the design of the Danley vented sub seems to hit all the right spots. In fact, I might be building two subs like that very shortly - for home use


Probably the ONE thing that blew my mind when I started to sim these boxes in hornresp was that *it's possible to flatten out the phase curve by manipulating the shape and the length of the port.*

This might seem 'old hat' to some of the wizards here, but it never occurred to me. I'd basically dismissed vented boxes years ago, because they always sound so 'slow' and 'sluggish' to me. And i'd long known that the phase rotation on a horn is 90 degrees, while the phase rotation on a vented box is 180 degrees. (IE, a horn *should* sound better because a horn has theoretically better phase.)

But researching these ported boxes made me realize a few things:

1) You can 'tweak' the phase of the design by changing the port length. Although the port is 180 degrees out of phase, the port introduces a time delay, and you can use that to tweak the phase. (IE, long port and short port do not have the same phase, even if the tuning frequency is identical.)
2) The 'Q' of the various resonances matters. For instance, just because I built a few ported boxes that sound like crap, that doesn't mean that all ported boxes sound like crap.










Here's an illustration of what I'm talking about, in regards to the phase response of a vented box. When we read about vented boxes, we read that there's a 180 degree phase rotation. But that's not 100% accurate. The phase rotation is dependent on the pathlength of the port.

The pic above illustrates the ideal situation. In the pic, I've shown how we want the sound at zero degrees phase rotation to sum in-phase with the front of the cone that's *also* at zero degrees phase rotation. Do this properly, and you not only get huge output, you also flatten out the phase response of the entire box.

I hope that makes sense. I would've made an animated GIF if I had the time.

Now that pic is the *ideal* situation, but it's hard to get to that ideal. For instance, forty hertz is TWENTY EIGHT feet long. And I don't got no room for a twenty eight foot long port.

But the 'trick', as I see it, is to juggle all the parameters to get close to that ideal. For instance, even a plain ol' sealed box will see phase rotation as frequencies get lower and lower. As the output of the sealed box begins to decay, the phase begins to rotate. So that's the 'trick.' You manipulate the output of the front and the back of the cone, so that the phase is as close to flat as you can get it.

When you get that right, it's pretty damn epic. In my home theater I currently have three subs. One is a bandpass, one is a tapped horn, and one is a vented box. And when I move about the room, it's not subtle how 'tight' the tapped horn is. And I think that 'tightness' is due to these tricks mentioned above.

But this trick doesn't just apply to tapped horns. You can do it with vented boxes too. Admittedly, it's easier to do with tapped horns. But I've been able to make vented boxes in Hornresp where the phase response is actually *superior* to a sealed box! To me, that's quite amazing; the output of a vented box with transient response that exceeds a sealed design.


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## Brian Steele (Jun 1, 2007)

Brian Steele said:


> It's an interesting design, but not a TH, as the length of the vent is too short. I'd like to see what the measured results look like compared to a simple vented box with a shelf vent that size. My concern is that there appears to be no internal flare on the vent, which could lead to increased distortion at higher power levels.


Well, waddya know, it does have an internal flare. See 

JL Audio HO110-W6v3 Product Spotlight - YouTube


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## sqshoestring (Jun 19, 2007)

hurrication said:


> I don't understand the allure of porting a trunk IB install. Going by my current understanding of ported boxes, I would think a ported IB trunk (assuming the trunk was 100% sealed) would yield: an absolutely massive peak at the port tuning, and an incredibly high group delay (40+ ms) at tuning.


Pretty simple for me: frequency response. My model is +1db peak at 35Hz and -3db at 21Hz. By ear it rolls off at 25Hz (-1db, but -2db from peak), so the model is somewhat close to reality.

If it were a box and ported I could tune at 14hz and have a new peak of +2.4db at 26Hz, and still be 0db at 12.8hz, -3db at 11.8Hz. I would have more and flatter output 15-50Hz, what is not to like? Sure I could tune higher and get a huge peak but why bother. At +1db now they shake my roof, I don't need more output even though I would get more.

Something to consider for sure but I'm not terribly worried about delay at <30hz, I'm happy just to have output there I can hear. The group delay does spike huge under 20hz, is it really going to matter? I'd be happy with a 15hz SS filter that would cut much of that down anyway, if I needed it which in my experience so far I doubt I would.

I might be better off tuning at 17hz, for a peak 3.5db higher at 20-23hz than I have now at 35hz (+1db). That would offset my cranking up the EQ at 20-30hz. That would roll off sharply at 15hz (+1.3db and dropping fast). Delay would go above 20ms at 23hz. To sum up, that would give me something close to flat to ear response down to <20Hz instead of the roughly 28hz I have now, and all just for slapping a port in. (IF it worked of course lol!) That is why I say even half the db gain would make it worth doing. 20hz in a car is not that easy.


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## svnuss (May 13, 2013)

Just got a great deal on 3 HO110W6V3 . They sound great.


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## Oscar (Jun 20, 2010)

HR input screen?


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## venki7744 (Feb 18, 2014)

Hi Pat,

Sorry for waking up the old thread. With my limited knowledge I tried modelling the JL sub in hornresp but failed miserably . I guess HR does not allow modelling Tapped Horn with a chamber. Any pointers to modelling this .

Cheers,
Venki


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## venki7744 (Feb 18, 2014)

Hi Patrick,

Any thoughts 

Cheers,
Venki


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## captainscarlett (Mar 15, 2011)

> I heard this just before christmas to be honest I wasn't impressed it was missing frequencys


'Increaded SPL' aside, when does personal listening preferences come into this?


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## venki7744 (Feb 18, 2014)

Thanks captainscarlett,

I am still curious to know how this can be modelled in Hornresp. I however was able to model something similar using Leonard Audio - Transmission line software. However I am not sure about the correctness of the program in predicting the response of a ported box. If someone could get me the dimension of the box including the port areas, I will try and model this using Leonard Audio and post the FR here.

Thanks,
Venki


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## captainscarlett (Mar 15, 2011)

Of the JL boxes I owned and have heard, I've never been blown away by any of them. The SQ was good, but nothing memorable. 

From what I see, even the CP108 employs the same or similar .. formula spoken about here. 

http://mediacdn.shopatron.com/media/mfg/9013/media_image/dev_1/CP108LG_W3v3_CA.jpg?1326169448

Wouldn't put it down as an SPL monster though!


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## Patrick Bateman (Sep 11, 2006)

venki7744 said:


> Thanks captainscarlett,
> 
> I am still curious to know how this can be modelled in Hornresp. I however was able to model something similar using Leonard Audio - Transmission line software. However I am not sure about the correctness of the program in predicting the response of a ported box. If someone could get me the dimension of the box including the port areas, I will try and model this using Leonard Audio and post the FR here.
> 
> ...


Hornresp can model things that aren't horns; the trick is to make that thing "fit" the model.

For instance, if you want to model a vented box with a flared port in hornresp, just do the following:

1) Model it as if it was a horn
2) In the segments where the horn is, *put the port there.* For instance, if your port is 30cm long and 10cm in diameter, make a horn segment that is the same length and volume. You can 'break it up' into three pieces to simulate a flared port.
3) The 'throat chamber' of a horn is the same thing as the box volume of a vented box. "VTC" and "ATC" set the volume and area of the throat chamber, respectively.

In summary:
1) The throat chamber of the horn is synonymous with the box volume of a vented box
2) The horn of the horn is synonymous with the port of a vented box

One important thing here: "VRC" and "LRC" are zero if you're modeling a Vented Box this way. Becauase as soon as you set the Length of a Rear Chamber (LRC) and Volume of Rear Chamber (VRC) then you're now modeling a single reflex bandpass box.

Check out some of the tutorials on hornresp for some information on what all the variables do.









Here's a pic. This is not a vented box btw, just took it from a Hornresp tutorial.

I'll admit there's a learning curve, but it's not nearly as bad as Akabak. I've been modeling loudspeakers since the early 90s, and Hornresp is easily my fave. There are some that go a little further (Akabak) but there are none that produce good results faster. I can crank out a decent design in about 30 minutes; the time consuming part is drawing the box in Xara.


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## venki7744 (Feb 18, 2014)

Hi Pat,

Thanks for responding, however this JL box looks like a tapped back loaded horn which I believe cannot be modelled in Hornresp. We might be able to model this in Akabak but never tried it. I myself try to model anything and everything hornresp hence already little familiar with how to use the tool. Any pointers on how to do this .

Cheers,
Venki


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## Patrick Bateman (Sep 11, 2006)

venki7744 said:


> Hi Pat,
> 
> Thanks for responding, however this JL box looks like a tapped back loaded horn which I believe cannot be modelled in Hornresp. We might be able to model this in Akabak but never tried it. I myself try to model anything and everything hornresp hence already little familiar with how to use the tool. Any pointers on how to do this .
> 
> ...


A tapped horn and a back loaded horn are the same thing, but with one difference : the driver isn't at the end of the line.

You can verify this by modeling a tapped horn and a back loaded horn in hornresp, and move the driver in the tapped horn all the way to the end of the line. When you sim it, you'll see the response is the same.

To model the JL box, just follow the instructions in my post from earlier today, it will work. The JL box is basically a vented box with a really big vent, a vent so big that the driver is actually IN the vent.


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## venki7744 (Feb 18, 2014)

Thanks Pat,

I will check this and get back on some FR.

Cheers,
Venki


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## captainscarlett (Mar 15, 2011)

Wonder if something like this can be employ in t-lines?


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## venki7744 (Feb 18, 2014)

Patrick Bateman said:


> I really think you're onto something, as far as the water jets go. If you think about how loudspeakers work, it's a lot like what a wine bottle does. A big woofer can move a liter of air twenty times in one second (20hz tone played at a volume that displaces a liter of air.)
> 
> So if it works for wine bottles, maybe it works for sub boxes? (The recommended port shape in the JBL paper is basically like a wine bottle.)
> 
> ...


Hi Pat,

I am back again, I tried modelling the wine bottle for Helix B12WDVC4 (which I know is not ideal for Horn/ported) in both Hornresp and Leonardo Audio - TL one thing interesting or rather confusing is the fact the both came up with different results eventhough HR matched the phase response predicted by you, the LA program predicted a totally different result. Now which one is accurate . Attached below are the screenshots of the model in both the programs and the FR and Phase. Any thoughts 

Cheers,
Venki


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## captainscarlett (Mar 15, 2011)

venki7744 said:


> one thing interesting or rather confusing is the fact the both came up with different results eventhough HR matched the phase response predicted by you, the LA program predicted a totally different result. Now which one is accurate . Attached below are the screenshots of the model in both the programs and the FR and Phase. Any thoughts
> 
> Cheers,
> Venki


Does that not qualify such programs as inaccurate. From HR to WiniSD


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## JoshHefnerX (Jun 13, 2008)

captainscarlett said:


> Does that not qualify such programs as inaccurate. From HR to WiniSD


The data could be bad, not necessarily the formulas.

Josh


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## Patrick Bateman (Sep 11, 2006)

venki7744 said:


> Hi Pat,
> 
> I am back again, I tried modelling the wine bottle for Helix B12WDVC4 (which I know is not ideal for Horn/ported) in both Hornresp and Leonardo Audio - TL one thing interesting or rather confusing is the fact the both came up with different results eventhough HR matched the phase response predicted by you, the LA program predicted a totally different result. Now which one is accurate . Attached below are the screenshots of the model in both the programs and the FR and Phase. Any thoughts
> 
> ...





















Looks about 90% the same to me. In the real world I doubt any difference would be audible. The Hornresp graph is on a 50dB scale that's ten octaves wide; the LA graph is on a 60dB scale that's half as wide. The Hornresp graph appears to have a much greater power input.

As for which I'd use, I'd go with Hornresp unless LA offers something that Hornresp doesn't. I use Hornresp for 80% of what I do, and occasionally I use Akabak for some things it can't do. (Akabak can model *anything*, and it's followup can model even more.)


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## captainscarlett (Mar 15, 2011)

Am i right in thinking, that if one kerfs or creates a round-over at the port mouth, then you only need calculate half the 'port end' in the overall port calculations? I assume it would be the same here.


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## Patrick Bateman (Sep 11, 2006)

captainscarlett said:


> Am i right in thinking, that if one kerfs or creates a round-over at the port mouth, then you only need calculate half the 'port end' in the overall port calculations? I assume it would be the same here.


I don't trust port calculators at all.
They'll get you "in the ballpark" but I always find that I have to adjust the length by as much as 25%

I always use a bigger port than necessary, then reduce it until I get the right tuning. (And tuning is verfied with an impedance sweep.)

As for the length, yes, that's based on the diameter over the majority of the port, not the diameter at the mouth. IE, if you have a 3" port that flares to 5" at the mouth, the length is calculated as if the port is 3" across it's entire length. But, again, measure the impedance to get the right tuning.


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## captainscarlett (Mar 15, 2011)

Patrick Bateman said:


> I don't trust port calculators at all.
> They'll get you "in the ballpark" but I always find that I have to adjust the length by as much as 25%
> 
> I always use a bigger port than necessary, then reduce it until I get the right tuning. (And tuning is verfied with an impedance sweep.)
> ...


Cheers Patrick.


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## captainscarlett (Mar 15, 2011)




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