# Getting the Most (SPL) Out of Your Sub



## Patrick Bateman (Sep 11, 2006)

Someone emailed me, asking about high efficiency subwoofers, so I thought I'd do a quick post about subwoofer efficiency.

First off, there's a handful of subwoofer "myths" that need to be dispelled right from the start. Big subwoofers don't need big amps; it's actually the opposite. Large subwoofers generally require large boxes, and large boxes are generally more efficient than small boxes. Another myth is that more expensive subwoofers are more efficient. Generally it's the opposite; expensive subwoofers are frequently optimized for small boxes, and small boxes are generally less efficient than big boxes.

So if you think that upgrading to a $500 subwoofer will buy you efficiency, it's generally the opposite.

Reading the specs can be misleading too, because some manufactuers rate their efficiency at 8ohms, some rate it at the woofer's impedance, and some specsheets are outright lies 

The one thing you *can* rely on is Hoffman's Iron Law which states: 
*"Hoffman's Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). The obvious implication is that to reduce the cutoff frequency by a factor of two, e.g. from 40 Hz to 20 Hz, while still retaining the same system efficiency, you need to increase the enclosure volume by 23=8 times! In other words, to reproduce ever lower frequencies at the same output level you need an extremely large box!"*

At this point, you might be wondering where ported boxes fit into this picture. A ported box is more efficient than a sealed box right?

Yes... and no. The ported box sacrifices low end extension for efficiency higher in the passband. In fact, that's how nearly all exotic boxes work. Bandpass, front loaded horns, back loaded horns, tapped horns, etc... To one extent or another they all trade efficiency in one passband for another.

That might not make sense, since everyone knows that ported boxes are more efficient than sealed boxes, and horns are more efficient than both.

Right?

Well here's a pic to illustrate my point. This is the measured response of two subwoofers that I've built. Each was measured at the same volume.

















The orange line is a tapped horn, with a single twelve. The blue line is a transmission line with dual twelves. In the pic the TL is the aluminum enclosure, and the TH is the wood one. The black one is a bandpass. The tapped horn sounds waaaaaaaaaaay louder than the TL. It easily *sounds* ten times louder. And it should - is uses a woofer with an efficiency that's over ten DB higher, in a _horn._

But look what happens at 45HZ - the response of the two boxes is virtually identical.

That's Hoffman's Iron Law at work. No matter how exotic the box is, or how many woofers we use, or even how big they are, there comes a point where we run into Hoffman's Iron Law.

Weird huh?

Anyways, for the original poster, I personally prefer the tapped horn. Here's why:

As I see it, the "ultimate" car sub would have gobs of output from 40-80hz, which is where all the action is in our music. Below that, the response would fall off. Due to cabin gain, we get 15-25 decibels in "free" output below 40hz. So I want it to kick like a mule between 40 and 80hz. Above 80hz, it would be great if the response started to drop, because I don't *need* output above 80hz. I basically need a couple of octaves, and that's it. Now you can make a sealed box do what I described, and you can make a ported box do it too. _But a horn, a bandpass, and a tapped horn are the only enclosure types that can *physically* filter out distortion._ That's the key. The efficiency is icing on the cake.

See that notch in the response from 100-150hz? Let's say a bass note hits at 60hz, and there's a ton of 2nd harmonic distortion. The 2nd harmonic will be at 120hz. That big fat notch from 100-150hz will reduce the volume of that distortion by over 90% 

Show me any other enclosure that can do that!

In addition, while the transmission line is capable of more output below 45hz (due to higher SD), I personally prefer to maximize the output from 40-80hz. Because of cabin gain, it's really easy to get high output from 20-40hz, we basically get free SPL in that octave.


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## Mless5 (Aug 21, 2006)

Want to design me a box ? Enjoyed the read, as always


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## huckorris (Sep 2, 2009)

Great post but I don't understand why there are two blue lines on the graph. Don't tell me I'm colorblind. 

I'm gonna take some time to digest it and research more about different enclosures.

Keep up the good work. Most if not all posts of yours I read are very informative and well explained. I wish I could give you kudos points, but you'd probably already be maxed out on them.


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## Mless5 (Aug 21, 2006)

huckorris said:


> Great post but I don't understand why there are two blue lines on the graph. Don't tell me I'm colorblind.


Put the glass down


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## huckorris (Sep 2, 2009)

Mless5 said:


> Put the glass down


?????


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## tintbox (Oct 25, 2008)

I just did and I still see two blue lines. Great info.


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## TREETOP (Feb 11, 2009)

I see 2 blue lines also.


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## Patrick Bateman (Sep 11, 2006)

huckorris said:


> Great post but I don't understand why there are two blue lines on the graph. Don't tell me I'm colorblind.
> 
> I'm gonna take some time to digest it and research more about different enclosures.
> 
> Keep up the good work. Most if not all posts of yours I read are very informative and well explained. I wish I could give you kudos points, but you'd probably already be maxed out on them.


Thanks!

I did two ground plane measurements, each one at the same distance. One is 45 degrees to the left of the sub, the other at 45 degrees to the right.

Since a 40hz soundwave is as long as a house, measuring it like that gives you some idea if the dips and peaks are real, or reflections off other things.

I measured this in the middle of my drive way, the blip at 70hz could be a reflection off the garage, which was about 20 feet away.

Subs are really difficult to measure, because of the preposterous frequency lengths.


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## digital (Sep 12, 2008)

If horns are so good, how come they are not too popular? When I asked about horn sub woofers in local car audio store, they had no idea what I was talking about.


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## Hispls (Mar 12, 2008)

Great so far...please continue...


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## Hispls (Mar 12, 2008)

Apparently this is why you don't hear much about tapped horns in car audio....though potential output seems obscene:


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## huckorris (Sep 2, 2009)

Patrick Bateman said:


> Thanks!
> 
> I did two ground plane measurements, each one at the same distance. One is 45 degrees to the left of the sub, the other at 45 degrees to the right.
> 
> ...


Thanks bateman. Lol. I love that name. Bateman.:laugh:

So how are the mergers and acquisitions going? :smash::dead_horse::z::knife::rifle::cwm23:


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## digital (Sep 12, 2008)

Hispls said:


> Apparently this is why you don't hear much about tapped horns in car audio....


Lol, obviously you can't fit the big ones in a car. But there is few designs which compare in size to ported dual 12" or 15" boxes.


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## Patrick Bateman (Sep 11, 2006)

digital said:


> If horns are so good, how come they are not too popular? When I asked about horn sub woofers in local car audio store, they had no idea what I was talking about.


Yeah, reminds me of the reaction I got when I tried to learn about bandpass subs back when they were popular.

I don't blame them though - if I owned a car audio store, I would steer my customers away from complex enclosures too.

Too easy to screw up, too much work, and no real benefit for the store owner. It's a lot easier to just build a sealed box and be done with it.


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## niceguy (Mar 12, 2006)

Good reminders.....those poor subs look like they're in coffins


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## Oliver (Jun 25, 2007)

Patrick Bateman said:


> Yeah, reminds me of the reaction I got when I tried to learn about bandpass subs back when they were popular.
> 
> I don't blame them though - if I owned a car audio store, I would steer my customers away from complex enclosures too.
> 
> Too easy to screw up, too much work, and no real benefit for the store owner. It's a lot easier to just build a sealed box and be done with it.


*Bingo !! ^^^^*

*Put your money down and take what I've got*


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## Hispls (Mar 12, 2008)

The SMALL one in the pics I posted was 60hz tuned (the biggest one was 20hz). By the length of these fellas, this has to work along the lines of TL just with the different loading.

Any plans for a tapped horn box that plays down to 40 that would fit in anything smaller than a herse.


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## Oliver (Jun 25, 2007)

I think Randy folded his


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## Patrick Bateman (Sep 11, 2006)

digital said:


> Lol, obviously you can't fit the big ones in a car. But there is few designs which compare in size to ported dual 12" or 15" boxes.


The TH-Mini isn't very big at all - I could get three of these in my car if I wanted to give up my back seat. The internal volume is a bit over 3 cubic feet. Factor in the woofer and the wood, and they measure 4.69 cubic feet. That sounds like a lot, but the boxes are relatively light, which makes them easier to throw around. A heck of a lot easier than moving an MDF box with a pair of JL 13W3s.

The pic above was one of the first five tapped horns built in the DIY community, before we learned some tricks to shrink them down to a manageable size.

Let's say you want a sub box in your car that hits like a hammer to the chest. Though subs can play down to ten or twenty hz, the frequency of a kick drum is about 60hz. So unless you're in the habit of playing movie soundtracks in your car, or cannon shots, 60hz is the frequency that's critical in the car. Not saying that 20hz isn't important, just saying that 60hz is *more* important if music is your priority.

Here's a comparison.

A pair of JL Audio 13W7 subwoofers retail for $1199 each. You can DIY a sealed box for $40. The box will be about 3 cubic feet. A pair of the JL subs have a sensitivity of 89db. Thanks to the wonders of cabin gain, that bumps up to about 95db at 60hz in the car.

Hopefully that makes sense.

A pic is worth a thousand words, so here's a graph of the JL's response (without cabin gain.)










I took the specs from here:
JL Audio 13W7-D1.5 W7 Series 13.5" subwoofer with dual 1.5-ohm voice coils at Crutchfield.com

Now the fun stuff, let's figure out the amplifier part. We're going to feed our JL subs three thousand watts, the most they can handle. A pair of decent 1500 watt amps will set you back $1000. The sensitivity of the pair of subs in our box is 95db at 60hz. With 3000 watts, that gives us 129.8db.

That may sound low, but remember this isn't a one-note ported box - this is a sealed box designed to actually _sound good in the car._ The kind of box you guys would run, not a one-note SPL monster.

So that $3238 for 130db. If you want to be a real egghead, that's $24.90 per decibel :surprised:

Now let's say you just use a *single* TH-Mini. You can pick up the phone right now and have one shipped to you for $1295. No need to build a box, just drop it in your trunk. Here's a retailer:

Danley TH-mini Passive Touring version PA Subwoofer w/ handle & rubber feet

Here's a pic :







Here's the spec sheet:

http://www.danleysoundlabs.com/pdf/TH MINI Spec Sheet.pdf

No need to guess on how loud it will play, just look at the spec sheet. It has a sensitivity of 101db. Add in cabin gain, and it brings us up to 107db at 60hz.

Since we're only using one woofer, we're going to use one amp. So we toss one amp, and feed the TH-Mini 1500 watts. With a sensitivity of 107db at 40hz, that gives us 138.8db at 60hz.

Factor in $500 for our amplifier, and that's $1795 for 139db, or $12.91 per DB. About half as much as the JL.

Honestly that's only half the story though. I think a lot of you will look at a number like 130db for a pair of JLs and chuckle - we all know they can play louder than that. A lot of guys will pour 3000 watts into a *single* 13W7. But it's out there at the lunatic fringe where the tapped horn will clobber the JL, for a few reasons:


Convection makes a huge difference in cooling, that's why we put fans on the heatsinks of our computers. There's no convection in a sealed box, so the JL is going to cook in one.
The entire basket of the woofer in the tapped horn is exposed, and at high excursion, there's going to be massive convection.
The TH-Mini is rated for 1400 watts, but that's the the thermal limit of the driver. Factor in convection and it's likely much higher.
The woofer in the TH-Mini has a larger voice coil diameter, which generally increases power handling
The TH-Mini is designed for night clubs and concerts, where it's played for hours on end, so factor that in with the power rating
Prosound gear is built like a tank
The mass of air in a horn sub reduces excursion on both sides of the cone, which prevents the woofer from being physically destroyed by excursion
Due to the increase in sensitivity, there's less of a need for an upgraded alternator
Due to the increase in sensitivity, losses due to overheating are minimized


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## Aaron Clinton (Oct 17, 2006)

*Nice info. PTS, built a box with a pair of Icon 10's in a TH and was doing insane numbers in the 20hz range.*


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## SSSnake (Mar 8, 2007)

This is great except when you start getting into high SPLs and small spaces... The strength of a horn over other alignments is the broadband loading of the driver (a port loads at a very narrow passband) resulting in higher efficiency. This acoustic transformer function is VERY helpful in free space. In a car, where there is VERY little airspace you will not see tremendous benefits from a bass horn of any type (been there done that). 

My results were so disappointing that I rebuilt both the horn and a the ported enclosure outside the car and took measurements. While in freespace the horn was much more efficient (down to cutoff) it did not enjoy the same gain in output when placed in the car.


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## Electrodynamic (Nov 27, 2007)

Patrick Bateman said:


> Honestly that's only half the story though. I think a lot of you will look at a number like 130db for a pair of JLs and chuckle - we all know they can play louder than that. A lot of guys will pour 3000 watts into a *single* 13W7. But it's out there at the lunatic fringe where the tapped horn will clobber the JL, for a few reasons:
> 
> 
> Convection makes a huge difference in cooling, that's why we put fans on the heatsinks of our computers. There's no convection in a sealed box, so the JL is going to cook in one.
> ...


The basket of a driver having fins on it has little to do with the thermal power handling of the driver. By the time the heat moves from the coil through the top plate and magnet and out to the fins on the basket, the coil could easily exceed its thermal limits. The main goal in thermal power handling is moving heat away from the coil itself, not the basket. Exchanging air around the coil is the best way to do the latter. Take a look at the power handling ratings on this driver. The reason for the insane power handling ratings is not fins on the outside of the loudspeaker, but the 70% air exchange they have _inside_ the motor, and more particularly, around the voice coil.

And with increased sensitivity (Hoffman's Law that you quoted earlier supports this) comes increased box size. In a car, and more particularly this forum, it's difficult to justify taking up ~5 ft^3 for a single woofer. And as SSSnake said, horns in cars don't have the huge benefit that they do outside of a high pressure environment (ie. a car).


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## Patrick Bateman (Sep 11, 2006)

Electrodynamic said:


> The basket of a driver having fins on it has little to do with the thermal power handling of the driver. By the time the heat moves from the coil through the top plate and magnet and out to the fins on the basket, the coil could easily exceed its thermal limits. The main goal in thermal power handling is moving heat away from the coil itself, not the basket. Exchanging air around the coil is the best way to do the latter. Take a look at the power handling ratings on this driver. The reason for the insane power handling ratings is not fins on the outside of the loudspeaker, but the 70% air exchange they have _inside_ the motor, and more particularly, around the voice coil.


I hope I didn't imply that it had to do with the *shape* of the basket. The reason the convection is greater in the tapped horn than in the sealed box is that THE ENTIRE SPEAKER is exposed. In a sealed box, the warm air being pumped out of the voice coil has nowhere to go. In addition, the fiberglass stuffing used inside of a sealed box increases the heat too.

And of course, everything we can do to keep the voice coil cool will increase power handling, reduce power compression, and increase the lifespan of the motor.



Electrodynamic said:


> And with increased sensitivity (Hoffman's Law that you quoted earlier supports this) comes increased box size. In a car, and more particularly this forum, it's difficult to justify taking up ~5 ft^3 for a single woofer. And as SSSnake said, horns in cars don't have the huge benefit that they do outside of a high pressure environment (ie. a car).


Is a five cubic foot box reasonable if it replaces eight 10" woofers? Or is a five cubic foot box reasonable is it replaces four 12" woofers?

Especially if the box weighs 40 or 50lbs?

Did the PA sub ever make it to the market? I heard there were issues. The B&C 12PS100 is rated for 1400 watts. I have a feeling this rating is more conservative than your average car audio rating. It's also quite reasonable, just $206.

B&C 12 PS100 is a 12" powerful woofer - B&C Speakers - B&C 12" subwoofer for 3-way speaker systems. B&C 12 PS100 powerful subwoofer speakers available now.

Can't find a price for the pasub on their site. The JL has an MSRP of $1199.

Anyways, thanks for discussing the subject of voice coil cooling. I agree, that is key. And I wouldn't recommend using more than one TH-Mini in a car - it will hit 130db without breaking a sweat. The only reason to use more than one would be to get into the 140s or the 150s.


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## Electrodynamic (Nov 27, 2007)

Patrick Bateman said:


> Is a five cubic foot box reasonable if it replaces eight 10" woofers? Or is a five cubic foot box reasonable is it replaces four 12" woofers?
> 
> Especially if the box weighs 40 or 50lbs?


If a horn subwoofer enclosure worked in a car, maybe. But horns don't work in a car like they do elsewhere due to pressure. There's too much contained space at the end of the horn (the car’s interior). Horn’s don’t like loading high pressure areas, they rely upon transforming from high pressure at the throat to low pressure at the mouth. Have you tried putting a tapped horn in a vehicle and putting it on a mic?



> Did the PA sub ever make it to the market? I heard there were issues. The B&C 12PS100 is rated for 1400 watts. I have a feeling this rating is more conservative than your average car audio rating. It's also quite reasonable, just $206.


There are no issues with the PA Sub. It's not available to the general public because they are selling them in large quantities to "other" companies. They require too big of an enclosure for car audio anyway, but they rock out with their **** out in PA applications.


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## Patrick Bateman (Sep 11, 2006)

Electrodynamic said:


> If a horn subwoofer enclosure worked in a car, maybe. But horns don't work in a car like they do elsewhere due to pressure. There's too much contained space at the end of the horn (the car’s interior). Horn’s don’t like loading high pressure areas, they rely upon transforming from high pressure at the throat to low pressure at the mouth. Have you tried putting a tapped horn in a vehicle and putting it on a mic?
> 
> There are no issues with the PA Sub. It's not available to the general public because they are selling them in large quantities to "other" companies. They require too big of an enclosure for car audio anyway, but they rock out with their **** out in PA applications.


A mic? What's THAT? I don't listen to music with a mic, I listen with MY EARS!!!

Just kidding 

Here's the response outside of the car. It's the upper trace, the lower trace is a transmission line with dual Dayton DVC 12s, which are basically an Adire Audio Shiva clone.








Outside of the car, the tapped horn has a bandpass response from 45hz to 125hz. So about an octave and a half of output. From 22.5 hz to 45hz response falls at a rate of 24db/octave. Basically, the woofer unloads at 45hz.

And the response IN the car:







In the car, the F3 points are similar. The difference in the car is that the efficiency is higher, thanks to cabin gain. You can see a boost that begins aroun 120hz, gradually raising output all the way to 20hz. We're picking up about 3-5 db at the top, about 6db around 45hz. Where we *really* see the effect of cabin gain are below 45hz, where the response falls at 12db/octave in the car, instead of 24db like outside.

Anyways, this is all by design. I designed the tapped horn so we'd have loads of efficiency from 40-80hz, where all the action is in our music. I know some people are chasing subs that play down to 10 or 20hz, but I've found that octave is overrated. For a home theater, it's great, for a car, not so much.

Also, the glue is drying on a second tapped horn, with three eights. If I'm lucky I'll post measurements before the weekend. Stay tuned...


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## djknowledge (Feb 12, 2009)

i wish i knew how to build a box, then maybe my original orion hcca would send even better then they already do.


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## Electrodynamic (Nov 27, 2007)

Unless I'm completely missing something, it looks like the output is very similar outside of the car and inside the car. How much power was used in both measurements? I can't really tell because of the image, but it looks like you've got ~139 dB of output from 50 hz to 100 Hz outside of the car and you've also got ~138 dB from 50 Hz to 100 hz inside the car.

If you think the last octave (20 Hz to 40 Hz) is overrated, why not chop your tweeters off at 10 kHz? 

A single (not two) ported 13W7 with a 1000 watt amp on it can reach to 140 dB regularly in a vehicle. That combination can be had for less than the $1795 you listed for the horn and 139 dB. And it takes less than 2.5 ft^3 ported as per JL's product manual.


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## Patrick Bateman (Sep 11, 2006)

Electrodynamic said:


> Unless I'm completely missing something, it looks like the output is very similar outside of the car and inside the car. How much power was used in both measurements? I can't really tell because of the image, but it looks like you've got ~139 dB of output from 50 hz to 100 Hz outside of the car and you've also got ~138 dB from 50 Hz to 100 hz inside the car.
> 
> If you think the last octave (20 Hz to 40 Hz) is overrated, why not chop your tweeters off at 10 kHz?
> 
> A single (not two) ported 13W7 with a 1000 watt amp on it can reach to 140 dB regularly in a vehicle. That combination can be had for less than the $1795 you listed for the horn and 139 dB. And it takes less than 2.5 ft^3 ported as per JL's product manual.


To hit 140db with 1000 watts, you would need a woofer with an efficiency of 110DB. (1000 watts gets you 30DB more output than 1 watt.)

The JL woofer has an efficency of 84DB.

Where's the other 26DB coming from?


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## Hispls (Mar 12, 2008)

Patrick Bateman said:


> To hit 140db with 1000 watts, you would need a woofer with an efficiency of 110DB. (1000 watts gets you 30DB more output than 1 watt.)
> 
> The JL woofer has an efficency of 84DB.
> 
> Where's the other 26DB coming from?


Cabin gain


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## Electrodynamic (Nov 27, 2007)

Patrick Bateman said:


> To hit 140db with 1000 watts, you would need a woofer with an efficiency of 110DB. (1000 watts gets you 30DB more output than 1 watt.)
> 
> The JL woofer has an efficency of 84DB.
> 
> Where's the other 26DB coming from?


Magic dee bee dust. 

The fact that it's in a vehicle (cabin gain). It's the same reason a Mag v4 can pull a 135 in 1 ft^3 sealed with 1000 watts and a sensitivity of 87 dB. Spl isn't all about sensitivity. If that were the case PA subs would rule the spl lanes. 

How much power were you using when you took your measurements outside and inside a vehicle?


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## Patrick Bateman (Sep 11, 2006)

Electrodynamic said:


> Magic dee bee dust.
> 
> The fact that it's in a vehicle (cabin gain). It's the same reason a Mag v4 can pull a 135 in 1 ft^3 sealed with 1000 watts and a sensitivity of 87 dB. Spl isn't all about sensitivity. If that were the case PA subs would rule the spl lanes.
> 
> How much power were you using when you took your measurements outside and inside a vehicle?


I already knew the answer - I was curious if anyone else would point it out 

The reason that a woofer with an efficiency of 84db can hit 140db with 1000 watts is because of cabin gain *and* narrow peaky alignments. That's why all the SPL boxes are one-note wonders.

Here's the ubiquitous graph of cabin gain:








Looking at the graph, we can see that it's possible to pick up 15, even 20db at 40hz. That gets us 75% of the way to our goal of an extra 26db, but to get that last 5-10db you gotta use a narrow-bandwidth alignment.

One of the reasons I'm such a fan of the tapped horns is they're resonant over a broad range of frequencies. So you get that extra bump of efficiency like a bandpass or a vented, but you get it over a broad range. Efficiency plus smooth response is a great thing.

If you look at the inside of one of these, you can see why they're resonant over a broad range, since there are reflections at the throat, reflections at the mouth, reflections which travel from mouth to throat, vice versa, and staggered reflections from the use of multiple woofers in a single line.

All those reflections smooth out the response.

Check out this thread here, I'll be posting some in-car and outside measurements of a new three-woofer TH.

http://www.diymobileaudio.com/forum/diy-mobile-audio/65945-small-tapped-horn-car.html

As for the amount of power in those graphs, I have no idea. I don't have an SPL meter. Generally I'm designing systems to have a target response, not necessarily maximum output. When performing acoustic measurements I use fairly consistent power levels and set the preamp for maximum clean signal.

Admittedly, I should purchase an SPL meter and a microphone that's accurate at high SPL levels. For the past year I've been too busy with the Unity horns to spend much on additional subwoofer measurement tools.

Also, I hope this thread doesn't sound like a giant advertisement for tapped horns. I think sealed boxes, vented boxes, and bandpass all have their place in car audio. I *am* a bit surprised that more DIY'ers aren't doing THs tho.


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## maddogrc (Sep 20, 2009)

what a read!

cheers for that


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## Electrodynamic (Nov 27, 2007)

Patrick Bateman said:


> I already knew the answer - I was curious if anyone else would point it out
> 
> The reason that a woofer with an efficiency of 84db can hit 140db with 1000 watts is because of cabin gain *and* narrow peaky alignments. That's why all the SPL boxes are one-note wonders.


If by "narrow peaky alignments" you mean broader bandwidth alignments than the tapped horn frequency response, then I suppose you could say that. 

Were you using 1 watt, or a thousand with your in-car measurement? If you were using a similar amount of power outside of the vehicle as well as inside the vehicle, it doesn't really speak volumes for any "advantages" of horn enclosures in a vehicle since the SPL levels you posted were almost identical.


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## huckorris (Sep 2, 2009)

I like the idea of the graph but I'm having a hard time reading it. Too many colors of similar hue.


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## snaimpally (Mar 5, 2008)

Fascinating stuff!! Thanks so much for sharing.


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## Oliver (Jun 25, 2007)

huckorris said:


> I like the idea of the graph but I'm having a hard time reading it. Too many colors of similar hue.


It shows that depending on vehicle size [ Ford F-350 or Mini-Cooper ] you will experience free amplification of the lower frequencies [ from 15 dBs to 20 dBs at 40 Hz ].

If you have an equalizer it helps to smooth out the input from your subwoofer to better blend with your other speakers.

and of course >

Hoffman's Iron Law states that the efficiency of a woofer system is directly proportional to its cabinet volume and the cube of its cutoff frequency (the lowest frequency it can usefully reproduce). The obvious implication is that to reduce the cutoff frequency by a factor of two, e.g. from 40 Hz to 20 Hz, while still retaining the same system efficiency, you need to increase the enclosure volume by 23=8 times! In other words, to reproduce ever lower frequencies at the same output level you need an extremely large box!


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## huckorris (Sep 2, 2009)

a$$hole said:


> It shows that depending on vehicle size [ Ford F-350 or Mini-Cooper ] you will experience free amplification of the lower frequencies [ from 15 dBs to 20 dBs at 40 Hz ].
> 
> If you have an equalizer it helps to smooth out the input from your subwoofer to better blend with your other speakers.


No not that. I'm having a hard time following some of the lines because lines of a similar color cross it too.

What factors, other than interior volume, determine the cabin gain? I know it might not a simple and easy question.


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## Oliver (Jun 25, 2007)

volume of an enclosure determines how loud it will be 

Power is a factor too !


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## Patrick Bateman (Sep 11, 2006)

huckorris said:


> No not that. I'm having a hard time following some of the lines because lines of a similar color cross it too.
> 
> What factors, other than interior volume, determine the cabin gain? I know it might not a simple and easy question.


Cabin gain is determined by the width, depth, and height of the car's interior. If you look at the graph, you'll see the smallest vehicles (Mini Cooper) have the most gain.

At some frequencies there's a _reduction_ in SPL. I believe this is due to dimensions which are a multiple of one-half, but don't quote me on that.

Here's an example of what I'm talking about:

Let's say the cabin of your car is 51 inches wide, and 102 inches deep. And let's say you put a sub inside that cabin, in the back corner, and you play a note that's 66hz over that sub.

The moment that you play that note, in the back corner of your car, the sound will radiate towards the front of the car. When it reaches the front of the car, it will reflect, and start heading towards the back of the car again. After completing that round trip, it will have traveled 204 inches.

A 66hz sound wave is 204 inches long, so when the sound reaches the back of the car, it will be "in phase."

At the same time that the sound wave is traveling from the front to the back, it is also traveling from the back to the sides, since sound waves expand spherically. (ideally.)

So that same sound wave starts at the back corner, expands out and hits the SIDE of the cabin, which is 51 inches away.

(Remember, the interior of our car is 51 inches wide in this example.)

When that sound wave hits the side, it reflects, and starts heading back to where it started, 51 inches away.

When the sound wave gets back to the corner, it's traveled 102 inches.

102 inches is one HALF wavelength of 66hz, which means that it will be 100 hundred percent out of phase with the note that we just played. When a wave is out of phase, it creates a deep and narrow cancellation.

Now look at the graph, and what do you see around 66hz?

Yep, a big fat null.

Does that make sense? I hope that helps to explain why some subwoofer locations in a car are smooth, others are not, and how cabin gain affects all of them.

I know that a picture would help make this clearer but it's 6am on a Sunday and I'm really too lazy to draw one


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## Oliver (Jun 25, 2007)

From home theater thread>

quote:
“standing waves” are created at frequencies where the wavelength of sound or multiples of the wavelength are equal to one of the room measurements. At the main seating area, these standing wave patterns of reflected sound are added together -- in and out of phase -- "*causing variations in the frequency responses that you hear*".


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## jsun_g (Jun 12, 2008)

Patrick Bateman said:


> And the response IN the car:


Very interesting read as always.

This looks like it'd be well suited to SPL competition but not for SQ. Just like putting a monster SPL sub in a ported box and tuning it high. Put a box like this in a CRX and go to some SPL comps


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## huckorris (Sep 2, 2009)

Thanks again bateman. Well explained and layed out.

Might an SUV most resemble a minivan? I've got a 1995 Honda Odyssey.


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## Patrick Bateman (Sep 11, 2006)

huckorris said:


> Thanks again bateman. Well explained and layed out.
> 
> Might an SUV most resemble a minivan? I've got a 1995 Honda Odyssey.


Yep. The effects of cabin gain will be dominated by the following:


The length, height, and width of the cabin.
Contrary to popular belief, the choice of upholstery will have little effect. These frequencies are so long, they don't care if it's cloth or leather.
The effect of cabin gain will vary with the number of speakers playing in this pass band. This is something I'd really like to investigate further, because it has the potential to smooth the response of our speakers, by sacrificing efficiency. I need to do some measurements on this one soon.
Where you mount the sub will make a difference. For instance, if you have a sub located dead center in the rear deck, and the side of the car is 48 inches away, there will be a notch in the response created at 70hz*. On the other hand, if there are two subs and each is located 16 inches from the side wall, there will be a notch in the response at 211hz. As you can see, the use of multiple woofers will smooth the response, and if you must use a single sub, push it up against the wall of the car. Whatever you do, don't put it in the center of the trunk or the rear deck.

* The notch is created when the wave is reflected back to the cone out-of phase, which occurs at 1/4 wavelength. (speed of sound / 48 inches / 4 ) = (13500 inches per second /48/4) = 70hz


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## Patrick Bateman (Sep 11, 2006)

jsun_g said:


> Very interesting read as always.
> 
> This looks like it'd be well suited to SPL competition but not for SQ. Just like putting a monster SPL sub in a ported box and tuning it high. Put a box like this in a CRX and go to some SPL comps


The number one reaction people have to my car is that they can't figure out why I'm doing things this way. I mean, there isn't a plethora of cars out there with waveguides on the dash and horns in the trunk. So let me take a moment to explain my goals. Here they are:


soundstaging
soundstaging
and
SOUNDSTAGING

Now that I have that out of the way, let me explain why I'm using a sub with just an octave and a half of bandwidth. We gotta go back two decades though, when all this madness started. Back then, I had sealed subs in the trunk of my 1985 hatchback, and no soundstage.

Determined to figure out why the soundstage sucked, I learned that subwoofers produce a ton of distortion. As much as 25-50%! When you combine 25% distortion with our ears crappy sensitivity to low frequencies, you wind up with a situation where _the subwoofer's distortion is more audible than the fundamental._

That's a big, ugly problem. Ever met an audiophile with a tube amp and some tiny speakers? Ever wondered why people drop twenty large on Magico Minis? Yeah, it's because subwoofers S-U-C-K.








I know you guys are into sound quality, so maybe I'm preaching to the choir. If not, continue reading...

Once you realize that subwoofers are hideous devices spewing distortion and muddying up the entire presentation, you start trying to figure out ways to fix things. The most obvious is to reduce distortion in the subwoofer itself. Here's a measurement of a Dayton woofer, with a shorting ring, which reduces distortion. In this graph, we're playing a fundamental at 30hz, and you can see the distortion at 60hz, 90hz etc...








Are you guys seeing what I'm seeing?

*When playing a fundamental at 30hz, 3rd harmonic distortion is just 20db below the fundamental, at 90hz.*

Just think about that one for a second or two. When you're playing the tunes at 94db, do you WANT 74db of distortion at 90hz?

Are you starting to see why it's so easy to localize a sub? You could set your electronic crossover to 40hz, and there will still be 74db of distortion.

*You can't get rid of it electronically.*

Once you realize that there isn't a filter or a device that will reduce distortion, you start looking for ways to reduce it. Here's a few...


Aluminum or copper shorting rings reduce distortion
Underhung motors reduce distortion
Bandpass subwoofers reduce distortion via a reduction in excursion, then filter it out physically on top of that
Ditto for horns
Loudspeaker arrays reduce distortion by reducing excursion and increasing efficiency

Anyways, this is starting to sound like Patrick Bateman vs Everyone Else in Car Audio, and I don't want to come off like that. I like soundstaging. I don't care about reproducing cannon blasts or watching a DVD in my car.

Because of my interest in soundstaging, I've invested a lot of time and experimentation into reducing subwoofer distortion, to bring the soundstage to the front of the car.


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## digital (Sep 12, 2008)

Interesting read. Given that the ears are more sensitive to sound at 90Hz and 60Hz than at 30Hz, harmonics are actually more audible than what the chart is showing.

Since I built a sonotube based sub woofer for home use, sealed car sub no longer sounds good. Not as clean. I am really looking forward to building autotuba and your TH-mini to see how will horns perform. They are bit tricky, with many angled cuts, and bit larger, but they might be worth it


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## jsun_g (Jun 12, 2008)

Patrick,
I'm not at all against you, I was just reacting to the in-car FR of the sub setup. I would be looking for more of a response that extends to the 30Hz range for my listening preference.

Thanks for posting the nonlinear distortion graph...I realized subs were not very "clean", but that 3rd harmonic is bad...and that's just with the sub at 94dB. Do you by chance have any nonlinear distortion plots of your tapped horn system? Are there any subs in particular that excel in nonlinear distortion?
Why is it that as frequencies get lower, distortion goes way up? Do the manufacturers just not pay attention to this when designing subs since sub distortion is a "given" and you supposedly are not so sensitive to it as you are in the midrange?

It would be really nice to see some more measurements of nonlinear distortion for more subs out there. I'd like to see how my entry level ID subs fare.




Patrick Bateman said:


> The number one reaction people have to my car is that they can't figure out why I'm doing things this way. I mean, there isn't a plethora of cars out there with waveguides on the dash and horns in the trunk. So let me take a moment to explain my goals. Here they are:
> 
> 
> soundstaging
> ...


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## Patrick Bateman (Sep 11, 2006)

jsun_g said:


> Patrick,
> I'm not at all against you, I was just reacting to the in-car FR of the sub setup. I would be looking for more of a response that extends to the 30Hz range for my listening preference.
> 
> Thanks for posting the nonlinear distortion graph...I realized subs were not very "clean", but that 3rd harmonic is bad...and that's just with the sub at 94dB. Do you by chance have any nonlinear distortion plots of your tapped horn system? Are there any subs in particular that excel in nonlinear distortion?
> ...


Heh, yeah, I'm just trying to be careful about getting dogmatic. In my opinion, Richard Clark pushed the envelope in car audio. But then he created a lot of controversy in the community with the amplifier challenge. Just trying to be careful not to go down that road.

Last week I was trying to figure out how to do distortion measurements with Arta, but it looks like I need to buy an SPL meter first. I'll do that shortly. I have a pair of DIYMAs, so I should throw one in a sealed box and we can figure out if my theories are correct. (IE, will a sealed sub produce more distortion between 80 and 320hz than a horn?)

Anyways, if I'm not mistaken, the distortion figures for 30hz that I posted are abysmal because of excursion. It takes four times as much excursion to produce 30hz than 60hz in a sealed box.

At the impedance minimum of a bandpass, ported, tapped horn, or horn, the cone is basically NOT MOVING at all.

Hence, an enormous reduction in distortion.

To my ears, the more *audible* improvement is due to the notch above the passband. Based on some feedback from you guys, I literally built another tapped horn, and I've had it in my car for the past week. I had this theory that multiple subs would remove the notch, and I was correct. The sub has almost four octaves of output, more than double what the last one had.

So the graphs on the new one look *very* good... But I like the sound of the old one better!

The same thing happened in my home theater. I was running two bandpass subs and a tapped horn, then I added an array of five sealed subs. A total of eight subs. Even though the array had higher efficiency, at any volume level, it sounded "grungier." Once you fired up the mains, you couldn't tell, but playing by themselves, the bandpass and tapped horns were audibly cleaner.

I need to wrap my brain around what's going on here, the jury is still out, because I haven't done any in-car measurements, and the box is only 90% finished. Once I finish this stupid Java code that's been killing me all weekend, I'll post the measurements here: http://www.diymobileaudio.com/forum/diy-mobile-audio/65945-small-tapped-horn-car.html

But my hunch at the moment is that the other one sounds better *because* of the notch at 150hz, not in spite of it.


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## Patrick Bateman (Sep 11, 2006)

digital said:


> Interesting read. Given that the ears are more sensitive to sound at 90Hz and 60Hz than at 30Hz, harmonics are actually more audible than what the chart is showing.
> 
> Since I built a sonotube based sub woofer for home use, sealed car sub no longer sounds good. Not as clean. I am really looking forward to building autotuba and your TH-mini to see how will horns perform. They are bit tricky, with many angled cuts, and bit larger, but they might be worth it


Yep. Once you start seeing the distortion figures on woofers and subwoofers, you start to see that a lot of problems in the midbass are due to the subs.

If your sub generates 74db of distortion at 90hz, I wonder what that does to the midbass response? If the sub is out of phase with the mids, it seems like that could reduce midbass "punch" quite a bit, since the subs are typically fed with two to eight times as much power as the midranges.

Maybe I should start doing my measurements at 110DB or something. I know that's what Danley does - he does them at 10x as much power, from 10x as far away.


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## sundownz (Apr 13, 2007)

I really cannot agree with the importance of 1w/1m SPL ratings on subwoofers. Not for their intended applications of playing really LOW frequencies anyway.

For example... in the MECA SPL organization you must produce a high SPL without popping a certain fuse rating. So... these competitors are pretty genius about enclosure design.

YouTube - Ric's Honda MECA SPL s1

Here is 145 dB at the vehicle head-rest with two DD 1508 8" woofers using a measured power of 660 watts. Standard vented enclosure.

I just measured T/S on the woofers he used yesterday on a pair I bought and they weigh in at 78.77 dB (we can round it off to 79 for ease). For two subs this should climb to 82 dB.

82 @ 1 w
85 @ 2 w
88 @ 4 w
91 @ 8 w
94 @ 16 w
97 @ 32 w
100 @ 64 w
103 @ 128 w
106 @ 256 w
109 @ 512 w
112 @ 1024 w

Not even a one note wonder box. Just a good, simple, design... and incredible output down to a very low note.

I had a picture of the box at one point but cannot find it... it's not incredibly large either, similar in size to a sealed dual 12" sub box (2-3 cubes).

If you are more concerned with the higher bass notes, though, then the efficiency does come much more into play. Many folks on here only play their subs from 50 Hz and down, though 

---

As far as efficiency in midbass and midrange I agree with that for sure... I've been trying to tell my SPL customers that for a few years now but they all want to install a million sets of traditional speakers.

We used a pair of 10" B&C Pro-Sound drivers and a pair of Selenium Horn tweeters in a truck for a customer and I cannot stand to be on the same side of the door as those speakers... other folks roll in with 20 sets of standard speakers and pale in comparison.

---

Interesting measurements in any event !


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## DaPhenom07 (Dec 12, 2009)

Patrick Bateman, you are my hero. haha. i dont have a sub yet but do plan on getting one in the future and wouldnt mind if you would help me in making a custom box. as always i enjoy reading your articles. im a big fan


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## T3mpest (Dec 25, 2005)

This is one area where I think patrick is making things way harder than they need to be. A tapped horn isn't gaining effeciency as it should in a car since the throat is being loaded at the end so it's all high pressure as has already been pointed out. Secondly effeciency rating at 1k dont' help us alot when dealing with subs. If you want to keep that number up at lower frequencies your going to need a very big box. The bigger box forces you to often use very small subs, which is why patrick is using tiny little eights instead of twelves or fifteens. Once you do that, no matter how effecient you are, you run out of displacement. The only advantage the "effeciency" gave you was running out of displacement with very low power. If you really want high effeciency and high maximum output to go along with it, why not simply use multiple ineffecient woofers in small enclosures? Plenty of subs that will only clock in at mid eighties in effeciency, but keep that effeciency at 1 cubic feet of airspace. Add in 6db's for each pair and 30db's of cabin gain and I'm not seeing the issue. Heck, you can even port them for more effeciency and ports will actually load properly in a car, which is something a horn can't do. Also, plenty of music goes down to 30hz and with cabin gain not getting super low bass is just silly, IMO. Flat response down to 20,15, hell even 10hz if your feeling froggy shouldn't be hard unless you in a freaking school bus.

There is alot of good theory here with tapped horns, effeciency, etc, but in fitting the theory to it's application (ie a car), isn't working in this case. Subs are already the most effecient drivers in the system for most of their bandwidth once we take cabin gain into account. If you want even more, or want to maximize output above say 30hz where most music is, port them and get some acoustical loading going on that actually works and then dial back what you dont' need or want with EQ. If that's too hard sealed alignments come out pretty flat with cabin gain taken into account so simply fit several woofers in smaller sealed boxes. Either way I think it's the same or better result for less work.


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## rexxxlo (Apr 14, 2009)

sorry to dig up all these old posts but Patrick's stuff has been on my list to sit down and read for a few months now when i had time to respond.

id really like to build a TH for my car but from what i understand a traditional car audio woofer wont work well i a TH 

what are the specs that are desirable for good performance in a th?

also kind of off topic 

would a horn or a TH work well if the doors and windows were to stay open, say for instance at a large show where the car might sit and be demoed for long periods of time?

i have a crx with a large ported box and output is ridiculous even to very low frequency, i can put literally thousands of watts into it and not break anything or have the sub bottom out, the whole car is flexing and rattling like crazy the air coming out of the windows is tremendous......but if i open the hatch to show someone whats in there it falls on its face and the woofers unload and they make all kinds of stress noises

i know not to many people here are into the spl competition but the crx is a highly coveted car and i havent been able to get a good answer why, some think its just that it fits in the rules well and has lots of room with no back seats, some think that its the shape of the hatch acting like a horn.
most of these cars the port is firing towards the rear of the car, with these cars having the super peaky box designs that use the resonance of the port to produce most of the output and a port firing to the rear does the port use the cars hatch as a horn?

how much does the shape of the car play into the cabin gian graphs?
for instance the same year honda civic hatch back is almost identical except the hatch is square and not sloped.




















and this picture is what the back of one of these cars looks like










obviously not going to sound good but is the enclosure technically inside of the horn mouth? 

i have read in other threads about the TH and horns in general that its not as crucial where the driver is placed it still helps to have it in the flare somewhat like the unity horn

sorry for the rant but thats years of questions all being asked at once.

hope this gets some serious answers


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## Patrick Bateman (Sep 11, 2006)

T3mpest said:


> This is one area where I think patrick is making things way harder than they need to be. A tapped horn isn't gaining effeciency as it should in a car since the throat is being loaded at the end so it's all high pressure as has already been pointed out.


When Lord Baccus blew up his sub, I literally invested an entire afternoon doing measurements of sealed subs and tapped horns in-car _and_ out. It was a LOT of work to do all the measurements, but I really wanted to find out once and for all:

Does cabin gain work on horns?

There have been a number of people who say *no*, that cabin gain works differently because of how a horn operates.

I wish I could post a five page thread with the results - I really *did* do the measurements, they're sitting on my laptop right now. Unfortunately, I got distracted with work, and I haven't had an opportunity to post them in any cohesive way. I started to do the work in a thread called "tapped horns - simulation and reaility" over on diyaudio.

Anyways, here's what I found when I pitted tapped horns against sealed boxes in-car and out:


Cabin gain works on sealed boxes, and it works on tapped horns.
Tapped horns have a HUGE efficiency advantage in their passband. In my measurements I pitted three eights in a tapped horn against a Diyma12 in a sealed box. The Triple8 had an advantage of about 12dB IIRC. In other words, you'd need 2000 watts with a Diyma12 to get you where a Triple8 will go with 125 watts.
Because the basket of the woofer is exposed in a tapped horn, mechanical noises are more audible. So you have to be cautious about what woofer you use - you're going to hear things that you wouldn't hear in a sealed or a bandpass design.
The measured impedance of a tapped horn is higher than what you would see with a sealed box, but it's not as high as what you'd see with a front-loaded horn. In other words, a "real" front-loaded horn is going to raise your impedance further, and that effect can be a real life-saver when it comes to extending the longevity of your woofer.
Without a doubt, the biggest danger in a tapped horn is overexcursion. In my measurements, I found that the gain of the tapped horn "drops off a cliff" below the tuning frequency. Below this point, the woofer is *very* exposed to detonation. So if you want very deep bass with a tapped horn, you should consider using a pathlength that will get you down to 25hz, or even lower. The Triple8 is tuned to about 30hz IIRC.

Based on these results, some would assume that I'm biased towards tapped horns. To tell the truth, yes, I am. While you CAN get the same output from a sealed box, you're going to need an array of them. For instance, the Diyma12 in a sealed box CAN match the Triple8, but you're going to need a few of them. In addition, you'll need some big amps, and you'll likely need to upgrade your electrical system. To those who say the tapped horn is too much work, I'd say that finding space and power for ten thousand watts of amplification is a lot of work too.

Now the tapped horn ISN'T a magic bullet - if you want bone crushing output from 15-30hz, I'd use a sealed box. A tapped horn can do the job down low, but it's going to by hyooooge. Personally, I'm biased towards huge output from 30-60hz. Heck, you could do both really. Use a TH for 30-60hz, and a sealed sub for 15-30hz. Your ultra low-frequency output will be limited, but it will be there. In a tapped horn, output is basicaly AWOL below the lowest tuning frequency.

Anyways, this is a bit of a "brain dump." I'm about to head out for NYE, and thought I'd post some thoughts on the Sealed VS Tapped Horn debate. There are a handful of measurements scattered around the Natural Bass thread, and the "Simulation vs Reality" thread. HTH.

PB


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## Brian Steele (Jun 1, 2007)

Patrick Bateman said:


> (snip)
> 
> Does cabin gain work on horns?
> 
> ...



I responded to this last night, but it seems my response disappeared (or perhaps I hit the "Preview" button instead, LOL).

THs are not "true" horns per se, as the mouth size is nowhere near the design requirements for a typical horn, so I don't think that comparing in-car FR measurements of a TH against those of another alignment really "proves" that cabin gain is the same for horns as it is for those other alignments. 

Did you repeat that test using something like the Autotuba?


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## thehatedguy (May 4, 2007)

That;s not a horn.



lordbaccus said:


> my horn does a 151.6db
> 1x 18" / 2x Saz3000d Sundown Audio ( strapped )
> box peeks @ 48Hz


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## thehatedguy (May 4, 2007)

T3mpest said:


> This is one area where I think patrick is making things way harder than they need to be. A tapped horn isn't gaining effeciency as it should in a car since the throat is being loaded at the end so it's all high pressure as has already been pointed out. Secondly effeciency rating at 1k dont' help us alot when dealing with subs. If you want to keep that number up at lower frequencies your going to need a very big box. The bigger box forces you to often use very small subs, which is why patrick is using tiny little eights instead of twelves or fifteens. Once you do that, no matter how effecient you are, you run out of displacement. The only advantage the "effeciency" gave you was running out of displacement with very low power. If you really want high effeciency and high maximum output to go along with it, why not simply use multiple ineffecient woofers in small enclosures? Plenty of subs that will only clock in at mid eighties in effeciency, but keep that effeciency at 1 cubic feet of airspace. Add in 6db's for each pair and 30db's of cabin gain and I'm not seeing the issue. Heck, you can even port them for more effeciency and ports will actually load properly in a car, which is something a horn can't do. Also, plenty of music goes down to 30hz and with cabin gain not getting super low bass is just silly, IMO. Flat response down to 20,15, hell even 10hz if your feeling froggy shouldn't be hard unless you in a freaking school bus.
> 
> There is alot of good theory here with tapped horns, effeciency, etc, but in fitting the theory to it's application (ie a car), isn't working in this case. Subs are already the most effecient drivers in the system for most of their bandwidth once we take cabin gain into account. If you want even more, or want to maximize output above say 30hz where most music is, port them and get some acoustical loading going on that actually works and then dial back what you dont' need or want with EQ. If that's too hard sealed alignments come out pretty flat with cabin gain taken into account so simply fit several woofers in smaller sealed boxes. Either way I think it's the same or better result for less work.


x1000billion


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## SSSnake (Mar 8, 2007)

> Quote:
> Originally Posted by T3mpest
> This is one area where I think patrick is making things way harder than they need to be. A tapped horn isn't gaining effeciency as it should in a car since the throat is being loaded at the end so it's all high pressure as has already been pointed out. Secondly effeciency rating at 1k dont' help us alot when dealing with subs. If you want to keep that number up at lower frequencies your going to need a very big box. The bigger box forces you to often use very small subs, which is why patrick is using tiny little eights instead of twelves or fifteens. Once you do that, no matter how effecient you are, you run out of displacement. The only advantage the "effeciency" gave you was running out of displacement with very low power. If you really want high effeciency and high maximum output to go along with it, why not simply use multiple ineffecient woofers in small enclosures? Plenty of subs that will only clock in at mid eighties in effeciency, but keep that effeciency at 1 cubic feet of airspace. Add in 6db's for each pair and 30db's of cabin gain and I'm not seeing the issue. Heck, you can even port them for more effeciency and ports will actually load properly in a car, which is something a horn can't do. Also, plenty of music goes down to 30hz and with cabin gain not getting super low bass is just silly, IMO. Flat response down to 20,15, hell even 10hz if your feeling froggy shouldn't be hard unless you in a freaking school bus.
> 
> ...


x10^(12+1)


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## Patrick Bateman (Sep 11, 2006)

lordbaccus said:


> *do you have plans for an Autotuba ?
> if so PM me please*


It's a lousy ten bucks 

Bill Fitzmaurice's products are a steal

Also, on the subject of piracy, I'm a software developer. So these crazy speaker projects are basically enabled by people actually *paying* for intellectual property.


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## chad (Jun 30, 2005)

thehatedguy said:


> That;s not a horn.


SHEEEEET you beat me to it this time, I'm slacking!


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## chad (Jun 30, 2005)

lordbaccus said:


> what would you classify it as?


Flared vent, it's not horn loading or even guiding a wave at the freq you are using it at.


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## Patrick Bateman (Sep 11, 2006)

chad said:


> Flared vent, it's not horn loading or even guiding a wave at the freq you are using it at.


The dimensions of a "real" horn get completely absurd at low frequencies. So *all* of these exotic box types are variations on a vented box. That's the whole reason we can't apply horn theory -they're not horns.

Here's an illustration of what I mean by this:







A couple of years ago I built a tapped horn that didn't have a flare. You can see it sitting in the corner of this pic. It's eight feet tall. This design was a real disappointment - it just didn't get very loud. Considering how huge it is, I'd expected a lot more output.

Basically, the design was a disappointment, but it was a learning experience. I learned that inefficient ports "choke" the SPL in a subwoofer. Ideally you want a really big port, but you can "cheat" by going crazy with the flare. Ideally both ends should be flared, but the flare at the mouth is more important than the flare at the throat.







Now here's another box, but with a smaller footprint. Note that the mouth has a HUMONGOUS flare. To get a mouth this big in a vented box, you'd have to use a SIXTEEN INCH port.

The point that I'm trying to make here is that 90% of the simulations assume that a port is perfect. And they're not; even a moderately sized port suffers from a reduction in efficiency. At the same time, these tiny horns don't behave like horns; they behave like transmission lines.

The exotic box types that I'm publishing, and that PWK is selling, are actually clever ways to integrate super-efficient ports. THAT'S how we're getting these huge efficiency bumps. Could I get the same output from a vented box? Possibly, but then I'd need a port that's the length of the car. Sixteen inch ports take up a lot of room.


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