# How to Get Louder With The Same Amp



## Patrick Bateman

Recently someone emailed me, and asked how to get the most SPL out of their existing amplifier. Basically they were in a situation where they already had an amp, and already had a woofer, and wanted to GET LOUDER.

I've dealt with this for a loooooooooooong time, so I thought I'd post some thoughts on how to do it. About twenty years ago I had a Ford Escort, a pair of MTX Blue Thunder tens, and a Hafler amp. The Hafler was something like 40watts, but it could handle nearly any impedance I could throw at it. So I learned a few tricks on how to make it GET LOUD.

So here goes:











My favorite method is to use an enclosure that is more efficient. I like tapped horns - I've been able to squeeze as much as 10dB more out of a driver using a tapped horn. That's like going from a 500 watt amp to a FIVE THOUSAND watt amp. I've published hundreds of posts on tapped horns, and there are three or four finished plans that I've posted, along with dozens from others. The drawback with tapped horns is that the box size can get kinda nutty. For instance, a Diyma 12 will work in a 1 cubic foot sealed box, but my dual Diyma 12 tapped horn is about 30 cubic feet!!!

So, admittedly, building a tapped horn might not be the best solution if you want to run a couple of twelves in the car  (I'm using dual eights in a tapped horn in my car, check out this thread: http://www.diymobileaudio.com/forum...65945-small-tapped-horn-car-2.html#post839067 )

If a tapped horn isn't practical, consider using a transmission line or a ported box. Also, *the efficiency of a ported box or transmission line is dependent on the efficiency of the port.* I can't stress this highly enough. You can get a HUGE bump in the efficiency of your boxes if you use more efficient ports. If you're using a three inch port, consider a six inch port. Or even an eight inch port! And don't even consider using a port if you're not going to flare it. Little things like this make a dramatic difference in the efficiency of a design, particularly at high power.

There aren't a lot of programs that can model this. The only free one that I am aware of is hornresp. Akabak can do it too - I believe it's free if not used for commercial use. Check the license.

To model the efficiency of a port in the aforementioned programs, you have to model the port as if it's a transmission line or a horn. If anyone's curious on how to do that, let me know. I can post some screen caps.

The second way to get more SPL out of your amp is to brace the heck out of your subs. If the side panel of your sub box is flexing even a fraction of a millimeter, that can reduce your SPL by a few dB. The panels in your subwoofer basically act like huge passive radiators, radiating out-of-phase with your woofer, sapping output from the system. The same can be said for the panels of the car itself. But it's a lot easier to install a brace in your sub box than it is to install a brace in your car 

Anyways, if you like your existing sub, but want to make it louder, feel the panels while running it at high power. *If the panels are flexing, a brace is going to make the box more efficient.*


Another thing that you can do to get more output from your amplifier is to tweak the impedance curve of the woofer.
















For instance, here's the impedance curve of an 8ohm woofer from Morel. Below 70hz, the impedance never dips below 10ohms. In fact, if you used this woofer over a single octave, from 20 to 40hz, the impedance doesn't dip below TWENTY ohms!

Does that make sense?

For instance, lets say you have an amplifier that puts out 500 watts into 8ohms. Based on the spec sheet, you buy two of the Morels, and you wire them in parallel. That's fine - nothing is going to blow up if you do that.

But let's get adventurous, and use a 70hz lowpass. Now those Morels aren't dipping below 10ohms in our our passband. So we can add a third. That means the impedance at 70hz is going to be 3.3ohms, and rising to a peak of 9ohms at 40hz. Thats going to get us a couple of dB more output, _with the exact same amp._

Now if we really want to get wacky, we could use a 40hz lowpass, and FIVE of the Morels. At 40hz we're going to have an impedance of 4ohms with five woofers. *Even though the spec sheets would have you believe that's a load of 1.6 ohms.*

Loading up on woofers like this can be tricky, because the amp is still going to "see" that the resistance of the circuit is very low. For instance, the electronic crossover in the amp is going to protect the amp from overheating by reducing the voltage delivered to the woofer at 100hz. But the amp still "sees" that the resistance is low, and the protection circuitry may kick in based on that. I don't know enough about amplifiers to be certain of this - if people familiar with protection circuitry can chime in, that would be great.

One way to circumvent the protection circuitry is to use a simple 1st order butterworth filter, AND the electronic crossover. Does that make sense? So the passive crossover is offsetting the impedance dip at 120hz, but the electronic crossover is providing the lion's share of the filtering duty. Now one might opt for a 2nd or 3rd order passive crossover, but that won't work. That's because 2nd and 3rd order networks have a capacitor connecting the positive and negative paths, and that capacitor will lower our impedance. And we want to RAISE the impedance, to "fool" the protection circuitry in the amplifier into thinking that our 8ohm woofer is actually a 10ohm, or even a 20ohm woofer!

Whew! I hope this makes sense. Massaging the impedance curve is a delicate art, but it's also one of the easiest ways to squeeze two or three Db more out of a design. And that's like going from a 10" woofer to a 12" woofer, but in the same footprint.

If you've ever been cranking your music really loud, and then *pow*, the amplifier protection circuit kicked in, chances are good that there was a big bass hit that happened to be at the impedance minimum of your enclosure. In the pic above, that would be 150hz.

The last "tweak" to getting every last decibel out of your setup, is a variation on the one above. In the one above, we're using filters to limit the bandwidth of our amp so that it never "sees" the part of the impedance curve that will make it burst into flames.















Here's a comparison of a perfectly sealed box, and a leaky one. Basically, a leaky sealed box has an impedance curve that's flatter than a perfectly sealed box. Leaks are the kiss of death for a ported box, a transmission line, or a tapped horn. They ruin the alignment. But in a sealed box, a leak can help us tweak the impedance. (Pics stolen from Aperiodic Speaker Enclosure Design )















USD Audio is the only company I am aware of that sells them. The pics above are from their site. That's the Grand National that they built. The Holdaways are great guys, and I'd heartily recommend hiring them if you want a shop that has expertise in this department. AP mats haven't been popular in years. I'm not sure why; if you know what you're doing, an aperiodic membrane can be used to get the last one or two dB out of a sealed box.

The way that this works is that the membrane flattens out the impedance curve. For instance, at 20hz your impedance may go from 8ohms to 12ohms. And *that* gives you an opportunity to dump more power into your woofer, without smoking the voice coil, and without running the risk of your amplifier bursting into flames.

OK, now for the warnings:


Don't even THINK about trying any of these tricks if you don't have a woofer tester. ( Dayton WT3 Woofer Tester | Parts-Express.com ) If you just start adding woofers, in the hope that it's going to work, YOU'RE GOING TO BLOW UP YOUR AMP. I guarantee it. You MUST KNOW THE IMPEDANCE CURVE. It's the only way you can do this effectively. The WT3 is a lousy $100, and that's a lot cheaper than a new amp.
Put your amp somewhere that it's going to stay cool. We're going to push it to it's limits, and we're trying to trick the protection circuits into ignoring a goofy load. It's going to get hot, so do everything you can to keep it cool. Consider buying some fans.
It's possible you might smoke some voice coils. I'm using the MCM 55-2421 in my car. It's $30. I'm not going to lose any sleep if I blow one up. I've built an access panel in my subwoofer, so that it's easy to replace a blown woofer.


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## Damaged1

HOLY CRAP what a box!!! 

Dude, you are my new hero...going to have to have a talk with you about my next box for my TC's!


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## bumpinP

Hey PB,

You just convinced me to flare my port. Have you ever flared a slot port? My thoughts is have it extend out of the the box, with a growing surface area. 

Any recommendations for how much to flare the port? Also should I flare both ends of the port? Will that have any effect on how I should calculate the slot correction?


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## oslouie

That, my friend, is too much of a box for me.


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## Patrick Bateman

bumpinP said:


> Hey PB,
> 
> You just convinced me to flare my port. Have you ever flared a slot port? My thoughts is have it extend out of the the box, with a growing surface area.
> 
> Any recommendations for how much to flare the port? Also should I flare both ends of the port? Will that have any effect on how I should calculate the slot correction?


Basically a port with a flare has less resistance than one without a flare. So lets say you have a 12" woofer and a 3" port. The port's are is a small fraction of the woofer's area. So at low SPLs, it works the way it's supposed to, but as you increase the volume, the tuning frequency begins to shift, and the output from the port begins to lag the output from the cone.

You might say that at low volumes, it acts like a ported box, but at high volumes, the resistance of the air makes the box act like a leaky sealed box.

For a slot loaded port, something like this would work pretty well:









Flares for Slot Ports

As far as flaring the inside of the port, yes, that improves things too.

The thing that's a bummer about flaring ports is that you really need a woofer tester to check the tuning frequency.


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## silentbass

really informative!!! thnx alot...gives me ideas for the future


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## The Baron Groog

I'd assume this has been covered many times on here but using search i can't find "The Big 3" so I'll post it anyway:

Replace the standard power and earth cable to and from alternator/battery and chassis. Most car manufacturers get away with what they can, replace these cables with 2g or 0g (depending on power req) and you have just improved your car's electrical efficiency, resulting in more watts available to your amp.


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## 94VG30DE

I was just going to say "turn up the gain", but since you went so much more in depth...  

So when you say you can feel the box "flex" (in reference to bracing), that essentially feels like a large vibration right? Because I guarantee I can't see or feel a single flex that quickly. I assumed all boxes vibrated.


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## Hispls

Bump for great justice. Found this thread from a google search and IMO it's well worth ressurecting for people to read.


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## ChaunB3400

the flared slot is a neat idea


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## Patrick Bateman

Hispls said:


> Bump for great justice. Found this thread from a google search and IMO it's well worth ressurecting for people to read.


Thanks! And a big plug for the Dayton woofer tester. Probably the easiest way to squeeze every last bit of efficiency out of any of the exotic alignments. (ported, tapped horn, aperiodic, single reflex bandpass, horn loaded, dual reflex bandpass, transmission line, etc)


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## Sine Swept

To OP - what is your highest achieved SPL ??

What size drivers? and how much power?


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## Calum

oslouie said:


> That, my friend, is too much of a box for me.


X16 bazillion.


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## Patrick Bateman

Sine Swept said:


> To OP - what is your highest achieved SPL ??
> 
> What size drivers? and how much power?


No idea.

I simply received an email from someone that was curious on how to raise their SPL, while using the amp/speakers that they had already.

If that's your goal, I'd manipulate two things to raise SPL:

*#1 - play around with the sub location in the car*
This is a no-brainer; people have been playing around with firing the woofer forward or backwards for decades.

But the thing is, *these wavelengths are extremely long*. For instance, 40hz is 28 feet long! So simply flipping the box around isn't enough. (It might *sound* louder, but that's mostly because we can't hear 40hz very well.)

To really get the most bang for the buck, you have to look at the dimensions of the car and how they relate to the sound wave. For instance, if you're trying to maximize SPL at 40hz, *you'd generally want to get the woofer about zero to seven feet away from all boundaries.* This will generally mean that you want the woofer in the center of the car, not the trunk.

Also, this isn't a subtle difference; it can be as much as six dB. So if you're trying to maximize SPL, a small box in the center of the car may outperform a big box in the trunk.


*#2 - manipulate the impedance curve.*
There are a ton of things you can do to manipulate the impedance curve. *And if you severely band-limit the enclosure, you can dump a lot more power into it.*










This box is a good example of this. It has three impedance peaks. If you band limit it severely, you'll likely find that it's overall impedance is higher than a sealed or ported box. Which means you can dump more power into it without blowing up your amp.





I concede that my credentials may seem to be lacking, since I don't actually *compete* in SPL. I just threw this thread up based on a request I received by email. Most of my projects tend to 'attack' these car audio problems from a weird angle. Plus, I steal a lot of my ideas from the prosound arena, where they've been tackling SPL challenges for decades.


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