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How to select an amplifier

DIY subwoofer amplifier guide.

Amplifiers produce power according to how they are designed. As they are measured in watts, it is important to know what a watt consists of.​

Watts = Volts (push, electromotive force, electrical force, etc.) x Amperes (current)​

W = V x I​


As you can get a total product (multiplication) from various numbers and combinations of numbers, so Watts can/may have multiple combination possibilities of types of power to arrive at that Watt number. It depends on how the amplifier is rated and what its design is. Add to this the amp can produce these components of Watts differently at different frequencies and output levels, based on the speaker load it is serving.

Ambiguous? You bet. ​

Confusing? Also, you bet. ​

How do you overcome a vague rating and "know for sure"? By testing. Our drivers are tough, start off low and slow and work your way up until you hear distress. Observe your amp power, if it is limiting at the same time there is distress sounds coming from the driver, then there is a good chance it it the amp that is limiting first. Protect your amp. 

If the amp is producing less than 100% power and there is distress sounds coming from the driver, then the driver is telling you to back off. 

The question is, what kind of power does the amplifier produce better, and what kind of power does the driver like?​

Our drivers like volts. So if you are able to get an amp that favors volts, get it. Amps that produce volts better and with more consistency/authority (again, not definitive, rule of thumb), may be more expensive, again depending on how it is made. This rule is a sliding scale, so there are grades/levels of "amplifier goodness".​

Does this mean that all inexpensive amps are junk? No, not in the slightest. It means that they will reveal their limitations sooner (applied voltage to the driver), and that means that there is the possibility that you might want to upgrade the amp at some point. ​

The good news is that you can always sell pro audio gear, it is never really a market that dies off due to it's diversity of applications. On the other hand, offloading a class AB will narrow your reach a bit.​

Watts to ohms ratings don't matter when working with an LDLC driver. I know someone is going to yell "blasphemy" and attempt to crucify me. But just read this part with an open mind. ​

Given that we know that an amplifier produces both volts and amperes, what we are actually looking for is voltage drop from one load to another, typically 4 to 8 ohm nominal. If the amplifier only produces (as a for instance) 5 volts drop when switching loads, then the appreciable difference in output between a 4 ohm load and 8 ohm load will be nil.​


Amp Class Guide​

Here is where Ohms comes in.

  • Ohms provide resistance and push back on the power coming from the amplified side of the amplifier. This affects how much and how fast the amplifier needs to work to make up power. Lower resistance (load, ohms) = faster power production.

  • Class D pro audio amps are designed to produce volts more easily and are generally optimized for 8 ohm speakers (loads). Our suggestion is to contact the amp manufacturer customer support and ask them what driver load the amp is optimized for. Relay that information to us and we will wire the driver for that amp based on that information. If the manufacturer is not willing to play ball or if their published specs don't give us enough information, the best we can do is default to what experience we have, and that is an 8 ohm driver for pro audio class D is generally a safe bet, but there are exceptions to the rule.

  • Class AB, get the biggest one you can get, send us the spec sheet, and we'll wire the sub for that amp.

Power Guide​

Our power ratings are done on Harbottle amps - high voltage capable of over 300 V p-p (peak to peak sinusoidal AC voltage), as per Data-Bass test results. 
All ratings are RMS and listed on the product page. If you want to conduct more in depth study of the M Series unit, simulate the parameters provided. 

A word on limiters.
You can run a limiter to protect a device from clipping. This can either be the amp itself if it does not have clipping protection built in, or the driver. So the limiter can protect the weakest link.
If you run a low power signal to amp clipping without a limiter in place and the driver can be safe because the effective temp rise of the coil will still be within the thermal limits. So 1000 watts clipped hard will be ok for the driver. But will it be ok for the amp? That's a question that needs to be sorted out on a per instance basis.
Now to get the most out of the driver with an amp at the maximum power rating of the driver, you will need limiters to prevent clipping the driver, otherwise the thermal limit of the driver can be exceeded and then you get the Back to the Future guitar situation in one form or another.


The Amplifier User Guide​

Customers are using the following amps in no particular order and they are all pleased with their system results. Let your budget and desire be your guide. This is not a list of recommended amplifiers. This is a list of amps used by customers only. 

  • Ram Audio

  • Crown

  • QSC

  • Sinbosen

  • Behringer

  • Powersoft

  • Lab Gruppen

  • Dynacord

  • Speakerpower

  • Emotiva

  • CVR

  • D-Sonic

  • VTV

  • Harbottle


Targets to shoot for

  1. Output voltage: 140 to 300 V peak to peak.

  2. If you can run 240V mains power, do it.

  3. If you only have 120V mains and 15 amp circuit, that's ok, just go for a more voltage based amp.

  4. All Harbottle subs will hit 5 Hz with authority... the amp needs to be stable down deep. Below low teens Hz can stress an amp, up distortion, and throw it into DC protect mode. Bass is hard to make. If you are running it hard and the content is there, our drivers will produce it. The question of your room reinforcing it is another discussion about physics. I can't change the laws of physics. 

  5. Reference the Funk 18.0 test results on data-bass (all of them) as a check for what is what. You will see a direct comparison between Pascal and Powersoft amps between those tests. The driver, cab, the builder, all of it is exactly the same except for the amp, and the differences is results are not exactly small. 


So why doesn't Harbottle pick an amp that will work and just tell me what to buy?

The short answer is that I didn't build it, so I know as much as the customer on what amps will work and what won't. I only know what I use, and I only use my own amps. 

The long answer is that there is a lot more to an amp than just a wattage rating. Matching an amp to a passive speaker is a complicated job, and the more you know about the amp itself, the more success you will have. If you go off of wattage alone, you will have to test and set up your amp to work with your speaker safely. If you are not confident in this process, then you will have to accept the risks that come with DIY.


If you are not experienced in extreme subwoofers and DIY subwoofers, there is a chance that damage may occur to the driver or the amplifier. Harbottle is not responsible for any damage that may occur in the testing, implementation, or use of a Harbottle DIY product.

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