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There has been alot of discussion relating to subwoofer design and building the past couple of weeks. Seeing as its been a while since I posted a speaker build, and I am doing final planning on my own subwoofer build in any event I thought I would share some of the design considerations and theory with everyone. I am not by any means stating that my way is the only or best way to do things. That being said - there are good reasons for most of the design choices I make, and I will do my best to explain these as this thread develops. Please feel free to ask questions along the way - it gives the final content much more depth & hopefully some people will learn things from it.
This is intended to be an informative thread rather than a "who has the best subwoofer" / bragging rights build, so let's try and keep it along those lines.
I will be using my own subwoofer build as the "model" here, so let's start out with what I will be working with:
Driver is a high efficiency 18Sound unit, the 18LW800. Data sheet: http://www.eighteensound.com/renderPdf.aspx?prj=true&pid=30.
The cost of this driver is around R4k.
Amplifier is a class D plate amplifier from Hypex, the AS2.100 More info and ordering from the Hypex online store: https://www.hypexshop.com/
The cost of this amplifier is 193 Euro excluding shipping, etc.
Right at the start, it helps to take stock of your situation. Here are some of the things I need to take into consideration for this build:
I find this to be a very important step in any build - subwoofer or otherwise. Get your mind straight from the start and everything else falls into place much easier!
What makes this build interesting / different?
1. High efficiency driver - I have measured mine at 98.24dB, 1W, 1m, half space.
2. Low powered amplifier - 100W per channel (2 channels). Bridged more gives 140W into 8 ohms.
What are the specific challenges for this build?
3. It's difficult getting really deep and solid bass out of high efficiency drivers - even when using 18 inch drivers as I am doing here.
4. Being HE, the cabinet will be on the larger side of large. Then again, this is an 18" driver so what are you expecting?
5. Large cabinets create interesting challenges relating to the structural integrity of the enclosure.
What are my specific requirements for this build?
6. Reasonable bass extention
7. Moderate cabinet size - it will be large, but try not to make it overly insane.
8. Low power compression - I want the driver to convert as much amplifier power into bass as possible. Power compression is the enemy.
9. Excellent integration with my main stereo speakers.
10. Low coloration - clean bass which is able to portray detail in the source material
11. SPL levels high enough to satisfy the bass requirements in my small to medium sized listening area (open plan).
12. Must work well for both music and HT. First priority is music.
Right, so now that's out of the way let's see what the points above mean for the build
1. High efficiency drivers are excellent at many things. The price to pay is low excursion (xmax), and usually low Qts. The low Qts translates to very little output gain near the resonating frequency (Fs) of the driver, so it will most likely start to roll off much earlier than expected for such a large driver. This may be beneficial in certain situations - together with room gain, it may provide a good low order rolloff which in turn will cause it to integrate easier with the main speakers for music listening. Bad side is that it will most probably lack the massive heaving bass very low down required for HT use.
2. Low powered amp isn't much of a problem here as we are working with an extremely sensitive driver. The specific amp I am using has built in DSP functionality via software on your PC. The 140Watt bridged mode power available from this amplifier will relate to just over 21dB worth of gain. Add this to a driver efficiency of 98.24dB, and we achieve a theoretical half-space SPL level of 119.24dB which is pretty decent.
For argument's sake, let's compare this to a more standard subwoofer driver with a rated efficiency of 91dB being powered by a 500W amplifier. 500W relates to around 27dB worth of gain. Add this to the driver efficiency of 91dB, and we achieve a theoretical half-space SPL level of 118dB.
As you can see, things are stacking up rather well even when the amplifier power doesn't seem and feel like it will be enough.
3 & 4. As discussed in point 1. The DSP function available on my amplifier will help sort this out.
5. The larger the cabinet walls become, the more difficult it is to ensure they are strong and rigid enough. Will need to employ some rather serious bracing techniques here.
6. The DSP function available on my amplifier will make my life easier here.
7. Simulating different designs and implementations will help a tremendous amount and help me focus my efforts.
8. High efficiency drivers by default have much lower power compression than standard drivers, so this one is sorted simply by choosing the correct driver.
9. Rolloff frequency and alignment, highpass filter frequency and alignment as well as cabinet Q will make all the difference. Simulations will help, but to do this right there is an amount of tweaking which will need to be done after the build is done.
10. The combination of the driver choice, and cabinet design will dictate this one. Again, simulations will be key, but tweaking after the fact will make it perfect.
11. If I can achieve peaks of 108dB, then I will be satisfied. From the "quick and dirty" calculations in point 1 this should be easily achieved as I have enough efficiency and power on tap.
12. There are some "tricks" to make a sub better for HT vs music. I will always lean slightly toward the music side, but ultimately there needs to be a good balance. Cabinet design, alignment and rolloff frequencies as well as DSP will help achieve this goal.
Next section - simulations and cabinet considerations
Ok, enough for now - more tomorrow!
Ian.
There has been alot of discussion relating to subwoofer design and building the past couple of weeks. Seeing as its been a while since I posted a speaker build, and I am doing final planning on my own subwoofer build in any event I thought I would share some of the design considerations and theory with everyone. I am not by any means stating that my way is the only or best way to do things. That being said - there are good reasons for most of the design choices I make, and I will do my best to explain these as this thread develops. Please feel free to ask questions along the way - it gives the final content much more depth & hopefully some people will learn things from it.
This is intended to be an informative thread rather than a "who has the best subwoofer" / bragging rights build, so let's try and keep it along those lines.
I will be using my own subwoofer build as the "model" here, so let's start out with what I will be working with:
Driver is a high efficiency 18Sound unit, the 18LW800. Data sheet: http://www.eighteensound.com/renderPdf.aspx?prj=true&pid=30.
The cost of this driver is around R4k.
Amplifier is a class D plate amplifier from Hypex, the AS2.100 More info and ordering from the Hypex online store: https://www.hypexshop.com/
The cost of this amplifier is 193 Euro excluding shipping, etc.
Right at the start, it helps to take stock of your situation. Here are some of the things I need to take into consideration for this build:
I find this to be a very important step in any build - subwoofer or otherwise. Get your mind straight from the start and everything else falls into place much easier!
What makes this build interesting / different?
1. High efficiency driver - I have measured mine at 98.24dB, 1W, 1m, half space.
2. Low powered amplifier - 100W per channel (2 channels). Bridged more gives 140W into 8 ohms.
What are the specific challenges for this build?
3. It's difficult getting really deep and solid bass out of high efficiency drivers - even when using 18 inch drivers as I am doing here.
4. Being HE, the cabinet will be on the larger side of large. Then again, this is an 18" driver so what are you expecting?
5. Large cabinets create interesting challenges relating to the structural integrity of the enclosure.
What are my specific requirements for this build?
6. Reasonable bass extention
7. Moderate cabinet size - it will be large, but try not to make it overly insane.
8. Low power compression - I want the driver to convert as much amplifier power into bass as possible. Power compression is the enemy.
9. Excellent integration with my main stereo speakers.
10. Low coloration - clean bass which is able to portray detail in the source material
11. SPL levels high enough to satisfy the bass requirements in my small to medium sized listening area (open plan).
12. Must work well for both music and HT. First priority is music.
Right, so now that's out of the way let's see what the points above mean for the build
1. High efficiency drivers are excellent at many things. The price to pay is low excursion (xmax), and usually low Qts. The low Qts translates to very little output gain near the resonating frequency (Fs) of the driver, so it will most likely start to roll off much earlier than expected for such a large driver. This may be beneficial in certain situations - together with room gain, it may provide a good low order rolloff which in turn will cause it to integrate easier with the main speakers for music listening. Bad side is that it will most probably lack the massive heaving bass very low down required for HT use.
2. Low powered amp isn't much of a problem here as we are working with an extremely sensitive driver. The specific amp I am using has built in DSP functionality via software on your PC. The 140Watt bridged mode power available from this amplifier will relate to just over 21dB worth of gain. Add this to a driver efficiency of 98.24dB, and we achieve a theoretical half-space SPL level of 119.24dB which is pretty decent.
For argument's sake, let's compare this to a more standard subwoofer driver with a rated efficiency of 91dB being powered by a 500W amplifier. 500W relates to around 27dB worth of gain. Add this to the driver efficiency of 91dB, and we achieve a theoretical half-space SPL level of 118dB.
As you can see, things are stacking up rather well even when the amplifier power doesn't seem and feel like it will be enough.
3 & 4. As discussed in point 1. The DSP function available on my amplifier will help sort this out.
5. The larger the cabinet walls become, the more difficult it is to ensure they are strong and rigid enough. Will need to employ some rather serious bracing techniques here.
6. The DSP function available on my amplifier will make my life easier here.
7. Simulating different designs and implementations will help a tremendous amount and help me focus my efforts.
8. High efficiency drivers by default have much lower power compression than standard drivers, so this one is sorted simply by choosing the correct driver.
9. Rolloff frequency and alignment, highpass filter frequency and alignment as well as cabinet Q will make all the difference. Simulations will help, but to do this right there is an amount of tweaking which will need to be done after the build is done.
10. The combination of the driver choice, and cabinet design will dictate this one. Again, simulations will be key, but tweaking after the fact will make it perfect.
11. If I can achieve peaks of 108dB, then I will be satisfied. From the "quick and dirty" calculations in point 1 this should be easily achieved as I have enough efficiency and power on tap.
12. There are some "tricks" to make a sub better for HT vs music. I will always lean slightly toward the music side, but ultimately there needs to be a good balance. Cabinet design, alignment and rolloff frequencies as well as DSP will help achieve this goal.
Next section - simulations and cabinet considerations
Ok, enough for now - more tomorrow!
Ian.
