Subwoofer for KEF LS50 monitors

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    Pontus on #1359

    I want to build a subwoofer mainly for music, my main monitors are the small but wonderful KEF LS50 (probably to be upgraded in the future). The crossover frequency would probably be 60-80 Hz. The room is about 70m3 (about 2500 cubic feet) but the space extends to other rooms so the effective volume is larger. The house is made out of concrete and there are large windows behind the loudspeakers. I sit approximately 3 meters from the loudspeakers.

    Cost isn’t really an issue (within limits, I work hard for my money) as I want to build the best possible sub that I can. If/when we move to a larger house I plan to build a second identical sub. The box size I have in mind is about 100-150 liters.

    I will also use my system for 2.1 or 2.2 cinema and possibly for 4.1 or 4.2 in the future. But as said, the main focus is on music.

    This is what I originally had in mind:
    – 1x 18″ EighteenSound 18LW1400, or 2x in a dipole configuration (separate enclosures)
    – Hypex DS8.0 amp module
    – 100-150 liters sealed enclosure (lowest end boosted by the amp EQ) to get below 20Hz with room gain.
    – DSPeaker AntiMode 2.0 DualCore to dampen room modes

    Then I read glowing reviews about the Acoustic Elegance drivers. What would you suggest from the AE range?

    Another alternative idea I have is to build a “chest” (about 200 liters internal volume) that could be placed between the main speakers. Two large drivers, one pointing to the right and the other driver to the left. I don’t know if it should be a dipole sealed (separated from each other) configuration or a stereo sealed configuration with an internal wall separating the speakers. I have had stereo subwoofers before and I really enjoyed the effect, but a dipole configuration would almost remove the vibrations and it would require one less amp module (but as I said, if I need several amps to get the best sound then that is what I will get). We have a white cabinet for DVD’s and CD’s between the speakers right now so I could get away with such a design if I manage to find a good solution for storing the media.

    High End sound quality for music reproduction from a relatively small enclosure is the goal. Therefore I will of course consider all alternatives such as vented or passive radiators if that is what it takes. I want to go totally overkill…

    I would very much appreciate suggestions or links to similar projects. I’m not an engineer and I don’t need to build anything unique, I enjoy building things that simply work. A proven project would be perfect. Thank you!

    stryke on #11381

    Hello. The 18LW1400 is really not a great option to begin with for subwoofer use in a home theater. For live sound where systems often only go down to 40-50hz it has enough excursion. When talking about possible HT use, you will want to go much lower. You will most often be limited by excursion before power input.

    The TD18H+ has 14mm Xmax vs 9mm Xmax of the 18LW1400 so it can play significantly louder within the excursion limits. It will be far more accurate due to the low inductance and flux modulation from our Lambda motor which you can read about going through these pages:

    A single TD18H+ in the 150L vented with 800W is about perfect. At 25hz that will get you about 112dB with far more output going up from there. I’m not sure of the cost on the Hypex amps and Antimode but they should be good options. I would also look into the Dirac Live from MiniDSP as well and possible rack mount power amps which may provide more power with less cost.

    With the woofers on both sides you will not get a dipole radiation pattern. They are close enough so they will be well within the wavelength of the highest frequency used so they will still perform as one source. Similar to other dual opposed subwoofers like the Submersive from Seaton Sound The benefit is cancelling net forces on the cabinet. You could definitely go this option if you wish.

    Pontus on #11382

    Thank you for taking the time to answer!

    I wrote dipole when I meant bipole. Opposing drivers to cancel out net forces sound like a good idea.

    I think that I would like to try dual opposed subfoofers. At the moment I only have room for one box in my living room but if I move to a larger house I could build new enclosures and go for a stereo single driver solution. This way I get to use both drivers right away.

    I’m afraid that I still have a lot of questions.
    1) Should I get the 4 ohm or the 8 ohm versions? I’m not sure but I think it goes like this: If I use the 4 ohm drivers I would connect them in serial for the dual opposed sub for an 8 ohm load. For single driver stereo use I would end up with 4 ohm loads. If I use 8 ohm drivers I would connect them in parallell for the dual opposed sub (4 ohm load) and for single driver use I would end up with a load of 8 ohms per subfoofer. How should I choose?
    2) Is the recommended volume 150 liters for dual opposed subs as well?
    3) Should the drivers share the same volume? If not, the total volume of the box with two chambers would grow to 300 liters which is starting to get big.
    4) Is the 150 liters net volume or gross volume? Should the displacement of the driver be taken into account?
    5) You wrote that 150 liters vented would be perfect. Did you mean to say closed? If you meant vented, what should the tuning frequency be? 25hz?

    I hope that you can find the time to answer my questions, I know it is a lot to ask. I should be able to design my own subs If I want to DIY but I’m not knowledgeable enough. I do love putting the things together though, and to proudly use something that I have built myself. Thanks again!

    stryke on #11383

    I would suggest going with a pair of 4ohm drivers. Run one off each channel of a pro amplifier, or you can bridge at 8ohm with them in series.

    Cabinet volume should really be as large as you can go within reason. The volume is always determined per woofer so it doesn’t matter if the box is divided. A pair of the 18’s in 150L vented is quite small. You really want to be closer to 150L per woofer. A pair of TD15H+ in 150L could work well though. Dividing the box is good in the odd chance that a woofer ever fails. That way the volume per woofer stays the same.

    The volume the woofer takes up is so minor compared to the box volume you don’t need to worry about it in a case like this. You could do closed, or you can do vented with tuning around that 25hz point to get much more efficiency down low.

    Pontus on #11384

    Are there any reasons why I would want the Apollo upgrade taking into account that I will be listening at moderate levels? If the SQ is better, then yes I will go for it, but if the difference is audible at high SPLs only then I will probably skip this option.

    stryke on #11385

    There are some benefits to the Apollo option as distortion is further lowered. How audible this is, I cannot say for sure. About 15-20% now of people order the Apollo upgrade. They typically want the assurance they have purchased the best possible option.

    Pontus on #11386

    The KEF LS50 is a small high quality 2-way coaxial minimonitor. At some point in the future I plan on using the subs as stands for the LS50’s and to use a relatively high crossover setting.

    I’m using the Lyngdorf TDAI-2170 (sold the AntiMode) all digital integrated amplifier which has built in DAC and room correction plus electronic crossover for stereo subwoofers. The amplifier allows for an amplifier delay in order to properly time-align the subwoofer with the main speakers. The amplifier comes supplied with a microphone and the DSP does correction to cancel out room modes.

    The stereo crossover allows for the following settings:

    Low pass filter
    Linkwitz Riley 2nd, 4th or 8th order
    Butterworth 1st, 2nd or 4th order
    Crossover frequency 20-9999Hz

    High pass filter
    Linkwitz Riley 2nd, 4th or 8th order
    Butterworth 1st, 2nd or 4th order
    Crossover frequency 20-9999Hz

    Where would you start experimenting with stereo TD18+ drivers? How high would you cross over and what filter settings would you use?

    stryke on #11387

    A single 18″ driver can go to about 500hz before it starts to beam and narrow to less than 90 degrees. The TD18H+ is actually flat far higher than that so you could go up that high if you want. This gives you a lot of range to work with. You could really cross over anywhere between 100hz and 500hz. The TD18H+ is going to give you cleaner output and far more efficiency almost anywhere in that range. It really just depends on your preference. Higher order xovers minimize interaction between drivers and are often easier to implement.

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