Dual 15" sealed subwoofer DIY project.
Discussion
Rather than drag the 'how often do you upgrade your hifi' thread further off topic, I thought I'd start this thread. I'm building a pair of sealed 15" subwoofers to replace a BK Monolith subwoofer as I need something a bit more powerful (I've blown two drivers over 5-6 years with the Monolith). I'm using Fi Q series 15" speakers dual 2ohms wired to give 4ohms to the amp.
I'm using a Beringer NU6000DSP amplifier which has been bench tested to be able to produce approx 1700 watts per channel into 4 ohms. This should be sufficient to drive the 1500 watt Fi speakers. The NU6000DSP has very flexible digital processing controls so it can be set to soft limit the amp's output to ensure that the expensive speakers can't be overdriven. It also allows individual delays, multiband parametric EQ and dynamic EQ all set using USB from a laptop (or the tiny panel display for those who like to do things the hard way.
Unlike many DIY sub builders I've been able to hear what these subs should sound like before starting as I am basically coping the subwoofers made and supplied by the dealer I bought my MK speakers from, namely the USC15. While they have some extra tweaks to the driver, hopefully mine shouldn't be too different and my 6.5 x 4 metre room is a fair bit smaller than their demo facility.
I received my MDF cabinets today, which have turned out great. I bought them from a guy on eBay called 'Gordy' as his prices were so good that I thought it wasn't worth the time and effort involved to build my own to save £60 or so. I still have to paint them of course and fit them out, but it's a good start.
Anyway, on with the pictures and I'll update this thread over Christmas, if not sooner, when I should receive the two Fi speakers.
Showing the front sub next to the Monolith for scale. This one will be painted satin black or covered with a dark grey speaker grille fabric to blend with the wall to the left of the photo:
This is the rear sub which will be painted satin white or covered with a white speaker grille fabric to blend in with the wall behind:
I'm using a Beringer NU6000DSP amplifier which has been bench tested to be able to produce approx 1700 watts per channel into 4 ohms. This should be sufficient to drive the 1500 watt Fi speakers. The NU6000DSP has very flexible digital processing controls so it can be set to soft limit the amp's output to ensure that the expensive speakers can't be overdriven. It also allows individual delays, multiband parametric EQ and dynamic EQ all set using USB from a laptop (or the tiny panel display for those who like to do things the hard way.
Unlike many DIY sub builders I've been able to hear what these subs should sound like before starting as I am basically coping the subwoofers made and supplied by the dealer I bought my MK speakers from, namely the USC15. While they have some extra tweaks to the driver, hopefully mine shouldn't be too different and my 6.5 x 4 metre room is a fair bit smaller than their demo facility.
I received my MDF cabinets today, which have turned out great. I bought them from a guy on eBay called 'Gordy' as his prices were so good that I thought it wasn't worth the time and effort involved to build my own to save £60 or so. I still have to paint them of course and fit them out, but it's a good start.
Anyway, on with the pictures and I'll update this thread over Christmas, if not sooner, when I should receive the two Fi speakers.
Showing the front sub next to the Monolith for scale. This one will be painted satin black or covered with a dark grey speaker grille fabric to blend with the wall to the left of the photo:
This is the rear sub which will be painted satin white or covered with a white speaker grille fabric to blend in with the wall behind:
Thought I might as well add that I've just installed my new MK S150T side surround speakers; picked them up last night from Gecko the UK distributor. They are the very first batch of white S150T speakers as MK have only just started making the 150 series in white following customer requests. I'd had a black pair on loan for the last couple of months waiting for these, so I already know how good they sound (though they blooming well ought to sound good considering the price).
Edited by OldSkoolRS on Wednesday 11th December 18:37
Thanks Crackie. 
Plan to use REW to do the initial setting up of individual EQ using the Beringer's controls, then running Audyssey XT32 afterwards. I may also implement a slight 'house curve' after XT32 as well if I feel the need. I've also used WinISD to calculate the driver excursions to assist with setting the limiter controls to a safe level (just putting it to 1450 watts limit seems to be all I need to do though as the sealed box limits driver excursion). With the 15" Q series and the natural roll off below 10Hz of the Beringer amp means I should be OK regarding not needing to filter any signal at the low end. As I'd only hit Xmax (not Xmech)at 5Hz @ 1500 watts anyway. Having blown 2 drivers on the Monolith over the years, you can tell I'm being very careful to protect these new drivers.
I've already used REW's room simulator to help me work out if adding a second sub was even worth doing (as I suffer a null with a single sub). It confirmed that a second sub at the back of the room helps smooth the response.
I've confirmed this in practice by using my second room XLS200 sub along with the existing Monolith and measuring (just using a spreadsheet and SPL meter as I haven't got the soundcard/mic for REW yet). This confirmed the second sub fills the null nicely, so the disruption of running the cabling will be worthwhile. I even ran XT32 with this odd pair of subs and get a much better result than I've ever had previously, so I'm just hoping that the slightly overkill choice of two matched 15" will be even better.
Plan to use REW to do the initial setting up of individual EQ using the Beringer's controls, then running Audyssey XT32 afterwards. I may also implement a slight 'house curve' after XT32 as well if I feel the need. I've also used WinISD to calculate the driver excursions to assist with setting the limiter controls to a safe level (just putting it to 1450 watts limit seems to be all I need to do though as the sealed box limits driver excursion). With the 15" Q series and the natural roll off below 10Hz of the Beringer amp means I should be OK regarding not needing to filter any signal at the low end. As I'd only hit Xmax (not Xmech)at 5Hz @ 1500 watts anyway. Having blown 2 drivers on the Monolith over the years, you can tell I'm being very careful to protect these new drivers.
I've already used REW's room simulator to help me work out if adding a second sub was even worth doing (as I suffer a null with a single sub). It confirmed that a second sub at the back of the room helps smooth the response.
I've confirmed this in practice by using my second room XLS200 sub along with the existing Monolith and measuring (just using a spreadsheet and SPL meter as I haven't got the soundcard/mic for REW yet). This confirmed the second sub fills the null nicely, so the disruption of running the cabling will be worthwhile. I even ran XT32 with this odd pair of subs and get a much better result than I've ever had previously, so I'm just hoping that the slightly overkill choice of two matched 15" will be even better.
Edited by OldSkoolRS on Wednesday 11th December 20:51
Yes, I should get myself sorted and order the mic & soundcard, been sidetracked ordering Christmas presents instead... I had some info saved about recommended soundcards and mics, but I'll have a look at the ones you mention as well given your positive experience compared to your work equipment.
Thanks for the help.
Thanks for the help.
Glad it's of interest, I'll make sure I keep it updated as the project progresses. It sounds promising with the results you got Rex, though I'll have to stop short of adding a further 18 like you. The reason I've gone for sealed is to hopefully integrate well with music too (I've found my second system BK XLS200 seems to work better in this regard, though in a smaller room and lower levels than I tend to run my main system.
Edited by OldSkoolRS on Saturday 14th December 15:59
That speakers looks a beast! I'm just going with 15" sealed subs as they can be relatively compact, yet should out perform the Monolith easily: This is a living room set up at the end of the day so I don't want anything too big/black/ugly to undo my work making an otherwise good looking (IMHO of course) room.
Trying to find a different rack for my amps, etc as this would allow the front sub to go into the left front corner and it will be even less obvious when you walk into the room. My original plan was to put 4 x 12" sub woofer speakers into a ceiling void, but REW room sim showed that the response wouldn't be very good in that location: Totally invisible subs would have been my ideal if I could have achieve that.
Trying to find a different rack for my amps, etc as this would allow the front sub to go into the left front corner and it will be even less obvious when you walk into the room. My original plan was to put 4 x 12" sub woofer speakers into a ceiling void, but REW room sim showed that the response wouldn't be very good in that location: Totally invisible subs would have been my ideal if I could have achieve that.
I was planing to seal the insides with neutral cure mastic as recommended to me on another forum. Likewise the stuffing will be a number of a particular type of pillow (hollowfibre I think) available cheaply from Asda. Of course as they are sealed I won't have to worry about the complexities of ports. I can see a surprising difference in response by adjusting the control that simulates how well sealed the box is when using WinISD, so I know it's important to do a good job sealing them.
@Redleicester; I hope you've had chance to enjoy that new centre speaker. Hopefully these boxes won't be shiny when finished as I don't want any reflections up to my projector screen. 
@Redleicester; I hope you've had chance to enjoy that new centre speaker.
Hopefully these boxes won't be shiny when finished as I don't want any reflections up to my projector screen. Edited by OldSkoolRS on Monday 16th December 20:07
I'm just going on what others have done over on the DIY subs section on AVforums. What is the purpose of covering the whole surface with resin? I'll be painting the outside surface, so I figured it was just the possible leaks around where the panels meet hence the sealant.
What resin would you use; the same stuff as used for fibreglassing or would this give off fumes that might effect the driver?
What resin would you use; the same stuff as used for fibreglassing or would this give off fumes that might effect the driver?
Ah I missed that post by Crackie as it was on the bottom of the last page.
Would I still need to to use the sealant on the internal corners as well though? If not I'll get some and give the insides a coat as I've just put the boxes out in my garage to clear space before Christmas...I might get chance to pop out there and do some preparation though. That'll give it plenty of time for any fumes to disappear before the speakers arrive.
I also need to order the connectors for the speakers, plus cable. The rear sub will be a 14 metre run from the amp by the time it's run around a door frame (behind the architrave which I'll replace) so I need to check what gauge I need to buy. I'm not a believer in expensive cable for the sake of it, but for 14 metres @1500 watts into 4ohms I think I might need to go for 4.5mm cable.
Watched 'Tron Legacy' recorded off one of the HD channels and it sounded very strong in the bass, even with my single BK Monolith, so I've left it on the PVR to check out the new subs once I have them built.
Would I still need to to use the sealant on the internal corners as well though? If not I'll get some and give the insides a coat as I've just put the boxes out in my garage to clear space before Christmas...I might get chance to pop out there and do some preparation though.
That'll give it plenty of time for any fumes to disappear before the speakers arrive.I also need to order the connectors for the speakers, plus cable. The rear sub will be a 14 metre run from the amp by the time it's run around a door frame (behind the architrave which I'll replace) so I need to check what gauge I need to buy. I'm not a believer in expensive cable for the sake of it, but for 14 metres @1500 watts into 4ohms I think I might need to go for 4.5mm cable.
Watched 'Tron Legacy' recorded off one of the HD channels and it sounded very strong in the bass, even with my single BK Monolith, so I've left it on the PVR to check out the new subs once I have them built.
Edited by OldSkoolRS on Tuesday 17th December 23:07
Thanks again Crackie. As you say 4.5mm is big enough, plus I have to run one section round a door frame, so I'm taking off the architrave to fit it between the frame and plasterboard. Any thicker and it'll get hard to fit in the gap (I hate seeing any cables on show so I literally only want the last 6" or so coming out behind the subs).
No news on the drivers yet, though they did say it would likely be the week after Christmas. I've probably left it a bit late to order the speakon connectors for the back of the subs and the ones for the input and outputs of the Beringer, but I may as well place the order tonight. Just need to double check what the type is for the amp end, though I think I might need to modify some existing phono cables for the amp input connection.
As you say 4.5mm is big enough, plus I have to run one section round a door frame, so I'm taking off the architrave to fit it between the frame and plasterboard. Any thicker and it'll get hard to fit in the gap (I hate seeing any cables on show so I literally only want the last 6" or so coming out behind the subs).No news on the drivers yet, though they did say it would likely be the week after Christmas. I've probably left it a bit late to order the speakon connectors for the back of the subs and the ones for the input and outputs of the Beringer, but I may as well place the order tonight. Just need to double check what the type is for the amp end, though I think I might need to modify some existing phono cables for the amp input connection.
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