Concrete sub

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Docfoster
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Concrete sub

Unread post by Docfoster »

Recently been working on my latest DIY project.
Focussed on cabinet design really.
I used 25mm MDF to build a sub cabinet for a Dayton Audio sub driver.
After finishing the woodwork, I poured in 2mm of bitumen on to each internal face, allowed to dry then poured in 3-4mm of concrete floor self-leveller.
I took a brief video of the concreting stage here...



I used a Dayton Audio SD315A-88 12" DVC driver. As it's DVC (dual voice coil) it can take a feed from each stereo channel of my existing amp. I built 2 passive crossovers at 75Hz to split the signal between the sub and the main speakers.

Image

To make the sub acceptable to other family members I covered it in a cream felt and screwed a table top on to it so that it can be used as an occasional table.

Image

Image

Image

I appreciate that the crossovers and the port will not be to everyone's liking here, but I am wondering about any parallels between concreting and steel lining...?

Anyway, pretty happy with the results, as shown in my grinning loon face at the end of this...



I'm currently tweaking levels to get things sounding as good to my ears as I can.
These users thanked the author Docfoster for the post (total 7):
savvypaul (Sun Mar 07, 2021 3:51 pm) • slinger (Sun Mar 07, 2021 3:52 pm) • Daniel Quinn (Sun Mar 07, 2021 4:41 pm) • karatestu (Mon Mar 08, 2021 7:19 am) • Colin Wonfor (Tue Mar 09, 2021 7:34 pm) • Wonfor14 (Wed Jun 16, 2021 2:01 pm) • NSNO2021 (Fri Aug 13, 2021 6:24 am)
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

antonio66
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Re: Concrete sub

Unread post by antonio66 »

Very nice of you to think of other family members Doc, I guess you could even tip your main speakers upside down and if by magic, another two side tables appear. Seriously well done Doc, pleased you're liking them.

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karatestu
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Re: Concrete sub

Unread post by karatestu »

Docfoster wrote: Sun Mar 07, 2021 1:57 pm
After finishing the woodwork, I poured in 2mm of bitumen on to each internal face, allowed to dry then poured in 3-4mm of concrete floor self-leveller.

To make the sub acceptable to other family members I covered it in a cream felt and screwed a table top on to it so that it can be used as an occasional table.
Fantastic work Doc. Nice thinking outside the box there, or should that be inside the box :lol: Good to put a face to a name, you are a good looking chap :grin: I also like the idea that it can be used as a table occasionally :guiness;

You will have increased the weight which is good for a sub, increased stiffness and pushed the box's resonant frequency up further out of band which can only be good. I take it the bitumen is to seal the mdf otherwise it would have soaked up all the moisture ? And provide some damping between the mdf and concrete.

When I steel lined my little 5" bipole cubes I couldn't quite believe the improvement even with only 3mm sheet steel. The bass was much tighter but I have to be careful as it is a mid bass speaker cab (up to 8Khz) and It would be impossible to raise the resonant frequency above the pass band. Luckily there is less energy the higher up you go so hopefully ok. I can't hear any obvious problems.

Top work :guiness;
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Wonfor14 (Fri Aug 13, 2021 5:13 am)
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Docfoster
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Re: Concrete sub

Unread post by Docfoster »

antonio66 wrote: Mon Mar 08, 2021 1:39 am Very nice of you to think of other family members Doc, I guess you could even tip your main speakers upside down and if by magic, another two side tables appear. Seriously well done Doc, pleased you're liking them.
Thanks Antonio! :-)
I am nothing if not empathic.
You are absolutely right about the main speakers.
I'm going to try that the next time the posh tea-set comes out.
These users thanked the author Docfoster for the post (total 2):
antonio66 (Wed Mar 10, 2021 12:53 am) • Wonfor14 (Wed Jun 16, 2021 2:02 pm)
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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Re: Concrete sub

Unread post by Docfoster »

karatestu wrote: Mon Mar 08, 2021 9:49 am
Docfoster wrote: Sun Mar 07, 2021 1:57 pm
After finishing the woodwork, I poured in 2mm of bitumen on to each internal face, allowed to dry then poured in 3-4mm of concrete floor self-leveller.

To make the sub acceptable to other family members I covered it in a cream felt and screwed a table top on to it so that it can be used as an occasional table.
Fantastic work Doc. Nice thinking outside the box there, or should that be inside the box :lol: Good to put a face to a name, you are a good looking chap :grin: I also like the idea that it can be used as a table occasionally :guiness;

You will have increased the weight which is good for a sub, increased stiffness and pushed the box's resonant frequency up further out of band which can only be good. I take it the bitumen is to seal the mdf otherwise it would have soaked up all the moisture ? And provide some damping between the mdf and concrete.

When I steel lined my little 5" bipole cubes I couldn't quite believe the improvement even with only 3mm sheet steel. The bass was much tighter but I have to be careful as it is a mid bass speaker cab (up to 8Khz) and It would be impossible to raise the resonant frequency above the pass band. Luckily there is less energy the higher up you go so hopefully ok. I can't hear any obvious problems.

Top work :guiness;
I agree with your analysis of the effects of increased stiffness.
I must say, I've never tried steel lining, but I would imagine the function is similar. Will try it one day.
The sub cab is remarkably inert to the touch when playing, even loudly.
The bitumen will certainly have protected the MDF from the moisture in the leveller. Which was a bonus! Though it's main purpose was dampening you mention. I've painted the inside of other DIY MDF cabs before and have heard the difference it can make. It's horribly messy stuff, but pouring it in this time was a bit less grimy that brushing on a couple of coats! I am considerably less attractive when covered in black sticky bitumen. ;-)
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Wonfor14 (Fri Aug 13, 2021 5:13 am)
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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Re: Concrete sub

Unread post by Docfoster »

Once the grin wore off the realisation dawned that I don't really want to be running a dub sound system all the time, so maybe a more nuanced approach is required.
Had a couple hours this morning to tweak the sub's level. I want the sub to provide bass weight, but I don't want it to be overblown, and I certainly don't want it interfering with overall clarity.

Fortunately, as the crossovers are external, tweaking levels is a lot easier than normal (I don't need to remove the driver and fish around inside the cab every time I want to make an adjustment)!

I've ended up with 2.5ohm in series housed on the crossovers.

Image

And 25ohm in parallel, simply attached via banana plugs to the binding posts.

Image

Together, this is probably achieving just over 3dB of attenuation, whilst keeping the overall resistance at a level that holds the crossover point at 75Hz.
As I'm not sure exactly what the impedance of the sub is at the crossover point, this is part science but a lot of art and listening!
These users thanked the author Docfoster for the post (total 2):
Wonfor14 (Wed Jun 16, 2021 2:02 pm) • Lindsayt (Sat Aug 14, 2021 7:28 am)
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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Re: Concrete sub

Unread post by Wonfor14 »

Hi Ben, what type of caps are they?
I might have the value you need in a Poly type or even a Paktron type. Catch up soon.

Best Col

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Re: Concrete sub

Unread post by Docfoster »

Wonfor14 wrote: Fri Aug 13, 2021 5:12 am Hi Ben, what type of caps are they?
I might have the value you need in a Poly type or even a Paktron type. Catch up soon.

Best Col
As ever Colin, you are very kind.
Total value of 133uF required (for 75Hz LR 2nd order), so I used a 100uF and 33uF. Both Mundorf electrolytics.
I have little to no knowledge of audio / longevity differences between types of capacitor. What are your thoughts on the pros and cons of poly and Paktron?

Edit...and as an aside Colin, it's quite amazing what your One4 amp can do with a decent dedicated bass cab attached! I'm liking the thought of your being proud of the depth, heft and clarity of the bass your beastie is chucking about. I did anticipate the possibility of providing a dedicated amp for the bass cab, but absolutely no need afaic; the One4 is plenty good enough to drive the whole frequency range.
Tbh I've always struggled to integrate active subs. Viewing this project not as a "sub" but rather as effectively the bass unit of a 3 way speaker has been the single most important ingredient.

Edit edit...As a footnote, I ended up with 4ohm in series to each channel of the bass cab (*in series* for reasons too tedious to explain), and about another 0.5dB as an L-pad.
System 1: JRiver MC24 > Dell Latitude 7270 > Asus Xonar Essence One Muses Edition DAC & pre- > One4 Class A power amp (with Dynamic PSU boards) > DIY Monacor SP-310CX speakers & DIY Dayton Audio SD315A-88 bass cab.
LC Audio Technology mains DC filter > Sovereign MTBPS balanced power supply
TQ (Wonfor) Ultra Black cables.

System 2: Anything with a headphone socket > Inca Tech Claymore > DIY Monacor SP-308CX speakers

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