# Build advice for SI HT18 home sub



## knever3 (Mar 9, 2009)

I have this half wall I plan on rebuilding to house the SI HT18 sub I have. The dimensions are 14" wide, 24" tall, 72" long. I want the sub on the living room side so I can have storage on the entry way side. The doors are useless because they are too small.

I would like a vented enclosure for low volume efficiency so I need you wizzards to design me a box to be part of this wall. The sub will be facing the living room adjacent to the outside wall. How big? Bracing needed? I will be powering it with 1450 watts off a bridged QSC RMX 1450 pro audio piece.

I haven't decided how I want to finish it either, most likely counter top formica I suppose.












































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## Hintzyboy (Mar 31, 2007)

Without knowing what that's made of, I wouldn't suggest using it as the main structure for your enclosure. It'd be better to build a hidden enclosure inside the cabinet. 

This is what I got when I plugged the recommended specs into a box calculator website. The recommended 8 cubes at 22 Hz uses up pretty much the whole thing.


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## Hintzyboy (Mar 31, 2007)

Also, it looks like there are electric baseboard heaters attached to the bottom of the cabinet. I don't know that I'd want to subject them to that kind of vibration, especially since they look a bit older.


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## daloudin (Nov 2, 2020)

If you completely remove the existing cabinetry and build the enclosure to the same dimensions out of 1" thick material with a double front baffle then you are looking at about 10 cuft sealed (after bracing and driver displacement) which would be about right for one HT18v3 Sealed. As mentioned above you are right at the absolute minimum dimensions for one HT18v3 Ported and there's no way I would suggest building an enclosure that size out of 3/4" material so it might end up even smaller than the aforementioned post. Given that you really don't have enough space in that size cabinet for ported I would recommend going with sealed.

Here's the model for ported at 8 cuft vs 20 cuft (Green) and 10 cuft sealed in Blue:



















The HT18V3 REALLY wants big airspace (not that the [email protected] is bad but [email protected] is MUCH better)...
Which becomes 72" x 24" x 26.19" so if you can spare another foot of space into the living room then you could do the 20 cuft and have a full depth counter top to work with... (click on this image to play with the dimensions on the actual website.) And if you put the slot port on the side against the wall you'll get even better boundary loading.


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## knever3 (Mar 9, 2009)

Wow! I didn't expect that much volume, thank you so much for the visual graphs and pictures. I planned to make tight doors and putting shoes in there, but don't know now. My wife would not be happy if we couldn't utilize the space to some extent. I plan on removing it and building from scratch so nothing is out of reach. I just want to build it once. I would need some good latches and seals to make doors work. Being it will be vented it's not as critical as a sealed enclosure, but I want a positive seal nonetheless. I don't plan on max volume since my front stage is just Definitive Technology xtr-50's. I just want better performance than my paltry 10" Eosone. The room volume is over 5,000 cu/ft.











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## Forddenial (8 mo ago)

Door weather stripping (that stuff in a roll with the adhesive back) around the perimeter of the cabinet door(s), sturdy hinges and those ikea fasteners to lock it closed when you want to use the sub. Magnet latch to hold the door closed when sub is not in use.

Maybe cut a shallow slot or recess the doorway lip a skitch so the door seals well without having to force it shut with the weather strip


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## daloudin (Nov 2, 2020)

knever3 said:


> Wow! I didn't expect that much volume, thank you so much for the visual graphs and pictures. I planned to make tight doors and putting shoes in there, but don't know now. My wife would not be happy if we couldn't utilize the space to some extent. I plan on removing it and building from scratch so nothing is out of reach. I just want to build it once. I would need some good latches and seals to make doors work. Being it will be vented it's not as critical as a sealed enclosure, but I want a positive seal nonetheless. I don't plan on max volume since my front stage is just Definitive Technology xtr-50's. I just want better performance than my paltry 10" Eosone. The room volume is over 5,000 cu/ft.
> 
> 
> 
> ...


Even at low volume, sealing doors would require hermetic seals with full perimeter clamping force and then you've still got the vibrating shoe laces and the shoes themselves dancing around inside the cabinet. You'd be way better off building the storage on to the back of the enclosure than trying to use the interior airspace. Even if you could seal the doors effectively, one high volume run at 1,450 Watts to show off and you run the risk of blowing out the seals and then there's wear and tear on the seals from opening and closing them daily... Not a good idea.

Spousal acceptance factor is critical for long term enjoyment. See how she feels about doubling the depth of the cabinet 1st to see how much room you have to work with and then we can compare alignments to optimize the output and bandwidth to match the XTR-50 which fall off a cliff around 90Hz. With 5k Cubic foot listening space you're going to need the Sub to provide at least some of the midbass and not just LFE output.

Do you have a DSP to Time Align the Sub to the Front Stage?


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## knever3 (Mar 9, 2009)

I don't have a DSP perse, but I do have Audyssey on my Denon 4308ci. I was planning on miniDsp after I get it done though. I thought midbass would be a problem, although I made a mistake and my speakers are the Mythos Two and Three respectively. A slightly better response, but a far cry from my Eosone RSF-1000's used for mains previously. 

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## daloudin (Nov 2, 2020)

knever3 said:


> I don't have a DSP perse, but I do have Audyssey on my Denon 4308ci. I was planning on miniDsp after I get it done though. I thought midbass would be a problem, although I made a mistake and my speakers are the Mythos Two and Three respectively. A slightly better response, but a far cry from my Eosone RSF-1000's used for mains previously.
> 
> Sent from my SM-G960U1 using Tapatalk


The Audyssey implementation on Denon receivers is actually quite nice but only for that one sweet spot in the center of the room or the primary listening position. If you have multiple listeners or an off-center seating position(s) then you usually better off starting with the Auto Tune in the center of the room and then giving the rears and overhead a little extra bump in delay but the Sub is usually pretty spot on... the limitation comes in having very limited EQ to resolve any problems and the Denon boosting too much if you happen to be at a room null when you make the measurement. That inability to average responses from different positions really hamstrings the implementation...

At least the Mythos 2/3 have more midbass than the XTR-50, though the spec stating they get down in to the Low 40s is quite suspect for me, but as long as you're not trying to push THX levels they get the job done. With a xover around 60Hz they should do fine and that will keep the Sub from being localized at all.

The 4308 has the full set of pre-out and external inputs IIRC so implementing the MiniDSP should be pretty straight forward and will be a huge upgrade.

Looks like your biggest hurdle is figuring out how to get enough space for the Sub - Unless you are willing to sealed and if you're not interested in shaking things off the wall then you might want to actually consider going sealed, you've got the power for it and once you get the DSP you'll be able to fine tune the output any way you desire with Sealed. Ten cuft sealed is not even at 0.7 Qtc so it will have way more midbass if needed...


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## Hintzyboy (Mar 31, 2007)

If you're gonna go through the trouble of building the speaker cabinet anyway, I think you might as well just tear out what you have and start fresh. The way I see it, you have 2 options. 

1. Build a full-height cabinet. Use the bottom as the enclosure and the rest can be storage configured to your liking. 

2. Build a full-depth counter as daloudin mentions. Use one side for the sub and the other for storage. 

Personally, I don't see an advantage in having that be a half wall. I wouldn't want to set anything on top of it given your intended use, and it doesn't look like there's a view to another room that would be blocked by a full-height unit.


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## Forddenial (8 mo ago)

Feng shui


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