# Installation of JBL In-Wall Subwoofer



## WeeWill123 (Feb 16, 2009)

I am a home theater newbie, as will be obvious from this post. I am disappointed in the bass that I get from my JBL HTI-88 in-wall subwoofer. I know that this is not a high end product but I suspect that part of the problem is the way that it is mounted in the wall. Right now there is nothing behind the subwoofer - just the empty space of a furnace room. I suspect that if I build some kind of case or enclosure behind the subwoofer, it will improve the bass in the home theater area. I see that there is all kinds of information in these forums about building your own speaker cabinets but I am bewildered and don't know where to begin.

Will building an enclosure behind my JBL HTI-88 subwoofer improve the sound? If so, how do I begin to figure out what to do? Thanks!


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## bobgpsr (Apr 20, 2006)

WeeWill123 said:


> Will building an enclosure behind my JBL HTI-88 subwoofer improve the sound?


No it won't. That would end up restricting the driver cone movement and cut your bass capability.

Sound like what you have is what we call an Infinite Baffle setup -- which is good. That is ok, but the bass fiends around here (those who want to get reference level +115 dB SPL bass) often end up using two or even four 15" to 18" subwoofer drivers mounted in a infinite baffle plenum.


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## WeeWill123 (Feb 16, 2009)

Thanks for your prompt response. As a newbie, though, I don't think I understand what an Infinite Baffle setup is. I just did a Google search on this and found at least a couple of websites that show people building a "manifold" box behind the speaker drivers. Is there a reason why I should consider doing this? Again, right now there is just an empty utility room behind my in-wall subwoofer - not even another piece of drywall.


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## drdoan (Aug 30, 2006)

Hi Willy, welcome. Keep reading, you will get enough knowledge here to help you. Bass is a fickle thing, and is not an easy "try one thing and it always works" thing! With proper knowledge and a "try and see (hear) attitude" you will ultimately get what you want. hope this helps. Have fun. Dennis


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## Wayne A. Pflughaupt (Apr 13, 2006)

Welcome to the Forum, Willy!


WeeWill123 said:


> I am disappointed in the bass that I get from my JBL HTI-88 in-wall subwoofer. I know that this is not a high end product but I suspect that part of the problem is the way that it is mounted in the wall. Right now there is nothing behind the subwoofer - just the empty space of a furnace room.
> Will building an enclosure behind my JBL HTI-88 subwoofer improve the sound? If so, how do I begin to figure out what to do? Thanks!


If I read your post correctly, the backside of the wall, where the furnace room is, there is no sheetrock, just open studs. If that’s correct, then there’s your problem. An in-wall speaker like your JBL is designed to work properly if both sides of the wall are finished out. In other words, the wall cavity itself becomes the speaker enclosure. So installing sheetrock or plywood on the furnace room-side of the wall will help things considerably. 

However, good subs require large drivers (12” or larger) and large enclosures, so even though you’ll realize an improvement by giving your JBLs a proper wall cavity to operate in, don’t expect any earth-shaking, deep bass.

That said, if you have this empty room available, you have an idea situation for a serious custom or DIY subwoofer installation, as the others here have noted. You could do an infinite baffle sub (where the entire furnace room itself would become the enclosure), or build a large cabinet that would sit in the furnace room and vent into your main room, with an in-wall grille to dress out the hole. If the DIY approach doesn’t appeal to you, you could do the same thing with a good manufactured sub – cut a hole in the wall to vent it into the main room, with a grille to cover the hole.

Regards,
Wayne


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## WeeWill123 (Feb 16, 2009)

Thanks, Wayne. That's really helpful. Yes, you have understood correctly that there is currently no drywall behind my JBL in-wall subwoofer - just empty space. I think I'll try putting a sheet of plywood behind the subwoofer and see if that makes any difference.

You can guess from the JBL speakers that this is a relatively low-budget setup. Still, I'm curious about this "Infinite Baffle" idea that a couple of people have mentioned. Even after a Google search, I still don't understand exactly how I would do this. What, precisely, would I have to do to turn my furnace room into an Infinite Baffle?

Thanks again!


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## Wayne A. Pflughaupt (Apr 13, 2006)

Just make sure the plywood is floor-to-ceiling between the two studs where the JBL built-in is (hopefully you knew that  ).

An infinite baffle sub might be a bit pricey for your installation, but you can find out more about them here.

Regards,
Wayne


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## redduck21502 (Oct 23, 2008)

Also, do you have a separate amplifier for the JBL or are you running it with one of the other channels?


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## WeeWill123 (Feb 16, 2009)

Thanks for the link. The photos posted there helped me to understand the Infinite Baffle concept much better than anything else so far. Now I think I get it, and no, an Infinite Baffle is not the way I'm going to go with my setup.

To answer your question, the JBL HTI88 is connected to the left/right front channels of my Yamaha RX-V3800 receiver. The left and right speakers are wired to the subwoofer.

Thanks again.


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## salvasol (Oct 31, 2006)

WeeWill123 said:


> Will building an enclosure behind my JBL HTI-88 subwoofer improve the sound? If so, how do I begin to figure out what to do? Thanks!


I found this information about your sub ....http://www.jbl.com/home/products/product_detail.aspx?prod=HTI88&CheckProduct=Y

After reading some documents,it seems that to get a better output you need to have it inside an enclosure (the manual assume that your wall will have drywall or you can use a back box for new constructions) :yes:

How bad do you want more bass??? ...after looking at the specifications you'll benefit from a better sub, either from a manufacturer or if you go the DIY route (the response of this JBL is 30Hz-100Hz (-6db), with some movies you benefit of having a sub that goes down to 20Hz).:yes:


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## redduck21502 (Oct 23, 2008)

You could probably get some better sound out of it if you hooked the JBL to a seperate amplifier. That's why i asked how it was hooked up. Plus, if your receiver has the LFE output, hooking it to an amp for your sub would likely make it sound better. Then you could set the receiver's crossover to 80 Hz set the channels to Small and your JBL would handle everything under 80Hz. That coupled with the wall cavity being closed up, and it should improve the sound.


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## bobgpsr (Apr 20, 2006)

salvasol said:


> After reading some documents,it seems that to get a better output you need to have it inside an enclosure (the manual assume that your wall will have drywall or you can use a back box for new constructions)


Really? I just now read the same material and do not see anything that explains how that sub increases bass output when it is enclosed. Please explain the physics behind that. A port will increase bass. An enclosure if small enough, can provide an air spring to refine and better control the speaker cone -- but not increase bass.


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## salvasol (Oct 31, 2006)

bobgpsr said:


> Really? I just now read the same material and do not see anything that explains how that sub increases bass output when it is enclosed...


I didn't mean that he will get more bass, what I meant was that the sub will perform better (he stated in the first post that he is disappointed of the sound from the sub, and most post suggest enclosing the sub, same suggestion is on the manual implying drywall or back box) :yes:


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