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Sealing a JBL 5628 subwoofer... A bad idea?

Bugal1998

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Hi all,

This is my first attempt at using a speaker modeling program and designing any type of enclosure, and I don't know what I don't know.

I've modeled (using my best estimates) the JBL 5628 subwoofer in WinIsd, and the SPL tracks very closely to JBL's published frequency response. I also noted that if I seal the virtual model of the JBL 5628 it has a Qtc of almost exactly 0.5 which I've read is considered ideal for subwoofer transient response for music (where midrange and upper bass is not a consideration).

Am I missing something obvious, or would it be reasonable to buy a pair of JBL 5628 subs and simply seal them for tight musical bass with very high output and good in-room frequency extension? This solution appears to meet or exceed the output of the Rythmik FV25hp through most of the frequency range from 10-120hz, and is nearly $1000 less per sub.

I have spare crown amps, space is not an issue (will eventually do quads), and they will be hidden from view.

The alternative would be quad (or even six) Rythmik G25hp subs but would be more expensive and would require dedicated outlets in each corner of the room further increasing expense.

So before I do something potentially stupid, what am I missing?

Thanks!
 
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Bugal1998

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If you have measurement gear and EQ to shape the frequency response, and they will get loud enough to have sufficient headroom for your use when driven by your amplifier, there's no harm in closing the ports.

Thanks, Jhaider...

I have both measurement gear and EQ capabilities, so I should be set.

I'm hoping this path will give me the option to switch between gobs of tight articulate bass for music and savage bass for movies (with less extension obviously). If not, I'd probably just go with quad Rythmik G25hp subs and call it good.
 

Puddingbuks

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Any update on this project?
 
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Bugal1998

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Any update on this project?

Nothing of note to share at this time... The rolloff seems steeper than modeled, but they're currently in a ~27,000 cu. ft. space and I have a deep null between 20 and 30 hz so it's hard to tell for sure. I'm hoping in about 6 months I'll have a dedicated and enclosed listening room with proper engineering for low frequency response... At that point I'll be able to do a better assessment.

They do sound tighter and cleaner sealed (and this is reflected in the DIRAC impulse response) and 16 hz will shake your clothing, but I prefer them unsealed in my open room (as does my wife).
 

RCAguy

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I'm thinking about mounting two 18in bare drivers in a Sheetrock-on-studs partition at one end of a large space. Wondering whether if the drivers were separated 20ft (at the floor loaded at 2pi) they would still couple for LF extension the way they do in a 5628?
 

Jim Matthews

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I'm thinking about mounting two 18in bare drivers in a Sheetrock-on-studs partition at one end of a large space. Wondering whether if the drivers were separated 20ft (at the floor loaded at 2pi) they would still couple for LF extension the way they do in a 5628?
On a mechanical note; mounting directly to drywall or plaster board is not recommended. The continuous duty cycle will flex the wallboard.

At higher output levels this will induce sympathetic resonance in the wall itself. Better to mount the drivers on a baffle that ports into the listening space.

http://basementsolutions.blogspot.com/2009/06/subwoofer-speakers-in-crawlspace.html

****

Bill Fitz Maurice has been supporting the DIY speaker community for more than a decade. His website offers some practical ways to achieve a similar aim, using modules specifically arranged to generate "pressure zones".

I built two of his Tuba HT folded horns and they are as large as I would care to have. (Getting the first upstairs from the garage was all I could manage, alone. I built the second in place so it needn't be moved.)

https://billfitzmaurice.info/forum/viewtopic.php?f=10&t=398

https://billfitzmaurice.info/THT.html
 
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RCAguy

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On a mechanical note; mounting directly to drywall or plaster board is not recommended. The continuous duty cycle will flex the wallboard.

At higher output levels this will induce sympathetic resonance in the wall itself. Better to mount the drivers on a baffle that ports into the listening space.

http://basementsolutions.blogspot.com/2009/06/subwoofer-speakers-in-crawlspace.html

****

Bill Fitz Maurice has been supporting the DIY speaker community for more than a decade. His website offers some practical ways to achieve a similar aim, using modules specifically arranged to generate "pressure zones".

I built two of his Tuba HT folded horns and they are as large as I would care to have. (Getting the first upstairs from the garage was all I could manage, alone. I built the second in place so it needn't be moved.)

https://billfitzmaurice.info/forum/viewtopic.php?f=10&t=398

https://billfitzmaurice.info/THT.html
Thanks
On a mechanical note; mounting directly to drywall or plaster board is not recommended. The continuous duty cycle will flex the wallboard.

At higher output levels this will induce sympathetic resonance in the wall itself. Better to mount the drivers on a baffle that ports into the listening space.

http://basementsolutions.blogspot.com/2009/06/subwoofer-speakers-in-crawlspace.html

****

Bill Fitz Maurice has been supporting the DIY speaker community for more than a decade. His website offers some practical ways to achieve a similar aim, using modules specifically arranged to generate "pressure zones".

I built two of his Tuba HT folded horns and they are as large as I would care to have. (Getting the first upstairs from the garage was all I could manage, alone. I built the second in place so it needn't be moved.)

https://billfitzmaurice.info/forum/viewtopic.php?f=10&t=398

https://billfitzmaurice.info/THT.html

Thanks, Jim. I'd certainly mout using a stiff baffle board, braced on the studs and added "fire stops," and not relying at all on the Sheetrock (except on the other side's of the studs and firestops for isolation at low pressure). What I don't know is whether two drivers 20ft apart would couple as they do when close together.
 

Jim Matthews

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. What I don't know is whether two drivers 20ft apart would couple as they do when close together.

We should put this question to Tom Danley. I was under the impression that two drivers will sound "as one" if they are within 1/4 wavelength of the highest frequency covered, when driven by the same signal.

What I do not know is what this arrangement might do to room modes - a serious concern with something that can't easily be moved.

****

The use of multiple drivers for higher SPL is sufficiently explained that I grasp the concept. The use of an infinite baffle to reduce backwave load on a woofer, less so. Room modes and dealing with the consequences of multiple LF drivers is above my paygrade.

Prior to building BFM Tuba HT with an ancient pair of Lamda (now AE) dedicated subwoofers I investigated mounting them in a crawlspace, through a single, slotted port.

It is my opinion that the next owners of my house might not share my enthusiasm.
 
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