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Need Help With New System Including Selection of In-Wall Passive Sub and Amplifier (1 Viewer)

WaltJohnson

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Aug 4, 2009
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walter Johnson
Please Help,

I've been collecting the pieces for our home theater/music system for the last year and now it is down to the subwoofer/amp before I start installing. I have put this system together on a tight budget off ebay (as you can probably tell from the equipment list below) The system is primarily going to be used for my two teenagers and their friends for televison/movies, xbox, and music (mp3s from a PC through an optical toslink cable).

Acoustics: The room is 12' by 23' with french doors and windows at each end. Of the remaining two walls, one is solid drywall since it faces the garage. The other wall faces the main portion of the house and has two doors. The wall that adjoins the garage will be the "rear" of the system and I plan on installing the subwoofer on this wall. Since it shares a wall with the garage, space is not an issue for the amplifier.

Current equipment (still in boxes) and how I believe they will be used:
A/V Receiver: Harmon Kardon AVR 635
Front Speakers: JBL Soundpoint SP6CII
Center Channel: Infinity ERSH V250
Surround Speakers: JBL Soundpoint SP6CII
Rear Speakers: JBL Soundpoint SP8CII

I'll be running 12 guage speaker wire for all the connections
I'll run RG6 with RCAs for the subwoofer amp connnection

Questions: I would like to stick with the in-wall configuration and install an in-wall passive sub with separate amplifier. I can only afford to purchase "pre-owned" equipment and have been looking at ebay to try to find compaible equipment. I have tried to do as much reasearch as possible but now need answers to some questions that may seem basic, but i just don't know.
  • Should I be looking for a subwoofer in the 12" range powered by a 200 wall (or higher) amplifier?
  • Many people are selling plate amplifiers for either DIY kits or that have been removed from free standing subwoofer boxes. Is there an advantage/disadvantage to using a standard subwoofer amplifier over a plate amp? What are the pros/cons of each?
  • When looking at amps and passive subs, I see that the inpedanceofdifferent subwoofers can be either 4 ohm, 6 ohm, or 8 ohm. The amplifiers' WILL LIST 8 ohm and 4 ohm. This is the question that will make me sound stupid, but will any subwoofer amplifier run any subwoofer, or do you have to match them up based upon the Impedance rating of the subwoofer?
  • I need to stay under $300 total for the amp and subwoofer. I've been looking at used Dayton, JBL, Velodyne, NHT, Eosone Polk, and M&K amplifiers. I've seen several of the Eosone Polk and M&K surplus plate amps lately on eBay. As far as subwoofers, I'm staying away from the low budget stuff and justing waiting it out for a higher quality used one to show up at a good price.

Please help. Also, please offer suggestions if you feel I am doing something wrong with the equipment I currently have.

Thanks,

----Walt
 

chuckg

Supporting Actor
Joined
Apr 27, 2004
Messages
921
Greetings!

If there's any chance of succeeding, I'd first try to get you away from an in-wall sub. It will be vastly easier to find and put together a sub that is in a box, ready to go. You will likely have better results in the finished sound quality, too.

Failiing that, I will answer: You aren't dumb to ask about the impedance. The short answer is, speaker impedance should be the same or higher than the amp's lowest impedance. The cheater answer is, any amp will drive any sub, but there is a question of how happy it will be to do so, and how well.

The difference between a plain old amp and a plate amp is that the plate is designed to be attached to the inside of a subwoofer box, and the plain old one is already in a box, and is meant to be mounted externally to the sub cabinet. Otherwise, there's no real difference at all. Amps made for subwoofers generally include some niceties like polarity switching and crossover (low pass filter) that plain old use-it-for-anything amps won't have.


Sounds like you've built up a decent system, and my only critique would be that you should try to replace the center speaker with another JBL SP6CII to match the other speakers. The reason being, when a voice moves from center to edge inthe soundfield, there might be a noticeable change in the tone of the voice if it moves to a completely different kind of speaker.



Hope I've been helpful! enjoy!
 

Robert_J

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Robert
Why in-wall? You are limited in enclosure size by the wall cavity.
  • A 12" sub will be difficult to install. I've seen some DIY in-wall subs that use low profile 10" drivers. Some of these will come in close to your $300 budget and probably sound much better than a retail model of the same price.
  • I'm not sure what you mean by 'standard subwoofer amp'. PE/Dayton has a sub amp that is rack mountable or shelf mountable. They sell the exact same amp in a plate version as well. In your situation, the plate amps that are removed from existing subs are not recommended. They have EQ/filters that were designed into that sub system. Using them with a different driver and enclosure will give you unpredictable results. Stick with a generic plate amp, PE sub amp like I mention above or a pro amp.
  • A sub amp rated at 250w into 4 ohms or 180w into 8 ohms will run any 4 ohm, 8 ohm or even a higher resistanc sub just fine. The higher the resistance the lower the wattage output of the amp. It will not safely run anything under 4 ohms though. Some heat up and go into protection mode. Others catch on fire.
  • Stick with Dayton or any other brand that did not come out of an existing sub. I've done that once only because I communicated with the engineer who designed the amp and confirmed there was no additional EQ to worry about.
You are already going to be doing some work on the wall, why not go with a DIY sub? I can help with that. In-wall isn't difficult to build. If you are willing to use the back wall instead, then an IB sub would be a HUGE improvement over any in-wall sub on the market. It can easily be done for your budget.

-Robert
 

Robert_J

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I agree with Chuck but if you really want to go the in-wall sub route then use this amp - http://www.edesignaudio.com/product_info.php?cPath=2_106&products_id=819
Two of these drivers - http://www.edesignaudio.com/product_info.php?t=2&products_id=106

Copied from another site so it isn't my design (thank John J. from AE Speakers):
The cabinet was 14" wide, 3.375" deep and 88" tall. Made from 1/2" mdf braced quite a bit. It gives just over 1.5 cubic feet of airspace.
http://www.aespeakers.com/pics/inwall_sub/in-wall-sub-exploded.jpg
http://www.aespeakers.com/pics/inwall_sub/inwallroom.jpg

This design is similar to the Snell in-wall sub that retails for $1,000 - http://www.snellacoustics.com/ProductDetails/3420.asp At one time you could get those exact drivers for $80 each. I think the eD drivers are just as well made.

-Robert
 

WaltJohnson

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Aug 4, 2009
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walter Johnson
Hey Chuck and Robert,

Thanks for the input, it is very helpful and appreciated. The reason I want to go with an in-wall is just to keep from having a box sub on the floor. My older son is 16 and my younger son just turned 13. Great kids, but I can just see the Mountain Dew "Live Wire" spilled all over the floor/carpet when it rumbles off because they used the sub as a coffee/end table or the inevitable "foot through the driver" when they are wrestling with buddies. It's never intended, but I grew up with two brothers and it always seems to happen. Also my wife (they never understand) believes that the room "just won't look right with a damn box sitting in it" always comes into play. Ahhh....gone are the days of a $30 couch, a $10 table, and the old Kenwood amp pushing vinyl through my KLH-1s in the corner of the room. The KLH's cost me more than my first car, but they sounded so sweet. Anyway, I digress.

I would love some input on the DIY sub project. I would really like to go in-wall, but I should have been more specific. The garage and the workroom are my domain and she couldn't care less what we (myself and son's) do with the wall space between the garage and their "entertainment" room. Therefore, I am not limited to the 3 1/2" of space between the drywall or the 14 1/2" of space between the studs. I (we) can design a box in any configuartion to get the amount of cubic footage of air space, baffles, porting, etc . That's kind of my ace in the hole. Also, I really do either have, or have access to, any type of tool/saw/implement of destruction you can think of (and the knowledge to utilize them correctly) to build whatever is necessary. I just lack the experience and expertise that you guys have to direct me to the correct design and equipment.

What do you think?

Thanks,

----Walt
 

Robert_J

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Robert
An IB or infinite baffle sub doesn't use a box. It uses a manifold. OK it is a box but one side is missing. Install it in your garage with the opening towards your entertainment room. Cut a hole in the wall. Here are some examples - http://home.comcast.net/~infinitelybaffled/page2IB-Gallery.html

There is no box to 'color' the sound of the sub. Quality depends entirely on the quality of the equipment used. Having two opposing drivers also cancels any mechanical vibrations of the cones moving. Try to pick up a sub with the cone moving 3" back and forth 30 times per second. It's like holding a jack hammer.

As you can see, IB subs go from simple to extreme. But the concept is all the same. By using large drivers, they don't have to work as hard. Not working as hard equals less distortion. Less distortion equals quality bass. With your $300 you can build a simple IB with dual 15's and a plate amp.

-Robert
 

chuckg

Supporting Actor
Joined
Apr 27, 2004
Messages
921
I say listen to Robert! The use of the garage space will make a huge difference...I was thinking you might mean a speaker screwed to the wall with little or no real box....but by using your garage, you can build whatever you want, and have nothing more than a grille in the house!
 

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