In-wall DIY Speakers?

Discussion in 'Home Theater Projects' started by Steve::Weaver, Apr 18, 2004.

  1. Steve::Weaver

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    I'm in the process of buying my first home. (Yay!)

    One of the first things I'm planning to do is build a dedicated home theater, but I'd like to do it in such a way that the speakers aren't visible. If it's not possible to get high-end sound this way, then I'll go another route, but it sure would be nice if everything was hidden behind acoustically-transparent fabric.

    I'm envisioning 7 identical speakers and a pair of serious-sized subs, probably driven by something in the price range of the 7x200w outlaw amp for the speakers, and whatever is necessary for the subs. I haven't found the perfect house yet, so I don't have any dimensions for the HT, but assuming I find one with an unfinished basement, I'd like to shoot for something like 20ft x 30ft. I'll be building a room within a room so to speak for sound-proofing, and I'll probably be putting the speakers into columns that stick out a few more inches from the walls, so there'll be plenty of depth for any reasonable-sized design, rather than being restricted to standard stud spacing-sized designs.

    Are there any speaker and sub designs that exist or could be modified to go into a wall without losing much in the way of sound quality? I probably won't be doing much in the way of music listening in the room, but movie soundtracks need to sound excellent. [​IMG] I'm going into this with the mindset of doing this right the first time, so while money is always an issue, I'll put as much time and money into it as necessary.
     
  2. Brian_J

    Brian_J Second Unit

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    I have not seen any DIY in-walls and have to assume they would be a real challenge to design the crossovers for. Top in-wall speakers have real enclosures. Check out Triad, James, etc if you want some of the betters. They come with a high price though.

    Brian
     
  3. Todd Shore

    Todd Shore Stunt Coordinator

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    If by in-wall you mean using a stud cavity w/ drywall for your enclosure, I would say don't do it. If you mean building a well braced enclosure into a wall or as part of the wall then I might be able to give a little insight.

    By using an entire wall as a speaker baffle you do away with baffle step. This makes designing a crossover easier since the bass/midbass losses don't have to be compensated for. If you are using well behaved drivers with wide, flat passbands active xovers can be easy to implement.

    It makes it harder if you are using or adapting someone else's design since the BSC has to be effectively removed from the crossover. Since most designers don't just "tack on" BSC to their crossover but instead integrate it this is not something most people would wish to do.

    I don't know of any off-the-shelf DIY designs, but if you are still interested I have some thoughts on imaging and depth of field.
     
  4. Todd Shore

    Todd Shore Stunt Coordinator

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    I just re-read your post. For sub designs do a seach for infinite baffle (IB) on this site. They are a step up, not down from a boxed sub.

    Regarding building into columns, I think it would be better if they were flush. Most builders of box speakers spend a lot of time and effort doing away with the hard edges encountered at the baffle edge so why go there?
     
  5. Steve::Weaver

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    I figured the subs would be easy, it would simply mean sound-proofing the equipment/storage room and have the rear of them face into there. I'm basically interested in any sort of speaker design that could be flush-mounted with the walls (or columns, which I think would look nicer) without destroying imaging and sound quality, since most of the designs I see recommend placement at least several feet from the walls.

    I may have also slightly over-estimated the size of the room I'd like to build. 15' x 25' would probably be more reasonable.
     
  6. Todd Shore

    Todd Shore Stunt Coordinator

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    Are you looking to use front projection for video?

    I am building out my front screen wall 16" to house the speaker enclosures. This wall backs up to a staircase which combined with the area behind the screen leaves plenty of room for IB subs.

    I went with active crossovers and DSP based parametric EQ and RTA and skipped the passive xover route. To enhance imaging I will be using 1/2" felt treatments around the drivers leaving a small hard baffle area exposed. Other portions of that wall will use fiberglass behind the cloth. Corner and sidewall acoustic treatments will also be used behind cloth.
     
  7. Steve::Weaver

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    What good is a dedicated home theater without front projection? [​IMG] My current HD-RPTV will go in the living room when I move, as will my current surround setup. (Harman Kardon 7.1 receiver and JBL speakers.)

    It sounds like you're doing something very similar to what I'm planning. Would you care to share your speaker designs, and any information on why you chose them?
     
  8. Todd Shore

    Todd Shore Stunt Coordinator

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    I'll be happy to share whatever I have.

    In short, I am using two Morel MW-164 midbass drivers, a Morel MDM-55 dome midrange, and a Stryke RT2W planar tweet. If I were to do it again I might go with another tweeter, but there is nothing in the planar that bothers me so I'm not replacing them.

    The dome midrange is in its own sealed cup and the tweeter is sealed as well. All are in 1.6 cu. ft. sealed enclosures lined with foam and stuffed with acoustistuff from PE. The front baffles are 1.5" and all other sides are .75". The rear of the midbass driver openings are scalloped to allow unrestricted air flow. The enclosures are dimensioned to allow them to be rack mounted in standard 19" racks. Basically, the area around the screen is made up of racks.

    For each speaker I am using a Behringer CX-3400 active crossover and one channel from a Behringer DSP8024 Ultra Curve Pro which is connected to my HTPC via MIDI for control. The CX-3400 is setup for mono 4-way and I am temporarily using a single Vifa P21 for bass duties. Crossover points are

    P21 < 250Hz > 2xMorel MW-164 < 950Hz > Morel MDM-55 < 3.5KHz > RTW2 tweeter

    For amplification I am using stacks of Alesis RA-100 stereo amplifiers. While I could get away with using a more powerful amp on the midbass and only using a single midbass per speaker, I don't like the idea of driving them that hard so two per speaker it is.

    You can see my current design goal at the following link:

    Media Room Project
     
  9. ThomasW

    ThomasW Cinematographer

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    Unfortunately most retail in-walls are really poor even if they carry high prices.

    Adapting a dynamic driver DIY config is certainly possible, but it can't be done properly without a custom designed crossover. This is done after taking good measurements of the drivers in-baffle performance. Use of generic XO's, either active or passive, doesn't allow for important things like baffle step compensation, zobel networks, etc. As a result the user gets less than optimal results.

    One option are the Bohlender-Graebener planars. These are sold by PE. They have optional grills and socks for in-wall installs. One would need to supplement the bottom end with a couple of 6.5" or single a 8" midwoofer per planar unit.

    Another possibly more interesting option would be to use the Magnepan MMGs. With the wood trim side pieces unscrewed in-wall mounting should be relatively easy. At $550/pr delivered and when combined with a sub they would be a very high-end system requiring minimal added engineering.
     
  10. Todd Shore

    Todd Shore Stunt Coordinator

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    Why would you need baffle step compensation or impedence compensation on an active in-wall system if you select the right drivers?
     
  11. ThomasW

    ThomasW Cinematographer

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    There are no 'right' drivers for in-wall use, just as there are no 'right' drivers for box speaker use. Each application involves a different set of compromises. Part of those compromises are custom crossovers.

    Regarding BSC, it's the baffle size as much as the driver's performance that determines the type and amount of compensation.
     
  12. Todd Shore

    Todd Shore Stunt Coordinator

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    Huh?

    The right drivers for an in-wall active system are those that have the appropriate FR for that portion of their passband that will be used and do not have any peaks that need to be tamed outside of the active xover with a notch filter or parametric EQ. Of course, those are also options if the desired driver DOES have a peak that needs tamed.

    It is always about compromises. One of the compromises in adopting an in wall system is the lack of depth of field. That is what they say, anyway. I'm not sure about that from my listening, though.

    Why do you need baffle step again? There is no step. My baffle for the front three speakers is 14' x 8'. At that point corner loading and sidewall reflections become the issue. But then, those are issues that have to be dealt with using in-room speakers, too.
     
  13. Steve::Weaver

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    Those Magnepan MMGs have 86dB efficiency and 150w max recommended power. Would they have the punch needed for HT?
     
  14. ThomasW

    ThomasW Cinematographer

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    Steve,

    Yes Maggies like higher current (power) levels. I know of no way to guesstimate if they'll do what you want/need. That's why I recommended the MMG's given the 30 day in-home trial period. They're certainly the 'easiest' option. And getting 7.1 channels won't break the bank.

    I have a pair suspended from a ceiling that I use for rears in my long HT.

    For bigger mains the MG12's or 1.6's would be an option. They're taller, wider and can certainly handle more power = more output. Now both of those are larger than a standard stud bay (13.5"). But it's relatively easy to modify a non-loading bearing bay to fit the speaker.

    The extremely shallow depth of any of the Maggies makes them easier to deal with as compared to trying to shoehorn 6.5"-8" midwoofers into a 3.5" deep stud bay.

    Note that like most planar arrays their vertical dispersion is basically limited to the height of the driver. That means that they need to be mounted at 'ear' level........
     
  15. Dean-P

    Dean-P Stunt Coordinator

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  16. Steve::Weaver

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    For my application the size of the standard stud cavity isn't important. There'll be room around this room for whatever I need (hopefully). Imagine cutting a hole in the wall and sliding a speaker of any size into it such that it's flush with the interior of the room. That's basically what I'm going for, but need something that won't be destroyed by being in that position. Most speakers have their preferred listening position well out from the walls.
     
  17. Todd Shore

    Todd Shore Stunt Coordinator

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    86dB with 150W power at 10' yields 98.1dB at the listening position for an individual speaker.

    At 12' it drops to 96.5dB.

    That is starting to cut it close for available headroom at max volume if you setup for around 75-80dB. If you are closer, say 8' your should be fine at 100dB max.
     
  18. ThomasW

    ThomasW Cinematographer

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    Then consider larger Maggies for mains (hint think 1.6s). Grab a pair of MMG's to get your feet wet, they'll make great 'effects' speakers.

    Although the stated efficiency is relatively lower than some dynamic speakers, that's no the whole picture. First, planars (they're a line source not point source) so they don't have the same SPL roll-off rate per given distance that standard dynamic drivers do. Second they'll play louder than the rated efficiency when the LFE is filtered out to a sub. Finally unless you're after rock concert SPLs, a 7.1 arrangement should have more than enough output.
     
  19. Steve::Weaver

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    It all sounds good. I think I'll audition a pair (and I can even do that before I move!)
     
  20. Todd Shore

    Todd Shore Stunt Coordinator

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    Right, 3dB attentuation per doubling of distance rather than 6dB.

    BUT, aren't those dipoles, requiring that they be out from the wall?
     

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