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Old 10th November 2005, 07:35 PM   #1
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Default in-wall speaker design

Hi there,

My house is currently being built and I have plans for whole house audio. I've purchased a bunch of the cheap 4" NSB drivers that I would like to use.

I'm a novice when it comes to speaker design. What kind of design issues are key for in-wall speakers? I've read that baffle step compensation is one issue to consider but what else is there?

Could somebody please point me in the right direction.

Cheers,

Exipnos
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Old 10th November 2005, 10:00 PM   #2
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I've found those NSB drivers sound a little "boxey" when in an enclosure. They sound really nice with a notch filter in an OB line array. Any chance of doing that?
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Old 11th November 2005, 07:52 AM   #3
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Thanks for the comments Carl - I ordered a large amount of NSB's and I will be doing OB line arrays for my HT room.

But I also need a solution for the rest of the house. I bought the NSB for their low cost and plan on using them for the whole house audio. Its more for background music and ambiance so no audiophile quality is needed (even though NSB probably are not associated with audiophile .

I was thinking of using 6 nsb per channel in a small line array to improve effiency and to limit distrortion from these cheap drivers. But I don't think I could do OB for the wall speakers. Is it possible to do something similar to these speakers for inwall?

Me and Dad, building Ultraflex:)

Maybe decrease the depth and make the side slots far wider. Also make the inner box very small. Would that give a small OB effect?

I'm also thinking to try the 3D spiral method so that I improve on the NSB bass.

3D spiral horn?

But I willing to try a regular inwall design if thats the way forward....

More help needed.

Cheers,

Exipnos
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Old 14th November 2005, 06:03 AM   #4
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BUMP.....

Anybody have any experience with in-wall speakers to share?
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Old 14th November 2005, 08:18 AM   #5
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Nope, but I can tell you this much -baffle step is not going to be a problem. That's an issue for conventional speaker cabinets and open baffles. Wall mounting will effectively present your drivers with an infinite baffle in that the front of the drivers will 'see' a practically infinitly wide and tall baffle (the wall) that they are mounted to, so no problems there -no baffle step compensation required. They'll do fine for background music -never loose site of the fact that Bose have made a virtue of spectacualrly low quality sound at huge prices, but it fits a 'lifestyle' (shudder), and for background sounds, millions of people are perfectly satisfied. Your NSBs, wall mounted, will be at least as good in this role, frankly, I suspect they'll be better. Save the good stuff for the dedicated listening system -you don't catch many Acapella owners (hybrid TQWT/front-horn with plasma tweeters costing a minimum of 30,000UK) using them for kitchen music while chopping up the veg.

Going for a dipolar design (open baffle in other words) with these for your HT room should be fine (lots of people have done it, and love them, as you can see), but you're going to need some help with low frequencies. Dipoles don't do bass well at all without some hefty help from subs (preferably dipolar themselves) and equalization (preferably active), due to the progressive acoustic cancellation as frequency decreases. Have a look at Siegfried Linkwiz' site if you haven't already:
www.linkwitzlab.com for everthing you'll ever need. Have you checked Jim Griffin's Line Source / Array white paper too?

Best
Scott
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Old 14th November 2005, 08:29 AM   #6
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Just to get really practical for a minute, what kind of walls do you have? This will be the major design consideration!
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Old 14th November 2005, 10:57 AM   #7
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Wall practicalities first. My walls are made out of Autoenclaved Aerated Concrete AAC also known as Sipporex or Ytong here in Europe. Majority of the walls will double leaf with 2cm mineral wool in between. Each leaf is 7cm sipporex. I therefore could use maximum about 7-9cm of depth.

So okay no baffle step problems. NSB sound is probably good enough for what I need and if I can beat BOSE sound then great! But how do I construct the speakers. Just a small box, no box or what? I was thinking of maybe running the NSBs full range so that I don't have to worry about crossover. Yes they get a bit nasty on the top but maybe I can improve that a bit by coating them and installing a phase plug. But thinking about it now wouldn't I get problems by running multiple NSBs full range? Shouldn't their CtC spacing be smaller to allow for full range?

For the HT and dipolar speakers. I'll definately try OB to see if I like it. I'm worried that I will like the sound becasue if I do then I need a solution for the low frequencies. I thought about adding 2 woofers in the base of each speaker to also play OB like linkwitzlab. But I need a cheap woofer prefeerable no more then 15$ each. Partsexpress has some 12" woofers around 10$. Will they work in OB to fill in the low end from the NSBs? I will go active on all speakers not by necessity but because I can and it will be cool But I wll do so via a PC solution running crossovers in software and also DRC.

If I don't like OB then I might be able to do a ported box and get some bass out of the NSB. I want to mimic the THX spec and make the surrounds go down to at least 80hz and then the subwoofer will take over. This way the speakers will be 2way and I will save some funds both in woofers and additional soundcard for their crossover....

But back to the in-wall topic....What to do here?
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Old 14th November 2005, 12:56 PM   #8
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Sealed enclosures for the in-wall jobs, or perhaps small reflex tubes. Grab a copy of WinISD (its free) and play around. You're never going to get monster bass, so go for a the flattest response you can. For background music, who cares anyway about if there's much bass -it's background, so serious listening is out. Beating Bose? Not difficult I assure you (loathsome things).

I don't know about the $10 Partsexpress woofers -what's their Xmax? You need a high Xmax if you're going dipolar because the driver has to work much harder than it otherwise would in a sealed or reflex enclosure. That's the hugely simplified version, there's more to it than that of course, but it serves as a good basic guide. If it's not particularly large, you can always go sealed, or bipolar push-push, or even vented -it would be a pity though, becuase the greatest benefits with dipoles are at the lower, not the higher end of the audible frequency spectrum (ironic, as that's the hardest place to get them working properly!)Chances are you will like the sound of OB speakers, though they take a little getting used to, because the colourations enclosures invaritaby add, and that most of us are used to, will be gone (a decent TL is probably the most neutral enclosure).

If you're going full-range with a line array, those drivers will need to be as close to each other as possible (think -frames touching, or 1mm apart at the most) to minimise comb-filtering. It might also be worth either mounting them on a concave, rather than vertical baffle, or heavily power-tapering the line.

Best
Scott
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