tall thin symmetrical wallmount... oh dear.

[tresch]

Hey guys! It's been awhile since I've done a speaker build, but I'm finally gearing up to do a couple more for some friends! The problem is that I've been out of the game for so long that I'm really running in to some mental blocks and I could certainly use an outside perspective to help point me in the right direction.

I'm building a set of wall-mount speakers for a friend. I should note up front that while I'm generally a function-over-form guy, in this particular case FORM is getting a bit of a nod over function. I've already built this fellow a full-on home theater system so that's what he uses when he wants the best quality sound, this installation is going in his living room and he's primarily concerned about it looking nice. Everything wall mounted with no visible wires.

To get down to the nitty gritty, I want to make some tall narrow speakers that mount flush to the wall for a nice lean look. For acoustic loading, if I can get away with it within the shape, I'd just do a ported design, but the long narrow shape seems to lend to a MTBL (is that the right abbreviation?) type of design, but I haven't touched anything quite that complicated yet. Plus, instead of being mounted at the top of the "tube," I want these to be vertically symmetrical, so the speaker is right in the middle of the thing.

For a driver I'm going to be using a MarkAudio CHR-70.

The problems I'm worried about:
1) Long and narrow will cause big internal resonances.
2) Said resonances will interfere with port tuning (unless very finely calibrated, at which point they can help?)
3) Speaker being mounted in the middle of the tube will make said peaks/nulls even worse

I know much of this can be alleviated with tons of stuffing material.. I was also thinking I could taper the top and bottom ends to help alleviate vertical reflections, but I'm wondering if port placement is going to be critical, or if there's a better way entirely...

Ultimately I should probably just build a prototype and see what happens, but I'm a bit nervous! It's been so long! I think mostly I just need some encouragement

For your viewing pleasure I have included a high fidelity visual aid

[chrisb]

2 C only, or will there be a center channel and bass management to LFE channel?

If the latter, you don't need LF extension any lower than say 100Hz, and could probably get away with something much smaller for the CHR70 - attached is a quickie concept of wall mount front row array (and wall mounted dual woofers) that as it happens, I've got on my bench at the moment.

A single continuous cabinet houses the L/C/ R and includes space for 2 open shelves between for chachkas or other family rated audio accessories. The cabinet can easily be hung on the wall with shop made French cleat, or Monarch Metal Fabricators Panel Z clip - indeed the trickiest part of the install is tidy feeding of wires to the enclosure

[tresch]

Two channel only, port tuned to 40-45hz or so, with a low frequency high pass filter to protect the drivers from big super low stuff

[planet10]

Originally Posted by tresch

Two channel only, port tuned to 40-45hz or so, with a low frequency high pass filter to protect the drivers from big super low stuff

CHR should be easily made into a thin box... you'll have trouble making it as big as you have drawn, i calc optimum size for CHR at 9-10 litres (and tuned a bit higher than you have indicated)

dave

[chrisb]

Originally Posted by planet10

CHR should be easily made into a thin box... you'll have trouble making it as big as you have drawn, i calc optimum size for CHR at 9-10 litres (and tuned a bit higher than you have indicated)

dave

Originally Posted by tresch

Two channel only, port tuned to 40-45hz or so, with a low frequency high pass filter to protect the drivers from big super low stuff

you should find something here

http://homepage.mac.com/tlinespeaker...aps-150909.pdf
or

http://homepage.mac.com/tlinespeaker...dix-191209.pdf

that would meet or be adapt to your requirements - just don't expect any deep bass without strain

[mashaffer]

For your form factor I would strongly consider transmission line or back loaded horn as that would allow you to put the excess space to good use. About 1/2 ft^3 is all that you want for a BR tuned to 40Hz.

I have played with this driver a bit (I am using it in my mini-console project) and in BR tuned to 40Hz with 2nd order HP filter it sounds quite nice but it is very easy to push it overly hard. Playing some African drums using a SE KT-88 power amp (and not at full output either) I was getting a little nervous about the excursion.

MiniConsole Speaker Enclosure Beta Test - YouTube

So I decided to put them in sealed enclosures and cross over to 8" woofers at 100Hz to prevent them falling prey to youthful indiscretion... not my youth mind you. In a second test using a non-optimal 8" I had on hand I found that the combination had much more authority and clarity even on mid-bass like tympani due, I presume, to not only the sturdier bottom end but to the FR being relieved from the stress and resultant distortion of high excursion.

Just something to consider. Great drivers IMO but best to remember that you are dealing with a 3" cone with only about 3mm Xmax and not much buffer beyond that.

Mark does have a woofer that could be used to augment if you wanted to go all MA or you could opt for one of his slightly larger FRs.

[tresch]

Actually, the dimensions I'm looking at aren't that far out of line. I want it to be sleek, slim. Right now the internal dimensions are 6x4x38 which is just a hair over 1/2 ft^3. This is just a test box, the final will have less internal volume due to the driver, the bracing, and the port(s).

Doing something transmission liney would be awesome, but I do not currently possess the knowledge to do that right.

I've built several boxes with these speakers (both ported and sealed with EQ) and are fairly comfortable with what they can handle.

My primary concerns are not the volume of air or the capability of the driver but specifically the SHAPE of the enclosure since it's so long and tube-like. I finally got around to just building a test box of the dimensions above and I'm going to take some measurements just to see how bad the internal reflections are and what sort of countermeasures I need to take to compensate. Wish me luck!

[Jim Griffin]

Tresch,

I've designed several mass loaded transmission line speakers (just search this forum for examples of my MLTL work) for drivers like the Jordan JX92S, Mark Audio Alpair 6, 10, and 10.2 plus CSS FR125, WR125, and EL70 (Mark Audio built) drivers. All of these designs place the driver a third of the way down the line so that the frequency response ripples are minimized. Martin King's MLTL spread sheets were used for these designs so a CHR70 variant would be likely realizable. MJK's designs take into account the placement of the port and driver within the tube so results are predictable and reliable. As the EL70 and CHR70 drivers are close family cousins, check out my design of a offset EL70 bipole MLTL at:

Offset Bipolar MLTL with CSS EL70 Drivers--Part 1

and the offset bipole drawing under my name at:

http://www.planet10-hifi.com/boxes-CSS.html

My bipolar design uses two MLTLs sandwiched back to back but for your needs you would have one MLTL mounted on the wall with the port exiting on the front of the speaker. The internal dimensions in the referenced post for this design are 27 sq. in. cross-sectional area and a 39" long tube. Those numbers are close to your desired values of 24 sq. in and 38" long. While not symmetrical as you desired, once you place a grill over the front baffle it would give you the tall, slim look that you sought.

Jim