Converting stand-mounted speakers to "bookshelf" type

[SQconstable]

I'm planning to have SR71 Zaph kits all around (left, right, surround channels). The center channel will be placed on an Omnimount rack above the 65" Mits DLP TV (max load = 30lbs). I may want to build it with 5/8" thick wood (with good bracing of course) to keep it light as 30lbs isn't a good max to build by.. might be too heavy.

Here's the questions.. Is the reason that most people build a 2-woofer, 1-tweeter center channel design (WTW) because of symmetry? I would have no problem adding an ER18 woofer to the already "perfect" SR71 kit, but I'd have to figure out how exactly to change the crossover in order to accomodate impedance doubling/halving (and also crossover points would change). Would it not be a good idea to "simply add another woofer" to an already great design? What would be the easiest way to do that? I do know that cabinet volume would be double (2 woofers instead of 1) so that is one con.

This brings me to another thought.. why not just use one woofer like the rest of the mains to keep everything nicely matched/balanced? Well, the tweeter would have to be positioned above the woofer, and that makes the height of the enclosure larger, at least around the tweeter diameter. I understand that I don't have to encompass the tweeter inside the enclosure, and there are designs out there that just use open baffles to "hold" the tweeter.

Why not use an externally mounted supertweeter like in high-end designs? I know these are sometimes extraordinarily expensive, but it would look very low-profile and sleek! Is there an inexpensive external tweet for this purpose?

Lastly, I think about coaxials as a possible solution. I do love my center channel speakers to be large because there's a lot of midbass stuff there these days. It sounds much fuller with a larger woofer too.. I know that with a coaxial, I'd be cool with even an 8" and I'd mount that in a box that wasn't too wide. I was thinking a sonotube idea would be really cool, as long as 15" depth was enough (that's the depth of my DLP).

What would you do? Should I just use get another Zaph kit and use half of it for the center, and maybe the other half for the center back in an in-wall install behind me? Or should I just understand that the center may need to be completely different in order to work with the aesthetic aspect? I'm open to ANY suggestions here. Whatever idea I choose, I'm making the enclosure for the center to have a height that is just barely larger than the woofer diameter to help keep it more slim looking. Of course, this means it needs to be either wider or deeper, but what have you found to look best? Wouldn't a sonotube type center be best or would that increase the effect of "there's something big sitting ontop of the TV!" ?

[ThomasW]

IWould it not be a good idea to "simply add another woofer" to an already great design?

Nope bad idea. An MTM is a completely different design requiring a new crossover. And a horizontal MTM is another completely different speaker

What would you do? Should I just use get another Zaph kit and use half of it for the center,

That's probably your best bet

[---k---]

I bet Madisound will sell you 1 & 1/2 a kit.

The MTM layout suffers from bad off-axis response. I think they are manufacturer's favorite though because of appearances. A vertically orientated TM is often as good as anything. So, three matching speakers up front will be perfect.

Coaxials - if you can design it. But it sounds like you're better off using a proven design.

[SQconstable]

Cool.. So let's assume I'm using 1/2 Zaph kit for the center. How would you position the tweet so it doesn't create too much height in the box? I'm assuming coaxially mounting that tweet is out of the question since it would change the response of the woofer...

Is that 27TDFC tweeter something I could carve out some of its mounting plate so that it touches the woofer closely? Hmm.. or I could mount the tweet to partially cover some of the woofer's surround. That shouldn't cause the tweet to be too forward, should it? I could mount the woofer to be in front of the tweet some too. I just feel that this is gonna look ugly either way ontop of a 65" DLP. Mounting below the TV is not really an option. It would be cool if TV manufacturers somehow made acoustically transparent screens already!

Here's another thought provoking issue: My left-right mains and TV will be ontop of an entertainment console (not hutch, not a shelf). The best way to give an imagery of it is to compare it to an ordinary wide, dresser. I guess it could be considered a "shelf". Anyhow, at the seating position, to make the tweeter ear-level, I would theoretically need to do the unconventional feat of designing the enclosures where the tweeter is on bottom, woofer ontop. Is it that big of a deal for mains since center channel speakers are sometimes top-mounted with no real concerns there? Or does the "tweets at ear-level" ideal stem from 2-channel listeners? I know that there is s small deal of off-axis tweeter forgivenesses, but considering that there will be off-axis behaviour from having the mains fire straight ahead (not at the listener), would it be a good idea to keep the tweeter at ear-level, vertical-wise, to help not accrue to much off-axis-ness? hehe

[---k---]

Cool.. So let's assume I'm using 1/2 Zaph kit for the center. How would you position the tweet so it doesn't create too much height in the box? I'm assuming coaxially mounting that tweet is out of the question since it would change the response of the woofer...

You should mount it just like Zaph designed it, otherwise the design will be compromised.

[SQconstable]

Hmm. Would that be much of an issue to have a tweet on the side of a woofer as the case with his design laying on its side? Miniscule? Also, think there's any problem with changing the baffle dimension ratio so that it is a more slim enclosure?

.. would be cool to see a center channel top-of-tv, slim design for this kit

[cjd]

The changes you're discussing are generally called "a new speaker"

If you're mounting above the TV, flip it so the tweeter is on the bottom. Otherwise build exactly to spec.

It would be really cool if people stopped trying to compromise the heck out of designs to fit around "the big glass box"

C

[SQconstable]

Thanks for the input. I think I'll just turn the speaker sideways and deal with the tweeter on the side of the woofer.

[SQconstable]

Converting stand-mounted speakers to "bookshelf" type

For the main left and right speakers in my HT setup, I'm going to be mounting them ontop of a piece of furniture (90" wide, 23" deep, and unfortunately 32" high) that acts as a stand for the TV as well as a component cabinet. These speakers are Zaph's SR71 kit http://zaphaudio.com/SR71.html , which you may know were designed to mount atop speaker stands:

"Do not place these speakers right up against a wall, or on a bookshelf. They may be small speakers, but they are not "bookshelf" speakers. They are by design stand mounted main speakers. If you do, you might need to try the reduced BSC crossover. While the frequency ranges affected by baffle step and boundary reinforcement are different, they do overlap and as such one can help compensate for the other. Please be aware that wall or bookshelf mounting is a severe compromise and generally all rectangular box speakers will exhibit ragged midrange response in that case. "

Is it just the midrange that exhibits an adverse effect when shelf-mounting, or is it also the bass too?

What exactly is it that causes a tv-stand to act like a shelf rather than a speaker stand? Is it the extra surface area that causes these extra resonances, reflections, etc? I understand that some of these variables are affected by how close to the edge of the furniture the speaker is sitting.

Is there a way to prevent a shelf/tv-stand-top from behaving like a "bookshelf"? Decoupling cones for the speaker's feet? More distance between top surface of the "shelf" and the loudspeaker enclosure? Being closer to the edge?

What about other enclosure design-specific things like:

1) mount tweeter on bottom, woofer on top: would this effectively create more distance between the woofer and the shelf to prevent resonances associated with bookshelves?

2) design rear port to aim higher rather than close to the furniture's surface: it makes sense that sound sources next to a plane cause unwanted increases(sometimes desireable though)


If I do design the port to be directly behind the top-mounted woofer, it would cause problems though. If you wanted to put a speaker on a shelf, what would you rather be furthest away from the "shelf" surface, the port or the driver?

[ThomasW]

Threads merged...

Let's not start a new thread for every question you think up....

Crossovers are designed with Baffle Strep Compensation, aka BSC. If you use our forum's search function you'll find out what this is and how it impacts what you're describing.

And this should help

http://sound.westhost.com/bafflestep.htm

[cjd]

Thanks for the input. I think I'll just turn the speaker sideways and deal with the tweeter on the side of the woofer.

Sideways will result in less than desirable lobing. What's wrong with keeping it set up properly?

[SQconstable]

Thomas, I felt that this issue is one that more DIY people have thought about than not. While it may seem that I am just posting new threads that all have some relation, I'm trying to contribute real scenarios while labeling the subject line exactly pertaining to the topic without overlap. This will help those that are trying to search for relevancy rather than read through many pages trying to find key words (which is the case for forum software). The only real thing common that I have with these two different threads is that I'm using the SR71 kit. I've seen NUMEROUS threads from other people here that have divided topics but deal with the same set of speakers/projects. Horizontal mounting of speakers/drivers (plus the number of woofers to the enclosure) is a different topic imo than converting stand-mounted speakers to work better on a bookshelf. I'm not sure that people would click on an MTM/WTW thread title in order to find something about the stand-mounted-to-shelf conversion. As long as people can see both topics separated when they search, that's cool. If not, it defeats the purpose of a good search, thus the reason I created separate topics with precise subjects (who likes to read through vaguely-titled threads to find that it didn't have to do with what was hoped for)? I figured that, out of all members, the moderator would appreciate my considerate, precise labeling of the title. I'm a more search-based researcher/reader though so I gear things for those people that conduct searches.

I wish people were MORE specific about what the topics were in their thread titles. It may be more tidy to the mods but for us that actually perform a forum search, it becomes a headache reading through hundreds of pages with multiple questions by a thread poster. UGH. I see that the reason that the Edit happened in the first post was because "Reason: shorten title". If my title is too long, shorten the available characters in that field.

Anyway.. what's wrong with keeping it set up properly? My wife nor myself will like the look of a tall 2-way speaker sitting vertically atop an already huge TV. I doubt that many DIY'ers like the look of a speaker ontop of their TV in a vertical fashion.

On the bookshelf/stand topic... rather than resort to BSC (and unwinding of inductors), I was trying to think of ways of tricking a furniture surface into acting more like a speaker stand. It is the cheaper option for DIY'ers imo.

[Jed]

Solution- turn the speaker on its side to see how it sounds in your environment or application. If this is the kit you want you'll have to live with some limitations for room placement etc. Bottom line you may or may not notice any differences. Isn't there a thread somewhere for Zaph's kit?

Jed

[SQconstable]

No threads specifically for the SR71 except this one: http://www.htguide.com/forum/showthr...highlight=sr71

The above issues are more of a general area of interest, not just something pertaining to the SR71 though. If I decided to not go with the SR71 combo for the center, I'd still follow the general information when building any speaker. I've had all these questions prior to getting that SR71 kit, so posting there would have been off-topic. Now that I am getting them, I won't post there because I'd then be making double posts Can't win..

[cjd]

Most of this *has* been discussed in the past in various places. This kind of "can I change this existing design in this or that way" thread is probably a good candidate for stuffing into the FAQ section some day.

C

[SQconstable]

You're right - I'm sure it has been discussed too, but try searching for such topics.. there's no way you're going to be able to sit there searching every single vague-titled post by lazy members to find these things hehe... Rather than spend another 8 hours searching here and other forums, I feel that's the moment to make a new thread. The best thing that members can do is try to think about the approach of their thread topic and title it so others in your shoes will be able to see it in the search results quickly

[Dennis H]

SQ, you just don't get it. Speaker crossovers are designed for a specific baffle size, a specific baffle orientation and a specific speaker location relative to walls and other boundaries. If you want to change any of that, you're a test pilot. There is no generic "fix" to the crossover for changing any of those things. It's a brand new crossover with all the design skills, time and effort that implies.

That said, if you have a receiver with an auto-EQ system built in, you can (within reason) adjust for where you put the speaker without changing the crossover. The receiver will attempt to flatten out the non-flat response because of where you put the speaker. Probably not as good as putting the speaker where the designer intended but not terrible either.

[---k---]

You're right - I'm sure it has been discussed too, but try searching for such topics.. there's no way you're going to be able to sit there searching every single vague-titled post by lazy members to find these things hehe... Rather than spend another 8 hours searching here and other forums, I feel that's the moment to make a new thread. The best thing that members can do is try to think about the approach of their thread topic and title it so others in your shoes will be able to see it in the search results quickly

Please stop with the complaining about the forum software, the way people title their threads, the moderation efforts... Uuuughhhhhh!

[cjd]

You're asking people that are incredibly picky about performance. A lot of whom have gone out of their way to dig way too deep into the technical stuff to squeeze that last bit of performance out of things.

Imagine asking to borrow a bible to use to raise your computer monitor up a couple inches. Some people would think it a terrible thing. And some people would just see a book stuck under the monitor to prop it up a bit.

People do things we would run screaming from all the time. Hell, people actually like Bose and think it sounds good!

So. You can do these things. Zaph has laid out pretty well what he'll support - if it's not what he designed and it sounds bad, not his problem.

FWIW I think "sideways" speakers look ridiculous. And glass boxes (er... TV's). But then again, I'm doing an acoustically transparent screen with exactly matching mains behind it... Like I said... in waaaay too deep, maybe. A purist, certainly. I mean, I'm making sure to measure and design the speakers behind the screen so it's *all* in the data and is *just* right.

On baffle step: it's about radiation patterns, and you can't trick physics (except in the movies!) When it's on a stand, below frequencies defined by baffle dimensions (re: wavelength) the output radiates spherically - above, hemispherically. So you lose 6dB below this "step" frequency simply because of that radiation pattern shift. Lots of good technical info out there far more accurate than this brief synopsis.

However, this illustrates the trouble trying to somehow make this specific to n number of random setup configurations: on a stand, on a mantle, on a TV, in a shelf, under a TV, next to a plant, a stack of DVD's next to it, your neice exploring that soft dome tweeter... all those things officially change this (as well as diffraction patterns and other stuff). None of it simple. Zaph has gone and provided more options than most, and they'll work pretty well however you use them. Trend your setup and see which profile it fits best.

These little changes are small - very few people could ever notice them even in a direct A-B test, and I'd bet a great number of them hang around here. And even some of us would have to listen carefully. In the end the brain does a pretty amazing job of glossing over the little stuff.

The really critical range for things like intelligibility is above the point where much of this has significant impact: sound may be chesty or lean, but you'll still understand it. With a sideways speaker, there will be points off to the side where you *can* lose intelligibility. If you've a crowd over to watch something, turn the speaker for the occasion - otherwise, leave it in the preferred position for SAF (that's both spouse and self approval factor here).

By the way, thread titles? Conversations don't lend themselves to careful indexing by title. And many of these topics end up being conversational. It's not a place to jump in, get a quick answer, and leave. We suck you in, and you spend your entire work-day reading threads to glean knowledge.

C

[SQconstable]

Haha I am definitely sucked in. In fact, each break from work that I can get, I'm on here and diyaudio. Sorry about the complaining.. I just slightly got on the defensive when my thread was joined although I shouldn't have really cared. No offense to you Thomas - you've always been helpful to everyone! I've gained some good knowledge through all of you guys even prior to signing up in '05. I find I'm always coming to this place for each project so I'm sure I'll be making a donation at some point. Knowledge is free but it's good to pay the ppl that bring it all together.

I understand that the crossover has an effect on the design, but in my line of work (audio engineering), I'm one to believe the room has even moreso an effect on overall acoustics. True, the ear can compensate for problems in the response. OH screw it.. I'm now considering my entertainment console a speaker stand at this point :P

How important do you think Zaph's ratios are with the LxWxH? This system was designed specifically for Madisound's MD14 enclosure with the pre-cut baffle, he says. I guess I know the answer to that. I was just thinking a curved enclosure would be prettier.. hmm I wonder what microphone Zaph used. They all have different responses. I could just build what I want and then pic a mic that makes the freq resp look flat!

[Jed]

Keep the internal volume the same, and the front baffle dimensions similar. Many people have built/adapted curved enclosures for designs here at htguide.com, but they kept the most important variables constant.

As for your mic comment, that's what calibration files are for.

[---k---]

hmm I wonder what microphone Zaph used. They all have different responses. I could just build what I want and then pic a mic that makes the freq resp look flat!

If I were Zaph, I would be offended by that comment. You're not giving people enough credit for the amount of work that goes into their designs.

See here for Zaph's measurement setup: http://zaphaudio.com/setup.html

edit: the rest, for the Christmas spirit also.

[Dennis H]

Edit: Aw nevermind. Christmas spirit and all that.

[Dennis H]

Okay, trying again with a more constructive tone.

I understand that the crossover has an effect on the design,

I still don't think you get it. The crossover IS the speaker. I'll bet if you sent your Behringers to Zaph (along with a briefcase full of cash ) he could redesign the crossovers and what you got back would blow you away with how much better they sound. Those HF problems you mentioned would be gone.

[Jed]

Edit: Aw nevermind. Christmas spirit and all that.

:lol: Where is that Reiki meditation CD!

[SQconstable]

I got ya.

you should check out zaph's feelings on crossover components. I wouldn't have offended him with my mic comment. Everyone go to sleep!

[cjd]

Well... Zaph uses a calibration file so his measurements are accurate.

You're right, room has a HUGE impact. Not something you usually deal with in the crossover though, particularly on a 2-way. Some minor (and often easy to blend in design-wise) room treatments can solve any issues not in the bass region, and trying to solve bass room response in the crossover isn't gonna happen - the level of work and the cost to accomplish that is just silly.

What it boils back down to is, what boundary conditions do you have, and what crossover does that point to? If you have room issues, work with a digital EQ system and probably entirely with the sub, and no EQ on the mains.

C