New Build CJD (Chris) MTM RS150

[mabrandt]

Hello all. I was directed here from the AVS forum. WHat a wonderful place. Wish I had seen this when I was building my sub a few years ago. I had a lot of fun doing that so I thought I would tackle mains and a Center next. My main concern is that I have a size limit on my center channel. It needs to fit in a space that is 18in wide by 6 3/4 inches tall. Using this space limitation, is it feasable to get a great sounding center with matching mains? As for the mains, large bookshelf type is what I'm looking for. I prefer that over towers. I just want them to match the center. These are for HT only. I do not listen to music over these speakers. That is another system in another room.

I have read another thread here that had the same problem, but that was a 6in max height. With modification, I might be able to go 7in. 18 max width is it tho. I did see one design, the Bose Buster that is almost perfect, but is there anything else I should be looking at. I'm still new at this and can follow directions very well even if I don't know the theroy behind a lot of this. It just needs to be detailed enough so I can do it.

[ThomasW]

My main concern is that I have a size limit on my center channel. It needs to fit in a space that is 18in wide by 6 3/4 inches tall. Using this space limitation, is it feasable to get a great sounding center with matching mains?

Hi,

You can get good quality sound but you won't get a good output level match since the size of the drivers in the center will be significantly smaller.

The Bose -Busters are a cute little speaker and work great as computer speakers. They can't possibly move enough air to function as a center in a real HT unless you're sitting just a couple feet in front of them.

The smallest 'real' center we have is CJD's at 7.5" ....

http://www.htguide.com/forum/showthread.php4?t=19887

The length can be reduced to 18", by leaving out the port.

[DeathMonk]

The Bose Busters have a center design..

That being said, it sounds like you have room for something bigger for L&R. Any bookshelf design you see around here would most likely sound better.

[mabrandt]

Hi,

You can get good quality sound but you won't get a good output level match since the size of the drivers in the center will be significantly smaller.

.

We rarley if ever crank it up to reference level. This being the case, does matching output level matter? Right now I have entry level JBL E50's for my mains and a their matching 2way center channel. I'm looking to improve this. Fortunately, I have all the tools and stuff and I sure had fun with the sub. Looking forward to this.

[---k---]

This is the forum of overkill. We like to build them big here. Which is unfortunate, because a lot of people come here looking to build small speakers.

Can you put the center channel on a shelf above the tv? If not, you might want to ask on the PE website. They have a larger variety of projects, though I don't have the experience with them to vouch for their quality. Several designers over there do good work.

Another approach you might want to take is to work with someone like CJD or Curt Campbell on a custom center. You pick the drivers (with help), build the box, ship them the box, wait, wait, wait, have them measure it and design the crossover, you finish the project. This is how the Khan's project has gone for me. It is enjoyable and gives me satisfaction of being a proud parent when others build my design, but I don't have to do the hard work.

(There are also people at PE's forums who will design crossovers for others based on manufacture plots and all computer simulations. This isn't the best way to do it, and doesn't get every drop of performance out of the driver, but it can provide satisfactory to good results.)

[Undefinition]

My main concern is that I have a size limit on my center channel. It needs to fit in a space that is 18in wide by 6 3/4 inches tall.

Isn't that about the same size as the TriTrix?

[mabrandt]

Isn't that about the same size as the TriTrix?

It is! The TrTrix is just a hair too wide at 20 inches. With a little inginuity, I could probably get something 19" wide into there. What it actually is for is a space that was supposed to be for a VCR. My first center channel was one of the old Radio Shack deals. It fit this perfectly and was not a bad speaker. The JBL I have now also fits. To be honest, I think the Radio Shack speaker sounded better. I have never liked the JBL. A question tho, The space for the center channel is enclosed except for the front. Does this present any problems?

[ThomasW]

We rarley if ever crank it up to reference level.

No one in their right mind listens at reference levels or they're quickly deaf.

The idea is to have enough Vd (aka swept volume of air) so as not to stress the drivers. How much Vd is needed is a function of the size of the room, distance from the speaker to the listening position, and how loud you want the speaker to play.

[mabrandt]

Hi,


The smallest 'real' center we have is CJD's at 7.5" ....

http://www.htguide.com/forum/showthread.php4?t=19887

The length can be reduced to 18", by leaving out the port.

This is also being recommended by others. In looking at the box plan, it shows it 21 1/2" wide on both the ported and non ported versions if I'm looking at it right. How do I adjust for that? If I go with this design, I'll probably want to do the ported version for the mains as I have no space limitaions other than they can't be the tower version. The proted non tower is fine. I don't think I would have a problem mixing ported for the LR and non ported for the center, would I?

BTW, my surronds are inwall Polks and unless I come up with an inwall design, they'll have to stay that way to keep peace. I'll cross that bridge after the fronts are done.

[johnathanwinter]

would it be possible to make this a built in? dont think about sliding the actual speaker cabinet into the space but make the entertainment centers' vcr slot the speaker cabinet. a couple of inches could be gained that way.

[mabrandt]

would it be possible to make this a built in? dont think about sliding the actual speaker cabinet into the space but make the entertainment centers' vcr slot the speaker cabinet. a couple of inches could be gained that way.

It is probably doable, but I am not sure how it would sound or anything. It is thin around the sides and the base is not very thick. I would also hate to mess it up as it is perfect for my tv, that is why I am trying so hard to keep it. The new XBR6 fits perfectly into it. It looks like it was custom built around it. If I can get this sized right, it will fit tight and look like a built in. I'll put the speaker cloth over the front and it will look like part of the cabinet. I won't even have to worry about a finish then.

[johnathanwinter]

It is probably doable, but I am not sure how it would sound or anything. It is thin around the sides and the base is not very thick. I would also hate to mess it up as it is perfect for my tv, that is why I am trying so hard to keep it. The new XBR6 fits perfectly into it. It looks like it was custom built around it. If I can get this sized right, it will fit tight and look like a built in. I'll put the speaker cloth over the front and it will look like part of the cabinet. I won't even have to worry about a finish then.

right on. good plan.

[ThomasW]

This is also being recommended by others. In looking at the box plan, it shows it 21 1/2" wide on both the ported and non ported versions if I'm looking at it right. How do I adjust for that? .

By building a sealed box 18" wide.

If this is going in an ET center, the 'on-wall' version of the speaker should be used.

[mabrandt]

Thanks everyone for the suggestions. I have decided to go with CJD's design. Should I just start asking questions over on that thread (which I have read twice) or should I just continue here? Building a sub was one thing. This is a lot different.

[---k---]

Using this thread will work fine and is preferred by our moderators. You MAY be able to change the title of the thread. There is a time limit on that, so maybe not. no big deal. Just ask your questions here.

[mabrandt]

Using this thread will work fine and is preferred by our moderators. You MAY be able to change the title of the thread. There is a time limit on that, so maybe not. no big deal. Just ask your questions here.

Thanks! I went ahead and changed the title. Meanwhile here is an editied version of what I posted in the original thread late yesterday.

I have decide to build these for a LCR setup starting with the center. If anybody saw my original thread looking for design ideas, the problem I have is this center will have to go into my ET which is 7X18 slot. No problem with depth as it extends almost 3' back. I have been told there is no problem with cutting the width to 18in as it is a sealed design. Do I then have to make it deeper to make up for the lost volume? The other question I have is on the height. Can I just lower it to 7" without making any other changes. It was suggested to me to make it out of 1/2" mdf to get the correct height. Would that be feasable? The speaker will fit flush with the face of the ET center and the opening it fits into has rounded corners. This being the case, should I just leave the edges of the box square? Since the box is not seen, I have no plans to finish it except for the front. Is a grill advisable or can I just put speaker cloth over it before sliding it in? Any and all recommendations are appreciated. After I get this done, I'll make the mains. That should be easier as I don't have to resize anything. Getting ready to order parts.

Thanks for the help!

[mabrandt]

Another question as I'm getting ready to order parts here. On Chris's web site at http://www.eldamar.net/audio/rs150mtm/ I'm looking at the BOM and schematic for the crossover for the RS28AS on the wall. The BOM calls for 4 inductors and all I see are 3 on the schematic. I know they talked about using 20ga in the thread on the woofer side of it if it is going in an entertainment center. That's the situation here but I'm having trouble understanding which one I use and where. I am guessing the extra inductor is if using 20ga. Is it in addition too or replacing?

Also, I dismantled the trim on my ET this evening to see how this shelf is put together. I have discovered that if I have too, it can be lowered enough to fit the full 7 1/2" height. It will involve trimming some doors and stuff but if the folks here really think it is needed, I think I can do it.

[ThomasW]

Bill of Materials

    * (2) RS150-S8
    * (1) RS28AS-4/li>
    * (1) 12uF capacitor
    * (1) 15uF capacitor
    * (1) 35uF capacitor
    * (1) 45uF capacitor
    * (1) 18ga .1mH inductor
    * (1) 18ga .18mH inductor
    * (1) 18ga .25mH inductor
    * (1) 18-20ga .8mH inductor
    * (1) 6ohm resistor (10W+

Looking at the other RS28 designs they all have 3 inductors. So the 4th (.25mH) listed in this BOM is a typo

[mabrandt]

Thanks. I am ordering the parts today. Can anyone answer my box sizing questions? To sum up, if I make it 18" sealed, do I have to make it deeper than the 12 1/2 " as specified in Chris's drawing. The other issue is can I make it 7" high. If I do, do I have to change anything else. It was suggested I can get the 7" without changing interier size by using 1/2"mdf on the top and bottom and use extra bracing.

Thanks!

[ThomasW]

You can add depth to the box to recover what is lost by decreasing the width. All in all it's not going to be a big deal given the use of an 80Hz crossover point for a sub.

I'd stick with 3/4" MDF unless you want to switch to something $pendy like 1/2" Baltic Birch ply

[BeerParty]

Can anyone answer my box sizing questions? To sum up, if I make it 18" sealed, do I have to make it deeper than the 12 1/2 " as specified in Chris's drawing.

Yes, you should. Your goal is to keep the internal volume of the box the same (or reasonably close, anyway).

The other issue is can I make it 7" high. If I do, do I have to change anything else. It was suggested I can get the 7" without changing interier size by using 1/2" mdf on the top and bottom and use extra bracing.

There are multiple issues here - one is internal volume. Since you will be changing the depth of the box already (due to decreased width), you don't need to worry about internal volume (you can increase the depth some more to account for lost height).

Another issue is the baffle height - when talking about tower speaker designs the baffle width is critical to the overall "design" and the designers tell you not to change it. I would assume the same holds true for a center channel's height, but will have to defer to other more knowledgeable people here.

You also need enough height in this box so the mid-drivers will fit (inside and out). Since this is going into an entertainment center, you probably will not be rounding over the external edges, but you need to make sure that the RS150s will fit into a box with an internal height of only 5 1/2" (which is what you will have if you use 3/4" MDF in a 7" high box).

Edit - Opps, Thomas posted while I was writing my reply - sorry for the duplicate info

[mabrandt]

Another issue is the baffle height - when talking about tower speaker designs the baffle width is critical to the overall "design" and the designers tell you not to change it. I would assume the same holds true for a center channel's height, but will have to defer to other more knowledgeable people here.

You also need enough height in this box so the mid-drivers will fit (inside and out). Since this is going into an entertainment center, you probably will not be rounding over the external edges, but you need to make sure that the RS150s will fit into a box with an internal height of only 5 1/2" (which is what you will have if you use 3/4" MDF in a 7" high box).

Edit - Opps, Thomas posted while I was writing my reply - sorry for the duplicate info

The inside driver width is just under 5 inches at 4.7834645669343 according to the specs on the PE site, so it will fit. Since this is in an entertainment center and will be flush with the face of it will that kind of act like a baffel extension? In reading here I had the impression the NO BCS crossover was designed just for this situation. I would hate to go in and rip out and redo my ET center unless it really made a big difference. I'm willing to do it, but I want it to be worth it.

In the mean time I went to buy the parts at PE and I doubled checked my bank account to verify funds for Pay Pal. (I have a seperate account just to use for internet stuff) and I find out my PayPal has been comprimised. Somone purchased a computer and charged it to my account. The seller is actually in England. Still trying to straighten it out. Now I got overdraft fees and all kinds of stuff. I called Paypal and they said everything should be fine. I got home from work and had a voice mail from the seller. He actually called me overseas to verify the shipping. I called him back but got his VM. Here's hoping he didn't ship it yet. I guess I'll use my charge card for the PE order until this gets fixed.

[---k---]

That sucks. I hope PayPal takes care of you.

[mabrandt]

That sucks. I hope PayPal takes care of you.

And get this. I asked Paypal why I got no e-mail that a purchase had been made. They said there was and to check my e-mail provider. Well the hacker had also gotten into my email and put filters on my account to trash anything from ebay, paypal and the seller. All my other mail got thru so I suspected nothing. So until I went in this morning to check my balance, I had no idea. I still wouldn't if I hadn't looked. LIke I said, this account is set up for just this type of thing so I am not out that much and Paypal says I'll get it back. Just a warning. I guess we should have different passwords for everything. He got the one and was able to get into my other stuff.

[mabrandt]

One of these days I guess I'll figure women out. This whole business of fitting it into the VCR slot was at the insistance of my better half of 30 years. As I was taking measurments last night to see what needs cutting to get it fit I was told in no uncertain terms that no cutting or modification to the ET will be allowed. She asked my why I don't just put it on the top shelf above the display. Duh! I asked that last week and was told it had to go where the old one was.

So anyway, I still want to do the same speakers, but now that I am putting it on a shelf just above the TV or maybe on the same shelf as the TV with the TV sitting on the speaker itself. (My Preference as it puts it in exact line with the mains height whereas with the VCR shelf it was lower than the mains), do I still do the inwall version?

Thanks!

[BeerParty]

So anyway, I still want to do the same speakers, but now that I am putting it on a shelf just above the TV or maybe on the same shelf as the TV with the TV sitting on the speaker itself. (My Preference as it puts it in exact line with the mains height whereas with the VCR shelf it was lower than the mains), do I still do the inwall version?

At this point I think you need to post a picture of the entertainment center.

[---k---]

Yes, you still want to use the on-wall version.

[mabrandt]

Here's a picture. This afternoon I moved the center I had up to where the new one will be. Excuse the mess as I have been playing around with it. The speakers to either side are my wife's stereo and the ones on top of them are the HT mains. I was reading a post elswhere here that was joking about using speakers for stands. LOL We have done it for years. These will be where the new ones will go. Puts them at ear level. I had tried the center right under the tv like I posted above, but it looked stupid. So up on top it goes. I have it angled down slightly and it actually sounds much better then where I had it. I have unlimited room up there.

[BeerParty]

So up on top it goes. I have it angled down slightly and it actually sounds much better then where I had it. I have unlimited room up there.

In this case I would go with the original baffle size per CJD's design, using the on-wall version as suggested.

[mabrandt]

In this case I would go with the original baffle size per CJD's design, using the on-wall version as suggested.

Sounds like a plan. For the mains that sit flush with the front on the left and right, would those also be considered InWall? Also, the plans call for 20ga inductors for an "in cabinet" design. I'm curious if this center on that top shelf considered to be in a cabinet? I don't think it is but I'm new to the way the sound waves and crossovers work.

Last question for a while. CJD recommended felt to cover the baffle if using speaker grills. I researched this and plan to do this. I read all different things about the thickness of the felt to use. What would be recommended here?

[ThomasW]

The plans call for 18-20 gauge. I'd use 18 gauge.

In-wall or on-wall really means the speakers are placed close to walls or structures that form boundaries that interact with the speaker.

Standard designs are engineered for the speakers to be place 2'-3' away from anything that works as a boundary.

Worry about felt when the speakers are built.

[cjd]

The 18g vs 20g difference is a slight reduction of energy on the bottom end through the increased impedance. In your use I'd agree with Thomas.

As it is, this design is expected to be closer to boundaries than most - it goes a bit anemic on the bottom end out in the middle of a room. Then again, I'm comparing to dual 10's which I find weak compared to quad 15's in the IB (I'm still trying to figure out how to get an IB to my living room... heh)

Felt, when you get there, is optional but helpful. You may not hear the difference in having it. Wool works best. Synthetics do very little. You can actually use old wool socks or sweater to great effect should that seem more promising (heyyyy, I could have my wife knit baffle covers for diffraction control! now there's an idea... combine both our hobbies....)

C

[mabrandt]

Thanks Chris, Thomas! I just finished with the straight cuts and will start tomorrow on the rest. Parts will be here Tuesday. Hopefully I'll have the center done in a few days.

[mabrandt]

Yesterday I got the box pretty much together, at least the sides, top and bottom and the bracing. I am waiting for The Jasper to cut out the driver holes before putting it on. It should be here today. I have 3 questions I am not clear on.

1. I see a lot of folks double up the front baffel to make it 1 1/2" thick. I know I did this on my sub. Is it necessary in this design? It didn't look like it on the plans. Not sure if it will make a difference or not.

2. Not wanting to mess with fiberglass, I ordered 2" wedge foam from Foam by Mail. Will this be sufficiant or will it be overkill? I saw other posts and 2" seemed to be what everyone was using.

3. What gauge wire do I use for connecting to the crossover and the connections in the crossover?

Thanks for the help. It's coming along.

[1Michael]

Always double up the baffle... :T

[mabrandt]

Always double up the baffle... :T

If this is true, why is it never shown on the cabinet drawings? You would think it would affect internal volume measurments.

[cjd]

It is not necessary - with the RS150 it takes extra work to clear out behind them on a 1.5" thick baffle as well, and I don't think these boxes have the width to support that!

[mabrandt]

2. Not wanting to mess with fiberglass, I ordered 2" wedge foam from Foam by Mail. Will this be sufficiant or will it be overkill? I saw other posts and 2" seemed to be what everyone was using.

3. What gauge wire do I use for connecting to the crossover and the connections in the crossover?

Thanks for the help. It's coming along.

Thanks Chris! Can anybody answer the other 2 questions?

Mark

[savage25xtreme]

Yesterday I got the box pretty much together, at least the sides, top and bottom and the bracing. I am waiting for The Jasper to cut out the driver holes before putting it on. It should be here today. I have 3 questions I am not clear on.

1. I see a lot of folks double up the front baffel to make it 1 1/2" thick. I know I did this on my sub. Is it necessary in this design? It didn't look like it on the plans. Not sure if it will make a difference or not.

2. Not wanting to mess with fiberglass, I ordered 2" wedge foam from Foam by Mail. Will this be sufficiant or will it be overkill? I saw other posts and 2" seemed to be what everyone was using.

3. What gauge wire do I use for connecting to the crossover and the connections in the crossover?

Thanks for the help. It's coming along.

I used all 16awg silver plated teflon coated hook-up wire for midwoofers and my tweeters. I think 12awg is recommended for large woofers. that 2" foam should work much better than the fiberglass, but maybe too good? I would keep it back a few inches from the baffle/drivers and you should be fine. :T

[acacia987]

I used all 16awg silver plated teflon coated hook-up wire for midwoofers and my tweeters. I think 12awg is recommended for large woofers. :T

Where did you purchase your hook up wire from?

[savage25xtreme]

a link Thomas posted in someones Statement thread....

hook-up wire

[---k---]

CJD and I've both used the silver plated wire from Apex Jr (link above). Very nice stuff. Solders real easily.

I've also used regular 14ga stranded wire from Home Depot and some real cheap 14ga stranded wire from the Menard's automotive department. I haven't attempted to hear the differences, because I doubt that I can. I pretty much believe that the wire from good wire from Home Depot or where ever will get you ~98% of the way there, and provides the most minor improvement, especially when compared to upgrade drivers or electronics. Use what your budget allows.

I use all 14 ga, because I have a stock pile of it. For the short lengths, it is adequate for woofers and all. Smaller gauge wire is nice for soldering to tweeter terminals and stuff, where you don't want to heat it up. USE DISCONNECTS, DON'T SOLDER TO THE TWEETER, though I've done it.

Damping is something that needs to be experimented with. The 2" foam is what a lot of people use. Try it out. Take some out, add some, add some pillow stuffing, take some out. See what you like. The RS150s seem to be very sensitive to stuffing.

[savage25xtreme]

I use all 14 ga, because I have a stock pile of it. For the short lengths, it is adequate for woofers and all. Smaller gauge wire is nice for soldering to tweeter terminals and stuff, where you don't want to heat it up. USE DISCONNECTS, DON'T SOLDER TO THE TWEETER, though I've done it.

this is one nice thing about the silver plated stuff... heats up really fast and solders fast so your not sitting there with your iron on the tiny tweeter terminals. just tin both with solder hold them together and put the iron on the wire... just takes about 5 seconds. I soldered mine on my BAMTM, worked great for me. maybe its a no-no...

[mabrandt]

Damping is something that needs to be experimented with. The 2" foam is what a lot of people use. Try it out. Take some out, add some, add some pillow stuffing, take some out. See what you like. The RS150s seem to be very sensitive to stuffing.

How is the foam lining the box changed after the cabinet is done? Do you just go in thru the woofer holes? I can see with stuffing, wasn't sure about the sides and how to play with that unless I left one side just screwed on. I was planning on glueing up everything. What does too much stuffing do to the way they sound? A sound neophite needs to know what to listen for.

Sorry for all the noobie questions. Until recently I was perfectly happy with my setup. Then due to a lip synch problem with my TV provider that they can't seem to fix I went out and bought a mid level receiver to replace my entry level one. This has controls to adjust the sync. The difference in sound was very noticible and with that in mind I was wondering what "good" speakers would do as eveything I read in the receiver forums says speakers effect it more than the receiver. I built the sub a while back and had fun doing it so here I am. So far so good.

Thanks for all the help!

Mark

[savage25xtreme]

what receiver did you get?