Anatomy of a Natalie-P / Modula MTM Tower

**Hdale85** · 24 July 2006, 13:18 Monday

I like that mahagomy ply...I wonder if I can find that around here.....too many decisions!

**Brian Walter** · 24 July 2006, 13:38 Monday

Originally posted by dCraig

3 - What should the port length be for a downfiring 3" port in a cabinet this size? I am Unibox challenged at the moment.
Comments?

If you are going to be setting the speakers on spikes right on top of carpet, I don't think you can use a downfiring port. You will need to go out the front, back or similar. As to the size, I would simply go with what is recommended in the writeup which I think is a 2" port. I don't think a pair of RS180's move enough air to need a 2" port.

Brian

**seattle_ice** · 24 July 2006, 14:19 Monday

Originally posted by Brian Walter

If you are going to be setting the speakers on spikes right on top of carpet, I don't think you can use a downfiring port. You will need to go out the front, back or similar. As to the size, I would simply go with what is recommended in the writeup which I think is a 2" port. I don't think a pair of RS180's move enough air to need a 2" port.
Brian

I think he meant 3".

**MarkR** · 25 July 2006, 04:24 Tuesday

Nice work dude. :T

1: 14ga wire is fine.

2: I'm not sure about the egg crate mattress stuffing, IMO these speakers deserve better. (maybe a real eggspert can chip in

ops: )

3: 11" (28cm) is the recommended port length for a 50l cabinet, IIRC down firing port onto the carpet is ok although the clearance between the port/speaker and floor should be as close to the diameter of the port as possible, you might be a little short on this number.

And yes they will definately move enough air to justify a 3" port.

**JonW** · 25 July 2006, 10:43 Tuesday

I'm not sure those Totem claws will provide enough clearance for the bottom firing port. I've got a pair of Totem speakers on claws. I haven't measured it, but I'd guess there's only an inch or so between the bottom of the cabinet and the floor. That might not be enough clearance for your port to flow freely. Just something to think about. And your woodworking looks very nice. :T

**dCraig** · 25 July 2006, 16:29 Tuesday

Originally posted by MarkR

Nice work dude. :T

1: 14ga wire is fine.

2: I'm not sure about the egg crate mattress stuffing, IMO these speakers deserve better. (maybe a real eggspert can chip in

ops: )

3: 11" (28cm) is the recommended port length for a 50l cabinet, IIRC down firing port onto the carpet is ok although the clearance between the port/speaker and floor should be as close to the diameter of the port as possible, you might be a little short on this number.

And yes they will definately move enough air to justify a 3" port.

Cool. I did the math by hand on the port size and length and it came out to 11.2 inches length for a 28 hz tuning with a 3" port. Jon Marsh recommended 11 inches and a Fb of 28 hz for maximum bas extension. I will probably still go with down firing since I bought Precision ports and the 11 inches would be too long to do a rear firing port. I will need to raise this up so the claws would be out. Oh well, I guess I can use them later. I am still toying with the idea of using a 90 degree bend with PVC but that is more work because I will have to create mdf flares for both ends AND the thickness of the PVC steals away more volume. I REALLY hate the idea of down firing ports, though!!!

**dCraig** · 27 July 2006, 00:38 Thursday

Updates coming tomorrow. Took some pictures of the crossover layout and one completed box. Pictures on the way.

**Hdale85** · 29 July 2006, 02:39 Saturday

What happend to that update! :P

**dCraig** · 29 July 2006, 13:40 Saturday

Originally posted by Dougie085

What happend to that update! :P

Had to get on a flight to Africa and ran out without making the post. All my pictures are at home. I will see if I can get access but I may be out of it for another 10 days

ops:

But here are some upodate comments. I put the crossover together and it fits through one of the woofer holes. Finished the sides of one speaker and assembled it but am going to test the finish with a different textured paint. the rust-o-leum plastic paint collects lint and fingerprints. Not good for this speaker. I will have to put some kind of topcoat on it. I did the downfiring 3" port and it may be a good way to go. My totem claws may actually work since I will put solid mahagony feet on the speaker exactly where the claws should go. That will allow me to raise it off the floor 1-1/2 to 3 inches at will! Cool. I lined the insides with the eggcrate foam but ay replace it if I don't like the way it sounds. Is sonic barrier worth trying? Turns out PE sent me all the parts I ordered but my order was missing a few caps for the second speaker. I think it should take me abotu three days to finish this when I return August 10th. Good thing I will be on vacation then.

**Hdale85** · 29 July 2006, 23:13 Saturday

You used that beautiful Mahaghomy ply and your going to paint over it!?!?!

**WillyD** · 29 July 2006, 23:35 Saturday

Originally posted by Dougie085

You used that beautiful Mahaghomy ply and your going to paint over it!?!?!

No kidding! What gives?! 8O

**Hdale85** · 30 July 2006, 00:18 Sunday

I wish a place around here carried that stuff....all I can find is Birch and Oak ply.

**dCraig** · 30 July 2006, 09:21 Sunday

Originally posted by Dougie085

You used that beautiful Mahaghomy ply and your going to paint over it!?!?!

Well, no. I used the mahagony for the baffle, top, bottom, and back. The sides are 1" mdf painted black with a 30 degree bevel cut along the front vertical edge. That way, the mahagony looks sandwiched between two black sides. Man, I wish I had remembered to post those pictures! I get the mahagony at Atlanta wood products, a local wood supplier. Depending on whether they are having a sale or not, it goes for about 50 dollars for a 4' x 8' x 3/4" sheet. It is veneered on both sides (nice equilibrium) and comes in medium and high quality. They also sell cherry, birch, walnut (I think) and oak. It really helps if you don't feel like doing your own veneer but you have to do those miter cuts (which can be difficult) or do edge banding (which does not look as good). I'm siting in Cape town trying to figure out how to get access to my servers at home to get the pictures. No luck so far.

**yousuredo2** · 30 July 2006, 10:06 Sunday

go to my pc...as seen on tv LOL

chris
Hey by the way, where are you around town...
I ive in dallas, about 25 miles west of atlanta...I would love to check em out at somepoint, if you dont mind...

**dCraig** · 30 July 2006, 14:11 Sunday

Sure. Once I finish the speakers we can plan a shootout!

**dCraig** · 09 August 2006, 01:39 Wednesday

Back online for a short time. Stuck in an airport in Germany for 5 hours. Africa to Germany to Atlanta in only 26 hours - what progress! Man, planes hate me. Anyway, I thought I would post some sketches of the finished speaker so you folks could get an idea of what the final product is supposed to look like. Snce I can't get to my actual photos I did these in Google sketchup and then took screen shots. Worked well. Thanks to Chris (whoever you are) for modeling the Dayton Drivers in Sketchup. :T That made my life a lot easier - then again, I WAS watching (read that as "hiding" from) a leopard walking through our camp when I used those driver models. Ain't technology grand? I can use a laptop in the bush but can't get a copy of GoTo my PC. Let me know what you think and send suggestions so I can maybe make changes when I get home tomorrow.

Images not available

I still hate bottom ports but it was the easy route.

**dCraig** · 11 August 2006, 02:40 Friday

Finally got home and here are a few pics of the actual speaker box. Sorry for the fuzzy picture of the crossover. My wife's the photography expert and she was asleep. I plan on cutting out an access panel on the back if the crossover won't fit through the woofer hole.

Questions:
1 - I plan to finish the crossovers using Radio Shack 12 ga. hookup wire. Any problems with that, do you think? Should I go with a lower or higher guage?
2 - I put dampening material on all walls except the baffle. Is that too much? Should I leave the top without any dampening?

The basic crossover:

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Nice shot of the bottom port hole. Not yet cut for the other speaker.

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The skeleton and the sandwich.

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More to come.

**opt-e** · 11 August 2006, 03:16 Friday

Originally posted by dCraig

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Wow I'm really diggin' this look. Can't wait to see the final piece!

**Hdale85** · 11 August 2006, 03:55 Friday

Yeah that looks much better then I imagined

**WillyD** · 11 August 2006, 04:15 Friday

Dude, excellent work. I am impressed.

**yousuredo2** · 11 August 2006, 10:00 Friday

WOW, I caint wait to come check 'em out, in person...
Looks great, and I bet they sound as good as they look too !

Now i need to get me a setup of tools like you...
great job, and enjoy...
chris

**ThomasW** · 11 August 2006, 11:00 Friday

The Radio Shack hook up wire is okay. Since you've done such a nice job you might want to splurge and get some mil spec wire from Steve at ApexJr. 14 gauge is great for woofers and the 16 for tweeters. Or buy only the 16 gauge then double the runs from the inputs to the crossovers. We use this wire it for our fancy projects.

Can't answer the question about the damping until you say what damping you're using.

**dCraig** · 11 August 2006, 11:34 Friday

Originally posted by ThomasW

The Radio Shack hook up wire is okay. Since you've done such a nice job you might want to splurge and get some mil spec wire from Steve at ApexJr. 14 gauge is great for woofers and the 16 for tweeters. Or buy only the 16 gauge then double the runs from the inputs to the crossovers. We use this wire it for our fancy projects.

Can't answer the question about the damping until you say what damping you're using.

I think I will splurge for the wire, thanks.
I bought the standard Acoustic Foam Egg Crate stuff from PE. 2-1/2" thick.

**ThomasW** · 11 August 2006, 12:31 Friday

That's pretty thick foam given the relatively small cross-section of the box.

You'll want to experiment with the amount of foam. I'd start off lining the top, back and sides above the lowest brace.

If you assemble the port pieces with duct tape, it can be removed to access the lower part of the box. Then glue it together when all the experimentation is completed

OT: perhaps we can get people using the SketchUp to share all their files in a common place. That way people wanting to play around with various designs don't need to reinvent the wheel just to get started.

**yousuredo2** · 11 August 2006, 13:49 Friday

sketchup has an option to publish your design, you can add key words, ect, to make it easier for others to find...
and when you have skethup, you look for models, and search for (???) what ever you are wanting...

**dCraig** · 11 August 2006, 15:12 Friday

The version of sketchup that I use is a free download from Google and it has an automatic option to publish your designs or to publish models of things like drivers so other people can use them in their designs. All of the models are publicly available and free to use. This program is amazingly simple to use. I did the design belowq in less than 5 minutes. Its wonderful for visualization and you can do dimensioned drawings as well. Finally, tou can use textures from any picture for your surfaces, even Google earth maps. Not too shabby.

- Thomas, thanks for the insight on the damping. I will start experimenting. Another question:
- I had planned on building both the Nat-P and the Modula MTM crossovers for comparison. Does the difference in sound show up at moderate playback levels or does it only show up when you blast the system loudly? Is there a difference in efficiency?

**dCraig** · 11 August 2006, 15:27 Friday

Oops. I forgot to attach the skechup image I was referring to. Here it is. Took me less than 5 minutes to draw and I am a Sketchup beginner. It took longer than that for me to upload the picture to a hosting site and drop it into this forum.

Image not available

**dCraig** · 11 August 2006, 21:02 Friday

Decided to put the drivers in to see what this might look like. I still have no idea what the grilles will look like (2 year old prevention barrier). I hope the finish of the wood looks like the wood on the walls behind the speaker but I fear the speaker will be lighter shaded. When I built the wall the mahagony ply sold by Atlanta Wood Products was darker. I might use a little Tung oil to darken it up, though.

Image not available

**yousuredo2** · 11 August 2006, 21:07 Friday

Resized it for you...
so you can see it all in the same screen..

**dCraig** · 11 August 2006, 21:32 Friday

Thanks.

**Hdale85** · 12 August 2006, 01:59 Saturday

Thats nice.....looks rounded sort of even though its not? I like that a lot! Might have to do something simaler with my TMWW's

**dCraig** · 16 August 2006, 08:55 Wednesday

Listening impressions and driver screws:

I finished one speaker completely and hooked it up to listen to the sound. These are really nice. The voices are amazingly lifelike and clear. The bass response is still being tweaked but there is a decent amount of it on certain music.It seems to provide a little more thump down around 28hz than it does on themore boomy ranges. I still have to build a riser for it to sit on so that the port is far enough from the floor but so far, I am greatly pleased with the sound. More impressions and pictures to come as I finish the second speaker.

By the way, anyone use "Pocket hole Screws" to hold thier drivers in? http://www.woodcraft.com/family.aspx...d=4878&cs=cart
I happened to have some laying around. Take a close look at my large photo post earlier in the thread. I used two sizes of pocket hole screws and they give the speaker a real professional look because they use a special box driver instead of phillips head and they have washer pan heads. I really like the look.

**FlashJim** · 16 August 2006, 09:11 Wednesday

Pocket hole screws are strong as hell and have a good look. They should work fine. I considered them when I put the feet on my sub. I ended up going with beefier sheet metal screws. The only drawback would be if you had to pull the drivers out more than a few times. I'd go with t-nuts and bolts.

PM me sometime. We seem to like the same toys. Also, I lived in Gwinnett for 10 years.

**dCraig** · 20 August 2006, 22:27 Sunday

So I'm wondering if I did sometrhing wrong with my port. I made an 11" bottom firing port but I don't really hear a difference between speaker response when the speaker is sitting directly on the floor versus when it is raised up 3". Should the difference in sound be striking, or more subtle? Speakers sound great but bass response is still not large.

**ThomasW** · 20 August 2006, 23:01 Sunday

No reason there would be a performance difference between the two orientations...

What kind of bass are you expecting from a pair of 7" woofers?

Have you run any frequency response plots? There could be room induced issues. It's hard to say whats going on without something concrete for comparison.

**MarkR** · 21 August 2006, 00:04 Monday

A bottom firing port with the speaker/port sitting directly on the ground, should make a difference??

Remember the port needs plenty of room to breath inside the cabinet as well as out. Maybe too much foam/stuffing or woofers wired out of phase?

**dCraig** · 21 August 2006, 11:20 Monday

Originally posted by ThomasW

No reason there would be a performance difference between the two orientations...

What kind of bass are you expecting from a pair of 7" woofers?

Have you run any frequency response plots? There could be room induced issues. It's hard to say whats going on without something concrete for comparison.

The amount of bass I am getting is ok, but less than, say, my Spendor S5e which are in a cabinet almost half this size and using a 6" midwoofer with a passive radiator. Drivers are not out of phase and stuffing is minimal (just the back of the cabinet. I am not too worried about how much bass I get because I plan on using a subwoofer with these and they sound great. But, the height off the floor does matter to me since I have two different ideas for stands. My understanding from all the posts is that the port tuning changes based on how close it is to the floor. If it does not matter then I will just use my Totem claws (1.25 inches) instead of building slightly taller feet (2.5 inches).

**dCraig** · 21 August 2006, 11:35 Monday

Originally posted by MarkR

A bottom firing port with the speaker/port sitting directly on the ground, should make a difference??

Remember the port needs plenty of room to breath inside the cabinet as well as out. Maybe too much foam/stuffing or woofers wired out of phase?

Woofers are in phase. Minimal stuffing so far. I will play with it a little more. Perhaps the difference is in qulaity of the bass rather than quantity.

**ThomasW** · 21 August 2006, 11:36 Monday

Closer to the floor creates a resistive load that will boost certain frequencies depending on the height. Are these sitting on carpet?

The Spendors likely have a higher port tuning that could give the impression of higher output.

Might run some fequency response plot of both for comparison.

Properly tuned the NatP will have more low bass than the Spendors

**dCraig** · 21 August 2006, 12:08 Monday

Sweet. They are sitting on carpet and I have yet to cement in the port so I can change tuning. What I find is that the quality of the bass response is quite good. I often find myself noticing that I feel some of the low frquencies more than with the Spendors. There is no boominess to these Nats at all (which is good). I'm going to A/B the Spendors alongside the nats and then do A/B with my Vandersteen 2Cs as well.

**ThomasW** · 21 August 2006, 12:42 Monday

Put a board or piece of tile under them....

**BobEllis** · 21 August 2006, 14:25 Monday

Maybe your port is tuned too low and you are not getting the gain you should expect. If you used the 11" length mentioned earlier it is too long. I just had my first listen to a set of Nat-Ps of similar dimensions yesterday. Very nice!

The tall-skinny geometry creates a quarter wave resonator for which you can use Martin King's mathcad worksheets to predict the response. I used a 3" ID port with a 3/4" roundover on the mouth, rear facing. The total port length is 5.5" flare face to straight inside end. It makes a big difference in the bottom end when the port is blocked.

I stuffed it spreading 20 oz. of fiberfill through the top 2/3 of the enclosure. This gives in room response to below 30 Hz. A five string electric bass is solid.

Hope this helps.

BTW, the friend I am building these for is quite pleased. He didn't realize that I was behind him when his girlfriend asked him how they sounded. His answer was (bleep) unbelievable - so clean, great bass.

**dCraig** · 21 August 2006, 15:05 Monday

Originally posted by BobEllis

Maybe your port is tuned too low and you are not getting the gain you should expect. If you used the 11" length mentioned earlier it is too long. I just had my first listen to a set of Nat-Ps of similar dimensions yesterday. Very nice!

The tall-skinny geometry creates a quarter wave resonator for which you can use Martin King's mathcad worksheets to predict the response. I used a 3" ID port with a 3/4" roundover on the mouth, rear facing. The total port length is 5.5" flare face to straight inside end. It makes a big difference in the bottom end when the port is blocked.

I stuffed it spreading 20 oz. of fiberfill through the top 2/3 of the enclosure. This gives in room response to below 30 Hz. A five string electric bass is solid.

Hope this helps.

BTW, the friend I am building these for is quite pleased. He didn't realize that I was behind him when his girlfriend asked him how they sounded. His answer was (bleep) unbelievable - so clean, great bass.

I did the port length calculation by hand and in Unibox. Unibox said 12 inches while the hand calculation (based on precision ports instructions) said 11.2". My port is flared on both ends. I will try dropping it down to about 6 inches (Flare to flare) to see what happens.

**BobEllis** · 21 August 2006, 19:59 Monday

WinISD also shows a longer port, but the MathCAD sheets showed good response with the shorter length and moderately stuffed at the top. While a typical BR box will have the walls lined but usually the center open, this version is stuffed more like a sealed box. The stuffing kills the upper resonances while letting the primary one show through. (so you get the benefit of the boost without the ripples in response in the upper bass/midrange)

Unibox and WinISD do not take into account the pipe like nature of a tall skinny enclosure.