Help choosing a design for some towers

[---k---]

Yes, the mids and the tweeter are in the same sealed chamber that is 6" deep by 16.2" high.

The Statements should be similar, though not exact. Looking at Jim's Cad versus mine, I got 11" wide, while he has 11.5" He used 3/4" roundover on the edges, I used 1".

Hopefully, I'll get some time this evening and post a link and all my construction photos. I took quite a few. I'll also get out the tape measure and double check that width. Maybe even figure out the depths for you.

Just remind me one way or another.

[bf_brock]

Thanks Ryan that would be great.

[tpremo55]

bf-brock: You'll have a very nice speaker with the Khans - I listened to them at the 2007 DIY event and was very impressed. Please be aware of some very significant differences between the Statements and the Khans however (in case you are not already). Besides the ported vs. sealed enclosures, the Statements have open back mid enclosures. As such, the crossover has significant modification to balance out the response due to additional reinforcement form the back-wave. The Khans (IIRC) were not open back mids (in fact, Ryan stated sealed above) and the crossover design pursuing. If you are looking for a nice enclosure design for a ported with a pair of RS225s, then the Statements are a great place to start. Be sure to remove the volume for the mid lines and bracing.

Good luck!

[---k---]

Yep, the width is 11". I think my Cad drawing is accurate. But, as they say: "Trust, but Verify."

I'm uploading the build photos now:

http://delayedbang.com/khanspire/Khanspire-Photos/index.htm

I'll be curious how you like them ported. In my 17'x17' room, they got good bass. I was listening to "Passion of the Drum" the other night (until my wife made me turn it down )

http://www.amazon.com/gp/product/B00006B1RI/ref=wl_itt_dp?ie=UTF8&coliid=I5Q9HHAMS7GH4&colid=5NCYKUSBPSUK

I flipped back and forth with and without the sub, I couldn't tell a difference. I saw signal to the sub on the Behringer DEQ display, but may be it was just really low. Those last two graphs are with and without the sub at each seat. You can see the type of extension and in-room response I'm getting. Though, I don't know how accurate those graphs are. That was my first attempt at measuring with a Maudio Pro and a real mic. I was having some problems getting the levels right.

[---k---]

Also, Note that I haven't updated the BOM and Crossover photos to CJD's new, improved crossover design. I'll try and update the BOM's this weekend. And, I just got the parts to rebuild the crossovers for the new version, so depending on how things go, I may get there - but doubtful.

[bf_brock]

Ryan - I didn't know CJD had a new and improved crossover. Definitely let me know how that goes once you get it assembled and let me know when you get the BOM updated. Thanks for the construction photos. Definitely helps to see how you did it. One question, why the use of two different kinds of damping materials?

Looking at those response graphs you are getting good in-room response from the Khan's. In my current house I probably don't need to go ported, the sealed would likely be more than adequate. We're probably only going to be living in the current place for another year. Once we move who knows how big the room will be that they get placed in. Might as well maximize the bass performance now. Besides is there such a thing as too much quality bass?

[bf_brock]

tpremo55 - My idea is to aim for similar volume and port tuning as the Statements have for the RS225's. That's pretty much all I'm taking from that design.

For down firing ports on these what is the recommended height off the floor? 2"-3"? Are spikes the preferred method of getting this height?

[---k---]

The updated crossover isn't radically different. It basically just a hair more aggressive at suppressing the metal cone resonance. It was pretty far down to begin with, so I'm not even sure if I'll hear the difference. The difference for me is 1 $5 inductor and a $2 cap. So, why not.

I used 2 different damping materials (OC703 and PE Sonic Barrier) because I ran out of the OC703. Actually, if you consider thickness, I used 3. I used 2" of rigid fiberglass on the back wall, then 1" everywhere else, and when I ran out I used 3/4" PE Sonic Barrier. The

For the bottom space, optimum you want same distance as the port diameter, so 3". 3" tall spikes is tough. You can see that Jim just built a wood base. I think this is where you need to be creative. You can port out the rear also like Todd did.

[bf_brock]

Ok, I think my original idea of how I was going to do the base plus spikes should work. Does it matter which damping material I use?

[---k---]

I got interrupted as I typed up that last response.

For mine, the box is big enough that I'm not using the foam/insulation to squash internal reflections that might reflect to the back onto the drivers. For this, the more the better, and hence using 2" on the back wall. But, this is likely a bit of overkill. Who knows. Overkill takes so little more effort.

With ported woofers, squashing the reflections is the only reason you'll need foam on the walls.

If you can get your hands easily on OC703, use it. Otherwise, I liked the PE Sonic Barrier. Use at least the 3/4" on all surfaces. If your budget allows, consider thicker on the back walls. Supposedly, in decent size orders, the Wispermat (which the sonic barrier is a copy of) can cheaper - only it doesn't have adhesive backing. JonMarsh and Zaph are fond of Wispermat.

If you're budget doesn't allow, several people have used egg create foam and say their happy with it. There are a lot of different opinions about this stuff on the net whether it is good or bad. Best not to get into it. Let your budget be your guide.

[bf_brock]

Another question - is the 1" round over required or any round over on the front baffle?

[---k---]

I'm going to give you the long answer to your question:

The mids and tweeter were measured in box, with the roundover in place. So, the crossover does take into account the edge treatment. Some people claim that the roundover doesn't make a difference. However, below is the simulated response of the mids and tweeter. You can see the difference the roundover makes. I think it can be quite a bit from 0" to 1" The difference between 0.75 to 1" is small.



Driver 2 is the tweeter. The other 2 drivers are the mids.

Note that the roundover is really only needed on the vertical edges. This is to smooth the mid and tweeter response. The top away is too far to impact. The woofers don't really benefit from the roundover due to the low frequencies they are playing.

[---k---]

If I did my math correctly, to get the same 100L enclosure as the Statements, you want to build these 17" deep and all other dimensions stay the same.

54"Hx11"Wx17"D = 120L

The mids take up 18.6L (external, internal is 15L). and a couple of liters for the bacing and the woofers, etc should bring you in at 100L net.

Use with a 3" Diameter, 4" long flared port and you should be good.

[tpremo55]

All this talk about internal reflections - you should talk CJD and Ryan into an open-back-mid design for the Khans. :T

[cjd]

If you're going to go for open back, why do some crazy super compromised "open back tunneled but only the upper mids" design? Just build a proper dipole! Really. As if those narrow rear tubes don't have reflection problems.



Aside from new surrounds, a set of Dipoles is my next personal project.

C

[bf_brock]

Thanks Ryan - Looks like I should use at least a 3/4" round over, so that's what I'll plan on. I double checked your math and I get similar numbers.

I see you updated your original thread with the current information. Did you get a chance to make the changes to your crossover?

[bf_brock]

cjd - Did you have a chance to see what changes would need to be made to the crossover to bump the dip in the RS28's response back up some? I'm not sure if it'll be necessary but I may be interested in trying it both ways to see what I prefer.

[tpremo55]

If you're going to go for open back, why do some crazy super compromised "open back tunneled but only the upper mids" design? Just build a proper dipole! Really. As if those narrow rear tubes don't have reflection problems.



Aside from new surrounds, a set of Dipoles is my next personal project.

C

Interesting assertion C – you responded as if I had insulted you (certainly not intended) rather than the technically descriptive and contemplative responses I have read in your other posts.

We all recognize that design mantras all have their compromises – even the Dipoles. Are the direct reflections (1 trip) that interfere with the rear surface of the cone reduced in a open-back mid design as compared to a design with a parallel and direct reflecting surface – absolutely. Do they minimize reflections as well as dipoles, probably not? But then room placement becomes much more troublesome with a dipole – correct?

I was very impressed with the Aethers and will consider something similar in the future as well as they get around one of the big drawbacks of dipoles for me (difficult bass response without active equalization) while still providing the sweetness of an un-“enclosed” mid.

I’d certainly entertain and enjoy further discussion outside of this thread and will not post more on the topic to bf_brock’s discussion.


Good Luck bf_brock - you've picked a great design to build and are making some interesting modifications.

[cjd]

Sorry, my response was mostly tongue in cheek, but serious at the same time. You lose an octave of open back going with the RS150 and have much more backwave restriction due to driver design (not a Neo motor). So it's really not suited to that style build. And your comment *was* as if we somehow could improve things going open back - something I would disagree with. I don't like mixed monopole/dipole through the core frequency range, from the few I've heard that do that. It puts this big transition right in the middle of one of the instruments I'm most critical of, as well, so...

The number of people that go around as if this open back mid thing is the best since sliced bread just gets to me sometimes I guess.

Get ALL your midrange opened up, for real.

I'm hoping I can accomplish a somewhat reasonable size as far as form-factor, but we'll see how it goes.

C

[cjd]

cjd - Did you have a chance to see what changes would need to be made to the crossover to bump the dip in the RS28's response back up some? I'm not sure if it'll be necessary but I may be interested in trying it both ways to see what I prefer.

The normal tricks all end up being worse overall - I can flatten out response through that region, but I then have to bring everything else down to a new level, since the tweeter is already un-padded.

C

[Jim Holtz]

If you're going to go for open back, why do some crazy super compromised "open back tunneled but only the upper mids" design? Just build a proper dipole! Really. As if those narrow rear tubes don't have reflection problems.



Aside from new surrounds, a set of Dipoles is my next personal project.

C

Why? One word..... Placement. The Statements series work great 18" from the back wall or even closer and 18" from the sidewalls. Try that with a di-pole.

Another problem is the limited SPL capability with a true di-pole Vs. our open back transmission line design. You get 90%+ of the di-pole benefits with out the limitations. It doesn't sound crazy to me. It makes sense for my listening room and Home Theater/music listening and I suspect for the majority of people with families that have combination rooms that do more than just listen to music and can live with speakers in the middle of the room and don't have large TV's sitting between them. :B

Just for conversation purpose, how can a 5"x5" tunnel with the back open, lined with one inch foam reflect soundwave back into the cone of the driver? It ain't gonna happen.

Next question....

EDIT: I see you responded to Todd after I posted my response. I do disagree with your assertion that it's a big compromise and I would happily challenge you to pick the transition from open back to closed back with blind listening. It is smooth as glass. I consider it the best of both worlds.

But, that's why there are so many different designs. Everyone likes something different.

Jim

[Jed]

I still wouldn't classify a short transmission line tunnel with an open back as a dipole, but it definitely has its advantages like Jim stated.

I'm also not so sure about the entire monopole to dipole transition from bass to midrange argument. The speakers I heard at RMAF sounded very fine which goes against the math. Though I can't say I heard similar drivers in an open baffle versus the same driver in a monopole to compare.

[---k---]

Thanks Ryan - Looks like I should use at least a 3/4" round over, so that's what I'll plan on. I double checked your math and I get similar numbers.

I see you updated your original thread with the current information. Did you get a chance to make the changes to your crossover?

Is there a reason you're scared by a 1" roundover? You can get a 1" roundover bit from Holbren.com for $23. The 3/4" is $17. To me, when you're spending this much $$ and putting in this much effort, what's another $6? Of course, if you already have a 3/4" bit, I understand totally.

I haven't got to the Khan's crossovers. I just finished the LineUp D4 that I've been working on and have been trying to put some miles on them.

[---k---]

Lets chill with the open back versus monopole versus dipole. THere's a place for everything.

[Jim Holtz]

Lets chill with the open back versus monopole versus dipole. THere's a place for everything.

Agreed. Sorry for the thread hijack. Back to regularly scheduled discussion...

Jim

[bf_brock]

Not scared of the 1" round over, just the cost of the bits from dealers near my house. Thanks for that suggestion on holbren.com. Have you actually ordered anything from them before?

[bf_brock]

The normal tricks all end up being worse overall - I can flatten out response through that region, but I then have to bring everything else down to a new level, since the tweeter is already un-padded.

C

Thanks for checking it out.

[cjd]

Check out MLCS for bits too.

[bf_brock]

cjd - Thanks, that was actually that I was trying to remember for bits.

[---k---]

Yes, I have ordered from both Hobren and MLCS. I have MLCS 30 bits set and a 1.25" roundover from them, never a problem that I could blame the bit on. I gave Holbren a try after a Fine Woodworking Magazine review rated them as good and MLCS as average. With my limited woodworking experience, they are equivalent to me. Holbren also sells Whiteside bits for a very reasonable price.

[bf_brock]

For clarification, the box dimensions are for 3/4" wood all around with the front panel being double thickness. Is this correct? And the 17" deep modification to make it ported is including this?

Would there be any real benefit to doubling the enclosure thickness all around?

[Hank]

I've been buying router bits from MLCS for years and have had no problems at all with them. I have their 1 1/4" radius bit:
#8659 -- $39.00

I must say I'm tempted to try the new Freud multi-flute bits.

[---k---]

Yes, 3/4" all around and 1.5" on the front. I have a spreadsheet I use to calc box volume, and it includes the thickness. You should be good.

CJD did double thickness on his big box (3/4 + 1/2). I only did 3/4 on mine. I think with the shorter dimensions of mine, double would be extreme overkill. We're all about overkill, so if you want to tackle double thickness, I won't talk you out of it. But my boxes weigh 89lbs + drivers, so say an even 100lbs. Your's are already going to be heavier than this because of the extra depth. CJD's are like 300 lbs. So.... but on the other hand, I can barely feel the bass when I touch the side of my cabs. Not sure about cjd's, but his wife has some decorations that didn't move when we were cranking some bass heavy stuff this afternoon, but it did move when I tapped the top of the cabinet.

Oh, and I used baltic birch ply which is lighter than MDF (but stronger). If you go MDF, and especially with double thickness, make sure you own a good dolly.

[JohnA]

Another source for router bits at reasonable prices, is woodline.com

[bf_brock]

Thanks guys. Oh and you actually answered another question I was going to have regarding BB versus MDF.

[kingpin]

We're all about overkill, so if you want to tackle double thickness, I won't talk you out of it.

someone mention the word "overkill".

But my boxes weigh 89lbs + drivers, so say an even 100lbs.

light speakers suck. :E :W :B

CJD's are like 300 lbs.

now there are a man's speakers. :W

If you go MDF, and especially with double thickness, make sure you own a good dolly.

A dolly helps for sure.

I think other than the obvious benefits of having a thicker front baffle it also adds a different look to the speaker. Also helps to add different styling cues.
My front baffles were 2"thick. Alone they weighed in at somewhere around 100lbs each. Then again not everyone is as crazy as me. :lol:

Something I did with my speakers also is when building them i attached a piece of 1\8"thick backer board to the back and bottom of the speaker(temporarily) so I could drag it around without worrying about damaging the surface and corners. This also helped out when it was time to move them, as if I needed to I could just re-attach them and drag them up and down the stairs.

Mike

[bf_brock]

Kingpin - My wife is pretty understanding of my audio/video fixations (even if she doesn't understand it)...but just looking at the speakers in your signature might strike a sour note.

I was thinking of doing double layer all around (1 1/2"). Then again my subwoofer is fairly large; 3/4" particle board with no internal bracing and like cjd's speakers I have decorations on it that don't move or even rattle. It's amazingly solid. So...What does that say?

[---k---]

I personally would rather brace well a single layer than use double layer. Laminating take time, and requires 2x more precision to get both layers to match up. But again, I'm not here to talk you out of anything. I've seen people who recommend a layer of MDF laminated to a layer of ply, to attempt to get the best of both worlds.

You might want to consider 1/2" + 3/4", just to save a bit on weight. You might also consider seeing if you can buy 1" thick MDF from a local supplier. Just other options.

Just make sure you adjust your dimension as required.

[bf_brock]

Is the port length 4" including the flares, or is the center tube 4" and then add the flares at the ends?

[Jim Holtz]

Is the port length 4" including the flares, or is the center tube 4" and then add the flares at the ends?

The 3" port length is 4" plus the flares using PE's make a port kit. That's based on a net of about 100 liters for the (2) RS225's.

HTH

Jim

[bf_brock]

That's what I thought but wanted to verify. Thanks!

[---k---]

Jim,
You beat me to it. Thanks.

[---k---]

Just FYI if you haven't ordered the parts yet. The shielded RS drivers are currently on sale.

(and that pisses me off. They always had the non-shielded, 4ohm version on sale when I was buying.)

[bf_brock]

What is the performance difference between the crossover parts that are changed in the "budget" vs. "upgraded"? I was really curious about what the difference is between the p-core and the air core.

[cjd]

Saturation of the P-core will change its inductance. When used well within the limits, that's largely moot, especially with regard to the monster 10mH inductor in these.

So, it comes down to: are you the type to round-over all the holes in your internal braces or not? If you are, you'll probably grab the air-core just to be a purist. Otherwise, the P-core will be fine.

I'd be more wary of using anything other than air-core elsewhere. I haven't actually looked at the budget build to see what all is in there.

C