MTM lobing vs Woofer spacing

[peter_m]

Quick question,
if the woofer spacing affects the lobing of MTM speakers, would there be any benefit to remove a little of the tweeter flange to bring the woofers as close as possible?

How much would there be to gain in the vertical listening window?

On an existing design and without modifying the x-over, would it cause more problems then benefits to do such a modification?

Any free software out there that models the lobing effect of two woofers?

Peter

[Martijn_H]

The closer the better! 8)

http://www.tolvan.com/xdir/

Martijn

[Kal Rubinson]

The general rule is to get any two or more speakers that are reproducing the same signals closer than 1/2 wavelength of the maximum common frequencies. In this case, the crossover frequency or a bit higher.

Kal

[peter_m]

Thank you for the software and the rule of thumb... just what I needed!

Anyone know if this is a good tool for baffle diffraction: http://www.tolvan.com/edge

Peter

[Martijn_H]

Thank you for the software and the rule of thumb... just what I needed!

Anyone know if this is a good tool for baffle diffraction: http://www.tolvan.com/edge

Peter

Yes it works very well. But remember that you cannot change the wide of the baffle without changing the filter. (bafflestep)

[peter_m]

Yes it works very well. But remember that you cannot change the wide of the baffle without changing the filter. (bafflestep)

Thanks Martijn_H, I am aware, juts wanted to see for my self how much effect it can have. It will be interesting to see on a graph.

I know I am not a genius, someone must have considered it before me. Why hasn't anyone tried to remove material from the tweeters to accommodate closer woofers? Is it just to maintain a certain ease of building? Is it not worth the extra work?

Peter

[Dennis H]

Why hasn't anyone tried to remove material from the tweeters to accommodate closer woofers? Is it just to maintain a certain ease of building?

It has been done but it doesn't get the woofers that much closer together with most tweeters. The W-W distance with 18 cm woofer frames and a 10 cm tweeter frame would be 28 cm. Carving up the tweeter might get it down to 26 cm, hardly worth the bother.

[Kevin Haskins]

Lets face it.... a couple cm doesn't make much difference. The rule is crossover as LOW as possible and keep the woofers as close together as possible. The result in even the best of circumstances is still poor. It makes more sense to me to look at other solutions if you can.

Of course I'm designing an MTM center channel next week so I'm a total hypocrite. ;-)

[Dennis H]

Hey Kevin,

Sorta indirectly related to driver spacing... As I recall, you were experimenting with a Neo3 dipole tweeter both with the big faceplate and mounting it directly to a rectangular hole in the wood. Did you ever reach any conclusions?

[Kevin Haskins]

Hey Kevin,

Sorta indirectly related to driver spacing... As I recall, you were experimenting with a Neo3 dipole tweeter both with the big faceplate and mounting it directly to a rectangular hole in the wood. Did you ever reach any conclusions?

Yea... I concluded two 6.5" drivers on an open baffle don't cut-it (at least for bass extension/output).

I put off my dipole project until I had a good dipole bass driver. I have the DPL-10s now but have yet to schedule the time to finish the project.

After I get my CNC machine finished I'll knock out a couple and finish of the dipole project, both with the DPL-10s and the DPL-15.

[Hank]

Kevin, mind if I ask how you're building your CNC - kit, or from scratch? How's it going?

[Biff]

These are lapped to get it all on the baffle, but Dennis Murphy does it a bit. I also have a pair of MTMs using NEO3s and PL18s and the NEOs are cut across the top to tighten things up. Some of the Hi-Vi tweets seem to have a three lobe pattern made for an offset overlap, too Of course, some faceplates are easy to pull and use as a rear munt and Zaphs D26 mount mod seems like a good example.

[peter_m]

Biff, nice cabinets!

Does using the solid wood color the sound?

[Kevin Haskins]

Kevin, mind if I ask how you're building your CNC - kit, or from scratch? How's it going?

I'm building a kit but its a fairly cheap one. A guy on the CNC Zone named Joe kicked out a design that looked simple and fun.

I'm in the early stages of assembly so I don't have many comments yet. I'm going to have about $3K-$4K in the project including the table, hardware, software and dust collection.

I'm hoping to design some new complex shaped speakers so it was pretty much necessary for prototype work. I don't have any desire to run it as a production machine.

[fjhuerta]

The result in even the best of circumstances is still poor. It makes more sense to me to look at other solutions if you can.

Do you mean that an MTM is always a compromise? I suppose it is - but what better alternatives are out there, considering the lower distortion of two woofers?

I'm considering building an WMTMW (RS225, RS150, RS28) - do you think the compromises wouldn't be as severe if I built an WWMT (RS225, RS52, RS28)?

[Kevin Haskins]

What I'd like to design is a good 5.25" Coax speaker with a full sized high quality 1" dome in the middle. Have it with a flat cone so that your not getting diffraction off the tweeter and the tweeter mounted on the same plane as the midwoofer. That way you don't have it at the base of the cone, causing response issues. It would be able to crossover low in center channels 100-200Hz and give you the same off axis response no matter where you measure.

[AlanH]

What I'd like to design is a good 5.25" Coax speaker with a full sized high quality 1" dome in the middle. Have it with a flat cone so that your not getting diffraction off the tweeter and the tweeter mounted on the same plane as the midwoofer. That way you don't have it at the base of the cone, causing response issues. It would be able to crossover low in center channels 100-200Hz and give you the same off axis response no matter where you measure.

This might be close to what you're asking for...

http://www.lautsprechershop.de/hifi/index_en.htm?/hifi/thiel_en.htm

Of course you better have your wallet ready! It also seems wrong to buy a US-manufactured driver from a German distributor. As far as I know Thiel doesn't sell directly to the diy crowd.

[Kevin Haskins]

That would be the concept. They must be pretty proud of them for $1000 per driver.

[AJINFLA]

What I'd like to design is a good 5.25" Coax speaker with a full sized high quality 1" dome in the middle. Have it with a flat cone so that your not getting diffraction off the tweeter and the tweeter mounted on the same plane as the midwoofer. That way you don't have it at the base of the cone, causing response issues. It would be able to crossover low in center channels 100-200Hz and give you the same off axis response no matter where you measure.

Geez Kevin,

I have to disagree with about everything about your desired design. The flat cone would provide no loading for the tweeters low end and no reduction in distortion where it is needed the most. Then there would be the issue of matching the directivities, not possible unless the tweeter could go way low (lower than a 1" dome), which then leads to the problem above. The tweeter mounted at the base of the horn is not what causes FR anomalies, as then every horn tweeter would suffer the same consequence. It is the discontinuities like the former attachment and surround. Also, having the drivers on the same Z plane is not much use, as it is the measured AC's that must be aligned. Then there is the delay induced by the XO itself.
Then there is the surround required for a 4" cone to displace enough to go down to 100-200hz and the fact that this would be taking place around your tweeter...
Take a look at the latest KEF and TAD designs for excellent coincident design. The latest Thiel is a real head scratcher. I would love to see how it measures vs it's predecessor.

cheers,

AJ

[Kevin Haskins]

Geez Kevin,

I have to disagree with about everything about your desired design. The flat cone would provide no loading for the tweeters low end and no reduction in distortion where it is needed the most. Then there would be the issue of matching the directivities, not possible unless the tweeter could go way low (lower than a 1" dome), which then leads to the problem above. The tweeter mounted at the base of the horn is not what causes FR anomalies, as then every horn tweeter would suffer the same consequence. It is the discontinuities like the former attachment and surround. Also, having the drivers on the same Z plane is not much use, as it is the measured AC's that must be aligned. Then there is the delay induced by the XO itself.
Then there is the surround required for a 4" cone to displace enough to go down to 100-200hz and the fact that this would be taking place around your tweeter...
Take a look at the latest KEF and TAD designs for excellent coincident design. The latest Thiel is a real head scratcher. I would love to see how it measures vs it's predecessor.

cheers,

AJ

Your right... we disagree. :W

[Biff]

Biff, nice cabinets!

Does using the solid wood color the sound?

No, but the gels on the backlights do - These are actually Cizek cabinets from about 79 or so, IIRC, and they are about 5/4 stock with amazing internal bracing.The Koa is beautiful wood and has about a bunch of coats of tung oil on them - that wood was d-r-y and needed some love.