Dipole gurus wanted

[Mazeroth]

I've been pondering over which dipole speaker to build (I've drawn up a lot) but I think I have it figured out. Unlike many conventional dipoles that are using dual 10" or 12" subs at the bottom, I'm looking to go with something along the lines of four RS225s at the bottom and crossing them over to my IB around 40-50hz. This is only temporary as my wife and I will be purchasing a house in 6-12 months, which is when the fun project begins! That's when I want to build stereo dipole subs with four RS390s on each side, eliminating the need for an IB and giving the four RS225s a dipole to cross over to. With Linkwitz's spl_max1 Excel spreadsheet, it looks like these will be flat under 25hz, NO problem. With drivers, materials, amp and a DEQ2496, this will probably be one of the best sounding sub $2000 subs out there I mean, why the hell not build it! I've sacrificed this last year and the coming by putting every penny I've earned into an account (investing, as well) which will be the down payment for our house. We've been living off her teacher's salary (barf) so I think I'm about due for a little splurge! :T

The part I'm stuck on is what to do up top for my mid/tweet. When I listen I'm generally in my seat and don't move, so I'm not so sure if I should be concerned with off-axis performance. That would lead me to believe I should be ok with an MTM, however, I remember reading something Linkwitz wrote that he felt that part of the improvements in the Orion over his Phoenix was
the lack of an MTM configuration. Also, D'Appolito (Mr. MTM himself) has done a lot of MT designs for Usher and others. That's not saying anything, but if the man who "invented" the MTM has been doing mostly MT designs then maybe that's saying something...who knows. Whatever I cross to will have to cross to the RS225s below 350hz (due to the center-center spacing of the mid and the bottom RS225 being less than a wavelength apart). After putting numbers into Linkwitz's spreadsheet it looks as though a single RS150 or RS180 will be able to do the job just fine. This will be on a ~13 inch wide baffle (Siegfried once said that the 13" baffle width is key to a smooth off axis transition between the dipole midrange and the monopole tweeter; don't know why, but I'm not questioning him). I don't think I'll need an MTM but if the lower distortion is really going to help a lot then I may just try it. It wouldn't make sense to build an RS150 MTM when I could just use a single RS180, right?

Also, I'm torn between the RS28 tweeter and the 27TDFC. I have an RS28 and 27TDFC here and they both sound great (I can't distinguish between them), and seeing how these will be crossed over around 1400-1600hz, I don't think either will have a problem.

I've only built two of my own speakers so maybe I just need to sweat it out and build a few prototypes and figure out what's going to work best. I love criticism (Thomas, you're the best) so if you have any PLEASE let me have it.

Thanks!

[Rick Craig]

I've been pondering over which dipole speaker to build (I've drawn up a lot) but I think I have it figured out. Unlike many conventional dipoles that are using dual 10" or 12" subs at the bottom, I'm looking to go with something along the lines of four RS225s at the bottom and crossing them over to my IB around 40-50hz. This is only temporary as my wife and I will be purchasing a house in 6-12 months, which is when the fun project begins! That's when I want to build stereo dipole subs with four RS390s on each side, eliminating the need for an IB and giving the four RS225s a dipole to cross over to. With Linkwitz's spl_max1 Excel spreadsheet, it looks like these will be flat under 25hz, NO problem. With drivers, materials, amp and a DEQ2496, this will probably be one of the best sounding sub $2000 subs out there I mean, why the hell not build it! I've sacrificed this last year and the coming by putting every penny I've earned into an account (investing, as well) which will be the down payment for our house. We've been living off her teacher's salary (barf) so I think I'm about due for a little splurge! :T

The part I'm stuck on is what to do up top for my mid/tweet. When I listen I'm generally in my seat and don't move, so I'm not so sure if I should be concerned with off-axis performance. That would lead me to believe I should be ok with an MTM, however, I remember reading something Linkwitz wrote that he felt that part of the improvements in the Orion over his Phoenix was
the lack of an MTM configuration. Also, D'Appolito (Mr. MTM himself) has done a lot of MT designs for Usher and others. That's not saying anything, but if the man who "invented" the MTM has been doing mostly MT designs then maybe that's saying something...who knows. Whatever I cross to will have to cross to the RS225s below 350hz (due to the center-center spacing of the mid and the bottom RS225 being less than a wavelength apart). After putting numbers into Linkwitz's spreadsheet it looks as though a single RS150 or RS180 will be able to do the job just fine. This will be on a ~13 inch wide baffle (Siegfried once said that the 13" baffle width is key to a smooth off axis transition between the dipole midrange and the monopole tweeter; don't know why, but I'm not questioning him). I don't think I'll need an MTM but if the lower distortion is really going to help a lot then I may just try it. It wouldn't make sense to build an RS150 MTM when I could just use a single RS180, right?

Also, I'm torn between the RS28 tweeter and the 27TDFC. I have an RS28 and 27TDFC here and they both sound great (I can't distinguish between them), and seeing how these will be crossed over around 1400-1600hz, I don't think either will have a problem.

I've only built two of my own speakers so maybe I just need to sweat it out and build a few prototypes and figure out what's going to work best. I love criticism (Thomas, you're the best) so if you have any PLEASE let me have it.

Thanks!

Having worked with the RS150 and RS180 I would use the RS180 in your proposed design. The RS150 isn't going to extend as low and the RS180 will also give you more output capability. If you want more output then a MTM is certainly possible.

I think the lack of an Usher MTM is more of a marketing decision and Joe's only doing what they ask him to design. I'm not sure why Linkwitz has such an issue with MTM's because you can alter the directivity with different crossover topologies.

[Mazeroth]

As far as altering the directivity are you talking about going with a 0.5 topology for one of the mids? If so that won't be necessary, due to a dipole not needing baffle step, correct?

Reading my post this morning I can't believe I actually posted that mess! I was up waaay late last night when I wrote it and it sounds really jumbled. Sorry about that

[ThomasW]

Reading my post this morning I can't believe I actually posted that mess! I was up waaay late last night when I wrote it and it sounds really jumbled. Sorry about that

I read it late last noc and thought ....a reply will happen in the morning.....

I'm with Rick the RS150 just won't cut it for dipole use.

I'm a big fan of MTM's simply for the increased headroom the dual midwoofers offer.

The baffle will need to be absolutely HUGE to get adequate output at 25Hz.

When remodeling I played with varying numbers of 12" since my small 4-12" IB was off line. It took 8-12"s with EQ to get the same output level as the IB, and the lowest octave simply wasn't there regardless of what I tried.

[Paul Ebert]

Unless you're trying to stick with the RS series, you may want to consider the Ascendant Audio poly midwoofer. You can find it here:

http://www.ascendantaudio.com/poly_6.5_page.html

I'm making plans to send a pair to Zaph for measurement.

I'm also considering the Visaton TI 100 that is creating such a stir, but that's a lot of $ and would probably need to be doubled up in your application.

Sounds like a nice system you're designing, but I think you may be in denial about how much discretionary income you'll have after closing day.

I'd make the purchases before that day arrives.

[Rick Craig]

As far as altering the directivity are you talking about going with a 0.5 topology for one of the mids? If so that won't be necessary, due to a dipole not needing baffle step, correct?

Reading my post this morning I can't believe I actually posted that mess! I was up waaay late last night when I wrote it and it sounds really jumbled. Sorry about that

Actually I meant altering the crossover acoustic slopes and still making it a true MTM, not a .5 design. I did that with an Accuton MTM dipole and the vertical coverage was much wider than a typical MTM. That particular design used a 5" midbass so a RS180 MTM would be more difficult. For a little more $ you could do a MTM with the Seas L15.

[Davey]

I'm not sure why Linkwitz has such an issue with MTM's because you can alter the directivity with different crossover topologies.

Linkwitz doesn't have any issues with MTM's....at least as far as directivity concerns. His reason for using them in the AA commercial designs and the Phoenix was SPL-related because of the lowish x-over frequencies and 2nd-order acoustic slopes.

For a dipole design like Mazeroth is contemplating I would go with 7" drivers in an MTM arrangement and try to push the crossover frequency down into the 140Hz (or lower) range. That should work good, give adequate output and allow using a baffle size that doesn't dominate visually like some I've seen.

Of course, there's more to it than simply throwing some drivers on a baffle and correcting the on-axis response to be flat.

Cheers,

Davey.

[Doug Lockwood]

That should work good, give adequate output and allow using a baffle size that doesn't dominate visually like some I've seen.

LOL.

Of course, there's more to it than simply throwing some drivers on a baffle and correcting the on-axis response to be flat.

True Fact!

IME, The baffle size determines the max SPL and crossover point of the midrange. I can get very loud with a 14CM Seas on an 18" baffle, crossing over at 300 Hz. A 13" baffle at 120 Hz would be a completely different thing!

For a dipole design like Mazeroth is contemplating I would go with 7" drivers in an MTM arrangement and try to push the crossover frequency down into the 140Hz (or lower) range.

If the RS225 are used in an H, U or W baffle, this is very sound advise. For a flat baffle, a wider range of trade offs exist.

[Paul W]

Stuff the RS390's in another IB. Trying to do a dipole in the lowest octave is a waste of good displacement...and your wife will likely tire of looking at them!

My vote for the dipoles:
2 RS315HF
2 Peerless Exclusive 883 or RS180s.
1 Seas T29CF001...maybe in a shallow waveguide. I'm dying for someone to try the 29CF...low-Q rolloff on the bottom, plenty of output for contouring the top end. TDFC over the RS28.

Because of the convincing and stable soundstage, WMTMW 1st choice. MTMWW 2nd chioce. Sure the WMTMW is big, but not as big as 8-15" dipole!

[AJINFLA]

Of course, there's more to it than simply throwing some drivers on a baffle and correcting the on-axis response to be flat.

Cheers,

Davey.

You forgot to add like I usually do....at a finite mic position @ X meters.
Though you would never know it reading many a thread on several forums :W .

cheers,

AJ

[Paul Ebert]

My vote for the dipoles:
2 RS315HF
2 Peerless Exclusive 883 or RS180s.
1 Seas T29CF001...maybe in a shallow waveguide. I'm dying for someone to try the 29CF...low-Q rolloff on the bottom, plenty of output for contouring the top end. TDFC over the RS28.

Paul, what would you think of the Peerless HDS tweeter as a cheaper option to the 29CF?

Thanks.

[Paul W]

The HDS may be another great candidate. Like the 29FC, it has longer linear coil travel than the TDFC. I would like to understand what causes the HDS impedance bump at 1500.

[Rick Craig]

You forgot to add like I usually do....at a finite mic position @ X meters.
Though you would never know it reading many a thread on several forums :W .

cheers,

AJ

Oh is that what they call power response? :rofl:

[Davey]

Oh is that what they call power response? :rofl:

Yep, that's part of it. I see you made a recent effort. 'Make you think about abandoning coffin designs and stepping up to the superior approach of open-baffles?

Cheers,

Davey.

[mikec]

I see you made a recent effort.

"Effort" would be the key word. I have to wonder if using a tiny winy 5" midrange driver was a conscious decision? Maybe future efforts (conscious or otherwise) will use a larger diameter driver to allow dipole operation below 400Hz. IMO much of the benefit of a dipole design extends well into the bass region. :W

[JonMarsh]

Stuff the RS390's in another IB. Trying to do a dipole in the lowest octave is a waste of good displacement...and your wife will likely tire of looking at them!

My vote for the dipoles:
2 RS315HF
2 Peerless Exclusive 883 or RS180s.
1 Seas T29CF001...maybe in a shallow waveguide. I'm dying for someone to try the 29CF...low-Q rolloff on the bottom, plenty of output for contouring the top end. TDFC over the RS28.

Because of the convincing and stable soundstage, WMTMW 1st choice. MTMWW 2nd chioce. Sure the WMTMW is big, but not as big as 8-15" dipole!

Pretty solid recommendation. I'd tilt toward the 883. On the tweeter, I'd probably have to suggest the T25CF001 based on distoriton, FR, CSD, and price/performance, considering the rang of tweeter's you're considering and others are suggesting. If price is not a serious issue, well, maybe the 66000, or the T29CF001. (which beggars the question of why am I suggesting those instead of what I'm trying out in my current project, a waveguide loaded C13-6. Maybe just 'cause I'm trying to be more "mainsteam" on recommendations than I feel compelled to be for myself...

[Jed]

Maybe just 'cause I'm trying to be more "mainsteam" on recommendations than I feel compelled to be for myself...

or how about the new C24 non wave guide- that's a bit more mainstream. I just don't like the idea of breaking off the mesh screen to get a flat FR. IMHO that should be thought out by the manufacturer.

[CraigJ]

Arvo Pärt Type 3 ?

O.K., so far we have built two thirds of the Arvo Pärt Type 3. For my rooom (and ears)I will be replacing the RS28's with the BG Neo 3pdr's. What about placing your Magnepan MG 1.6 on top of the Arvo's lower section? 8O

Good luck.

Craig

[Evil Twin]

O.K., so far we have built two thirds of the Arvo Pärt Type 3. For my rooom (and ears)I will be replacing the RS28's with the BG Neo 3pdr's. What about placing your Magnepan MG 1.6 on top of the Arvo's lower section? 8O

Good luck.

Craig

Something I've suggested ThomasW try with his MMG's, but he doesn't want that large a footprint. I think getting the Maggies off the bass work by 200 Hz or so to be a big plus to their sound, but it should be a dipole auxiliary, not monopole. JMO, of course.

[CraigJ]

"but he doesn't want that large a footprint"....Size is also very subjective. I find the Arvo 3's to appear smaller because they are only 2" thick and 48" tall. How about an RD50 next to the RS12's in a similar size? Oops, isn't that the Debussy?

Evil, glad to see that you are getting a little more free time

Craig

[Rick Craig]

Yep, that's part of it. I see you made a recent effort. 'Make you think about abandoning coffin designs and stepping up to the superior approach of open-baffles?

Cheers,

Davey.

No, I'm not abandoning the coffins so I'll have something to be buried in

Obviously open baffle designs aren't for everyone due to placement issues or the possible need for extra amps, active crossovers, etc. I do think there are some good alternatives to deal with room issues, such as line arrays and active room correction / equalization.

[JonMarsh]

"but he doesn't want that large a footprint"....Size is also very subjective. I find the Arvo 3's to appear smaller because they are only 2" thick and 48" tall. How about an RD50 next to the RS12's in a similar size? Oops, isn't that the Debussy?

Evil, glad to see that you are getting a little more free time

Craig

Well, it's all relative- I've been averaging three weeks travel a month for some time now- leaving for Italy on business tomorrow.

BUT, there has been some progress finally on the Type 3, with baffles fabricated, crossover parts bought, cocobolo bought for the trim (expensive but beautiful), waveguides milled on a new router table, etc. Gonna try to take some time off at Thanksgiving (they don't have Thanksgiving in Austria, you know... , so who knows? Have simulated the baffle response and a first pass crossover design (used to purchase parts), now I hope to have some baffle measurements before Thanksgiving weekend is done.

[JoshK]

waveguides milled on a new router table, etc.

What kind of bit do you plan to use? I have a router table but I hadn't thought to use it for waveguides.

[JonMarsh]

Just a flat bottom bit for milling the back side of the MCM waveguides after cutting off the threaded insert. Nothing from scratch- at least not yet.

[JimS]

Something I've suggested ThomasW try with his MMG's, but he doesn't want that large a footprint.

Doesn't anyone else find this slightly humorous?!?!? :B I guess we can let it slide since it's for his "small" system . . .


Jon - glad to see they're letting you back out for occasional visitations :T

Not that I would ever suggest that aesthetics should interfere with speaker design, but can't help wondering if the TC1000s on sale now would look pretty good with the 883 up top - in an industrial sort of way . . .

[ThomasW]

Doesn't anyone else find this slightly humorous?!?!? :B I guess we can let it slide since it's for his "small" system . . . .

It's of course preposterous, but I really want to keep the footprint of the speakers in the family room ~18". So I could use a single RSS390 dipole, BUT I have a plan for something slightly more radical than just some modified MMG's sitting on a dipole woofer....so stay tuned...... :B