New Dipole Construction

**JonMarsh** · 25 March 2007, 13:34 Sunday

Hi Ron,

you have questions, I have opinions, which is to say, not definitive/you must do this/answers, but just some suggestions/comments.

Question #1, Midrange: 1 or 2 Hi Vi M8A's? I have 4 of them, and have room on the baffle to do an offset MTM with the mids on one side and the waveguide on the opposite. But I don't want to waste a driver if I don't need it.

What's your planned woofer to midrange crossover frequency, and your overall desired maximum SPL? With a lowish crossover on the 8's to 12's, I'd suggest going with two. Doesn't push them as hard individually, keeps Xmax into the more linear region. SPL_Max spreadsheet from Sl is a good guide. But running the DVC woofers up high may be getting into their nonlinear range due to inductance rise and inductivity modulation. With a crossover frequency ~200 to 250 Hz, you might go with a single M8a. Play around with EDGE to see the tradeoffs in offset mounting, though don't go too extreme- you also need to move the mic position in a set horizontally to get a good idea of the power response.

Question #2, Woofers: 2 Madisound 1252DVC woofers or 1 original Titanic 1200 woofer? I have 4 of the Madisound drivers as used by SL in his Phoenix, and a pair of the Titanic 1200's that I was going to use for an HT setup. I know the woofers aren't up to the quality of the mids and tweeters, but I'm not investing any more at this point.

Well, from an acoustic radiation resistance, I'd say you're better off with the 4 of the Madisound drivers than two of the Titanic 1200, but that's just a gut feeling. Look at the overall impedance curves and swept volume; both swept volume and minimal impedance rise are important.

Question #3: I wouldn't mind going passive between mid and tweeter (see below) but would implement the dipole cancellation compensation on the mids actively. Thoughts?

In my offset Arvo design I didn't need any appreciable diopole mid bump compensation. Passive crossover with active mid bump EQ comp seems quite reasonable - you should be able to implement a simple crossover above 400-500 Hz, letting your DCX2496 take care of the stuff below that.

JMO.

Someday you might want to try some RS315HF on the bottom end... could be quite an upgrade, especially when they're on sale.

Have fun- I'm working on work stuff today, wish I was gluing up the new Arvo Isiris test baffle instead!

~Jon

**RonS** · 26 March 2007, 10:53 Monday

Hi Jon,

Originally posted by JonMarsh

Hi Ron,

you have questions, I have opinions, which is to say, not definitive/you must do this/answers, but just some suggestions/comments.

What's your planned woofer to midrange crossover frequency, and your overall desired maximum SPL? With a lowish crossover on the 8's to 12's, I'd suggest going with two. Doesn't push them as hard individually, keeps Xmax into the more linear region. SPL_Max spreadsheet from Sl is a good guide. But running the DVC woofers up high may be getting into their nonlinear range due to inductance rise and inductivity modulation. With a crossover frequency ~200 to 250 Hz, you might go with a single M8a. Play around with EDGE to see the tradeoffs in offset mounting, though don't go too extreme- you also need to move the mic position in a set horizontally to get a good idea of the power response.

I haven't decided on the final crossover points yet, was waiting to see how the test measurements worked out. With the H frame I was crossing around 120Hz, was hoping for a bit higher with the flat baffle. With the 16" wide baffle that I want to use I don't have much room to play with as far as driver positioning goes if I use a pair of M8A's and the waveguide.

Well, from an acoustic radiation resistance, I'd say you're better off with the 4 of the Madisound drivers than two of the Titanic 1200, but that's just a gut feeling. Look at the overall impedance curves and swept volume; both swept volume and minimal impedance rise are important.

In my offset Arvo design I didn't need any appreciable diopole mid bump compensation. Passive crossover with active mid bump EQ comp seems quite reasonable - you should be able to implement a simple crossover above 400-500 Hz, letting your DCX2496 take care of the stuff below that.

JMO.

Someday you might want to try some RS315HF on the bottom end... could be quite an upgrade, especially when they're on sale.

Have fun- I'm working on work stuff today, wish I was gluing up the new Arvo Isiris test baffle instead!

~Jon

I can't seem to find the specs on the original Titanic 1200 anywhere, very frustrating. I can't remember it's Xmax, would like to compare one vs. two of the madisound drivers. Yes, one day I'll probably upgrade the woofers, but at this point I've got so much stuff lying around with no results yet that I'm hesitant to spend any more money.

Ideally I would like to do everything below the mid/tweeter crossover point with the DCX and passively above that point, just to keep the number of amps down. I'm unclear about your comment about a passive crossover above 400-500Hz. Are you suggesting that I can create a simple crossover between the mids and tweeter around 1200Hz? As you know the M8A has a huge resonance peak just above that. I was thinking of something along the lines of a CE filter at 1200Hz done passively with active dipole boost and mid bump filter if needed, but have no way of calculating it. Then again, Zaph was able to do a very simple 2nd order on the waveguide with one cap, would be nice to keep it so simple

Thanks for your guidance, it's just what I needed.

Cheers,
Ron

**JonMarsh** · 26 March 2007, 11:55 Monday

Arvo Part Biamp

Have a look at this post, it should give you some ideas about active biamp Arvo Part; it would need to be modified considering the characteristics of the waveguide, and I think you'll still need a CE crossover as I implement here for a more conventional tweeter- just adjust the transfer function for the measured behavior of the Seas.

**RonS** · 26 March 2007, 15:20 Monday

Thanks Jon. Is that crossover schematic for 2 Hi Vi M8A's? I'm sure I'll have more questions for you once I've studied the schematic and thread in further detail

Cheers,
Ron

**JonMarsh** · 26 March 2007, 15:47 Monday

Yup, for two HiVi M8a in series. The low pass for the woofer is an active module plus an LF EQ circuit I use with the Arvo that's a passive line EQ. The midrange to tweeter crossover is pure passive, and in this particular case was for optimizing the performance above 300 Hz or so, while the LF crossover was a standard active mode (LR4 or so, if I recall correctly).

This is similar to what we came up with for Tom, and that was a specific implementation for someone using the original baffle design.

If you have measuring equipment, I can make some crossover suggestions from your data files once you have things put together. The mid to tweeter will be different on the tweeter side, I'd offer to dummy up a 27TDFC with a waveguide here, but I'm so short of free time it's ludicrous (other than when traveling in airplanes or in hotel rooms at night sometimes- if I don't get in too late).

**RonS** · 26 March 2007, 17:34 Monday

Hi Jon,

Thanks for your generous offer

Once I have the baffle all done with the drivers installed, I'll take some measurements and see where things stand. But since I'm knee deep in house reno's (we're putting the house on the market soon) I have very little time for myself :cry:

Thanks again for all of your assistance!

Cheers,
Ron

New Dipole Construction

New Dipole Construction

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