Duplex 605B crossover experiences needed

[tgroendahl]

Having just started enjoying my recent acquired pair of 605B?s, temporary mounted in simple 3,6 x 4 feet open baffles, I am now considering what to do about crossovers.

The drivers impedances are LF=16 Ohm / HF=8 Ohm. Somewhere I saw 605B specs where Re for the 605B is stated as "8/16 Ohm", so maybe this explains the different impedances.

The original Altec N-1600 (D-version) crossovers that came with the drivers, didn?t sound good at all.

Then instead I put a 5uF Jensen cobberfoil PIO pertinax-encased capacitor in series with the hf-driver, with carbon resistors, 9 ohm in series + 27 ohm in parallel, to adjust the hf-level, and voil?, the soundstage opened, and the music became very involving, thus without deep bass because of the lack of enclosure.

I realize that I must make a real filter, because of disturbing resonances and peaks plus lack of resolution in the 1 - 2 Khz region, compared to my beloved 12" vintage Philips drivers: http://homepage.mac.com/tgroendahl/PhotoAlbum2.html

I would much like to hear other 605B owners listening experiences with the Markwart 605A/B phase-corrected filter.

Has anyone tried to re-create the original Altec filter with modern supreme parts with good results, or is the Markwart filter simply the ultimate solution to match these fine Duplex drivers?

Amplifier is a 2A3 SE.

Regards,
Thomas

[Old Guy]

Hi- My experience with Altec crossovers is that they are just basic simple units. There is room for improvement. Building them with better parts (primarily caps) might improve them slightly.

I do know the Duplexes respond well to biamping.

As far as any crossover the most you can hope for is "the best so far". The art is constantly iimproving. I understand the crossover you mention to be quite good.

[tgroendahl]

Hello Old Guy,

The crossover I refer to, is one that I learned about here on the Altec site: http://home.earthlink.net/~jmarkwart/

For a long while I have been playing with the Philips 12" drivers, crossed to a pair of Fostex T-825A with the simpel 1. order filter that I now try on the Duplex. The Philips driver is rolling gently off after 5Khz (where the 5uF capasitor rolls of the hf-unit) so there is no need to filter it.

The Altec Duplex has been the speaker of my dreams for many years, and I was lucky to get a pair on eBay earlier this year.

[MANZANITA]

Hello Thomas;

Jeff Markwart's crossover works pretty well although it is set up for 16 ohm impedance for both the LF and HF sections. So if you have a 8 ohm H.F. section you need to recalculate the components in the HF section to maintain the intended performance. I am not aware of a stock 605, be it A or B model that was split impedance wise. The DCR values should be between 9 & 12 ohms for both the LF & HF sections. If some one in the group is more up on this issue it would be great to hear from them.

It would be interesting to know what your DCR values are for both of your 605B's. I have operated the 605A in a dipole configuration with great success with the deep bass chores being provided with a pair of NHT 1259 sealed box woofers (+ 200 wpc plate amps). Power for the 605's was provided by a highly modified "T" amp (about 4 clean wpc).

The dipole baffle board is roughly 24" Wide by 48" tall with 12" rear facing tapered and angled wings. F equal with this baffle-wing combo is around 180 hz and -6 db is around 90 hz.

[donaldpatten]

Thomas
Congratulations! The N1600 is easy to make a copy.
Here are the parts you need for each one you build:

16 ufd 200 volt cap poly ( not electrolitic )
4 ufd 200 volt cap poly ( original was a oil filled bath tub )
20 ohm 10 watt non inductive wire wound resistor
5 ohm 10 watt ni ww resistor
25 ohm 10 watt pot ( HF attenuator )
1.0 mH coil # 18 AWG air core
dual input connector ( banana jack )
4 position output connector ( IEC screw type )
a sheet of plexi glass 13 x 17 x 0.25 cm
and a few cable ties

The spec 16/8 ohms as I understand, was to cover the actual 12 ohm design. If you measure the woofer DC Resistance it will be about 12.
If you want to make the coil:

Wind 165 turns of #18 awg ( 1 mm dia ) on a 3 cm rod.
The finished coil cross section should be 15 x 15 mm.
I' ll find the schematic.
Don

[donaldpatten]

N-1600 schematic
http://audiokarma.org/forums/showthread.php?t=39472
or search audiokarma , dlp4341 , 605A Xover
Don

[tgroendahl]

Thanks a lot!

I have now measured dc resistance: LF=11,5 Ohm / HF=9,2 Ohm.

According to the "construction hint" page on Jeff Markwarts site, there are two kinds of HF ribbon voice coils. The early aluminum type that is screwed on, and the later cobber type, that has push-on terminals. It seems that mine has the early screwed-on types mounted. This also affects the values of the hf components.

The LF magnets has the engraved # 391116, and the cones are stamped # 21184-2, they appear to be quite new, so the drivers was probably reconed at some time.

The N-1600 schematics (thanks for the link!) looks quite simpel as well.

The big question is then how the original N-1600 filter recreated with high-end components would compare in sound quality to the Markwart design. It seems to me that many are using Jeffs design.

Thomas

[MANZANITA]

Thomas;

Jeff's crossover IMHO(the version with the adjustable mid frequency EQ) is much better than the Altec origninal. I built a duplicate of the Altec N1600 using high quality components as well as Jeff's EQ version. The duplicate was an improvement over the original and I am sure most of the improvement was due to the fresh caps.

However, Jeff's to me was much more musical than the N1600 original or copy. As for the dipole set up I wrote about in my previous post, I designed a totally different crossover to better support the low power input and to correct for dipole anomallies.

[tgroendahl]

Thanks Manzanita.

I would much prefer to stay with open baffles, the sound is so relaxed and yet very forward.

My current test baffles seems to be the same size as yours. I am aware that if the driver should play deeper, it will require very large baffles.
I wouldn?t mind if the result will be good, since I?m not so crazy about the idea of a sub.

Guess that the baffles then should be around 7 by 7 feets. http://melhuish.org/audio/baffle.html

Maybe in addition the dc resistance in the lower octaves could be increased a bit in order to gain a higher system Q, with hopefully 3dB more output at Fs.

Also I have considered to construct an enclosure of around 9 cubic feet, with aperiodic vents on the back baffle.

May I hear your opinion?