[mark]

Hi all,

1st post. Hope I'm not asking silly questions.

Does this OB approach make sense? A pair of 300b monoblocks driving 8" full range (Audio Nirvana super 8" cast frame) in a narrow open baffle, for low midrange up. Plate amps driving 15" woofers in H frames for low midrange down (200 hz) . Open baffle stacked on H frame like Martin Kings design.

Thank you for your help.

MJ

[richidoo]

Welcome to AC, Mark. Sounds like a very nice project you have planned!

Audio Nirvana driver specs say that the sensitivity is 95.8dB/W/m, with 8 ohm minimum impedance. The 300b should be OK, with about 8 watts. The rising frequency response of the driver should match well with the SET's gentle high freqs. On the other hand, single driver speakers often prefer transconductance amps (current source.)
http://www.passdiy.com/pdf/cs-amps-speakers.pdf 
I know a few people using single driver speakers with SETs, and loving it!

With open baffle, it is much easier to use active crossover as you are planning, because you can easily match the woofer level to the full ranger with the twist of a volume control... The full range driver might need to be high pass filtered around 100Hz so it doesn't muddy up the bass. You can accomplish this with a low level filter before the SET amp, or with an inductor between the amp and speaker, which will be more expensive and more distortion depending on the quality you buy. The woofers will definitely need a low pass filter, just make sure your plate amp has built in crossover function. A -24dB slope setting will be useful to keep the woofer out of the way of the full ranger, that's the standard home theater setting. Try to get a plate amp with infinite phase angle adjustment, not just "0 and 180" or other fixed degree settings.

Don't forget about the baffle step response of the full ranger. It will roll off by -6dB at some frequency, and could screw up your crossover if not accounted for.  Read more about that on John Murphy's site or use Quarter-Wave software to calculate it, and compensate. It's great software for what you're doing.
Please post your progress and some pics!! Have fun!
Rich

[mark]

Rich,

Thank you very much. Very helpful.

A few questions:

"The full range driver might need to be high pass filtered around 100Hz so it doesn't muddy up the bass. You can accomplish this with a low level filter before the SET amp, or with an inductor between the amp and speaker, which will be more expensive and more distortion depending on the quality you buy."  [/i]

How can I learn more about low level filters? Is this electronic or passive?

"Try to get a plate amp with infinite phase angle adjustment, not just "0 and 180" or other fixed degree settings."

Any suggestions for a plate amp?

Thanks agian,

Mark

[richidoo]

Low level just means that the filter comes before the power amplifier, aka "active" crossover filter. The signal is low voltage (<1V,) so small passive components or opamps can be used to filter. When the filter is applied after the power amp, like a passive crossover inside a speaker, it has to be able to handle high voltage and current.

The filter will be electronic, but it could be powered or unpowered, depdnding on the complexity you need. To make a 4rth ortder filter I thikn you will need a powered circuit. A digital crossover like Behringer DCX2496, or analog like Bryston, or a simple custom circuit using opamps (cheapest).  Check out the links to get up to speed. Google "crossover filter calculator" or similar for figuring out exact parts.  Since your bass has its own crossover and amp, you only have to design a filter for the full range driver, so you get to choose hgh or low level. In that case there is no advantage to high level. If you were designing a whole speaker and wanted standard amps to power it, then a passive high level crossover is the norm, and usually cheaper, if only for the fact that only one amp powers the speaker. But some of the best passive crossover parts can cost more than an amp.  There are also some really simple in line filters for car audio, I will have to find the link, or maybe someone else knows it? miklorsmith has recommended them a couple times on AC.

More info:
http://sound.westhost.com/biamp-vs-passive.htm
http://sound.westhost.com/dwopa2.htm#filters
http://sound.westhost.com/articles.htm
http://sound.westhost.com/projects-3.htm
http://www.linkwitzlab.com/crossovers.htm
http://www.trueaudio.com/st_index.htm See topics 11, 12, 13

There are a lot of good plate amps. I am not an expert on that. I have seen some in Madisound catalog, Parts Express, etc. Of course there are fancier ones to match any budget. You can get better advice on that from somebody else.

[panomaniac]

Hi Mark, and welcome.

Your rig should work well.   You're putting the right amps where they need to be.  By 300B I suppose you mean single ended?   That should work well for your AN8 in the mids and highs.  SET amps do seems to mate well with single drivers or horns.

And a plate amp is going to tbe the right thing for your OB bass.  There you will need both power and a low crossover point or some other sort of EQ.  That can often be achieved with the crossover built into a plate amp.

For a passive line level crossover, see here: http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
Very easy to do and not a bad idea for your rig.  You may also want to put a small inductor in series with the AN8 to tame its rising response.  0.2~0.6mH usually does the job for most FR drivers.

Have fun with it and let us know how it works out!

[tubamark]

Rich,

Thank you very much. Very helpful.

A few questions:

"The full range driver might need to be high pass filtered around 100Hz so it doesn't muddy up the bass. You can accomplish this with a low level filter before the SET amp, or with an inductor between the amp and speaker, which will be more expensive and more distortion depending on the quality you buy."  [/i]

How can I learn more about low level filters? Is this electronic or passive?

"Try to get a plate amp with infinite phase angle adjustment, not just "0 and 180" or other fixed degree settings."

Any suggestions for a plate amp?

Thanks agian,

Mark

Plate Amps from MCM electronics [ http://www.mcmelectronics.com/search.aspx?C=3829441&K=subwoofer%20amplifier ]
have constant variable phase adjustment 0-180 degrees.  Perform well, good price.

-- Mark

[markC]

I'd be interested to know how many of you use other than "0" phase adjustment on their plate amps?

[mark]

Thanks Richidoo, Panomaniac, Tubamark,

Baffle size is my next question. How does one go about determine dimensions?           

With the 15"woofers in H-frames driven by plate amps, I assume the full range drivers ( AN Super 8 cast frame) can be narrow. Would 18" be about right? How about height?

Respectfully,

Mark

[mark]

Hi All,

Any suggestions re: below?         

With the 15"woofers in H-frames driven by plate amps, I assume the full range drivers ( AN Super 8 cast frame) can be narrow. Would 18" be about right? How about height?

Many thanks,

Mark

[Badwater]

Mark,

Read this thread:

http://www.audiocircle.com/index.php?topic=59619.0

Check out this system I built using an Alpha 15 w/plate amp,  vintage Electrovoice SP12B and Fostex T90A supertweeter.  It works. Not sure about the AN Super 8; you should probably model it see where it takes you.  Martin King's website is the best source of info on this project.

http://gallery.me.com/marilynladieu#100295

Details of my project are buried in the above thread,

Bill