Reworking my Passive Crossovers..... (Opinions wanted) (1 Viewer)

[Brett DiMichele]

Hey Folks,

I was doing some research on my internal passive cross
over circuits in my mains today let me go into a little
depth as to what I have for mains.

My Main L/R speakers are Acoustic Research AR-9 Towers
from the Hi-Res line. They are "Near Full Range" and
play down to 32Hz @100DB after that they start rolling
off fairly fast.

The driver compliment is a pair of Mag-Alloy hemisphereical
5.25" Mids a 1" Plasma Hardened Titanium Dome and a
10" high excursion side firing bass reflex sub.

The Crossover Network allows Bi Amp and Bi Wiring and
the Points are 100Hz and 3000Hz.

My question is why would you cross the Mids so high?
I think they should have been crossed at the THX standard
of 80Hz they should easily be able to reproduce from
80Hz to 3K Hz and this would make seperate sub integration
a whole lot easier.

My goal is to integrate my own D.I.Y sub and basicaly
not use the 10's in the AR-9's when my sub is complete.
I have a continiously variable x-over on the sub amp
I can set from 120Hz all the way down to 40Hz so I can
integrate if I want, But I keep thinking my Mids would
sound better crossed at 80 and letting the dedicated
sub play down from 80..

What do you think?

I plan on yanking one of the passive crossovers and
examining it to see what value caps they have on the
Mids and I could replace that cap with a foilized poly
audio grade cap from Parts Express and see how it sounds.

I know doing this is a hit or miss deal, crossovers are
tough cookies to crack and I probably won't improve
anything but I need to make some modifications inside
the cabinents anyway (adding V-Blok to the mid's enclosures
and adding acoustic tiles to the back of the mids enclosures
to break up any axial standing waves that may exist.

Do you think it's worth a shot?

Hit me with your complete honest opinion, harsh or not!

 

[Brian Bunge]

Brett,

I checked out the specs for the AR9's and noticed that while they list the crossover points, they don't list the slopes. Just as a guess, I'd assume it was at least a 2nd order crossover, which means you'd have to replace not only a capacitor, but also an inductor. If it's an even higher order crossover then you'd have 3 or more components to replace.

I assume AR chose the crossover point which they felt best integrated the mids with the 10" driver. Have you listened to the speakers with only the mids connected? Try that and see how much extension you're getting. If possible, use test tones and an SPL meter to find out what your in-room -3dB point is. If your receiver's crossover allows for adjustment, try to set it somewhere in that range and then cross your subs over there as well.

If they don't play down very low then keep the 10's running and integrate the sub with them at a lower point.

 

[Brett DiMichele]

Brian,

I may have to keep the 10's running.. Without them it's
hollow sounding and I attribute that to the high x-over
point for the mids..

I am not sure what order crossover is in there I need to
pull one out and take a look at the design.

If I scan the PCB in, can you help me make sense of it's
layout?

I really didn't wanted to try and stick with just using the
AV12, I can cross it over as high as 120Hz so I should be
able to integrate it without the need for the internal 10's
but I wanted more out of the mids, and cross the sub lower..

At any rate I do want to do some internal cabinent mods
and pulling the crossover won't be a problem. When I do
I will scan it in and post a good picture..

 

[Mark_E_Smith]

I would hold off on the opinion of 100 Hz is not low enough. When you get your sub in you might find that it is allot tighter and the bass is great. I will bet the -3 dB is about 80Hz anyway. My system uses a 10" w a 10" PR and a ribbon tweeter that crosses at 800 Hz. The bass was muddy and weak I added a M&K sub and just configured to support the bass, it is now tight and very defined. That said when I redo the mains I am targeting flat to just 100 Hz with the LT sub(s) taking over to 20 Hz. BTW I am using an Onkyo TX-787 also.

I plan on yanking one of the passive crossovers and

I know you really like your ARs, but you are approaching designing your own, like me. You are just a year behind.

 

[Brett DiMichele]

Mark,
There is no doubt I am getting to the point where I want
MORE, More of what? More of everything I guess..
I don't think my AR's are unimpressive, I just want to
tweak, I have this need to piss around! I am never really
happy with anything (not even my cars)...
I am the exact opposite of "if it ain't broke don't fix it"
I am more like.. "If it ain't broke, your not trying hard enough!"

The internal cabinent mods I plan to do is not something
I think any Mid Level speaker company would do, as it is
the AR9's are very well constructed, the cabinent within a
cabinent design was suprising to be honest, most companies
would use a sealed back midrange, AR actually built 2 small
Mid enclosures within the main enclosure..
I just think I can tweak those enclosures a bit, they need
a little more pollyfill than what AR put in, and while I am
at it I want to dampen the enclosures so there is no chance
of resonance and I want to put that acoustic tile in the
back of the enclosures to stop any chance of standing waves
that may be in there.. (there probably is...)
What do you honestly think of your 787? I just don't know
what I think of mine.. First off it's never driven my 9's
any time I turned the volume up and the bass hit the receiver
went into thermal overload (wussified amps...)
It doesn't sound bad, in fact DTS sound tracks blow me away..
2 Channel isn't bad at all.. But I want better, and that is
why I am trying all these tweaks and cheap tricks and such..
It's all about playing anyway..

 

[BruceD]

Brett,
Rather than modifying what you have, you could try a very transparent active xover like the Marchand XM9-L, which you can get even cheaper in kit form.
I think this would be better than mucking with AR's OEM passive xovers which are probably optimized to their current drivers capabilities.
I've been using one for the last 4 years in my setup and it is really transparent (it gets good reviews over at AudioAsylum).
This way you can manipulate the crossover frequency and have level controls for the high-pass, low-pass, and the exact xover frequency (3 level controls).
It also uses fairly steep (24dB/octave) Linkwitz-Riley zero phase offset xovers.
Marchand

 

[Mark_E_Smith]

Brett,
I have never even heard the fan come on and I have played mine at 100 dB for 30 to 40 min several times. My system is very efficient though. My honest opinion is; it is a good receiver, I wish it had one more s-video inputs and one more toslink. The switching between Direct 5.1 and analog is really stupid, not on the remote or auto sensing. Sonically I never did an A/B to anything that I would call a reference and it wouldn't be fair as the only thing I had that I would consider exceptional was a stereo. From memory it seems to do a good job electronically. My opinion is that once you get to this level of amp they are all pretty accurate. It is way better than the Sony PL it replaced

 

[ThomasW]

Do NOT substitute a Marchand XM9 for the stock XO in the AR's. Passive XO's have things like bafflestep compensation built in. The Marchand doesn't. Also the passives can have different XO slopes for the different drivers. The Marchand is 24db/octave only.

Don't misunderstand the XM9 is a great XO at a great price. (I have 5 of them!), but it's not a generic replacement item for any passive XO.

Also unless you know what you're doing leave the stock XO's alone.

And do continue to use the 10"s even after you've built your sub. Trying to get adequate SPLs out of the little 5.25" drivers will result in their destruction. Drivers that small run into a problem called 'radiating/radiation resistance' when being driven hard. They simply lack adequate displacement to move enough air. If the XO point is lowered from 100Hz to 80Hz there probably isn't enough Xmax and the midrange cones will be on the floor with the first loud passage.

As for the "THX" standard it's bunk. It's a marketing tool to gouge mfgrs and make the public pay extra for something that's utterly unnecessary.

Instead of hacking up your current speakers. Build a kit or design something from scratch. AFTER it's successfully working, sell your intact stock AR's

 

[BruceD]

Thomas,

Hopefully Brett understood I was guiding him towards using the Marchand as a xover between the AR9 and a sub without changing anything in the AR9.

In other words leave the AR9 completly stock and use the Marchand to blend the sub with the AR9. This would allow him to tweak and play with a sub xover and his room.

I never meant to indicate the Marchand would substitute for the AR9 passive xovers.

 

[ThomasW]

Bruce

In his initial post he talks about already having an amp with a variable frequency XO for his sub.

 

[Brett DiMichele]

Thanks for all the advice thus far.
Bruce, I allready have enough crossovers I don't want an
active crossover between an allready active crossover in
the receiver and a passive crossover in the speakers themselves.
Tom,
I understand that crossover design is an art form and that
it takes very skilled knowledge and equipment to build a
crossover from scratch. But would it be that difficult to
experiment with just the one frequency slope?
I know the THX thing is just a set of specifications and a
price a manufacturer has to pay to get it.. But my point is
that the Receiver is a THX certified component and as such
crosses over at 80Hz where as the speakers do not.
It just seems to me that the mids can handle 80Hz without a
problem, they are super efficient (92Db 1W, 1M) it doesn't
take much to drive them to very good levels.
Here are the specs on the raw mid driver (AR uses the HiVi
Research Mag Alloy 5.25" units)
* Power handling: 35 watts RMS/50 watts max
* Voice coil diameter: 1"
* Nominal impedance: 8 ohms
* DC resistance: 6.5 ohms
* Frequency response: 50-6,000 Hz
* Fs: 50 Hz
* SPL: 85 dB 1W/1m
* Vas: .35 cu. ft.
* Qms: 2.46
* Qes: .57
* Qts: .46
* Xmax: 2.5 mm
* Net weight: 3.75 lbs.
* Dimensions: A: 5-1/2", B: 4-1/2", C: 4", D: 3-7/8".
Now, I know this is an off the shelf version, I am sure
that AR had HiVi tailor these to thier own specifications
because this driver models well in a vented enclosure but
in the AR9's they run them sealed (They do run them vented
in the AR15 and AR17 though) and they say these can play
down to 50Hz
In a 2 way system they recommend crossing over between 2 to
5Khz
It also goes on to say these are perfect for use in a 3 way
as a midrange in a small sealed enclosure which is exactly
how they are implemented in the AR1's, 9's, 7's and 5's.
But I think I need to get the new sub into operation and
see if I can tie it all together with the 10's running.
Because I honestly love the way they sound when the 10's
are providing the extension below 100Hz they sound full..
But take away the sub section and you left with 100Hz and up
and that sounds nasal and hollow (I guess anything would
that is only playing down to 100...)
I will try running the mains as large, with the external sub
and then I will try running the mains as large with the
extenal sub only (disconnect the internal 10's) and see
what I get both ways.. Either way I can't set them to "small"
because the receiver will cut the mids/highs off at 80 and
send everything else to the sub and that won't work since
the internal crossovers won't accept anything 80Hz and lower
to begin with.
As far as DIY speakers go.... Someday... Unfortunatly the
DIY mains I want to build are hardly a "Rookie" kit.. I want
to built a single full range driver main, using a Manger
bending wave transducer in a folded horn enclosure that
will play down to 80Hz (all from one driver!)
Or I would like to build something with Boehlander (Sp?)
Ribbons...
But these aren't rookie things, and I don't have the equip
to do that level of wood working, and I don't need to spend
thousands of dollars on the equip, and I don't really need
another hobby!

 

[ThomasW]

Brett

Or I would like to build something with Boehlander (Sp?) Ribbons...

They make great drivers . I have a couple of designs that use their RD-75's. Am working on a center that uses the RD28, and Jon's making a array with the RD50's.

For a 'mid-fi' product the AR speakers are actually quite good. I still suggest starting with a kit speaker and leaving the AR's intact. In order to properly use the AR drivers you need a set pretty sophisticated measurments of the drivers in the baffle to get a well design XO. XO's can't be designed by using the mfgr's stated specs.

 

[Michael R Price]

Sage advice, Thomas. Brett, you really should just build new speakers. As for which speakers... maybe a line array, or something high-efficiency. You could probably use a proven design that wouldn't be too much work and would still provide very nice results. It depends, how much time and money would you be willing to put into it and how much better than the AR9's do you want to get?

 

[BruceD]

Brett and Thomas,

Sorry I wasn't specific enough.

Here is a more specific comment on what I was trying to say.

Do you know what type of xover and slope the sub amp has for it's low-pass?

The Onkyo HT receiver has what type of xover and slope on the high-pass, on the low-pass? Then how are the main AR9 speakers defined, as Large?

I was essentially thinking of driving your DIY sub on the 10 inch woofers Bi-amp side of the AR9. In other words, using a crossover between the sub and your 10 inch woofers.

You could certainly try this first with the sub amp's own xover, but do you know the slope characteristics of that xover?

Does your sub amp xover provide for summing L&R bass into a mono output signal?

 

[Brett DiMichele]

Tom,
Have you seen or checked the specs out on the Manger Bending
Wave Transducer?
Don't get me wrong it still needs to be integrated with a
good quality sub it's not "Full Range" as in 20 to 20 but
it does cover tweeter and mid duty and from everything I
have read it's nothing short of revolutionary. Time alignment
and Baffle Step are not even issues since the sound all
radiates from one concentric area on the diaphram.
As for my 9's yes for Mid Fi they are very good.. They are
among the upper mid fi's and IMHO better than some of the
other speakers that always get praise here on the forums.
They are Stereophile B rated and we know Class A is reserved
for the exteme esoteric 15K + speakers...
I have no doubt DIY gets you a much higher level of performance
for less money since your labor doesn't factor in...
I want to do something DIY but not just yet.. I have too
many other things I need first before I even think about
better speakers..
I need better source gear, better amplification and to get
all the bugs worked out.. then a new set of speakers
And I think I will just keep the 9's for movies and have
another set for 2 channel only.. Maybe a real dynamite set
of Bookshelfs for starters and then something more complex
later on?

 

[ThomasW]

Have you seen or checked the specs out on the Manger Bending Wave Transducer?

Haven't heard one. I have my doubts especially given the cost and the concept. Actually they've been around for quite a while. Available, then unavailable, then available, then unavailable......That's not the kind of company I give my money too.

 

[Brett DiMichele]

What do you mean about the cost?

They are $600.00 a driver, you need 2 that's a grand give
or take... They have something in the order of 24 Neodydium
magnets per motor..

I dunno, I just read some third party documentation and
looked at some folded horn plans.. Looked interesting
and different.

I have no idea about the company's history though.

 

[Michael R Price]

So Brett, are you considering DIY amplifier/preamp/DAC?

 

[Brett DiMichele]

Mike,

As soon as I finish my masters in electronics.... In other
words no, I will not be making my own amps or pre amps any
time soon.

It is hard enough just to build something as "simple" as
a speaker which is anything but simple. Something as complex
as a power amp or pre amp I will leave to the professionals
and yes I will overpay for them.

I have my eye on a PreAmp and Power Amp but unfortunatly
I can't come up with that much cash.

The Pre I have in mind is the Parasound HALO Pre and it's
one stout component.

The Power Amp is the real killer though, it's made by Butler
Audio who makes high end tube gear for the car audio world
this is thier first venture into tube home equipment the
amp is a 5 channel hybrid tube power amp that puts out 240
watts RMS x 5 Channels at 4Ohm it's a monster and the price
tag is actually a bargain at $3295.00 considering what
something of this caliber would cost from CounterPoint or
some of the other big names in tube amplification...

And for a CDP I really want an Ah! Njoe Tjoeb 4000 but if I
go with good amplification and pre amplification I may be
able to forgo the Ah! and just go with a good Marantz Professional
CDP..

Just those 3 components I would be looking at 5 grand.....

Nope that ain't happening any time soon...

 

[Michael R Price]

OK, ouch that's some serious money. :frowning: I do agree with the "do it right or don't do it at all" philosophy here though.
I'd suggest you look into buying a good used 2-channel amp for your mains, that would probably bring the most improvement for music and not cost too much. Actually I shouldn't say that because I haven't yet tried a good DAC and preamp.
This stuff is simpler than you may think, some of these things are available as kits which you just solder the components onto a circuit board, bolt it on a heatsink and wire it up to a simple powersupply. In fact, I just finished the power supply for one channel of my big amplifier, it took about half an hour! Before reading up about this stuff I had no electronics experience. Okay, I'll stop trying to convert you to DIY electronics now.