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Old 6th November 2012, 03:31 PM   #1
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Default ar38s speaker cross over capacitor value

Anyone can help i need the ar38s speaker crossovet capacitor uf values
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Old 7th November 2012, 05:30 AM   #2
system7 is offline system7  United Kingdom
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6uF 50V non-polar
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 7th November 2012, 12:46 PM   #3
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Default ar tweeter crossover

Is it 2 pieces of 50v 6uf tks
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Old 7th November 2012, 03:34 PM   #4
system7 is offline system7  United Kingdom
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A picture is sometimes worth a thousand words.

Here is the Acoustic Research AR-38S crossover schematic.
Attached Images
File Type: jpg Acoustic_Research_AR-38S_Crossover.JPG (85.3 KB, 147 views)
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Well, there it is! Best regards from Steve in Portsmouth, UK.
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Old 26th February 2013, 10:15 PM   #5
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Just to pick up an old thread...
Thanks for posting the diagram for the crossover of the Acoustic Research AR38s System7. Can anyone tell me what the 6uF capacitor in parallel with the woofer coil is for? My AR18s have no crossover for the woofer and rely on mechanical roll off. I'm wondering if anyone has tried modding the crossovers on the AR38s?
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Old 27th February 2013, 05:48 PM   #6
system7 is offline system7  United Kingdom
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Quite an uninteresting thread, IMO. Not much response from the original poster.

But I can tell you are different. Acoustic Research speakers were made in a time before computer modelling. The idea was the bass had a natural rolloff, much like this SEAS CA26RE4X: H1316-08 CA26RE4X

This leads to the SEAS A26 kit:
The Madisound Speaker Store

Click the image to open in full size.

Click the image to open in full size.

Your Acoustic Research AR-18S speakers are not a million miles away. FWIW, 0.46 mH and 6uF on the AR-38S is a TANK which notches a peak at 3kHz and straightens out phase with any luck. I really wouldn't attempt a crossover mod on the disimmilar AR-18S to attempt the same without knowing more details.

Generally speaking, you have to replace the foam bass surrounds every ten years or so. Maybe replace the 5uF 50V non-polar capacitor. Otherwise enjoy the unique sound and liveliness.
Attached Images
File Type: jpg Acoustic_Research_AR18S.JPG (54.3 KB, 97 views)
File Type: jpg Acoustic_Research_AR38S.JPG (34.8 KB, 96 views)
File Type: jpg AR18S_Crossover_Schematic.JPG (76.1 KB, 26 views)
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Well, there it is! Best regards from Steve in Portsmouth, UK.

Last edited by system7; 27th February 2013 at 05:52 PM.
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Old 28th February 2013, 01:24 AM   #7
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Hi Steve.
That's very polite describing them as "unique and lively"!
Thank you for your help. I've replaced the caps and foam surrounds in the AR18s pair and the AR38s. The tweeters in the 18s sound light, airy and clear. The exact same model tweeters in the 38s sound harsh, edgy and forward. Any ideas on how to tame them?
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Old 28th February 2013, 05:49 PM   #8
system7 is offline system7  United Kingdom
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Graveyboat, you are an ENTHUSIAST!

AFAIK, the AR-18S and AR-38S have the same tweeter:
http://www.classicspeakerpages.net/l...erDrawings.swf

Therefore you are actually hearing cone-breakup from the notched 10" bass of the AR-38S, here shown WITH the notch.

Click the image to open in full size.

You might disconnect the 6uF bass notch capacitor and hope for a similar sound to the AR-18S. Notches are a double-edged sword. They increase cone output above the notch frequency. We can only hope the different 10" bass rolls off OK.

Below is the tweeter response with a simple 6uF capacitor. Crosses over at about 1.5kHz by the look of it.

I throw in the AR-4X crossover and the AR-48S just for fun. I know forum genius wolf_teeth did some work on turning the AR-4X tweeter filter to second order by adding a coil, but can't dig it up right now.
Attached Images
File Type: jpg AR-18S_Tweeter.JPG (72.7 KB, 14 views)
File Type: jpg AR-38S_Woofer_WithNotch.JPG (113.9 KB, 12 views)
File Type: jpg AR-4x_crossover.JPG (36.0 KB, 24 views)
File Type: jpg AR-48s_crossover.JPG (59.9 KB, 26 views)
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Old 1st March 2013, 10:26 AM   #9
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And you sir, are a Champion!
I was wanting to see the response curves for the tweeter and woofer and....here they are!
This is exactly the information i wanted, so thanks again.
The harshness does appear between 2.5K and 5K, which is where the peak is on the woofer response curve.
As an experiment with the 38s, I'm going to remove the 6uF cap from the notch filter, so I only have the coil in series as a 1st order crossover. This starts to roll off at about 2000 hz?
If that still sounds unsatisfactory, I'll try bypassing the coil on the woofer, and using a 4.7uF cap in series with the tweeter instead of 6uF, to simulate the same setup as the 18s.
I think you are correct when you suggest it is the cone breakup on the 10" woofer I am hearing.
I do like the sound of AR acoustic suspension speakers.
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Old 1st March 2013, 07:12 PM   #10
system7 is offline system7  United Kingdom
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I was mistaken in identifying the SEAS drive unit used in Madisound's kit, actually it's this very smooth A26RE4 baby:
H1411-08 A26RE4

I did wonder if a 3.3uF TANK capacitor might notch the AR-38S 4kHz bass cone breakup better, but nothing worked terribly well in my sims. Losing it altogether might be best. Dunno really.

I did find some issue whether the tweeters were ferrofluid cooled in Ar-18S and AR-38S model. Again, not too sure.

Sorry, Graveyboat, It's really up to you to fix this issue. The modern approach is to lower woofer inductance and apply electrical filtering after a coil. It's a measure of AR's genius they did most of this stuff mechanically.

c.f. the high inductance SEAS CA26RE4X with the SEAS CA26RFX .

The second driver will benefit form a (1.2mH?) bafflestep coil and some electrical capacitor rolloff. The first one is fixed.

Wharfedale did a similar layout with the 10" bass Melton 2 on about 1.5kHz crossover, pictured below. Second order tweeter filter, 10uF/0.18mH along with a bass bafflestep coil I'd guess to be around 1.5mH. I liked that speaker even if the midrange was subdued.
Attached Images
File Type: jpg Wharfedale_Melton_2.JPG (47.1 KB, 25 views)
File Type: jpg Wharfedale_Melton_2_Crossover.JPG (56.2 KB, 20 views)
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