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Old 24th January 2011, 02:24 AM   #21
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Quote:
Originally Posted by bear View Post
I'd go with 5kV or higher caps.
Since it is cheap enough to get the higher voltage caps, why not?
No argument here. There isn't much difference in cost between 3kV & 5kV 3300pF ceramic caps.
I was just trying to make sure he knew not to try using caps with lower voltage ratings.

Quote:
Originally Posted by bear View Post
Measuring along the multiplier the drops appear to be pretty even... about 1.5kv per, iirc...
Referring back to the schematic in post #18...
I measured roughly 1kV for the first cap in the multiplier, C8, and 2kV for C6, C7, C9, & C10.
Output is series of C8 + C9 + C10 = 1kV + 2kV + 2kV = 5kV.

Last edited by bolserst; 24th January 2011 at 02:30 AM.
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Old 24th January 2011, 08:38 PM   #22
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Default Caps are on the way...

Mathieu: I am off to the post office to send your caps this afternoon. thanks and best regards Moray James.
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Old 2nd February 2011, 06:41 PM   #23
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I received everithing
- Yellow caps, thanks you Moray James
- 3300 nf +/-20% caps
- 1N4007 Diodes

I'll assemble everything asap, and keep you informed,

Mathieu
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Old 2nd February 2011, 07:30 PM   #24
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Thanks for letting me know. Have fun and watch where you put your fingers those caps can knock you on your back side. Best regards Moray James.
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Old 3rd February 2011, 02:32 AM   #25
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Quote:
Originally Posted by Acoustannoy View Post
I received everithing
- Yellow caps, thanks you Moray James
Mathieu
Just FYI, HV ceramic caps have nice feature: to short without the warning. I would opt for the film ones.
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Old 8th March 2011, 08:53 PM   #26
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Quote:
Originally Posted by bear View Post
Wrong caps - but the ones you changed MUST be of VERY HIGH VOLTAGE or they will break down. Did you save the old ones? Note the ratings - iirc like 15kv or so!!!

The caps you want to change are the ORANGE ones. Do those first, then the diodes, or both at the same time... never the diodes first. The caps failing kills the diodes... although the diodes failing might kill the caps too...

The impedance of the Acoustats does not fall like most ESLs... the interface is patented and that is part of the point of it.

In the second image the big series resistor seems to be overheated and has some burn spots, hard to tell from the pix...

Biamp? Not a plan - the Acoustat does not have a "xover" as you expect - it does not have highs coming from one transformer and lows from another, they overlap by several octaves! One could bi-amp but it would be slightly tricky and it is unclear what advantage you'd have... there might be one, but it is somewhat unclear, and in the event one amp was inverting and the other wasn't you'd have real problems until you figured that out...

For the diodes try looking at an electronic distributor in your part of the world, or if you mail order from afar, almost any major USA (or British, probably German too) distributor will have diodes of a suitable PRV... you can series two diodes to get the required PIV in a pinch...

_-_-bear
FYI - the bias multiplier capacitors are not consistently BLUE. Many brands were used over the years, some brownish-yellow, some blue, some orange. This is not an audio-critical part, so the choice of brand or dielectric type is not important. I would recommend any general-purpose ceramic-disc capacitor, as long as the voltage and capacitance is the same. These are the five capacitors clustered around the five high-voltage diodes.

And about those diodes - the originals were rated at 25-mA, 10-kV, so virtually any diode with similar ratings, and similar physical size, will work fine. Diodes with a higher current rating have no sonic advantage, and their larger size may make mounting difficult. This is one application where you do NOT want ill-fitting parts sticking up in the air above the board.

I agree with Bear that bi-amping Acoustat speakers is not practical, and I doubt you'd gain much, if anything, by doing so. Which is not to say that some folks haven't done biamping...just my opinion that it won't help your problem.

Unless you have a very early interface (and you do have a later model) I would NOT recommend replacing the original 0.01-uF, 6-kV coupling capacitors. The originals are custom-made for the application, and have a polyproylene dielectric, so there isn't much room for improvement there.

What type of fuses are you using? Acoustat always recommended slow-blow fuses. If you use the fast-blow type, you will have 'nuisance' blowing on musical peaks.

Keep in mind that using an under-powered amplifier, driven into clipping, can cause more problems than using a large-power amplifier.
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Old 30th March 2011, 07:41 PM   #27
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Dear Andy,
Nice to meet you on DIY.
Years ago, I carefully gathered your previous articles on the audio circuit together with J.Stickland releases. Now I found here on DIY many good advises. DIY is really one of the best Audio websites in the world !

Acoustats are still among the best speakers I've at home, they stay in my living room and I listen to them almost every day. It took long time before I found the right amplifiers for a decent price.
Now they are droven by a pair of Electrocompaniet AW180. One day, I will certainly switch for McIntosh, but this can wait : I'm quite happy with the Norway's amps.

Here I come to my questions, dear AcoustatAnswerMan !
I obtained sustantial sound improvement by :
1- choice of the cables and earth grinding -the Acoustat are extremly sensitive to the wiring-

2- changing the type of the C2 caps wich are directly connected to the pannels :
=> I tried WIMA caps ang obtained a smooth precise sound, but I was warned by our DIYcolleagues that the caps I choosed are too low in max tension. So I switched back to the original yellow ones.

3- adding two steps to the tension elevator ladder. The power handling is
improved together with dynamics : see curve 2 in comparison with the original curve 1 : the impulse answer is noticably higher. But the sound is more 'projected' in the medium area. Measurement curve 2 seems to confirm this, with a less flat response in the medium area.
=> What is your opinion ?

4- Adding a subwoofer in the very low area.
- The Sub is made of a JBL 15inch speaker with a carver PM1.5 amp and Behringer active filter. Works great from 20 to 60hz. Response curve is N3. not very flat but low freq. measurement is almost impossible. This improved the power handling and stereo at high levels, and gives a deep and dynamic bass.
BUT... until today I could not find a good hi-pass filter for the acoustats.. I tried actives one but the result is very poor, the sound is not so rich andtransparent. Then I switched to a simple condensator between the preamp and the amp. The result is better sounding, but the slope is only 6db/oct, and still not as natural as without any filter (see curve 4, without -blue- and with -red - 20 Nanofarad Cap).

=> What would be a good way to low-cut the Acoustats at about 40-50Hz with a 12db/oct slope ?
- Passive filter seems to me a logical solution but i'm peharps wrong. Where can I find good caps ?
- I hurd about Kaneda 12db passive filters but I have not any experience in this.
- Or should I go in the direction of a classical 12dB passive filter between the amps and the Acoustat ? What is the impedance to consider at 60 hz ?

I hope I don't ask too many questions in the same time,
Regards,
Mathieu
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Old 31st March 2011, 02:16 AM   #28
j beede is offline j beede  United States
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FYI: I owned the original Acoustat 2 and then the 2M "medallion" (taller, full range). For amplifiers I have used ARC ST-70-C3, Sumo 9, Ampzilla 2a, Amber Series 70, Threshold 400a, and Dynaco 400. I liked the Sumo sound the best, but the Dynaco 400 would produce SPL and bass out of the 2-panel Acoustats like nobody's business (this was a few years ago). Using the crazy e-bass track from the Stereophile test disk #3 I measured peak SPL of 102db on my Radio Shack digital SPL meter from a near field listening position. I am pleased that Acoustats are valued today--they were not much appreciated in the late 70s (X and monitor series) and 80s thanks to H. Pearson and his "credit card" coloration comments. I have owned many ESLs (never Infinity SS nor KLH-9); the Acoustats played the loudest. The M-L CLS were the most detailed. Quads the most missed.
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Old 6th April 2011, 10:45 PM   #29
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Funny to see someone mention H. Pearson, whose negativity toward Acoustat may have helped lead to the demise of the company. Other audio reviewers, such as J Peter Montcrieff, were much more positive on Acoustats IIRC. I can tell you with great certainty that the ventings of well known reviewers make huge differences for audio companies, for better or worse (usually the latter it seems).

I respectfully disagree with Andy that the Acoustat experience proves that such a speaker is not marketable. One bad experience is not proof, and there are numerous companies who somehow stay in business making electrostatic speakers, including Quad, Martin Logan, Soundlabs, Sanders, etc.

I just think in the Acoustat experience "mistakes were made" and not necessarily all on the part of the Acoustat companies (original and Hafler), but on the side of reviewers, distributors, dealers, and sheep (people) not seeking out the best product.

The Acoustat represented, and still represents, a high water mark in the pursuit of realistic volume levels in a full range electrostat, and at a reasonable price. The Acoustat people apparently had the vision of being the great speaker for nearly everyone, not just the extremely wealthy or those who accept low volume levels.

Perhaps some of the problem was selling at too low a price? Other electrostat companies stay in business at much higher retail price levels. Maybe give up the idea of making a big hit, like the original Dynaco amplifiers were, because of high value for the money.

Anyway, another area where I respectfully disagree with Andy is about biamping. It is true that Acoustats are less in need of a subwoofer than nearly every other electrostat. They have bass, and the property of dipolar bass is particularly wonderful in not stimulating the nearly universal 110Hz ceiling-floor resonance and possibly other modal responses. Actually, it's quite possible to utilize the lowest room mode(s) to augment the bass in the 30-40Hz range, and you end up with amazing "planar bass".

And on the other hand, getting a subwoofer to work right is pure hell. But now all the variables (such as the need for modal damping in most rooms) are well understood, and the tools we have (like the Behringer DCX 2496 which features 48dB/octave Linkwitz Riley, digital delays, and EQ) are incredible.

While the planar bass may be satisfying to some, I want the real bass, down to 16Hz with room gain. Here is my recipe: LR48 crossover at 82Hz, DCX, pair of SVS PB13 subs. Last year I used Tact room eq, but that didn't solve all the problems. Now I'm going without any EQ (and it still sounds great) and exploring bass traps.

If you cross over much higher than 82Hz, you will start having your sub excite the floor-ceiling resonance, then you are toast without EQ (which doesn't really work either, that's what I was trying to do last year).
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Old 7th April 2011, 01:24 AM   #30
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charlesp210, the "biamping" that was being referred to was separating the two transformers inside the interface and running separate amps to them. Adding a subwoofer is a different subject. I do that routinely, fwiw.

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