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 Post subject: Re: Musical System
PostPosted: September 17th, 2017, 11:04 pm 
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Location: Parkville, Maryland
The plates on the back and bottoms of the enclosures actually create a system of constrained layer damping. Constrained-layer damping is a mechanical engineering technique for suppression of vibration. Typically a viscoelastic or other damping material (in my case RTV silicone), is sandwiched between two sheets of stiff materials that lack sufficient damping by themselves. The ending result is, any vibration made on either side of the constraining materials (the two stiffer materials on the sides) are trapped and evidently dissipated in the viscoelastic or middle layer (converted to heat). If you wonder how aircraft can block the engine and air stream noises so effectively is because of constrained layer damping. the marble slabs on top do the same thing but I adhered a layer to the marble so as it would be a permanent feature.

The result in practice is lack of sympathetic vibrations from the enclosure that would add so-called "box coloration" to the reproduced sound. That's the best a DIY guy can do without the resources of the likes of Magico of Wilson to fabricate outrageously expensive enclosures made of extruded aluminum or cast resin respectively. One British manufacturer actually makes an enclosure of two enclosures one within the other with a constrained layer in between.

To answer Shasha's question -- MDF is dense and cheap and essentially somewhat non-resonant as compared to straight hard woods of plywood. Of course there are different grades of plywood. Old school manufacturers used ordinary plywood. But a lot can be said of thick luan plywood that can make for a nice enclosure for serious $$$.

In the case of my Altecs they were fabricated with thick well-braced veneered plywood that was glued and screwed together.

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 Post subject: Re: Musical System
PostPosted: September 18th, 2017, 11:23 am 
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SoundMods wrote:

To answer Shasha's question -- MDF is dense and cheap and essentially somewhat non-resonant as compared to straight hard woods of plywood. Of course there are different grades of plywood. Old school manufacturers used ordinary plywood. But a lot can be said of thick luan plywood that can make for a nice enclosure for serious $$$.


I was not asking a question. Since Chris asked about sonic characteristics of marble, I was trying to lead him into the answer.


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 Post subject: Re: Musical System
PostPosted: September 18th, 2017, 11:33 am 
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Pelliott321 wrote:
Walt has spent much effort in perfecting his system. I use the word "perfect" for to my ears his system is what I feel as about as perfect sounding that can be pulled with a rock being dragged through a dirty alley. I have heard many systems over the past seven years I been associated with CAF, at our show as well as RMAF, Axpona, and the NYC shows and Walt's (IMHO) is the most musical system I have heard.
I feel I have been lucky to experience it.


You are right, its not just the speakers, it his system.

Walt uses all high-end audio gear and modifies them to sound perfect. He talks about synergy of the components.

My visit to his place is an eye opener and a learning experience. One of the lessons is, building a good DIY component is only half the journey. The other half is voicing it, and Walt is very good at voicing the systems.


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 Post subject: Re: Musical System
PostPosted: September 18th, 2017, 1:04 pm 
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SoundMods wrote:
To answer Paul -- stacked stock Quads (as manufactured) with the inputs wired in series with one amplifier. Peter Walker mentioned that you would need a 150-watt amplifier for that configuration. That was then -- this is now. Experiment with trial configurations for the best result. Just keep in mind that electrostatic speakers like voltage since the stators do not complete a circuit. Once I learned that lesson with my "late" Acoustats I found that they were easy to drive.


Walt:

The statement about not completing the circuit is not correct. The speakers are capacitive so if a DC voltage is applied to the speaker there is no current. But they will complete the circuit with an AC signal and therefore draw AC current. The higher the frequency, the more the current. That is one of the reasons early transistor amps had such a hard time with electrostats. The transistors were slow and when the output frequency went up, they could not turn on sufficiently fast to provide enough current into such a reactive load.


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 Post subject: Re: Musical System
PostPosted: September 18th, 2017, 1:21 pm 
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Using a constrained layer construction is a very good way to damp resonances as Walt says. However, it is more effective to prevent resonances before they start. Two ways to do that are to have the size and shape of the box such that you minimize internal standing waves at the frequencies that will be produced inside the box. The second way is to break up the surfaces of the box into various different sizes and shapes to prevent the walls from resonating at the frequencies produced. Many of the high end speakers go to great lengths to do this. Here is a statement from the German manufacturer Tidal:

But building our cabinets from TIRADUR and TIRALIT is just one aspect. Another one, at least as same important, is how it is designed even to the smallest details.
Our deliberately positioned and deadened supports, CAD simulated bracings and chambers avoid the swinging of the exterior walls and yet perfectly house all inner parts, such as they do control and air flow of the sonic and air compression just to name a few.

I'm including a photo of the bracing in one of their speakers. Also is a photo of my attempt to break up the sections of the truncated pyramid I will be using for the bass section of the eggs. Note that the sizes qand shapes of rthe walls are broken up by the random spacing and angles of the attached ribs. Not in that photo is the cross braces to provide cancellation of expanding and contracting forces on the two large side walls.


Attachments:
Base braces_small.jpg
Base braces_small.jpg [ 298.9 KiB | Viewed 19266 times ]
Tidal cabinet.jpg
Tidal cabinet.jpg [ 82.93 KiB | Viewed 19266 times ]
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 Post subject: Re: Musical System
PostPosted: September 18th, 2017, 2:30 pm 
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Actually -- on the subject of electrostatics -- when I had my Acoustat 3s they would give my Threshold 400-watt/channel amplifier a workout and it would actually go into clipping.

That said -- to make a long story short -- a 50-watt/channel tube amp. connected through an auto-transformer step-up brought the Acoustats under control and they kicked ass much to the embarrassment of that MIGHTY Threshold.

The moral of the story? The screens wanted voltage not current. It was an issue that I hadn't thought about since the "wisdom" of the self-proclaimed "experts" said you need a lot power. With a 4-ohm load demanding current the Thresholds could deliver that power, but the Acoustats didn't need or want current -- they were hungry for voltage. It took re-reading a reference on the subject that it finally sunk-in to my audio brain.

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 Post subject: Re: Musical System
PostPosted: September 23rd, 2017, 10:09 am 
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SoundMods wrote:
Here are two photos of one channel -- front and rear views. These photos do not tell the tale however. Just what you see when listening to music.


Walt,
That's a nice looking system. Can I ask what tweeters you're using in those pyramid shaped boxes? They look like they could be JBL 2405s. I'm curious to know where you cross them over and at what slope. I've always had trouble integrating super tweeters in horn systems but I've gotten best results with steeper slope crossovers. But often I just skip it and let the compression drivers naturally fall off or perhaps give them a gradual boost in the crossover.
Thanks in advance.
---Gary


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 Post subject: Re: Musical System
PostPosted: September 23rd, 2017, 10:13 am 
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If I remember correctly the Wharfdales used sand between inner and outer wood enclosures.


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 Post subject: Re: Musical System
PostPosted: September 23rd, 2017, 10:40 am 
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I had a Wharfedale 60 with the sand filled space between the inner and outer walls and the box was very solid. It was a 2 way with limited HF response. I added a tweeter to suppliment the 5" cone "tweeter" and changed the crossover but still not a great speaker.


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 Post subject: Re: Musical System
PostPosted: September 23rd, 2017, 10:41 am 
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GaryB wrote:
SoundMods wrote:
Here are two photos of one channel -- front and rear views. These photos do not tell the tale however. Just what you see when listening to music.


Walt,
That's a nice looking system. Can I ask what tweeters you're using in those pyramid shaped boxes? They look like they could be JBL 2405s. I'm curious to know where you cross them over and at what slope. I've always had trouble integrating super tweeters in horn systems but I've gotten best results with steeper slope crossovers. But often I just skip it and let the compression drivers naturally fall off or perhaps give them a gradual boost in the crossover.
Thanks in advance.
---Gary


They're 077s. Just 6-db/octave and I used a capacitor decade and my RTA to dial in the crossover value. When the Altec horns and JBLs met in the middle then I went about dialing them in terms of overall sound quality. If you'll notice in the picture they are time aligned with the big horns. The cool thing about the add-on tweeters was that I got the expected extension but they had greater impact on the quality of the mid-range. The mids seemed to open up more with greater transparency. Nice!


Attachments:
JBL 077 Add on Schematic 062913b.jpg
JBL 077 Add on Schematic 062913b.jpg [ 69.11 KiB | Viewed 19233 times ]
JBL 077 Add-on Tweeter Crossover r.jpg
JBL 077 Add-on Tweeter Crossover r.jpg [ 54.06 KiB | Viewed 19233 times ]

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