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In the Forum: Audio Discussions
In the Thread: Constructing LF modules to the limits
Post Subject: Different factors affecting bass qualityPosted by haralanov on: 4/28/2009
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 Romy the Cat wrote:
Sand damping it beautiful, it is well-recognized, but you do pay cost for it, in your case the cost is space.

I know that Romy… but without the massive amounts of sand, there are always some vibrations felt when I touch the baffles with my hand. In my case I intentionally made the enclosures that big because the need of wider front baffle for purely sonic reasons.

 Romy the Cat wrote:
Would the positive results you report be different if you have hermetic wood made compartments filed with sand without using the fabrics to hold the sand?

My original idea was to use double walls with sand between them, so I made some experiments and came to the conclusion that the air volume inside the box has some disturbing sound signature which “speaks’ through the cone and I was clearly able to hear it.

 Romy the Cat wrote:
Sure, the fabric walls is good as it has “some” elasticity but I do not think that the 25W/8565-00 driver might in this volume develop the pressure to be able to stress the fabrics-shaped sand walls.

Romy, its not about the pressure. There is a huge difference in sound with hard and soft (sand based) walls even at 1mm excursion from the driver.

 Romy the Cat wrote:
I wonder if the effectiveness of your dumping will change with time.  In a few months, when the sand in your enclosure will be settled, try to flip the enclosure upside down and see if the un-compressed, disturbed sand will have a new effect to sound.

I already made that experiment before gluing the top of the enclosures. I was not able to hear any differences when the sand is hard pressed in the cavities. Actually it was very hard to compress down the sand because it is very homogenius and it is very difficult to raise its density.

 Romy the Cat wrote:
If you feel that 25W/8565-00 is a good driver then try many of 25W/8565-00. You might try it using both channels on one side and playing mono recordings…

That was the first thing I made when I finished the enclosures. Wow. The difference is really huge. The authority of sound, the weight of bass notes they give, the ability to portray the real size of the instruments, the sense of scale to all recordings, the evenness of the bass in the room…. I am really motivated to use 4 drivers per side, up to the ceiling, in the way you use them, but with freedom to time align all 4 enclosures because they will be separated from each other.

 Romy the Cat wrote:
The  25W/8565-00 are superbly sensitive to damping by amp, and a fraction of Ohm here and there do make a lot of difference.

I know that and for this reason I use maximally short cables as I can, which are also very thick. They are amazing at very low frequencies – fast and harmonically potent. The drivers are wired directly to the power amp (of course not solid state amp)- there is no coil of any kind.
I read your comments about the supersensitivity of 25W:

http://www.goodsoundclub.com/GetPost.aspx?PostID=1619

It is not my experience. I realize it is sensitive to some degree, but not that much. I tried to find the reason why they behave in this way in the context of your acoustic system and I think I know the reason if it is the wiring diagram of your LF section:

LF wiring illustration.JPG

 Romy the Cat wrote:
Why do you feel that the front baffle shall be as wide as possible? Where and how you cross them?

I do not “feel” that – it is what my ears said at the time when I stick the back sides of two loudspeakers next to the L&R sides of the tiny experimental enclosure (30cm wide) ScanSpeaks were mounted to. The sound have totally different influence to the listener this way. The sense of scale just doubled when the front baffle became twice as wide. The feeling is like you horn load the driver, but the horn has very very little gain. I don’t know how to explain this in English…. It is easy to try this with your bass towers. They are line-level crossed at 64Hz, first order.

 Romy the Cat wrote:
Did you try to use a regular pressed wood board as you use but to pile up a 75 pounds bag of sand atop?

Yep. The side walls of the enclosures are vibrating too much for my taste, even the sand filled bag was over 50kg. It helped a little to control the vibrations – but they were still there.

 Romy the Cat wrote:
What driver over 10kHz you use with this LF section?

I use small Bulgarian made ribbon tweeter from 80’s with alnico magnet system and ribbon size 55x10mm. The model is called “ВЛД 40”.

 Romy the Cat wrote:
If you feel that you are too crazy then I need to disappoint you saying that I know people who pressurize the enclosure and pump inside of the box a replenishable inert gas…

I have my reasons to believe this not too effective method to allow 25W show its potential…
In past I have tried with almost all imaginable damping materials to see what will happen. Dynamat Extreme, natural wool, memory foam (Tempur) and many others. Nothing is as efficient as the sand.

 Romy the Cat wrote:
I see you put some kind of condom atop of the driver basket. What is it?

It is soft polymer which damps the micro vibrations of the driver’s chassis and at the same time gives the driver aerodynamic share to allow the back wave of the cone to be radiated undisturbed. The outеr layer is from velveteen again because purely sonic reasons.

 Romy the Cat wrote:
Try to put a foam wrapper around the center poll of your enclosure.

Good idea, thanks.

 Romy the Cat wrote:
What is your feeling before and after the sane when you scratch the surface of the driver with your nail (my favorite test). The scratching the driver surface it like playing cello – by listening the harmonics of that “scratch” one can say a LOT about the bass quality…

You are absolutely correct about this test. I usually tap the cone first to determine the low frequency behavior of the driver/enclosure as a whole and the second part of the test is scratching the cone – this gives me an idea of the upper spectrum of the driver.
Before the sand filling there was some kind of sonic boom coming from the inside of the box when I tapped the cone with my middle finger, even the speaker walls were lined with natural wool. Have in mind without sand Q of the enclosure is lower because the bigger net volume of the box. With the sand applied I quickly understood what was the pure tone of my 25W/8565 drivers – deep, rich and full of body.

 Romy the Cat wrote:
Be advised that I never was able to find a SS PP amp that was able to do proper bass….

Solid state amps are out of my scope and they should be used only in context of powerful DJ installations Wink

Best regards,
P. Haralanov

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