Audiodav unfortunately not a good idea. The acoustic filling in speakers essentially makes the enclosure seem about 30% larger to the woofer than it actually is lowering the system resonance frequency and improving low bass frequency response. It is a bit hard to explain but it does this by making the system more isothermal. When air is compressed it heats up further increasing pressure. The opposite is true under vacuum. The stuffing absorbs this heat on the compression stroke and releases it under vacuum stabilizing the temperature inside the enclosure making the enclosure function as if it were larger. What you have done is decrease the low end reach of your speaker and raised the resonance frequency which is going to increase the volume of the midbass which is what you are hearing.
Mike |
Thanks Mike. Good to know it from the profi side. All in all, this has improved muchly the sound for me. Interesting. Maybe the midbass was the issue and the trade off is about improving it. |
It is possible to overstuff speakers, but removing it should make it smaller and therefore increase the bottom end (at the cost of a faster rolloff).
I know at least one very experienced professional speaker builder (Lee Taylor) who thinks all stuffing is bad and removes the sense of impact and liveliness.
The best way to learn of course is to DIY your own speakers ... (evil laugh)
Best,
E
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It is possible to overstuff speakers Yes I think it is...I hardly believed how much acoustic wool I took out from such a small speaker. I know at least one very experienced professional speaker builder (Lee Taylor) who thinks all stuffing is bad Lol...I assume it is a nice sarcastic joke ;) Lee Taylor (from Leema) has built my speakers.... |
The acoustic stuffing "tricks" the air inside the enclosure into "thinking" the enclosure is larger than it actually is (the stuffing slows down the air molecules). The size of the enclosure and amount of stuffing is part of the designer's tuning of his loudspeaker. To remove some or all of the stuffing is to redesign the loudspeaker. Are you a speaker designer? ;-) |
Removing the stuffing just sounds better. Been there done that. If the volume should have been larger maker it larger to begin with. Hel-loo! Stuffing is really a simple case of monkey see monkey do.
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The original paper on this was done by Acoustic Research in I think it was 1954. They released the first "acoustic suspension" loudspeaker shortly there after the AR-1. Before then most speakers were infinite baffle and much larger like Bozak speakers of the time which did not use any stuffing.
bdp24 the air molecules "moving around" does not explain the increase in enclosure size perceived by the woofer . As I explained above it is a thermal-barometric principle.
Obviously, a speaker can be over filled which happens as soon as you start compressing the acoustic cotton. It has to just fill the enclosurewithout compressing it.
I think "monkey see monkey do" insults the intelligence of many thoughtful speaker designers out there. An excellent manual on the subject is The Loudspeaker Handbook by John Eargle.
Audiodav if you like the sound better than let the force be with you:) |
@mijostyn...........................
Bozak did use acoustical stuffing inside their speakers. The walls and back were covered in a half inch thick padding that was stapled to the inside of cabinet. I should know, I sold and replaced many a woofer and tweeter in Bozak speakers back in the 70’s. |
stereo5, yes you are right. My father had a pair of B302as and as you describe they had I think it was fiberglass insulation probably between 1/2 to 1" thick stapled to the inside wall of the cabinet. They were doing that I think to reduce resonance in the enclosure walls although I can't see how that would work. It would not in any way work in the same way acoustic cotton works in a smaller sealed enclosure. To work the cotton has to just fill the entire cavity. Also in a larger enclosure the pressure (temperature) changes are not as extreme so even if you filled the entire cavity the effect on the systems resonant frequency would be negligible or greatly reduced. The point being that it is not acoustic stuffing in the usual sense, it is dampening of some sort. Maybe there is an old Bozak designer around that could fill us in:)
Mike |
Without it, it will make the bass sound boomy |
@mijostyn...………………...
Sadly, Rudy Bozak is no longer with us. I met him in the early 70's. I drove my company's truck to The RT Bozak Manufacturing Company on Connecticut Ave. in South Norwalk, CT. I was picking up an order of speakers and I met him on the loading dock! He showed me around the entire factory (They made all their own drivers) and even treated me to lunch at a Greek diner down the street. What a nice man. He had some talented engineers, they are probably all gone now.
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@audiodav
A lot of good comments, I am not familiar with your speakers, but I assume that you have sealed box woofers, the comments are reflecting such. I would recommend that you do a search and read about the spec called QTC. This spec reflects the smoothness of your bass using a woofer in a sealed box. A flat response has is a qtc of .707. As your box gets bigger Q goes down, then as the box gets smaller, Q rises. So in a larger boxQ will drop, below that number, say .6, your woofer will roll off faster and eventually takes a dip, your speakers lose deep bass and develop a dip. As your box size goes down, Q rises, a Q of 1.0 will have a significant hump in bass response normally causing boomy bass.
I prefer a QTC of .7 to .8, but many designers like a lower Q to design for room settings, I’ve seen speakers with a QTC as low as .5. If your speaker had a Low QTC, It is possible that when removing the stuffing that you raised Q to a more flat consistent output.... I really don’t know this about your particular speakers, but it is certainly a possibility.
You can slowly add fill to your boxes, as your boxes become stuffed, as others have stated, it will act as though you are getting a larger box, once you get totally stuffed, the stuffing has the opposite effect, once are travel starts being restricted, stuffing starts reducing air volume in the speaker.
This is the basics of how and why, I hope this helps,
Tim
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Another, less technical, way to think of it- not that any of the above is incorrect, its not-
The sound coming off a driver doesn’t just come out the front and into the room. It goes off the back and into the speaker cabinet as well. So now just imagine if there was another mini speaker playing music inside the cabinet. For sure some of the sound it makes is gonna come out through the driver and you will hear it.
Well, that is exactly what happens with every speaker cabinet. The drivers send just as much sound back into the cabinet as out to the room. The sound that goes into the cabinet, by the time it bounces around and comes back out the front there’s only one word for it: distortion.
Now sometimes at certain frequencies this distortion is just right to actually reinforce the same frequency coming off the front. When this happens, if it brings up a dip in response then we are happy and say the speaker is flat. But if it reinforces a peak we complain and say the speaker is boomy. So another example of how people can prefer even something as seemingly obviously bad as distortion.
But its not just the low bass that comes out. All the sound at all the frequencies bounces around in there, and the less that’s attenuated inside by stuffing the more that’s gonna come out the front.
Any one particular individual might like this distortion. With his ears. His music. And equipment. In his room. Speaker builders usually try and design for a wider appeal. That means designing for lower distortion, less color, more neutral tone, etc. That’s why they stuff em. |
I'm sure. My father's B302a speakers were a glorious part of my childhood. With a Dynaco stereo they would play 95 db or so beautifully.
He had an Ampex real to reel and the prerecorded tapes he had were incredible, a lot of Jazz and classical. I miss the hiss:)
What a dummy I am. I spoke to an old friend of mine who was into Bozaks. The insulation was to kill resonance between 500 and 600 Hz, the wavelength of the inside of these large enclosures! I should have thought of that.
Millercarbon, I'm afraid it does not quite work that way accept at certain frequencies that keep ringing after the cone stops as in the Bozak example above. Inside the enclosure sound waves are pressure waves that at low frequencies help determine how the cone moves. Sound from the midrange driver which is open in back in the Bozak does not leak out through the woofer cone. The woofer cone is too stiff and heavy for that. Very high frequencies might but in this case the tweeters are mounted on a bracket out in front of the woofer. At low frequencies the whole cone moves influencing it's frequency response. The enclosure vibrating is a problem and is a form of distortion. In the B302a Bozak this created the very warm bass that a lot of people like my father loved. That enclosure was a musical instrument! It was just 3/4" plywood without any bracing. Nobody would make a speaker like that today. But in that Bozak it was euphoric as hell.
Now I am all for Room Control which is actually speaker control. Most people use it in subwoofers only and downplay it for full range use. I use it to equalize the satellites so that they have absolutely identical frequency response curves right out to 20 kHz. The result is pristine imaging. No two identical drivers are exactly the same and no two drivers occupy the exact same place in space. Two identical speakers in two different locations sound different to various degrees. We locate sound sources by differences in volume and phase (arrival times between ears.)
So, if you want a voice to image dead center the sound of that voice has to arrive at both ears at exactly he same time at exactly the same volume. If the volume of various frequencies contained in the voice is louder in one speaker than the other you essentially dissect the voice and spread it out. The image becomes bloated. Most people try to control this with room treatments. It is much more accurate to use digital speaker control where you are actually measuring the exact frequency response of each individual loudspeaker and correcting them so they are exactly the same. Works great:)
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