There is plenty of information on stuffing of sealed enclosures for best bass response. I have not found much information on the rationale for stuffing mid-range cone driver enclosures. Intuitively it would seem that critically damped Q = 1/sqrt(2) = 0.707 is not so important, but what are the most relevant stuffing parameters to optimise?
I assume the aim is to minimise the wave returning to the cone rear. What is the best stuffing material for this? Is there anything with significantly better performance than fibreglass? The folklore about long-fibre sheep wool advocated by A R Bailey's work on transmission lines, is based on the reduction in sound speed which increases the transmission line effective acoustic length. I don't see this as relevant to sealed mid-range enclosures.
Are the recommended stuffing densities for sealed bass enclosures appropriate for sealed mid-range enclosures?
Is it possible to overstuff a mid-range enclosure? What are the audible effects?
I would appreciate links to serious articles on these questions.
I assume the aim is to minimise the wave returning to the cone rear. What is the best stuffing material for this? Is there anything with significantly better performance than fibreglass? The folklore about long-fibre sheep wool advocated by A R Bailey's work on transmission lines, is based on the reduction in sound speed which increases the transmission line effective acoustic length. I don't see this as relevant to sealed mid-range enclosures.
Are the recommended stuffing densities for sealed bass enclosures appropriate for sealed mid-range enclosures?
Is it possible to overstuff a mid-range enclosure? What are the audible effects?
I would appreciate links to serious articles on these questions.
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In general, yes. If using a synthetic fiber stuffing (acousti-stuff, fiberglass, rockwool, etc), fill the enclosure, but not to the point where the stuffing is compressed. If using long fiber sheeps wool, I prefer to tease the wool first until it is very fluffy and then fill the enclosure at a rate of 1 lb / cubic foot, which comes out to 16 g/liter.
yes. it takes a lot, but it is possible.
The more you stuff the enclosure, making it effectively smaller and potentially making Q>0.707, the more difficult it will be to design the crossover and a achieve a total Q <=0.707.
The audible effect of stuffing an enclosure is that it reduces reduces standing waves and reflections, which would otherwise would come back through the speaker cone and cause constructive/destructive interference which may result in some minor peaks and valleys in the frequency response.
Polyester stuffing works just fine. There will be negligible difference going to some exotic stuffing material and beyond a certain point adding more stuffing leads to diminishing returns and even negative effects if it causes the volume of the enclosure for become too small.
There is some information here and while published in the context of a reflex bass enclosure, the effect is exactly the same for any sealed enclosure - you're trying to avoid the sound coming from the back of the speaker driver escaping from the enclosure, be it either by coming out a port or the driver's cone, and also avoid standing waves developing in the enclosure - the latter not being as significant of a concern for higher frequency drivers where the sound waves are much shorter relative to the dimensions of the enclosure.
https://sound-au.com/articles/boxstuff.htm
The audible effect of stuffing an enclosure is that it reduces reduces standing waves and reflections, which would otherwise would come back through the speaker cone and cause constructive/destructive interference which may result in some minor peaks and valleys in the frequency response.
Polyester stuffing works just fine. There will be negligible difference going to some exotic stuffing material and beyond a certain point adding more stuffing leads to diminishing returns and even negative effects if it causes the volume of the enclosure for become too small.
There is some information here and while published in the context of a reflex bass enclosure, the effect is exactly the same for any sealed enclosure - you're trying to avoid the sound coming from the back of the speaker driver escaping from the enclosure, be it either by coming out a port or the driver's cone, and also avoid standing waves developing in the enclosure - the latter not being as significant of a concern for higher frequency drivers where the sound waves are much shorter relative to the dimensions of the enclosure.
https://sound-au.com/articles/boxstuff.htm
It may be that normal, fabric-store-grade polyester pillow stuffing works just fine, but to be fair to the original poster, I want to add a contrary thought.
I have never done a subjective comparison between normal polyester stuffing and other materials such as acoustistuff, rock wool, shredded denim, sheeps wool. However, there have been several people on this site who say that normal polyester stuffing is not as good, and I took their advice seriously.
https://www.diyaudio.com/community/...ds-shootout-thread.356130/page-5#post-6301135
evaluate what you laying around with frequency response and impedance tests
I do not know if you can get it anymore. But i had very good result with aramid fibre(twaron)also sold as angel hair. I tried fibre fill and sheep wool but liked the aramid fibre best.
JBL does/did not recommend any stuffing according to a old paper i read. But that was for midrange compression driver.
Why do you need to stuff a sealed midrange enclosure? Wouldn't just lining the inside with felt or similar to stop cone reflections be enough?
jeff
jeff
I don't think that would be quite enough. What we want to do is absorb the rear wave as quickly as possible.
To expand a bit on what I said... The sound coming off of the back of the midrange cone is contained within the midrange enclosure, but it will reflect off of the walls and "bounce" back and forth. The faster this energy decays the better. Acoustical absorption, either foam type or fiber type, is the most effective way of decaying this energy down to insignificance.
I find polyester batting to be useful to hold other stuffing in place. In the USA, "batting" is a loose, non-woven cloth-like material that would be used inside a quilt blanket. It comes in a roll rather than as loose fibers. It might have a different name in other regions.
A single layer of batting can hold loose rockwool, shredded denim, or wool in place, and keep it out of the driver voice coil gap.
I should also mention melamine foam as a very good absorption media.
A single layer of batting can hold loose rockwool, shredded denim, or wool in place, and keep it out of the driver voice coil gap.
I should also mention melamine foam as a very good absorption media.
The midrange driver's Fc and "Q" are relevant to achieving a correct filter response for the crossover and cannot be ignored.
Mike
The crossover is a MiniDSP digital crossover so the driver free air mechanical resonance does not affect the crossover filter parameter settings.
The objective for a high quality midrange cabinet is typically to provide a similarish loading to the front while preventing any significant levels of rear sound radiation being returned to the rear of the cone. Cabinet related resonant frequencies typically used to extend the output of woofer drivers should be well below the high pass crossover introduced by the crossover. The reason for this is that resonances degrade the transient response and this is usually avoidable assuming high sound quality is an objective and the low frequency extension sufficient. A high quality midrange cabinet should have a relatively large volume in order to help absorb almost all rear sound radiation. This enables the stuffing to be light near the driver and more dense further away. The reason for this is sound is reflected at a change in impedance and the larger the change the more sound is reflected. Stuffing next to walls is fairly ineffective because the particle velocity is low here. The best location is quarter a wavelength away from walls where the particle velocity is highest and squeezing air through/around fibres meets most resistance leading to the most energy dissipation. Another reason for a relatively large volume.
If you follow the approach of a relatively large volume, light stuffing near the driver, denser further away with plenty away from the walls then the effectiveness of the type of stuffing becomes fairly unimportant as does geometry detail in most cases. Without significant design constraints (e.g. only having a tiny volume available) it is rarely an area requiring much design effort which is likely the reason you have found relatively little on the topic.
Yep... stuffing a midrange enclosure is easy to get right, there are many ways to do it which work well, and you have to go significantly off the rails before it goes wrong.