The key is damping the vibrations with huge amount of sand, preferably quartz sand. The wider the contact area with the walls is, the better damping. The other side of the problem are the air-born resonances inside the enclosure. There are only two ways to eliminate them completely – with proper geometry of the box and using “soft walls”, because the standard damping materials are not efficient at low frequencies.

I used thin velveteen layer to hold the sand at proper position without leakage inside the enclosure. The result is amazing – first effectively damping the vibrations of the baffles and second – absorbing all the energy from the back wave inside the box. As we Bulgarians say: “One shot – two rabbits”

This way the only sound I get comes from the cone of my modified ScanSpeak 25W/8565-00s taking the box 99% out of sonic equation. I definitely know why Romy likes so much this driver even I do not have proper amplification at the moment. It is capable to throw absolutely wonderful tone, it makes the Sound full of body and weight, very harmonically rich and the same time very transparent. I listened to the box before the sand filling and the sound was different – the bass was stronger, but not so defined and with less finesse (I do not mean blurred), definitely there was some kind of sonic fog. Now the bass notes are much more meaningful, allowing me to consume musical content more easily. Almost forgot – one of the secrets for proper low bass is having the front baffle as wide as one could afford

Haralanov,

Here some raw cements of my on it, without any particular order of importance….

1)      Sand damping it beautiful, it is well-recognized, but you do pay cost for it, in your case the cost is space. Sand is very little compressible damping and if you have the same volume with no sand then you would have  the resonance of the whole enclosure a few dB lower, or you would have almost twice smaller enclosure for the same bass. It is important to understand that when I say “the same bass” I mean the bass in term of SPL pleasure per power. However it is very much not complete or even overlay important characteristics as it has no indication about the quality of bass that is much more complex category.

2)      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? 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.

3)      You need to take under consideration the not only the sand walls were beneficial but the face that you have the internal cavities of irregular shape – very good for Sound. Kharma Exquisite used the same idea of the internal irregular cavities…

4)      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.

5)      If you feel that 25W/8565-00 is a good driver then try many of 25W/8565-00. I have single driver enclosure, 2-drivers enclosure, 4-drivers enclosure  and 6-drivers enclosure . If I have space I would have 20 of the 25W/8565-00 drivers enclosure. More drivers- mean less exertions of each driver and – oh boy ! they do sound phenomenally with little power… You might try it using both channels on one side and playing mono recordings…

6)      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.

7)      Why do you feel that the front baffle shall be as wide as possible? Where and how you cross them?

8)      Did you try to use a regular pressed wood board as you use but to pile up a 75 pounds bag of sand atop?

9)      What driver over 10kHz you use with this LF section?

10)   Do you know that you might not feel some of the compartments to the full capacity and to to shape sound in own way? You might try to bare into the sand some plastic air bubbles from packing material…. 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…

11)   I see you put some kind of condom atop of the driver basket. What is it?

12)   Try to put a foam wrapper around the center poll of your enclosure.

13)   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…

14)   Are you planning to drive this thing with SET? Be advised that I never was able to find a SS PP amp that was able to do proper bass….

The Cat

Romy the Cat wrote:

10)   Do you know that you might not feel some of the compartments to the full capacity and to to shape sound in own way? You might try to bare into the sand some plastic air bubbles from packing material…. 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…

As an alternative to Romy's suggestion you could try a mixture of sand and polystyrene beads as this will prevent the sand to become a compact mass.

Cheers,

Tuga

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.

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?

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 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.

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…

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.

Romy the Cat wrote:

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

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?

Romy the Cat wrote:

What driver over 10kHz you use with this LF section?

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…

Romy the Cat wrote:

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

Romy the Cat wrote:

Try to put a foam wrapper around the center poll of your enclosure.

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…

Romy the Cat wrote:

Be advised that I never was able to find a SS PP amp that was able to do proper bass….

haralanov wrote:

There is a huge difference in sound with hard and soft (sand based) walls even at 1mm excursion from the driver.

If it so ten it is an interesting found. As I understand it is about the “stopping wall”. I wonder if the positive effect you report would be identically favoriteable for 100Hz and for 30Hz. That way I asked you where and how you cross your LF section. I think if to think further in this direction then it is possible to use the “hard wall” but to make the surface of the wall not flat but with high indentation textile, like a high bas-relief. Then the leading edge of the pressure of wave will not hard-bounce from the wall but will be time-damped, mimicking what you do with you soft wall. I think it is a cool idea and I never seen it done in hard surface inside the speakers. Pretend that you have the profile of the inners wall of enclosure like on the image below, with irregular high of the peaks, and made not with soft foam but with hard wood. That would be very cool to experiment with….

haralanov wrote:

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:

Yes, it is my wiring diagram only I have all 6 drivers 25W or the 10”.  Sure, I would need to go for all parallel connections and rewind the transformer for 0.8R secondary. It is somewhere at the bottom of my list to do… sometimes….  BTW, one of the reasons why you might have less sensitivity to the damping change because your SET amp might use some global feedback, does it?

haralanov wrote:

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.

Interesting! I never looked into it.

haralanov wrote:

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: 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 Best regards, P. Haralanov

This is very interesting observation. I am in away envy that Petar went for a set of large woofers (4x23”!). This is the way to go! Unfortunately I did not experiment with it even I had the drivers and means to do it. My problem was with the fact that I need the woofers to be in time alight position and faced directly to the listening location. Pilling up the boxes of multiple 18” or 24” footer in the mid of my room would be very destructive to the way how my room “feels”. So I juts can afford to do it from decor perceive, so I never went there.  Still, the biggest reason however was not the decor consideration but that I feel very satisfied with the 25W drivers. I would like to add even more of 25W drivers, in fact I did plan to rebuild my woofer towers, putting 8-10 drivers per channel and increasing the depth of the boxes: I do not want to ad width of the baffle that I would like to keep at 12”. I never went anywhere with this project and I do not know if I will.

haralanov wrote:

The second reason why I switch to considerably bigger woofer units is because they have much better tone (if properly made!). It is the same as reproducing a midrange with an optimized for midrange reproduction driver, instead of array of 10 tweeters. Well, using 10-20 tweeters to reproduce midrange will give you some midrange sound, but that sound is very far behind the sound of the dedicated midrange driver in context of tonal department.

With my very enthusiastic support of the haralanov’s bass move I would like to tone that the above quite is not truly accurate presentation of what is going on. First off all the collection of 10 tweeters are not the same of the collection of 10 woofers. Woofers do not suffer from HF lobbing and Woofers can form line-array that has a LOT of benefits at LF. It is not only about the better or worse individual woofer but about using the line-array benefits as well. Also, about the “tonal department” – it is depends how the woofers are used. In my case I cross then at 3rd and 4th order (different for L and R channels) at 20Hz. There is truly no “tonal department” in those frequencies and with such a steep orders.  I would say that it more colors the midbass channel then indicate own tone. So, I presume that in this context we can talk about tone of woofers. It of cause would be very different if the woofers are cross as 40Hz or at 80Hz… I do not insist that 25W drivers are great tonal drivers at any range and I do admit the there are many other woofers with paper suspension that are much more tonally capable.

haralanov wrote:

There is another reason why I switch to bigger woofers, but this reason is indirect, because I can get the same effect by using a lot of 10 inchers. This is because sometimes I really love to listen at ultra loud levels, and I don’t want to have compression, distortion and dynamic restrictions in the low bass range when listening at 110-115dB. There will be around 2500 (there is no mistake in the number) liters of air behind EACH of the 4 woofers. May be in future I will add another pair of 23 inchers per side in order to have better dynamic reserve when listening at 120dB levels. And not at the last place, I kicked the 25W woofers out of the system, because they tend to have just a slight taste of very soft rubber in the bass tone. This taste is very delicate, because the soft rubber is not directly in your mouth, but you feel the rubber as some kind of after taste after eating rubber in the previous day (just like eating garlic) but you can still feel it in your mouth/ear...

I am with you with the dynamic restrictions at 115dB. I do feel that 25W have it but are you sure that it is drivers but not your amplification? To drive them to 115dB at 20Hz would take an immense amount of power. What I observe is that with multiplication of 25W driver the effect of dynamic restrictions much softening and become very malleable, up to the point to be addictive in a way. I kind of like that very sort of “soft clipping”. It might not “impressive” but it is more forgiving and more naturally sounding to me.

About the “taste of very soft rubber in the bass tone”. At wish range? If you use then at 150Hz then they do sound like rubber garbage and nothing else. With drop of crossover point the rubber tone is gone and get converted to own very interesting infection of almost 2 harmonics. If you use them at let say 60Hz and sharp filter then I would not disagree that they have rubber sound. I do know rubber sound and it is not what it is as Sound of 25W does have differences that usually are eaten by the rubber suspension in the rubber sounding drivers. I would call it not “taste of very soft rubber in the bass tone” but rather the “driver own character” and I would like to note that I am not hate this character and differences of the bass notes are still well exposed though the 25W own character.

In the end I think the real test would be to make the an array with 8 or 10 ScanSpeak 25W drivers per side and to make two boxed with large woofer and compare at 20Hz. If one would ask me then I would bet on the large woofers. Still I do not think that line-array of the small drivers will be uncontestable. I do feel that line-array of the small drivers might be “enough”.

I know that it sounds like by saying all of it I justify my laziness not to going for large woofers. Still, I would like to remind you folks that among many of my diagnoses I am very prone to undertake some crazy audio projects. I have drivers, I have machines in the basements and I have a carpenter who only expects the command “fetch” as he will start to cut the wood in my basement -  when I get back from work the woofer boxed would be sitting there. I never went for it as I feel that the even my current small-array of 25W drivers is enough and does not give me a any frustrations for now.

haralanov wrote:

Now let’s get back to the topic. There are some things that my 25W woofers cannot do, no matter how much of them one is going to use. This is also true for any 10” woofer existing on this planet. The restriction is entirely due to the cone size. The behavior of a 10” cone is very different in comparison to a much bigger, lets say 23” cone, because the bigger cone couples very effectively with the surrounding air (just like horns!) because of its large radiating area for a given voice coil. When you have larger area, you have better control over the cone movement, because now there is more “attached” air which causes this control. But the moving mass must be as little as possible! Make some very simple experiment: Take a piece of cardboard with a size of approximately 22”x22. It must weight around 80-100 grams. Now try to make some wind, while waving it back and forth. You have to note it is not so easy to move it, because you feel high air resistance against your attempts to move it easily. Now take your phone (its weight must be approximately the same) and perform exactly the same movements with in the air, while holding it in your hand. Is there any wind? No? That’s for a reason. Do you think it is harder to control your hand movement because there is no air resistance that damps the inertia of the phone in your hand? Congratualtions! Now you know how the voice coil feels while pushing a small cone :-)

haralanov wrote:

My bass channels will use 2x23” underhung woofers per side. The scale and authority of the big woofers (if they are properly made!) is absolutely unmatched by a stack of several smaller ones due to the above mentioned reasons. Take a look at the cones...The second reason why I switch to considerably bigger woofer units is because they have much better tone (if properly made!). It is the same as reproducing a midrange with an optimized for midrange reproduction driver, instead of array of 10 tweeters. Well, using 10-20 tweeters to reproduce midrange will give you some midrange sound, but that sound is very far behind the sound of the dedicated midrange driver in context of tonal department.     There is another reason why I switch to bigger woofers, but this reason is indirect, because I can get the same effect by using a lot of 10 inchers. This is because sometimes I really love to listen at ultra loud levels, and I don’t want to have compression, distortion and dynamic restrictions in the low bass range when listening at 110-115dB. There will be around 2500 (there is no mistake in the number) liters of air behind EACH of the 4 woofers. May be in future I will add another pair of 23 inchers per side in order to have better dynamic reserve when listening at 120dB levels. And not at the last place, I kicked the 25W woofers out of the system, because they tend to have just a slight taste of very soft rubber in the bass tone. This taste is very delicate, because the soft rubber is not directly in your mouth, but you feel the rubber as some kind of after taste after eating rubber in the previous day (just like eating garlic) but you can still feel it in your mouth/ear...

oxric wrote:

I wish you good luck with the wide-range effort

oxric wrote:

My own personal exposure to widerange drivers has never been very positive but the theoretical benefits of such a design cannot be denied.

oxric wrote:

an 18" driver is equivalent to roughly 3x10" and a 23" driver to 5x10" drivers in terms of cone area, so I can see the benefit of going for 4 such drivers equivalent to 21 10" drivers no less.

oxric wrote:

I hope that your driver, if you mean for it to be commercialised can be used to good effect in a smaller enclosure!

haralanov wrote:

Romy, I do agree with all your comments. It is true that the magnitude of the rubber taste very much depends on the crossover frequency. I used them below 64Hz, but with first order filter, implemented before the amp that drives them. With that kind of setting there is very slight rubber taste, and it is absolutely not annoying, but it is there and I’m able to hear it. I intentionally do not use steeper filters. I very much like the way how bass arrays portray the low frequency scale and size. A pair of woofers listened at 90dB are far below the level of sonic 3D effect (sorry for the stupid phrase, but I cannot describe it accurately in English) which one gets by listening to an array of 4 woofer pairs, listened again at 90dB. With arrays, bass has size and physicality – not only SPL level, as is the case with only one pair of woofers. But you know all that much better than me, because you are listening at bass arrays for years. The point is to have as much radiating surface through the vertical plane as possible. I will move to live in my house in the province and I have quite a big room there, which I will use only for listening (it has solid floor and quite a good acoustics) so I can afford to put as much woofers as I want, and may be I will end up with 8 x 23” woofers in order to have very even bass response at my listening chair.

haralanov wrote:

I simply prefer speakers which do not have their own “intelligence” at/around their Fs.

This is a noble but controversial desire. If you true would like to accomplish it then dive your woofer with negative output impedance. But… you will feel a need to EQ drivers as no one makes the drivers that can work without reliance upon the Fs.

PS: haralanov, and everyone, I constantly ask people to do it. In the top of my gallery where you input imaged there is a note: “Attentions: before uploading, please, name your images identifiably.” Would you be so kind to comply? It is not my administrative wish, it is a necessity. The images are being uploaded to Site_Images directory if my server and as they accumulated it is getting too slow to open the gallery. So, I have a process that moves the User Images to the Site Images directory and updates the reference in the user posts. If you name your image too generic, in the way how your camera does it, like “DSC_1417.JPG” for instance, then when the image is moved to the Site Images directory with many thousands images then it might meet the existed image with the same name.  I did not write a provision for it and I feel it is not too difficult for posters to mane own images with  own unique name.

Again, I do not agree with all notion of Rubber sound that Haralanov seeded.  I can not speak what was in the situation that “be” described and 400Hz crossover. I do have the 8” version of 25W driver (I think it is 21W) and my feeling that it sound along the line with 25W driver. I would say that from what I heard in the sound of 21W it has more rubbery sound then 25W. The problem is that I do not attribute or associate the character that 25W or 21W drivers have to Rubber at all. It might “feel” that it is sort of like rubber and looking at the driver it is very easy to conclude that the rubber is the guilty party. I do not feel this way.

The 25W footers are made with Styrene-Butadiene rubber wish is synthetic polymer and frequently used for many different things. SkanSpeak calls the suspension ofthe 25W woofer as "non-inertia" suspension. Sure this is just marketing things BUT when I first touched the 25W woofers I did get a feeling the it is not a regular rubber as SkanSpeak probably used much thinner rubber on those drivers, Put in this way: many other drivers the I touched did not impress me with this feeling of suspension non-not intensive softness. For a first time I touched them it was when John Dunlavy upgraded his SC-IV model in end of 90s to the SC-IVA replacing whatever woofer the model SC-IV had with the 25W. It was very good move for those speakers and I did noted that SC-IVA had much more interesting bass then SC-V or even the SC-VI. This  thin rubber suspension on the 25W driver does not feel like rubber to me when I touch it and it more feel like ailed foam or even leather.  In my view it does has different feel to touch when I move the driver by hand.

Now about the allegations of the rubber sound. Well, we all understand that word “allegations” is not literal here but still let talk about it a bit more. In my assessment what you guys call rubber sound of the 25W driver (and I do know what you are talking about) is not rubber sound but the sound of the driver compression. This driver is 88dB sensitive and it behaves like any other 88dB driver. If you take let say a good 15-18” woofer then they would be 97-101dB sensitive, the 12-13dB difference in sensitivity got to be heard. OK, let see how the 25W woofer compresses sound.

In my past I had a number of powerful SS amps (BAT, Spectral, PassLab, etc) that I was experimenting to drive my woofer towers. The best SS amp that I had was Lamm M1.1. Lamm M1.1 was very interesting amp and I have seen a number of commercial ported speakers that never were famous for their bass performance and Lamm M1.1 transformed them into very different bass. So, I was trying in my past to drive my woofer towers with different SS amps. It was OK but ultimately I did not like it and I do concur that it had very sever dynamic restriction and did sound almost like rubber. 

It was in 2000-2001, and I use a pair of Lamm ML2.0 to drive my speakers.  One day I took one of my Lamm ML2.0 from left channel and put it to drive bass towers of my right channel, listening it in mono version. It was truly fantastic as all, absolutely all problems that I hear in the woofer towers with 4x25W driver were gone. It was so wonderful that I immediately played to Lamm for another pair of ML2.0 SETs and frankly I never looked back.

If you look further down the line of my past, the period that is well covered already in my site then at the time when I made my first 3 Channels Melquiades DSET ( at that time I called it Super Melquiades) I was not satisfied with the sound of the bass transformer I had after I added extra two woofers. The impedance of the woofers dropped from 8R to 4R and the new transformer that I has was 6.1R or something like this. I order another transformer that I think was 5.3R. I might be mistaken with the numbers but what I am not mistaken hat there was HUGE difference in the sound of my woofers between 5.3R and 6.1R transformers. You understand that we are taking about very minor change in loading that in most of the cases shall not be auditable. At that time I use 100Hz second order and the difference in sound moderated by loading was VERY substantial.

So, what I am trying to say, BTW, I do remember that I did said it before. There is something in the 25W driver that is very nice. I think that combination of that cone (I use the pimpled cones only), that soft suspension, the masses and anything else makes it very sensitive to loading. My woofers boxes are overtrumped, that makes them even more sensitive to loading.  The soft “saturation” of the SET amps looks like makes the dynamic limitations of 25W drivers to sound very human and very none annoying. In the end with properly SET loaded and many drivers in line-array I truly report that I had no negative qualities you guys associated with this driver and I did liked it a lot. I do concur that it was not the perfect in absolute send but I do not associated it with rubber suspicion but with other factors: low reverberation time in the room, restricted power of my bass amp, inability to put another 16 2W driver in use and so on.

 I do sincerely feel that in that in that time in that small room I had the best bass I heard in audio anywhere. It is very much not ego thing but just my testimony. From certain perspective it was in a way even bass-better then what I have now in my current listening room (not all together but from only certain restrictive perspective). Do I recognize the 25W problems? Of cause I do but I would not name the rubber suspension but rather the dynamic restrictions. If the 25W was let say 10dB sensitive then it would be much more interesting.

So, in the end of the day I feel that you guys call the dynamic restrictions of the driver as “rubber sound”.  In reality with a good SET bass amp those dynamic restrictions are very pleasant and very transparent.

For sure using the larger driver with very different topology is other way to go and there is nothing wrong with it. However, the different sound of the larger woofers is not necessarily is an indication that there is something wrong with 25W woofers, particularly if the efforts were not spent to make the 25W to sound properly. If I have an option to go for 8x24” woofers or 32x25W woofers (or whatever will be an equivalent in volume displacement) and if I had no other considerations (room, location, positions, boxes… etc…) then I truly do not know what I would select. I know that if 25W woofers had extra 10dB sensitively and had extra 10-15dB of compression point then I would not doubt about my choice as I feel that there is something very nice, very organic, very pleasant and very sort of speaking human in the sound of the 25W driver. Not it is NOT the tone-wealthy driver (like some others) but it still has that “something” that makes it to be loved my me.

Romy the Cat wrote:

Here is the idea that I had for the “ultimate bass” for my room. Below is the picture of Macondo one channel as it is now from my listening position. So, if I find a way to deal with the wall edge at my ceiling  then I might replace the current 72” woofer tower with 110” woofer tower of identical width (marked in red at the photo), make it 4 deeper and put in there 8x25W driver per channel.  One 18” driver has as much air displacement as 3.2 ten inch drivers. So, 8 drivers in term of displacement are the same as two and half 18 inchers….

Romy the Cat wrote:

Here is pretty much the idea that I had – a very tall line array with min footprint and with more of less corrected timing error by angling the front baffle. At the picture below the curvature of positioning of Macondo channels is not depicted (for sake of graphic simplicity) but the idea is well exposed.