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In the Forum: Audio Discussions
In the Thread: Constructing LF modules to the limits
Post Subject: A LF solution of seismic proportions then!Posted by oxric on: 9/22/2011
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 haralanov wrote:


Rakesh, during the last year, there were some very important moments in my own realizations about the methods of low frequency reproduction.
I totally abandoned my Scanspeak bass modules and now they are resting in my garage. I intentionally have my listening without the low bass channels, because I first have to make the rest of the audio-band to sound just the way I want it to sound. During the last couple of months practically all of my efforts are concentrated towards the construction of my wide-range 12” channel, because it is the core of my system. 
 


Hi Haralanov,

Thanks for the response. Very scary.

 I wish you good luck with the wide-range effort. You certainly sound like you know what you are doing and I for one would like the opportunity to hear your driver once you have completed its construction. My own personal exposure to widerange drivers has never been very positive but the theoretical benefits of such a design cannot be denied.

Sorry to hear you abandoned the Scanspeaks though as at the time you sounded very pleased with the direction of that project. It is certainly the sort of LF solution that 99% of people might just be able to accomodate after all.



 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 :-)
 




With regard to the practical aspect of your LF project, I am both shocked and spellbound. Well, without being an expert, and at the expense of stating the obvious, 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. But a 10" driver can be used in a 100 litre enclosure to good effect, which one can build fairly easily. But how does one accomodate four 2500 litre enclosures? I hope that your driver, if you mean for it to be commercialised can be used to good effect in a smaller enclosure!

Just to be clear four 2500 litre enclosures (ie. 70cmx70cmx500cm to accomodate your drivers or variations such as 100x100x250cm) is a really huge volume which would take up 10m3, that is 8 percent of a decent 6x7x3m room. To put this in perspective, I calculate one channel of my horn system to take up about 1m3 of total space.

This is not to mention either the material cost and complexity of controlling internal vibrations in such huge enclosures or the problems in terms of positioning such massive structures in a listening room where their large surfaces become yet another area where one has to be careful with reflections from the MF drivers.



 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...
 


You must must have a very understanding family to play that loud and your tympana must have been soaked in titanium at birth! But seriously, if the 23" inchers are really that good, let me know when I can try a pair.

Best regards
Rakesh



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