How to increase Sensitivity?

[ahasz]

I've been involved with DIY audio for the past year now, and I have completed one project. I've been contemplating a reference level loudspeaker on par with some of the big Wilson's or Tony Gee's Andromeda, and I have a question about speaker sensitivity.
I have been looking at the specifications for Wilson's X1 and it has a sensitivity of 95db/watt. That seems really high, considering none of the drivers used (in their DIY available incarnation) have a sensitivity that high. After researching the drivers it looks like Wilson is using (most likely in modified form) the following drivers:

Focal Audiom TD120 dx tweeter (93.5db)

2 Scan Speak 18W 8545K Midrange units (87.5db)
Focal Audiom 13VX woofer (89db)
Focal Audiom 15VX woofer (? most likely the same as the 13vX)

I'm not sure exactly which tweeters are used as the two rear-firing tweeters, but that is not important. what I am wondering about is how he is pairing the bass and midrange drivers together to get a sensitivity so high?! I imagine the midrange drivers are playing the same frequencies, so that should add 3db to the sensitivity in their range, from 87.5db to 90.5. It would also seem likely that the two bass drivers are working together as well, increasing their sensitivity to 92db. I'm guessing that since the X1's are ported that increases the sensitivity in that range too. I don't know how much though.
Is it possible to increase sensitivity anywhere in the crossover? I can't think of how that would be done, I only know how to use resistors to dampen my drivers.
I'm not actually trying to clone the X1's, I am just trying to get an understanding for how they function.


My sencond question is about power handling. In my speakers I am using a Vifa XG18 mid-bass driver as my Bass unit. They are listed as having a short term max power handling of 70w. In my sealed cabinet speakers they seem to move quite a lot at less than one watt of power. They seem to move most when I am listening to jazz and the bass player strums low notes. I understand they move the most at lower frequencies, but I just worry that they will break somehow. I don't really listen to music at high volume levels. I have my amplifier (Sony Str DB 780, rated at 100 wpc) playing at a maximum of -28db, and usually much less. I assume that 0db would be 100 Watts, but at -28db my amp should be putting out ~0.1953125 watts of power. Maybe I am just being paranoid, but I worry about my drivers! I would hate for one of them to exceed it's Xmax and ruin the voice coil.


There are still many holes in my knowledge of speaker building and techniques, so it wouldn't surprise me if some of what I have surmised here is incorrect, but hey, that's what these boards are for, right? I would appreciate any help you can give me! Just so this thread isn't just about questions, here is a picture the speakers that I made. They sound great!

Thanks,
Andrew

[IMGHTTPDEAD]http://www.andrewhasz.com/diy/top.jpg[/IMGHTTPDEAD]

 

[simon5]

The drivers Wilson use are probably 8 ohms drivers.

If Wilson connect them in parallel, the sensivity goes up by another 3 dB because impedance now dropped at 4 ohms. You need a better and more powerful amplifier which can support 4 ohms...

2 18W in parallel so 87.5 + 3 + 3 = 93.5 dB/2.83V
2 13VX in parallel so 89 +3 + 3 = 95 dB/2.83V

Watch out, sensivity and efficiency are not the same thing. In that example, the efficiency will stay the same, you'll not get another 3 dB because of impedance drop. Always check if the speaker is rated at 2.83 volts or 1 watt.

 

[tktran]

Thing is the Wilsons use a single 7" midrange, so how do they get the sensitivity that high?

 

[Audiophilenoob]

Thing is the Wilsons use a single 7" midrange, so how do they get the sensitivity that high?

there are plenty of fantastic midranges that are efficent... the PHL 6.5" immediately comes to mind

 

[ahasz]

Whoops, I think I messed up with the Wilson models, the Scan Speak driver's are used in the MAXX, and that has a listed sensitivity of 92db and 4ohm impedance, so I guess that all makes sense. How on earth they get the X1 to have a sensitivity of 95db (according to Stereophile between 95 - 96.5db) to 97db (according to their own literature) at 8 ohms still baffles me. How much of an effect does porting a driver have on the sensitivity/ efficiency?

Thanks a lot for the info Simon5.

tktran
Wilson uses 2 midranges for all of the fullsize models. here is a picture of the MAXX with the scan speak drivers

[IMGDEAD]http://www.andrewhasz.com/diy/wilsonx1open.jpg[/IMGDEAD]

 

[johninCR]

They lie cheat and steal any way they can, since there is no standard. One method commonly used is in room (not anechoic) with the measurement taken at 2m, then add back 6db to extrapolate a 1m measurement. That method actually makes some sense, since the sound will be more cohesive at that distance, but reflections help to increase the measured SPL.

 

[Mos Fetish]

Andrew

Very nice finish on your speakers. Are those veneer strips on the sides? How eaxctly did you achieve that and is it stained?

Mos

 

[ahasz]

Hi Mos Fetish,
Thanks for the compliment! My speakers are made of solid douglas fir. I bought long 2"x10" planks of it and cut out the shapes to make the speaker with. Those shapes were stacked up and glued. I know that solid woods conduct vibrations more than say MDF, but even at descent volume levels the enclosures are pretty much dead. I didn't use a veneer, instead I stained the wood with a self-mixed combination of red and brown. I put about 20 coats of clear gloss on top of that, which took forever.
I actually documented the whole process here: http://www.andrewhasz.com/speakers/speakers.html

I also just took a video of the woofer moving and am wondering if this is normal. http://www.andrewhasz.com/diy/basstest.avi codec is xvid. In person It looks like they both move the same amount, so I guess either they are both fine, or they are both equally broken.

 

[squalor]

http://www.andrewhasz.com/speakers/project2/broken/images/2.JPG
Man, I would have been .38 hot and in tears at the same time. inspected...............jerks !

 

[johninCR]

http://www.andrewhasz.com/speakers/project2/broken/images/2.JPG
Man, I would have been .38 hot and in tears at the same time. inspected...............jerks !

That brings up a previously undiscussed benefit of open baffles. Customs doesn't have to break them open to inspect for contraband.

 

[Mos Fetish]

Thanks for the link, Andrew. Very interesting.

I asked about your finish because, despite the grain going in different directions, being patterned and colored differently, it still looks just as good as a solid sheet of veneer.

Sonus Faber do a similar thing vis a vis their finished look. The multiple boards on each side of a their Cremona or Amati don't match but they look just as good as solid veneer sheet.

Mos

 

[ahasz]

squalor,johninCR: That was one of the most frustrating things that has happened to me in a long time. I only wish it had been intentionally "opened". Better to know they seriously needed to get into it because of some fear of what's inside, be it rational or not, than to know it happened because of extreem carelessness bordering on negligence.

Mos Fetish: That is the beauty of working with real wood vs. MDF. You get a nice result and it is seemless all the way around without adding a veneer. Right before I left for Germany I visited a few high-end stores and I got to see the Sonus Faber Amati and Cremona. Those are some of the most amazing speakers to look at. Compared to the Wilsons in the store across the street they looked like instruments instead of machines.

Would there be enough interest on this board if I posted a new thread about my speakers? Perhaps other people would want to discuss them but won't click on a thread about sensitivity.