Hi everyone, just registered to this board and it seem greaqt. I have a question. I currently own 4 Redline ODE-12 subwoofers (they were top of the line 8 ohm subs sold in the late 80's for car audio use and were manufacture by Electrovoice I had paid $1800.00 CDN for them back then). I have a couple of band pass boxes that I inherited from a friend, the boxes seem to require a sub with a higher VAS than my subs seem to have, through some searching I have found out that you can increase the VAS by increasing the mass of the cone (which will also decrease sensitivity), my question is which would be the best way and or material to use to acomplish this increase in mass. I just thaught I would ask before I experimented beacause I don't want to ruin these speakers. Thank you for your help in advance. Ben
By adding mass you are not changing the Vas of the driver. You are changing the moving mass of the cone which then lowers the driver's resonant frequency. The Vas term is the equivalent air volume that produces the same springrate as the driver's suspension. Adding mass does not change the suspension stiffness.
Adding mass to the driver lowers the resonant frequency, raises Qts, Qms, Qes and lowers efficiency - which means you get less SPL with the same power. It does not change Vas at all.
The best thing you could do is measure the woofer parameters or have them measured by someone. It is easy to do with just a voltmeter, a couple resistors and your soundcard equipped computer.
Then calculate the relevant box volumes and tuning frequencies in your BP boxes.
Plug these numbers into a modeling program and then you can play around and see what mods you can make to the box to make the speakers work.
The best thing you could do is measure the woofer parameters or have them measured by someone. It is easy to do with just a voltmeter, a couple resistors and your soundcard equipped computer.
Then calculate the relevant box volumes and tuning frequencies in your BP boxes.
Plug these numbers into a modeling program and then you can play around and see what mods you can make to the box to make the speakers work.
I'd suggest building a smaller box, or decreasing the volume of your existing box (bricks or bracing) instead of trying to make the driver work with a bigger box.
You should measure the T/S so you have some reference thou.
dave
You should measure the T/S so you have some reference thou.
dave
A couple of years back I tried to get the T/S paremeters but ran into roadblocks, the distributor had changed hands a few times and Electrovoice was not at liberty to divulge the specs to the woofers as those were property of the end seller. I did buy from Parts Express a tool called the Woofer Tester, I plugged the woofer into it and ran the tests and noticed that the VAS would change when I added weight to the cone (coins), I also noticed that when Kicker came out with their Solobaric line of subs that they had very heavy cones compared to their regular line of subs, the Solobaric line was made to work in small enclosures. My mind logically thought that mass would solve my little problem because of the 2 observations above, glad I was straightened out before I could damage them. Thanks
Loudspeaker units Vas _ suitability v.s HiFi
Hi there......I'll throw this quickie in; a similiar question was posed to me last year by someone who thought he could put a speaker unit from a car boot into a Hi Fi enclosure.
I'm a bit suprised that Electrovoice would sell 8 ohm units for car use, most who have power ghetto blasters fitted in cars have bridged amplifiers which heave out enormous power, albeit not into 8 ohms but 4 ohms or less.
point 1
Speakers for car boots (those are the ones that boom like ell') are designed specifically with high Vas. The suspension and compliance requirements are different to hi fi chassis types as cars are a pretty tough environment either being left in the hot sun or cold and humid.
point 2.
Car boots aren't really suited for reflex loading so chassis speakers designed for the back parcel shelf fixing, acoustically behave like a large closed box. Car boot area volume is quite high (7or more Cu ft) so that implies a chassis speaker with a high Vas and a relatively high Qts factor can be used. Then things move.
point 3.
A speaker unit designed for car boot app'n will look acoustically small in an under-sized hi fi box and will sound boomy as the reduced box volume will raise the Q.. The bass cutoff frequency will be very high with lack of bass. Some models have moderate Qts (under 0.4) that permits fitting in hi-fi enclosures. This is a classic example where an 8" unit can often sound better than a 15 incher.
For example; there is a massive difference in Qts between Eminence 15" 427 and 427HiPer model (Qts of 0.87 & 0.38) Both are high power models with low 4 ohms impedance. One has to study the intended application and the massive differences in enclosure size to get a fit with a particular unit.
High power Speaker units designed for car use sometimes have built-in coil pump ventilation, the windage noise would be noticeable for hi-fi use, but not with a failing differential.
Chassis speakers vary in specifications just as people do.
My advice if one has chassis units which have come out of a car and the spec /markings vanished, then flog then as car speakers and start again with speaker units specifically for your application. Sorry I couldn't be more negative but it's really the proper course to take.
Posts 2 & 4 sum it up. Tampering with cone physics (other than adding mass i.e reducing resonant freq for a drone unit) is best left alone as there are too many comflicting parametêrs.
😀 rich
Hi there......I'll throw this quickie in; a similiar question was posed to me last year by someone who thought he could put a speaker unit from a car boot into a Hi Fi enclosure.
I'm a bit suprised that Electrovoice would sell 8 ohm units for car use, most who have power ghetto blasters fitted in cars have bridged amplifiers which heave out enormous power, albeit not into 8 ohms but 4 ohms or less.
point 1
Speakers for car boots (those are the ones that boom like ell') are designed specifically with high Vas. The suspension and compliance requirements are different to hi fi chassis types as cars are a pretty tough environment either being left in the hot sun or cold and humid.
point 2.
Car boots aren't really suited for reflex loading so chassis speakers designed for the back parcel shelf fixing, acoustically behave like a large closed box. Car boot area volume is quite high (7or more Cu ft) so that implies a chassis speaker with a high Vas and a relatively high Qts factor can be used. Then things move.
point 3.
A speaker unit designed for car boot app'n will look acoustically small in an under-sized hi fi box and will sound boomy as the reduced box volume will raise the Q.. The bass cutoff frequency will be very high with lack of bass. Some models have moderate Qts (under 0.4) that permits fitting in hi-fi enclosures. This is a classic example where an 8" unit can often sound better than a 15 incher.
For example; there is a massive difference in Qts between Eminence 15" 427 and 427HiPer model (Qts of 0.87 & 0.38) Both are high power models with low 4 ohms impedance. One has to study the intended application and the massive differences in enclosure size to get a fit with a particular unit.
High power Speaker units designed for car use sometimes have built-in coil pump ventilation, the windage noise would be noticeable for hi-fi use, but not with a failing differential.
Chassis speakers vary in specifications just as people do.
My advice if one has chassis units which have come out of a car and the spec /markings vanished, then flog then as car speakers and start again with speaker units specifically for your application. Sorry I couldn't be more negative but it's really the proper course to take.
Posts 2 & 4 sum it up. Tampering with cone physics (other than adding mass i.e reducing resonant freq for a drone unit) is best left alone as there are too many comflicting parametêrs.
😀 rich
Simply speaking, Vas is just a measure of how stiff the speaker's suspension is. More specifically, it's the volume of air that would make a spring as stiff as your suspension. Stiffer suspension, smaller Vas. There's no way to change it without tearing the speaker apart. You obviously don't want to do anything like that with those nice drivers so I'd just stick them in the boxes you have and see how they sound. If you like them, fine. If you don't, build some new boxes tuned to the drivers.
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