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Speaker sensitivity. 81dB vs 87dB ?

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  • Speaker sensitivity. 81dB vs 87dB ?

    I have the urge to build something, and can't decide what. My current speakers are roughly 81dB 2-ways using 8 ohm drivers. My amp is 100w, into 8 ohms. I could build speakers with two 6.5" woofers, and bring the sensitivity up 6dB. I'm trying to decide if this would be worthwhile, and thinking that it would reduce potential clipping. I really don't know how often I'm clipping now. Thoughts?

  • #2
    You'll have to provide a lot more information, including what you have now, usage and room size.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      Room is 13 x 17 with an opening (7' wide) into the rest of the house. Eight foot ceiling. Current speakers are 6.5" Peerless HDS with a CSS LD22 tweeter in sealed boxes. The amp I'm planning to use is an Outlaw RR-2150 (190w into 4 ohms. ) . https://www.stereophile.com/content/...s-january-2008 I also have a HK Signature 2.1 with similar power.

      Speakers are full BSC, and 6' from the wall. I use a sub, but might port the new speakers, and eliminate the sub. Speakers are not high-passed, but can be. They blend with the sub better with the natural roll-off. Seating is 9' from the speakers.

      Music is varied. Some of my favorite artists are Mary Black, Bonnie Raitt, Mark Knofler, Larry Carlton, Clapton, Dave Grusin, etc. Not interested in rap, or classical. Rock and blues mostly.

      My intention is to use drivers I currently own. I have a second pair of 6.5" HDS woofers, and a couple options for a mid, if I decide to go that route.

      To clarify, I'm not looking for a design recommendation. I'm trying to decide if the additional sensitivity would actually be of much benefit. Since I'm not high-passing, the odds of the amp clipping is increased. I don't hear any issues currently, but I might be loosing a little fidelity at higher SPL. I recall that many members here have much larger amplifiers, and feel that they need them.

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      • #4
        Do you often run your current speakers to their limits? Two woofers may provide 6dB greater voltage sensitivity, but only 3dB greater max SPL. If SPL is the main concern, upgrading the sub or adding another and high passing the 6.5" midwoofer is the best route.
        "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
        exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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        • #5
          Originally posted by dcibel View Post
          Do you often run your current speakers to their limits? Two woofers may provide 6dB greater voltage sensitivity, but only 3dB greater max SPL. If SPL is the main concern, upgrading the sub or adding another and high passing the 6.5" midwoofer is the best route.
          This is a second system in my living room. My HT room will play louder. I don't see excursion issues at all with a single 6.5", when it's high-passed. My 10" sub gives up before the mains do. It's the weak link currently. It's an RS270P in a sealed 1 cu-ft box. I should check excursion without the high-pass, but I think it's reasonable.

          On occasion, I push the system harder, but usually, I'd do that in the HT room.

          The tonal balance is better without the 80hz high-pass. My pre-pro only offers 80hz.. I adjust the sub low-pass with the controls on the plate amp.

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          • #6
            Originally posted by dcibel View Post
            Two woofers may provide 6dB greater voltage sensitivity, but only 3dB greater max SPL.
            Two woofers doubles Vd, which gives 6dB greater max SPL. However, if the sub is the weak link I'd fix that first. I see no point in increasing the mains capability when the sub already can't keep up. I'd put the existing RS270P into a ported box and then add a second, not only to provide adequate output but also to smooth the room response.

            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #7
              Originally posted by billfitzmaurice View Post
              Two woofers doubles Vd, which gives 6dB greater max SPL. However, if the sub is the weak link I'd fix that first. I see no point in increasing the mains capability when the sub already can't keep up. I'd put the existing RS270P into a ported box and then add a second, not only to provide adequate output but also to smooth the room response.
              I agree, but I was more in the mood to build mains. The sub is the weak link with "some" music. Are you familiar with Telarc "Spies"? https://rateyourmusic.com/release/al...f_espionage.p/
              This one might challenge the sub as well. https://www.youtube.com/watch?v=-DzCSHHFc0M

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              • #8
                Originally posted by billfitzmaurice View Post
                Two woofers doubles Vd, which gives 6dB greater max SPL.
                I should have been more clear. Double Sd = 3dB gain. Half the impedance from running 2 woofers in parallel = 3dB voltage gain, for a total of 6dB with respect to voltage, but a power gain of only 3dB. you will get 6dB extra max SPL, but only if you provide 3dB more power into the system. It's only 3dB more "efficient".
                "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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                • #9
                  I'd say it's worth it as the extra Sd also decreases distortion in the woofer range at all volumes, which is the most attractive benefit to me.
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                  • #10
                    Originally posted by dcibel View Post
                    I should have been more clear. Double Sd = 3dB gain. Half the impedance from running 2 woofers in parallel = 3dB voltage gain, for a total of 6dB with respect to voltage, but a power gain of only 3dB. you will get 6dB extra max SPL, but only if you provide 3dB more power into the system. It's only 3dB more "efficient".
                    That's why you should avoid bringing power into the equation whenever possible. When you think about volts instead of watts it's much easier to understand why two parallel wired drivers have 6dB higher sensitivity than one, and 6dB more maximum SPL than one. It's also far more accurate when doing most calcs, because power isn't a constant into any impedance load the way voltage is, and impedance varies with frequency.
                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

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                    • #11
                      Originally posted by DanP View Post
                      I'd say it's worth it as the extra Sd also decreases distortion in the woofer range at all volumes, which is the most attractive benefit to me.
                      It's a case of deciding what's good enough, and where to stop. The current speakers are really good at modest spl. As they are pushed harder, it's hard to determine if the amp is clipping slightly, or if the tweeter is simply distorting slightly. I don't want to go overkill on this system, but a second woofer is easy enough. I could add my 4" Peerless HDS as a mid, and cross the tweeter slightly higher. But, the 6.5" has lower distortion than the 4" in the 400 to 2k range. The 10" RS270P is considerably lower distortion than the 6.5" below 500hz, but I only own one. They are on sale currently! On top of all that, I prefer the smaller box of the current speaker.

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                      • #12
                        Originally posted by billfitzmaurice View Post
                        That's why you should avoid bringing power into the equation whenever possible. When you think about volts instead of watts it's much easier to understand why two parallel wired drivers have 6dB higher sensitivity than one, and 6dB more maximum SPL than one. It's also far more accurate when doing most calcs, because power isn't a constant into any impedance load the way voltage is, and impedance varies with frequency.
                        Right, and I'm trying to figure out if the amp is trying to supply more voltage than it can. If the speaker is 6dB more sensitive, then it's less likely to be the amp distorting some of the dynamics.

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                        • #13
                          Maybe. You'll get 6dB more voltage sensitivity, but at the cost of the doubling of the current draw. Still, running with subs to handle the bottom I don't see a 100WPC amp being stressed.
                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

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                          • #14
                            This weekend I tested the idea by putting together a 3-way with 6dB more sensitivity. The 3-way was similar to the 2-way in that it used the same tweeter, and same size mid. The woofer is 4 ohms. This is not a real fair test, but, it was something to do. The 3-way plays about 6dB louder than the 2-way with the same volume level setting on the pre-amp. With music, the improvement was substantial. Unlike most 3-ways I've tried, the x-over for this one currently uses only 7 parts. Usually, I'm at twenty or more. The xo is not "finished", but I was really surprised by the sound quality. Odds are, I'll add 7 more xo parts to "improve" it. I only own one of the woofer that is used. I'm trying to decide if the expense, and wood work are worth the added performance. A second option is a 2-way with the same woofer, and tweeter in some existing boxes that can be altered for the drivers. This would be much less work, and expense.

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