How much power is needed to move 3 7" woofers

[Darkwing_duck]

So I've been wanting to run my Polk rti12s as full range speakers for quite some time now.

They have 3 7" woofers. Rated 50-500 watts @ 8 ohms. -3db is 30 db. Total freq is from 20 hz...not sure how loud those notes would play though...

My denon x4000 is rated at 125 watts per ch @ 8 ohms

I do get significant bass with music and movies with a 2.0 setup. Music I can feel the lowest notes in popular hip hop, rap, top 40 songs.

But I have the curiosity of an unadulterated cat.


I want to know how much power I will need to get those woofers moving. Right now, with the grilles removed they barely tremble even with bass heavy songs like Stronger - Kanye West but I can " feel " the bass no doubt. It's there alright. With movies I can hear the grumble and at times feel the bass. It's like a deep growl with tight snapping bass. Sometimes I feel my couch vibrate only for a few seconds though. I'm guessing the receiver runs out of gas at that point. Even then I barely see the woofers flexing.

So how much power would I need to get them to flex? I know majority of the power will be used by the woofers and a small amount is used up by the tweeter midrange drivers which is why I'm looking high powered amps. Woofers eat power.

Would 300 watts be sufficient? 400 watts?

I've been looking into the Emotiva XPA 100 which on sale ATM...250 watts @ 8 ohms. These are monoblocks!

Should this be sufficient enough for those woofers or other woofers should I invest in more lively full range towers down the road ( Either SVS ultra towers or Arx A5 towers )

I've also been looking into pro amps such as the Crown XLS series....2500 series is rated at 440 watts @ 8 ohms for under $700!

Obviously I'm gravitating towards the Crown xls amp....value over looks here...but I could also get 2 XPA 100 monoblocks for under $1000 which is to me the deal of the month

 

[markw]

just buy a sub and be done with it. You can't get blood out of a stone.

 

[templemaners]

just buy a sub and be done with it. You can't get blood out of a stone.

+1. This is what a dedicated subwoofer is for, and for the amount of money you're looking to drop on amps, you should be able to find a pretty good sub.

 

[j_garcia]

+2. More power is going to give you more output, not more extension, no matter what you do. If you want proper 20Hz performance, you need a sub, period.

300W+ would be major overkill for those speakers. Your receiver isn't out of juice, your speakers simply cannot reproduce the bottom octave completely.

 

[ski2xblack]

Is this just so you can see more excursion for the woofers? That seems headed in the opposite direction of improved audio performance. Getting cones started and stopped is much easier if they don't have to move much, which is why larger drivers, or as in your case, multiple drivers, have an advantage. Also, that movement will modulate higher frequencies that the woofers also reproduce, and more movement results in more modulation.

Have you fully assessed your power use to determine if buying a high power amp would be of any practical benefit? Even being overly conservative, say, expecting to have 20db of available headroom over average power levels, which are probably a watt or two, maybe more if you sit far away, but the point is you may not need more power. I agree with the other posters. Subs and implementing bass management/room eq is screaming out to you as a more pragmatic solution, given what you have provided so far.

 

[AcuDefTechGuy]

I assume the RTi12 is similar to the RTiA9: Impedance reaches a minimum of 4.49 ohms at 67 Hz and a phase angle of –49.39 degrees at 22 Hz, Sensitivity: 90.5 dB from 500 Hz to 2 kHz.

Minimum impedance > 4 ohms, Phase Angle < 60 degrees, Sensitivity > 90dB, should be pretty easy to drive.

Assuming a distance of 3m and peak total SPL of 100dB in 2.0 music mode, your speakers will need 45 watts into 8 ohms and 90 watts into 4 ohms.

My personal peak total SPL from 2 speakers is 94dB, so 100dB would be deafening to me.

 

[Darkwing_duck]

just buy a sub and be done with it. You can't get blood out of a stone.

Sheesh.....talk about being cut and dry.

 

[Darkwing_duck]

I assume the RTi12 is similar to the RTiA9: Impedance reaches a minimum of 4.49 ohms at 67 Hz and a phase angle of –49.39 degrees at 22 Hz, Sensitivity: 90.5 dB from 500 Hz to 2 kHz.

Minimum impedance > 4 ohms, Phase Angle < 60 degrees, Sensitivity > 90dB, should be pretty easy to drive.

Assuming a distance of 3m and peak total SPL of 100dB in 2.0 music mode, your speakers will need 45 watts into 8 ohms and 90 watts into 4 ohms.

My personal peak total SPL from 2 speakers is 94dB, so 100dB would be deafening to me.

I dont know anything when it comes to speaker performance. I just assumed more power meant more woofer movement which means deeper extension ( ie reaching the speakers -3 db point )....my goal isnt really max spl. Honest! My current config is loud enough! Just having the X4000 power them both full range is enough for me at the moment.

Actually, im listening to Love Lockdown - Kayne West and this song has LOTS of deep deep bass notes...in fact thats the beat behind...the beat. Its a 4 beat pulse over and over again and this rti12s are literally making my spine vibrate and I only have the volume at -17

This is exactly what I want from a pair of speakers. Full range sound without a sub to avoid over powering notes or localization problems. I also enjoy the cohesiveness from a complete tower package. Kinda like a all in one easy setup...manuever the towers and thats it. No subs to fiddle around with or anything. Simplicity in its simplest form.

For the record, these rti12s are given me more satisfaction than I imagined they would. I was just CURIOUS if more power would yield better performance.

I do have plans to integrate two subs in the near future but for music purposes I like a full range tower =D


So to be clear, more power wouldnt produce deeper extension ( if the speakers are capapble of it ) it would just make me deaf?

I guess either way, I cant go wrong with the XPA 100 monoblocks for the price $299! EACH!

 

[Darkwing_duck]

Is this just so you can see more excursion for the woofers? That seems headed in the opposite direction of improved audio performance. Getting cones started and stopped is much easier if they don't have to move much, which is why larger drivers, or as in your case, multiple drivers, have an advantage. Also, that movement will modulate higher frequencies that the woofers also reproduce, and more movement results in more modulation.

Have you fully assessed your power use to determine if buying a high power amp would be of any practical benefit? Even being overly conservative, say, expecting to have 20db of available headroom over average power levels, which are probably a watt or two, maybe more if you sit far away, but the point is you may not need more power. I agree with the other posters. Subs and implementing bass management/room eq is screaming out to you as a more pragmatic solution, given what you have provided so far.

Ok maybe I wasnt clear with my goal....When I said 'seeing them flex' i assumed this implied the speakers were receiving adequate juice to "open them up"

Thats all Ive been seeing on forums. Having enough power to open a pair of speakers up. Its like a veil is lifted from them and you hear stuff you didnt notice before.

All that crap. So I assumed if i fed them appropriately they would open up and it would also mean the woofer cones would flex or excursion would happen. So what you are telling me is that this visual delight im soo eager to see is actually a counter productive nuisance for speaker cones...Gotcha!

 

[Ricardojoa]

I would say the reason why those woofers arent bouncing hard are likely due to the low tunning frequency of the ports. If the frequencies played get closer to the tunning frequency, the less the woofer moves, the more bass is reinforced through the ports. Once the played frequencies gets below tunning, the woofer will bounce crazy.

 

[AcuDefTechGuy]

I was just CURIOUS if more power would yield better performance.

Only if the speakers require more power. So usually not.

 

[ski2xblack]

Beware the marketing hype and anecdotal reports, particularly if you have a wad of cash burning a hole in your pocket.

I do believe that it's good to err on the high side, following the strategy of "too much is just enough" since watts are fairly inexpensive and clipping is a no-no. Considering that, the application of more power runs into it's own limitations if taken to the extreme. Personally, I don't want a hint of thermal compression coming from my speakers, or to put them at risk by applying too much power. So I would advise to first determine if you really need it, and if you do, be cautious when applying it. Also, how much more would XPA 100's get you above what you have now? A db or two, maybe?

 

[markw]

I would say the reason why those woofers arent bouncing hard are likely due to the low tunning frequency of the ports. If the frequencies played get closer to the tunning frequency, the less the woofer moves, the more bass is reinforced through the ports. Once the played frequencies gets below tunning, the woofer will bounce crazy.

Amen to that. brother. Anyone that ever played vinyl with vented speakers knows that quite well. That's why subsonic filters came into being.

 

[zhimbo]

Thats all Ive been seeing on forums. Having enough power to open a pair of speakers up. Its like a veil is lifted from them and you hear stuff you didnt notice before.

Yeah, you'll hear things like that a lot. One should learn to tune out those sorts of vague anecdotal reports. Unused headroom in your amp doesn't do anything. It just sits unused. There is every indication that your speakers are not particularly difficult to drive (other than vague anecdotal reports, that is; the specs are all very manageable looking).

Of course, big amps are undeniably cool, so by all means get one if you really want it. But for actual sonic improvements, that's WAY down the list.

 

[Darkwing_duck]

Ok ok I see all your points. But Polk rates these speakers up to 500 watts....marketing ploy to make folks think " Wow! " or there is truth behind their power claims? After all I'm not solely looking for pure spl output. I already know the formula, double the power to get 3 more dbs but when speaker manufacturers state numbers like that...you begin to wonder

 

[fuzz092888]

Ok ok I see all your points. But Polk rates these speakers up to 500 watts....marketing ploy to make folks think " Wow! " or there is truth behind their power claims? After all I'm not solely looking for pure spl output. I already know the formula, double the power to get 3 more dbs but when speaker manufacturers state numbers like that...you begin to wonder

Rates it to 500 watts peak? Average? A bit ambiguous. We also have no information about the drivers themselves. That rating could be right before the speaker explodes. It could be with an unpleasant amount of distortion. It could be with a specific distortion number in mind, which could still be unacceptable to many. If these speakers live up to their "Efficiency" rating (wrong word BTW), which may be bloated and add theoretical room gain, then 500 watts is way more than a person would need in an average living room at 12 feet away.

At a listening distance of 12 feet, with some room gain (3db), and placement near a wall or corner (within 4 feet/add 3more db), accounting for distance loss (~11db), you get around 106db at the LP with 140 watts. THX reference is 85db with 20db of headroom, making 140 WPC plenty. Even if we subtract 3db from their "Efficiency" rating as a safeguard, your power requirements given the same situation is only 210 WPC to hit THX reference peak volumes.

 

[Darkwing_duck]

I think when I asked about woofer excursion some of you folks may have assumed I would be entering a domain where speaker damage or threatning distortion levels would be present....I would not want that at all obviously.

However to show you guys what I had in mind when I set out to create this thread for answers this is where it came from!

[video=youtube_share;Hs_f4rG21H4]http://youtu.be/Hs_f4rG21H4[/video]

The legacy speaker video review. At the 4.20 mark there is a pan across the woofers where you see them "flex". I dont see that on mine but I sure as hell feel the throbbing waves. Easily hit 30 hz with room gain in my cave because of my Denon X4000. So the legacys are 500 watts rated at 4 ohms being powered by an XPA 1 monoblock....1000 watts @ 4ohms into those behemoths.

If im beating a dead horse by asking this question again, dont hate, im just ignorant ....Is this why you see cone excursion? Because they are being driven with the max wattage specified at a frequency below that of the tuning frequency of the ports?

If so, these polks are rated at 30 db at -3db....if I throw some sub-bass content at it....below its port tuning freq; 30 hz maybe 25-20 hz...test tones....dubstep tracks....will I see it then?


Thanks guys!

 

[fuzz092888]

The reason you're not seeing the woofers on the Polk's move is either because of the alignment they're in or because they have very limited excursion limits. It has nothing to do with pumping as much power as possible through the woofers. I'm unclear as to why you want to see the woofers move. If they're doing what they're supposed to then leave it alone. If you just want to see something move get a subwoofer. At least then you'll have a more difficult time destroying the driver, which you're sure to do if stay on this path with the Polk woofers.

No offense to you as a person, but I find the endeavor of making the woofers on the Polk move a bit asinine. Especially since you already said they're working just fine. As has been suggested, just get a subwoofer. You'll get to see the driver move and if you get a half decent one you'll stand much better odds of not destroying it.

 

[Darkwing_duck]

The reason you're not seeing the woofers on the Polk's move is either because of the alignment they're in or because they have very limited excursion limits. It has nothing to do with pumping as much power as possible through the woofers. I'm unclear as to why you want to see the woofers move. If they're doing what they're supposed to then leave it alone. If you just want to see something move get a subwoofer. At least then you'll have a more difficult time destroying the driver, which you're sure to do if stay on this path with the Polk woofers.

No offense to you as a person, but I find the endeavor of making the woofers on the Polk move a bit asinine. Especially since you already said they're working just fine. As has been suggested, just get a subwoofer. You'll get to see the driver move and if you get a half decent one you'll stand much better odds of not destroying it.

Because it has a cool factor of 1 000 000 000 x 10. Thats like asking someone why would they want to leave their speaker grilles off all the time when the speaker performs perfectly well with them on. Sometimes speakers, especially full range towers, just look bad-*** with the grilles off.

Speaking of bad-***, have you seen videos on youtube of speaker excursion from playing "Bass I love you" [video=youtube;2OD0Thy03z8]http://www.youtube.com/watch?v=2OD0Thy03z8[/video] Thats pretty cool, you know it is

 

[Darkwing_duck]

The reason you're not seeing the woofers on the Polk's move is either because of the alignment they're in or because they have very limited excursion limits.

Thank you. This never came across my mind and I agree with this 100%. Like someone said earlier, we dont know what type of drivers are used in the towers so it could be said that the design of the drivers are just not excursion-sensitive. Cool.

Thanks guys. Finally made a thread where folks were kind enough to help out