take a deal on a velodyne DD10 or...

[Tmart]

I know this covers some of the often trod 2 subs or 1have larger sub, but wanted to get ur thoughts. I can get a velodyne DD10 for $850 (open box, NL warranty) to pair with my DT 10" supercube 1.
Is it a disaster to mix those subs? I assume i would need to preamp for added power?
Should i try for 1 larger sub knowing i can never really fill that space?
80% HT, 20% 2 channel music
here are the particulars:
Rec room is really big! 40'x20'x8' ceiling. Listening area at one end is is15' wide with seating 10' back.
amp: Onkyo TX-NR1009
fronts: Klipsch RF83's,RC 64 center (i know, i know. Horn tweet-whole other thread!
surround: klipsch RS42
surround back: klipsch CDT 3650(in ceiling)
Front height: monoprice msq 8425(just added to see if i like 9spkr setup) inwall
tv & BD are samsung LN52B750, BD P3600 for what its worth.
thanks!

 

[Irvrobinson]

The DD10 is meant for a small room; you have a very large room. If $850 is what you have to spend, I'd go for something much larger, like a HSU VTF-15H, and then save for a second one.

 

[Tmart]

Thanks for the advice. How about power needs with 2 subs & current amp?

 

[Irvrobinson]

The RF83s are so efficient that amp power is practically immaterial. The Onkyo probably works just fine.

The Hsu sub is self-powered, but I'm guessing you really need two of them for that room.

 

[Steve81]

The RF83s are so efficient that amp power is practically immaterial. The Onkyo probably works just fine.

I would note that while the RF-83s have a high measured sensitivity, they do dip below 3 ohms in impedance (in spite of the 8 ohm nominal rating) per S&V, as does the RC-64 center.

Test Bench: Klipsch RF-83 Home Theater Speaker System | Sound and Vision Magazine

While the Onkyo isn't a pansy receiver, that could lead to trouble a lot sooner than you might expect if you assumed the Klipsch speakers were just a benign 8 ohm load. Unfortunately, I know of no full impedance plot for the RF-83 to give a better answer.

 

[Steve81]

The DD10 is meant for a small room; you have a very large room. If $850 is what you have to spend, I'd go for something much larger, like a HSU VTF-15H, and then save for a second one.

Fully agree here. A big room means you can kiss things like room gain goodbye, which is going to make the job of any subwoofer much more difficult. In the $850 ballpark, the Hsu looks like a pretty good choice. Another possibility I'd toss out which is costlier, but considerably more powerful, is the Rythmik FV15HP with the 550 watt amplifier for $1174 plus shipping.

 

[Irvrobinson]

I would note that while the RF-83s have a high measured sensitivity, they do dip below 3 ohms in impedance (in spite of the 8 ohm nominal rating) per S&V, as does the RC-64 center.

Yeah, I know, but with 100db/2.83v efficiency, even if the Onkyo can only muster 20W into whatever impedance, there's going to be a lot of sound coming out of those speakers.

 

[macddmac]

My buddy bought the HSU VTF- 15H at RMAF a couple of weeks ago. We brought it back to his enormous room ( 12000 cubes) and were shocked at how good it sounded. Everything I had read to that point led me to think that he would need at least 2 and he might to properly pressurize that space, but my point is that it sounded great as is. Start with one and see what you think.
Cheers, Mac

 

[Irvrobinson]

Start with one and see what you think.

That's actually good advice, and was my strategy when buying a sub. I thought I'd need two, but ordered one just to see how things sounded. I never ordered the second, but my room isn't 40x20.

 

[Steve81]

Yeah, I know, but with 100db/2.83v efficiency, even if the Onkyo can only muster 20W into whatever impedance, there's going to be a lot of sound coming out of those speakers.

Certainly you won't mistake them for little cube speakers.

Still, if you assume a 4 ohm nominal load instead of 8 ohm nominal (not altogether undeserved given the actual minimum impedance), you're dropping sensitivity per watt by 3dB; so when you go to an SPL calculator such as http://myhometheater.homestead.com/splcalculator.html , instead of 100dB, you pop in 97dB. With 20 watts into 4 ohms at 10 feet, suddenly you're looking at 100dB instead of say, 107dB if you assumed 50 watts per channel into 8 ohms with 100dB sensitivity w/ 1 watt.

 

[Irvrobinson]

Certainly you won't mistake them for little cube speakers.

Still, if you assume a 4 ohm nominal load instead of 8 ohm nominal (not altogether undeserved given the actual minimum impedance), you're dropping sensitivity per watt by 3dB; so when you go to an SPL calculator such as Peak SPL Calculator , instead of 100dB, you pop in 97dB. With 20 watts into 4 ohms at 10 feet, suddenly you're looking at 100dB instead of say, 107dB if you assumed 50 watts per channel into 8 ohms with 100dB sensitivity w/ 1 watt.

Alright, I give up. Uncle!

 

[Steve81]

Alright, I give up. Uncle!

LOL. Suffice it to say, as a Klipsch owner, the thought has crossed my mind before

 

[Tmart]

This is great stuff.
Steve, thanks for the link to S&V. I read up on the impedance issue a bit, but still not sure what that should mean in practical terms for me. Other than possibly noting some dips in sens. at certain frequencies, do I need to nurse these RF's a bit if I'm listening for long periods or high output? Is the take-home - more power is never a bad idea?
MacDD & Irv: Thanks for the recommendations. I think I will try the Hsu first and see how it sounds solo. Use the current DT sub on another system or sell to offset costs i suppose?
Thanks all!

 

[3db]

I would note that while the RF-83s have a high measured sensitivity, they do dip below 3 ohms in impedance (in spite of the 8 ohm nominal rating) per S&V, as does the RC-64 center.

Yes without knowing where in the response curve it dips and what phase angle is at that dip, its difficult to assess.

 

[Steve81]

Steve, thanks for the link to S&V. I read up on the impedance issue a bit, but still not sure what that should mean in practical terms for me. Other than possibly noting some dips in sens. at certain frequencies, do I need to nurse these RF's a bit if I'm listening for long periods or high output?

Glad to be of use! There's no special need to nurse the RFs more than any other speaker: if you hear signs of distortion or strain, turn the volume down until those signs disappear. Even with their relatively low impedance, I'd expect it not to be a major issue until you're pushing fairly high volumes.

Is the take-home - more power is never a bad idea?

Not exactly. You want an amplifier that is competent at driving low impedance loads; in simple terms, it needs to be able to deliver good amounts of current. As an example: 50W into 8 ohms equates to 20 volts and 2.5 amperes of current. 50W into a 2 ohm load on the other hand equates to 10 volts and 5 amperes of current. This is no insignificant difference (more current = more heat), especially when coupled with how impedance and voltage sensitivity are related.