RS315 Sub power requirements?

[Jim Holtz]

My son is interested in a sub so I recommended the RS315 HF version. I'm trying to figure out how much power this needs. We're on a budget of course so if we don't needs a 500 watt plate amp, it would help make his dollars stretch further for the center channel he also wants.

Thanks for the feedback!

Jim

[JonMarsh]

This is a moderated senistivity woofer, for extended bottom end without much EQ, consider a 3 cu ft enclosure. A 250 watt plate should be fine, IMO. The HF was designed for large enclosures, lower Le, with large VAS, and a two layer instead of four layer VC (lower Le, remember?) So, it doesn't have the power handling of the HO version. Best with modeate power, sealed, maybe ported, large enclosures, or, of course, dipole.

~Jon

[Jim Holtz]

This is a moderated senistivity woofer, for extended bottom end without much EQ, consider a 3 cu ft enclosure. A 250 watt plate should be fine, IMO. The HF was designed for large enclosures, lower Le, with large VAS, and a two layer instead of four layer VC (lower Le, remember?) So, it doesn't have the power handling of the HO version. Best with modeate power, sealed, maybe ported, large enclosures, or, of course, dipole.

~Jon

Thanks for the quick feedback Jon. A couple questions. I'd planned on going sealed just to keep cabinet size down and he has a smaller room where it'll be located. I'd ran the numbers in Unibox and came up with about 1.6 cubic feet. I noted that you recommended 3.0 cubic feet. Did I caculate it incorrectly?

Also, will 250 watts be enough to drive the RS315 to full volume?

Thank you for your help!

Jim

[JonMarsh]

What kind of alignment were you shooting for, Jim? The raw Q of the driver is about 0.44. A classic Butterworth 0.707 alignment is not critically damped, but an alignment of 0.5 is. With the usual in room boundary lift, 0.707 is not maximally flat in room - it usually results in a hump in the response, depending on the distances to back and side walls. I usually shoot for an alignment closer to an IB tuning, with Q in the range of 0.5 to 0.57. The roll off is slower, there's more deep bass without using as much EQ or power. That's what the RS315HF is designed for. If you want small box and a more conventional tuning, with an LT transform and EQ, then you'll need more power, and you'll need the HO version. The HO version has a lower Qts, and four layer voice coil will handle more power. BUT, it actually won't put out more LF, as the Xmax is actually 15% lower. But, if you want a small box, then it's your driver.


Just my 0.02.

[Jim Holtz]

What kind of alignment were you shooting for, Jim? The raw Q of the driver is about 0.44. A classic Butterworth 0.707 alignment is not critically damped, but an alignment of 0.5 is. With the usual in room boundary lift, 0.707 is not maximally flat in room - it usually results in a hump in the response, depending on the distances to back and side walls. I usually shoot for an alignment closer to an IB tuning, with Q in the range of 0.5 to 0.57. The roll off is slower, there's more deep bass without using as much EQ or power. That's what the RS315HF is designed for. If you want small box and a more conventional tuning, with an LT transform and EQ, then you'll need more power, and you'll need the HO version. The HO version has a lower Qts, and four layer voice coil will handle more power. BUT, it actually won't put out more LF, as the Xmax is actually 15% lower. But, if you want a small box, then it's your driver.


Just my 0.02.

Jon,

Thanks for the very detailed answer. Yes, I was shooting for a .707 alignment to keep box size down to better fit in his smaller home. I didn't mention that this will be for home theater rather than music 95% of the time. He'll be using it with the Modula M/T's I built for him and probably crossing somewhere around 40 - 50 Hz to give movies the "couch shake" that's missing without a sub. The rest of his system is very inexpensive and he's not a critical listener.

Thanks again for your feedback.

Jim

[JonMarsh]

Well, you can proceed as you plan- I'm just a little "obsessive" about the details and optimizing the choices. The bigger box would give you more deep bass for movies without needing as much amplifier power. If he can find a way to tolerate the size, I hope he can go for it.

Just ask anyone who has an IB what they think about it compared with a conventional box sub.

~Jon

[Jim Holtz]

Well, you can proceed as you plan- I'm just a little "obsessive" about the details and optimizing the choices. The bigger box would give you more deep bass for movies without needing as much amplifier power. If he can find a way to tolerate the size, I hope he can go for it.

Just ask anyone who has an IB what they think about it compared with a conventional box sub.

~Jon

Well, it's true. A couple inches does go a long way! I did a little box sizing and I can come up with the 3 cube cabinet with just a couple inches more than what I was planning. I'll see if I can make it work.

Thank you again for your help. I appreciate it.

Jim

[SE-Raider]

Jon:

What do you mean by the statement that a classic butterworth is not critically damped? I have always been told that the optimal alignment for SQ is .707. Is this not the case? Are you saying that an alignment closer to .5 will have better damping? I'm a little confused; could you briefly describe the interrelationship between Q, box size and sound quality in a sealed enclosure?
Also, many are considering either the HO or HF Dayton subs. do I understand you correctly that the HF will give better SQ but in a larger enclosure, and that the HO is best only when the application calls for a small box?

Thanks for any enlightenment....

[Mazeroth]

I'll let Jon get into the technicals about Q, but I'll tell you about my experience. I've built subs of many different alignments, ported, etc. from a 1.0 Q to my newest sub, my infinite baffle! My theory is you can never have too large of a sealed box. Build it as large as you possibly can, within reason. Your lowend extension will thank you, or better yet, you'll be thankful for the lowend extension :T

[ThomasW]

What do you mean by the statement that a classic butterworth is not critically damped?I have always been told that the optimal alignment for SQ is .707. Is this not the case?

0.707 is maximally flat, critically damped is 0.5.

The main issue with .707 is that's anechoic, add in room gain and you're not longer maximally flat.

[JonMarsh]

Jon:

What do you mean by the statement that a classic butterworth is not critically damped? I have always been told that the optimal alignment for SQ is .707. Is this not the case? Are you saying that an alignment closer to .5 will have better damping? I'm a little confused; could you briefly describe the interrelationship between Q, box size and sound quality in a sealed enclosure?
Also, many are considering either the HO or HF Dayton subs. do I understand you correctly that the HF will give better SQ but in a larger enclosure, and that the HO is best only when the application calls for a small box?

Thanks for any enlightenment....

As another friend pointed out to me on the phone today, there tends to be some confusion in folk's minds between "maximally flat" and "critically damped".

A Q of 0.707 for sealed box speaker is a Butterworth 2nd order alignment- it is maximally flat in the passband (anechoic near field), down 3 dB at Fb, then quickly starts rolling off in the low end at 12 dB/octave. It is NOT critically damped. The impulse response has some overshoot and takes a bit of time to settle. Then, there's also the question of how the anechoic response with Butterworth alignment will work in an actual listening room, where you get conversion from 2 pi to 2pi then 1 pi space depending on the spacing from adjacent boundaries at various frequencies (determined by wavelength relationships)

A Q of 0.5 is critically damped in the time domain, down 6 dB at Fb, and has a roll off rate shallower than 12 dB per octave initially, more like 7-9 dB, then gradually steepens. So, the transient response is better damped (well, there is the room to consider, but GIGO always applies), the -10dB point is lower in frequency, and with room lift being frequency dependent, it's my experience that it's easier to tune the driver position in room so that the in room response is perceived as fairly flat, deep, and articulate, without any extra low midbass "bloom". Of course, some folks like their bottom end a bit Rubenesque, you know who you are, we don't need to argue the merits one way or another- it's a free country, after all, not Red China, where there's one way or the Highway.

Regarding the HF vs HO subs, your summation is representative of my viewpoints, as well as the physical realities. The HO has less compliance, the Fs changes less in a small box than the HO, the cone mass reportedly is higher, the VC is four layer for higher power handling (read- can handle some extra LF EQ to over come box roll off), BUT, the actual Xmax is less, so it will be more limited in LF output when used in similar enclosure concepts- unless you do something like comparing a carefully optimized ported HO sub with a sealed HF sub, then the port output will tip things in the HO favor until you get below the tuning of the box and the port unloads.

If you HAVE to use a small sealed box with EQ, then the HO version is the way to go because of higher thermal power handling- for that reason only. I'd recommend evaluating any proposed design in Unibox, LspCAD, or similar, so that you can model the tradeoffs accurately. Power ratings are an inexact science, too, so a little conservatism there wouldn't hurt. They could have made the HO VC longer, but then Qtc and sensitivity would have suffered. Tradeoffs, you know.

~Jon

[JonMarsh]

I'll let Jon get into the technicals about Q, but I'll tell you about my experience. I've built subs of many different alignments, ported, etc. from a 1.0 Q to my newest sub, my infinite baffle! My theory is you can never have too large of a sealed box. Build it as large as you possibly can, within reason. Your lowend extension will thank you, or better yet, you'll be thankful for the lowend extension :T

Agree completely, within reason- the bigger the sealed box, and the closer to an IB alignment or something in the range of Q=0.5, the better, IMO. Note that all the drivers recommended for IB's are typically in the 0.4 to 0.45 range.

[ThomasW]

Of course, some folks like their bottom end a bit Rubenesque, you know who you are....

I like the bottom end of my women and my bass Rubenesque ..... :wink:

[SE-Raider]

Thanks guys. Never heard those two concepts contrasted or adequately explained. Definitely cause to rethink subwoofer plans, since both accuracy in frequency response and in impulse response would be a priority for me.

[ThomasW]

http://personal.stevens.edu/~jling/

[Dennis H]

http://personal.stevens.edu/~jling/

Yikes, I find those distortion numbers for the RS315HF quite disappointing. The Peerless XLS 830500 does much better down low.

http://www.linkwitzlab.com/woofer3.htm

[ThomasW]

I just threw that in for grins. I think he's pretty new to measuring business....

[JonMarsh]

Unless you see the drivers tested by the same person with the same technique, it's not wise to compare different testers. I wouldn't ever do bare driver dipole testing sitting on top of the bench.

Compare with this, for example.

[ThomasW]

It's important know how many poker chips are used to elevate the driver.... :wink:

[Dennis H]

Okay, sorry I panicked.

I went back and read what Monte wrote since he tested both drivers.

I think this driver will be a first rate performer in both dipole applications and box applications. It seems about as good as the XLS in the mid bass region with some frequencies possibly better on the XLS and others better with the RS. Generally the two are close in the mid bass region. The RS is better at very low frequency and will also be better than the XLS at frequencies above 100 Hz. The RS is also the quieter of the two making it a much better choice for any dipole application than the XLS.

[JonMarsh]

Okay, sorry I panicked.

I went back and read what Monte wrote since he tested both drivers.

:T

~Jon

[JonMarsh]

I just threw that in for grins. I think he's pretty new to measuring business....

Eewwwwww, a StinkPad for speaker testing! I don't even like those for email! :