SVS vs. VPMS (1 Viewer)

[Tom Vodhanel]

John,Greg...

No need to close down the thread...I think it is very interesting.

Michael, All I know about the 15" PR is what BC mentioned to me in the past...he said it was 120g on another forum. He wouldn't say anything else about it.

There are easy to follow formulas to determine the tuning point of the enclosure once you know the enclosure volume,the radiating area of the PR,and the weight of the PR.

TV

 

[Jack Gilvey]

There are easy to follow formulas to determine the tuning point of the enclosure once you know the enclosure volume,the radiating area of the PR,and the weight of the PR.

It's also fairly straightforward, once the radiating area and excursion capabilities of a PR are known, to figure out its linear SPL limits at a given frequency, to show what is and what is not a plausible anechoic performance claim.

 

[Dustin B]

The other question I still haven't found a decent answer for (besides the Vd like Jack wants to know) is what exactly this slot loading of the PR accomplishes.


Heh, Jack I decided see what would happen if I entered a Tempest with a single PR15 at 120g into LspCAD in a 180L enclosure. Tune came in at 34hz and it would take 64000W to get it to 115dB at 20hz (1m free air) and the PR15 would have to be capable of 920mm p-p excursion :p) Not saying it isn't a nice sub above 30hz, but like Jack and Tom say, the numbers just don't add up.

Edit: decided to try something a little different. Used the Maelstrom instead of the Tempest and reduced the tune to 28hz (186g). Now it only take 16000W and the PR to be capable of 575mm p-p.

And then if you reduce the tune to 20hz (380g) it will take 6000W and a PR that can do 260mm p-p (still 1/4 meter just doesn't seem likely).

 

[Dennis XYZ]

The other question I still haven't found a decent answer for (besides the Vd like Jack wants to know) is what exactly this slot loading of the PR accomplishes.

It looks to me like that would give it some of the characteristics of a PR box and some of a ported box. As well, there's the possibility he's using a stiff spider rather than the limp one the sim programs assume. Designing a PR system is more art than science. The sim programs can model one possible way of building a PR system but that's certainly not the only way. Cheney has been building them for many years so he may have a few tricks that others haven't thought to try. Users seem to confirm his performance claims so it's a bit of a stretch to assume he's doing anything fraudulent just because we don't understand how his subs work.

 

[Jack Gilvey]

Users seem to confirm his performance claims so it's a bit of a stretch to assume he's doing anything fraudulent just because we don't understand how his subs work.

Didn't see anyone claim fraudulence, just looking for something other than "it woofs" as far as performance data is concerned. Sure, a sub can be made really loud and impressive over 30Hz without too much effort, just the thing to impress for HT. The loudness is all I've heard users "confirm". Similar testimonials can be found for just about every sub made.

 

[Michael R Price]

Woah, it looks like the numbers really don't add up. However, I think we shouldn't go by that 120 gram number. That's really absurd.

What I ask is, if the tuning is as high as it seems, how come the driver doesn't bottom out from the huge material under tuning? I think we may be using the wrong numbers here, that's all. I still agree the VMPS is underported (displacement wise).

Also, how does the system work with both a 12" and 15" active driver in it? I've never heard of any other sub using two different sized drivers.

 

[Dennis XYZ]

Geez, Jack, I wasn't trying to pick a fight. I've never heard a VMPS sub (have you?) but experienced people whose judgement I trust have heard them and say they work well. Cheney has said he likes Q=.7 boxes. Setting aside for a moment how he achieves that tuning, let's get back to basics. A 15" active driver plus a 12" active driver in the same box certainly have plenty of dispacement for deep bass. Heck, a sealed box with a Tempest and a Shiva can put out lots of deep bass with a little EQ. If we really want to know how the tuning works, somebody will have to tear one apart and do some Clio measurements. As we have no idea what the T/S parameters are for his drivers or his PRs, any theorizing that it can't possibly work seems a bit premature.

 

[John A. Casler]

From what I am able to gather neither Jack nor Tom has ever heard the VMPS SUB.

I find it as interesting to surmise that something that one hasn't heard doesn't work, as questioning the ears of those who have heard it.

I personally make no "specific" claims other than personal perceptions which can certainly be affected by many things like I mentioned earlier even a "vibrating floor". So I am not nor have I quoted any manufacturers claims when giving opinion.

I mentioned that "specs" and perfromance figures only give one a general idea of how something will perform.

40 yd dash, Bench press and Squat numbers are certainly important to a football player, but they won't tell you if he is any good or not. Now certainly a 7 foot basketball player had the advantage, but may not do the job in all situations.

So forget about formulas and just take a listen to any sub you might be interested in, because in the end the numbers will not be what makes you happy. The sound and music it makes will and there is only one way to hear and "feel" that.

What if a test only shows the LARGER to ouput 105 or 100 or even 90dbs at 20Hz. Will that make it perform any less in my room?

Nope.

Will it still be worth the price of admission?

Yep!

It would seem that even though we all share the same hobby we don't all share the same opinions about sonics and objective vs subjective opinions.

But.. We do all share the passion that drives us to enjoy the result.

I've been in this "fray" since the early 70s. I have discussed "Bass" (and many other things) with Lee Kuby (Citation), Jon Dahlquist, Saul Marantz, Harry Pearson, Cory Greenberg, Arnie Nudell, and spent hours with Jonas Miller (M&K) playing with various Sat/Sub configurations in his shop back in the 80s. As well as many others who most would not recognize.

Let me tell you, Bass is many things to many people. If you don't know what your looking for you might get lucky and find it by accident, but if you are lucky enough to listen and learn what Bass can be, then you are on your way.

Foley, is not real! So if your only concern is reproducing explosions then buy the loudest, deepest, cheapest rig you can.

But as Lee Kuby used to say, "real bass in a concert hall is something that you have to sit and evaluate, then see if you can reproduce it in your own system". Lee used to comment how he developed the HK Citation 16 to offer the dampening charachteristics needed for the Woofers of the time (SUBS were not really as much a part of the soundscape back then)

He also used to remark about "Bass Heads" who accentuated the Bass "too much" so that in music it was not realistic.

Jonas, on the other hand was one of the Pioneers of Subwoofers and satellite systems and I was lucky enough to visit regularly and get to play with his latest incarnation.

So when we are talking musicality, we need to consider integration, timbre and other factors more than "specs only".

Since this is a Home Theater forum, I would expect that the primary focus would be reproducing Movie sound, but many are also interested in music, and that homogenation and its ratio is a fun thing to play with.

Best regards,

John Casler

 

[Dustin B]

what I meant by reference level was 00db on my Denon, having calibrated it to 85db with AVIA

I'm not sure what you mean by this. It doesn't matter what the volume levels on your receiver say, all that matters is what the SPL meter says at your listening position. So if you put Avia in and get everything to read 85dB. Then eject Avia and put in a different DVD without changing any levels on the receiver you are at reference level (and all the peak output numbers I mentioned above are valid). If you do the above but set the sub higher than 85dB, what I said above is still true.

The only situations in which this is not the case is if the DVD was not recorded using the same definition of reference level as Avia for DD or if DTS/some other format is being used (I find I have to turn my system down a few notches with DTS discs).

 

[Michael R Price]

John, I agree with your point about not having heard the VMPS. However, with subwoofers there aren't really any special tricks. You only have so much displacement and so much power. This is why we can make comparisons like "a Tempest will be comparable to an SVS Ultra." We know almost exactly how much displacement, port area, and power these subs have. With the VMPS... we don't know for sure but we can make educated guesses (such as a guess that the PR does not have the displacement of the three Adire PR-15s that would be required to vent a good 12" and 15" driver).

"40 yd dash, Bench press and Squat numbers are certainly important to a football player, but they won't tell you if he is any good or not." Problem here is, the numbers usually DO describe how good a subwoofer is. This is why us DIY folk are inquiring about the performance claims of the VMPS.

"So when we are talking musicality, we need to consider integration, timbre and other factors more than "specs only". " I agree that we don't know how to describe musicality with specifications. But that's another discussion.

 

[Dennis XYZ]

Problem here is, the numbers usually DO describe how good a subwoofer is. This is why us DIY folk are inquiring about the performance claims of the VMPS.

Agreed. So somebody needs to measure one. Until then we are all just flapping our lips.
As a DIY guy myself, I've never had very good luck with PR designs. My preference is for low-Q sealed boxes with EQ. But I'm always willing to learn something new. If Cheney's unconventional approach works better than the conventional PRs I've tried, I'd like to understand how it works.
Questions I have:
The Vd of the PR seems low. Even allowing for some room gain, he must be getting more output from the drivers, and less from the PR, than a conventional PR design. How would you build a driver to act like that? Presumably low Q and low Fs?
The Mms of the PR seems low. It apparently doesn't sag much even though it's bottom mounted. How does he keep it tuned low with the light Mms? Of course, small Sd allows lighter Mms with the same tuning but it still doesn't seem like it's enough.
What does the slot loading do? Is it like adding mass to the PR or length to a port?
How does PR suspension stiffness affect things? An infinitely stiff PR would be like a sealed box. A heavy, limp PR is the conventional method. So, how does something in between act? Like an aperiodic vent?
So many questions and so few answers. Who has access to a VMPS Larger and a Clio setup? That's the only way we will get answers that satisfy everybody.

 

[Jack Gilvey]

If Cheney's unconventional approach works better than the conventional PRs I've tried, I'd like to understand how it works.

Before wasting time on assumptions that it's an "unconventional approach", I'd like to see actual measurements of the output down low. The obvious answer to all your questions is that the performance isn't quite what's claimed by some (spare me the anecdotes, they don't help anyone looking for facts). If it's all for real, then we can see what's up. So far, I see people that say it's loud. Cool.

 

[Neil Joseph]

Interesting analysis.

Just remember guys to keep discussions civil and level headed.

Thanks

 

[Dennis XYZ]

Before wasting time on assumptions that it's an "unconventional approach", I'd like to see actual measurements of the output down low. The obvious answer to all your questions is that the performance isn't quite what's claimed by some (spare me the anecdotes, they don't help anyone looking for facts). If it's all for real, then we can see what's up. So far, I see people that say it's loud. Cool.

Well, a little skepticism is always a good thing in this hobby.
About the "unconventional approach," I merely meant there are several things I've never seen before - small, down firing, slot loaded PR.
About the performance numbers, we do have a very specific claim from Brian Cheney.
"115dB/1m SPL at 20Hz for 2.5% THD"
I'd assume that's with a corner loaded sub, mic on the floor, in a not-too-big room.
Nothing I've heard about Brian leads me to believe he would lie about his specs - too easy to bust him if he's lying - but, if anyone has measurements that contradict his claims, I'd like to see them. My guess is the guy's for real. You don't win best of show at CES (all high-end audio components, not just speakers) by being a con man. You do it by building a good speaker. It's unlikely we would all consider his speakers the best we've heard but most of us would probably agree that they are pretty good.

 

[Jack Gilvey]

if anyone has measurements that contradict his claims, I'd like to see them.

Too funny. So now it's up to the consumer to disprove manufacturer claims for which no verification is offered in the first place? I'm sure he's "for real" and he's not a "con-man", never suggested anything else...I asked about something very specific, you proffered the generalizations.

 

[Michael R Price]

"I'd assume that's with a corner loaded sub, mic on the floor, in a not-too-big room."
Tom Nousaine measures subs corner loaded at 2m in a large room but provides corrected values using the transfer curve of a smaller 2136ft^3 room. The Stryke cube with the HE15 and three long excursion 15" PRs is capable at 110.1 dB at 20Hz with 10% THD in the small room (per the Nousaine chart here: http://www.stryke.com/pics/power15-maxspl.gif). It's safe to assume 4-6db gain from moving to 1m. This puts the Stryke sub at about 115db/1m/20Hz/10%.
Does the VMPS sub have the same output with *one fourth* the distortion of the Stryke cube with three serious 15" PRs? That would have to be a real small room. I think Brian should back up these measurements somehow.

 

[Eric Wood]

Jack, go on Harmonic Discord and ask for someone in the Jersey area to let you listen to their VMPS subwoofers or even RM2's or 40's. I know there are some very satisfied owners in New Jersey. You will not know the facts unless you hear them for yourself.
I am going right to the source in August, traveling from Columbus to San Fran to get my answers!!!!!!!

 

[Steve Zimmerman]

You will not know the facts unless you hear them for yourself.

I'm all for auditioning, but unless you've got the proper instruments with you then simply listening for yourself isn't going to tell you whether or not the THD number is accurate.

--Steve

 

[Brian Bunge]

I'm all for auditioning, but unless you've got the proper instruments with you then simply listening for yourself isn't going to tell you whether or not the THD number is accurate.

Steve, I agree completely. At least with a test disk and a Rat Shack meter (and compensation chart) one could get an idea if the sub will even reach 115dB at 20Hz. God only knows about the THD though!
Brian

 

[Eric Wood]

Ok, I will get the Radio Shack meter, but what disc is the end all beat all? By the end of August you will get your answers! I will include room dimensions and equipment used. Anything else?:alien: