The VMPS Patent, Parts I, II, III, IV

buffer · « **Reply #140 on:** 20 Oct 2005, 05:13 pm »

Brian,
I don't need to tell you the FF1 SRE (and SuperTowerIII) is sort of a different animal from your other speakers due to the fact the mid panels are placed in a very thin and narrow enclosure.

Will there be any way for FF1/STIII owners to take advantage of this new technology?

If not on mids, would the difference be dramatic if we at least applied this invention to the free swinging treble units (located on the baffle)?

Thanks,
Brian U

_scotty_ · « **Reply #141 on:** 20 Oct 2005, 06:23 pm »

Josh,you have pretty effectively described the problem, the midrange driver doesn't turn off,even with the second pole that Brian has added,which by the way makes that portion of the crossover non-quasi-second order.
If you take a look at the Neo8 response graph you will find that it has a peak in output centered at 12kHz of some 13dB in magnitude, the driver Brian uses has a similar problem at 10kHz and it is also about the same size with the added wrinkle being that at 20kHz it is still 3dB hotter than it is at 1kHz.
The combfilter response anomalies are a result of too shallow a slope in the xover and the two drivers not being perfectly in phase in the overlap region. Brians device does not solve this
phase induced problem as far as I can see. A higher order network on the midrange to tweeter, implimented at 3.5Khz, would go along ways toward fixing this problem. Limiting the midrange drivers contribution to the frequency range that it is better suited to would have the added benefit of cleaning up the HF
reproduction as well as eliminating the on axis combfilter response
problems.
Scotty

ctviggen · « **Reply #142 on:** 20 Oct 2005, 06:48 pm »

What would be the detriment(s) of a higher order crossover for the midrange to tweeter interface? Also, is the problem lobing on axis? I assume by this you mean that near the tweeter/midrange interface lobing would be caused in certain frequency ranges. If that is what you mean (and it's true), then the new device would not fix that, although it might modify it somewhat.

Xi-Trum · « **Reply #143 on:** 20 Oct 2005, 07:47 pm »

Brian, would there be any benefit to extending the flat surface to cover the spacing beween the panels as well?

Tim S · « **Reply #144 on:** 20 Oct 2005, 08:21 pm »

If you need a beta tester for a verison of this for the older RM1's, I'll happily volunteer. My room is untreated so I can provide a view of the benefits in an untreated room as well.

I see this will be available on the new RM1a's. Will there be versions for upgrading older RM1's as well?

Tim

ehider · « **Reply #145 on:** 20 Oct 2005, 08:36 pm »

Per Scotty's suggestion:

"Brians device does not solve this phase induced problem as far as I can see. A higher order network on the midrange to tweeter, implimented at 3.5Khz, would go along ways toward fixing this problem"

That question that comes to my mind too as why has Brian not considered a higher order network at 3.5Khz like Scotty suggests? Based on the measurements I have seen of the VMPS speakers there do seem to be some serious comb filter issues that need to be addressed. Any insights from Brian would be greatly appreciated!

ctviggen · « **Reply #146 on:** 20 Oct 2005, 08:43 pm »

What measurements? Do you mean room measurements or on-axis measurements? I don't think room measurements would tell you much, but maybe I'm wrong.

ehider · « **Reply #147 on:** 20 Oct 2005, 08:57 pm »

The measurements I am referring to are comb filtering anomolies that seem to be present in many of Brian's designs. These measurements have been published before on the net by someone other than Brian.

From this engineer's perspective the comb filtering problems seem to be due to Brian's choice in filter slopes and frequencies as related to his chosen drivers and their inherhent interaction with each other. It seems to me (and others) that Brian could eliminate many of these comb filtering issues if he chose a different crossover slope near 3.5 khz.

warnerwh · « **Reply #148 on:** 20 Oct 2005, 10:04 pm »

It's interesting that so many people have great ideas for Brian and how to design HIS speakers. He makes a great product that is outstanding for the money and has had great reviews going back well into the early eighties. Numerous owners including myself have heard many designs other than VMPS but ended up buying VMPS speakers.

I'm not dissing you guys but if you know so much about speaker design you should design some yourself and see how far you get. Vmps has stayed in business since 1977 with little or no advertising. I'm sure Brian has already thought of all those things and more. There's a little more to it than what 99.9% of people realize I suspect. You guys are lucky Brian is a nice guy. Personally in my profession I don't appreciate beginners trying to help me. Not that I'm an ass but because they should keep their mouths shut til they learn more and their advice may be of some use.

ctviggen · « **Reply #149 on:** 20 Oct 2005, 11:36 pm »

OK, I'll ask again -- what measurements? Please post a link if they've been published. I haven't seen them. I'm not trying to tell Brian how to design speakers, as he knows speaker design and I don't. I'm just interested if this is true or not. (Not that it'll make much difference to me, as I can't hear any "dramatic" lobing effects. I like the way the speakers sound, and I'm more interested currently in acoustics than speakers or speaker design. Nonetheless, as a former engineer, I'm always interested in learning more. Scotty seems convinced, though I don't know why.)

ohenry · « **Reply #150 on:** 21 Oct 2005, 12:17 am »

I hereby dub thee... Zorro

JoshK · « **Reply #151 on:** 21 Oct 2005, 12:29 am »

gentlemen, let's not get into a debate about measurements, cause I am pretty certain any measurements you come up with for either side I can argue against. Geddes posted a really informative paper on measurements on the correlation with human hearing, and the limitations of masking, etc. Very intriguing read and correlates well with my understanding of hearing, fwiw.

yes I do believe that first order & quasi-second order, et al, have comb filtering/lobing problems, but it is a design tradeoff for time coherency and lack of group delay. Of course, I can easily argue the other way on that too. There are no absolutes and on axis FR measurements tell you nothing....almost, they can only highlight a some problems, but systems are full of them, so pick your poison.

I think ehider is referring to Dennis Murphy's measurements? He showed a deep null ~10khz, but fairly narrow (which has been shown to be inaudible in pro audio studies, if i understand correctly). But this was also an early version of the RM1, iirc (spiral tweeter and all).

I am not hear to argue for or against BC's choices of design philosophy but I'd prefer if this thread stay out of VMPS bashing. I own a pair of RM40s, but then again I own a pair of speakers with totally different design philosophy and I like them both. Go figure.

ehider · « **Reply #152 on:** 21 Oct 2005, 01:08 am »

To answer ctviggen's statement that he would like to see measurements showing the effect of comb filtering anomolies on a VMPS speaker, see below:

Hi Eric,

John Casler moderating here.

Bob ask for a link.

I don't see any value in posting these old measurments that Brian has explained many many times in the past.

They are for a speaker that isn't even in production any longer.

You are welcome to post Bob a link, but they don't belong here in this thread.

Thanks for your understanding.

JoshK · « **Reply #153 on:** 21 Oct 2005, 01:14 am »

ouch....

is this in room or in an anechoic chamber (or outside up on a pedestal)?

btw,....fr curves aren't the end all be all, I'd rather see ETC curves, they are more informative...that and impendance curves. But these aren't great to say the least...just don't tell me they were taken by GR Research.

ehider · « **Reply #154 on:** 21 Oct 2005, 01:53 am »

Hmmm,

The measurements that I posted show the exact issues that from a speakers comb filtering due to crossover design choices. These anomolies are still present in the speaker we have been talking about and are EXTREMELY similar in terms of using the graphs I presented to EDUCATE AudioCircle readers. They are NOT there to slam VMPS or talk badly the design decisions itself. Hell, I never even offered up any opinions to what comb filtering issues mean to me personally in a speaker designer's playbook

Earlier in this thread I asked Brian to respond so we could all learn from his corner. He designed the speakers afterall

The WHOLE POINT of my posts are to EDUCATE everyone who is curious with VALID informative measurables, not just conjecture and speculation.

For those graphs not to be posted is a serious dis-service to anyone reading these threads that is trying to understand the relationship of comb filtering occuring due to crossover slope selection. I have to seriously wonder about this decision to block the measurements I posted. As far as I'm concerned it speaks to a complete and total lack of understanding of an attempt to just answer another poster's question where he asked ME POINT BLANK for measurements so he could understand what I was saying

Brian Cheney · « **Reply #155 on:** 21 Oct 2005, 02:19 am »

The old Dennis Murphy measurement of the RM1 is irrelevant, since we don't know how he did it. Also, he has said very nice things about the 626 on the Madisound board and elsewhere so he's OK with me.

Yes, higher order filters will reduce the lobing effect in the crossover region at the expense of phase integrity and poor filter transient response (i.e. ringing). I have explained my choice for filter topologies. The invention goes beyond this.

ehider · « **Reply #156 on:** 21 Oct 2005, 02:52 am »

Hey Brian!

Thanks so much for answering my inquiry (sort of)

. Of course you had to assume (incorrectly since you couldn't see what I posted) and thought that I was posting the Murphy measurement WHICH I WASN'T

, but since we are now offering censorship on AudioCircle, I guess we all have to D R E A M about what measurements EHIDER actually attempted to post

To take this thread further toward understanding what Scotty and myself have inquired (without those pesk measurements that serve no one here on AudioCircle) I do have another question for Brian:

If you were to cross to the tweeter at 3.5kHz, would you really need this new device on the front of the speaker's baffle instead

It seems to me as if the off axis response of the already narrow tweeter is better than that of the planar mid playing through a narrow front baffle slit? Therefore you could actually kill two birds with one stone with a this sort of implementation within your crossover instead. Have you tried both and listened to the difference. Any insights will be greatly appreciated

John B · « **Reply #157 on:** 21 Oct 2005, 02:54 am »

OK, so here's the soundstaging effects at three listening positions.

Center Seat (sweet spot): (positions relative to room boundaries and height, top spot being closer to ceiling, middle being what it is, and bottom spot close to ground level.

Acoustic Bass........................Vocal...... ...............................Strings

Strings................................ ..Harmonica............................ .Drums

Right Seat (against right wall):

....................................... .........................Harmonica..... ..Acoustic Bass

..............Strings.................. ....................................... .....Vocal....Drums

Left Seat (against left wall)

Harmonica.............................. ....................................... ....................

Strings................................ .Vocal................................. ..Strings.........

Acoustic Bass......Drums........................ ....................................... ......

Of note: this is with the speakers on axis with my center listeniing position, not towed in to where they are 2' in front of listening position. I'll give that a shot tomorrow to see if soundstage placement changes.

ctviggen · « **Reply #158 on:** 21 Oct 2005, 11:11 am »

I think that modifying the crossover and the new baffle/waveguide solve two completely different "problems" (assuming the crossover is a problem -- as Brian says, there are benefits and detriments to what you describe). Constant Directivity will not be benefited by modifying the crossover -- the midrange panels are still much larger in width than the tweeter. The new baffle/waveguide basically spreads the sound to provide a more even power over a larger range (at least this is the way I think of it, for now, until I can take the time to understand more).

They're really two completely different problems.

ctviggen · « **Reply #159 on:** 21 Oct 2005, 11:13 am »

John B, could you compare without the modifications? Just looking at your data without comparison doesn't really tell me much, although it is a very interesting way of looking at things.