[JDUBS]

Hey Guys

I saw this ad on Audiogon last night:

http://cls.audiogon.com/cgi-bin/cls.pl?spkrfull&1177123169

Has anyone heard a Supravox OB like this one?  It looks mighty impressive...and very much full-range.   

-Jim

[maxro]

It seems a shame to have used such nice drivers and not have even gone to the trouble of flush-mounting them.

The corner braces on the backside have what appear to be holes in them. Some sort of helmholtz standing-wave traps, perhaps?

Max (long time lurker, first time poster)

[alotaklipsch]

Already sold, there are some threads on AA about the design, and conception

[JoshK]

Yes, that is a very interesting design.  One even a rocker like me could enjoy.  Of course, I'd do a few things different, but that is not the point.  Someone will enjoy them.

[JohninCR]

Max,

Nice catch regarding the holes in those corner braces.  I didn't notice them on the first pass.  I couldn't find anything on AA discussing that aspect of the design, but based on the hole size and limited volume inside, they aren't functioning at very low frequency, so they must be a trap tuned at a resonance of the cavity though having a hole at the top is confusing unless there's a divider inside making each consist of two traps.  Ingenious, if that's what it is.  It's given me an idea for improving my use of Helmholtz slots in the next U-baffle that I build.  I've used that kind of action on what I call my OB-RLH, where I use a Helmholtz slot to load an expanding pathway, but I've been trying to figure out a way to capture a larger percentage of the very low frequency content of the rear wave.  This gives me some ideas that may work even better.

[maxro]

...they must be a trap tuned at a resonance of the cavity though having a hole at the top is confusing unless there's a divider inside making each consist of two traps.

That's what I was figuring. With the upper chamber, being of smaller volume, tuned higher than the lower (both in location and tuning) chamber, due to the shallower depth of the U at the top. A very clever design, indeed.

I've noticed that a few designs from http://www.audiopur.de/english/index_hifi.htm have helmholtz traps inside their vented cabinets.

[JDUBS]

I went back and forth with the builder a few times.  He's turning this into a finished product priced at $5-$6K depending on driver complement.

JoshK, what is your opinion of a speaker like this relative to the Arvo, especially in terms of power handling and "rock / metal playability"?

-Jim

[JoshK]

I'd have to hear it, but the design looks to hold promise.  I am working on two designs for which I have drivers for.  One the Arvo part, the other with DDS ENG-90 waveguides w/ BMS 4592 compression drivers, JBL 2223H 100db 10" mid and Lambda 15" 95db 15TDXs.  I have wanted to have the dynamic impact that Dr. Geddes' Summas had ever since I heard them.  There is just something about hi-eff speakers (full range, not single drivers) that is very inticing.

Dmason is getting a pair of Supravox's, you should ask him about how they sound.  He heard them at a friends I believe and ordered himself a pair.

[celebrat]

Hi.
I am the luck guy (I hope) who bought the Supravox OB speakers. I found out about OB after getting a RWA Sig 30 amp. I'm not much of a DIY person, but this looked so intriguing that even if I don't like the sound I can build something for the drivers. The seller says the bass is great but I was surprised w/ no box for the bass. I'll post again when I get it up and running. Thanks

[JohninCR]

Hi.
I am the luck guy (I hope) who bought the Supravox OB speakers. I found out about OB after getting a RWA Sig 30 amp. I'm not much of a DIY person, but this looked so intriguing that even if I don't like the sound I can build something for the drivers. The seller says the bass is great but I was surprised w/ no box for the bass. I'll post again when I get it up and running. Thanks

Did he explain the corner braces with the hole top and bottom?

[Russell Dawkins]

One of the guys involved with the design is a friend of mine - Lou Reda, I was talking to him an hour ago and alerted him to this thread. I can ask him about the holes. They look like they may be countersinks enabling angled bolts into the corners to me.

[JohninCR]

If they aren't some kind of Helmholtz trap, they should be.  There will definitely be a resonance between those parallel sides, and the frequency is predictable.  It's simple math from there.  I wish I had that driver compliment to work with.  I bet they'll sound great.  Don't be afraid to tune them to your desired placement with damping material in back, especially down in the woofer section.

[JoshK]

try industrial felt to kill the resonance

[maxro]

try industrial felt to kill the resonance

Wouldn't that favour absorption of the higher frequencies? I think the Helmholtz traps would work better as they could be tuned specifically to the U-frame's resonance(s), leaving the higher frequencies alone.

[MJK]

If they aren't some kind of Helmholtz trap, they should be.  There will definitely be a resonance between those parallel sides, and the frequency is predictable.  It's simple math from there.

There won't be any resonances between the parallel sides. We discussed this in another thread and I layed out my reasons why they won't occur and have run the finite element model to prove it. Resonances between parallel sides on an OB this big is a red herring. I think the ease of construction reason makes the most sense.

[JohninCR]

Martin,

For once I think I'm going to have to disagree with you on this one.  I've put all manner of shapes on the backside of a baffle, and those with parallel sides have been the most problematic except in the bass region, where the shape doesn't seem to matter much.  Resonance may not be the accurate term, so I'll change it to "bad things".  If you put a full range driver in what is essentially an undamped open backed box, bad things are bound to happen, just as they would if you put the same shape surrounding the front side of a full range driver.

[JohninCR]

Martin,

Are you saying that waves coming from the backside of the Supravox will not reflect off of those side panels?  Then at the frequency where 1/2 wavelength is equal to the distance between the 2 parallel panels, won't there be a response peak just like when the same thing happens in a room?  What am I missing, because it seems pretty basic?

[maxro]

There won't be any resonances between the parallel sides. We discussed this in another thread and I layed out my reasons why they won't occur and have run the finite element model to prove it. Resonances between parallel sides on an OB this big is a red herring. I think the ease of construction reason makes the most sense.

Not to question your authoritah, but wasn't that to do with an open-top U frame? I would figure the shallow sides at the top ought not to be much of a problem. But, the depth at the lower portion of the sides, in combination with the hard, reflective floor of the speaker, I think would have some resonances or echoes of some sort.

[Rudolf]

I must admit that I still have reservations against MJKs almost complete "ignorance"  of most parallel wall resonances. But with regard to this Supravox baffle I don´t expect any resonances too - even in the lower portion. There will be some bass augmentation by the folded back wings which could easily be taken for a resonance.
Lets look at a mirror image simulation in EDGE:



Curve 2 is for the plain 46"x20" baffle. Curve 1 is the response for the same baffle with side extensions (as shown - I didn´t care to model them better to the original). Floor level is at 0.8 m. Listening distance 2.5 m.
We all know that the influence of those extensions will be even greater when they are folded back as "wings". But even the influence of the side extensions could easily (and wrongly) be interpreted as some kind of 200 Hz resonance. So we should be very careful to distinguish between different effects and their relevant causes.

Just for the records: A lambda/2 resonance between the wings would be expected ~ 340 Hz - just where the plain baffle response has its maximum. So for a preconceived opinion their would be many traps to step into.

[MJK]

Are you saying that waves coming from the backside of the Supravox will not reflect off of those side panels?  Then at the frequency where 1/2 wavelength is equal to the distance between the 2 parallel panels, won't there be a response peak just like when the same thing happens in a room?  What am I missing, because it seems pretty basic?

John and maxro,

I think what you are missing is the damping provided by the large open back, the acoustic impedance will be essentially all resistive at the frequencies you are calculating. This will transfer sound energy into the room and not support the build up required to produce a standing wave. This was described in the other thread. It is very similar to the relatively large mouth of a horn efficiently transferring energy into the room and not reflecting it back into the horn to generate standing waves, same concept with this OB geometry.

I think Rudolph's explanation and example is right on the money. The sides change the radiated sound field and you hear a difference. It is the change in the polar response and the change in the frequencies of the peaks and nulls that you are observing, not a resonance between the side panels.

Martin