The BlindStone OB

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scorpion

The BlindStone OB
« on: 16 Nov 2010, 06:16 pm »
Let me start a new thread about what I already published in the 'Audiosyncrasy' thread. I brought the speakers to a Hi-Fi Forum DIY show in Uppsala this weekend with apparent success.

This is what my current outfit looks like:



The Mid- and Tweeter panel sits like this:



On its own baffle ancored by a 30 pound stone to prevent resonances to spread to the units.

To answer Rudolf's questions:

1st: Separate Bass and Mid- Tweeter Baffles. Great success, No resonances what so ever is transferred from Bass to Mid- and Tweeter units.
No own resonances occur even on the 20 x 60 x 1.8 cm spruce glue lam baffle. Mid- tweeter-baffle is ancored to a 15 kg heavy stone. See picture.

Units on each side are 2 Eminenca Alpha15s on 40 x 50 X 2.8 Spruce glue lam cm baffles put together with piano hinges. Midrange is 18 Sounds 6ND430 working between 250 - 2000 Hz and B&G Neo3W Tweeter above 2 kHz. All crossovers are executed in Behringer DCX2496 with 48 dB/octave slope.

This setup is the result from some ongoing experiments also with No Baffle as inspired by Stig-Erik Tangen's long diy-Audio thread. My best experiment with No Baffle looked like this:

[

scorpion

Re: The BlindStone OB
« Reply #1 on: 16 Nov 2010, 06:32 pm »
I'll go on here.

The No Baffle experiments were no success. At Times Ambience was too plenty. And above all No Consistency was gained for CD recordings.
They could sound almost a little Hip  Hap, mostly too thin in High Bass low Midrange area as at least I was used to here them.
Just putting the small 20 x 60 cm baffle restored sound to what I was used too. So I settled on this baffle width. Which is also so small as to preserve Constant Directivity almost up to the chosen 2 kHz crossover point.

To hang the units I had no real success. They seemed to engage with bass resonances. I had better sound from binding the mid unit rather thight with my old Venetian Blind ropes to the setup. But as said CD-recordings showed very unequal result. Live Radio Broadcast on the Net, like from NRK.NO radio did a lot better also with the No Baffle. But as a whole my judgment was of no real use. The smaller baffle is very much more consistent to produce good results.

/Erling

studiotech

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  • Posts: 420
Re: The BlindStone OB
« Reply #2 on: 16 Nov 2010, 10:21 pm »
I have a pair of 6ND430 here too.  Testing them out for a friend.  Sound great.  One of the best cone mids I've heard in a while.  I wonder if part of what I like is tha rather shallow cone.  Seems like alot of other cone drivers I tried over the last 2 years all sounded like when you cup your hands in front of your mouth.  The 6ND430, even run fullrange did not have that effect IMHO.

 My friend is using a pair with Raals in an MTM.  Should be a sweet, high SPL monster run with a pair of subs.

Greg


Saurav

Re: The BlindStone OB
« Reply #3 on: 18 Nov 2010, 02:52 am »
Another member of the 6ND430 / Neo3 fan club :)

Previous version:



That shows the Audax PR170M0, which I replaced with the 6ND.

Current version:



versus rider

Re: The BlindStone OB
« Reply #4 on: 18 Nov 2010, 06:17 pm »
nice work :notworthy:

Saurav

Re: The BlindStone OB
« Reply #5 on: 18 Nov 2010, 09:07 pm »
nice work :notworthy:
If that was directed at me, thanks. A friend set up a DIY CNC machine, so I... err... went a little crazy. You can see my woodworking skills (or lack thereof) in the first photo :)

scorpion

Re: The BlindStone OB
« Reply #6 on: 18 Nov 2010, 09:10 pm »
Thanks,

I will go a little bit further in explanation. Evidently the 6ND430 is a good speaker. At least the best dynamic midrange I have played with so far. I am a bit jealous about the Neo10s which couldn't be delivered to me by 'black import' at Easter time this year. I have had a long going mail discussions with Sales Managers at B&G Radia about this unit going back to the time ProRaum in Germany put out a design with them. Meniscus was telling they would sell them eventually but couldn't meet my time window this time. May be later. I have no doubt they are great. 6ND430 is a very good alternative though.

The most real improvement in this design is the division of Bass- and Mid- Tweeterpanels. Definition is absolutly improved by avoiding bass influences to spread via the baffle to the other units and may be also overall clarity. It is easily heard and does imply restrains for building with all units on the same baffle.

Regarding the No Baffle experiments I was surprised by the great variation in response that I found. I have no good explanation to the thruth that I got very much more consistent and likeable ('realistic') results just from putting a small baffle like my 20 cm (8"). Without baffle I had a massive EQ with 15 dB shelving going to put out level sound with 300 Hz as crossover frequency. With the narrow baffle I can go down to 250 Hz without EQ, why ? To me the Constant Directivity argument is valid. We probably play in more symmetrical environment most of the time to make the intuitive strenght of the argument valid. Also some toe in of the speakers seem to improve the stereo sweetspot.

Regading Rudolf's question about angeling the bass panels I have no answer yet. Too little time to try. But I don't suspect any radical improvments in my room. Bassresponse doesn't seem that sensible. The room is fairly lively I think but seems to do OB sound justice.

P.S. I had favorable comments about the Neo3 performance in Uppsala.

/Erling

Rudolf

Re: The BlindStone OB
« Reply #7 on: 19 Nov 2010, 03:14 pm »
Hello Erling,
thanks for your detailed description. I see that positioning the Neo3 with regard to a conventional cone midrange driver follows a sort of standard – which I am going to put into question. :wink:

Lately I finally licensed my ARTA software and took the effort to do some 180° polars of my dipole speakers. While measurements of the front hemisphere were fine, the rear hemisphere was sort of shocking :o :



To the right you see how I mounted the drivers with respect to the baffle. The acoustic center of the (forward radiation of the) SPH 176 is supposed to be just behind the baffle (2.5 cm inside the baffle front). I positioned the tweeter dipole (two DT-25N back to back) between the AC and the voice coil, thinking this would be appropriate. This is how it looks in real life:



How wrong I was. I got a big suckout at the crossover frequency of 2 kHz. I had to move the tweeters forward to get a somewhat decent rear radiation pattern:



The difference in tweeter positions between right and wrong is only 4 cm in my case. While my first mounting position was led by theoretical considerations only, I have tried different positions for the new one – from 4 cm behind the first mounting to 4 cm in front of the actual best position.
I believe that getting a better rear pattern helped to get a smoother front pattern too. At least the new position does not sound worse than the older one. My ears believe it to be an improvement, but I always believe it sounds better when I know the measurements are more linear. :roll: :lol:

It would be interesting to see some backside measurements of the Neo 3 in combination with cone midrange drivers too. And certainly my findings should be a strong argument to move to the Neo 10 as midrange driver. :D

Rudolf

scorpion

Re: The BlindStone OB
« Reply #8 on: 19 Nov 2010, 06:12 pm »
Hi Rudolf,

Very interesting measurements and a bit thoughtuppsetting. With regard to 6ND430, it is very shallow compared to most other cone speakers as Greg said above.
So my mistake I think will be considerably below 4 cm if physical alignment is the only reason for the measurement results.

But it is interesting to see the improvement. How did you placed the microphone in distance to the speakers and with regard to the axises ?

/Erling

Rudolf

Re: The BlindStone OB
« Reply #9 on: 19 Nov 2010, 09:20 pm »
Hi Erling,

fine that I got you interested.
The center-center distance between both drivers is 13 cm. The microfone was 40 cm from the baffle front at the height of the separation between tweeter and midrange driver. This makes for a distance difference of 1- 1.5 cm to both driver positions on the baffle. Measurements where done in room with 1.5 m being the shortest distance from the drivers to a wall.

You don't need to do all polar steps. 0° and 180° would be sufficient. You have to rotate the baffle for 180°, NOT moving the mic. If there is a considerable difference between both measurements around the crossover frequency, you should investigate further. I would suggest to measure the Neo 3 at the actual mounting position and then changing the Neo to the front of the baffle (> 2 cm difference?). If this results in a change between both 180° measurements at the crossover frequency, you are in for a more precise investigation. If nothing changes, I am guilty of a false alarm. :duh:

My trial of explanation:
The acoustic center of a cone driver (where the air is moved) is NOT the voice coil, but somewhere in the middle of the cone (green square):




For the 90° radiation there is not much delay between front and rear (blue lines). But between 0° and 180° (green lines) there is a delay (for 180°) caused by the way of sound around spider and magnet. This delay will move the (virtual) acoustic center of the rearward radiation to the front of the baffle (dotted green line). The length factor for this is not the depth of the driver, but the width of the spider/magnet. The acoustic center of a tweeter should be in the middle between the usual acoustic center (green square) of the midrange cone and the virtual acoustic center of the rearward radiation. This middle position should usually be in front of the baffle and not in the back!

Does this sound like a good explanation or is it just rubbish?  :scratch:

Rudolf

ttan98

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Re: The BlindStone OB
« Reply #10 on: 19 Nov 2010, 09:46 pm »
Rudolp,

Thanks for your input, I am curious, about the twin dome tweeters,

1. I  suppose you connect them in parallel?
2. Are they in phase, i.e. +ve to +ve OR out of phase, +ve to -ve, I think latter is correct?

your comment please.

scorpion

Re: The BlindStone OB
« Reply #11 on: 19 Nov 2010, 10:14 pm »
Rudolf,

I'll be away during the weekend. But I will try measuring in the beginning of next week.
Thanks for your explanations.

/Erling

Rudolf

Re: The BlindStone OB
« Reply #12 on: 19 Nov 2010, 10:22 pm »
ttan98

they are connected in parallel and out of phase. Both moving in the same direction. As you can see from the diagrams they loose their dipole pattern above 4 kHz. The Neo 3 is good for 6 kHz AFAIK. :xmas: will probably be my time to "upgrade" to the Neos. Maybe some parcel will fall off my sled :green:.

Rudolf

scorpion

Re: The BlindStone OB
« Reply #13 on: 5 Dec 2010, 08:18 pm »
Rudolf,

sorry for the long wait. I have had a problem with a power supply in my equipment.
But eventually a measured response and look at it:



Then with Neo3 at the front (18 mm difference):



I only took 0 and 180 degrees here so the effect is clearly seen. The lighter blue curve is the front response and the little heavier black one is for the backward response. Conditions were the same as for your measures. Interesting indeed. I can do some new a bit thicker baffles (28 mm) to be able to adjust optimally for the Neo3. I have to put it on a movable wodden band. But mostly I think 6ND430 is to blame, it is not so very open at the back.

To know is a good thing.  :D

/Erling
« Last Edit: 6 Dec 2010, 06:11 pm by scorpion »

scorpion

Re: The BlindStone OB
« Reply #14 on: 6 Dec 2010, 06:50 pm »
I also tried some polar response measurements. Here is the on axis and 30 degrees off response in this graph.
The light blue is on axis.



/Erling

panomaniac

Re: The BlindStone OB
« Reply #15 on: 7 Dec 2010, 04:33 pm »
The acoustic center of a cone driver (where the air is moved) is NOT the voice coil, but somewhere in the middle of the cone (green square):

Acoustic center at what frequency?  Doesn't it change some? (phase)

k97psd

Re: The BlindStone OB
« Reply #16 on: 7 Dec 2010, 07:59 pm »
Been awhile Erling. Looks like I gave up on the 6nd430 a little prematurely as yourself and alot of others are having great success with it. But isn't that the nature of audio in general , never being satisfied with what you have and trying to improve on it. Anyway I have my 6nd430's like new low hours in the trading post if anyone is interested. Also my compliments to Saurav very slick looking baffles.


Kevin


Rudolf

Re: The BlindStone OB
« Reply #17 on: 8 Dec 2010, 05:04 pm »
Acoustic center at what frequency?  Doesn't it change some? (phase)
You are right, it does change with frequency. What we need most is it's location at the Xover frequency - to get both drivers involved properly aligned.

Rudolf

Rudolf

Re: The BlindStone OB
« Reply #18 on: 8 Dec 2010, 05:25 pm »
Thanks Erling,

that's what I wanted to see :wink:. I built a provisional wooden slide for my tweeters to move them around:



I don't believe there will be a perfect alignment between a planar and a cone speaker, but we should know the compromise to agree on. The bad thing: The right position doesn't seem to be where pure intuition would have placed it.

Rudolf
www.dipolplus.de

scorpion

Re: The BlindStone OB
« Reply #19 on: 8 Dec 2010, 06:20 pm »
Rudolf,

I was also thinking of some way to move the tweeter and measure for the best position. The front placement seems a little better and probably the best place is a little bit further back. Moving from placing the Neo on the back of the baffle to the front does not change the forward alignment very much, shouldn't we see more difference ? There was no optimization with regard to the forward response in this case, everything remained the same as it was when the Neo3 was placed at the back of the baffle.

/Erling