Audio Nirvana Standard 8 DCR CommonSense Audio
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Audio Nirvana Standard 8 DCR

 
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Jervill2



Joined: 09 Dec 2013
Posts: 3

PostPosted: Mon Dec 09, 2013 6:11 pm    Post subject: Audio Nirvana Standard 8 DCR Reply with quote

I've been working on a cabinet for the standard 8 for the last few months. I was not really too keen on the Monitor or 1.3 as I had originally planned to build so have been experimenting on another arrangement.

I've chosen to try a DCR- Dual Chamber Reflex- instead. There are articles on the theory of this configuration and that is what spurred me on to try. I reckoned that the bass response an octave above the tuning frequency would be better defined making the transition to the mids sound 'smoother' on the Standard 8.

I made different prototypes using the dbdynamix calculator as the guide. I used slot ports and round ports with tuning in the range of 40-50hz.


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After doing listening tests on all, I arrived at this:



It measures 40"x9"(w)x8"(d) approx. The ports have been placed in the back and the cab is tuned to approximately 50hz. This gives the best compromise for output and bass definition. Since it is a DCR, the two ports will both output 50hz and the driver chamber port will output up to an octave higher to approx. 100hz. The ports were placed at the back for two main reasons really, one is to reinforce bass against a surface and the second was because there were sounds escaping from the driver chamber port higher than the port tuning. This seems to have worked as there is more clarity. Only the driver chamber has been lined with accoustic foam. The resonant chamber has been left bare only because this seemed to make for better sound.

How does it sound? Like a big standmount speaker with punchy and fast bass. Loaded into corners then they may not need BSC, (they don't need correction when listening at lower levels). There is an 11ohm resistor on the +side. With this correction, the shouting ceases at high levels and the bass becomes more taut. I will be adding a 2.5mH inductor later on.

Although the BSC will sap power, the DCR design is more efficient so the trade-off for me is reasonable. All the tuning was by ear so I don't have measurements.

Anyway, I think the DCR concept is worthwhile to pursue for AN 8s.
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Brad Kizer
Site Admin


Joined: 20 Jun 2009
Posts: 166
Location: Toledo, OH

PostPosted: Wed Dec 18, 2013 8:32 pm    Post subject: Reply with quote

Hi,

I for one really appreciate posts like yours. Nice work.

As your finished design suggests David's drivers can be versitile.

Again, thanks for your photos and post.

Link to http://dbdynamixaudio.com/
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WPM



Joined: 25 Sep 2012
Posts: 11
Location: Sea World, Texas

PostPosted: Sun Dec 22, 2013 9:19 am    Post subject: Reply with quote

+2 on that. I love to see varying designs for use with the AN drivers. Nice work indeed. Brad, thanks for the link. There is some very good information there. I am going to have to incorporate some of those techniques into my future 5.6 cabinets with 15" coax's.
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Jervill2



Joined: 09 Dec 2013
Posts: 3

PostPosted: Mon Jan 20, 2014 8:36 am    Post subject: Reply with quote

After a few weeks of listening and experiments, I thought it'd be a good idea to give some feedback on my progress.

First off, I've re-read my first post and there is a typo on my part. It is the resonant chamber, not the driver's, that output up to approx. an octave of the tuning frequency. The best explanation of the concept is from here:

http://www.claudionegro.com/projects/speaker/dcr/dcr.html

As the frequency lowers, the driver will be damped around two frequencies: the tuning frequency and about an octave of that. Driver excursion will be lower at these points therefore reducing distortion. I think for trying to push the 8 to extend and output in to this area (<80hz), this characteristic of the DCR is advantageous.

I tried both round and slot ports in this configuration. The round ports gave a higher output for the same tuning and was easier to build. I chose slot ports for two reasons mainly. First, was the port configuration provided good bracing. Second, since I'm in a small listening space, the slots' outputs dropped sooner when the volume was cranked up (I figure because of the larger port surface area). This helped control booming in the room. If I had a bigger space, then round ports would probably be my choice to try first.

As far as BSC goes, this is my compromise as I can't play with the speaker placement. I will try the correction though between the amps at a later date. I have tried 3db, 6db and currently 10db of attenuation. In my opinion, the necessity and compromise of how much attenuation depends on the type of music generally listened too.

I am planning another rebuild to see if I can improve some things. I will try increasing the wall thickness to 1". The cab is excited around 80-90hz from what I can hear (slightly in music, apparent in a tone sweep). I'll be trying to shift this upwards. This will add an inch to the depth to keep the same tuning. Also, I will place the resonant chamber's port to face forward just to see if there is anything to be had. The final final version will eventually be built using Birch ply, hopefully late summer.

About me, this is my first attempt at building and 'designing' speakers. At the moment, I am avoiding simulations so that I can build a practical base for my knowledge. With my personality, I'd be simulating more than building if I went that route. Plus, I don't want my listening impressions to be biased by too much theory at the moment. I drive the speakers with all valve amps, 2a3 SE. I'm sharing my project so hopefully others trying or wanting to try the DCR configuration can post and bounce their ideas here.

Thanks guys.
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4krow



Joined: 21 Jun 2011
Posts: 31
Location: wyoming

PostPosted: Tue Jan 28, 2014 1:38 am    Post subject: Reply with quote

Ok guys, it's been quite awhile since my last visit here, and I am pleased to new posts. This OP intrigues me, because, I love experimenting, and reading about others doing the same. I have not heard of such a cabinet in the past, with the possible exception of a cabinet designed at Decware audio. Same idea, different specs. Anyway, this design should have caught on long ago. If I were adept with port design, I would gladly jump in. Having said that, I do have a thought about a simple BSC circuit that I have found elsewhere. It is designed by Paul Joppa of Bottlehead audio. What I like about it is that instead of straightening out the trouble at speaker level, it is done as a passive circuit between the pre-amp and power amp. This circuit does not amplify, but simply attenuates the signal in specific spots of the spectrum, as chosen by the user. I am probably not the guy to best describe it, so you can run over to the Bottlehead site and look at "The Fix". I have made the circuit myself, but have had little time to use it. What I will say is that I really appreciate the difference that it makes in the treble, as my hearing has diminished over the years. That's my two cents worth.
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Jervill2



Joined: 09 Dec 2013
Posts: 3

PostPosted: Wed Feb 05, 2014 3:37 pm    Post subject: Reply with quote

I was completely unaware of the DCR concept before. I only knew of the Fostex DBR. I came across it actually using the other calculators in dbdynamix. I was looking at their TL and Horn calculators when the heading 'Tri-tuned dual chamber bass reflex' piqued my curiosity. Looking around, apart from Claudio Negro's work, there's not a lot of home audio enthusiasts writing about it on the net. It is though quite known and used in car audio.

I am enjoying them and, to me, they are quite good. Why they aren't more popular for home builders, I don't know. (My cotton ears may have me biased Shocked). This is one reason why I started this thread. I'm hoping other experimenters are having a go. I'm interested in their feedback and results.

The Dbdynamix calculator calculates everything and gives all the panel dimensions. It's just a matter of typing in specs then letting it do its thing. (With my ones, I tweaked certain panel measurements based on previous prototype results.). I buy the mdf in measured cut panels, so I have only what I need. It costs me about £30 per set plus glue, sweat and tears to put them together. Actually cheaper than playing around with audio caps and much more satisfying Very Happy.

It is Paul Joppa's circuit I was looking to try for the BSC. Before this, I've only experimented with filters to cut out <20hz from pre to power as I figured the SD speakers struggles <40hz anyway. All this experimentation will resume after the final set are finished.
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4krow



Joined: 21 Jun 2011
Posts: 31
Location: wyoming

PostPosted: Fri Mar 14, 2014 7:04 pm    Post subject: BSC and bass/treble Reply with quote

I keep getting tempted when i look at your design with these speakers. No doubt, the AN drivers are one of the best choices for this.
The BSC circuit, according to PJ, is an intelligent idea that does not penalize the power amp with an additional load, but rather puts it in between the pre amp and amp, as you had mentioned in your post about the 20hz rolloff filter. What's really cool, is that it uses some of the same thinking that Yamaha used with their natural Sound series amps way back. They simply lowered the mid range rather than boost the bass and treble for the effect of a loudness control. The idea is that it is preferable to attenuate a signal rather than amplify it. With that, the PJ circuit lowers the midrange about 2-4db, then the volume knob is increased, and when it comes out the other end, the bass is relatively louder than the mid range. This can also be done in the treble. In both cases, there are selectable frequencies that can be chosen. I find that I use the circuit at the 4db setting for bass and treble. This circuit has a gentle slope of 6db per octave, and does not make calling attention to itself.
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