Last of the GR Research builds - 5.1 kit

[captrajesh]

Yes, only the Front Towers are ported designs. The Centre, Surrounds and the Subwoofer are sealed boxes.

The proposal yours is interesting to say the least. I've not gone through the threads linked by you fully but just speaking my mind. The bubble wrap thingy may be OK for small woofers but as the woofer goes bigger, the Bass would go lower and so do the standing waves inside the box which may overwhelm the bubble wrap. I may be wrong here, just speaking what's going on in my mind.

50mm Rockwool having density of 48 kg/M3. MOQ is 90.42 sq.ft @ Rs. 1858/-

Forgot to mention that the 50mm thick sheet would comprise of two 25mm sheets and thus can be separated.

 

[keith_correa]

Don't you intend mass loading/damping the walls [bitumen sheets???] to prevent panel resonances? If not, I suggest that you implement this. Will take up very little volume and would be very beneficial and inexpensive to implement.

Your braces are going to break up standing waves so there's a plus there.

For lining, I suggest that you use the open cell foam [the only problem with using this is that it deteriorates with time - ugh!] OR the Rockwool on all inner surfaces including the front [not around the woofers though]. Then you need to prevent/minimize the wave from being radiated back to the driver cone so a wad of fluffed out polyfill placed behind the drivers [from top of enclosure till a little under the woofer] should take care of that. Then you may need to loosely stuff the area from under the port to the bottom of the enclosure. That's about all I would do if I were you.

P.S. - It's all about experimenting to get the sound you want.

 

[captrajesh]

Don't you intend mass loading/damping the walls [bitumen sheets???] to prevent panel resonances? If not, I suggest that you implement this. Will take up very little volume and would be very beneficial and inexpensive to implement.

Yes I did.

Affixing the bitumen sheet on the cabinet walls

The above pic was shown in this post: http://www.hifivision.com/diy/61146-last-gr-research-builds-5-1-kit.html#post675843

There was only one pic and hence could've been missed easily. I should've taken more pics of fixing of Bitumen sheets.

For lining, I suggest that you use the open cell foam [the only problem with using this is that it deteriorates with time - ugh!] OR the Rockwool on all inner surfaces including the front [not around the woofers though]. Then you need to prevent/minimize the wave from being radiated back to the driver cone so a wad of fluffed out polyfill placed behind the drivers [from top of enclosure till a little under the woofer] should take care of that. Then you may need to loosely stuff the area from under the port to the bottom of the enclosure. That's about all I would do if I were you.

P.S. - It's all about experimenting to get the sound you want.

Thanks for the pointers. I had bought the below foam sheet which is 0.75" thick. Density is not known. I'll have to work it out. I'm planning to use it for comparison with the Glass wool. Will post the results once it's done.

Incidentally, I had taken samples of Glass wool as well as Rock wool. Both are same in texture and physical characteristics. Will post the pics later as they are currently not with me.

 

[captrajesh]

I had bought the below foam sheet which is 0.75" thick. Density is not known. I'll have to work it out.

I had measured the density. It's about 30 KG/M3 and he thickness is 18 mm. We thought of lining one of the tower speakers but it was insufficient. Even with partial lining of the box, the results of "clicking the finger inside the box test" was impressive.

I'll buy one full sheet tomorrow and experiment further.

 

[Danny Richie]

You guys are making the assembly way to complicated.

I cover every butt joint with wood glue and use a finishing nail gun to tack everything together. It will hold everything together great until it dries. And it won't split the MDF unless you get too close to the ends. Finishing nails don't come out. The head even gets buried into the wood. And the glued butt joint is more solid and stronger than the MDF itself.

On the binding post cups used in the A/V-1RS. They are ideal for this design to leave room for a connection between the back of the speaker and the wall. Just about anything else would keep you from being about to mount them.

For higher quality connection options I only use the Electra Cable tube connectors. They are the best connectors out there. Electra Interconnect Cables

Lastly, don't put bubble wrap in your speakers. The bubbles will take up air space and reduce cabinet volume. They also won't do much to absorb standing waves in the box. Sound waves will pass right through them like a thin plastic bag.

Open cell foam in good on the walls and loose fiberglass is my preference for additional absorbing material. Polyfill can be used too if you don't like handling fiberglass.

 

[keith_correa]

the results of "flicking the finger inside the box test" was impressive.

What "test" is this?

 

[captrajesh]

I cover every butt joint with wood glue and use a finishing nail gun to tack everything together. It will hold everything together great until it dries.

Yes, that's how we made the cabinets. But instead of nails, we've used self tapping screws.

don't put bubble wrap in your speakers. The bubbles will take up air space and reduce cabinet volume. They also won't do much to absorb standing waves in the box. Sound waves will pass right through them like a thin plastic bag.

Open call foam in good on the walls and loose fiberglass is my preference for additional absorbing material. Poly fill can be used too if you don't like handling fiberglass.

Thank you for the advise Danny. Yes, that's what I'm using.

What "test" is this?

LOL It's my own nomenclature. Actually I wanted to say "Clicking the finger inside the box test" Edited the post accordingly.

After lining the speaker with "No Rez" and fixing the baffle, my carpenter shoved his hand through the woofer hole and clicked the fingers to note how much of the sound is heard. He was pretty impressed to note that it is barely heard. The same test was conducted after lining the speakers with open cell foam and the results were as impressive.

 

[keith_correa]

After lining the speaker with "No Rez" and fixing the baffle, my carpenter shoved his hand through the woofer hole and clicked the fingers to note how much of the sound is heard.

If you have the "No Rez" sheets why would you need any additional lining and why would you need to apply bitumen sheets to mass load the panels? What am I missing here?

 

[captrajesh]

If you have the "No Rez" sheets why would you need any additional lining and why would you need to apply bitumen sheets to mass load the panels? What am I missing here?

Oops, sorry for the confusion. Ishould've mentioned at the beginning of the thread but missed it somehow. In addition to my speakers, I'm also making the X-LS & X-CS speakers of FM Sethu_NR who had requested me to keep his kit and build it along with those of mine and patiently waited all along for the build to materialise. The No Rez sheets were used in his speakers.

Now for the rest of the pictures of the Subwoofer build:

The inner box

The Stainless Steel feet for subwoofer were procured from Magma.

The original hole was not only too small to accommodate a bolt sufficiently thick to fix the feet but also was a through hole. Hence, they were modified to enable affixing them onto the outer panel of the subwoofer. The holes were made bigger and also threaded to accommodate bolts of sufficient thickness.

Fixing of feet onto the outer panel.

Epoxy Resin glue was used to prevent loosening of bolt on constant vibration of the subwoofer[/U]

Outer panel with the feet fixed.

 

[captrajesh]

Processing the river sand involved the following activities

Removal of dust and extremely fine clay particles was attempted by tossing the sand and blowing air through a fan like farmers winnowing the agricultural produce to separate out the chaff. Though dust was removed, this tedious process also resulted in loss of fine sand grains.
I figured that it is easier to wash the sand multiple times to get rid of the mud and clay.

Sanitising the sand to rid it of Fungal spores and Insect eggs was done by boiling the sand thoroughly after which, it was dried.

Sieving the sand was carried out to separate particles into fine, medium and coarse particles and pebbles.

Medium sand was used to fill the subwoofer. Some pics of subwoofer building.

Inner shell

Fully finished subwoofer

 

[captrajesh]

Because of the complexity of the design and build, making of the surround speakers has been the most rewarding experience from the viewpoint of learning carpentry techniques.

Tools used

Angled Circular Saw

Angle measuring tool

Hole Saw

 

[captrajesh]

The router bit used for chamfering the backside of the woofer hole.

Forgot to add the picture earlier.

As the build is progressing towards the finalisation, the work is getting more critical, delaying the progress. We have made the speaker grills with teakwood strips. Here are some build pics of the grills.

Affixing of a plywood piece at the bottom to handle the weight of sand and transferring it to the spikes

The (almost) finished speakers

We need to round off the edges of all the speakers which will be done using the circular saw. It has a special arrangement to do so while the subwoofer would be done with the router because of it's bulk.

 

[jls001]

I wonder if the grille frame would interfere with the dispersion of sound in the front baffle? I mean, it seems quite thick and could disrupt the path of the sound wave. Just wondering aloud

 

[vapmax]

Rajesh sir,
I too belong to Trivandrum (SBTian too ..now in Kottayam EDP) Where in Trivandrum you are getting this done? Vadayakkadu?

Vipin

 

[hydrovac]

I wonder if the grille frame would interfere with the dispersion of sound in the front baffle? I mean, it seems quite thick and could disrupt the path of the sound wave. Just wondering aloud

Good build capt!

The best grille is no grille. Next to that you want as little as possible... an important but often overlooked effect is that of the grille frame on the sound.

I personally cannot predict the outcome, but I suspect it wouldn't be good.
A whole lot of diffraction. Thick grille frames have a way of mucking up the lower HF/mid-range... (to what degree I do not know) and certainly affecting frequency response.

But the only way to know for sure would be to do a with grille and without grille measurement of the FR.

 

[captrajesh]

I too belong to Trivandrum (SBTian too ..now in Kottayam (EDP) Where in Trivandrum you are getting this done? Vadayakkadu?

Their old workshop is in Killipalem where the build is progressing. They have opened a new workshop at Pappanamcode Industrial Estate.

I wonder if the grille frame would interfere with the dispersion of sound in the front baffle? I mean, it seems quite thick and could disrupt the path of the sound wave. Just wondering aloud

The best grille is no grille. Next to that you want as little as possible... an important but often overlooked effect is that of the grille frame on the sound.

I personally cannot predict the outcome, but I suspect it wouldn't be good.
A whole lot of diffraction. Thick grille frames have a way of mucking up the lower HF/mid-range... (to what degree I do not know) and certainly affecting frequency response.

But the only way to know for sure would be to do a with grille and without grille measurement of the FR.

@Jls001 & Hydrovac, thank you very much for the advice. Point well taken. Will discuss with Santhosh & get back.

 

[captrajesh]

@Jls001 & Hydrovac, thank you very much for the advice. Point well taken. Will discuss with Santhosh & get back.

I went to the workshop yesterday evening. They had rounded the edges of all the grills by then. I need to figure out what to do now. The frames are 2 cms thick.

BTW, they are planning to deliver the speakers today.

Actually I too felt that the grills were quite thick but was convinced by their argument that the grill cloth would foul with and muck up the cone movement.

I wonder if the grille frame would interfere with the dispersion of sound in the front baffle?

The best grille is no grille. Next to that you want as little as possible... an important but often overlooked effect is that of the grille frame on the sound.

Thick grille frames have a way of mucking up the lower HF/mid-range... (to what degree I do not know) and certainly affecting frequency response.

I remember quite vividly my experience confirming this while I had the Acoustic Portrait speakers. Hence all my listening sessions were with the grills removed.

the only way to know for sure would be to do a with grille and without grille measurement of the FR.

From my experience, I don't even need to go that far. A simple listening session would be enough.

 

[Fantastic]

The frames will cause ripples in the upper mid range and HF. The degree depends on the dimensions of the frame and the distance from the driver. How audible it is depends on how much ripple and where it is prominent. But it could 'colour' the sound from what it would have been without the grille . However you might consider that room acoustic effects might be more severe than this.

Your grille cloth might kill more HF than the frame itself ! Test the frame without the grille cloth. I doubt that you will really hear the ripples easily. Add the grill cloth and it will cause a loss !

I have not yet come across a unit that sounds as good with and without a grille cloth. Others with open grille and strings/wires etc. were OK.
One speaker with a moulded front baffle was designed so well that the speaker does not see the edge of the frame. Only the grille cloth ,which was quite 'see through' . However it sounds better without the grille cloth . So the grille cloth might eventually be the biggest culprit.

You can also stick on felt or open pore foam ( about as thick as the frame ) all around the driver ( up to the grille frame edge !) so that the sound sees an absorbent on its way to the edge of the frame. That should reduce the signal level considerably as it reaches the 'edge' and reduce the ripple to negligible levels. You will find this on many old generation commercial speakers.
But you need to check if the grille cloth is the bigger devil !

Maybe a metal mesh will be better than a cloth grille . Not the perforated sheet metal type but the wire mesh type . Used in some speakers even today. You get very fine mesh in the market. ....brass, ss, steel etc. Shouldn't be too fine ! The open area should be quite high with fine wires for the mesh. Some companies do use very fine perforated steel sheet. But I doubt you can get that here.

 

[keith_correa]

Your woofer is not flush mounted on the baffle and the tweeter is - This probably is causing more diffraction than the grille frame. Will you hear it?

I've never heard the difference with the grille FRAME on/off. If there is a difference, my lead ears don't hear it though what little is left between my ears MIGHT. Yes, I've tried it in my usually anally retentive journey. I have heard people say that an angle on the inner edges of the frame helps - IDK if it does but it would certainly not hurt to implement this if you can.

The difference I hear is with the so called "grille cloth" applied to the frame. The ones that are purportedly used for this purpose are just not acoustically transparent enough and my ears can hear the highs being muffled. Very noticeable. I skip the "grille cloth" and use nylon dupatta's instead. VERY acoustically transparent. Cover your mouth with the cloth and blow out lightly - you will easily know the difference between good and not so good.

We need to round off the edges of all the speakers which will be done using the circular saw. It has a special arrangement to do so while the subwoofer would be done with the router because of it's bulk.

How on earth do they do that with a circular saw. Did you take any pics?

 

[jls001]

I've not bothered with grille cloth for my X/LS Encore but experimented extensively with tweeter rings (blame Keith). This is basically an oval ring cut a bit larger than the tweeter's radiating area, about 4-5 mm thick (of soft rubber sheet so that it can be stuck to follow the curves of the tweeter, sliced off from a yoga mat).

It definitely changed the directivity of the sound emanating from the tweeter, and was more focused and more likable than without when I finally got it right. Right now I'm running without the tweeter rings as I gave it away to a friend. Must make a pair again.

So that's where I was coming from, Capt.