trifidmaster
member
Joined: 03/01/03
Posts: 86
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Well, I am at the point to start to build a pair of grot box-es for my acoustically
treated studio place.
Q: was any DIY grot-box approach already discussed on
this forum (any other forum)?
trif.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Well, I wait a few more days if anybody can give me an info if this DIY was discussed or
not yet.
If there is enough interest I can start to post pictures and describe
steps how my diy project progresses. I would like to know what is the oppinie of the forum
about this idea.
trif.
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Q00
member
Joined: 01/10/02
Posts: 815
Loc: South coast
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Hey dude,
I did a search and this is all it turned up
http://www.soundonsound.com/forum/showflat.php?Cat=&Number=58532&page=5&vi
ew=collapsed&sb=5&o=&fpart=1#58532
--------------------
"Saying that you do is just gold plated XLR elitist bulls**t!" - ow
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Q00, Thanks!
BTW: I have been concidering to make the box from plastic/plexi
glass to mimic the acoustics of the majority of the tv sets/boomboxes (instead of making
the enclosure from MDF).
Another point is to use a single drive instead of 2-3
speakers and use closed design - so no porting.
trif.
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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Good project idea!
Have you considered an elliptical speaker for it? Can you still
get them? Elliptical was a popular compromise for single speaker systems.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Hi Jim Y,
I plan to use SC5.9 8 Ohm (art. no. 8006) magnetically shielded
oval full range driver from Visaton. The speakers are relatively small, their length is
90.5mm, and are 50,5 mm wide. The full specs of this speaker can be found on:
www.visaton.de
What do you
think?
I will start to post some images as work progresses.
trif.
Edited by trifidmaster (10/02/06 10:34 AM)
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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Well, I like the idea of that driver. I've a feeling something similar is used in a
commercial "grotbox". Can't remember what - was it the pyramid shaped things SoS reviewed
a while back?
I'm not an expert on speaker characteristics, but if this link
works others can have a go!
This is the manufacturers response graph. The lower
plot is the impedance versus frequency.
Has a general "smile" curve while I have a
feeling a mid-peak would be more desirable. But perhaps cab design can tweak that?
I was thinking elliptical after seeing in SoS a feature showing a mono speaker the
Doors early stuff was mixed on. Those mixes still stand the test of time IMHO.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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In the local radio/electro shop they had a few choices for oval speakers, so I selected
the above mentioned speaker.
In the same shop purchased a set of very cheapo
spekaers (although cheap, they are 3 way speakers) - they are made from kind of black
plastic (I think the wall thickness is around 3-4 mm). I have been also considering using
plastic box used for small electronics projects, but I could not find a suitable one.
Luckily the front baffle of those speaker is fastened with 4 screews, so I could
easily unscrew the screws. After this litle work I had 2 rather nice boxes without the
front plate.
At this moment I am busy with making the front plate from 5mm
thick plexi glass...and I will start soon the cutting out for the speaker.
However I do not know where should I place the speaker. Into a center position, lower,
horizontally, vertically. Any input is welcome.
trif.
Edited by trifidmaster (10/02/06 03:31 PM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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The photo of the selected speaker:
Here is the photo of the opened/empty plastic
speaker box:
And the plexi baffle with 4 holes and the planned
speaker position. I would like to know if the speaker position is going to be OK - any
input is very much welcome.
trif
Edited by trifidmaster (10/02/06 08:00 PM)
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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It would seem logical to have it centred.
The little I've found out though is that it
should be offset to top or bottom. This is because equal paths over the baffle creates a
response dip.
In other words, pretend there's a tweeter or port to make room for.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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OK, I will place the speaker horizontally and a bit lower.
BTW: I am curious if
the set will really be able to mimic the "consumer sound".
If my grot-box
speaker project turns out to be ok, I will make another set fully from (deep blue colored)
plexi-glass.
Menatime I have already purchased a kit for the power amplifier.
Here is the link:
http://www.velleman.be/be/en/product/view/?id=9184
trif. 
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Update:
The cutout for the speaker is ready.
I also painted the baffle and I
will post pictures later today.
Q: Should I put foam into the box, or should I
go without the foam?
trif.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Update:
Originally I have made the front baffle(s) from 5 mm plexi glass, but I was
not satisfied with the result.
I have changed the baffle material to 4 mm
PVC. Here is the design of the front baffle.
I am still not sure about putting foam into
the box. Any input is welcome.
BTW: my grot-boxes are not intended for mixing
purposes, but "checking" my mixes made on my studio monitor system.
trif.
Edited by trifidmaster (16/02/06 11:05 PM)
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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I'd be tempted to put some foam in.
Yeh, I know it's only a Grot box, but
purpose made ones are not just bad or average speakers, I believe they have a peaky mid
range and being infinite baffle (closed) have a good transient response (fast). All better
for exposing faults in a mix.
Edited by Jim Y (18/02/06 01:18 PM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Jim Y, and forum,
Do you know where could I get a typical response of a "good"
grot-box?
trif.
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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Have you seen this SoS review of the Triple-P Pyramids?
http://www.soundonsound.com/sos/mar04/articles/tripleppyramid.htm
Don't have a curve for you, but Hugh's review suggests a response with a gentle
rolloff either side of a 1.5Khz peak is the thing.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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The Triple-P Pyramids look very nice. Is here anybody who has them?
I am
curious how my grot-boxes will "show up". My room is acoustically treated, and my monitors
within this room show very nice response curve. I think measuring my own grot-boxes in
this room is OK.
Within a few days I will assemble the boxes. More update will
come as work progresses.
trif.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Update:
Here is the photo os the prepared baffle:
And the back of the speaker with wires:
trif.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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More pics:
the foam what I have used to put into the boxes:
I have cut the foam and used contact glue to
glue it into the speaker boxes.
The cut foam:
Here is the contact glue used:
And the "filled" box:
I have put foam onto the inner side of the
baffle, too:
And finally I have placed the baffle into
place. I have glued the baffle into place, fastened with 4 screews (in the 4 corners), and
sealed it with black silicon:
Another pic of the finished unit:
Now, it is tea time
trif 
Edited by trifidmaster (23/02/06 11:32 AM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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...and the used glue and silicon:
I let the glue and silicom to dry for a
couple of days.
trif
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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I have finished the boxes. After the glue and the silicon became dry, I have closed the
boxes.
The next pictures shows the back of the box as well as the legs. I have used
simple rubber legs
The legs are for to use them on table, however I am
going to put them on stands. I am not sure yet what kind of stand am I going to use, but
one candidate is a rather cheap microphone stand.
And here is the final look
of the ready speakers:
They are pretty, are not they?
I am really curious how "god" will they sound. But I still need the stands and the amp.
As soon as all is together I will do carefull frequency sweeps/measurements.
P.S.: Menatime I have soldered together the stereo amp for the speakers.
trif.
Edited by trifidmaster (26/02/06 09:13 AM)
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Q00
member
Joined: 01/10/02
Posts: 815
Loc: South coast
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Look sweet to me dude.
--------------------
"Saying that you do is just gold plated XLR elitist bulls**t!" - ow
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IvanSC
Joined: 08/03/05
Posts: 7548
Loc: UK France & USA depending on t...
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not sure about "God" but they look really pro mate. Be interesting to see how much part
the cabinet resonance plays in the overall sound. Look like you might have to hang them
from the ceiling with bits of fishing line to isolate them! I can almost hear them
vibrrrrrating off the edge of your desk!
--------------------
Me? But I`m such a loveable old bugger!
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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I am still waiting for the "stands". As I said, I will use "cheap straight microphone
stands for my boxes. I do not know how much they are going to resonate.
Note:
I am now building the power supply for my amp. Asap all ready I will post more photos.
trif.
Edited by trifidmaster (11/03/06 05:15 PM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Finally, today the stands arrived. I have already placed them into their "potential"
position into my setup, I have indicated them with read arrow in the pic:
The end of this mic stand has a thread, it seams to
be a standard mic thread. Now I need to develop a connection piece between this thread and
the bottom of my grot box speakers (in which I have M5 thread).
Here is the photo of
the stand thread:
Does anybody know the specs for such a mic thread? Is it
UNF, metric,...?
trif.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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I wanted to edit my previous post, but it is not possible anymore.
Update
(15/03/2006):
I have done some "research" about the thread. It seams that it is 3/4"
thread. Can anybody confirm this, please?
If this is the case, what I need is a
converter piece between 3/4" and M5.
trif.
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Hugh Robjohns
SOS Technical Editor
Joined: 25/07/03
Posts: 11358
Loc: Worcestershire
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There are two 'standard' thread sizes for mic stands. The European one is 3/8-inch
whitworth, the American one is 5/8-inch UNF (I think).
If you have a trawl
around the www.canford.co.uk web
site in the mic accessories section you'll find a range of adapters and tehre is a table
there showing all the standard thread sizes and pitch data. They also sell mounting plates
and stuff that you might find handy to mount your speakers.
hugh
--------------------
Technical Editor, Sound On Sound
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Dear Hugh, thanks. The page you listed certainly contains useful infos.
Luckily in the local DIY shop I could find the below picted "connection elements", with
the correct thread:
It also had a inner piece, into which I
have glued a 5 mm bolt:
And after the inner part is inserted:
..and srewed to the bottom of the
speaker:
And finally the speakers on the stands:
I am satisifed with the result. At this moment I
do not know what the sound will be, how the speakers are going to resonate...
In the upcoming updates I will post pictures of the ready amplifier.
trif
Edited by trifidmaster (17/03/06 08:26 PM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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The front of my amp:
The back:
and the inner part of the amp:
and the external power supply:
After I connected all the parts together I have
listened to some commercial tunes. Well, how does it sound? Crappy, and kind of tong,
tang, tong...
The stereo image is very tight. The vocals are very strong as
are solo instruments including cello. I have played a litle bit with the positioning of
the speakers, I moved them a bit closer to my seating position. I have fairly low level of
bass but even-certainly not enough to make any judgement for mixing the low end.
That is it up to now.
I expected to have my grot boxes sound nicer.
But I remember that they should be not nice sounding. It would be certainly interesting to
listen to some "professional" grot-boxes for comparison.
Now, it is time to
check my own mixes, and see what can be revealed. I think I need to learn these
grot-boxes.
Any comment/suggestion is very much welcome.
trif.
Edited by trifidmaster (30/03/06 09:24 PM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Sorry to tell you ladies and gens, but one of the speaker did not survive my initial
tests. The rating of the speaker is 10W, maximum 15W, and it is a 8ohm speaker. The amp
per channel can give maximum 15W/8 ohm. Perhaps I was driving the speaker to loud.
The other speaker is still running.
Anyhow, I have returned the speaker,
and it will be replaced. So, now I have to wait until the replacement arrives.
Meantime, I have ordered another speakers:
http://www.visaton.de/english/artikel/art_378_1_3.html
This is a
bit stronger speaker, again magnetically shielded.
At this moment I do not know if
should I build a wooden box around it, or go again for a "plastic" solution.
Any
comment on this?
The stand (made from a mic stand) resonates much to much, so
I think I will have to go for another type of stand for my grot-boxes.
Does
anynody know what listening level should I use for the grot-boxes??
trif.
Edited by trifidmaster (31/03/06 06:29 PM)
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Next: I will add a potmeter to the amp. This is actually described nicely in the amp kit
(pages 8 and 9), but I did go for the potmeter less solution (this is also possible to
do). It is obviously good to have the potmeter, so I can control the volume of the
grot-boxes independently from my mixer main fader. I already have the correct
potmeter.
Is here anybody who has experience with grot-boxes? I like to know
what should I really hear from them.
trif.
Edited by trifidmaster (01/04/06 12:54 PM)
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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I suspect you may not fully understand the purpose of a "grot" box. There have been some
SoS speaker reviews of such beasts where the design criterea and usage is very well
explained.
Without access to an anechoic testing chamber, it's going to be nearly
impossible to know if your speakers meet those criterea.
At the very least you
should have use for them as a comparative reference. It matters little how good the
speakers sound, the question is do your mixes still work using them? Listen to commercial
mixes of similar material first, and note how they cope. The essential balance of the mix
should survive the limitations of the grot box, not in hi-fi splendour, but still
intelligable. For example, if a hi-hat either disappears or dominates, the entire feel of
the music can change. If a bass melody is important and you can't hear it, you need a bass
sound with more harmonics. And so on.
On another point, as you managed to blow
a speaker, are you sure that amplifier doesn't have a DC output fault?
Excuse me if
I'm teaching Grandma to suck eggs 
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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JimY,
Thanks for your comments. I have re-read the SOS article what is mentioned
earlier in this thread. Is there any other article about "grot-boxes"?
I have
"studied" other infos on the net, but I did not find not so much about "grot-boxes".
As I told I have NO experience at all with grot-boxes. Asap as the broken speaker
is replaced I will do some frequency sweeps, what I will post here. And surely I will do
some mixing work with them.
Any further comments/ideas/guidances are very much
welcome.
Update about the amp
I have added an input potmeter.
..and now the front became:
Note: The LED (red) is not yet connected.
trif.
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Scottdru
Cool Dude
Joined: 17/12/02
Posts: 4392
Loc: NYC: isle off the coast of Eur...
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Those look pretty sweet!
There's a DIY auratone thread at John Sayers' forum that might
be of interest to you if you haven't seen it already. I don't have time at the mo to hunt
down the link, but I did post it in a thread here (either here in the DIY forum or in the
MRT forum) some time ago . . . but I think you have to register for that forum in order to
see the pics.
One suggestion I would make is that I doubt the foam you put in
there is doing you much good . . . probably better to get something with more density.
Some OC 703 (or rockwool product of similar density) might be a better bet, I would
think, as this will have the density to give you some LF absorption in that cabinet. I'd
guess that even OC 701 would be better than what you have in there now. I know you're not
dealing with really low frequencies here, but I still think it would be better to get
something with more density, as it will have an increased absorption coefficient at ALL
frequencies.
--------------------
Scott
--Where are we going and why am I in this handbasket?
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Scottdru,
Thanks for the comments.
1st, I like to finish this project. Wat is
remaining is the replacement of the blown speaker, do frequency sweeps (and decay times),
and follow the steps described by JimY and the very few articles published about the
grot-boxe usage.
I have seen the "Killatone" project on the John Sayer's
forum. (Indeed, registration is necessary to see the pictures).
I have a
good book about speaker design with a few exanmples. In that book (what I have mentioned
it in another topic in this forum) there is a very small speaker project, and it looks a
bit similar to the "Killatone". I have already started to make the boxes from MDF for both
designs. But I leave these to be discussed later. First I want to see how my "plastic"
grot-boxes will perform.
I have thought so, that little acoutic foam or no
foam will "mimic" the radio/television speakers.
Of course I can put 701/703 or
equivalent into my current boxes, but this will bring me further from mimicing the
radio/television speakers, I think. Any further comment is welcome.
trif.
Edited by trifidmaster (18/04/06 10:07 AM)
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Scottdru
Cool Dude
Joined: 17/12/02
Posts: 4392
Loc: NYC: isle off the coast of Eur...
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Quote trifidmaster:
Scottdru,
I have thought so, that little acoutic foam or no foam will "mimic" the
radio/television speakers.
Of course I can put 701/703 or equivalent into my current
boxes, but this will bring me further from mimicing the radio/television speakers, I
think. Any further comment is welcome.
I guess my thinking on this is that I'm not sure most TVs have their
speakers mounted in small, sealed boxes as these are. Also, foam you have put in there
doesn't look like it is acoustic foam to me, and I would suspect that it wouldn't have the
necessary absorption to counteract some of the resonances introduced by a sealed
cabinet.
Also, as Jim Y points out, a grot box isn't just about mimicing TV
speakers, etc. exactly, but rather having something that might have a similar
response or voicing, but that has some precision with regard to transients, etc.
This is why he suggested putting some acoustic foam in there, to damp enough of
that resonance to allow the speaker to sound basically as it is designed to sound on its
own, without being adversely affected by the sound pressure/resonances inside the cabinet.
My guess is that such a small sealed cabinet (particularly) like this could have a
negative effect on transients and general clarity at certain frequencies if it is not
adequately damped.
On the other hand, in a TV, while the speakers might not
be mounted in the most ideal of cabinets, at least there is someplace for the sound
pressure from the back of the driver to go!
Not all foam is "acoustic foam".
Acoustic foam will have certain properties (density, gas flow properties, etc.) that make
it more effective at absorption of sound pressure than other types of foam. Proper
acoustic foam should be effective as well as 701 or 703 for this purpose, but I suggested
the fiberglass because it might be quickly and easily available for low cost.
That said, I do not claim in the least to be an expert on speaker design. The above is
based on my instinct as to the effect of the sealed box on the driver. Perhaps you have
seen something in some of the designs in your speaker design books that disagrees with my
thinking?
--------------------
Scott
--Where are we going and why am I in this handbasket?
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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I don't think I've seen mineral or glassfibre used as cabinet wadding. The danger surely
is of particles of this stuff getting into voice coils or anywhere else it wouldn't be
welcome. A plastic foam or even lambswool is more common.
Some kind of testing
could be done on the finished items. ETF lets you adjust the gate time in which the
results are calculated, so you can filter out reflections from the room by choosing a gate
time a little longer than the test mic distance (guess, 1 metre away, gate time 4ms?) -
you'll get the measurement of the speaker in other words, not the room.
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trifidmaster
member
Joined: 03/01/03
Posts: 86
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Well, I have put into the boxes the acoustic foam sold for speaker builders, see one of my
post. Perhaps I could put 2 times more foam into it.
I am still waiting for the
speaker replacement - perhaps this week it will be delivered.
I have used
another software to test/measrue my room, and I think it will be OK for measureing the
speakers.
Someting extra/OT: Meantime I have added a set of JBL Control One
speakers into my setup - but, they are much too good to be used as "grot-boxes", I think.
trif.
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Scottdru
Cool Dude
Joined: 17/12/02
Posts: 4392
Loc: NYC: isle off the coast of Eur...
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|
Quote Jim Y:
I don't think I've
seen mineral or glassfibre used as cabinet wadding. The danger surely is of particles of
this stuff getting into voice coils or anywhere else it wouldn't be welcome. A plastic
foam or even lambswool is more common.
Hmmmm . . . to tell you the truth, it seems like most of the speaker
cabinets I've opened up over the years used fiberglass damping. But, again, FWIW.
If the stuff trifid got was specifically meant for speaker builders, then perhaps
I'm off-base in my assumptions as to the properties of that foam. 
--------------------
Scott
--Where are we going and why am I in this handbasket?
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Jim Y
active member
Joined: 30/03/04
Posts: 1160
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Maybe fibreglass in the States Scott? They don't seem to like that stuff Europe side. Most
common I've seen is like an albino acoustic foam, and I think that is what Triffidmaster
used.
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