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Old 27th August 2002, 06:23 AM   #1
navin is offline navin  India
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Default lots of questions

I am planning to build a smal speaker with a small sub (if you can call a 8" woofer a sub).

The small speaker will have a 6" Vifa woofer and 1" Vifa tweeter (models TC18WG49 and TC26TG05) the specs can be got from http://www.d-s-t.com/vifa/index.htm.

below this speaker I intend to add a small 8" woofer (active).

The 8" will provide bass reinforecement and also compensate for some difraction loss. The 8" woofer is a repaired Eminence woofer approx TS specs are Fs=35Hz and Qts 0.45. The cabinet of this woofer will act like a stand for the 6" 2 way described above.

1. can I use a 2ay 12db series XO with the Vifa drivers.

2. To make the cabinetry simple I intend using 4'x8' sheets of MDF and making the height of the speaker 4' (48"). Is this too tall? Should I put the 6" on top of the 1" so that the 1" can be closer to listening height (36-38").

3. At what height on the baffle should the 8" be? Roy Allison claims it should be as close to the ground as possible, else where I hear the center of the bass driver should be 16" (40cm) from the ground. And my common sense tells me it should as close to the 6" 2 way as phyisically possible so that all the sound is coming from as small a point as possible.

4. I intend to bend the cabinet side walls a la Sonus Faber Amati and Wilson Benesch Act 2. How thick a MDF can I bend. If the MDF is less than say 8mm (so that it is easier to bend) should I use layers. If I am using layers can I use lead sheet 2-3mm between the layers?

5. I intend to bolt the drivers to the cabinet instead of using screws as I want to integrate the drivers as solidly to teh cabinet as possible. Does is make sense to veneer the cabinet so that the bolts are covered/hidden. What are chances I burn a woofer or tweeter out. Usually I hear only tweeter burn out.

6. The baffle will be 30mm MDF. Since I am bolting the drivers shold I use a 3-4mm metal plate on the inside of the baffle so that the bolt does not bite into the wood?

7. I intend using a truss rod for each of the 6" and 8" drivers. The truss rod will be a plastic or metal tube filled with either lead shot, sand or thermacol pellets. Which combintion wouldone recomend?

Since I do not have regualr access to the net please email me at navin@vsnl.com

Regards
Navin
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Old 27th August 2002, 11:07 AM   #2
Raka is offline Raka  Europe
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Default Bass positioning

Hi,

What is your speaker for?

If you are going to sit down and listen carefully, the drivers should point to you (toeing should be very studied), but if you are going to do the ironing or washing up, I think they must be fitted only for looking purposes.
The positioning of the bass speaker, since the wavelenght is far greater than the distance, has only to do with the room floor interaction. Unafortunately, only the tests will tell you the best positioning. I usually preffer the sound of woofers away the floor.

Bye.
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Old 27th August 2002, 11:48 AM   #3
navin is offline navin  India
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the speakers will be for listening to music as well as part of a HT system.

the center speaker will either a MMTMM using 4 shielded Vifa 4" midbass and 1 shielded 1" Vifa tweeter or a MTM using 2 shielded Vifa 6" woofers and 1 shielded 1" Vifa tweeter. I prefer teh MMTMM as it is 2" lower in ht. but I have enough drivers to build both and decide.

the rear speakers are not known yet. presently the best bet i have a 2 old Boston Acoutics A40 or A60 speakers lyingboxed in my garage.

The front speakers will double as HT and Audio so those are what I want to build first.

Thanks.
navin
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Old 27th August 2002, 03:15 PM   #4
Schaef is offline Schaef  United States
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Default Only Question 4 answered

Well, I can only comfortably approach your question #4, about the MDF stuff. Bending MDF and the ease there-of depends heavily on several factors. First is the amount of bend you want to do, and over what length. Secondly is the thickness of the material being bent. Finally would be the type of material itself. (MDF in this case) The thinner the material, the easier it is to bend and to get a tighter radius. Be careful with MDF, it is not that strong structurally, so if you go too tight, it'll just break. Not knowing how much of a bend we're talking about here, I can only make some general suggestions. First, going with the thinner MDF will make the actual bending easier, and yes, I would laminate a couple thicknesses together for speakers. As to the lead in between layers, I don't know. The biggest thing I would worry about would be securing the MDF to the lead sheet. Personally I wouldn't do it, too many things to go wrong. I would HIGHLY recommend building a jig for the sides so that you get a consistent form for all four sides. (two for each speaker)

Okay, I lied, I'm also going to comment about the baffle. Instead of putting a sheet of lead on the back to keep the bolt from biting into the wood, what's wrong with just a large washer? Again, much easier to work with and less to go wrong. I prefer to keep things simple when it comes to complex projects.

Hope this helps you out some!
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Old 27th August 2002, 04:42 PM   #5
SteveG is offline SteveG  United States
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Quote:
2. To make the cabinetry simple I intend using 4'x8' sheets of MDF and making the height of the speaker 4' (48").
Is this too tall? Should I put the 6" on top of the 1" so that the 1" can be closer to listening height (36-38").
The tweeter should be at ear level. The mid should usually be below it.

Quote:
3. At what height on the baffle should the 8" be? Roy Allison claims it should be as close to the ground as possible,
else where I hear the center of the bass driver should be 16" (40cm) from the ground. And my common sense tells
me it should as close to the 6" 2 way as phyisically possible so that all the sound is coming from as small a point as
possible.
Well, where are you crossing the woofer over? The wavelengths at most bass frequencies are so big that there will be no problem with integrating the sub with the mid, even with a large distance between them (although you might want to consider front-back distance between the two because of phase problems which will mess with your crossover). I would put it as close to the floor as is possible. You will need all the bass augmentation you can get with a little 8".


Quote:
5. I intend to bolt the drivers to the cabinet instead of using screws as I want to integrate the drivers as solidly to
teh cabinet as possible. Does is make sense to veneer the cabinet so that the bolts are covered/hidden. What are
chances I burn a woofer or tweeter out. Usually I hear only tweeter burn out.
That's up to you... personally, I wouldn't take the chance of something going wrong and having to destroy my cabinet to get in the enclosure.

Quote:
6. The baffle will be 30mm MDF. Since I am bolting the drivers shold I use a 3-4mm metal plate on the inside of the
baffle so that the bolt does not bite into the wood?
I would use (correct name slips my mind right now) the nuts that are made for this- they have raised areas to bite into the wood on the back of the baffle.
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Old 27th August 2002, 05:47 PM   #6
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""I would use (correct name slips my mind right now) the nuts that are made for this- they have raised areas to bite into the wood on the back of the baffle.""

In the UK they're called T-nuts......

Rob
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Old 27th August 2002, 06:00 PM   #7
navin is offline navin  India
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yes i was thinking of using t nuts.

the sides would be 16" deep. the front would be 10" wide, the back would be 3" wide.

yes i need all the help I can use with the 8". However I am not looking at big bass. I have a 4 month old son (http://www.pbase.com/advani - shameless proud dad plug here :-) ) so mt SPL needs are limited.

Also my son is the reason I am considering HT. We prefer to watch the TV nowadays than theater or live concerts.

Also the 8" will be active so there is room for some active EQ.

about veneer I might allow access to the tweeter (those I have blown - MDT 33 from morel that too) but I have never blown a woofer even in my "120db or bust" days. Well I blew out a JBL 2245 once - connected it to 220V AC but I was young and crazy then.

The Spica TC 50 as well asl other well known brands use the tweeter under the woofer so I was wondering if there was any advantage to this. To me this allows me to have the tweeter at ear level and save some wood cutting (albeit simple cuts).

thanks a lot guys but so far no one has taken up question 1. help! :0

Regards
Navin
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Old 27th August 2002, 07:02 PM   #8
SteveG is offline SteveG  United States
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I need a little more explanation with question 1... Why a series 2 way? Wouldn't a parallel 2nd order 2 way be the easiest? If you don't have the test equipment, have madisound do a crossover for you with leap... easiest way.
As far as mounting the woofer over the tweeter, it has been used in systems that have a first order network and are floor standers, because of the tilt provided by the crossover network (see Loudspeaker design cookbook).
I have a set of MTM's using two P17WJ's and I find the bass to be extended, but lacking in comparison. One reason I believe this is the case is that they are tall, and the port are mounted fairly high on the front... I'm not getting any help from the room this way. Why use more power from your sub amps than you have to? It will be cleaner with some help from the room- more sensitivity=more volume with less power, cone excursion, etc.
Steve
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Old 27th August 2002, 08:12 PM   #9
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Quote:
Originally posted by navin
so far no one has taken up question 1. help! :0
Series XOs above 1st order get really tricky and i have seen little DIY on them. The text book formulas i have somewhere, i'd suggest starting out at Andy Graddon's site -- haven't got the URL handy (and i'm sneaking this post in when i should be working).

My friend Chris (the guy i get to build any cabinets that have to be presentable) just went thru a bunch of experiments building a curved back box. There is a specific, but somewhat pricey material that he says is all he will use. I'll see if i can get him to come explain.

dave
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Old 28th August 2002, 12:58 AM   #10
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There is 1/2" plywood which can be bent to any shape. Apart from being pricy it also doesn't seem to be hard. Available from building suppliers.

The other alternative is to use ribs (which will also serve as braces) with matrix construction (like B&W) and use wet plywood or MDF.
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