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Old 26th May 2004, 03:56 AM   #1
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Default Could I make a 1/4 scale Altec 828 A7 cabinet...

For a 4 1/2" driver?

What's the good and bad on doing that?

Curious Cal
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Old 26th May 2004, 05:38 AM   #2
Variac is offline Variac  United States
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There is a guy already that makes a miniature A7 using smaller drivers. I suppose you know about this?
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Old 26th May 2004, 01:09 PM   #3
sreten is offline sreten  United Kingdom
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Hmmm........

It depends what you mean by 1/4 scale ........

Cone area will be ~ 1/16 of the full size cabinet but the cabinet
internal volume will be 1/64 of the full size cabinet so something
has to give, basically bass extension.

A full 2 octaves of bass extension for the same efficiency.
Or lose 18dB of efficiency for the same bass extension.

A compromise would be to lose one octave of bass and 9dB efficiency.

Due to scale the c/o frequency goes up two octaves.

My idea of 1/4 scale would be 1/4 the cone area, i.e. an 8".
So cabinet dimensions would be halved and internal volume
would be 1/8 the full size speaker.

If you accept a reduction of 6dB in sensitivity you'd
only lose a 1/3 of an octave of bass extension.

Due to scale the c/o frequency would double, up one octave.

So nominal specs would be :

44Hz to > 22Khz
c/o 1.8KHz
~ 100W
93dB/W
15 x 12 x 27 inches
~ 22 lbs



sreten.

(Basically 3dB efficiency = 1/3 of an octave of bass, or 3dB
extra efficiency for the same bass = double the cabinet volume)
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Old 26th May 2004, 06:11 PM   #4
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i canīt see the point why one would make a smaller A7. The A7 is a very large Box good for ~40Hz to < 1000Hz. A smaller one would not bring any bass and be some kind of middle freq. Horn with a higher bass very bad ported enclosure. It would make sense to cut the ported enclosure away, make some kind of mid horn from 200Hz upwards, and use another speaker for bass.

The evolution step from the A7 828 i donīt see in making a smaller one, but in building a larger like the 210! (first i need a larger house)
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Old 26th May 2004, 08:46 PM   #5
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Quote:
Originally posted by Variac
There is a guy already that makes a miniature A7 using smaller drivers. I suppose you know about this?
No, but I would be most interested

Quote:
Originally posted by sreten
Hmmm........
It depends what you mean by 1/4 scale ........
What I mean is a cabinet scaled down so that a 4" woofer would replace the 15 or 16"
ie: 1/4 scale or 1" = 4"

Quote:
Originally posted by till
i canīt see the point why one would make a smaller A7. The A7 is a very large

The evolution step from the A7 828 i donīt see in making a smaller one, but in building a larger like the 210! (first i need a larger house)
I want these little guys to sit beside my A7's and be a litlle brother if you will.

As far as bigger, I already own a pair of the 210 cabinets. You're right, they don't fit in the house. Look in the back of the photo and you'll see the open backs of the A4's

You see, this project is an extension of my little aluminum speakers that I wanted to look kind of like the A7. It didn't work and the cabinets are far too small for the woof to develop.

I don't need anymore speakers, I have enough. This is just for fun.

Thanks for your help so far,

Cal
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Old 26th May 2004, 10:04 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Cal Weldon

What I mean is a cabinet scaled down so that a 4" woofer would replace the 15 or 16"
ie: 1/4 scale or 1" = 4"

I want these little guys to sit beside my A7's and be a litlle brother if you will.

Cal
Well you can certainly make them.

But the effect of the bass front horn can be judged by comparing
it to the size of your head, you wont get the controlled projection
that is a feature of the A7 design.

There is a very good reason why the slot in front of the bass
driver is just about perfect for getting your head stuck in it.

But I digress :

So say 7.5" wide, 6" deep and 13.5" high.
(larger if you are not 1/4 thickness ply)

Now that isn't that small, especially if you say sod it I want
some bass and change the depth to something more sensible.

First problem is the tweeter unless you want to go
the dreaded piezo route which I presume you don't.

Neverless this certainly looks the part you need :

http://www.partsexpress.com/pe/showd...number=280-062

Unless you can find a similar dynamic tweeter.

The bass / mid front loading is probably going to cause more
problems but neverless you can make the slot a little wider
than the scale would indicate and not worry about the lower
slope section of the horn in the original.

All this means is you could easily use a larger driver than 4".

http://www.partsexpress.com/pe/showd...number=295-301

Seems as good as any, you just need a little care in c/o design.

Though you could reuse those ali drivers you have.

Due to the much smaller cabinets baffle step can't be ignored.

Finally due to 1/4 scale major alterations are needed for the port
tuning arrangements, this would also decide the depth of the cabinets.

sreten.
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Old 27th May 2004, 04:08 PM   #7
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Quote:
Originally posted by sreten
Well you can certainly make them.
Good

Quote:
[i]There is a very good reason why the slot in front of the bass
driver is just about perfect for getting your head stuck in it.[/B]
You found that out too?

Quote:
[i]But I digress :[/B]
I'll say

Quote:
[i]if you say sod it I want some bass and change the depth to something more sensible.[/B]
Sound quality not as important as looks

Quote:
[i]First problem is the tweeter unless you want to go the dreaded piezo route which I presume you don't.[/B]
Gasp, argh, uh, no

Quote:
[i]Unless you can find a similar dynamic tweeter.[/B]
I would love to find something like a multicell out of an Altec 604

Quote:
[i]Though you could reuse those ali drivers you have.

Due to the much smaller cabinets baffle step can't be ignored.[/B]
Oh yes it can. These are for show, not for auditioning or monitor use

Quote:
[i]Finally due to 1/4 scale major alterations are needed for the port tuning arrangements, this would also decide the depth of the cabinets.
sreten. [/B]
All as original as possible please

Thanks Sreten, your input is always valuable.
Cal
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Old 28th May 2004, 03:46 AM   #8
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Quote:
Originally posted by Cal Weldon

Sound quality not as important as looksCal
You could cheat with the bassresponse if you use an Aphex 204.

http://www.aphex.com/204.htm
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