Don't quote me on the Vas figure by the way - I've not done any type of calculation! 🙂
The bass/mid driver will naturally roll off gently at high frequencies while the tweeter will gently roll in courtesy of its capacitor.
There will be a quite a wide area of overlap where both are contributing the same frequencies to the sound. So there's no danger of the frequency ranges not meeting.
Go ahead with your mock up cabinet - even cardboard boxes are good enough for prototyping!
The bass/mid driver will naturally roll off gently at high frequencies while the tweeter will gently roll in courtesy of its capacitor.
There will be a quite a wide area of overlap where both are contributing the same frequencies to the sound. So there's no danger of the frequency ranges not meeting.
Go ahead with your mock up cabinet - even cardboard boxes are good enough for prototyping!
Vas is 226 litres. DATs V3 is working fine. Calibrated it properly. Used the 25% of Fs to find the correct weight to use for the added mass method. So I am hoping I have gone about this the right way. So the Vas I got it 226 litres.
Anyone want to hazard a guess of the Xmax so I can drop that in Unibox as well...?
Here's a link to a page with the parameters of what appears to be this woofer or very similar:
ReproMania.NET | Tesla | Reproduktory basove | ARN 738
Note that Vas is in the 200 L range. Since this thread title is about tweeters, I'd start a new thread asking for enclosure help with "Tesla" and the model# in the thread title in hopes of finding someone familiar with this driver.
ReproMania.NET | Tesla | Reproduktory basove | ARN 738
Note that Vas is in the 200 L range. Since this thread title is about tweeters, I'd start a new thread asking for enclosure help with "Tesla" and the model# in the thread title in hopes of finding someone familiar with this driver.
If this driver is anything like the ROLA of the same era they were often used in open back boxes or boxes with slotted backs covered with leaky cloth and actual box size doesn't really matter much. If you want a sealed box anything around 60 to 90 litres "should" work depending on how much you stuff it. I second the use of cardboard boxes for trial boxes and baffles. Free boxes at any Bunnings store, if the screws won't hold glue in another thickness of cardboard with school glue PVA
The Tesla ARN738 speaker is typical for that period in time in that it would have been intended for use in sealed enclosures of around 40 to 60 litres internal volume. Rola (later Plessey) speakers from Richmond, Victoria, did not manufacture speakers for 'acoustic suspension' applications. A Rola 12UX certainly performed very well fitted to a large tuned bass reflex enclosure or in an even larger fully sealed cabinet.
Well the very early ROLA I am familiar with were typically in open backed stereograms, just like cheap guitar speakers. Very small magnets etc. Plessey in sealed boxes I have seen often, interestingly I have a pair of HE Plessy midrange hear but made by Foster, very efficient but need new cones due to rat damage while in storage
My experience is with drivers like the one in the picture which I just grabbed from the net
My experience is with drivers like the one in the picture which I just grabbed from the net
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In Australian we say sik **** but if you don't know what that means it could potentially be offensive.
Great find, at least I confirm the Vas. I am happy that my hard earned results on DATs finally are accurate. I also know now that the frequency range is up to 2000hz, I might need a mid driver.
Any chance you can find the tweeter driver somewhere?🙂 Lol!!
Hey Galu,
Can you also provide me with a diagram with a mid driver in place? With the same concept. Just in case I have to add a mid.
The owner says he doesn't like mids and if I end up putting one in the mix to attenuate it a little, he hates forward mids...
Point being, is I will attempt without a mid but so I can analyse the schematic one with a mid driver will teach me a lot as well.
I think I will go as large as possible aesthetically, and will definitely make it a leaky sealed box to play with the Q. Ill have to work out how large to make the hole in the back.
Thanks for the cardboard box idea I didn't know that, I thought a proper sealed enclosure is the only way to get an idea of how it will play out
It will be that slow roll-off we talked about after 2k so the tweeter will do, no point is adding a midrange to this particular driver.
I think our use of dedicated woofers is a reasonably modern idea, say 1950 onwards? May the 60's.
The hole in the back ? Well make the whole back panel removable because that was often how the boxes were made, rear mounted woofers accessed via the removable back panel.
Many of the old 3-Way speakers I get given are a big wide range driver, 10 or 12" plus a sealed back 3" or 4" tweeter with a 5.6 / 3.3uF cap in series and a 2" sealed back tweeter with a 2uF in series.
These book values are for higher frequencies but because of the shallow slopes they work, or at least they worked "well enough", in older speakers they may have used slightly different values because standard values changed at sometime.
I think our use of dedicated woofers is a reasonably modern idea, say 1950 onwards? May the 60's.
The hole in the back ? Well make the whole back panel removable because that was often how the boxes were made, rear mounted woofers accessed via the removable back panel.
Many of the old 3-Way speakers I get given are a big wide range driver, 10 or 12" plus a sealed back 3" or 4" tweeter with a 5.6 / 3.3uF cap in series and a 2" sealed back tweeter with a 2uF in series.
These book values are for higher frequencies but because of the shallow slopes they work, or at least they worked "well enough", in older speakers they may have used slightly different values because standard values changed at sometime.
Adding a mid driver would be a needless complication in this case.
As Moondog55 says, the bass/mid driver does not suddenly cut off at 2,000Hz but will roll off slowly while the tweeter slowly rolls in. The combined output of the two drivers will ensure there is no gap in the frequency coverage.
It may be useful for you to know that midrange is defined as the range of frequencies from 500Hz to 2kHz. So, you see, the ARN 38 as already covering the midrange.
Wharfedale called 'a leaky sealed box' a 'Distributed Port (DP)' enclosure.
The back of a DP enclosure is drilled with an array of small holes, then lined on the inside with a soft woolen cloth like that used to make overcoats.
An enclosure of volume around 60 litres requires 60 holes each of 1/2" diameter to be drilled in the back. The centres of the holes should be spaced at a separation of 3/4" to form a neat array of holes (I suggest 12 rows of 5 holes).
Obviously, experimenting with the number of holes allows you to 'play with the Q'.
There is also what is often termed the "Telephone bandwidth" it runs from 300Hz to 3000Hz, and I try and use a wide band midrange to cover this frequency range. Just something to keep in mind for your next project.
In older stereograms with those ROLA drivers I think it was commercial pegboard, lots more but smaller holes
I think the pegboard was more about keeping prying fingers out and allowing ventilation rather than providing acoustic resistance as is the intention of the DP enclosure.
Here's an alternative approach to providing acoustic resistance in order to lower the Q of a sealed enclosure.
Aperiodic Enclosures - Great Sound Stereo Speaker Manual
Aperiodic Enclosures - Great Sound Stereo Speaker Manual