Hi all,
I’m entirely new to speaker builds, but I am keen to try it out.
I snagged a well working pair of Tangent Acoustics TM1 ported two-way speakers a few years back for next to nothing (300 Swedish crowns (like $27USD)).
The cabinets are not in the best cosmetic shape and I’ve been thinking about building a new set with the drivers from these, and possibly the cross-overs as well if possible/recommended.
The drivers are:
Where should I begin?!
I’m entirely new to speaker builds, but I am keen to try it out.
I snagged a well working pair of Tangent Acoustics TM1 ported two-way speakers a few years back for next to nothing (300 Swedish crowns (like $27USD)).
The cabinets are not in the best cosmetic shape and I’ve been thinking about building a new set with the drivers from these, and possibly the cross-overs as well if possible/recommended.
The drivers are:
- tweeter - KEF T27-SP1032
- woofer - KEF B200-SP1014
Where should I begin?!
As far as I can remember, that B200 went mostly into compression boxes, sometimes with a passive radiator. Find some original KEF design and work with it. A 19mm tweeter is not really the right choice for a 20cm midbass.
Those are 50 year old standard range drivers (i.e. not premium range but not budget range either) that are unlikely to be still in spec due to aging. They could well be useful for experimenting with but are likely to be a false economy in speakers you intend to keep given the price of wood, crossover components, etc... and the longer life and better performance of modern standard range drivers (e.g. SB Acoustics) for around £50 a midwoofer and £30 a tweeter.
Good bass response tends to require a large surface area and in a smallish volume will require high power. At low frequencies the laws of physics dicate that there is a trade-off between cabinet size, bass extension and efficiency often referred to as Hoffman's Iron Law. So if you stick your current B200 in a smaller cabinet you should expect the bass response to be worse. Also the room resonances in an acoustically untreated room usually have a stronger influence on the quality of what we perceive at low frequencies than the shortcomings of reasonable hi-fi speakers (i.e. not tiny plastic computer monitors).
Good bass response tends to require a large surface area and in a smallish volume will require high power. At low frequencies the laws of physics dicate that there is a trade-off between cabinet size, bass extension and efficiency often referred to as Hoffman's Iron Law. So if you stick your current B200 in a smaller cabinet you should expect the bass response to be worse. Also the room resonances in an acoustically untreated room usually have a stronger influence on the quality of what we perceive at low frequencies than the shortcomings of reasonable hi-fi speakers (i.e. not tiny plastic computer monitors).
As I’m entirely new to this - it might be a good starting point anyways? I’ll check out some original KEF designs. I think the Cadenza used the same setup. The TM1’s are on the larger side. I know that for example Tangent Acoustics TM3’s did use the same drivers as well.
If I like the bass with closed ports, what can I conclude from that other than that it sounds more to my liking? That a sealed box of smaller volume might work?
How much box volume is really needed for that driver can only be determined by measuring TS parameters and later a simulation. I think that B200 midbass has too big a Q factor for bass reflex. In general, the higher the Q factor, the larger the box required. Maybe this existing box fits just to be closed and add more damping inside. So try it first. Find a cloth, socks, sponge, anything and try it.
Where should you begin?
Here:
The small magnet B200 SP1014 was used in the compact infinite baffle KEF Chorale speakers along with the T27 SP1032 tweeter.
The enclosure dimensions were (WHD) 280 x 470 x 220 mm / 11 x 18.5 x 8.7 inch: https://www.radiomuseum.org/r/kef_chorale.html#
The internal volume was 20 litres.
Here:
The small magnet B200 SP1014 was used in the compact infinite baffle KEF Chorale speakers along with the T27 SP1032 tweeter.
The enclosure dimensions were (WHD) 280 x 470 x 220 mm / 11 x 18.5 x 8.7 inch: https://www.radiomuseum.org/r/kef_chorale.html#
The internal volume was 20 litres.
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You will get less bass extension with a smaller enclosure, regardless whether it's vented or sealed.
jeff
Learning curve with anything, over a long period you get a pretty good idea of what is actually going on.
The audio world can spin you in circles of suggestions.
Looking at that speaker. It is typical suspension and average magnet.
Reality a speaker suspension is so loose or so tight.
The magnet force is this strong or this weak.
Well defined math to calculate what that suspension and whatever magnet force it has will want for box volume , the end.
Q of .7 or 707 is the minimum and the common choice for smallest possibly size box . After that .5 or .577 will be =Bigger
Taking account of those 2 basic things mentioned. Suspension/ Mechanical Quality ( Qms) and Magnet/ more electrical (Qes)
Do the math and you get = total Quality or (Qts)
If Qts or Total Quality is little higher around .5 to .6 or more
That speaker will want a Bigger box to meet a cabinet Q of .7
If Qts is little lower .3 usually pretty powerful magnet or .4 slightly less
The speaker is more likely to be ok with a small box to get cabinet Q of .7
The world seems interested in smaller and smaller boxes.
You can do that. Just dont waste your time with magic imaginary theories.
Find a speaker of the size you like with Qts of .3 the end, but it in the small box it wants.
I can tell you right now it is highly likely that speaker is around ,5 Qts and that large box it is in, is what it wants. Dont get smaller
Unless by some magical change the manufacture put it in a .600 or .577 box size. Then it can go smaller to .707 box size = doubt it
Enjoy it. A cabinet rebuild would just be the typical extra bracing, and smooth up the front baffle without those hard overhanging edges.
Then add whatever finish you like.
If you want small boxes. Its gonna be the same or different suspension type, and a good size magnet to get Qts to .3
Buy that speaker, calculate .707 cabinet Q= It will be small. And enjoy
The audio world can spin you in circles of suggestions.
Looking at that speaker. It is typical suspension and average magnet.
Reality a speaker suspension is so loose or so tight.
The magnet force is this strong or this weak.
Well defined math to calculate what that suspension and whatever magnet force it has will want for box volume , the end.
Q of .7 or 707 is the minimum and the common choice for smallest possibly size box . After that .5 or .577 will be =Bigger
Taking account of those 2 basic things mentioned. Suspension/ Mechanical Quality ( Qms) and Magnet/ more electrical (Qes)
Do the math and you get = total Quality or (Qts)
If Qts or Total Quality is little higher around .5 to .6 or more
That speaker will want a Bigger box to meet a cabinet Q of .7
If Qts is little lower .3 usually pretty powerful magnet or .4 slightly less
The speaker is more likely to be ok with a small box to get cabinet Q of .7
The world seems interested in smaller and smaller boxes.
You can do that. Just dont waste your time with magic imaginary theories.
Find a speaker of the size you like with Qts of .3 the end, but it in the small box it wants.
I can tell you right now it is highly likely that speaker is around ,5 Qts and that large box it is in, is what it wants. Dont get smaller
Unless by some magical change the manufacture put it in a .600 or .577 box size. Then it can go smaller to .707 box size = doubt it
Enjoy it. A cabinet rebuild would just be the typical extra bracing, and smooth up the front baffle without those hard overhanging edges.
Then add whatever finish you like.
If you want small boxes. Its gonna be the same or different suspension type, and a good size magnet to get Qts to .3
Buy that speaker, calculate .707 cabinet Q= It will be small. And enjoy
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Easy… Tangernt TM-3 was the exact same drivers & XO in a smallish box. Same size as RS-2. The shape & proportions i find very nice.
http://www.thunders.ca/tangent/tm3.php
dave
http://www.thunders.ca/tangent/tm3.php
dave
Measuring the old drivers several times, I noticed that Qt is always higher than what is written in the datasheet (if there is such information in general). That driver must have a Qt of the order of 0.5-0.6, I don't believe that it really likes the 20l box. KEF put those 8" drivers in small compression boxes, but corrected them with series capacitors of 600uF or similar. Wharfedale 505.2, the same case.
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As with most new drivers as well. Few of s have the same kit as the factories and they collapse the T/S curves in a different place.
dave
The Tangent TM-3 measured (WHD) 250 x 370 x 285 mm.
The internal volume of the sealed enclosures would have been somewhat less than 25 litres.
P.S. I've just revisited the dimensions of the KEF Chorale. They would actually be in accordance with an internal volume of somewhat less than 28 litres!
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Could there have been some magic in the crossover that allowed the drivers to function well in the smallish sealed box?