SpeakerTalk

[RGBE]

Time ago I constructed a pair of speakers with B139, B110, and Celestion HF 1300, HF 2000 and IMF TL 80 style crossovers. Their internal volume is about 43 liters, closed enclosures.




But their bass -to my ears- seems too dry and congested and not too extended. I have tried to convert them to reflex removing one tweeter and experimenting by partially blocking the hole with a cloth. That made the bass more vivid and interesting but, of course, with a one note sound...

I imagine that the problem is their scarce volume and that 43 l is too little for a B139 and wonder if it could be enlarged by means of adding some electronic trick, as I believe you have recomended here, some resistors or capacitors...
¿Have you any ideas?

[speakerguru]

I can't remember how big a Cantata was but that is what you should be comparing your system to. I'm sure someone else will chip in with Cantata or CS9 details.

If you can measure the resonance frequency and Q of your system then a single opamp biquad circuit will let you eq down to whatever you want. I can calculate values for you if you want to pursue this.

[audiolabtower]

The CS7 had the B139 and was around 70 litres I think and the Cantata around 60, similar to the 75 litres of the 105 and CS9. Maybe the 43 litres is a little constricted for it?

[RGBE]

speakerguru, many thanks for your very kind offer but, unfortunately, I don't know much about electronics and would not be able to measure the parameters you require and even less build an "opamp", that don't know what it is but sounds terribly difficult!

My idea of using some simple pasive electronic device to lower the resonance frequency of my speakers arises from the faint memory of an article I read, time ago, in Speaker Builder where the resonance frequency of a B139 system was lowered adding -I believe- a resistor or capacitor, or both to the crossover input terminals (?). But now, triyng to find it in my modest Speaker Builder collection would be a bit difficullt.

Another way to save my system woud be to convert it to reflex, if you find it adequate and are so kind to give me some idea about duct size, length etc.

[RGBE]

audiolabtower Many thanks, I think you are right and my system volume is too small. But KEF in its B139 data sheet recomends a volume of 30-40 liters for totally enclosed box, thow the CS7 closed volume is, as you say, 70 liter (?) I don't understand it.

[speakerguru]

[iso]

Closed box LF alignment for B139/SP1044 seems to be quite optimal with Cantata internal volume. Even with 40 years old drive units.

One funny note about this volume is KIT version of Cantata. Kit baffle was slightly shorter than the original Cantat baffle. If I remember correctly, difference was 15 cm... so Cantata Kit internal volume was 16 litres less than Cantata/CS7 volumes, which were actually quite close to 70 litres... even Cantata specs say 60L.

Best Regards

Kimmo

[proffski]

Are we getting confused with the KEFs Conjugate loading of the LF driver as in the C80 and KEF 105 for example?
Link: http://www.mightyoak.org.uk/kef/R105-1.jpg

I see that the C80 had an internal volume of 47L using the B139 SP1212 4Ω driver.
C80: http://listeninn.com/Website/Used-Speakers/KEF-C80-Info.htm

Taken from KEF Page:

C80

“Substantially the largest C-Series model, the slim, elegant, floor standing C80 was very much the Reference Model 104/2 for the cost conscious audiophile.
The famous B139 provided exceptional bass quality and extension for the cabinet size and the new polypropylene-coned B160 allowed high sensitivity and power handling along with low colouration through the mid-band.
The C80 was the second C-Series model to benefit from KEF’s ‘conjugate load’ crossover network design, originally developed for Model 104/2.
The net effect on your hi-fi system of replacing a conventional 8 ohm speaker with one which presents a 4 ohm constant resistance is that you can double the sound power output of your existing amplifier without any increase in distortion."
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

[RGBE]

[proffski]

If I have the time in the next few days I shall enter the driver parameters and run a couple of simulations for the two enclosure volumes. Assuming I can find the software...
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

[RGBE]

[quote proffsky]I see that the C80 had an internal volume of 47L using the B139 SP1212 4Ω driver.
C80: http://listeninn.com/Website/Used-Speakers/KEF-C80-Info.htm
[/quote]

I would be very happy to know that the C80 volume was 47 liters -very close to my 43 l- if the B139s SP1212 had the same acoustical characteristics of my SP1044s. Do you think they are equal in the acoustic aspects?

[RGBE]

[RGBE]

[proffski]

I honestly do not know at this moment if the Thiele / Small parameters for the two drivers are the same. I am sure that trawling this site and the internet will come up with the information required. I have the information somewhere here, but finding it... is another matter.
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill

[RGBE]

I have found this Online Loudspeaker Enclosure Calculation. Do you think it is of any practical use?

http://www.micka.de/org/en/index.php#ideal

I have tried to run some curves with it about the B139 (SP 1044) in my 43 liter boxes, closed and reflex, but feel very unsure about the parameters I have to enter and the final generated results.