The loudspeaker Odyssey
High Pass Power Filter For The T90A Tweeter
A pair of high pass second order Linkwitz-Riley filters @10Khz were built for the Fostex T90A tweeters to compliment the FF165WK bass reflex speakers ( pictured below ). The capacitor used is Sprague Atom Vitamin Q 1µF/200V and the T-pad is Clarostat CIT 43 - 8Ω.
The HP filter could be @ 8Khz, build with the values in yellow lettering but an LP filter @ 8Khz is mandatory for the FF165WK as phasing might occur among other artifacts.
Fostex FF165WK in Bass Reflex Box
Having tried several Fostex models of the FE series, I wanted to try my luck with the FF series .
After some careful thought, the FF165WK driver was chosen and put in a 18 liter bass reflex box tuned at 54Hz, as recommended by Fostex .
The sound was rather impressive, especially at the lower end, but the high frequencies sounded as if the box was covered by a blanket (a thin one).
The need for a tweeter was eminent and a pair of T90As was handy, so they were added with a first order high-pass filter . That filter was a capacitor in series with the positive transfer line. Several values were tested before choosing .52µF as the final value.
The sound improved immensely, but there is space for more experimentation, so the next step will be the trial for a second order high-pass filter at the 10Khz range and the use of a T-pad.
Commission On A Shoestring
Building a pair of loudspeakers on a tight budget is not an easy task especially when you realize that the box costs far more than the driver.
To cut a long story short on the left is one of the bass reflex loudspeakers that employ the Visaton BG20-8 drivers in a 30 lit. enclosure tuned @ 40Hz.
Note that the price justifies the sound of the drivers. There is a distant plan that at the time Magrathea will restart production and economics improve, the place of BG20-8 will be taken by the Fostex FF225WK, but that sounds more like science fiction.
Yet Another Pair Of Bass Reflex Speakers
It is sad to let drivers rot away in their boxes.
So after some careful thinking I decided to built a pair of loudspeakers with a couple of Fostex FE 168EΣ full range drivers and a pair of FT17H tweeters that were dying in their boxes.
The inner volume that was chosen is 20.5 liters, the port is 5cm in diameter and 6.5cm in length. The series to tweeter capacitor is 2µF and an 8Ωhm volume control for the tweeter was added.
The UREI 813 Experience
No matter what you say for those speakers it is not enough. It is the kind of speaker that will be never produced again. It has endless hours of research on its back and some patents as their Time Aligned X-overs.
They were given to me by Mr. Nikos Papazoglou an audio pioneer and distinguished musician who was been using them as main monitors in his “late” studio.
I drive these loudspeakers with an 8 watt 300B SE amp. and trust me I get enough db SPL to throw a party.
Their sound is as big as their volume, 325 liters, and they are the reason I want to build a smaller version with new components .
The final product in a 250lit. enclosure using just the UREI 604 driver .
Here is one of the finished loudspeakers with the 604 drivers and the N-1500 X-overs in the 250 liters vented boxes.
These loudspeakers are not the ones that the average music lover would put in his living room but trust me they are the ones that it is worth listening music to.
It is the kind of loudspeaker that brings out the best of good recordings and spares nothing to bad ones . It is a huge and very loud monitor that devours complex waveforms and makes cheap nintendo/reason productions sound as they have to , like shit.
I think there is no reason to mention their strength to the low end of the spectrum that is so vivid that takes your breath away and gives you the feeling of a panic attack if played loud.
They are not as analytical as the Fostex FE207 in the mid range region nor as responsive in fast transients but they are the monitors to listen to your final product after a long day’s remixing.
They are not the kind of book shelve speakers that are used for ambient noise but the ones to let you dive into music.
For the faint at heart , the ones that take in account the WAF factor , a loudspeaker like this one is a good reason for rebellion.
The Bass Reflex Experiment
The experiment started with a box of 35 liters and a port of 8cm diameter x 18 cm length. The drivers used were Fostex FE207E full range and Fostex FT17H tweeter. The cutoff capacitors used were in the range of 0.47µF ≈ 1.5µF. After extended listening the Fostex tweeter was replaced with a Vifa for smoother sound. The conclusion was that there was no need for any tweeter so the Vifa stayed in place just to block the hole. The next trial was with a pair of bullets ( phase plugs ) that made the sound more focused but in conjunction with the paper cone driver they could make your ears bleed. So off with theme bullets. The last trial was the Dammar varnish ( Talens Dammar Varnish Glossy No : 081 ) that was applied on the inner cone of the FE207E and stayed for drying over night. Alas finally everything sounded as it was supposed to do.
In conclusion the best that can happen in a single driver bass reflex speaker, is the Dammar varnish.
I have to mention that the box was treated internally with sonex acoustical foam.
This is the Fostex T90A tweeter on a wooden base
The next experiment was with a box of 45 liters in volume employing a port of 8 cm in diameter and 6 cm in length. The box was treated internally with sonex acoustical foam. Dammar Varnish was applied on the inner cone of the FE207E and a Fostex T90A tweeter was employed. The cutoff capacitor was 1.5µF / 200V PIO and an L-Pad was used to lower its volume. After extensive listening the tweeter was too much for my taste so it was abandoned.
In case you are interested the difference between the 35 and 45 liter box is that the 35 L has punchier lows than the 45 L that sounds more relaxed at the bottom end.
I could risk to make the analogy of an electric bass compared to a double bass.
On the left is the finished loudspeaker having volume of 45 liters, the port is 8 cm diameter and 6 cm long.
On the right is the stand of the speaker which is H shaped steel 24 X 23 cm, 30 cm high and weighs a ton.
Here is a pair of bookshelf monitors, the box volume is 10 liters
the port is 5 cm in diameter and 8 cm in length.
The drivers are Fostex FE127E and the box is treated inside with sonex acoustical foam.
Although they are not the best monitors, they are much better than the Horortones and good enough for listening music in the background.