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PostPosted: 15 Sep 2020, 18:00 
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Location: australia
Hi Bruno, I followed the method on this website http://diyaudioprojects.com/Technical/B ... alculator/ to achieve a 4 dB reduction and I posted on The DIY TL Facebook page for advice. You may prefer to use a metric version or convert imperial inches to SI units.

I initially thought I should go with the full 6db, but as I have the speakers in a small room 10m^2 approx and close to the wall, there is likely to be some bass reinforcement from the room. I didn’t use a zobel circuit in this case. The inductor and resistor I could get locally were 1mH and 3.9 ohms. The resistor value precision is low though measuring 4.2. I’m still to try the approx 2 and 3 ohm resistors yet but I think 4 ohms is about right given my Vb compromise.


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PostPosted: 16 Sep 2020, 01:27 
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Fine Woodo, I see - Thanks ! :idea:

I'll have a look to your inputs when I'll be back home. ;)

Cheers,

-tbln

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PostPosted: 30 Sep 2020, 16:54 
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Hi Woodo,

So I made some tests about a BSC filter on my Triangle T17FL2 32L enclosure to see if it was worth to go further. The answer is yes indeed, but maybe not completely in a BSC strategy stricto-sensu...

If you look to the frequency response curve of the T17FL2 Full-Range speaker below :

Image

You notice like me that the 1kHz to 10Khz zone is enhanced about 3 to 5dB, let's say circa +4db average. At 30° incidence, this is still obvious though less marked :

Image

With a baffle width of 30cm (12"), I calculated a BSC with the calculator of the forum you directed me to, and cross-checked with other calculators, to find a 1.2mH // 2R9 for a -3dB BSC, midpoint located at 387Hz.

Image

Not so far from your 1mH // 4R0 BSC, but I think that the final value should be higher than 2R9 fro me, hence the midrange enhancement noticed. Since I put a pot to search the correct R value, I should come to a compromise, but as high as 6-8R seems already to be in the ballpark, with probably a // cap (to be determined) in order to increase the extreme treble a bit...

By the way, did you stayed with your BSC at 1mH // 4R0 finally ?

Cheers,

-tbln.

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PostPosted: 01 Oct 2020, 17:34 
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Hi, I haven't changed the value as yet, but I do intend to try the full 6db recommended. I expect the closeness to the rear wall is helping the bottom end and 4db is about the sweet spot for me. Its likely something that needs to be tuned to taste. Using a variable resistor is a good approach. :up:

I have not made my own measurements of the speaker output, just working of the manufacturers data at the front of this thread and putting this into XSIM - snips attached. I understand factory measurements are made on an open baffle in an anechoic environment so may differ markedly from my room with windows, plaster walls and wool carpet floor. The effect of this I do not really know. I do hope to buy a usb microphone at some point. I'll add that to the list with the oscilloscope :)

It would appear 7.5 db would flatten the rising response somewhat around the midpoint noting this reduces the high frequencies that are already rolling off without the BSC. I have yet to learn how to compensate the falling response above 10khz, although my hearing probably doesn't care too much.

I should add I used the 15 degrees off axis response as this is what I tend to use in the room.


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PostPosted: 02 Oct 2020, 15:51 
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I see - Thanks Woodo ! ;)

I have not made measurements too, but again, I think I'm very close to your last test (1mH // 7R5) since after several listening at different loudness levels, on different tunes, I came to that compensation circuit as being satisfactorily sounding :

Image

Image

It certainly both correct the Baffle Step of the cab and the Mid / Hi-Mid excess of the T17FL2, plus it enhances the extreme-treble, thanks to the 1.5µF capacitor, to correct the drop over 10KHz.

If you want to correct such an extreme-treble drop, I think that the // capacitor is easy to do and worth to test, because in my case, it does the job very well. I tested values ranging from 0.47µF to 4.7µF and found 1.5µF to be the adequate value (1µF was a bit under, 2.2µF was a bit too much).

With that simple RLC filter, the potential of the T17FL2 loudspeaker is plentifully revealed :thumbsup: ... How did I not think of it sooner ? :confused:

Let me know if the // cap tip works for you too ! :)

Cheers,

-tbln.

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PostPosted: 03 Oct 2020, 21:35 
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Thank you @tbln. Will have a play on xsim and buy a few capacitors to experiment with. I cut up the wood for a 35L tapered TL too. Not sure when I will put together but this might improve the low end.

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PostPosted: 04 Oct 2020, 03:39 
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Fine Woodo !

Let us know further... ;)

Cheers,

-tbln.

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PostPosted: 08 Oct 2020, 15:27 
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The final version of the BS, MID and Extreme Treble corrector is done : The BLACK BOXES... :D

Image

I slightly increased the total value of the Extreme Treble corrector from 1.50µF to 1.66µF, by playing the Audiophile Game : put capacitors in clusters... :D

Whatever, it does the job very well, fully as expected, so it's OK ! ;)

Cheers,

-tbln

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PostPosted: 11 Oct 2020, 04:29 
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Nice boxes, neatly done. I’m still to make the trip to our local electronics supply store 20km away Anything out of the ordinary generally has to be ordered overseas or interstate. But it looks like, similar to you, the cap required to bring back >10khz a small amount is around 1.6-1.7uf. the closest metalised Polypropyene at jaycar is 1.5uf. Next is 2.2uf. I’ll try and get a couple next week.

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PostPosted: 11 Oct 2020, 16:14 
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Thanks Woodo !

So you simulations give you circa 1.6-1.7µF too : fine ! It's where I came too : between 1.5 and 1.8µF, maybe 2.2µF at most.

I took the caps and coils I had on hand in my boxes and drawers...

1.5µF PMT = polypropylene (PP) metallized film - Oh, I thought that it was also Mylar (polyethylene-terephthalate PET = polyester PET) film.
0.15µF MKT = polyester (PET) metallized film.
10nF silver mica = OK, I added it here rather for the Audiophile God's Sake... :D

As far as I remember, you speaker is a bit less responsive in the treble end than the T17FL2, so you may need a tad higher cap value than me - but again : it also depends on your taste, right ? Only tests will tell you... ;)

Let me know - cheers !

-tbln.

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