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Old 8th September 2010, 06:22 PM   #171
kayelem is offline kayelem  United Kingdom
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Hi Alan,

Quote:
Originally Posted by alan-1-b View Post
with all the test equipment that you have, if you can measure the Impedance minimum of the SEAS tweeters at whatever frequency such occurs in the useable portion of their bandwidth, {or nearest frequency to}, then please do and Post here - for both samples as there may be variation.
That's one of the things I was intending to do; the SEAS datasheet isn't all that clear. At the very least, I'll sweep a generator up and down and find the minimum. If I'm feeling enthusiastic, I'll take more measurements and plot them.

I've also got a couple of 8.2F knocking around from something else, all the original Erie caps and a box of 70 1F Russian caps that'll do for the odd experiment - I'm not buying anything decent until I've established what's needed. (I've also got a reasonable selection of w/w resistors in the 0.5Ω to 100Ω range; not all values but enough to make up pretty much anything with series/parallel combinations.)

Sound... My curse is that I've heard multitracks and masters in studio control-rooms. It's led to my aim with my systems being "as close as possible to what the engineer heard in the control-room". But this is with a near-zero budget which precludes having a large active Dynaudio monitor system in the living room. Hence I do the best I can with what I've got, it keeps getting better (and it's both fun and educational.)

Kat
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Old 9th September 2010, 11:47 AM   #172
kayelem is offline kayelem  United Kingdom
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Hi,

I've been experimenting...

First, I made two assumptions. One was that the impedance of the HF2000 around the crossover frequency is 4.8Ω (based on an impedance plot of four of them, posted in the '66' thread a while ago.) The other was that the impedance of the SEAS unit around the crossover frequency is 7.5Ω (based on the plot in the SEAS datasheet.)

With the SEAS driver connected to the original treble filter, the filter doesn't have the load it was designed for. What happens if I 'fix' that?

Two 27Ω (2% 10W) resistors in parallel with the SEAS driver works out as 4.8Ω.

This sounded better integrated, the tweeter sounded less obviously separate from the bass/mid drivers. There was still an obvious step up in level, though.

Next, I connected the bass/mid crossover input to one channel of an amplifier and the treble crossover input to the other channel. Each channel was fed from separate outputs on a 4-channel audio interface (with L+R source summed and routed to both of these outputs.) Now I could wind the treble level up and down and, usefully, the DAC levels in 'alsamixer' are in dB.

3dB attenuation of the treble output (w.r.t. the bass/mid output) produced the most natural-sounding results, the step in level disappeared. Comparing with the unmodified 44, it sounds a little brighter but not excessively so and much more detailed. It's very easy to pick out individual instruments and sounds, even those low down in the mix. Male and female vocals sound natural and convincing. Particularly well engineered/produced recordings have an amazing sense of depth to them. (Bear in mind this is currently a monophonic system with one centrally-placed 44...)

So, 3dB it is. The back of an envelope and the parts available meant another two 27Ω resistors in parallel with the tweeter (so 6.75Ω in parallel) and three 0.47Ω in series (1.41Ω total), between the crossover output and tweeter.

Results? Terrible. The odd thing is it was nothing obvious. Just the music ceased to be engaging. Two-dimensional, flat, boring, lifeless, veiled...

I've gone back to the previous bi-amped mono arrangement; all original Celestion treble section components, a pair of 27Ω in parallel with the tweeter and the treble level reduced by 3dB before it hits the amplifier.

OK, it's a start; that's one thing which works and another which doesn't

Kat
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Old 9th September 2010, 01:16 PM   #173
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Hi Alan,

Just to clarify...As a starting point, I will change the 6uF Jantzen cap to the 10uF MKP. I realise that I am left with a 3.9uF cap where a 3.6 is required, but for now, I will leave that to evaluate.

I will buy some 15 Ohm W22 or W23 Welwyn wirewounds for paralleling with the Seas 19TFF1.

I will buy some 1 Ohm WP4S Welwyn wirewounds for series attenuation between the 10uF cap and Seas input.

On paper this should give me close to a flat response (-1.6dB) IF the tech-specs are correct, right?

For me, that's a good starting point. I order from Farnell about once a week at the moment, as I'm building hi-fi like crazy, so it's no hassle to buy more resistors later if needed.

Just thought I'd check with you first.
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Old 9th September 2010, 03:12 PM   #174
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Also, Alan...if copying 66s is not optimum, can you tell me about the best way to make my 2.1mH and 3.2mH inductors.

If buying a cheap inductance meter, hubs and wire is the same price as buying them off the shelf, I'll make them for sure.
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Old 10th September 2010, 05:35 PM   #175
kayelem is offline kayelem  United Kingdom
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Hi,

After realising I'd made a stupid mistake I've scribbled more calculations on a different envelope...

(In my defence, I had 'pulled an all-nighter'; several pints of coffee is a poor substitute for sleep.)

So... I'm now currently conducting listening tests with 3 x 27Ω in parallel with the driver (Russian mil-spec 2% 10W), one 1Ω between crossover and driver (Welwyn W23), original Celestion crossover circuitry otherwise (4F, 140mH, 6F). Results seem favourable.

My (rough) computer simulation suggests this has ironed out a lump (9dB @ 15kHz) in the original response, produces a slight rise (~3dB up @ 20kHz) but has, overall, flattened the response off. That includes a flatter combined response of the mid and treble drivers. Note that this is all simulated electrical response (using simplified driver models, a resistor and an inductor in series), not real-world acoustic response.

However, it seems to translate into something which sounds good - and is a vast improvement over the unmodified one (without really sounding different; it's still a Ditton 44.)

If I can drag myself away from playing music (difficult!), I think I'll modify the other 44 and see what this is like in stereo.

Reading back, I note that Alan and myself seem to be converging on the same point from different directions; this is probably a good sign

Oh; has anyone else noticed the crossover frequency is more like 'just over 4kHz', rather than the 5kHz suggested by Celestion promotional material?

Kat

Last edited by kayelem; 10th September 2010 at 05:42 PM. Reason: Clarification
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Old 10th September 2010, 06:58 PM   #176
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Quote:
Originally Posted by LucasAdamson View Post
Also, Alan...if copying 66s is not optimum, can you tell me about the best way to make my 2.1mH and 3.2mH inductors.

If buying a cheap inductance meter, hubs and wire is the same price as buying them off the shelf, I'll make them for sure.
I should say that high volume "congestion" is quite apparent in these speakers. The sound tends to get muddy and a touch distorted in the broad range of the low mids when played loud, and it's partly this saturation of the bass circuit inductors which I suspect causes it. If there's a way to fit a grade of inductors that absolutely won't saturate in a 15' square room, that would be awesome.
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Old 10th September 2010, 07:45 PM   #177
kayelem is offline kayelem  United Kingdom
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Hi Lucas,

How powerful are your amplifiers?

This isn't something I've noticed; when testing a pair of 120W amplifiers I'd been modifying, I once tested at quite high level. Some distortion was present - until I put a pair of ear-defenders on!

I've also observed transients being clipped on a 'scope when using a 30W amplifier at 'average listening level' (which measured at about 4W.) This didn't sound obviously distorted, more just a muddying and smearing of detail.

Amplifiers I'm using in rotation on this system:
  • Marantz 1150 - 85W/ch.
  • Musical Fidelity B1 - 32W/ch. but with a slightly crafty PSU circuit which allows delivery of 80W/ch. pulse.
  • The two 120W amps mentioned above.
If one assumes transients in 'typical programme material' (whatever that is!) of 10dB relative to the average level, and an average listening level of 4W, that works out as requiring 40W/ch. to avoid clipping of transients. A 'loud' listening level averaging 10W would require 100W/ch. and so on. So I stick to a 'rule of thumb' of using amplifiers rated at a minimum of 10x the average power needed for a reasonable listening level on any given pair of speakers.

Room size here is approximately 12' square, by the way; with two alcoves either side of the chimney breast and a bay window. Speakers are opposite the window with the sofa in the bay (and heavy velvet curtains which are seldom opened) and the fireplace/alcoves are on the left as you're sat on the sofa. (Too small, really; and acoustically 'tricky' but I've managed to make it work.)

Kat.
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Old 10th September 2010, 08:19 PM   #178
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My amps are LM3875 Gainclone amps - much like an average 50WPC domestic power amp, and very clean and musical.

I realise now that it may have been the fault of certain compressed MP3s that caused me grief. I listen to a lot of lossless files and they are considerably cleaner. Muddiness of such MP3s shows up particularly at higher volumes for some reason - perhaps the reason is too obvious to mention - it's louder!

It was whilst listening to a very loud playing of Abracadabra by Steve Miller Band (my 4 year old loves to dance, so I play him what caught my attention when young, and he loves it) that it sounded quite awful, and had my wife come in from the kitchen telling me it was too loud. Checking now, it is a 128kbps MP3 file I downloaded from the interweb, so yes, perhaps it is to blame.

When music distorts, yes, it's too loud very very quickly!

I would still like air core inductors at some point though.

I always thought that the Marantz 1150 is a lovely amp, by the way. It looks way cool too
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Old 10th September 2010, 09:53 PM   #179
kayelem is offline kayelem  United Kingdom
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Aha, the curse of mp3...

(I notice the difference between 320k mp3 and FLAC; 320k isn't too bad but FLAC is better.)

I'm still curious as to what contribution those ferrite-cored inductors are making, and at what level it starts to get serious. As I'll shortly have the other 44 crossover on the bench, I'll hook the bass section to a 120W amp, load the output with a resistor, and have a play around with my distortion analyser (Sound Technology ST1700B.)

My current opinion (and it's only an opinion, I may be wrong) is that replacing the ferrite-cored inductors with air-cored inductors won't really make much difference. The problem is there's a 4th-order low-pass filter between the amp and the driver. Replacing it with 3rd/2nd/1st is inadvisable as Celestion must've used a 4th-order filter for a reason (the bass driver gets 'a bit funky' somewhere above the crossover frequency?) and, though 4th-order filters are 'unpopular', replacing it with 3rd/2nd/1st would mean replacing the bass driver as well. Then one would have to tweak the mid crossover to integrate the mid with the bass, maybe replace the mid as well. Oh, and replace the cabinet with one of the correct volume to match the new bass driver...

This turns into "grandfather's axe" rather rapidly; "Yeah, they're Celestion Ditton 44s; I just replaced all three drivers, redesigned the entire crossover and built a new cabinet..."

I'm fairly happy with what I'm listening to at the moment (I just need to do the same mods to the other one.) I haven't had to change much, it didn't cost much, and it sounds 'the same but better' (more transparent, more detail, clearer, cleaner.)

Losing the 4th-order passive filter should make a huge difference. That means connecting the driver directly to an amplifier and sticking a 4th-order LPF ahead of the amp, which is... non-trivial.

The revised 'active 44' plan involves:
  • Klark Teknik DN800 (as I've already got one.)
  • Musical Fidelity B1 for high.
  • Sansui AU-317II for mid.
  • Marantz 1150 for low.

I need to modify the DN800 filter cards for the appropriate crossover frequencies (it's currently configured as four 2-way crossovers), fit more terminals to the 44s and rewire...

Kat
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Old 11th September 2010, 01:10 AM   #180
kayelem is offline kayelem  United Kingdom
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Air-cored inductors...

I've just used this online inductor calculator to work them out (and find out roughly how much wire would be needed.)

Aiming to get the same (or slightly lower) DC resistance as the ferrite-cored inductors means using 1.33mm wire, about 256m of it in total for all six inductors.

A quick look on eBay and I find 4kg of 1.32mm enamelled copper wire (about 328m), for 49.96 + 8.96 P+P.

I don't think I'll bother winding air-cored inductors any time soon; 60 would get me a few more s/h records...

Kat

Last edited by kayelem; 11th September 2010 at 01:12 AM.
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