Something stirs in the Undergrowth

[Paul Barker]

I am very busy this week on a big install near Selby 3 days then Thursday Gloucester: estimate and that's the week gone.

In a week or two it might settle down.

At least with open baffles they forgive a lot.

But a reflex isn't that bad.

I remain impressed with Edgar Titans. But probably will never have a pair of my own.

[IslandPink]

I'm just at the computer , the system has been altered a little, and I'm listening to Weather Report 'Black Market' which will please Nick .
I currently have :
Tapped horn played from left amp channel, with lowpass filter in the amp at ~150Hz .
B&C 8PE21 on the floor, played from right channel, full range.

Pretty good because the 8-incher has rising response up to about 800Hz , which sort-of blends with the tapped horn .... well , better than you might think . It goes out to >5K , not very clean up there, but useful .

The Tapped horn starts and stops very quickly . Definitely the best bass I've ever had. Bass lines are easy to follow . Also it seems substantially lower than the Onken, although it's only down to 35Hz, but I think every 5Hz below 50Hz brings in some good extra 'stuff' .

Now I need to finish the Pass F4 amps, because the ~1.7R driving impedance from the 300B amp gives some unevenness on the Freq response of the tapped horn, plus it doesn't go quite as low as it should .

[chris661]

It's good to hear you like.

Wait till you get 'em up and running in stereo. The sheer output capability of them keeps on suprising me.

Yeah, high output impedance amplifiers will interact with the impedance curve of the tapped horn, giving a strange response. In that respect, I prefer solid state.
What slope crossover are you running?

Chris

[IslandPink]

Hi Chris
Well it's only a 1st-order slope at the moment - I haven't got a simple way of doing a 2nd or 3rd-order low-pass in the amp as it is currently .
All of this is very rough and ready at the moment .
Ultimately it will be driven from a Pass labs F4 , filtered up-front, maybe using a valve buffer with the time constants . Work in progress ( in my head ) currently !

[chris661]

You'll find they give a much cleaner sound with a steeper slope: the mess just above the usable range needs to be filtered off well, or it'll interfere with the midrange output.

Adding some more resistor-capacitor networks to the input allows you to effectively stack up passive line level filters to give a steeper slope.
Watch out for phase changes though, you might need to reverse driver polarity or something.

That said, these active filters I'm using have worked a treat, no noticable nasties in the sound or anything (well, perhaps some more experienced ears than mine could comment at Owston, but all sounds good to me)

Chris

[IslandPink]

Actually I was surprised ( and pleased ) that the sound doesn't dissolve into a distorted mess just above the useable range. It's OK at least up to 200 , not bad at 230 if it's low in the mix .
Still , I will be using 2nd or 3rd-order in the end . Inductors of the right size will be handy in this .

Re: active filters - tell me Chris, did you use anything of that sort at the last Eggborough with the 6EM7 amp on the FE126e drivers ?
-because that was 'proper' audio as far as I could tell - very realistic presence & tone . If you did have an active filter on there, then I might change my mind about the whole business .

MJ

[chris661]

There was no active crossover on the amp per se, but I'd expect there to be some HF filtering amongst other things in the iPod itself.

Swings and roundabouts - there's far more op-amps in the signal chain than I could ever add.

We'll see how it sounds at Owston, but the only difference I've been able to tell between the 6EM7 into the Fostexes and the active XO into the Tripath into the Fostexes is accounted for just by playing the Tripath through the Fostexes.

The only major difference between the two was in the bass, there was certainly a difference there, but the rest of the range was more subjective: some like the extra 2nd harmonic from the slightly too loud SET, others might not.
By giving the bass duties to the subwoofers, I've taken away the thing that set the two amplifiers apart.

If you like, we can do an AB comparison of plugged in through the active filter, and plugged straight in to the amplifier. There'll be a difference in bass output (disconnect the subs), so picking some material that allows us to focus on midrange content would be probably be best.

Chris

[chris661]

Well, having tried the Fostexes alone driven by the Tripath amp, and then crossed over with subwoofers,

- the sound as a whole changes a little due to the new presence of low bass.
- the sheer dynamics and SPL available now are very impressive: I'm confident these will fill the room at Owston. Alone, the Fostexes get cone break-up before such SPLs are achieved.
- there's no noticable degrading of the sound: you have to remember that the distortion introduced by the speakers when turned up will be much greater than when the crossover is introduced and there's no noticable cone breakup at the same level. At lower levels, where such problems are irrelevant, there's no noticable degrading of the sound (as I said earlier).

Test track (for flicking in between the two set-ups) was Mother by Pink Floyd.

Chris

[IslandPink]

Thanks for the info Chris.
I need to try this some time in my own system, but luckily my current system plan does not require digital crossovering to work .
If you're using IPod as source then it's not certain it would be inaudible when using a full-on vinyl system like mine.
I do remember hearing Jean Michel le Clea'ch 's system at ETF2004 where he had a TAD2001 digitally crossed to a big bass box using cabasse drivers. The horn was a Marc Henry plaster LeCl horn, very nice. However i was underwhelmed by the sound - but very impressed by a similar TAD2001 driver on the stock rectangular TAD wooden horn, in Thomas Mayer's system in another room . This system did not use digital crossovering . So...this was a good comparison which has stayed with me in the back of my mind . Both systems used SE DHT amps that were entirely 'trustworthy', btw.

[IslandPink]

So, I've been mulling-over the mid-bass horn . I'm assuming the Fane 8M re-make buy will go ahead .
http://www.diyaudio.com/forums/group-bu ... n-run.html
Have now got measured data on the Fane from John Hasquin that is a lot different to the datasheet from Fane . It is interesting and probably not too far off, though, as the actual measured responses from real horns seem to agree :
http://www.diyaudio.com/forums/multi-wa ... ld-13.html
So, I was thinking I'd build a Hyperbolic with about 85cm or 90cm length and 3500cm^2 mouth . I was a little concerned about the amount of ripple on the response. The only way I could reduce this was to enlarge the throat to eg. 5 inches, but everyone reckons the Fane needs about 4" throat . Hmmm ... wasn't 100% sure I should proceed . See attached picture -

[IslandPink]

So, to continue...I was seeing all the discussion on the thread linked above, about sims of big ( 5000cm2 to 7000cm2 ) full-mouth 110 or 125Hz Tractrix horns , thinking it would be nice to have the space for such a thing .
Then today, I was mulling over the situation and thought - "what happens if you model eg. a 120Hz tractrix, but instead of giving it a full-sized mouth, how does it look if you cut it off early, say to 4000cm2 or 3500cm2 ? " ie. how quickly does the ripple start to show ?
Well, I did it and was surprised to find it doesn't show up very much even at 3500cm2 - result

So here, see a simulation of a 120Hz tractrix, about 80cm long, throat 4" , cut to a mouth size of 3500cm2 - ie. about 75 x 50cm if built as a rectangle . This is looking like it will be my approach now .
Hoorah !!

[Paul Barker]

Well I have no idea how you simulate this stuff but what you are saying seems good.

~I have never been able to understand simulation software for anything.

[chris661]

That last one looks good.

Mark, that's the same iPod I used for the Egg meet through the 6EM7.
If you're not sure on using them, I'd be happy to let you try your source through my crossover and speakers (use your amps if you like, it's all buffered so there should be no problem mix-and-match-ing) at Owston.
They're very cheap to try, just need the right RC values and some op-amps...

Chris

[IslandPink]

Well that was an impressive sound you got from the 'pod there then. I thought they were MP3 ? - I once heard MP3 through a stereo at that bit-rate and it didn't seem very interesting .
Well there you go .
Sorry to disappoint ( maybe ) but I might not get to Owston if it's in the middle of June. It'll depend on the weather - if it's going to be sunny there's no way I'll come out of North Wales , it's prime time for photography and mountain-climbing !

[chris661]

Ah, no, I was using Apple LossLess, bit rates are usually about 900-1200kb/s, so it's much better than the highest bit rate mp3 (320k).

That's fair enough about the weather, it is a fair treck there. It'd be good to collectively show everyone how brilliant tapped horns are...

Chris