Something stirs in the Undergrowth

Dedicated to those large boxes at one end of the room
steve s
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#2221 Re: Something stirs in the Undergrowth

Post by steve s »

Yes was that those twin 15" or 18" in open back boxes that pete knocked up one year.. he had cheap old amp driving them but he needed to damp the insides to remove the coloration ... but hadn't
The previous year I had taken twin 15" in open baffle U frame and they all visited my room to listen.. mine sounded ok with the damping in..
speedy steve' s efforts where quite good I liked his tapped horns and those real tweeter but the time he brought a fuĺl system the amplification was not quite there in my view.
It was after listening to those systems that I came to the view that one good amp beats an average amp for each horn / speaker at the volumes we need
Realistic tone is about good amps and quality speakers working in harmony.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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IslandPink
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#2222 Re: Something stirs in the Undergrowth

Post by IslandPink »

Good info, thanks Steve and I agree with you re. amps, especially from mids upwards where the compression drivers really demand low distortion at low signal levels.
Ali Tait wrote: Tue Oct 16, 2018 9:06 am Don’t know if you’ve seen this Mark, thought it might be of interest-
http://zero-distortion.org/diy-horns/
Thanks, not sure if I've seen the whole lot of that before, the pics of Guy's horns I had seen, perhaps the Karel Schees system... but will have a proper scan through later. The set-up by Karel Schees is one I would really like to hear - so much of the combination, drivers etc makes sense. The comment about piano notes floating out at you is something I understand exactly - that's what I've briefly heard and want to regain.
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Ali Tait
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#2223 Re: Something stirs in the Undergrowth

Post by Ali Tait »

Yes, can get an element of that with the OTL, hoping for more of it with the pinnacle.
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#2224 Re: Something stirs in the Undergrowth

Post by IslandPink »

vinylnvalves wrote: Tue Oct 16, 2018 10:29 pm I remember Guys horns too, they were very dry for my taste, good for classical/operatic music. From what I remember they didn’t go too low. Now for bottom end it was Pete’s ( I should coco) system , that came a couple of years later, with the wall of bass drivers which had more realism. I am probably going to get abuse for saying this... I don’t think bass horns will ever work in a domestic situation, unless you live in a mansion and have the room. As power is cheap nowadays a wall of drivers similar to the BD orphean can get you along way to the low distortion a horn brings, maybe without the colouration.
My bass horn attempts.. have kept our wood burning stove going for years.. birch ply burns well :)
I send on my offcuts to a bloke at work who has a woodburner, he does quite well from me.
A few points worth discussing , I have been thinking a lot while in the Lakes and since coming back.
Incidentally the current horn mod sounds better than I thought, when I listened again , although it still only points the direction to what's needed.

I would say you're almost correct in saying bass horns won't work in a domestic situation but I think it can be done.
I'm convinced now that flat phase over the bass, as much as possible is what's required ( ie. low group delay ) and that amplitude (SPL) being flat is a luxury and can be traded-off, for practicality, in the frequencies below 250Hz. This what Ron Clarke said in a posting years ago on DIY audio and I'm sure from practical experiments so far, this is true.
The horns shown in Guy's set-up are not bass horns. They are really very much like straight versions of where I was with my folded horn until 3 weeks ago, in length and mouth size. They are horn-loaded to the low-mids, with output to 70 or 80Hz but I guarantee the phase will be rotating and the group delay poor, under 120Hz.
The other option for low group-delay bass is sealed boxes, or BIG OB units, with drivers in the 20Hz or so resonance, so you can get low phase shift at least from 50Hz upwards, when loaded. No doubt those other options shown at the Wam were along those lines.

I think a full bass horn that can do 40Hz to 250Hz or so , is not practical ( agreed ! ).
If you split the band this gets more practical -
Tapped horn , which has pretty flat phase for an octave or a bit more, can take you from 40Hz to 80 or 90Hz in a manageable package.
The next ( crucial ) horn has to have flat phase from 80 or 90Hz up to where your mid-solution starts, eg. 300Hz ; even if the amplitude is falling off a bit below 100Hz.

So this is where the tricks have to be used, but my experiments so far, and one or two key listening experiences, tell me that the upper bass/low-mid horn has to be something like the long back-loaded horns as used on the Fostexes or the Klipsch, or the big Tannoys. What I can see from sims ( looking at phase ) and listening, with the past three stages of mods, is that you have to load the driver down like a bastard, with a really SLOW expansion for 2m or more, to get the phase to go flat to under 100Hz.

Now there are two trade-offs inherent , compared to the 'luxury' ( converted chapel ) approach with the full bass horn -
(I) the amplitude with have some peaks & dips in the region 80-300Hz. Some of this can be covered by the tapped horn, and the mid solution ; also the room is doing all sorts of mad stuff in this region anyway.
(ii) You will have a disconnect somewhere , usually 2 wavelengths, somewhere around 250 to 350Hz. This is at least not as much as the 3 wavelengths at 300Hz the big Tannoys have - which I didn't notice when listening about 10 years ago ( but might hear now ) . You can avoid this with DSP if you think that's good enough to your ears ... :D ... as long as you don't have a back-loaded horn where the 2.5m mismatch is physically part of the design.

Need a breather, but a bit more next on loading/length comparisons on the horns I've been studying vs. my testbed.
ps. note that the path length in the upper-bass/mid horn will be very similar to that in the tapped horn, so you do not need another mismatch between upper and lower bass.
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#2225 Re: Something stirs in the Undergrowth

Post by IslandPink »

Somewhat spookily, I just spotted a very interesting comment from Steve Schell ( via 'Hollowboy' ) about horn subs ( post #15 ) , which backs up everything I was saying about the flare rate for my upper bass horn :
https://www.diyaudio.com/forums/subwoof ... rns-2.html
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vinylnvalves
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#2226 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

Going to the lakes, clears my head, as well as my wallet.
The taped horn you leant me was flat and punchy, it need about 10 msecs of delay from memory, which was a challenge at the time, predsp.
Just remembered a very good bass system in a small space, was a guy who in his through lounge/diner had used his two redundant chimneys as transmission lines, upset the birds on the roof I would imagine.
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#2227 Re: Something stirs in the Undergrowth

Post by IslandPink »

Flat and punchy is fine - it can't be expected to have much tone if it's only working over one octave or 1.5 octaves - Nick and I had pretty good results with it driven by miniDSP together with the Mk2 folded horn ( I think ) and I would expect more improvement with a longer upper-bass/mid horn. It starts and stops quickly which is not common in that Freq area.
Did this bloke you knew use young children help stuff the TL lines ?
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chris661
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#2228 Re: Something stirs in the Undergrowth

Post by chris661 »

Mark, here's a consideration - crossovers introduce phase shifts, and steeper ones result in more. Tapped horns generally need a fairly steep crossover to cut down the "hash" above their operating band, so you'd be looking at quite a lot of phase shift within the electronics feeding the subwoofer.

A good 12-15" bass unit in a large-ish sealed box is where I'd look for 30-300Hz with a reasonably flat frequency and phase response. Something to consider would be going for a bigger box with a port tuned very low. It'd get you a bit more very-low-frequency output, and a way of altering the response a little to gel better with your room, but the phase shifts in the 60-300Hz range would be minimal.
I'd then probably build it up as a classic-ish 3-way. Go for your dual Fostex 5" mids and then the ribbon tweeter for the last couple of octaves. OB if you like, though that does add complications in that there's additional frequency (and therefore phase) response shifts.

Chris
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#2229 Re: Something stirs in the Undergrowth

Post by IslandPink »

Thanks Chris, I had considered the sealed sub, and would recommend it to others, if I had the time there's quite a nice S&B 12" unit that's ideal for something like a 150L cabinet. It would be good to hear that, and as you say, the upper limit is a lot more helpful for integration.
However I have the 5ft high tapped horn already and like what it does below 100Hz. With a suitable mid/upper-bass horn that can get down to below 100Hz, the crossover point might only have to be 80Hz. There's a fair bit of experimentation that can be done with either a sub amp , or that plus DSP, which seems to work OK down there from our experiments. 'FIR' might be possible too, I know Nick has aspirations ( for when he's ditched the day-job' :D ) to try out some of his own ideas on that.
Something like this combo must be possible given what Kevin Scott appears to have done with the V.O., which uses a folded horn down to 70 or 80Hz then a massive sub horn from there down to 20 or 30Hz.
One advantage of the tapped horn is that it can be placed approx. where the mid/upper-bass horns stand, since the path length is the same ( if using a conventional LP filter + amp. )

Bear in mind this combo is for the 'back burner' or 'end game' system, not the OB-based one. My focus really needs to be on getting the second OB finished and the tweeter amp, now, but can't help to continue thinking-out the horn-based system.

One might ask what the horn based system will do over the OB one - from what I've heard ( fleetingly ) a horn can do something in the lower-mids and upper bass that I've not heard from any boxed or OB unit.
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#2230 Re: Something stirs in the Undergrowth

Post by IslandPink »

For Simon's benefit , this graph helped me clear-up my confusion on first-order slopes and filter calculators . Check the -3dB and -6dB amplitude points and note the corresponding slopes ( 3dB/octave and 6dB/octave , respectively - bearing in mind 20db/decade is approx. 6dB/octave ) :
Butterworth_response.jpg
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#2231 Re: Something stirs in the Undergrowth

Post by simon »

I'm a little confused (no change there). I can only see one curve - the 6dB/octave slope with the -3dB point. Where's the 3dB slope and -6dB point?

Do you mean SB ACOUSTICS SB34NRX75-6? I'm using one in a 124L sealed cab with Alpair 12Ps in the James inspired tv console I've built this year. I'm surprised by just how much info I was missing, and songs have taken on a different perspective with that bottom end grunt. I like it a lot and have considered adding one to the Quasars, but James thinks it needs to be a 600L cab with a Supravox 400GMF :-D. But 600L is huge and I'm not sure I'd be able to get it up the stairs anyway...
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#2232 Re: Something stirs in the Undergrowth

Post by IslandPink »

Well, I was hoping you could see from the plot, at the -6dB point on that curve you've just about joined the straight part of the 6dB/octave slope. Also a quick check with a ruler tangent to the -3dB point shows it's about half the slope
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#2233 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

Having recently heard some foam surrounded 15” bass drivers ( JBL 2235. I think). The micro dynamics in the bass octaves were the best I have heard. I believe these drivers are like hens teeth. Beyma 15BR100 are meant to be very similar but also discounted. I have been wondering about buying a blown pair of 15” drivers and resurrounding them with foam surround instead of the usual cloth opens, as the foams more flexible it will change the TS properties in the right direction.
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#2234 Re: Something stirs in the Undergrowth

Post by simon »

Ah okay, I see. I was over-thinking it.
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#2235 Re: Something stirs in the Undergrowth

Post by IslandPink »

I was going to post more but a fire alarm took us outside for over 40mins, some people nearly froze.
Then I found this :
https://www.tubecad.com/2017/11/blog0403.htm
Every time Broskie looks at anything, something new and useful comes out of it !
The modified series one here with the steeper slope for the tweeter ought to be the solution for the 3-way Quasar, if you could work out all the values.

Edit : the first article is even better - I will be reading through this in detail tomorrow.
https://www.tubecad.com/2017/11/blog0402.htm
I'm sure James D will love this if he hasn't already seen it.
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