Something stirs in the Undergrowth

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Retsel
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#2731 Re: Something stirs in the Undergrowth

Post by Retsel »

Hey Island Pink, I read through your audio journey over the last months and recently have been following more closely your most recent steps to find a lower midrange/midbass solution.

I am in a similar quest. I am finishing an audio room (19 feet by 26 feet with vaulted ceiling) and transitioned from Lowthers in open baffle to inserting the Lowthers in front waveguides. Previously in a smaller living room (12 feet by 20 feet), the Lowthers in open baffle served me well. But the larger audio room allowed using the Lowthers in front waveguides and I find this a better solution for the larger room. However, the Lowthers are only good down to 500 hz in the front waveguides (vs 150 hz in open baffle), and I am planning on a low frequency tapped horn (10 to 40hz) for both audio and home movie theater and I need bass/midrange from 50 to 500 hz.

What I have tried so far is open baffle, transmission line midrange and Karlson speakers. If what you are looking for is nice smooth bass/midrange, the open baffle and transmission line options are good options. The problems with these two are:

Lack of dynamics. Both of these options do not have the better micro/macro dynamics of controlled directivety, front horn systems.

Recessed soundstage. Front horns push the soundstage forward while open baffle and transmission lines do not, so there is a soundstage mismatch.

The Karlson speaker on the other hand is like a horn, tapped horn actually, and pushes the soundstage forward similar to my waveguides. The Karlson design attemps to smooth out the frequency response above the 2 octave window of tapped horns, however it is not perfect at smoothing out the frequency response above 250 hz or so. I cannot fully endorse the Karlson speaker concept because the Karlson boxes I purchased are 40 year old boxes made from lower cost 5 ply plywood and some of the plys are delaminating, creating annoying buzzing resonances in the midrange. I need to build a new set of Karson boxes to fully test out this speaker design. But the dynamics are outstanding and the soundstaging matches well the front waveguides.

If going down the open baffle route, I can think of two things to do to try to match the dynamics of front horns. I recall an experiment that Magnetar (Mike Bates) did to try to get open baffle bass to match front horns. He used something like 6 9 inch drivers with a Q of 0.6. Apparently that many drivers achieved high efficiency and because of the large surface area, the speakers coupled well with the air which resulted in very good dynamics.

The second thing you might want to try is a "Kazba" speaker design (if I have the name right). This design is discussed on DIY audio and it uses a driver on an open baffle, but places Karlson style baffles on both the front side and back side of the speaker box. Lower Q drivers, such as 0.4, are preferred and the Karlson baffle helps to push the soundstage forward and improves the dynamics relative to conventional open baffle designs. This could be a better match for front waveguides. The downside relative to a conventional Karlson design is that you are still pushing bass towards the back of the room.
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#2732 Re: Something stirs in the Undergrowth

Post by IslandPink »

Hi Retsel - nice to have you here !
Some good points there to dicsuss. I will have to get a bit more time tomorrow to comment. I was working today and it's been a bit rushed getting ordinary 'stuff' done this evening. I am working on getting the OB/horn test bed working, though.
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#2733 Re: Something stirs in the Undergrowth

Post by IslandPink »

That's quite a big room there - nice, but i can see your problems with a Lowther on OB. I am not sure how the Xmax will work out below 100Hz , but my room is about 23 x 14ft. Yes, once you put a front horn or waveguide on the Lowther, it's only reinforced higher up, so it becomes a higher frequency solution !
I didn't find the horns i was working on finally all that good for micro-dynamics, that was one of the disappointments. The lower extension was fine, usefully below 100Hz, but the quality of tone and low-level was not good enough.

Interesting that Mike Bates tried OB with more drivers. It does not surprise me he needed lots of drivers - my impression is that he listens at about 20dB louder than i do !
I find that dynamics don't have a lot to do with the number of drivers - loudness is a poor substitute for dynamics. It's mainly about low phase shift, or low group delay. The use of higher Q eg. 0.6 there is significant though - that will help to keep the output flattish down to under 100Hz, and the group delay will be good into the upper bass.
It's a tricky business though, because as Q goes up, efficiency goes down. I'd like to keep efficiency to at least 93dB/w in the lower midrange.
I could of course doubel-up on the Lowthers ( at a cost ! ). The other option is using the Supravox 285 as the lower midrange driver - but i think its performance in the 400-800Hz region is a bit lacking in comparison to smaller cones - when you are trying to blend to something as good as a compression driver above 600.

I haven't looked at the Kazba, but will look that one up. The Karlson, I've been a bit suspicious of, because it only seems to be one guy ( Freddyi ) who is ever pushing the concept. The claims for it seem a bit too much like a 'free lunch' . However you have some first-hand experience , so that's good.

It will be interesting to see what happens with the soundstage. In the past i don't think I had the cone driver placement correct vs. the horn. However it may be that there's just going to be a mismatch as you say. I suppose one option then, would be to go to sealed box for the lower mid - at the cost of a slight loss of tone and openness.
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Retsel
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#2734 Re: Something stirs in the Undergrowth

Post by Retsel »

I think that phase issues can affect micro-dynamics as well as all dynamics. This argues, though, against any speaker with any audio output from the back of the driver since throughout most of the audio range, this rear wave is out of phase with the front of the driver - including open baffle, reflex, transmission line (less so because the backwave is subdued), backhorn, tapped horns..., and argues for closed box speakers. I am not sure that this assumption is always supported by listening tests though. It would be important to determine what affect this has and the extent of the effect.

Another factor for micro-dynamics is the room effect. Room reflections will mess up every part of the audio playback. I found a post by Joseph Crowe where he compared the spectrogram of a Lowther driver in a front horn with the same Lowther driver in open baffle. http://croweaudio.blogspot.com/2016/12/lowther-dx3.html Clearly, the room reflections cause havoc on the listening experience, and the front horn was head over heals better than open baffle speakers, which by their very nature are more directional than other speakers. When my first pair of Lowthers were damaged and I moved to a good set of transmission line speakers, I was disappointed in the audio playback. Clearly the less directional quality of sound and increased room effects of the audio playback ruined the sound, and this in a room with only insulation exposed in the walls and ceiling. A room with sheetrock installed on the walls and ceiling would have been even worse. An audio friend of mine has it right, the only way to listen to omnidirectional loudspeakers is in the near field - like 5 feet away so that you are listening to much more direct sound.

I think another factor for microdynamics is the speaker construction. I think that lighter cone drivers coupled with highly compliant surrounds and spiders contributes to better microdynamics, but this is just a theory based on little data and I would be interested in other views on this. My Lowthers and EVM 15L drivers both are lighter cone drivers, but this may just be a coincidence.

My Lowthers in front waveguides (3 feet deep conical horns) are likely directional down to 500 hz. One of the issues I may be hearing is if I have a power response mismatch between my Lowthers in waveguides and my lower midrange/bass speakers I have tried. The Karlson speakers are somewhat directional even in the bass region, which likely better matches the power response of the upper midrange/treble of the Lowthers than the transmission line and open baffle experiments I have tried, but I would need to measure to be sure but I don't have the software to measure this.

Speaking of tone, my DX4s in these waveguides along with the Karlsons with EVM 15L speakers was the best midrange tone I have had. I was switching out diffusers for my Lothers and I blew out the former of one of my Lowther drivers. I ordered DX65 cones instead and I am still trying to get back to my previous audio nirvana, but that is another story.

The last comment about Mike Bates. I suspect that he has done more comparisons between different speaker designs than most speaker designers who are often limited by the company owners who have preconceived notions about speaker types and limit their research and development. I went to one of his beers and ears events at his house. It is quite impressive to hear 105 db at the listening position with no distortion. Of course it soon drove me from the room. I followed his projects over time and was so impressed at the list of speaker drivers he tried and different speaker types. Mike occasionally posts on Audio Roundtable I think, and I traded a couple of e-mails with him when I was doing research on Karlson speakers. I am not sure what he is up to as he did not seem that willing to correspond and the phone number I had for him did not work anymore. I should try again.

Retsel
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#2735 Re: Something stirs in the Undergrowth

Post by IslandPink »

Slow progress, sorry. I have been through about 4 iterations of the support for the compression driver here, it still needs more hacking and alteration !
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#2736 Re: Something stirs in the Undergrowth

Post by IslandPink »

Thanks for the additional thoughts, Retsel. Might come back to comment more on that.
Retsel wrote: Mon Jan 04, 2021 5:19 am I think another factor for microdynamics is the speaker construction. I think that lighter cone drivers coupled with highly compliant surrounds and spiders contributes to better microdynamics, but this is just a theory based on little data and I would be interested in other views on this. My Lowthers and EVM 15L drivers both are lighter cone drivers, but this may just be a coincidence.
I tend to agree with you, and my criterion in recent years has been the Rms value. Light cones are good up to a point, but have more trouble with breakup modes. A slightly heavier cone with more BL is often better. I think that a driver operating in the midrange needs to have an Rms of no more than about 0.8 to sound really open at low signal levels.

Progress in recent days, enough to do some testing. I have got the horn driver mounted up, finally it required a 2 1/2 " high piece of scrap 18mm ply, to stop the horn drooping at the front ( Ooh Er ... etc )
HornOB2021_baffle.JPG
HornOB2021_test.JPG
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#2737 Re: Something stirs in the Undergrowth

Post by IslandPink »

Some tests of the Yuichi using REW and the Behringer USB box of tricks -
I tested the horn first from about 0.75m away -
Yuichi415_75cm_Average2.jpg
Then quite close, about 20cm from the fins-
Yuichi415_20cm_Average1.jpg
Clearly the driver is pretty flat, as most of the peaks & dips smooth out when you get closer .
I suppose the level above 5kHz will come up if you are in a listening position , over 2m away - this is a known feature of horns like this which are increasingly directional in the HF - this one will do that at least in the vertical section.
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#2738 Re: Something stirs in the Undergrowth

Post by IslandPink »

Fostex FF225WK on the baffle, somewhat less impressive :
Fostex225_nocross_Average1.jpg
That was with the horn in place. I thought maybe the 300Hz dip would look different if I removed the horn, which does overhang the cone quite a lot.
No ! - here are a couple of tests without the horn.
The green is the average from above, and the blue and brown ones are the new tests.
Seems to be worse at 300Hz !
Fostex225_Average_and_removedHorn.jpg
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#2739 Re: Something stirs in the Undergrowth

Post by IslandPink »

With the aid of MH Audio, I concocted a rough 2nd-order low-pass for about 450Hz.
I used two laminated-core chokes to get 5.3mH, and a 25uF Ansar cap.
Result when tested is below. As with all these , I did at least three slightly different microphone positions, plus some 1/24th octave smoothing.
As you can see there is an annoying shelf from 150Hz to 400Hz, before you properly get into the 12dB/oct downslope.
Fostex225_450LP2nd_Average1.jpg
However, I think it's worth a listen, and then a test. The test will be a faff to set up, as I need two amps, in order to get the levels right owing to the >12dB efficiency difference.

As an aside, I'm going to check the FF225WK datasheet and see if you would expect it to be low around 300Hz.
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#2740 Re: Something stirs in the Undergrowth

Post by IslandPink »

There's nothing on the Fostex trace around 300Hz, and nobody else seems to have measured it or at least posted a measurement. I did a couple of additional scans with the speaker pushed back further into the bay, and it's clear there's a lot going on in the room between 100Hz and 400Hz. Maybe there's a suckout from the room, where it was first positioned. Perhaps SimonC is out there lurking, with that model of the room that he ran up in the software ?
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#2741 Re: Something stirs in the Undergrowth

Post by IslandPink »

So I had a listen today with the 300B & 45 amps wired in.
It sounded quite good at first, quite dynamic and some beef to the male vocals. Then I started hearing things wrong with female vocals, on the horn. Ran the horn on its own. I always thought that the Yuichi was nice on everything. Not so.
Now this whole project feels a bit like Father Ted and the dent in the car :
TedDent.JPG
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#2742 Re: Something stirs in the Undergrowth

Post by simon »

It's no use Mark, you'll never get it absolutely right :-D

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#2743 Re: Something stirs in the Undergrowth

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IslandPink wrote: Sun Feb 21, 2021 10:12 pm So I had a listen today with the 300B & 45 amps wired in.
It sounded quite good at first, quite dynamic and some beef to the male vocals. Then I started hearing things wrong with female vocals, on the horn. Ran the horn on its own. I always thought that the Yuichi was nice on everything. Not so.
Mark,

The response curve of the horn looks nice to me - I've had good results with worse, but those needed some hammering into shape.

Could you check the distortion plots, and maybe response at the listening position, to see if we can figure out what's wrong?

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#2744 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

IslandPink wrote: Sun Feb 21, 2021 10:12 pm So I had a listen today with the 300B & 45 amps wired in.
It sounded quite good at first, quite dynamic and some beef to the male vocals. Then I started hearing things wrong with female vocals, on the horn. Ran the horn on its own. I always thought that the Yuichi was nice on everything. Not so.
Now this whole project feels a bit like Father Ted and the dent in the car :
TedDent.JPG
Mark.. need to work back, what have you changed since the horns were sounding good? We’re you previously running then with passive crossovers? As you know the reflected loaded back thought the OPT’s changes the working line.
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#2745 Re: Something stirs in the Undergrowth

Post by Scottmoose »

Mark -just as a minor note regarding the response shape of the 225 (I haven't been following closely due to work & lecture-writing commitments) & assuming these are regular gated in-room measures, your filter is likely to be interacting with the Fs impedance peak, resulting in a rising output in roughly the 100Hz - 200Hz region before baffle rolloff occurs & altering the desired transfer function / FR. This is quite a common occurrence with low-pass [passive] filters at low frequencies & often seen with 3, 4, 5 ways & the ilk, or low-crossed 2-ways using a wideband mid-tweet.
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