audio-talk

IIRC, the EQ ended up as follows:

2nd order lowpass
38Hz notch
100Hz boost

With varying filters required to achieve the right shape in each place.

The 38Hz notch, IMO, was very very necessary. If you play Hey Now by London Grammar, the bass notes should be even in volume, with the very bottom note (33Hz) being slightly quieter. The 38Hz resonance (which is +18dB in a narrow region) meant the bass was exceptionally uneven: when that note hit, the resonance was distractingly obvious.

The 100Hz boost was the one I'd like to get rid of, by finding a solution in the acoustic domain. Given the size of the wavelengths involved, though, such treatments could be physically large and expensive.


From my measurements, the bass drivers integrated well with the mids, although I can understand why there might be some question mark over the phase: the large dip a little way below the crossover point would call the crossover into question. The mids drop very steeply at 200Hz, and the measurements with woofers included show good response to about 140Hz before that big 100Hz dip comes into play. Given that the 100Hz dip all but disappeared with close-mic'd measurements, it's my belief that the room is the problem here.


One thing I didn't investigate was the contribution of the woofers further up the frequency range. Adding another 2nd order low-pass at 400Hz (so the resulting slope is 4th order) would further reduce some of the metal-cone breakup "mush" happening up in the kHz range. I did something similar with the bottom woofers on my current speakers, at something like 400Hz (a fairly gentle initial rolloff - keeping phase shift minimal) and 700Hz (much steeper, but SPL is down, so phase shifts aren't going to cause cancellations).


I've done a little research into ways of absorbing narrow frequency bands acoustically. The best commercial products seem to promise strong absorption in a band as narrow as one octave. That might be worth a look for the 100Hz dip, but the 38Hz peak is much narrower, so I think that one will have to stay as EQ.

Chris

I definitely think it would be worth measuring these speakers again, Chris. Blocking up the chimney opening in Colin's room made a very audible difference with these speakers, I would love to see more science on what exactly the new in room response looks like with that rather large 'room port' removed, and then go from there. Also, we didn't get time to try the speakers without the 100Hz boost but with the 38Hz notch, for example.

One thing I didn't investigate was the contribution of the woofers further up the frequency range. Adding another 2nd order low-pass at 400Hz (so the resulting slope is 4th order) would further reduce some of the metal-cone breakup "mush" happening up in the kHz range. I did something similar with the bottom woofers on my current speakers, at something like 400Hz (a fairly gentle initial rolloff - keeping phase shift minimal) and 700Hz (much steeper, but SPL is down, so phase shifts aren't going to cause cancellations).

Also, purely, subjectively speaking, the "200Hz" roll off, sounded better to my ears as it reduce the bass bleed thru' into the mids, but re-reading your reply, Chris, section, again I think this warrants a second pass to get the best out of these speakers and trying the above, rather than just lowering the 3db point as we did.

Also, we didn't get time to try the speakers without the 100Hz boost but with the 38Hz notch, for example.

I think we did but I may be wrong.

Perhaps you're right, but I don't think it got a fair evaluation.

Andrew wrote: ↑Fri Dec 16, 2022 1:37 pm Perhaps you're right, but I don't think it got a fair evaluation.

Maybe, I got the sense that it was wanting the LF level pushing up to far trying to get the energy that was being lost in the notch and that was making the collision with the mid range worst. That's why I suggested taking that notch out. It may be that the same could have been done by moving the LP point down as we did next.

Nick wrote: ↑Fri Dec 16, 2022 3:11 pm

Andrew wrote: ↑Fri Dec 16, 2022 1:37 pm Perhaps you're right, but I don't think it got a fair evaluation.

Maybe, I got the sense that it was wanting the LF level pushing up to far trying to get the energy that was being lost in the notch and that was making the collision with the mid range worst. That's why I suggested taking that notch out. It may be that the same could have been done by moving the LP point down as we did next.

I think we should get the measuring gear out again and knock this on the head, the speakers are worth getting right, aren't they?

Oh yes, as I said. I was just describing what we did and why, not suggesting it was correct or final.

Is everything symmetrical in the room? Shape, speaker position etc. If so, it’s likely to be on both speakers and difficult to fix

My room is very asymmetrical and I have a 70Hz notch on the left speaker only (bay window), so I have boosted the right speaker - I couldn’t put enough power in the left speaker to make any difference at all

Brian

brig001 wrote: ↑Sat Dec 17, 2022 5:32 pm Is everything symmetrical in the room? Shape, speaker position etc. If so, it’s likely to be on both speakers and difficult to fix

My room is very asymmetrical and I have a 70Hz notch on the left speaker only (bay window), so I have boosted the right speaker - I couldn’t put enough power in the left speaker to make any difference at all

Brian

Pretty much, especially once we blocked up the fireplace with acoustic dampening panels. The theory is the chimney was acting as a port on the room, in the same way a speaker port causes boom.

Andrew wrote: ↑Thu Dec 15, 2022 4:50 pm I definitely think it would be worth measuring these speakers again, Chris. Blocking up the chimney opening in Colin's room made a very audible difference with these speakers, I would love to see more science on what exactly the new in room response looks like with that rather large 'room port' removed, and then go from there.

It would be quite easy (with approx dimensions), and also amusing, to model the room with the chimney as a large bass reflex enclosure.

Bit of fun.

There's usually too many losses involved, even with a fairly solid brick construction like Colin's, for Helmholtz effects to significantly kick in, although there may be some; standing waves of some kind are quite likely though, and that chimney is evidently having some effect. We'll see in the new year; either Chris or I will get over there & measure the in-room again and probably womble about with ridiculous quantities of temporary damping materials.

IslandPink wrote: ↑Sat Dec 17, 2022 9:44 pm

Andrew wrote: ↑Thu Dec 15, 2022 4:50 pm I definitely think it would be worth measuring these speakers again, Chris. Blocking up the chimney opening in Colin's room made a very audible difference with these speakers, I would love to see more science on what exactly the new in room response looks like with that rather large 'room port' removed, and then go from there.

It would be quite easy (with approx dimensions), and also amusing, to model the room with the chimney as a large bass reflex enclosure.

Well I aint blocking my chimney

One of the best LF I have experienced, was when I went to a party, decades ago, where the guy had put bass drivers in the fire places, so using the chimney as transmission lines of a sort. Bet it was noisy on the roof, he was a big reggae fan, so not someone you wanted as a neighbour.

Scottmoose wrote: ↑Sun Dec 18, 2022 8:34 am Bit of fun.

... We'll see in the new year; either Chris or I will get over there & measure the in-room again and probably womble about with ridiculous quantities of temporary damping materials.

That would be great Scott. It would also be great if Chris could join us (likely, Andrew, me and Nick) to arrive at a few final consented agreed settings for the bass tuning. I do believe these speakers are worth taking the extra effort to bottom out the room issues affecting the bass response and I really appreciate having friends with the knowledge and willing ness to help achieve this.

I have been talking with Andrew about suitable dates for a mini meet my place early in the new year to coincide with him travelling down from Scotland to visit his mum. A couple of dates in late January 2023 have been identified, these being Saturday 21st or Saturday 28th.
Either these dates are fine with me and this will give me time to make a bespoke custom acoustic panel to fully block off the fireplace opening.

EDIT.
Andy, (aka gninnam) is coming over tomorrow (Tuesday 20th Dec.) to listen to the speakers. So it'll be interesting to have his views and thoughts on the speakers. Hopefully the current warming in the the weather holds as all the snow we had last week has now gone and we have light rain instead of the snow showers.

Oh my god
Went round to Colin's today to listen to the newest creations in his music room and to say I am jealous is the understatement of the century!

First off, they are quite imposing on first acquaintance but as the room is a good size you soon get used to them - the finish is very nice indeed and the go-faster strip around the cabinet works very nicely too in breaking up the depth and making them seem to be not as deep.

With the temporary bass trap in the fireplace and no changes to the eq of the bass amps I sat down in the chief pilots seat and was impressed straight away by the clarity and detail being presented and boy, the bass was nicely controlled and seemed to thrive in the room - some tracks we listened to seemed to take the bass down so low that I thought my innards were going to explode.........

Vocals (especially female) came across very life like and piano and strings sounded just right - can you tell that I was impressed?
I could waffle on for a lot more but if you haven't heard (or seen) them yet you need to as that would be the best way to live the experience.

The only niggles I have with them are that they are too big for my room and I couldn't afford them

Thank you Colin for a great day of idle banter, great tunes and a lovely lunch plus many cups of tea - would love to have another session once you have dialled in the frequency response for the final 5% that appears to be astray though I know I wouldn't be able to notice it.

Cheers