audio-talk

Getting good lower-midrange on these sort of systems is a real headache. On any system where you want efficiency, it's a pain too - the cone size you need for low distortion and headroom down at 150 to 200Hz is incompatible with nice vocal/instrument overtones at 2000Hz. It's not such a problem with a sealed or ported box , with less than 90dB efficiency, but then the low bass is either way down, or badly delayed.

This is cheap enough to have a punt on, so I’ll give it a go with the Bastanis 18” on bass.

When I get time...

This may be of interest.. with respect to OB design. I do wonder if there is a bit of snake oil going off regarding the tube connectors being audibly better than binding posts...

IslandPink wrote: ↑Sun Feb 28, 2021 6:17 pm Getting good lower-midrange on these sort of systems is a real headache. On any system where you want efficiency, it's a pain too - the cone size you need for low distortion and headroom down at 150 to 200Hz is incompatible with nice vocal/instrument overtones at 2000Hz. It's not such a problem with a sealed or ported box , with less than 90dB efficiency, but then the low bass is either way down, or badly delayed.

Mark,

A 6" PA midbass might do exactly what you're looking for here. The 18Sound units are decent - I have a pair of 6ND430 in small PA cabinets. They cover 70Hz-2kHz at astonishing levels, and sound great doing it.

They might not be so happy in an OB, though. There are a couple of other versions available: the 430 is the longest excursion, rubber surround, and lowest efficiency. There's one with about 3mm of Xmax which adds a couple of dB, and a dedicated midrange version with basically zero Xmax, but really really high efficiency.


Chris

Gosh, 2 months since I last posted. There has been some progress, though things move slower in Covid-land. So to recap, I really liked what the SB Acoustics SB34NRX75-6 did in a sealed cab, adding lots of low bass, but it was rigged up in the middle of the room as best I could and not domestically acceptable beyond a trial, even in my play room/office. A longer term solution was required.

I'm still intrigued by Steve's 18" bass driver partially loaded with a vent (if that's the best way of describing them) but they scare me cos I don't understand how they work! And if I one day experiment with DSP and find that I don't hear deleterious artifacts then Vic's solution might be interesting too.

But, to move things forward in stage 1 (and with a good deal of help) I went with a development of the SB sub idea by building 2 vented subs using SB Acoustics SB29NRX75-6, £130 each. The plan is to use them below the Supravox 285GMFs to give the "grunt" from the boxes but retain the tone of the 285s in OB. So genuine 4 way speakers. The 285s, 208eZs and T90As are to be mounted in a miniQuasar on top of the subs. I still feel like I have some unfinished business with the Quasars - the ones I built weren't great and resonated a fair bit. MDF is a poor choice for OB.

The design of the subs is an SBB4 alignment and predicts an F3 of 25Hz. It uses a tweaked Qes with some additional R to raise Qts from 0.35 to 0.38.

Here's one of the boxes before lining and the top putting on And the smaller baffle And here's a complete speaker. Very pretty

Looking good Simon - have you had a listen yes?

Ray

Very interesting.

Good work !

Sorry, tea got in the way. So at the moment I'm not using the 285s - GM70 directly to the 208s rolling off somewhere below 200Hz, the T90As with a cheap 3116 class D amp with a simple 1st order cap filter, and more 3116 amps with built in low pass active filter at 180Hz for the SBs. I have two 3 way 4th order Linkwitz Riley active filter boards from eBay and I'm waiting for parts from Mouser. This will "get me going" with 4 way.

I've been listening in the late afternoon/evening whilst working for a couple of weeks now and I'm quite pleased. I'm not a musician and don't have "golden ears" but I can't hear any artifacts of vent noise or resonance. It's no doubt there to some degree but I haven't identified it yet.

I can't get to my REW plots right now but I measured it pretty flat to below 20Hz. (The 285s look a bit bumpy but that's another matter.) What I'm really liking is that if there's low bass on a record it plays it. I haven't listened loud at all, nor felt the urge to, but it just sounds very controlled and clean to me. And the tone in the 285 area is pretty good, better than I expected. For most sane people this might be all they ever need.

I'll try and dig out some measurements tomorrow, but I think the real adventure will start with the active filters and introducing the 285s.

Gosh, you have a long tea time!

Looking good and sounds like you've got to a solid position from which to experiment/develop.

Looks great as do the numbers Simon.
It’s way beyond what I would be allowed.

I love the bench Simon.
which cramps do you use?

Ray P wrote: ↑Thu Apr 08, 2021 7:30 am Gosh, you have a long tea time!

How very dare you .

Well, I started cooking tea at 7.45, ate at 8.30, watched a couple of hours of TV at 9, then time for bed and another day over.