audio-talk

The question I forgot to ask is what are the disadvantages of going from the optimal QTC of 0.5, obviously less damped for a subwoofer. I know from the low QTS drivers I have heard is their speed of response is beguiling, but they are lightish cones with big motors, where as this is a heavy cone with a big ish motor.

From what I have heard of them in my friends Linkwitz speakers they are nimble keeping up with the 8” lower mid driver, so my logic is they shouldn’t sound that different in a large sealed cabinet.

Well, you've got dipole vs monopole room interaction. It's probably the biggest effect you'll hear below 100Hz. If you room has a big peak (or dip), no amount of tinkering around with Qtc=0.5 or 0.6 or 0.7 will save you.

For instance, my room has around 15dB of gain at 40Hz, and even more at ~10Hz. When the differences in cabinet alignments might only be a few dB, you can see why I tend to go for sealed boxes (easy to build, reach the lowest notes) and EQ the speaker + room combination.

Chris

Here are my simulations with the drivers in a reasonable box... ( hopefully will arrive before the 31st - as coming from EU )

Nice design! Good tweak of Qts. I really like the group delay plot too and being a sealed box the excursion is nicely under control too..

It s good to have lots of power available to trade efficiency against low end performance

Any recommendations for decent software to model vented subs? I've used WinISD, which has sealed, vented, and 4th and 6th order bandpass and is simple to use to get quick illustrations. But how would I model different alignments, say SC4? I'm probably exposing my little knowledge with this question...

Thanks I'll have a look

When I'm quickly knocking out designs for comparison/evolution purposes I use two different sources...

First port of call https://www.ajdesigner.com/speaker/ either online or the downloaded versions

Second opinion http://www.mh-audio.nl/Loudspeakers.html#top and for the three main reflex alignments http://www.mh-audio.nl/Calculators/BRA.html.

Then I use various serious pieces of software for detailed design if I'm trying to optimise in software before building cardboard mules

Thanks James, hours of endless fun here

What I like about a Jeffs spreadsheets are you can switch between a sealed cabinet, bass reflex, and passive radiators quite quickly. The different alignments for bass reflex can be accomplished, you just need to know what Qtc and Vab your after. I even do open baffles and infinite baffles with it if you set the volume to 10x VAS for IB and 20xVAS for OB as a rough guide.

Jeffs spreadsheet looks really interesting - I haven't looked at it before but I will now - thanks for posting the link.

These turned up today... not bad 6 days from Germany. They are unused.. have a cosmetic blemish on one of the drivers, which I couldn’t see without a light. They have come out out of a pair of Grimm DMF subwoofers. Unfortunately they removed the instrumentation for the feedback from the driver .

Going to take some breaking in with 52mm pp of cone movement. Luckily I have a spare 500w amp module.

They will sit in their boxes until after Xmas.. as have too many other things to do before the end of the year. Need to read up on current amplifiers as they are meant to be better for subwoofers.

Looking at the underside of the cone, it looks as if the accelerometers were stuck on with double sided tape as I can see a witness of the pad residue. I came across this site when browsing, you can buy servo drivers and retrofit kits to add to existing drivers, not that expensive really. https://piratelogic.nl/ Is it a coincidence they are close to the Philips site and Grimm Audio. I have worked with Philips in the past - the brain power they could put on a job put U.K. technology companies to shame.

Good value if that's the only defect on them.I was a bit surprised at the size of the accelerometer - thought they were a lot smaller and neater these days !
I suppose if you use servo driver is it part of the dela that you have to user an accelerometer with it ?

I was a bit surprised at the size of the accelerometer

Yep, I assumed it would be mems based.