SLOB project

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Ray P
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SLOB project

Post by Ray P » Sun Dec 15, 2019 4:25 pm

I've been wanting to do an open baffle project for several years and I've finally decided on my approach, which I plan to progress during 2020. I've decided to build some SLOBs! No, not these;

Image

...these;

Image

It's an open baffle with a slot-loaded bass driver (slot-loaded oped baffle = SLOB). The design comes from Nelson Pass and is a domesticated follow-up to his earlier slot loaded experiments, covered here;

http://www.enjoythemusic.com/diy/0911/s ... peaker.htm

Here are the drawings of the Pass's domesticated SLOB;

https://www.diyaudio.com/forums/pass-la ... ost4922459

I plan to use a high-efficiency full-range drive unit on the baffle so I can run it with my flea-power OTL amps. My thinking is to use the Pass active crossover that's available from the DIY Audio store and to a chip amp for the bass unit.

Maybe take a leaf out of Mark's book and use acrylic sheet for the baffle with birch ply for the bass unit cradle come baffle support.

Lots of planning to do and pennies to save! Hoping Santa brings me some cash to get things underway!

Anyway, as always, interested in comments from the floor.

Ray

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Re: SLOB project

Post by IslandPink » Sun Dec 15, 2019 4:46 pm

Ray P wrote:
Sun Dec 15, 2019 4:25 pm
Anyway, as always, interested in comments from the floor.
I don't want to dent your enthusiasm... :)
Construction pics are on my thread if you search for 'SLOB'.
See what you can make of it - it ought to work according to Nelson and JC Morrison.
"Peridots and periwinkle, blue medallions Gilded galleons spilled across the ocean floor" ( Mitchell )

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Re: SLOB project

Post by Ray P » Sun Dec 15, 2019 4:52 pm

Thanks Mark. I did search earlier but didn't see anything - maybe another senior moment! I'll try again.

In the meantime, these are the bass units Nelson Pass used - probably play it safe and stick with them.

https://www.parts-express.com/eminence- ... --290-4512

Ray

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Re: SLOB project

Post by IslandPink » Sun Dec 15, 2019 5:00 pm

:D
SLOB_search.JPG
"Peridots and periwinkle, blue medallions Gilded galleons spilled across the ocean floor" ( Mitchell )

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Re: SLOB project

Post by Ray P » Sun Dec 15, 2019 5:48 pm

Thanks Mark, I found them straight away after you mentioned them in your first post - maybe I mistyped the search query?

There's a fair bit to read through on your thread - still to finish that - but I surmise that you didn't build the Pass SLOB but experimented with slot loaded bass and didn't progress with it?

The Pass SLOB seems to be well regarded in the research I've done and seems like a good fit domestically to my room (not too big/dominant/etc) so I'll give it a go. I don't have your talent for speaker experimentation so I'll play it safe, especially regarding the bass element, and I still expect to learn a lot...

I need to think about what full-range unit's to go with on the baffle - a pair of PM6As aint cheap!

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Re: SLOB project

Post by Ray P » Mon Dec 16, 2019 7:42 pm

So what are the panels thoughts on these;

https://www.lii-audio.com/index.php/pro ... s-fast-10/

or these;

https://www.lii-audio.com/index.php/pro ... 5-in-pair/

for the full range drivers for this project.

They are both well regarded from the research I've done. I'm close to pulling the trigger on the 10in units as they're on offer for a good price.

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Re: SLOB project

Post by Ray P » Mon Dec 16, 2019 8:08 pm

For information/reference, these units are employed in a number of DecWare open baffle designs;

https://www.decware.com/newsite/speakers.html

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Re: SLOB project

Post by IslandPink » Mon Dec 16, 2019 8:09 pm

I have seen those discussed but not many have bought and it would be v.interesting to hear them. The 10" are the ones I'd be most interested to see/hear. They should get you down to about 150Hz fairly flat, then I presume you are going to use the SLOB bass - hopefully with a more powerful amp ?
I like the ridges in the output part of the cone, as Coral, also the B&C 8PE21 used a ridge/groove mid-way out and their midrange was very flat.
"Peridots and periwinkle, blue medallions Gilded galleons spilled across the ocean floor" ( Mitchell )

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Re: SLOB project

Post by IslandPink » Mon Dec 16, 2019 8:19 pm

At Q = 0.5 , the sensitivity will likely be about 96 to 97dB/w in the midrange. I would like to see some more T/S data to see where Qms ( mechanical damping ) sits, given the comment about aluminium voicecoil. It will be great if they are the biz, as it would give me an option to improve the OB's I have, where the mid sensitivity hampers the bass a little by forcing an Lpad for the bass feed.
"Peridots and periwinkle, blue medallions Gilded galleons spilled across the ocean floor" ( Mitchell )

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Re: SLOB project

Post by Ray P » Mon Dec 16, 2019 8:32 pm

Hi Mark. Yes, the 10in units are the ones I'm most interested in.

I'm thinking along the lines of the Nelson Pass active crossover (from the DIY Audio store), feeding my OTL amp for the full range unit and an LM3886 chip amp (40W) for the SLOB bass units.

The crossover is configurable, but not adjustable on the fly so I'll need to use something like minidsp to establish the required settings before finalising the crossover build.

I don't think they've been a roaring success sales wise but I've not seen any disappointment from anyone who has bought them and posted about their experience, though there do seem to be plenty of people who write them off simply because they're from China so can't possibly be anything than poor quality rip-offs.

One thing I am wondering about is baffle size, should I buy them. The Pass SLOB baffle I'm working from is sized for a lowther (PM6A) but these are 10in instead of 8in and I have no idea how to work out if the baffle needs to be resized to suit? Any thoughts/steers would be welcome?

Ray

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Re: SLOB project

Post by IslandPink » Mon Dec 16, 2019 9:33 pm

Usually the OB area / wings are determined on the basis of the bass roll-off, not what the midrange is doing.
I never found out really how to simulate the slot-loaded bass plus the baffle - it doesn't lend itself to Hornresp, that's for sure.
I would not risk going too small, how does the size of mine, which are closely based on James's Quasars, strike you ?
ps. I can dig out who supplied the Perspex and CNC machining on EBay, when/if you need that info.
"Peridots and periwinkle, blue medallions Gilded galleons spilled across the ocean floor" ( Mitchell )

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Re: SLOB project

Post by IslandPink » Mon Dec 16, 2019 9:51 pm

Actually the data is there for the newer ones -
https://www.lii-audio.com/index.php/pro ... 0-in-pair/
and the Qms is high, so that means low Rms and good low-level detail.
If I put them on a big volume which equals either Infinite baffle or large OB, they look like this with 2pi radiation.
Lii_10_SPL2pi.JPG
Usually this is a bit pessimistic for a room, so I suggest 94 to 95dB in the mids.
It would be higher if the BL was higher ( Qts lower ) but the bonus you get is they extend quite far into the bass, flat, which means the SLOB bit will only need to do the low and mid bass region.
On this graph the software doesn't know anything about the whizzer and centre of the cone decoupling at high frequency, so the HF will be better than this.
"Peridots and periwinkle, blue medallions Gilded galleons spilled across the ocean floor" ( Mitchell )

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Re: SLOB project

Post by Ray P » Mon Dec 16, 2019 9:55 pm

Thanks again for the continued interest and help Mark. I don't plan to change any aspect of the construction regarding the SLOB structure and associated 'wings' and I plan to use the same drive units - I am working on the basis of that being the safe option for achieving some level of positive performance. I'm not planning to reduce the size of the baffle, rather questioning if it needs to be increased a little given if I go for the 10in full-range units - it's a mystery to me how to go about working that out so maybe more research is needed. Ho hum...

I found this place that seems to have 'reasonable' (but certainly not cheap) prices for acrylic and associated machining but another option might be handy if you could find the information.

https://www.cutmyplastic.co.uk/acrylic- ... /H100-W50/

Before I get to thinking about acrylic though it'll have to be some MDF or cheap ply for the baffle to get some level of confidence in the outcome before spening out that sort of money. For the SLOB structure I'll go straight to good quality birch ply and be done with it - just need to make some sort of strong/durable arrangement for having removable baffle panels.

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Re: SLOB project

Post by Ray P » Tue Dec 17, 2019 7:06 pm

Well, that's my Christmas present sorted, I've taken the plunge and ordered a pair of the 10in units.

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Re: SLOB project

Post by Ray P » Tue Dec 17, 2019 7:38 pm

I've started to try and get a handle on MiniDSP; conceptually simple but lots of detail for the devil to lurk in but I've got plenty of time to learn about it.

If I'm only going to use MiniDSP as a lead to configuring the analogue active crossover I don't want to spend more than necessary and it looks like the basic MiniDSP 2x4 will be sufficient to do the job. Do any of you chaps use MiniDSP?

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