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Old 8th November 2017, 10:35 PM   #1
CharlieM is online now CharlieM  United States
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Default sanity check

Hi all,

I need a sanity check on a speaker design Iím drawing up for a hi-fi buddy (see image below). Lest anyone ask; Iím not building it-- just helping with the design and letting my buddy use my stretching jig so he can pay someone else to build it.

If I ever learn how to build a passive crossover for an ESL I may build a few to sell on Etsy in my old age but right now I have full time job and I havenít the energy or time for it.

My friend likes my wire panels but prefers dipole bass and he didnít like multi-woofer dipole line array I suggested. So we compromised with a woofer-under-panel design, using a Peerless SLS 12 in a modified U-baffle crossing in at around 250Hz.

Perhaps this could be a stand-alone speaker up to moderate volume but I figure the SLS 12ís in an OB would max out early on the bottom end. But since my friend has a pair of OB subs (two AE 15ís in each one) for the the low bass the SLSís can be chopped off sharply at around 60Hz, which we think solves that problem.

I like the look of the design but I have some concerns -- comments and opinions welcomed:

First concern: The speaker might be easy to tip over forward, since the feet do not extend forward of the baffle board and there isnít much weight on the rear. The step up transformers will be placed at the rear end of the base but their weight alone might not be sufficient. I suppose we could place a dumb bell back there, lol.

Bigger concern: With the woofer so close to the panel and no box around it, would its pressure waves overwhelm the diaphragm; driving it into the stators or just adding a nasty boom? I recall the old ML Statements used a vertical dipole woofer array with a space between it and the panel which I believe served to vent the woofersí pressure waves. So-- Iím wondering if we should add a slot in the baffle board between the woofer and panel as a pressure vent. Adding a slot there would detract from the esthetics so I suspect my friend wouldn't like that.

So now Iím wondering if we could add a slot between the baffle board and base, to vent the pressure into the space between the base and floor-- a vent there would not be visible from the front. Would that be an effective option? Do we need to I need to worry about any of this anyway or is it just my paranoia?

Chaz

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Old 8th November 2017, 11:01 PM   #2
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You will need digital signal processing with that configuration. Why not use two woofers back to back in a sealed box?
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Old 8th November 2017, 11:40 PM   #3
CharlieM is online now CharlieM  United States
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Thanks Badge,
DSP we got... but back to back woofers is a viable option to be considered before pulling the trigger on this project.
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Old 9th November 2017, 12:43 PM   #4
CharlieM is online now CharlieM  United States
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Forgot to mention: I already had several sealed box and TL configurations drawn up but my friend is dead set on dipole bass. Whatever we end up with will be tri-amp’d with Sunfire amps thru a Rane DSP crossover. Hopefully, it will be easier to build than previous designs, not too pricey, and a parts list and drawing will be available to anyone who wants it thru my website.
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Old 11th November 2017, 04:55 AM   #5
bolserst is offline bolserst  United States
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Quote:
Originally Posted by CharlieM View Post
… With the woofer so close to the panel and no box around it, would its pressure waves overwhelm the diaphragm; driving it into the stators or just adding a nasty boom? I recall the old ML Statements used a vertical dipole woofer array with a space between it and the panel which I believe served to vent the woofers’ pressure waves. So-- I’m wondering if we should add a slot in the baffle board between the woofer and panel as a pressure vent. Adding a slot there would detract from the esthetics so I suspect my friend wouldn't like that.
Exciting the diaphragm resonance frequency with the back and forth particle velocity along the null axis of the dipole woofer is certainly a concern. Having a single woofer at the end of the panel rather than a whole row along the length of the panel will excite the resonance less. But, it is tough to predict if it will be intrusive or not without testing it. You have some SLS woofers in your Ripoles, so you might “borrow” one and hold it in free air while playing a sine wave close to the resonance frequency of your ESL panels. Then try bringing the woofer near the panel’s middle and ends and see what happens.

If excitation of the diaphragm is a problem you could add some acoustic damping in the form of thin crafting felt to the rear stator between the first few crossbars closest to the woofer…a minimal aesthetic impact. Another alternative you might try is to extend the top of the U-frame for the woofer to lengthen the path for the air motion directed upward and thru the panel. As it is now, that path looks to be shorter than to the sides(ie path of least resistance), so that is where the highest particle velocity will be.
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Old 11th November 2017, 12:47 PM   #6
CharlieM is online now CharlieM  United States
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Thanks Steve,

Your advice is insightful as usual. Some felt tucked between the rear crossbars would be easy to do!

Another mitigating factor just occurred to me: Since my friend will use the big AE dipole subs for the low end, the SLS woofer below the panel will be chopped off sharply at 60 Hz (possibly higher), which should limit the cone excursion significantly.

My only interest in this project is having a simpler and verified design to post on my website. However, I fear that if my friend can't find someone to build this thing from my drawing, I may get roped into it and I really don't have time for it (getting lazy in my old age).

Chaz

Last edited by CharlieM; 11th November 2017 at 12:52 PM.
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Old 11th November 2017, 05:22 PM   #7
bolserst is offline bolserst  United States
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Yeah...very easy it to get sucked into other peoples projects

I meant to comment on your first concern about the stability as far as tipping.
I agree that you will likely need to add some mass to the back end of the base, or extend the front feet forward.
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Old 11th November 2017, 05:55 PM   #8
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What are the speakers in your avatar?
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Old 11th November 2017, 06:18 PM   #9
bentoronto is offline bentoronto  Canada
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sanity check
I ran a giant OB bass for a while and agree the sound can be nice. I had several feet of irregularly shaped perimeter and other baffling pieces. But as wiser others have commented, it's a challenge.

There's a compromise that might be called "leaky sealed box" where you have a large foamy filled box with no or little back on it. Lord only knows how to simulate that, but I sure wouldn't care. Sort of like a Linkwitz U and the basic driver Fo stays where it belongs (naturally boosting a bit the lower end of the music band*); but unlike a simple baffle, while mostly passing woofer frequencies out the back it is absorbing a lot of upper freq and noise emanating out the back.

B.
* you do want only naturally sourced music, don't you?
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Last edited by bentoronto; 11th November 2017 at 06:25 PM.
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Old 11th November 2017, 10:17 PM   #10
CharlieM is online now CharlieM  United States
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Quote:
Originally Posted by scottjoplin View Post
What are the speakers in your avatar?
Those were my first ESL's built in 2008 using perforated metal stators. My latest speaker shown below uses segmented wire stators:

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