I'm helping my brother repurpose some speakers for a new place that he's putting together. Amongst them are two old W-Bins containing B&C 18TBX1000 drivers. I took the opportunity to do some measurements of one of them (see attached). They are vented, and I used the transfer function method to measure the contribution of the vent to the output.
Apart from a narrow dip around 119 Hz, these W-Bins seem to have a pretty decent and smooth output. -3dB point is at 45 Hz, and the vents tune the chamber to around 33 Hz, which is pretty low, but it seems to do the job, with the vents adding around 2dB of additional output between Fb and 60 Hz. The vents are two 3.5" cylindrical tubs though, which might be on the small side for a 18" driver.
I told my brother that I might design a different box for him based around the same drivers, but I think it might be a bit difficult to get something noticeably better than these W-Bins, considering the type of music that they usually play.
10-JUL-2021: Added corrected response curve, as previous measurement included the impact of my car stereo's "ASL". See post #20
Apart from a narrow dip around 119 Hz, these W-Bins seem to have a pretty decent and smooth output. -3dB point is at 45 Hz, and the vents tune the chamber to around 33 Hz, which is pretty low, but it seems to do the job, with the vents adding around 2dB of additional output between Fb and 60 Hz. The vents are two 3.5" cylindrical tubs though, which might be on the small side for a 18" driver.
I told my brother that I might design a different box for him based around the same drivers, but I think it might be a bit difficult to get something noticeably better than these W-Bins, considering the type of music that they usually play.
10-JUL-2021: Added corrected response curve, as previous measurement included the impact of my car stereo's "ASL". See post #20
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Poor bracing or cabinet construction will certainly add to your woes, but I think that at least some of the wiggles are ¼ wavelengths of bend to mouth or throat to bend dimensions in the folded horns. For example the 98Hz peak would correspond to a fold that is approximately 870 mm of effective acoustic path distance from the mouth.
Your measurements are what I would expect. I did a lot of measurements of subwoofers in the mid 1980s. I had access to a very large performance stage 22m deep x 40m wide with an 18m high loft and could position the cabinets more than 6 metres from any reflecting surface, allowing valid indoor (free from air movement interference) free space measurements to below 30Hz. I measured a number of W-bins, J-scoops and reflex cabinets with MLSSA. I never used W- or J- bins by choice after this.
Your measurements are what I would expect. I did a lot of measurements of subwoofers in the mid 1980s. I had access to a very large performance stage 22m deep x 40m wide with an 18m high loft and could position the cabinets more than 6 metres from any reflecting surface, allowing valid indoor (free from air movement interference) free space measurements to below 30Hz. I measured a number of W-bins, J-scoops and reflex cabinets with MLSSA. I never used W- or J- bins by choice after this.
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I should add that I also sold my prized custom Krix built transmissions lines that I took my first bank loan to buy, once I learned to identify and hear the the time domain aberrations that folded acoustic lines create. If I listen to a recording of a vocal, glock or a piano, etc, I want it to sound like a vocal, glock or a piano or a piano in the room I am in, not one that sounds like it is in a room at the other end of a folded acoustic line.
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what's their dims? are they from DB Keele's 80's plan?
Early 80's Don Keele & Mark Gander / JBL horn plans
Early 80's Don Keele & Mark Gander / JBL horn plans
Apart from box and driver resonance, any peak in the impedance curve is related to a response anomaly, often caused by the suspension or dust cap. The peaks in a typical folded system are at least an order of magnitude greater than a typical reflex design. Just for fun look here:
bass reflex impedance curve - Google Search
W-Bins are a lot of fun! They do need bracing and a sturdy construction though. Panel flex and vibrations do give large horns a bad rep. It is not unusual that the panels flex more then the driver diaphragm excursion in unbraced thin plywood wall boxes.
ROAR18? They will have about the same usable passband but despite what Hornresp says, they will have a lot more output. Probably at least 10 dB more output from the same drivers. Two 3,5 inch ports will compress heavily at high output levels.
Brian,
Such a small chamber with an Fb of 33Hz should have far less output (around -15dB) than the Fc of the horn (near 60Hz), which would suggest that if your cabinet is similar to the Keele/Gander W-bin, the bass response should also be similar if measured half-space outdoors rather than using "the transfer function method to measure the contribution of the vent".
Mark Gander published his white paper on "Dynamic Linearity and Power Compression in Moving-Coil Loudspeakers" a few years after that ported W-bin design, the ports may be more useful for venting heat than LF reproduction ;^).
A bit more LF output below 60Hz could probably be achieved using a TH of similar volume, but doubt it would do more above.
Cheers,
Art
It does resemble the Keele W-Bin plan. However the front panel is 11 inches wide (the Keele Plan has 10 inches), and the vents are 9" long (the Keele plan has 8 inch vents). The box is also almost an inch deeper than the Keele plan, at 30.9".
The Keele W-Bin has a response that drops off after 60 Hz. I was curious about why my measurement showed a response down to 50 Hz. Then I realised what happened. I used my car audio subwoofer amplifier to provide the power, and while I'd set the EQ flat, I forgot to disable the "ASL" function in the deck (sigh). What a numpty. I'll have to repeat the measurements to get a more accurate FR.
Vented W-bins (like 6th order BP alignments) can be expected to have three significant impedance peaks within their usable passband. This one shows those peaks. However the upper ones aren't really clean, which is usually a sign of panel resonance / insufficient bracing.
I did a little study of how panel resonance can impact the impedance curve here - The Subwoofer DIY Page - Projects : Using Impedance Graphs
I believe you are right. When I did the measurement, I forgot to turn the deck's "ASL" function off, and I suspect that it added a bit more at lower frequencies. I will have to repeat the measurements.
The transfer function approach was used to determine how much extra the vents added to the output of the horn. It can be prone to errors though if there's any wind noise and the like (and I just happen to live on a street called "Windy Trace" for good reason).
Agreed. These vents are way too small and the distortion that they generate is actually audible.
I'd actually designed a TH to replace these W-Bins many years ago (The Subwoofer DIY Page v1.1 - Projects : "Proof of Concept #4"), but the project was never completed beyond preliminary testing because the owner got wrapped up in another project that was considerably more important to him. I also wasn't very happy with the build quality of the box (big leak around the driver), so I didn't pursue it any further on my own. If revived, I'm going to watch the carpenter with an eagle eye to ensure he follows my instructions to the letter.
And now that my brother now has the contract to run the club and he's rebuilding it, I might have another stab at replacing these W-Bins with "true" subwoofers.
Ahhhhh, ok, makes sence (strong 40hz).
So the 100hz z-blip is mouth resonance then ?
24" tall x 30" deep x 48" wide usually goes down to 60hz.
That explains why the drums on foreigner's "juke box hero" pounded me when i owned one.
Don't forget the free gain from the w-bin.
I liked the impact like feeling of bullets in movies (when i was misusing it as a subwoofer).
W-bin seemed to have more impact than my 4x18's.
Not more pressure, just more slam, at 16' back (also a dead spot for the 18's).
The no bass near it but getting pounded down the hall was weird though when i had it upstairs run on 80hz f-mod (6db rolling i read in a test).
So the 100hz z-blip is mouth resonance then ?
24" tall x 30" deep x 48" wide usually goes down to 60hz.
That explains why the drums on foreigner's "juke box hero" pounded me when i owned one.
Don't forget the free gain from the w-bin.
I liked the impact like feeling of bullets in movies (when i was misusing it as a subwoofer).
W-bin seemed to have more impact than my 4x18's.
Not more pressure, just more slam, at 16' back (also a dead spot for the 18's).
The no bass near it but getting pounded down the hall was weird though when i had it upstairs run on 80hz f-mod (6db rolling i read in a test).
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Than ks for the link; that's an informative series.
It begs the question: how do you secure the necessary anthropoidic dampers to the top of you bass horns these days?
Ok, I had a chance to do a quick redo of the FR test this weekend. This time I made sure that the car stereo's ASL feature was disabled.
The response looks more like those old W-Bin responses. The vents still add around 2dB of output between 30 and 60 Hz, but output in that range is a good 5~20 dB below the maximum output from the W-Bin.
The response looks more like those old W-Bin responses. The vents still add around 2dB of output between 30 and 60 Hz, but output in that range is a good 5~20 dB below the maximum output from the W-Bin.
