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Not just another speaker build.

I like 'em! Funky looks great...there's an early KEF look about them too., PU18 can turn grown men into Paddington Bear...it gets everywhere.
 
I've still got some crossover experimenting to do, but at the moment the midrange sounds a bit small compared to my previous 10" 2-ways. The bass driver also has quite a lumpy frequency response that would be better crossed lower than the current 450hz to remove some bumps. I'm quite tempted to lop the off and build a larger mid-enclosure for a bigger driver.
 
Here's the 1mtr frequency response measurement of mk1 crossover. It's good down to 200hz. Not sure why there's a dip at 330hz. (The red line is with the tweeter polarity reversed).

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Just noticed there's a blip in the impulse response between 2.8ms = 357hz (0.96mtr) to about 3.5ms = 285hz. So the dip is a reflection. Thought I'd gated them out, but obviously not.
 
I've had the circular saw out and the cut the back off the speakers because I'm not happy with anything to be honest.

Starting with the Faital 6RS140 midrange. I don't like the dip centred around 1khz as can be seen here:

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It's not inherent in the driver response because I took an open baffle measurement to check (Blue line is the open baffle. It's wider and higher than the original baffle but shows the driver shouldn't have a dip)

kOSUJv3l.jpg


First I tried lining the inside of the enclosure (tight up tp the driver) with 10mm x 25mm wool felt but even with a couple of layers it didn't make much difference (Blue line shows a slight increase around 800hz to 1200khz area).

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I then decided to cut some 2" x 8" holes around the baffle to see if that cured the problem with internal reflections.

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Unfortunately it gave this response (Blue line) The red line is where I covered the holes in duct tape.

NyYS3Ncl.jpg
 
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I removed the back panel to see what that would do (Blue line)

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That's looking much better. I then put a load of wool stuffing in the back (red line)

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That's better again (flattened the 200hz to 500hz hole), but I still had a problem with the 5khz and 7khz breakup. So I did this:

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And got this:

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The red and blue line are both drivers at the same volume. That should make crossover design much easier. Just got to do the other cabinet, and then I've got some more experimenting to do in the woofer enclosure. I've already done a load of port measurements and found that I'd completely overstuffed them.
 
What did you do in the last picture, struggling to see exactly what? Does that mean the final will be an open baffle for the midrange?
You're braver than me though, I'd have b*ggered them up and had to shell out another £150.
 
Yes, they will now be a sort of hybrid open-baffle midrange enclosure. The enclosure has 2" X 8" cutouts on the top and sides, and the rear panel is removed. They are also heavily stuffed will wool toy stuffing material. I will need to cover the back in acoustic grill material to stop the stuffing falling out. I tried stuffing the 2" x 8" slots, but it didn't do much.

The last picture is with all the combined modifications. 2nd from last picture is Scanspeak style slits filled with viscoelastic caulk to reduce the breakup peaks at 5khz and 7khz. Without doing this I'd need two notch filters to to remove the double breakup peaks. I already tried a wide Q notch filter (passive) to try and hit both peaks at the same time, but it just messed up the frequency response and phase was tracking badly.
 
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I'm not really feeling the love in this thread :( If it wasn't for JimmyB I'd be quite depressed. Maybe people don't understand the significance of what I've done? Or maybe it's the thread title (does sound a bit cocky, although that wasn't my intention). Or maybe I come across as the village idiot, who can't possibly know anything about loudspeaker design because I'm dyslexic, useless with grammar and punctuation etc?

When I modified my speaker cabinet and achieved the frequency response that I did, I was really pleased with myself (To be honest I was surprised at the lack of feedback, as I was expecting to hear people say, nice one Matt, you nailed that etc, but apart from Jimmy, I was met with silence :( ). I've Googled "open baffle" and "hybrid open baffle" etc, and I couldn't see anything out there that looks like what I did. The 2" x 8" slots weren't just a random thing, I realised there was a problem centred around 1khz, and where there should have been a peak due to baffle diffraction, there was a dip. It could have ONLY been caused by something inside the cabinet (or been inherent in the driver, but a quick and dirty open baffle experiment proved that wrong), and due to the size of the wavelengths, had to be near the baffle edges (hence the slots near the baffle edges).

Right, I'm going to ask the questions that I hoped others would ask - Why do I want a peak at 1khz? Two reasons, One, That's the presence region. Look at the Falcon LS3/5a frequency response (here). A peak here makes voices sound alive, a dip here is my worst nightmare (dull, undefined midrange).... Two, to get good phase with a midrange bandpass filter, it needs to look like this target curve below (grey line). As you can see, the frequency response of the Faital 6RS140 in the 8.5" wide cabinet (black line) has a nasty dip around 1khz and doesn't follow the target curve in LspCAD (you can also see the breakup problems at 5 and 7khz). I don't know why I said I needed two notch filters to reduce the breakup (post #52), I only actually needed two parts, but i still think it's better to fix the problem at source, rather than try to hammer the problem into shape with extra parts (hence the Scanspeak style slits to the driver).

rR8qkw7l.jpg


So what do the 2" x 8" cabinet slots actually achieve?

The red line is open baffle, but with no slots. The blue line below is the same, but with the 2" x 8" slots (both have the rear filled with wool) (EDIT: not sure if Giffs work, so I'm uploading the Blue line separately) (EDIT, EDIT: NO GIFF DON'T WORK)

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As you can see, the slots fill in the 1khz dip and flatten the frequency response below 600hz, but not only that, I get all the benefits of an open baffle speaker, but without the drawbacks. If you've ever tried to fit a door in a very small space (cupboard door for example) with no ventilation, you will struggle to close the door because the air pressure is so high (you really have to push the door hard). Imagine a speaker in a small, sealed enclosure. I'm convinced this is why most sealed speakers sound dead at low volumes. They are fighting the air pressure inside the box. I once built a sealed 3-way - and as an experiment I fitted an exhaust vent (not a port). It sounded so much more alive and free with the vent.

I don't believe that the benefits of an open baffle speaker are due to the sound bouncing around all over the place causing dips and peaks due to sounds being in and out of phase. I believe it's because the motor (magnet power) isn't fighting against the air pressure inside the enclosure. To make things worse, most speakers designed for sealed enclosures have a high Qes (weak motor).
 
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I didn't actually click that you were aiming for an uplift at 1kHz, I thought you were trying to flatten out the dip and deal with the breakup modes at 5 & 7 but the holes were a surely novel way of going about it. Effectively constructive feedback in a very specific frequency range.

I see what you're getting at about a small sealed box providing too much air pressure that a small motor system won't be able to overcome but I'd have put that down to a poor design. A small motor should be able to cope well in a infinite baffle design where there's little internal air spring. Not sure I put that very well, hmmm.

TBH I've never heard an open baffle speaker, maybe I should mount a couple of drivers on some half sheets and try it out.

Anyway, keep going as I'm interested in seeing the finished beast and how you deal with the integration and bass issues you mentioned! I'm learning a lot here.
 
TBH I've never heard an open baffle speaker, maybe I should mount a couple of drivers on some half sheets and try it out.

Open baffle sounds more alive at low volumes, and I've got no doubt it's because of the lack of air pressure.

A magnet doesn't have infinite power over a driver. The weight of the speaker cone, magnet power and suspension compliance have a large influence over the subjective speed of low frequencies. The Vifa M21 woofer as used in the Snell k, JPW ap 1,2, 3 and heybrook HB1 has a very weak motor (high qes), but the bass sounds incredibly tight in a small, sealed enclosure. Put the same driver in a larger sealed enclosure and the bass, although more linear (flatter frequency response) sounds a lot slower and less tight. It's not just the frequency response that's causing the subjectively slow sound (a peak at around 100hz from the small enclosure does give an extra tight kick to bass), but it's also the weak motor (magnet). A well implemented ported speaker with a low MMS (cone weight) and low Qes, will have the speed of a sealed speaker but more linear response and higher efficiency. Once you've heard how a good ported speaker CAN sound, you won't want to go back to sealed.
 
Fatmarley - don't be dejected; not everyone understands the art-science of loudspeakers, I know I don't. I'm here to learn and appreciate.

Thank you. At least I know more than one person is interested.
 
I'm not really feeling the love in this thread :(
I'm quite intrigued at what you're doing, but have been watching it silently, as I couldn't think of anything useful to add the to the conversation. I'm hoping to proceed on a build soon myself, so I'm always keen to see how others are proceeding.

I'm sure there are many other lurkers like me, so please continue to include us as avid audience members in your journey.
 
I'm quite intrigued at what you're doing, but have been watching it silently, as I couldn't think of anything useful to add the to the conversation. I'm hoping to proceed on a build soon myself, so I'm always keen to see how others are proceeding.

I'm sure there are many other lurkers like me, so please continue to include us as avid audience members in your journey.

Thanks Mike, Much appreciated.
 


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