Pair Monacor SP-60/4 in a stuffed port aperiodic cabinet? What size cabinet? - Page 3 - diyAudio
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Old 19th September 2012, 03:33 AM   #21
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OK, so a ~75.33 Hz tuning [Fb].

OK, with this tuning you’ll run out of linear travel at ~2 W, so allowing for a little overdrive, 5 W max below Fb. Hope your limiter never fails.

At only 5 W, the vents can be quite small, 2.5 cm dia. x 5.3 cm long.

Again, you can put the vents wherever they will fit since the diameter of a 75 Hz WL is ~57.55” and/or where they sound best overall to you, though in theory you shouldn’t be able to hear any difference unless you overdrive the cab so hard that the vents audibly ‘whistle’/’chuff’.

That said, the pioneers of audio concluded that for a simple reflex like this one, putting the vents as close as practical to the driver is best overall, so your call.

GM
Thanks for the briefing. Does it help to tune the port a bit lower?
Well, anyway, the question is how do we get more power with less x-max?
With 2w power handling, apparently I've got an epic design flaw.
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Old 20th September 2012, 01:38 PM   #22
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You’re welcome!

No, that makes it worse.

Tune it higher and or make the cab bigger and/or use your limiter to protect it below ~90 Hz.

Well, it will increase with increasing frequency, so it will really depend on how much of the lower vocals you want to project.

Generally speaking, the telephone BW [~250-3000 Hz] is adequate and if for high speech intelligibility in a noisy environment you want a flat BW from ~125-2000 Hz, rolling off at ~3 dB/octave out to a ~5000 Hz cut-off.

That said, the main criteria for PA use is controlled directivity over whatever horizontal and vertical arc is required to cover the audience, so with a bipole in a bike basket, a lot of acoustical energy is wasted being reflected off the ground and broadcasting to the birds overhead, so I’m thinking that rolling the speaker off below 200-250 Hz will probably be a good plan and will maximize available power short of resorting to horn loading.

GM
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Old 21st September 2012, 12:23 AM   #23
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Thanks!
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No, that makes it worse.
And so does this:
The ClipNipper is a headroom booster for small amplifiers, and could triple the x-max, since it dampens the clipping without cutting bass impact. That is much different than PA type limiters that cut power

Fortunately, I have records that the first ingan clip detector, ClipNipper's grandma, was an asymmetric soft clipper operating at the full speed of the feedback loop. Well, she could stop x-max when the polarity is known. This direct type was never built--only the LDR limiter/compressors and 4n25 soft clippers were built. But the direct type is the only one fast enough to halt a cone at a precise point. I'll have to just simply try it.
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Old 21st September 2012, 01:02 AM   #24
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I think I'll be okay on the x-max situation. Monacor has bumpers. Plus I'll be trying to help it not use the bumpers. First steps are getting the amp input caps, amp output caps and cabinet tuning all brought into balance. Next is halting both the amplifier and the x-max via asymmetric soft clipper. And lastly are the boosters, ClipNipper and possibly UltraBass.

For increased broadcast range without removing bass, the UltraBass circuit has a roll-off of its own, but injects a substitute of the low bass harmonics without the fundamental. This is the low bass sound of radio stations and headphones, plenty loud but without the physical impact.
Here's the briefing: HeadWize - Project: The Psychoacoustic Bass Enhancer by Jan Meier

I'm actually hoping to do without that circuit, but building one anyway, just out of curiosity.
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Old 2nd April 2013, 12:04 PM   #25
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How did it turn out?

Thinking of building a very similar boombox to yours.. The soft clipping sounds good as well ! :-)

Do you think the monacors give enough HF response on their own, without any boost?

Thanks!
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Old 2nd April 2013, 04:33 PM   #26
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A bit too heavy for what I wanted. The Monacors do need companion tweeters.
I wish I'd used the 8 ohm woofers to help the amplifier operate more efficiently, and that way I could have used the TA2021 instead of the lackluster TA2020. I didn't need the ultrabass circuit because 1000u series to each of 4 ohm woofer did the "progressive current drive" trick just fine for facilitating good cabinet tuning. Could have used 470u (or nearby figure) with 8 ohm woofers. Oh well.

The soft clipper plan sort of failed due to variable voltage from the battery, but it is possible to use a transistor to amp the clip detect pin so that it can run an LED or two LDR, and a wide dynamic range LDR such as used for 50k version of lightspeed attenuator can do the job.

Much better way to do soft clip thing, is equip the woofers with passive crossover, and then bi-amp the tweeters with a different amp. Then the woofers don't emit clipping and the tweeters never clip anyway. Lots more useful power!
Well, I had picked the 4 ohm woofers because they can use half-size inductors in the crossover.

The solar panel thing turned out to be a huge inconvenience, because I ended up using a whole pack of 14v zener, each with its own series resistor and then one big ordinary diode series to that thing (14.7v total), this unit parallel with the solar panel for restraining the output of the solar panel to the safe range for both the amp and the battery. There's also an MBR735||1N5819 series to the solar panel's cable (to prevent battery discharge). So, output is actually 14.5vdc (or less), and some heat. I re-planned and put a big square plastic (not glass) 5W solar panel on back, and there was just barely enough room to fit a speaker back there with it. Sheer overkill in bright sun, but nearly insufficient on a cloudy day. It does stay fully charged if set in a windowsill, and it wouldn't have ever needed a power cord if only I had used 8 ohm speakers. Should have attached the solar panel with double-stick velcro because bi-polar speaker doesn't work so well with left channel pressed up against a window.

As far as using it on the bicycle rack, no way!! This turned out much too heavy and would cause a crash. So, actually, my plan failed.
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Old 2nd April 2013, 05:14 PM   #27
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Plan may have failed, but no project is ever a failure if you learn from it :-)

Shame about the soft clipping circuit, I was intrigued!

Very valid point about the dual amplifiers. I guess that using one TA2020 (with 2 of the 4R drivers), and one TA2024 with (one / two 8R softdomes) would work well.

Then you could drive the TA2020 into clipping a little to make that few dB more noise.. As bad practice as that is!
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Old 2nd April 2013, 05:18 PM   #28
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Best part is, TA2024 amplifiers are only £4.20 on ebay.. Delivered
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Old 3rd April 2013, 05:15 AM   #29
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Then you could drive the TA2020 into clipping a little to make that few dB more noise.. As bad practice as that is!
Yeah. But when it comes to the TA2020, it was definitely going to clip anyway, so that racket might as well be lost into the woofer crossover, and not go into the tweeters.
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