Monacor SPH-60x in a tapered Transmission Line - diyAudio
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Old 4th January 2012, 01:15 PM   #1
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Default Monacor SPH-60x in a tapered Transmission Line

Greetings builders!

As the title suggests Im trying to build a pair of Tapered Transmission Line enclosures (So>Sl, narrower at the exit) with Monacor SPH-60x; however there is a problem there seems to be a little shortage of actual project on the internet. For some reason people seem to avoid this type of TL and prefer the expanding geometry even though the theory states that it is more advantageous (easy to get right, good frecv. response, small enclosure).
Ive seen a few project for the expanding type TL with the Monacor SPH-60x, not to mention BIBs and horns and bass-reflexes but I could only find one with the contracting geometry Im looking for to build, its in French and its here - http://www.baieaudio.com/ftp/tl_baie_audio.pdf .
The french project looks like this:
Tuning frequency 60hz (=Fs)
Sl/So=0.5, 300cm2150cm2
Length 123 cm
0.2 offset, and 2/3-3/4 stuffing, based on information from MJKings work, cabinet sizes not included.
At end of the document, the owner said that it was the best enclosure for the SPH-60x after building a bas reflex, TQWT and an open baffle - more bass, better defined, sweeter mids and richer highs too.
Not only that but I think I saw somewhere that a Qts of 0.40.5 (SPH60x has a Qts of 0.42) is the best for a tapered TL so the French commentator might be right, it is the best enclosure for this driver.
There might be other projects on the internet but in german, it seems to be a very popular driver on this forum - hifi-forum.de but I dont speak german so I dont know.

Im not planning to build the French project unless its really good, I would prefer something smaller than 27 liters, and tuned lower then Fs (60Hz), however I am interested in a good transient response and open midrange and I dont know how the cabinet design affects that. Other then that I still dont know how to get them in a column shape without that triangle look or the cartoonish expanding skyscraper.

So anybody had any experience with a Monacor SPH60x in a TL with contracting geometry?
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Old 4th January 2012, 07:33 PM   #2
hm is offline hm  Europe
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Hello,
i made a simple double horn with the Monacor,
but i dont prefer it for a direct driver the max. stroke is not very high,
my double horn make 89 dB 1 W 1 m, down to 35 Hz,
take a look kornett
with plan, feedback, measurement and simulations.
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Old 4th January 2012, 08:59 PM   #3
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I know about the Kornett, you posted before in 2008 about it in another SPH-60x thread, but it presents no interest for me, way too large and way to complicated; i like the simplicity of the fullrange concept, and i'm searching for a way to make o column looking enclosure for this loudspeaker that will produce pleasant musical midrange above all else.
Like I (actually didn't) said, i chose the tapering architecture for the fact that it is the smallest and has the flattest frequency response in the low end... it's better at midrange than the bass-reflex and that's why i chose the TL. Plus it may be the best suited enclosure for the given parameters.
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Old 5th January 2012, 11:24 PM   #4
GM is offline GM  United States
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Quote:
Originally Posted by krakatoa View Post
I would prefer something smaller than 27 liters, and tuned lower then Fs (60Hz), however I am interested in a good transient response and open midrange and I dont know how the cabinet design affects that.
Greets!

They used MJK's Classic TL Alignment Tables to design it, so it should perform well based on my experience with TQWTs.

I've no experience with this driver, but I've been told it's a drop-in replacement for the old Radio Shack 40-1354, which I have experience with in various TL alignments including TQWT, so shrinking it and lowering its Fp will only make for less bass/higher F3. Just doing a quick calculation, I would want about 40 L for a 42 Hz tuning.

GM
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Old 6th January 2012, 06:33 PM   #5
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I'm having the impression I haven't been understood.
I want a TL with tapering geometry, where the section narrows towards the open end, the one that is the smallest and shorter of the three geometries - tapered, straight and expanding. The expanding TL is called TQWT in the MJKing documents from quarter-wave.com not once but on numerous occasions, I don't even know if the tapered TL has any name or abbreviation.
I knew about the RS 40-1354 being a very similar driver, however the TQWT plans I've got from this forum where for a 36 liter enclosure so 42 l is more then allot and 42 hz is way to low for a driver with an fs probably above 60... or at least that's how i see things, but anyway i'm not interested in an expanding type TL. I don't know of any tapered TL with this driver.
When I said that i wanted to tune bellow 60 Hz (=fs) i was thinking about 50-53 Hz.
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Old 6th January 2012, 09:21 PM   #6
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No, you've been understood; I just suspect you've misunderstood GM. He (and I, having adopted it) usually uses the term TQWT in a traditional sense, i.e. for a reverse taper line, or the opposite of how it's commonly used today.

Either way, making a quick calculation of my own, it looks like he has a ~max flat alignment to 0.707Fs in mind, which is the lowest practical tuning in the majority of cases, probably with a high taper ratio (12:1 or more).

Last edited by Scottmoose; 6th January 2012 at 09:30 PM.
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Old 6th January 2012, 09:48 PM   #7
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Hi Krakatoa, i can not give you an answer, just some ideas.

The best thing to do is to work with MJKs spreadsheet and find a compromise between size, geometry and SPL (frequency).

My own designs always have some narrowing of the line. For ease of contruction the line can be divided into several straight sections with different (smaller) cross sections.

For this driver i would excpect the cabinet could be tuned to 50 Hz og maybe even 45. This can be simulated with Martin J Kings software, which i can reccomend.
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Old 7th January 2012, 01:20 AM   #8
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Ok I get it, 42 hz is the lowest of all alignment for SPH-60x with a box of 40 liters, but i don't want to go that low so I can get away with less volume. Anyway, i know from a document in german/english from somewhere on the internet that the lowest frequency for this driver is 50Hz, so I take that as a point of reference.

I would recommend MJ King's software too, but it's not in (my) the budget so I'll just press the "skip" button. I'm planning to make the best estimation based on numerous projects and info I can find on the internet, Hornresp data, the free excel alignment calculator from quarter-wave.com etc. and buid 1-3 versions to see which is best. The simulations aren't 100% percent accurate, and the final judge is how I feel about the way it sounds in the room I'm using them.
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Old 7th January 2012, 05:12 AM   #9
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Quote:
Originally Posted by Scottmoose View Post
No, you've been understood........
Correct, you 'read my mind'.

GM
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Old 7th January 2012, 05:24 AM   #10
GM is offline GM  United States
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Quote:
Originally Posted by krakatoa View Post
Ok I get it, 42 hz is the lowest of all alignment for SPH-60x with a box of 40 liters, but i don't want to go that low so I can get away with less volume. Anyway, i know from a document in german/english from somewhere on the internet that the lowest frequency for this driver is 50Hz, so I take that as a point of reference.
OK, I chose the lowest practical Fp since you weren't specific. At 50 Hz, 20 L should suffice, though as I noted earlier, less is always less, so F3 will be higher than in a larger cab; though as you note, it may not be enough to matter in-room, but not being you or having your room I can only recommend cabs large enough to allow as much tuning flexibility as practical.

Regardless, good luck with it and please let us know what you built.

GM
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