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Old 1st May 2006, 08:55 PM   #11
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Now that looks very impressive indeed. How did you model the Onken in MathCad? Or am I asking for trade secrets there? (my apologies if that's the case).

Bigger cabinets are better? Now, who was it who has taught me that principle over the course of a certain other thread... ;-) Cheers Greg. You've opened my eyes to quite a bit.

Regards
Scott
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Old 2nd May 2006, 01:23 AM   #12
GM is offline GM  United States
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Greets!

You can't accurately model one in any program AFAIK, but assuming the specs are reasonably accurate it's close enough IMO. Anyway, nothing special, just run the numbers in an Onken calculator and use the PORTED WS. Since the vents are distributed along its height, just position the vent in the middle and calculate its radius based on their total area using whatever length the calculator says, then if you don't like it, change it to suit as I did with this one, hence the 'hybrid' moniker.

Here's the n = 6.34 Onken alignment I started with:

GM
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File Type: jpg supravox 215rtf64 n = 6.34 onken.jpg (25.1 KB, 382 views)
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Old 2nd May 2006, 10:32 AM   #13
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Got you. Thanks Greg
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Old 7th May 2006, 06:25 PM   #14
fred76 is offline fred76  Philippines
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Default 8" Vs. 6.5"



Okay, so there's no going around it if I want to get the most out of the RTF64 re: Needs cabs w/ large footprint. Maybe it would be do-able if the drivers can be mounted offset on the front baffle??? If the mounting is not centered on a wide baffle at least there will be some distance between the L/R drivers in my narrow room; less tendency to "shout". I'm just not sure how the offset will affect the response...

I'm more used to 8" drivers, but I won't discount 6.5" widerange/wideband drivers... Generally speaking, what are the pros and cons of 8" Vs. 6.5" if both are high performance with similar efficiency??? I know that larger drivers "move more air", but will it be significant if driver sizes are close? Plus let's say if the difference in Fs is very minimal between the drivers, ~4Hz higher for the 6.5"...

The real advantage with 6.5"rs (usually has much lower Vas) in this case, is the smaller footprint for enclosures. So a BIB would be an obvious candidate.

Thanks!

fred
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Old 7th May 2006, 10:17 PM   #15
GM is offline GM  United States
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Default Re: 8" Vs. 6.5"

Greets!

You can offset it some, ~0.618:1 max, but if depth isn't a major issue, a MLTL is your best bet for making it narrower.

Well, all things being equal, it takes a little less than two 6.5" drivers to match an 8" in area and the higher the Fs, the higher Qts must be to tune it low, so you're going in the wrong direction for convering the LF BW. Really, the easiest thing to do is sim some to compare.

GM
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Old 8th May 2006, 11:37 AM   #16
fred76 is offline fred76  Philippines
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Hi GM,

Yes, enclosure depth is not a major issue. I could go with MLTL with the RTF64. Now the only prob is I don't have any engineering or higher math background, so doing MathCad sim/models etc. is out of my league. No way really to compare or come up with a design of my own. Any help on this dept would be greatly appreciated...

I linked a TL-like design for the RTF n my #1 post. It uses a Helmoltz resonator:

http://www.bd-design.nl/contents/en-..._ISOMETRIC.pdf
http://www.bd-design.nl/contents/en-...GULAR_18mm.pdf
http://www.bd-design.nl/contents/en-...GULAR_18mm.pdf
What do you think?

I would be using low powered tube (se and pp) amplification, so I guess I wouldn't need any passive Eq network with these fairly linear drivers (at least on paper).

Thanks for the reply!

regards,
fred
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Old 8th May 2006, 04:41 PM   #17
GM is offline GM  United States
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Greets!

I've yet to read a review of this cab design by anyone whose opinion I trust and can't model it, so don't have a clue beyond the fact that ignoring the resonator, it will otherwise need considerable stuffing to be relatively smooth just like any end loaded pipe. Then again, with low power you may need to trade the smoothness of the MLTL for the rippling gain of an unstuffed pipe. I assume the resonator is designed to ~fill in the 3rd harmonic's dip, so it may be OK. Only one way to know for sure though!

With SE power, I would need to know the amp's output impedance or its DF, not its nominal tap rating(s).

GM
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Old 9th May 2006, 08:22 PM   #18
fred76 is offline fred76  Philippines
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Hi GM,

The TL+resonator design needs heavy polyfill stuffing for the chamber part, where in the middle of that chamber there is a partition panel having 5 holes in it (purposely designed). The top part of the resonator hole is also covered with stuffing as illustrated in the .pdf top section plans. ~1.5" thick damping material on the bottom of the enclosure is also needed. And that's about it as far as stuffing goes, but hopefully it's a good compromise between smoothness and gain for my app... For a pipe like this I don't know if enclosure volume would still play a big role as I noticed that the RTF has a relatively higher Vas compared to other 8" offerings from Fostex, etc... Will try it first with cheap ply. There's only one person I read about who tried this enclosure with the RTF Bicone version, but there are no real impressions on how they sounded.

The zero nfb SE amp has an output impedance of 1.6 Ohms.

Thanks!

fred
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Old 9th May 2006, 10:05 PM   #19
GM is offline GM  United States
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Greets!

A pipe is just a vent, so it's response is very Vb dependent until you reach a point of diminishing returns.

Which brand/model is this? I've never seen a nfb SE amp with an OPI this low.

GM
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Old 10th May 2006, 10:50 AM   #20
fred76 is offline fred76  Philippines
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Hi GM,

It's kit amp by sun audio (with lots of mods) from Japan. It's a basic SE amp really, although I guess most off the shelf SE amps from the from the west use lower primary impedance on the OPT for slightly higher power, hence ~2 to 4 Ohms DF on average.

I read an article from this webpage a few years ago on how to calc DF for tube amps (SE, PP, OTL).

http://www.transcendentsound.com/amp..._impedance.htm

Basically just get the plate impedance of the output tube... Calculate the impedance ratio between pri & secondary of OPT (primary / secondary tap). Then the plate impedance of output tube is divided by the ratio of primary and secondary, then you get the DF value...

Perhaps it's too general a calc for the outputstage only, and not taking other factors into consideration???

I guess all is well If the pipe's Vb is "okay" when used with the RTF64 driver.

Thanks for the reply!

fred
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