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Old 12th December 2004, 02:55 PM   #191
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Default Re: Re: Mono-pole vs Bi-pole

Quote:
Originally posted by planet10

GM -- you need to shake the brain-washing...

For a tube amp with proper taps you will get the 3 dB of extra sensitivity whether you connect in series or parallel... 6 dB is an artifact of MJK assumming everyone is using a SS amp with high damping (1/2 of the 6 dB gain from parallel is from assumming that the SS amp doubles its power into 4 ohms and -3 dB in the case of the series connection comes from the SS amp putting out half as much power into 16 ohms. (ie the 6 dB difference between parallel & series is purely that into 4 ohms the amp is providing 2 W & into 16 ohms a 1/2 W -- this is a completely false assumption if you have a tube amp)

dave

I hope I am not being brain washed! If so, here is your turn!

Ok, I think I got most of your comments.

What do you mean by a "tube amp with proper taps"?

To summarize what you have said, if one uses a tube amp to drive this bi-pole, the sensitivity will be about 93dB regardless of weather it is wired series or parallel.

Cheers,
Gio.
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Old 12th December 2004, 04:45 PM   #192
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Quote:
The bi-pole port radius should be SQRT(2 * 0.75) = 1.225". I have attached a MJK mathCAD simmulation of the larger port.
Yes, that's the correct formula. Something strikes me odd about using a 2.5" port though. The modeling shows little difference other than slightly lower port velocity and slightly higher box tuning.
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Old 12th December 2004, 07:01 PM   #193
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When Tim specified the bi-pole he gave a 2" port... for the monopole i divided the area in half, it came out to 1.4x something diameter so i just rounded it to 1.5" since that is a standrad size in NA... it may need to be a tad longer because of that approximation.

Until someone actually builds them, the port size is really just a close approximation.

dave
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Old 12th December 2004, 07:03 PM   #194
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speaking of monopole... here is the up-to-date round-top folded monopole....

dave
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File Type: gif diya-frref-roundtop-mono.gif (17.2 KB, 3445 views)
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Old 12th December 2004, 07:09 PM   #195
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Default Re: Re: Re: Mono-pole vs Bi-pole

Quote:
Originally posted by gmilitano
What do you mean by a "tube amp with proper taps"?

To summarize what you have said, if one uses a tube amp to drive this bi-pole, the sensitivity will be about 93dB regardless of weather it is wired series or parallel.

Tube amps have taps on there output transformers, typically at least 4 & 8 ohm, or 8 & 16 ohm (or 5 & 10 ohm on some older German OPTs). The idea is to connect the speaker to the one that is closest to your speaker. Now if your speaker doesn't correspond to the right tap (ie a 16 ohm speaker on an 8 ohm tap) you will get a little less power (in the case of the example shown usually a little less distortion also), but in the end the power output differences between taps is usually not all that great, and the best way to determine which one to use is the one that sounds best.

Yes... real sensitivity of 2 speakers in parallel or series will be 3 dB greater than a single one. And tube amps (and most SS amps for that matter) are happier with higher impedance (it is just that the SS amp typically puts out less maximum power -- ie it has a relatively more robust power supply just by changing speaker impedance)

dave
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Old 13th December 2004, 01:13 AM   #196
Optical is offline Optical  New Zealand
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I have two questions:

First, is the purpose of this reference speaker simply for doing A/B test with other speakers. Or to provide a flat full range response?
Personally i would prefer a reference speaker with a flat response to compare others to, rather than a speaker modelled to sound 'good'..

Secondly, does anyone know where to get Fostex drivers in New Zealand?

Thanks guys, keep up the good work
Matt
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Old 13th December 2004, 03:47 AM   #197
jeremyg is offline jeremyg  United States
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Quote:
Originally posted by planet10
speaking of monopole... here is the up-to-date round-top folded monopole....

dave

I think i may give these a go next weekend...got some time on my hand...now this is basically my first DIY home audio project. Sence it looks "cute" according the the boss....i got the approval..so with that...i had one question...would anyone have any recommendations on stuffing...as in how much and where exactly.

thank you
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Old 13th December 2004, 04:38 AM   #198
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Quote:
Originally posted by Optical
I have two questions:

First, is the purpose of this reference speaker simply for doing A/B test with other speakers. Or to provide a flat full range response?
Personally i would prefer a reference speaker with a flat response to compare others to, rather than a speaker modelled to sound 'good'..

Secondly, does anyone know where to get Fostex drivers in New Zealand?

Thanks guys, keep up the good work
Matt
I believe the suggested designs in this thread provide an adequate standard to base future builds against when taking price, performance and construction requirements into consideration.
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Old 13th December 2004, 04:40 AM   #199
MarkMcK is offline MarkMcK  United States
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Greetings full rangers,

I would like to follow up on Matt's (optical) first question. How are you using the word reference?

By the dictionary definition of the word "reference," you don't have to have flat response. Still, it ought to be a known quantity or quality.

This is, however, different from the way "reference" has been used in ad copy to refer to certain loudspeakers. There the reference to reference has implied superior performance (flatness or whatever).

This brings me to the driver selected by the vote of I believe seven people. One of the voters made the comment about a preference for shielded if the shielded and unshielded versions had the same performance. I have not tested the FE126E or the FE127E. I can only comment on what is listed in the spec sheets. From the spec sheets, however, the drivers are not the same. The motors (magnets and BL) are significantly different. The 126 uses a 440 gram ferrite magnet, the 127 uses a 100 gram ferrite magnet. The 126 has a specified BL of 5.92, the 127 is only 4.14. The 126 is rated at 93 db and the 127 is rated at 91 db.

The published frequency responses of the two drivers are also different. The 126 appears to be up as much as 3 or 4 db between 500 and 7 kHz above the 2 db lesser sensitivity of the 127.

In addition, even Fostex's rather smoothed response graphs show two drivers that do not meet rated response bandwidth even with a plus or minus five db range. For example, both drivers' output is falling fast above 15 to 17 kHz. The two drivers are also significantly different in output between 500 and 7 kHz.

As I already stated, I do not have access to either the 126 or the 127. I do have access to the FE103E. I do know how an engineering quality frequency response test of the FE103E compares with the Fostex published response of the FE103E. While I will not know for certain unless I test, I have little reason to expect that Fostex changed their test set up just for the 126 and 127 drivers. (As an aside, I love the way Fostex changes the vertical sizes of their published graphs. Makes it so much easier to compare frequency response differences from driver to driver.)

Now, I have a one-time proposition for the thread and the thread contributor who owns a company that sells the FE127E. If you will donate a driver, I will test the driver and publish the response in this thread. In addition, I will build the monopole TL box and test the box and the driver.

I do have some experience testing TL designs. I published a couple of reviews of Fried's TL loudspeakers during the 1980s. And I still have the data in a digital format that I can access to use as a TL reference. I also have a reference four-inch driver that I can compare to the 127 in the exact same test set up.

Good designing and good building,

Mark
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Old 13th December 2004, 07:20 AM   #200
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Quote:
Originally posted by Optical
... does anyone know where to get Fostex drivers in New Zealand?

Hi Matt,
Syntec in Auckland is the Fostex agent. Ph 263 9885. I spoke to Conrad when I phoned recently with an enquiry about drivers.
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