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Old 7th October 2004, 05:55 PM   #21
MarkMcK is offline MarkMcK  United States
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Eric,

We are in complete agreement. In a conventional magnetic circuit, there is an assymetry in flux induced inductance front and back of the gap. Reducing the inductance in front of the gap seems an illogical direction to go if you want symmetrical conditions of operation.

To all,

Crossover revisions have been made and the new results are posted to the Web site. Preliminary listening results are encouraging but I really feel the need to pause here and do more extensive listening tests.

There may now be a gap in design updates while I am evaluating, but I am still feeling motivated to work on this project and there are still lots of refinements and design extensions to implement.

Good designing and good building,

Mark
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Old 11th October 2004, 02:27 PM   #22
MarkMcK is offline MarkMcK  United States
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Greetings All,

Well, the intensive listening tests were so successful they did not have to last very long. I took a pair of the modified buy out polypropylene woofers in .4 cubic foot sealed enclosures with the Vifa tweeter recessed and front loaded on the road this weekend and did listening sessions in various environments, with varied set ups, and associated equipment. The speakers were evaluated as stereo music loudspeakers and as main speakers in home theater set ups.

The general concensus was that the loudspeakers are neutral in sound quality with exceptional detail and imaging.

I specifically asked each evaluator for details about problems with the sound. Respondents indicated that the speakers were bass shy in the extreme bottom end and that they would benefit from a sub woofer. One respondent also stated that he thought there might be a slight problem with the extreme top end (a slight lacking of "edge") but that if there was a problem he adapted to it quickly. He stated that he could no longer hear whatever it was after the second track and couldn't hear whatever it was from then on.

I will add a photo of the loudspeakers in their unfinished MDF enclosures to my Web site very soon. I will also provide a description of the tweeter mounting. The acoustic performance of this combination is already posted to the Web site.

The one woofer, one tweeter combination is a stand alone success. That success allows me to then go on to the design and construction of an array knowing that the sound of the basic components will not be a problem. The design goals for the array are increased bass performance and higher linear range SPL while preserving the acoustical qualities of the simpler loudspeaker design.

I will also try different tweeters in the basic two-way design. Why mate a $28 tweeter to a $5 woofer if you don't have to?

I am also developing a copper plug design for the woofer. I am not doing this because it will cause any change in the performance, but just because it will look cool. If it does no harm, why not?

Good designing and good building,

Mark
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Old 26th October 2004, 03:13 PM   #23
MarkMcK is offline MarkMcK  United States
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Just an FYI update.

I have published crossovers for the 5.25 Poly woofer and two new tweeters.

You can find the information at:


http://madspeaker.com/Projects/proje...oneertweet.htm

and

http://madspeaker.com/Projects/proje...145TBtweet.htm

Good designing and good building,

Mark
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Old 26th October 2004, 08:59 PM   #24
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Quote:
Originally posted by MarkMcK
Just an FYI update.

I have published crossovers for the 5.25 Poly woofer and two new tweeters.

You can find the information at:


http://madspeaker.com/Projects/proje...oneertweet.htm

and

http://madspeaker.com/Projects/proje...145TBtweet.htm

Good designing and good building,

Mark
thanks
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Old 3rd November 2004, 03:14 PM   #25
MarkMcK is offline MarkMcK  United States
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Small diameter drivers appear to have a problem with low frequency acoustic reproduction independent of T/S characteristics. When Fs is low in frequency, the acoustic output begins to fall off at frequencies higher than predicted. A logical question sourced from this observation is whether multiple drivers closely spaced will acoustically couple and act as if they were a single driver larger in diameter.

By the experiment I devised and conducted, it appears the answer is yes. When closely spaced, small diameter drivers can be made to act as if they were larger in diameter and come closer to the low frequency acoustic reproduction predicted by T/S analysis.

It has not been easy to control for variables in the test execution. Without control of the variables other than acoustical coupling of drivers, experimental conclusions would be suspect. Still, with the construction of specialized test jigs and careful implementation, I believe that the results I post here accurately reflect the performance difference due to acoustical coupling of the two closely spaced drivers.

There is a measured increase in low frequency output such that the combined response comes closer to T/S derived expectations for this driver. In the case of this 5.25 inch advertised diameter driver with Fs in the mid 60s, its performance was already close and simply coupling two drivers achieves maximum response. Adding more drivers to the closely spaced array is unlikely to provide additional performance improvements.

Like all design, there are both positives and negatives to the technique of acoustically coupling multiple drivers. There are indications in these tests of both additional benefits and liabilities caused by using even two drivers in an array. Positively, there is smoothing of individual differences in driver performance. Negatively, there is evidence of accentuation of problems shared by both drivers, even at relatively low frequencies. This is particularly evident in the response just under 200 Hz where the bump and then dip in response is greater than either driver alone. With just two drivers, none of the negative consequences are critical. Whether that will hold true when using more than two drivers in an array will require further testing.

Good designing and good building,

Mark
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Old 15th February 2005, 08:07 PM   #26
MarkMcK is offline MarkMcK  United States
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Just wanted to post an update about early designs using this driver. First, PE still has them listed on their Web page as in stock.

Second, I have quite a few hours now listening to the 299-145 and the Vifa tweeter. I still like them very very much. In the simple sealed enclosure I used with the Vifa tweeter you can push them right up against a wall and not lose any imaging capability. They are great for small rooms. They are great for bookshelf speakers.

And now the real reason for my posting here. I have been playing around in the full-range forum recently. I have been trying to work with the Fostex FE126 and 127 in a full-range system. The price of the Foxtexs is similar to what you would pay for a 299-145 and a Vifa tweeter combination. The enclosure for the 299-145 and Vifa is about the same internal volume and no more difficult to make. The sound quality is not similar at all. I do not know how to place a numerical value on relative sound quality, but the 299-145 Vifa combination is easily somewhere between 10 to 100 times better than the FE126 or 127. Unlike the Fostex, this speaker has something close to real bass. It does not need BSC. It is clear and detailed across the entire spectrum. It does not sound compressed at any frequency.

We have an excellent library where I live. The last couple of days I have been listening to an Eric Clapton collection. It is so easy to hear the changes as recording capabilities improved and different studios were used. The early Yardbird stuff is very distorted. By the late 1960s and Cream, the vocals have become very good. I think maybe better than they will be later. One of the amazing changes was how much natural ambience was present on vocals during the late 60s. By the late 70s, vocals have really dried.

And it is not just vocals. On the Cream selections, I can just as easily and clearly hear Jack Bruce's bass lines as Clapton's lead.

If you want a small speaker to use as a reference, then this is it. If you want an inexpensive loudspeaker to just listen to for the sheer joy of listening to music, then this is it. If you want to bring the price down 10 USD, then use the Tang Band tweeter. Almost as good.

Good designing and good building,

Mark
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Old 15th February 2005, 11:36 PM   #27
gl is offline gl  United States
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Hi Mark,

Thank you for all the great work with the 299-145 driver. I bought 28 of them a couple of months ago with the intention of building some cheapo arrays to play with. I also made sure the PE person on the phone associated your name with the order.

I have three questions:

1) A 7/8" dowel makes for a very loose fit plug. There's quite a gap. Is this O.K?

2) Are you still planning on publishing the DIY copper phase plug design?

and

3) How about a dimple mod kit to replace the glue bands? It would be a lower mass solution. PE seems to have an endless supply of these drivers so there could be a good demand for mod kits.

Thanks again.

Graeme
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Old 20th March 2005, 02:20 AM   #28
MtnBob is offline MtnBob  United States
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Smile Thanks and some ??

My thanks too, Mark, for all your work with these. I just got 14 of these (used the link on your website). I am doing a HT setup and thinking of using 2 per speaker, maybe dipole or whatever, I'm making a bunch of protos to check out.
But to my questions - you say the phase plugs should be 19mm long. I have pulled the dust caps off 4 and the pole piece to end of vc is 20 mm on each one. All the phase plugs I've ever seen project past the vc. So I'm wondering if 19mm is right or if my samples are different - ?
The other question concerns the xo and tweeter. It looks like the crossover is around 14000 Hz. That's about the top of my range (too much Hendrix and Stones back in the 60s) so I'm wondering if I even need a tweeter. If so, I'm looking at the PE 279-234 - another buyout. I know I prefer textile domes, but like you said, a tweeter that costs 5 times as much as the woofer seems like over kill.
I'm looking forward to your next steps with this driver.
Thanks again for all of us who didn't get the engineer gene and can't afford all that testing equipment.
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Old 21st March 2005, 11:12 PM   #29
MarkMcK is offline MarkMcK  United States
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An offering of copper plugs and a Whisper Kit for the cone are both possible. While PE has not run out of the drivers, they will eventually. Didn't seem to make too much sense to develop a commerical product for a closeout. Dimpling the cones is also much simpler. Doesn't take many dimples. While I have both, most of my listening is done to the glue ring set. Removing the mass of the glue rings makes no improvement in performance. Other factors are dominating by this point in the modification. I will think about a Whisper Kit for the drivers over the next couple of weeks. I will get back to you.

There may also be one more modification in the works for this driver. I have been doing some basic research into surrounds and I have been having some interesting results. That information may apply to this driver. Time will tell (when I find the time to apply it to this driver).

As to other questions. . . The larger the diameter the cone, the less important is the phase plug. It really just fills the void in the center of the voice coil. If it is not filled, the air mass in it resonates and interferes with the desired output. The plug can be just slightly recessed or slightly long. Neither is a problem to the ear or to the test equipment. Again with diameter. A little off is no problem. A lot off is. 95% of the improvement is getting rid of the dust cap and then displacing the air filling the voice coil tube.

Also, you might try listening to the modified driver without a tweeter. The woofer alone will handle all musical fundamentals. The tweeter really just adds a little air. Synthesized effects do benefit from the extra half octave. I can't really testify to how hearing loss may impact one's ability to hear the things a tweeter does above 13 or 14 kHz.

In sum, compared to all the other closeouts deals posted to this forum in the past, this one is the real deal.

Good designing and good building,

Mark
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Old 25th March 2005, 03:56 AM   #30
MtnBob is offline MtnBob  United States
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Mark, thanks for clearing that up. I'm going to try pairs of these in several different baffle/box configurations - MMs, I guess.

gl, if you really like the copper look, you might try the local hardware store. Get some end caps for 3/4" copper tubing. I picked up one to check it out and it measured 25 mm OD x 23 mm H. Buff them up and spray with clear lacquer. Don't know if being hollow might cause problems, guess you could stuff it with something.

The ski lift closes the 27th Might get more done though

MB
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