Does A beyma woofer and a Tang band tweeter make an excellent 2 way system? - Page 2 - AVS Forum
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post #31 of 47 Old 04-04-2013, 10:57 AM
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Quote:
Originally Posted by LINEARX View Post

,
" it has been years since I've used a non-compression driver in a design. "
`
I've looked at many compression drivers anticipating a possible 2 way project sometime in the future.
Many of the compression drivers have poor performance data compared to domes but a few show excellent stats but were the more expensive ones.
If I remember right they were in the $100 dollar range and up.
Which particular compression drivers have you had experience with?

You can get a DNA-350 for about $60. It is very similar to the well regarded DE250. The SEOS-12 is $28 if you can use a 12" wide horn. They also have the EOS-6 horn that is $11, but the DNA-205 CD that goes with it doesn't seem to be for sale separately. You can see it in some of the kits. I think the EOS-6 with DNA-205 was around $50-60. I don't think you can get a quality CD and horn that can play low enough for a 10" woofer for less than that.

If you moved to an 8" driver you would have more options. Something like this build is awesome value in a smallish package: http://www.diysoundgroup.com/forum/index.php?topic=53.0
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post #32 of 47 Old 04-09-2013, 11:49 AM - Thread Starter
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That doesn't seem too difficult, replace the dome tweeter with a CD (compression driver) and a waveguide, modify the crossover, and wahlah I've got the ultimate.
In reading all the latest SEOS stuff, it seems you end up with a 75 to 90 degree zone of coverage with a CD and waveguide
and narrower as the Hz goes up, but they don't call that "beaming". They don't talk about harmonic distortion either.
What I'll do is, I'll finish my projects with the dome tweeters THEN do another project with the same woofer but add the CD and waveguides.
Like everyone ALWAYS ends up doing whether the drivers have been "measured" or not, I'll do a listening test and comparison of the two
versions and decide which one I like best. It's what DIYers do.
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post #33 of 47 Old 04-09-2013, 01:06 PM
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Sounds good linear. This "beaming" won't make your speakers sound "bad" per se. It is just a configuration I would avoid generally because it is tough to design around.

The SEOS-15 and SEOS-12 are nominally 90degree horizontal horns. They are also 1" devices similar to the 1" dome and when they become acoustically large at HF they do beam which you can see. The advantage is that they ARE beaming from ~1khz+. The problem with an acoustically small driver on a baffle (like your 1") dome is that it isn't "beaming"...and you are trying to mate it to a woofer which IS beaming in that range. That discontinuity creates an unevenness in the reflected sound which is a vitally important part of sound presentation in a small room.

You might also notice that some tweaking of the on-axis frequency response might be needed just above the crossover range. This is commonly called a BBC dip where the designer drops a few dB across a range to counter the excess off-axis energy of a 1" tweeter. This on-axis dip is an unfortunate compromise IMO because it doesn't allow for an even on-axis response which is important too.

This is actually related to why most near-field monitors don't do very well in the a Hifi setting where there are early reflections. The near-field monitor which typically uses a 1" dome is built to have an exceptionally flat on-axis response without much concern for the off-axis response because it is both distant and absorbed. When you place them in a more normal home setting, the waistbanded directivity gives too much total energy (reflected + direct) above crossover which wasn't a problem in the near-field studio setting.
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post #34 of 47 Old 04-09-2013, 03:27 PM - Thread Starter
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`Thanks Coctostan. I noted there were compromises that had to be made especially in the shaping of the waveguides.
I also noted that you were an active participant in the wave guide formula permutations. Good work.
The listening area can be made to augment the speaker system no doubt. I hadn't done much to control reverb/ reflection/ absorption/etc., until I mated these two drivers and was able to notice a difference on the RTA. Part of the problem was a 6ft glass patio door along one wall.
After one trip to "Big Lots" for a king sized velvet bed quilt and some clever cutting, stitching, and joinery, I ended up with a dark wine colored curtain the likes of which you'd only see on-stage in a New York Broadway theater. I got much WAF and approval with THAT move.
This project is going to take a while. It's all good though. I have no time limit on any of my projects.
As long as it takes to get it right, is how long it takes.
`
Oh, when you were testing the various CDs were you able to HEAR much difference between the:
1) B&C DE 250
2) Denovo DNA-360
3) Dayton D250P
4) Selenium D220Ti
`
The above units vary in price from $128 to $75 to $49. I'm wondering if there's $79 dollars worth of audio quality difference from top to bottom?
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post #35 of 47 Old 04-09-2013, 05:44 PM
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You are definitely going down a good path to learning. With that glass wall you will reap even more benefits from controlling directivity tightly. You might try toeing your speakers in to mitigate those strong early reflections.

This the Denovo is a clone of the DE250 and the differences are undectectable. I believe the Dayton is also a DE250 clone. The D220ti is entirely different. It uses a titanium diaphragm which IMO should be avoided. Titanium has harsh breakup and simply doesn't sound as good as a plastic (lots of names are used like Mylar, PETP, etc...all good).

If your budget the DNA-205 is a really good option. It is chaper because it cannot play as low as the DNA-360 but it should be good crossing to a 10" on a SEOS-12. Here is a kit that you could emulate using these parts except with your Beyma 10": http://www.diysoundgroup.com/waveguide-speaker-kits/fusion-series-kits/fusion10-pure-kit.html
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post #36 of 47 Old 04-09-2013, 07:39 PM
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Quote:
Originally Posted by coctostan View Post


If your budget the DNA-205 is a really good option. It is chaper because it cannot play as low as the DNA-360 but it should be good crossing to a 10" on a SEOS-12. Here is a kit that you could emulate using these parts except with your Beyma 10": http://www.diysoundgroup.com/waveguide-speaker-kits/fusion-series-kits/fusion10-pure-kit.html

How does the correlation between CD and woofer work? The lower the CD can go the larger diameter woofer can be? trying to get a handle on the general characteristics of loudspeaker design.
Thanks
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post #37 of 47 Old 04-09-2013, 08:50 PM - Thread Starter
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Quote:
Originally Posted by cogeng182 View Post

How does the correlation between CD and woofer work?
`
We've been discussing how a woofer and a tweeter should "match in dispersion" at the point of crossover. Coctostan has demonstrated how important it is to have the woofer's crossover be below the frequency where the dispersion narrows. For a 10" woofer it's about 75 degrees at 1700Hz. A compression driver with waveguide can crossover easily at that frequency and still play up to 15,000Hz and above. That's a good match point for this 10" woofer and some particular compression drivers..
When either driver enters it's narrow dispersion pattern it's called "beaming" and beaming creates an undesirable audio distortion anomaly in the field of dispersion.
A compression driver can play lower than a cone tweeter, some down below 1000Hz. With that capability you could cross-over to a larger 12-15 inch woofer for a more powerful but very accurate 2 way speaker system.
`
My project started with a 10" woofer and a cone tweeter. I had intended to crossover @2300Hz but am retuning for a much lower crossover in the 1500-1700Hz range to avoid playing the woofer into its "beaming" frequency and match it to any suitable compression driver and waveguide.
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post #38 of 47 Old 04-10-2013, 06:13 AM
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LINEARX, thanks for the detailed reply, makes it much easier for people to learn the fundamentals.

So it appears that when going from a smaller to larger woofer, the frequency at which the dispersion narrows decreases. Would that be correct?
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post #39 of 47 Old 04-10-2013, 07:50 AM
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Quote:
Originally Posted by cogeng182 View Post

LINEARX, thanks for the detailed reply, makes it much easier for people to learn the fundamentals.

So it appears that when going from a smaller to larger woofer, the frequency at which the dispersion narrows decreases. Would that be correct?

That is generally correct. The shape of the cone will also impact that but you can get a good ballpark. The rule of thumb is that a driver will narrow to -6db @ ~90deg when its diameter is equal to 1 wavelength (actual cone diameter between surrounds...not nominal...a 15" woofer is usually about 13.5" dia). For instance, a 1000hz wave is ~13.5" therefore a typical 15" woofer with an actual 13.5" diameter cone would narrow to -6db @ 90deg around 1000hz.

The best practice is to measure the off-axis response of each driver on its baffle. The baffle also plays a role in directivity.
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post #40 of 47 Old 04-10-2013, 02:12 PM - Thread Starter
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In researching the change in cross-over for the Tang Band tweeter to a lower Hz, I notice that my intended cross-over @1500Hz moves the tweeter impedance onto the instep of the impedance spike.
The tweeter impedance goes from 6.6ohms at 2300Hz to 8ohms at 1500Hz.
I don't know yet if that will affect the voicing of the tweeter but it has a definite impact on the cross-over components.
The question arises, should a tweeter have an impedance compensation network/zobel? I've never seen anyone use a zobel on a tweeter.
Or should I just go ahead and reconfigure the cross-over components using 8ohms instead of 6.6ohms?
Or, doesn't it matter?
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post #41 of 47 Old 04-10-2013, 02:53 PM
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Crossing that tweeter so low and using generic crossover calculators is a recipe for failure.

Mike
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post #42 of 47 Old 04-10-2013, 07:56 PM
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Quote:
Originally Posted by LINEARX View Post

The question arises, should a tweeter have an impedance compensation network/zobel? I've never seen anyone use a zobel on a tweeter.
A zobel of the usual type, a series R and C shunt with the driver will make little difference.

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Originally Posted by Face2 View Post

Crossing that tweeter so low and using generic crossover calculators is a recipe for failure.
Agreed. Apart from the dispersion discussion above, you need to consider the non linear distortion of the tweeter operated that low. Excursion increases 4x for every octave lower and tweeter have very little linear excursion.

To design a passive xover for this pair of drivers, you need the FRD and ZRD curves and to use PCD or some other simulator to help optimise it.
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post #43 of 47 Old 04-10-2013, 10:40 PM - Thread Starter
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By using a "generic" cross-over design on the Tang band tweeter, what failures are likely to happen?
The Tang Band factory suggested a cross-over no lower than 1800Hz.
What am I getting myself into if I cross at 1500Hz?
`
A9X-308, do you have a recommendation for a simulator besides PCD?
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post #44 of 47 Old 04-11-2013, 01:04 AM
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Originally Posted by LINEARX View Post

A9X-308, do you have a recommendation for a simulator besides PCD?
No, I gave up passive xovers a long time ago.
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post #45 of 47 Old 04-11-2013, 03:59 AM
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Quote:
Originally Posted by A9X-308 View Post

A zobel of the usual type, a series R and C shunt with the driver will make little difference.
Agreed. Apart from the dispersion discussion above, you need to consider the non linear distortion of the tweeter operated that low. Excursion increases 4x for every octave lower and tweeter have very little linear excursion.

To design a passive xover for this pair of drivers, you need the FRD and ZRD curves and to use PCD or some other simulator to help optimise it.

What are FRD and ZRD curves?

Also, how do you figure out what a low frequency wavelength is? I am trying to understand the math that Coctostan used when determining the -6db at ~90 where the woofer starts to narrow.
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post #46 of 47 Old 04-11-2013, 04:47 AM
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Quote:
Originally Posted by Martycool007 View Post

What are FRD and ZRD curves?

Also, how do you figure out what a low frequency wavelength is? I am trying to understand the math that Coctostan used when determining the -6db at ~90 where the woofer starts to narrow.

Marty - the FRD and ZRD files are frequency response (including phase) and driver impedance, respectively. They contain data points for each frequency level that would plug into a tool like PCD to help simulate system response based on crossover changes.

Typically by measuring both on and off-axis response of a woofer, one can determine a proper crossover point target.
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post #47 of 47 Old 04-11-2013, 05:18 AM
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Quote:
Originally Posted by A9X-308 View Post

A zobel of the usual type, a series R and C shunt with the driver will make little difference.
Agreed. Apart from the dispersion discussion above, you need to consider the non linear distortion of the tweeter operated that low. Excursion increases 4x for every octave lower and tweeter have very little linear excursion.

To design a passive xover for this pair of drivers, you need the FRD and ZRD curves and to use PCD or some other simulator to help optimise it.

I've seen others use this tweeter that low with good distortion results. That is not an issue.

I agree that using generic crossover calculators and not measuring the frequency response does make this an effort in futility. A $90 Dayton mic, free REW software, and free PCD are all Linearx needs (I think he already has a WT2 for impedance). From there he can simulate the crossover and get an accurate frequency response. Generic crossover calculators might not even be in the ballpark to be honest.
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