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Multi-Way Conventional loudspeakers with crossovers

simplicity vs fully active ?
simplicity vs fully active ?
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Old 2nd June 2011, 12:43 AM   #1
Designated Marksman is offline Designated Marksman  United States
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Default simplicity vs fully active ?

Hi all, this is my first post on diyaudio and actually my first post on a forum ever I think. Anyway, I am in need of some advice and figured this would be the place to come.
I am trying to decide if going fully active is really worth it. The reason I ask is because my system is rather simple.

My system: Amplifier: Virtue Audio Sensation 901, Source: Nad T585 or Xbox 360,
Speakers: My own design using HIVI M6N, Fostex F85K 3", Radio Shack dual radial horn and first order filters. Subwoofer: Powered Isobaric using Peerless 257h 10" and 240 watt Dayton amplifier. All drivers are in separate cabinet except full range and tweeter so that I can provide baffle compensation.

Now I know that my speaker design is somewhat flawed so I am looking for a tweeter to replace the old radio shack unit. When I designed the speakers I really didn't take into account beaming effects. I only looked at FR response and T-S parameters. The crossover points are rather high now but I can't remember exactly what they are. Maybe 1,100 and 12,500. I am thinking of getting a tweeter with a low fs and response so I can relieve the fostex of the highs using lower crossover points. This system does sound good when listening to rock, progressive, and almost anything done in the studio. Classical is ok except violins sound pretty bad especially solo violin.

Now I can either buy some expensive tweeters and new crossover components or I can go active with dsp. As I understand it going active would allow me to use a lower cost tweeter in this design, use steeper slopes and correct for the phase and time coherence.

It seems like going with dsp and active would have more distortion compared to Virtue Audio amplifier (power amplifier with alps pot) and speakers that have 2 inductors and 4 caps per channel. I did not use a noble, or any other type of filter on the speaker system.

What do you guy's think?
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Old 2nd June 2011, 02:43 AM   #2
planet10 is offline planet10  Canada
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simplicity vs fully active ?
You already have a REALLY good tweeter, the FF85K (also a hot commodity). XO it 300-400 Hz. If you go active (pr PLLXO) you can use an amp towards the current amp end of the spectrum.

I got good results with a simple series XO to a pair of CSS EL166. This one was inspirded by Tysen, a smaller 2-way with SDX7 and biamped using a PLLXO

Any XO below 200 Hz really should be active.

dave
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Old 2nd June 2011, 02:50 AM   #3
tinitus is offline tinitus  Europe
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I can recommend to build a ribbon super tweeter
I just use 3R3 series resistor, and 1uf or 1.5uf series cap
works quite well
I have pictures if interested
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Old 2nd June 2011, 06:45 AM   #4
Designated Marksman is offline Designated Marksman  United States
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Dave, The intent I had was to use the FF85k as a midrange, but the Radio Shack horns (leftover's from prevous system ) I am using now start dropping at a high frequency. That is why the crossover points are so high. They acctually might not be as high as I stated but pretty close. The reason I want to use it as a midrange only is to prevent beaming issues. Also, when playing violin the ff85k seems to have a strange resonance in the higher notes and sounds like crap to me. IF I stay passive I would like set Low Pass below 5.2 KHZ to the ff85k, because that is where it should start beaming. I would like to set high pass below 2,352hz to the ff85k to avoid beaming from the HIVI m6n midbass.

Considering a 1st order slope for both points how many octaves from the beaming points (lack of a better term) should I place the acctually crossover points?

In other words, would placing the crossover points at 2.6khz and 1176hz be enough attenuation (6db) to reduce beaming or is more attenuation required?

By the way I wouldn't actually choose those points because I would take unity gain in the midband into account as I did in the previous design.

Also I don't think I want to go line level passive, because I only have 1 amplifier ( Virtue Sensation). It is an integrated design with passive preamp (alps pot). I don't have a seperate preamp.

If I ever decide to go to active I would do it with something like this DEQX Products unless something came along that cost less and had the same sound quality and control. Do you think something like that and several lower cost amplifiers would have more distortion than just improving the speaker design and Virtue Sensation ( Virtue Audio. We make audio lovers audiophiles. Better sound by design. )that I have?

Tinitus, I am intrested in ribbon designs; hell I am interested in all speaker designs. It seems most of them do not have the ability to crossover as low as I may want with a 1st order crossover though. I would like to see pictures especially if it does what I need.
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Old 2nd June 2011, 07:29 AM   #5
planet10 is offline planet10  Canada
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simplicity vs fully active ?
Fully activemeans 1 amp per driver, for a 3-way you'd need 6 amplifier channels. Qith just 1 amp the DEQX becauses a VERY expensive & grossluy underused DSP EQ.

The miniDSP is more price compatible with the rest of your kit. You will still need one amp per driver.

FF85KeN (what i call it after i tweak it) is one of my favorite drivers.

Click the image to open in full size.

FF85K extends well past 20k (Fostex claims 32 k). It has the dispersion you would expect from a 3/4" tweeter (you have to think of this driver as a dome that size with a huge surround) that can go down to 300 Hz (at least). The top end does start climbing above 15k, and some of the bat ears around here comment on that. It does need to be toed in significantly (Tysen for instance is toed about 30 degrees).

I've not heard the virtue, supposedly one of the better Class D amps (all the people i've talked too that have had them certainly like them), but with all of the Class D amps i've had, any speaker that is very revealing in the top will shown up the high frequency hash they typically suffer from. Perhaps FF85 and your amp are just not a good match.

dave
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Old 3rd June 2011, 02:52 PM   #6
Designated Marksman is offline Designated Marksman  United States
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I knew that I would need 1 amplifier for each driver in a fully active system. It seems to me that there would be more distortion problems with a fully active system compared to what I have now. Plus it seems that it would cost much more to get the same or better performance even when considering the "Evil" crossover. Am I missing something?

I know that the FF85K is a good driver, but it seems to me that trying to get it to operate as a great tweeter is asking too much. When I look at the FR graph per Fostex it shows that the response starts dropping around 5khz off axis. Does this not indicate that at this point the driver starts beaming? Dave, are you suggesting that the FF85k resembles a concentric co-axial driver in operation except with a dome? I thought that Fostex used the aluminum dust cap only to extend the on axis frequency response. If it actually operates similar to a concentric radiator that is cool. Even if thinking of it as a 3/4" dome with a huge surround would it not still have the same polar characteristics of any other 3" cone speaker. I thought the cone and surround is supposed to be taken into account when dividing the speed of sound by the circumference of the driver to determine the frequency beaming starts to occur. Am I wrong?
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Old 3rd June 2011, 03:39 PM   #7
AllenB is offline AllenB  Australia
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So if it does beam above 5k, is that such a bad thing?
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Old 3rd June 2011, 07:07 PM   #8
planet10 is offline planet10  Canada
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simplicity vs fully active ?
Going active offers the potential to dramatically reduce distortion.

The 3/4" dome attached to the voice coil gives the FF85 the dispersion character of a waveguide loaded 3/4" dome tweeter.

When we 1st got these, we worried about how we would sell these at the price we'd need to to make them worthwhile. When we listened to them we realized that we had something that would go head-to-head with domes that cost more.

dave
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Old 3rd June 2011, 10:29 PM   #9
Designated Marksman is offline Designated Marksman  United States
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Hi Allen, I guess it is up to each speaker designer to decide if beaming in a speaker is a bad trait. I know some people support the idea to the extreme. They design systems that beam or have controlled directivity throughout as much of the audible frequency band as possible. I am open minded, but I think that it is beneficial to have all drivers within a system exhibit similar dispersion characteristics. In other words they should all have controlled directivity, or all minimal directivity. This is all anecdotal on my part however.

What is the difference between controlled directivity and beaming? Are they the same just different terms?

From what I understand, when a speaker "beams" it sounds like the signal is coming directly off of the diaphragm. When the speaker is not allowed to start beaming the signal (Instruments) sound like they are originating from the air, thus improving soundstage, imaging, and possibly timbre. Controlled directivity may or may not have that characteristic.

I can say that one of the biggest wow experiences I have had in audio was when I took 2 coaxial car speakers and put them in a single Styrofoam box. I placed the box in the floor with drivers pointing up. The drivers where run as a stereo pair. Obviously the Frequency Response sucked, but when you hear a single instrument sound as though it is originating at a precise point beyond the room boundaries it is awesome! I was probably 16 at the time and didn't have the money to try and use this concept in a proper hifi context. Now I am afraid to experiment with omni, because I've never listened to a high-end omni design and don't want to waste money on a failed experiment.
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Old 3rd June 2011, 11:47 PM   #10
Designated Marksman is offline Designated Marksman  United States
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Dave, thanks for the clarification on the ff85k. How do you think that it would stack up against these tweeters in the high frequencies?

Bohlender Graebener Neo8-PDR
ScanSpeak Discovery R2604/8320 1" Tweeter Ring Radiator
ScanSpeak Illuminator R3004/6020-00 1" Tweeter Small Ring Radiator
Vifa XT19TD00-04 3/4" Ring Radiator Tweeter
Fostex T250D Pure Magnesium Dome Tweeter
Eton 26HD1/A8 Symphony, Magnesium Dome Tweeter
Accuton C30-6-023 1.2" Ceramic Dome Tweeter

I would probablly cross them over to the fostex ff85k in a 3 way passive. Or possiblly a new 2-way design and use the fostex for something else. I know most of those tweeters are alot more expensive than the ff85k, but sometimes cost dosen't mean everything. The fostex unit may be alot better in the high frequencies than I am giving it credit.
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