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Multi-Way Conventional loudspeakers with crossovers

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Old 12th August 2013, 12:07 PM   #1
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Default Build combining existing speakers

As a follow up to my initial post about building floorstanding speakers.....

I have a set of cheap floorstanders, the bass is taught but the cheap cabinets have a lot of resonance (12mm chipboard I think) or maybe 15mm. Cabin resonance is massive.

I have a pair of decent bookshelf speakers, not great but they do sound pretty good, midrange is much better, bass is deeper odly than the floorstanders at low levels.

Anyway I was thinking of building a new set from the three 8 inch bass drivers (a side) from the floorstanders and using the 6.5inch woofer from the bookshelf speaker as a mid and using the tweeter from the bookshelf also.



Is this a terrible idea (I could always reconnect the drivers back in place)???



I was thinking of just leaving the crossover from the mid to the tweeter in place, and taking the majority of the bass work from the mid to the three 8 inch speakers.


Some of the challenges I have: no experience building full range speakers, differing sensitivities, (90db bookshelf, 93db floorstanding speaker).


Was thinking of a crossover around 120hz, not really sure though. Additionally would I want a slope? I assume output will fall with frequency response. I'm not sure how it works but maybe I could have one bass driver starting from 120hz and the others starting from say 80 or something to get a smooth response.

I was targeting a response of around 40-50 hz as the lower limit, but I would want it to be flat until there. So I'd guess a ported design around 45hz ish.

Obviously I don't know theile small parameters, could buy measuring equipment?

Was thinking this might be a good projct because I can learn a lot without having to spend THAT much money (only cost is wood plus crossover). Was thinking I would from 25mm mdf to make the cabinet absolutely dead (would brace it aswell).

In the future I could possibly swap out the drivers for better parts? First thing would be the mid driver I'd guess, but that's another story. I wanted to build the cabinet to an exceptional standard, so everything wrong would be due to the drivers/crossover.

Thanks a lot for an advice. If it's generally better for me to build 2 way standmounter first I will do that.

Budget is roughly 150 for wood and crossover for this. (Flexible).
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Old 12th August 2013, 10:04 PM   #2
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First, specifically what is the brand and model of each speaker you plan to scavenge? That's the speakers not the driver, though if you have brand and model on the drivers, that would be of value too.

Next, any specifications you might have on those existing speakers would be helpful, especially the existing crossovers.

To accomplish this project, you are going to need to know the working range of the existing drivers. In a 3-way, likely there will be no problem with the 8" drivers. However, the 6.5 is going to be critical. It must reach up high enough in frequency to join with the tweeter. Assuming the crossover is not too low, you should have no problem with the tweeter.

Next, how do you plan to wire THREE 8" bass drivers to yield a reasonable final impedance?

THREE 8 ohms speakers in parallel are 2.67 ohms. THREE 8 ohm drivers in series are 24 ohms. Neither of these combinations is likely to work.

One 8 ohm speakers running full time within its frequency range, combined with TWO 8 ohm speaker in series for a Half-Way configuration would yield an final impedance at the low end of about 5.33 ohms, which might be workable. Above the Half-Way crossover, the impedance would be 8 ohms assuming you are using 8 ohm drivers.

Though there are other configurations possible. You could use the 6.5"+tweeter as the are now, then add two 8" in series as either a 3-way Low-Bass, or a 2.5-way Low Bass. In this case, you could leave the 6.5"+tweeter in the cabinet it is in now, and then build 2x8" into another cabinet. In the 2x8" you could have just the crossover necessary to blend the 2x8" with the 1x6.5" in which every configuration you choose.

As to cabinet material -

Chipboard = NO!

Particle Board, Plywood, MDF = Yes

3/4" (19mm) or thicker with braces. You could glue 3/4" to 1/2" (13mm) or 3/4" with 3/4" together for the front panels. I suppose even 3/4" with 1/4" or 3/8" for the front panels. For the sides and back, 3/4" (19mm) is probably sufficient, especially if you are on a budget.


Crossover -

Given the unusual configuration of drivers, I don't see any off the shelf crossover working. If you insist on using a generic crossover, you can build one yourself using on-line crossover calculators for the specific nominal impedances you have.

Balance or Different Sensitivity ratings -

Normally the low-bass driver sets the level of the speaker system. The midrange and tweeters are then attenuated to equal the level of the bass driver.

It depends on which configuration you choose, as to how this particular aspect of attenuation will be implemented.

For what it's worth.

Steve/bluewizard

Last edited by BlueWizard; 12th August 2013 at 10:13 PM.
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Old 13th August 2013, 10:00 AM   #3
AllenB is offline AllenB  Australia
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You could begin by stacking the two sets of boxes somehow and adding a crossover between them.

This would be better if you disconnect the higher drivers from the floorstander and change t he value of components at the woofers. You shouldn't need to open the bookshelves to cross them.
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Old 13th August 2013, 02:45 PM   #4
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Adding MDF panels internally to dampen resonances and use two lateral braces length wise will pass the knuckle wrap test by raising the resonant frequency much higher, a very good thing. Also can extend the length of the enclosure by taking four panels forming a box with the top and front missing and wrap this to the outside at the base of the other. Since this enclosure will be taller the added width will help with stability. Cut out a new baffle and place over the old. This can add a sense of styling and artful form to a design if angled front to back etc.

Have done this on many occasions when I just couldn't pass up some cheap boxes.
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Old 14th August 2013, 12:31 PM   #5
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speakers are athena b2, (6.5+dome tweeter) and valdus 500 (bad midrange + cheap, cheap tweeter)

the valdus speakers have a resistance of 4-8 ohms quoted, but I think it may be even worse than that.

I'm really unsure of how crossovers work, but I was thinking of just leaving the bookshelf speakers be (crossover wise) and splitting the signal so the bookshelf speakers receive everything above a certain frequency (say 150hz) and everything below goes to the bass drivers, would this lead to a crazy impendence? The amp is a nad c370 if that helps.
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Old 14th August 2013, 06:08 PM   #6
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Without an active crossover going that low passively is nearly impossible and quite expensive to try and then fail.
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Old 14th August 2013, 08:45 PM   #7
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Can we assume you mean the Wharfedale Valdus 500?

This speaker has 3 bass drivers, though I think they might be combined as 2x low-bass, and 1x mid-bass.

If the Athena B2 sound pretty good, then I would leave it as it is for the first round of design.

Use the bottom two drivers from the Valdus 500, and put them in a box like a short tower speaker. On top of that box set the 2-way bookshelf Athena, then work out the best low/mid crossover between the two speakers. Given that the Bookshelf is a full range speaker, I think the crossovers are somewhat wide open. Just off the top of my head, I would suggest 300hz or 500hz. Though several things need to be taken into consideration in the final decision.

That is at least proof of concept.

But you must determine how the existing Valdus are wired. I suspect it is wired as either a 2.5-way with the bottom two providing the n.5 aspect, or it is wired as a 3-way with the lower two drivers providing the low-bass. Specifically determine if the bottom two drivers are working together as one, and determine if they are wired in series or parallel.

Then determine the functional impedance of the drivers. This can be done by putting a small power resistor (5 ohms or 10 ohms) in series with the driver, running a 1khz tone through it, then quickly measuring the voltage across the resistor and the speaker. The ratio of the two voltages will help you determine the ratio of impedance, and that will give you a ballpark impedance on the driver.

In essence, with this conceptual design, you are adding the bass weight of 2x 8" bass drivers from the Valdus to the more sophisticated mids and highs of the Athena speakers.

Since you have a bass driver and tweeter left over, you could put them into a bookshelf speaker, and work out a good crossover for them.

Though I don't know the impedance of the Valdus bass drivers, I don't see a good situation where you can use all three drivers in one project.

I think what I have suggested here, gives you the best outcome with the least amount of modification and hassle.

Steve/bluewizard

Last edited by BlueWizard; 14th August 2013 at 08:59 PM.
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Old 14th August 2013, 09:18 PM   #8
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As to the two 8" bass drivers in their own box. If the impedance is in the neighborhood of 8 ohms, I think I would still wire them in series, though parallel would probably work.

If they are greater than 8 ohms, I have seen a few 12 ohm speakers, then I think it would definitely be best to wire them in parallel.

If they are 4 ohm or 6 ohms and if they are currently wired in series, then I would continue to wire them in series.

Two drivers in series outputs the equivalent of one driver on its own, but you gain in the areas of low distortion and higher power handling ability.

If, you do as I say, and if you can find the right balance, and if you like the result, then you can rebuild the speakers into a single larger cabinet, if you feel it is necessary.

The Valdus 500 are intended to be DJ speakers. They sacrifice a bit of sophistication in exchange for LOUD, HEAVY BASS, and HIGH POWER. For a DJ, that is probably a fair trade-off. But it falls a bit short for quality HiFi listening.

Just a thought.

Steve/bluewizard
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Old 14th August 2013, 09:51 PM   #9
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Quote:
Originally Posted by Greebster View Post
Adding MDF panels internally to dampen resonances and use two lateral braces length wise will pass the knuckle wrap test by raising the resonant frequency much higher, a very good thing.
Swotching from MDF to quality plywood will push panel resonances even higher, hopefully high enuff that they won't get excited.

dave
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Old 14th August 2013, 10:14 PM   #10
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Quote:
Originally Posted by planet10 View Post
Swotching from MDF to quality plywood will push panel resonances even higher, hopefully high enuff that they won't get excited.

dave
I like using " MDF so weight isn't too bad and then brace with hardwood ply, seems todo a pretty good job. Certainly helps those el cheapo boxes
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