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Old 6th April 2004, 12:42 PM   #1
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Default 2-way or 2.5 way for me?

I've been planning on building a 2.5 way Usher system for a while, but the more I think about it, the more I wonder if there's really any advantage to the 2.5 way. I'm not getting any extra extention, and since my f3 is going to be somewhere around 48-50hz, I'll be running a sub. If I've got a sub to take care of the sub-50hz region, is there still really any benefit to the 2.5 way vs. a traditional 2 way with a single woofer? All I can think of is that the added sensitivity will require less padding on the tweeter, but I'm not sure how much that matters. Does a heavily padded tweeter lose some dynamics compared to an unpadded tweeter? Other than that, power handling and maximum output seem to be the only advantages to the 2.5 way.
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Old 6th April 2004, 01:13 PM   #2
rabbitz is offline rabbitz  Australia
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The 0.5 woofer is good for BSC up to the BS frequency, BS/F3=115/baffle width in metres. The sub will not help you there. And yes, it does make quite a difference.

Actually using the 0.5 woofer for BSC only made no difference the the tweeter padding as it only brought those nasty BS frequencies up to where they should be, so the SPL of the speaker remained the same.
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Old 6th April 2004, 01:50 PM   #3
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On a 2-way, doesn't the BSC attenuate the woofer above the desired frequency in order to give a smoother response? If so, it seems that the tweeter would have to be attenuated accordingly.

Overall, I'm trying to find out if there's a legitimate difference in sound between a 2.5 way and a 2-way using the same drivers with a crossover that has the BSC factored in.
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Old 6th April 2004, 02:09 PM   #4
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The BSC I'm talking about is not in the crossover but using the 0.5 woofer to provide the compensation by placing it at the back of the enclosure in line with the front woofer.

I went this way as I didn't want to do it in the crossover which would attenuate the speaker too much for me (roughly 82dB via BSC in xo vs 88dB via BSC with 0.5 woofer) and is a pain in series xo anyway. My original crossover for the 2-way remained the same and the added 0.5 woofer was rolled off using a 1st order crossover. The SPL of the speaker was exactly the same as before but the BS was gone.

If it's got BSC in the crossover, you don't need the 0.5 woofer for this purpose.
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Old 6th April 2004, 02:41 PM   #5
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I understand the function of the .5 woofer in BSC. What I am trying to do is get feedback in terms of how it sounds compared to using the same drivers in a conventional 2-way that employs BSC in the crossover instead of using the .5 woofer.

I understand how both methods work. I'm trying to find out how the sound compares.

Like you said, using BSC in a 2-way reduces the sensitivity dramatically. That means that I would need to pad the tweeter considerably, and I'm questioning the effect that will have on the sound quality of the tweeter.
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Old 6th April 2004, 03:02 PM   #6
sreten is offline sreten  United Kingdom
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Yes, a 2.5 way tweeter will run 6dB higher
sensitivity than in the 2 way case.

Its hard to say which arrangement will sound "best".

If your not a volume freak then a stand mounted sealed
2 way is ideal for use with (ideally stereo) subwoofer(s).

If you like it loud then a sealed 2.5way will be 6dB louder, (if your
amplifier drives 4 ohm easily) which is a significant difference, also
your subwoofer(s) will need 6dB more volume capability.

You'd expect the 2.5 way to sound cleaner at the
same level as the 2 way due to lower distortion.

Its really a question of do you need the extra 6dB level ?

I'd regard differences in treble quality as marginal.

Edit : another option of course is line level BSC.

sreten.
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Old 6th April 2004, 03:13 PM   #7
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It's always been a very blurred line between "need" and "want" for me. I live in an apartment with the landlord's bedroom directly below my living room, so 95% of my listening is done at very low levels.

But sometimes the Metallica fan in me likes it a whole lot louder.
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Old 6th April 2004, 04:29 PM   #8
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I would say that a two way with BSC would "techinically" sound better because your not having to worry about the second woofer adding to the midrange at a different location to the fuller range mid/bass, thus maybe improving driver integration and imaging somewhat. However I have never done a 2.5 way so cant comment on how this does affect the sound.

It also depends how loud is loud to you. A sealed box overdamped to improve power handling would still allow for good SLP, and because your going to use a sub the less bass produced by this alignment is negligable.

I have just finished a speaker which is two way using 8" vifa midbass and it has full 6dB BSC it goes loud enough to say the least. This too is in an overdamped with a Q of about 1.1 sealed box. The driver though does have a stock sens of 91dB so the speaker is thus 85dB, I dont think you'll get 91 out of a single usher. Also price is something to consider 2.5way costs more then a 2 way.

If you think you will want the higher SPL and are competent at designing xovers and dont mind spending the money then there isnt really any reason not to go with the 2.5 way.

But denis murphy has designed a two way using usher drivers so if you dont have success with your xover you could always build his.
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Old 6th April 2004, 04:55 PM   #9
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Dennis Murphy's crossover is one of my main reasons for considering the 2-way. The 2.5 way that I'm considering would use the crossover that D'Appolito designed for the Usher CP-737. My own crossover skills are quite rudamentary right now, and until I'm better I am going to stick with proven designs.
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Old 6th April 2004, 07:10 PM   #10
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Aha so your choice is sort of d'aps 2.5 way or murphys 2 way.

Both are renowned designers so I would say either would be great.

There is nothing bad about a 2.5 way, nor is there anything bad about a 2 way. Simply you get more SPL out of a 2.5 way and lower distortion because of the higher sensativity the drivers dont have to work as hard for a given SPL.

If you are prepared to spend the money for making the 2.5way then id choose that option. If you dont like the 2.5 way, which is unlikely, then you can always make the dennis version albeit 2way, if they use the same drivers.
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