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Old 6th August 2001, 01:45 AM   #1
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I was wondering what and acceptable difference in the db rating of different drivers. I would like to purchase:
- Peerless 10" Woofer 831724 rated at 89.7 db
- Peerless 6.5" Woffer 850122 rated at 86.6 db

The main question I have is how will the 3 db difference in ratings would affect the sound from the speaker? I was told by a gentleman at a local electronics repair shop that the drivers should be within 2-3 db of each other. Any suggestions on other drivers would be great.

I would like to keep the price of the drivers to under $50 each because I live in Nova Scotia and the exchange rates aren't the greatest.

Also any recommendations on tweeters to match would be great. I have been thinking about the Vifa D27TG-35 or the Focal TC90Tdx, but this isn't for definite.

Thanks in advanced.

Jeremy Hopkins

[Edited by baby_huey0 on 08-05-2001 at 09:00 PM]
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Old 6th August 2001, 02:10 AM   #2
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Personally, I'd add some attenuation to the more efficient speaker, because you will definitly notice a 3db difference. It will sound fine at first, but once corrected it will sound twice as good due to the eveness of the sound. I had the same problem in my own DIY setup, and left the 3db difference untouched for 2 months after building them, and then added an L-pad. I did mine with a 4ohm and an 8 ohm resistor (one in series and one in parallel). It truely opened up the sound, also allowed louder listening... Do not overlook this, it will be noticable!
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Old 6th August 2001, 04:08 AM   #3
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Jeremy,
It is difficult to impossible to find drivers with matching efficiency specifications. Getting too obsessed with matching the efficiency is futile anyway, because the crossover (presumed to be passive in this case, yes?) will have a bit of loss here and there, thus unbalancing the drivers.
Matching the relative levels of the drivers should always be handled in the crossover (whether active or passive). It goes with the territory.
In theory, you can match drivers of any efficiency to one another--the caveat being that you will be pulling the more efficient driver down to the level of the lesser one. This will make the finished speaker somewhat less efficient, overall, as power losses in resistors in the crossover don't do anything but provide small amounts of heat. But that doesn't mean you can't or shouldn't do it.

Grey
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Old 6th August 2001, 11:53 AM   #4
Geoff is offline Geoff  United Kingdom
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Jeremy

As Grey has said, it is most unlikely that you will find a combination of drive units that does not require some attenuation in the crossover. However, try to ensure that the mid-range and tweeter are more efficient than the bass unit so that the attenuation is required on these units. This will reduce the power loss in the attenuator as there is less energy in the higher frequency signals.

Also, additional resistance in the bass driver circuit will affect the enclosure alignment. You will not know the exact series resistance required for the attenuator until the enclosures have been built and tested, but you cannot design the optimum enclosure until you know the value of this resistance. Chickens and eggs come to mind. To prevent this problem, restrict any attenuation to the mid-range unit and tweeter.

Geoff
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Old 6th August 2001, 05:41 PM   #5
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Would the 850488, rated at 89.2, be better? The reason I want to keep the 10" driver is because it is onsale at madisound at the moment, so if I purchase them there that will be my choice. If not I might use the 850136( all drivers from Peerless), its an 8" driver rated at 89.7.

Could anyone help me in desigining the crossover. As you can see I haven't chosen the drivers for definite yet, but could you at least point out a website to goto, or even recommend a type of crossover. I am still reading through the Loudspeaker Design cookbook, and haven't hit the crossover section yet. Any help would be great.

Thanks

Jeremy Hopkins

[Edited by baby_huey0 on 08-06-2001 at 12:58 PM]
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Old 6th August 2001, 07:02 PM   #6
Geoff is offline Geoff  United Kingdom
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Jeremy

I suggest you keep to your 89+dB woofer but try to find a more efficient mid-range driver (90+dB). The higher the overall efficiency, the less amplifier power is needed.

Rod Elliott has design information for both active and passive crossovers at his Audio Pages:

http://www.sound.au.com

Geoff
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Old 6th August 2001, 10:33 PM   #7
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Jeremy,
Something related to what Geoff said--a series resistance on the woofer will drop your damping factor through the floor.
I'm a big fan of active crossovers. Passive crossovers are a pain in the rump. The downside is that active crossovers imply multiple amps, which means more money (but are also an excuse to fiddle...).

Grey
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Old 7th August 2001, 02:37 AM   #8
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I would just love to make an active crossover for at least the subwoofer section. Since I will be running these off of an old Technics integrated amp, active is out of the question for now. If all goes well I should be able to get a pre/power combo next summer. The only good thing about the amp is that I can run it in four channels instead of just two.

Thanks to everyone for their advice and help.

Jeremy Hopkins
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Old 8th August 2001, 11:30 PM   #9
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Default Crossovers

WellI got everything chosen(for now at least). I'll be buying all Peerless drivers: Tweeter 811815, Mid 850488, Woofer 850136.

I think the sensitivities match in theory: 92, 89.2, and 89.7 (respectively). I don't really know what is ment by attenuation, any help?(I have a small idea). How do I do it and what do I need.

Because of cost reasons I am probably going to use a first order three-way crossover(maybe a second order). I want to cross over at 2kHz/200Hz. I did some preliminary calculations, I just wanted to post here to see if I actually did them all right.
C1=0.01445mf
C2=0.1537mf
L1=0.413mH
L2=4.6964mH
I hope that these are at least somewhat correct. If they are completely wrong then the first 2 years of Electrical Engineering has done nothing, but I'm not even in it anymore(but I'm still in engineering).

One other question, if I can't find an exact or very close match to a value should I go above or below that value?

Cheers

Jeremy Hopkins

[Edited by baby_huey0 on 08-08-2001 at 09:14 PM]
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