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Old 12th June 2002, 04:17 AM   #1
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Default Reasonable low frequency cutoff

I am looking to build a pair of highly efficient speakers (97 db 1w/1m) or greater. So many of my questions lately have been about this and I appreciate everyones help. Now I have pretty much determined that to get a reasonable sized enclosure and use affordable drivers ($100 USD or less) I will have tune the enclosure so the f3 is in the 50-55 range.

My question is how will this sound for both music and home theater. I will be using it with a subwoofer, but it seems to me that maybe this f3 is too high. I find that the subwoofer I own, a velodyne cht100 is somewhat rumbly and wouldn't necassarily blend well with the rest of the sound comming out of these speakers that I am going to build. Just in my opinion it seems that rumbly bass is good when it is real low, but it is not good when it is still in the range of say a bass guitar or low brass instrument. So how do I deal with this. Do I just need to invest a lot more in a better subwoofer, should I give up on the high efficiency speakers and go with something less efficient with wider range, or shoudl I just make huge enclosures and try to find a way to fit them in my room.

Please anyone who has any thoughts speak up.

Thanks,
Mark
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Old 12th June 2002, 06:35 AM   #2
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Well, I should point out that most PA cabinets have a cutoff in the 55-60 Hz region. The size of the cabinets are usually about 3 cu ft for a 15 inch speaker. 12 inch speakers will of course require smaller cabinets.

People make their living playing music with these cabinets, so obviously they cannot be super deficient in bass with that cutoff. Whether listening at an event, for which a 55 Hz cutoff is adequate, will fill the bill when you are home alone and listening to music might be another story.

I should point out that Peerless has a new set of PA speakers coming out. I don't know what they cost, but Peerless generally includes a lot features found on more expensive speakers on their reasonably priced models. I think it is the SLS PA series located here:
www.peerless.dk

Whatever model you decide, you might try downloading BoxModel, a freeware DOS program. When you fill in the Thiele-Small parameters for the speaker you are running in it, it gives you the calculated sensitivity. If you look at response charts, you find the calculated sensitivity is almost always right on. You would be surprised how much the calculated sensitivity, especially with high SPL rated speakers, varies from the real number!

Most PA speakers are rated 2 or 3 dB higher than the calculated sensitivity. One Eminence model was rated 5 dB better than what it is! (In fairness, Eminence is a pretty good brand, and most of the time the variance is in the 2 or 3 dB range-about the same as most other PA speakers).

Oh, by the way, when shopping for high SPL speakers: remember that a 4 ohm speaker will look 3 dB more sensitive than it really is when driven by 2.83 volts. That is because at 2.83 volts, a 4 ohm speaker will draw two watts while the 8 ohm speaker will only draw one! Hence, a 4 ohm speaker will get a 3 dB better rating when it is driven at 2.83 volts for SPL measurement-which most of them are.
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Old 12th June 2002, 02:54 PM   #3
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Thanks for your reply, now I have another related question. At what point does sound become directional? I have heard many people say that the ear is unable to determine where very low frequencies are originating from. So what is the frequency range where this begins to happen. I am sure it is diffrent for every person, but I am just looking for an approximate number.

Mark
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Old 12th June 2002, 03:15 PM   #4
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well about 40Hz if you want it to be convincing.... most conmercial sub crossovers are 80Hz but it's easy to pick the location change if you are a critical listener.
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Old 12th June 2002, 06:56 PM   #5
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Also it depend on how much high frequency resonances the sub is putting out. If you can avboid having much of them, it is harder to locate. Some drivers, alighnments, crosovers,are better than others-don't ask, I don't know! A good argument for a steep filter, but maybe that has other problems.
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Old 12th June 2002, 10:14 PM   #6
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Allright that helps, I wanted someone to confirm what I had found with my subwoofer, anything above about 45 hz I can start to hear where the sound is coming from. So I guess I need to continue work on a highly efficient speaker that can get down to 40 or 45 hz. Since anything above that will be directional it will have to be coming from right place in the room.

Another related question for anyone. I have been able to design a few speakers that shoudl provide decent bass extension down to 45 hz and are on the high end of efficiency around 94 hz. However these all use one driver for the low/mid section. I woudl like to use 2 drivers in parallel, for the benefits of reduced distortion and higher efficiency. What are everyones opinions on that, is it worth the effort or shoudl I look at designs that are just using one driver?

Mark
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