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Old 19th October 2001, 11:06 PM   #1
jteef is offline jteef  United States
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First of all, I listen to a whole lot of electronica with a lot of material in the lower octaves.

I would love to stick with a 2 way setup, but everything I have tried to model thus far doesn't seem like it will work very well. i.e. woofers needing to be lowpassed at 800-1200hz vs tweeters needing to be high passed at 1.5-2khz. A substantial gap. I realize I am not going to get an F3 of 30hz in a 2 way sealed cabinet like I want so 50-55hz might be more reasonable. I am hesitant to go ported now because the music i listen to is relatively fast and these will likely be delegated to a surround sound role when I have the opportunity to build or buy what I want for my mains.

One thing I have considered is adding a 1-3 ohm resistor in series with the voice coil of the midwoofer to raise QES and shift the F3 down 10-20hz. I know this will kill the efficiency, and increase box volume, but I should have plenty of power. What are the other effects this might have on the sound ?

I would like to keep each channel all in one cabinet no taller than about 4 feet high and 12-15" square on the bottom. Going to a 3 way design, or even an MTM will likely push me over budget. I might consider a pair of bookshelf's and a separate sub, but then money and power start to become the determining factors.

I have 120 watts x 2 into 8 ohms, and around 190x2 into 4 ohms (until i can upgrade the transformer) to work with now, and I will probably build another amp with some the national semiconductor overture series IC's for 40 or 50 more watts per channel available for biamping.

Any ideas or designs you have had success with given my parameters?

Thanks a lot

jt

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Old 20th October 2001, 02:37 AM   #2
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A) Is that 500 bucks going to include the cost of the enclosure itself-the wood, glue, etc.-or the cost of the drivers and crossover?

B) Why do you think that acoustic suspension crosses over higher than ported designs? If anything, a ported design suppresses cone motion, (but NOT output), through it's greatest range-the lowest octave. This makes for less intermodulation distortion through the midrange. Anyway, I don't think you are going to get a two way that goes down to 30 Hz, ported or acoustic suspension.

Assuming that the 500 bucks is for drivers and crossover only, I think your parameters for 30 Hz through 20,000 Hz and up for 500 bucks can be met. It would be a 3 way, though.

[Edited by kelticwizard on 10-19-2001 at 10:11 PM]
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Old 20th October 2001, 04:37 AM   #3
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Might want to consider these, completed they'll end up right in your budget.

http://www.adireaudio.com/cd/kit281.htm

Numerous builders have been very pleased with the performance. If you want to ask question of builders post on the DIY section of HomeTheaterTalk forum. They had many builders due to a group buy a while back
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Old 20th October 2001, 04:47 AM   #4
jteef is offline jteef  United States
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If i implied that i thought acoustic suspension crossed over higher than ported, i didn't mean it. I mean to say that of the drivers i have modeled so far, they all needed to be crossed over fairly low. I understand I wont see 30hz in a sealed 2 way design, so I am willing to give up some low end for now. If I can get down to 50-55, I will be satisfied.

I've looked so far at the focal 7k4411, scan speak 18w/8545 and 18w8546, and peerless 850122. I guess I could go 3 way if i used cheaper drivers. But then I am into another amp for the mids, or expensive passive xovers.

$500 for drivers, electronic crossovers and 2 sheets of mdf. So figure about $420-450 for the drivers. Exact figures aren't of great concern, but I would rather stay closer to $500 than $600.

jt
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Old 20th October 2001, 05:16 AM   #5
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The ScanSpeaks have approx 50% more Xmax and much lower Fs (28Hz), so they're a better choice than the Focals. But like most 6.5" drivers they are limited as to how loud they can play in a 2-way MT config. In a MTM config they would be extremely good, but $$$$

You might find Tony Gee's Andromeda of some interest.



[Edited by ThomasW on 10-20-2001 at 08:42 AM]
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Old 20th October 2001, 06:20 AM   #6
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One woofer I would recommend would be the Peerless 831727, a 10 1/2" model. This used to be one of the best subwoofers you can buy. The super-pushers have taken over, but at + or - 9 mm, this one still isn't that far behind today's new subwoofers.

Available http://www.madisound.com for $54. The crossover to the midrange-both lowpass for subwoofer and highpass for mids-together should cost about $25 or less. This is for a 200 Hz crossover You want to spend no more than $225 a side. So far, you have only spent $90.

With that big woofer expense out of the way, you should still be able to afford an MTM configuration, crossing over to the Peerless 10 1/2 inchers at 200 Hz or so.

The MTM configuration using 6 1/2 inchers is nice, but consider intermodualtion distortion. The highest notes on the piano are about 5,000 Hz. If you cross over at 2,000 Hz, (about an octave below), then all but the top octave on the piano will be played by the same woofers you expect to pump out bass at 45 Hz or so. There has to be muddiness.

At 2 cu ft., the Peerless 10 1/2" is 3 dB down at 30 Hz. At 3 cubic feet, it is 3 dB down at 25. These volumes and prices are well within your parameters.

Remember, two mids require only one crossover. Two 5" or 6 1/2" mids, a 1" tweeter and crossover should be possible for $135-the remainder of your $225 per side budget.

You should be able to have the focus of an MTM plus the bass of a real subwoofer for your price.

This is just a suggestion.

[Edited by kelticwizard on 10-20-2001 at 01:42 AM]
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Old 20th October 2001, 06:56 AM   #7
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The Peerless is an interesting budget woofer, but will most likely have problems functioning as a 'subwoofer' given the fact it starts to roll-off pretty quickly below 75Hz. Also one should consider poly cone breakup modes and the fairly small 39mm voice coil. It's always best to use drivers in the FR range where they are most pistonic/linear=flattest response. This avoids most distortion based problems

Click the image to open in full size.

[Edited by ThomasW on 10-20-2001 at 02:03 AM]
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Old 20th October 2001, 12:55 PM   #8
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Well this is definitely a thread I can go with. For the last 3 months I have been designing a set of speakers. In your budget you mentioned on about $50 for crossovers. As I quickly found out, this is not enough for a 3way speaker. The price of my speakers have doubled from $500 to $1000(Canadian) very easily.

You also mentioned using Focal or Scan-Speak. These drivers are very expensive, I know they are less in the US but they still aren't cheap. Something from Seas, Audax, or Peerless migth be a little cheaper and still give you great sound. The Seas or Audaxs were recommended by Tony Gee to me. I'm using all Seas drivers: 25TAC/D, P17REX, and P21REX. It comes out to about $570cdn, which is about half that American probably(between taxes, exchange etc.)

I think in the end I would agree with ThomasW on the Kit281s. They would probably give you enough low end to satisfy your needs. Also with the money you would save under $500 you could save it to buy a Shiva, then all your bass needs would be satisfied.


[Edited by baby_huey0 on 10-20-2001 at 07:59 AM]
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Old 20th October 2001, 01:27 PM   #9
Super is offline Super  United States
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Another project I've seen for 500 bucks can be found at http://www.speakerbuilder.net

Take a look at the Veritas speaker. It uses a ribbon tweeter, dome midrange, and has dual 10 inch drivers in a sealed cabinet. It could be what you're looking for.
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Old 20th October 2001, 04:41 PM   #10
Wizard of Kelts
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In reference to the Peerless 10 1/2 inch subwoofer, Thomas W. wrote:

"will most likely have problems functioning as a 'subwoofer' given the fact it starts to roll-off pretty quickly below 75Hz."

Thomas, the chart you showed is one of the Peerless subwoofer in free air!

If you took the free air response of the Shiva, it would have almost exactly the same response curve as the Peerless. It will roll off gradually down to 21 Hz, where it will be about 8 dB down, (the Peerless will be 9 dB).

Bass reflex and even sealed boxes require woofers with a low Q to start with. That means at the free air resonance, they will be several decibels down. Any quality subwoofer designed to go into a reflex or sealed enclosure will be the same way. When placed in a box, the low frequency range raises up.

I have used these woofers, and I am more than satisfied. As far as the voice coil goes, yes it is only 1.5 inches diameter, but it is a 4 layer wound on a fairly long voice coil, (1 inch). The Peerless is rated at 220 watts music power.

Poly cone breakup? Well, I haven't measured it, but most breakup starts in the higher ranges. Cross over at 200 Hz, and it probably won't be much of a problem.

The Peerless SWR 260 is an older subwoofer, but it was ahead of it's time. It has a shorting ring to prevent voice coil "suck in", (a condition where as the speaker approaches the tuned box frequency, it travels from the midpoint to the end of it's voice coil and and clips the wave form in one direction). American subwoofer manufacturers virtually ignored the problem, European manufacturers dealt with it only on extremely expensive models. The SWR 260 dealt with it at a resonable price.

This speaker may or may not be the way for jteef to go. It has been superseded by other subwoofers now, but at much greater cost. At $54 each, I think it is a good place to look when building a "keep it under budget" system.

[Edited by kelticwizard on 10-20-2001 at 11:46 AM]
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