Help with a project

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Help with a project

Postby malium » Sat Aug 28, 2010 11:10 pm

First, hello to all diy-ers!

I really need some help with my future project. The project is a bit "off", but I hope here are some good souls willing to help.

I would like to build a pair of speakers that would give me solid performance for music listening, and for watching the movies.
Cause of the room size where they will be paced (5 x 4m), and because of the furniture setup, and overall looks of the room, I would like to have a stereo system, and not the 5.1 system.
From the same reason, I would like them to be strong on the bass area, for the movie effects (and by this to avoid using a separate woofer), but I also want to enjoy in quality music as well, so I do not want them to be boomy.

Problem one:


Now, my crazy "interior design idea", is to build speakers in the wall corner. To build a wooden front baffle, and "attach" it to a wall corner. Doing this would make a triangle shaped cabinet, but I would make a narrow wooden rear end that would flatten a 90°angle of the walls. So in the end, the speaker box would be shaped as a trapezoid, built from wooden front baffle with drivers, and eased concrete wall corner. This speaker boxes should be as shallow as possible, but I would have plenty space in the height, cause they would be made from floor to ceiling (about 2,5m).
My question regarding this is, is this even possible? What should I expect from boxes made like this? Should I treat the part of the walls inside of speaker somehow?

Problem two:

I already have some drivers laying around that I would like to use for this project.
I have four new pieces of JAMO 10" woofers with this specs (all specs that I have, they are OEM, so there is almost no info on them):

Impedance: 4 ohms
Vas: 173,9 l
Fs: 33,7 Hz
Qms: 7,53
Qes: 0,37
Qts: 0,35


I also have four new pieces of this TVM midwoofers:

http://www.winboxsimu.de/Galerie/ARN-188-05-8.pdf

And in the end, I have four new pieces of:

http://cgi.ebay.com/NEW-1-Silk-Dome-Twe ... dZViewItem


I would like to use this drivers in this project, from the simple reason - I already have them.
I am searching for an advice on how to combine them, to use them all or some, to build separate cabinets inside the speaker box for some of the drivers, crossover ideas, any other ideas or comments...

Problem three:

Well, the third question is, what to use to run them after they are built? I do not have any experience on this as I was on computer 5.1 systems till now... So I do not know much on how much power would this speakers need to run fine. I am not chasing any extra high volumes, doe. I have one plate amp from Soundworks 510d, rated at 500W (150W for sub, 70W x 5 for satellites), I do not know if I can use it anyhow, or I should buy some stereo amp, receiver or something... Please advice.

After all

I know this is a big amount of questions, and that the project is a bit off, but I would like to finish it with some of Your help. I would make a project log, and share this project with You folks.


Many, many thanks in advance, :?

Malium
malium
 
Posts: 5
Joined: Sat Aug 28, 2010 9:51 pm

Re: Help with a project

Postby llung » Mon Aug 30, 2010 7:35 pm

malium wrote:First, hello to all diy-ers!

I really need some help with my future project. The project is a bit "off", but I hope here are some good souls willing to help.

I would like to build a pair of speakers that would give me solid performance for music listening, and for watching the movies.
Cause of the room size where they will be paced (5 x 4m), and because of the furniture setup, and overall looks of the room, I would like to have a stereo system, and not the 5.1 system.
From the same reason, I would like them to be strong on the bass area, for the movie effects (and by this to avoid using a separate woofer), but I also want to enjoy in quality music as well, so I do not want them to be boomy.


This is a very reasonable thing to do. You can easily enjoy both music and movies without a center channel or subwoofers as long as you have full-range (or "large" in HT setup speak) speakers. But for full surround sound, you'll need rear speakers - something to keep in mind because if you decide to add them later, you'll want to use the same drivers you're using on the front speakers to maintain the same sound.

You can also go "small" on the front speakers and use one or more subwoofer for the overall system. Most AV receivers have bass management and can re-route the bass to a single sub just as easily as they can to "large" front speakers.


Problem one:


Now, my crazy "interior design idea", is to build speakers in the wall corner. To build a wooden front baffle, and "attach" it to a wall corner. Doing this would make a triangle shaped cabinet, but I would make a narrow wooden rear end that would flatten a 90°angle of the walls. So in the end, the speaker box would be shaped as a trapezoid, built from wooden front baffle with drivers, and eased concrete wall corner. This speaker boxes should be as shallow as possible, but I would have plenty space in the height, cause they would be made from floor to ceiling (about 2,5m).
My question regarding this is, is this even possible? What should I expect from boxes made like this? Should I treat the part of the walls inside of speaker somehow?


Are you implying that the corner walls of your room will be part of the speaker cabinet? or that the speaker cabinets will be placed at the corners of the room? I would not do the former; the latter is fine. Using the existing walls as part of the cab is begging for trouble as walls are never flat nor form true right angles; the walls will resonate (if wallboard); air will leak; among all sorts of other problems.

Problem two:

I already have some drivers laying around that I would like to use for this project.
I have four new pieces of JAMO 10" woofers with this specs (all specs that I have, they are OEM, so there is almost no info on them):

Impedance: 4 ohms
Vas: 173,9 l
Fs: 33,7 Hz
Qms: 7,53
Qes: 0,37
Qts: 0,35


I also have four new pieces of this TVM midwoofers:

http://www.winboxsimu.de/Galerie/ARN-188-05-8.pdf

And in the end, I have four new pieces of:

http://cgi.ebay.com/NEW-1-Silk-Dome-Twe ... dZViewItem


I would like to use this drivers in this project, from the simple reason - I already have them.
I am searching for an advice on how to combine them, to use them all or some, to build separate cabinets inside the speaker box for some of the drivers, crossover ideas, any other ideas or comments...


Sorry, don't know anything firsthand about these drivers. Looking at the specs - note that the JAMO are 4 ohms but the mid and tweeters are 8 ohm nominal so keep that in mind when designing your crossover. Also the midwoofers are less efficient (rated 85 dB, 1w/1m) than the tweeters (89.6 dB) so you've got work to do there. Xmax on the mid is 7mm (footnote 5 is not shown) but I'm guessing that's peak to peak and not one way. With a rated "noise" power of 60 watts I wonder how loud this driver will go. Luckily your room is not that big; but it's up to you to decide how loud you want this to play.

Problem three:

Well, the third question is, what to use to run them after they are built? I do not have any experience on this as I was on computer 5.1 systems till now... So I do not know much on how much power would this speakers need to run fine. I am not chasing any extra high volumes, doe. I have one plate amp from Soundworks 510d, rated at 500W (150W for sub, 70W x 5 for satellites), I do not know if I can use it anyhow, or I should buy some stereo amp, receiver or something... Please advice.


Take the specs on the Cambridge Soundworks system with a grain of salt as far as power goes. That said, are you happy with the volume it puts out? Can the 510d be used as just an amp by simply disconnecting those little cube speakers and sub?

If you don't or can't use the 510D, then all you really need is a simple AV receiver. You can get a decent, older, Yamaha / Denon / HK / Marantz / Onkyo on eBay for around $150 or less (depends on power, brand, shipping cost, etc.) It'll cost even less if you buy a Pioneer, Technics, Sony or other mass market brand. You'll have to do some research for individual models (flaws, features, etc) so that may take some time to iron out. Get one with the same kind of features you want (Dolby Digital or DTS for instance if you ever plan on adding rear surround speakers). Of course, you can go with a standard 2 channel receiver for cheap if sound processing is not important but you will likely lose the ability to steer your bass. My point is that since you're not gunning for fancy features, you have a wide range of choice to play with on the used market. Just make sure the unit can interface with whatever your source player is.

Another option is to get just amps, not a receiver, since your computer can do all the sound processing for you. This may be cheaper or more expensive, depending on what you buy. If you go with your original plan of just 2 channels, and you stick to 2 full-range speakers, all you need is a 2 channel amp (or receiver used as an amp). Lots of options here.

As for power, when in doubt, get more than you need and don't turn the volume up. That's better than not having enough. My first receiver was all of 25 watts per channel. I still use it today and it works great. My bet is that you'll be fine with 50 watts but why not aim for say 75 or 100 watts or more? And don't forget it's all about how efficient the speakers are, how loud they can play max, how much power you can deliver to them and how loud you want them to play. It's not all about amp power.

good luck
-lou

After all

I know this is a big amount of questions, and that the project is a bit off, but I would like to finish it with some of Your help. I would make a project log, and share this project with You folks.


Many, many thanks in advance, :?

Malium
llung
 
Posts: 80
Joined: Wed Nov 14, 2007 11:00 pm

Re: Help with a project

Postby DVDdoug » Mon Aug 30, 2010 7:58 pm

I think this can work!

Have you ever built a speaker before? Do you have a speaker building book? Do you know how to wire-up a crossover?

What should I expect from boxes made like this?
You never really know what a speaker is going to sound like 'till you build it. But in a given price range, you can usually build a better-sounding speaker (with higher quality drivers) than you can buy.

I would like them to be strong on the bass area, for the movie effects (and by this to avoid using a separate woofer), but I also want to enjoy in quality music as well, so I do not want them to be boomy.
For designing a proper box and predicting bass response, I recommend you download a copy of WinISD (FREE!!!). (The bass response depends on the interior volume, port dimensions, and the speaker's Theile/Small parameters.) It's most important to get a good subwoofer design to prevent wimpy or boomy bass. But, it won't hurt to plug-in the numbers for your mid-woofer too.

When you place a woofer in a corner the bass gets boosted, and it can get boomy. So, you might have to experiment. You'll get even more boost if you place the woofer near the floor (or ceiling) where 3 walls come together.

You will need to isolate the mid-woofer from the subwoofer. You'll effectively need 2 separate boxes or a "box in a box". (I assume the tweeter has a sealed back and doesn't need to be isolated.)

It's generally a good idea to fill or line the box with fiberglass or some other acoustic "stuffing". This helps to prevent resonances, standing waves & "ringing" inside the cabinet. (The triangular shape helps with that too!)

Well, the third question is, what to use to run them after they are built?
I have one concern with the Soundworks amplifier. A "real" subwoofer should cross-over at about 80Hz. From the size of the original satellite speakers, I'd say they don't go that low and the crossover will be set to a higher frequency. Since your mid-woofers can go down to 80Hz, a home-theater receiver with a lower subwoofer crossover point would be a better option. (You can configure most HT receivers for 2.1.)

Many HT receivers are intended to drive powered/active subwoofers & they don't have a power-amplifier channel for the subwoofer. So, you might need to use the Soundworks subwoofer amp. (In this case the Soundworks internal crossover is not a problem since it's crossover frequency is higher than the receiver's, it won't have any effect.)

I'd recommend wiring the tweeter and mid-woofer with a passive crossover as a 2-way design, and then wire & drive the subwoofers separately.

Since you'll have 2 subs, 2 mid-woofers & 2 tweeters, do you know about impedance and series/parallel wiring? (Parallel wiring of 2 speakers halves impedance, & series wiring doubles impedance.) It depends on your amp, but be careful about wiring 2 the two 4-ohm subs in parallel... The 2-ohm load might blow the amp! :(

I do have a slight concern about the 6 ohm tweeter. Most crossovers are designed for 4 or 8 ohms. You might want to look for a crossover design program. If you connect it to a 4-ohm crossover, it will "kick in" at a lower frequency, and there will be (more) overlap between the tweeter & midrage and yo might get a "bump" in the frequency response (and an impedance dip). If you use it with an 8-ohm crossover, it will kick-in at a higher frequency and there may be a gap/dip in the frequency response between the midrange & tweeter.

As far as power... Well, speaker power ratings are often suspect and it gets tricky... You can burn-out most tweeters with an average amplifier & test tones. But, one rule-of-thumb is that you can use an amp with twice the power rating of the speaker, with normal music, as long as you don't drive the amp into distortion. With music instrument amps (i.e. guitar amps), which are often driven into distortion, the rule is reversed... Use speakers with twice the power rating of the amp.

Any "average" receiver with 75-100W per channel is OK with most "average" speakers as long as you use the system for normal listening. If you have parties with loud-distorted music, you're in the danger zone unless you're using heavy-duty PA speakers.

The thing is... Music is unpredictable. Every song has different frequency-power distribution, and every song has a different peak power to average power ratio. We could be absolutely safe by using high-power pro PA type speakers, or by using a way-underpowered amplifier. But, most people get by safely just by not driving their speakers into distortion.

Worst case.... You burn-out a driver. You built the system and you can easily replace the driver with a higher-power unit! :P
DVDdoug
 
Posts: 73
Joined: Tue Apr 21, 2009 10:52 pm

Re: Help with a project

Postby malium » Tue Aug 31, 2010 11:05 pm

This is a very reasonable thing to do. You can easily enjoy both music and movies without a center channel or subwoofers as long as you have full-range (or "large" in HT setup speak) speakers. But for full surround sound, you'll need rear speakers - something to keep in mind because if you decide to add them later, you'll want to use the same drivers you're using on the front speakers to maintain the same sound.

You can also go "small" on the front speakers and use one or more subwoofer for the overall system. Most AV receivers have bass management and can re-route the bass to a single sub just as easily as they can to "large" front speakers.


Yes, I did some tests regarding the difference between the stereo and the surround, and I think I can live with stereo. It will look nicer in my new place (no extra wires, stands), I will profit in quality of music playback, and I wont loose anything in movie playback, as I do not have enough space to properly arrange additional speakers...

Are you implying that the corner walls of your room will be part of the speaker cabinet? or that the speaker cabinets will be placed at the corners of the room? I would not do the former; the latter is fine. Using the existing walls as part of the cab is begging for trouble as walls are never flat nor form true right angles; the walls will resonate (if wallboard); air will leak; among all sorts of other problems.


Yes, my idea was that the wall corners of my room be a part of the speaker cabinets. I do not think they will resonate because they are made from concrete? Also, I could treat them with something if there is some negative impact of the material by itself (concrete)... But I have seen that people are making subwoofer boxes from concrete, so I think maybe this design could be an advantage for the woofer sections? I agree that the possible leeks could be a problem, but I think I could solve this with a little brain storming...

Sorry, don't know anything firsthand about these drivers. Looking at the specs - note that the JAMO are 4 ohms but the mid and tweeters are 8 ohm nominal so keep that in mind when designing your crossover. Also the midwoofers are less efficient (rated 85 dB, 1w/1m) than the tweeters (89.6 dB) so you've got work to do there. Xmax on the mid is 7mm (footnote 5 is not shown) but I'm guessing that's peak to peak and not one way. With a rated "noise" power of 60 watts I wonder how loud this driver will go. Luckily your room is not that big; but it's up to you to decide how loud you want this to play.


Yes, I know that there is the difference in the resistance, but as my original plan has two woofers (Jamos) per box, I would connect them in series. Then they should act as one 8 ohm unit? Right? Did not quite understand Your note on the mids. I have tested them, and they play surprisingly well as mids. And they are pretty loud.

Take the specs on the Cambridge Soundworks system with a grain of salt as far as power goes. That said, are you happy with the volume it puts out? Can the 510d be used as just an amp by simply disconnecting those little cube speakers and sub?

If you don't or can't use the 510D, then all you really need is a simple AV receiver. You can get a decent, older, Yamaha / Denon / HK / Marantz / Onkyo on eBay for around $150 or less (depends on power, brand, shipping cost, etc.) It'll cost even less if you buy a Pioneer, Technics, Sony or other mass market brand. You'll have to do some research for individual models (flaws, features, etc) so that may take some time to iron out. Get one with the same kind of features you want (Dolby Digital or DTS for instance if you ever plan on adding rear surround speakers). Of course, you can go with a standard 2 channel receiver for cheap if sound processing is not important but you will likely lose the ability to steer your bass. My point is that since you're not gunning for fancy features, you have a wide range of choice to play with on the used market. Just make sure the unit can interface with whatever your source player is.

Another option is to get just amps, not a receiver, since your computer can do all the sound processing for you. This may be cheaper or more expensive, depending on what you buy. If you go with your original plan of just 2 channels, and you stick to 2 full-range speakers, all you need is a 2 channel amp (or receiver used as an amp). Lots of options here.

As for power, when in doubt, get more than you need and don't turn the volume up. That's better than not having enough. My first receiver was all of 25 watts per channel. I still use it today and it works great. My bet is that you'll be fine with 50 watts but why not aim for say 75 or 100 watts or more? And don't forget it's all about how efficient the speakers are, how loud they can play max, how much power you can deliver to them and how loud you want them to play. It's not all about amp power.

good luck
-lou


I already have the 510d amp, so I could use it by disconnecting the woofer and the satelltes, but I am not sure in the quality of the results. I will simplify my doubts later on.

I think this can work!

Have you ever built a speaker before? Do you have a speaker building book? Do you know how to wire-up a crossover?


Hey, an optimism, that is what I like. :D

Yes, I have build a speaker before, but I just followed the project log. I can build a crossover, but I do not understand them completely. :oops:

For designing a proper box and predicting bass response, I recommend you download a copy of WinISD (FREE!!!). (The bass response depends on the interior volume, port dimensions, and the speaker's Theile/Small parameters.) It's most important to get a good subwoofer design to prevent wimpy or boomy bass. But, it won't hurt to plug-in the numbers for your mid-woofer too.

When you place a woofer in a corner the bass gets boosted, and it can get boomy. So, you might have to experiment. You'll get even more boost if you place the woofer near the floor (or ceiling) where 3 walls come together.

You will need to isolate the mid-woofer from the subwoofer. You'll effectively need 2 separate boxes or a "box in a box". (I assume the tweeter has a sealed back and doesn't need to be isolated.)

It's generally a good idea to fill or line the box with fiberglass or some other acoustic "stuffing". This helps to prevent resonances, standing waves & "ringing" inside the cabinet. (The triangular shape helps with that too!)


I have already downloaded a WinISD, but I have to download something that will explain me the results I am getting... Also, I cannot find out all of the parameters for Jamos.

I will comment on the other later on.

I have one concern with the Soundworks amplifier. A "real" subwoofer should cross-over at about 80Hz. From the size of the original satellite speakers, I'd say they don't go that low and the crossover will be set to a higher frequency. Since your mid-woofers can go down to 80Hz, a home-theater receiver with a lower subwoofer crossover point would be a better option. (You can configure most HT receivers for 2.1.)

Many HT receivers are intended to drive powered/active subwoofers & they don't have a power-amplifier channel for the subwoofer. So, you might need to use the Soundworks subwoofer amp. (In this case the Soundworks internal crossover is not a problem since it's crossover frequency is higher than the receiver's, it won't have any effect.)

I'd recommend wiring the tweeter and mid-woofer with a passive crossover as a 2-way design, and then wire & drive the subwoofers separately.

Since you'll have 2 subs, 2 mid-woofers & 2 tweeters, do you know about impedance and series/parallel wiring? (Parallel wiring of 2 speakers halves impedance, & series wiring doubles impedance.) It depends on your amp, but be careful about wiring 2 the two 4-ohm subs in parallel... The 2-ohm load might blow the amp! :(

I do have a slight concern about the 6 ohm tweeter. Most crossovers are designed for 4 or 8 ohms. You might want to look for a crossover design program. If you connect it to a 4-ohm crossover, it will "kick in" at a lower frequency, and there will be (more) overlap between the tweeter & midrage and yo might get a "bump" in the frequency response (and an impedance dip). If you use it with an 8-ohm crossover, it will kick-in at a higher frequency and there may be a gap/dip in the frequency response between the midrange & tweeter.

As far as power... Well, speaker power ratings are often suspect and it gets tricky... You can burn-out most tweeters with an average amplifier & test tones. But, one rule-of-thumb is that you can use an amp with twice the power rating of the speaker, with normal music, as long as you don't drive the amp into distortion. With music instrument amps (i.e. guitar amps), which are often driven into distortion, the rule is reversed... Use speakers with twice the power rating of the amp.

Any "average" receiver with 75-100W per channel is OK with most "average" speakers as long as you use the system for normal listening. If you have parties with loud-distorted music, you're in the danger zone unless you're using heavy-duty PA speakers.

The thing is... Music is unpredictable. Every song has different frequency-power distribution, and every song has a different peak power to average power ratio. We could be absolutely safe by using high-power pro PA type speakers, or by using a way-underpowered amplifier. But, most people get by safely just by not driving their speakers into distortion.

Worst case.... You burn-out a driver. You built the system and you can easily replace the driver with a higher-power unit! :P


Ok, since You have covered almost all of my ideas and doubts, here is some more doubts in more detailed version:

The speakers:


My idea is to built a separate sealed cabinets for Jamos. This cabinets would be about 50l (calculated by some online calculators). So, one finished speaker would be made from 2 x 10" Jamo woofer, each one in his, about 50 l cabinet, connected in series. One woofer would be placed at the bottom (near the floor) of the finished speaker, one on the top (near the ceiling). In the middle of the speaker box, there would be a cabinet for two TVM midwoofers and a tweeter, or tweeters.
I am not sure should I use one ore two tweeters for one speaker. Is there any gain from using two tweeters?
I am aware of the the resistance issue, and I will try to build the speakers to match the resistance dictated by the amp.


Crossovers:


Well, if I understood, the only way is to learn something in details, from books and sites. There is no golden universal type of the crossover I could use for such a design?

The amp:

Ok, I will back down from the idea of using the 510d amp. It has to many drawbacks. But my main doubts regarding this are:

If I use a budget AV receiver that I have (Pioneer VSX-416), I could only get use of two amp outputs (front - 2 x 100W) for running this speakers. I cannot get use the rear or center channel outputs for getting some additional W? Cause the receiver would send the surround sound on this outputs, right? If so, would this 2 x 100W front outputs be enough to run this speakers? I am a bit confused here, cause all subs that i see have more than 100W assigned, so I am afraid that my woofers would have a serious lack of the W?

I have read a lot regarding this, and all over the forums I see some confusing guidelines. Some people are saying that stereo power amplifiers like NAD, Rotel and so, are giving much more performance in music playback then the standard AV receivers. But, some of them also claims that the opticall connection gives a big quality difference over the analog connections. So, I am not sure, which is more? AV receiver, optically connected, or the stereo amp, analog connection?

In the end, I think I found a solution, but I need You confirmation. Rotel RB-976 is a 6 x 60W amp. It has a possibility to bridge the outputs to get a 3 x 150W. As its consumption is rated at 700W, I think it is a much stronger device then my AV receiver who is rated at 5 x 100W, but its consumption is rated at 240W. So, If I buy this Rotel, I could dedicate 4 of its outputs to run my woofers, and two to run the rest. Do You think this would maybe be the best solution? Any other ideas or thoughts?

Many, many thanks.
malium
 
Posts: 5
Joined: Sat Aug 28, 2010 9:51 pm

Re: Help with a project

Postby DVDdoug » Wed Sep 01, 2010 7:32 pm

Yes, my idea was that the wall corners of my room be a part of the speaker cabinets. I do not think they will resonate because they are made from concrete?
I think this is fine.

I would connect them in series. Then they should act as one 8 ohm unit? Right?
Right.

have already downloaded a WinISD, but I have to download something that will explain me the results I am getting...
A perfect speaker would have a flat frequency response curve. The basic idea is to design the cabinet so that the bass extends as low as possible and to avoid any big resonance bumps that will make the speaker sound boomy. (You probably don't want any peaks/bumps greater than +3dB.)
I am not sure should I use one ore two tweeters for one speaker. Is there any gain from using two tweeters?
The voltage from the amp is "constant" (it doesn't change when you change impedance). Two speakers in parallel will play louder than one speaker (+3db), since both speakers are getting the same voltage/power. Two speakers in series will play quieter than one speaker (-3dB) since the voltage is split between the two speakers (and given the same total voltage, you get less total current/power with the higher total impedance). And of course, two speakers can handle twice the total power as one speaker.

Now, funny things can happen when the (short-wavelength high-frequency) soundwaves mix in the air, and you'll never see a studio monitor with more than one tweeeter. But, it usually works OK if you mount the speakers close together in a "vertical array". (I have 4 tweeters in a vertical array... Long story... :D )


I can build a crossover, but I do not understand them completely.
I may bave built a crossover once, but I usually just buy one. Since most of us home builders don't have anechoic chambers and all of the equipment to properly test a speaker, I've never considered using an "advanced" crossover designs.

I think the most common is a "12 dB per octave" (2nd order) design. With this design, there is an inductor & capacitor for both the woofer & tweeter, and if there's a midrange it needs two inductors & two capacitors.

If I use a budget AV receiver that I have (Pioneer VSX-416), I could only get use of two amp outputs (front - 2 x 100W) for running this speakers. I cannot get use the rear or center channel outputs for getting some additional W?
Probably not a good idea. You might be able to set the rear outputs to be the same as the fronts, but the settings would get messed-up at some point and I'd say it's not worth it. And, 100W should be plenty.

The problem is, I don't think your receiver has a subwoofer speaker output (I think it's 5x100W, not 6x100W). This means you need to use 3-way passive crossovers, or get a separate amp for the subwoofers. I was assuming that you were going to use a 2-way passive crossover and build a 2-way speaker plus a separately driven subwoofer (this is typical for home theater).

I have read a lot regarding this, and all over the forums I see some confusing guidelines. Some people are saying that stereo power amplifiers like NAD, Rotel and so, are giving much more performance in music playback then the standard AV receivers.
There's a LOT of nonsense in the audiophile community! All speakers sound different, but most amplifiers sound alike (in proper blind tests ;) ). Look at power, noise, distortion, and frequency response, and ignore any "audiophile terminology". With modern electronics it's cheap and easy to build a low-noise, low-distortion amp with flat frequency response... Just about the only spec to worry about is POWER. For more on this, take a look at Audiophoolery by Ethan Winer. And, if you find that useful or interesting, you can watch Dr. Winer's AES Presentation on YouTube.

So, I am not sure, which is more? AV receiver, optically connected, or the stereo amp, analog connection?
From a computer? Computers often have cheap (noisy) soundcards, and in this case a digital connection is better. ( It doesn't matter if the digital S/PDIF connection is optical or electrical. Its the same digital ones zeros.)

In the end, I think I found a solution, but I need You confirmation. Rotel RB-976 is a 6 x 60W amp.
I don't think the Rotel has a crossover or "bass management". So, you could use it for the subwoofers if you drive it with the line-level subwoofer output from the receiver.
DVDdoug
 
Posts: 73
Joined: Tue Apr 21, 2009 10:52 pm

Re: Help with a project

Postby llung » Thu Sep 02, 2010 1:26 am

It's getting a little long so I'm just gonna comments on some stuff without quoting.

- Cabinet and wall - Concrete is nice but the hard part is going to be making the rest of the cabinet mate with the concrete wall. Yes, people do make very heavy enclosures with concrete including the baffle. If you can pull it off, I'd love the see the results. But remember that if you can't figure out how to make it right, and you end up making a "regular" 6-sided trapezoidal box, you're not going to eat into your space much more - practically just the thickness of one wall in two directions. Of course making a tall cabinet, either as a separate structure or into the wall has its challenges - good luck!

- Impedance, SPL and sensitivity; series and parallel wiring - If you wire your woofers in series, yes the impedance doubles. Likewise if you wire two in parallel, you halve the impedance.

But that's not all that happens. Remember that you want your total system (where system = all the drivers + crossover) to play at the same volume (SPL or Sound Pressure Level) for a given input level. You currently have drivers of different impedance (4, 8, 6) and different sensitivity. Sensitivity is expressed in dB usually as 1 watt at 1 meter or as 2.83V at 1 meter. For an 8 ohm driver, 1 watt equals a voltage of 2.83v so these 2 expressions are equivalent. But if the driver is not 8 ohms, they are not equal so you have to be careful in comparing specs for your design. A 3dB difference represents a doubling / halving of power.

Now you don't have sensitivity numbers for the Jamo woofers. But if you put 2 in series, you'll double the impedance. Since you have 2 drivers, you have twice the surface area and thus a +3dB gain over a single driver. But since you've doubled the impedance to the amp, the amp is delivering 1/2 the power at the same given voltage. Each driver in turn only sees half of the voltage from the amp or 1/4 of the original power (half of the half that the amp is producing). So each driver is at -6dB or -3dB for the combined two drivers (twice the surface area). Add this to the +3dB for correlated sources and your net gain is 0dB. In other words, 2 drivers in series gives you no added sensitivity (2.83v / 1meter). If your 2 drivers are not correlated - they are widely separated relative to the wavelength they are producing - you don't get the full +3dB from acoustical summing and you'll end up with less than 0dB gain.

If you wire 2 identical drivers in parallel, you'll get something similarly weird. Your net impedance now drops in half so your amp delivers twice the total power. Each driver sees the full voltage since it's wired in parallel so there's no net loss per driver. You can twice the surface area so that's +3dB and another +3dB for correlated sources for a net +6dB gain. Again if the drivers are not close to one another, your net gain would be closer to 3dB.

- crossover - Your mid woofers are 8 ohms, 85 dB while your tweeters are 90.9 dB (2.83v/1m). That's a huge difference. If you double up the mid-woofers to try an gain 6 dB, you'll get close but your impedance will drop to 4 ohms. Normally you try to present as consistent an impedance as you can to the amp. Likewise, you try to flatten the impedance of each driver so that the crossover does its thing correctly - remember that the typical slope calculation for a crossover assumes a non-changing impedance across the operating range. You can see on the graph for the tweeter just how much it changes with frequency. My guess is that you'll be ok but keep the slope no less than 12 dB/octave; 24 db if you can.

If you plan on driving the Jamo woofers separately, it'll be to your advantage. My recommendation is to build them as subs and for initial simplicity, drive them from a common subwoofer output of a home theater receiver. I've just done the exact same thing and it works beautifully. Here's the rational.

Let's say you build what essentially is a 3way speaker - the crossover is much harder to get right. It's much easier to design a decent 2-way. To complicate matters, you don't know how sensitive the Jamo's are. We know that the mid-woofer/tweeter combo can do roughly 91dB (2.83v/1m) which is very efficient. But without specs on the Jamo, you might be way off. And generally speaking, woofers tend to be less sensitive so the odds are against you, unless you double up in parallel (not series). But parallel woofers will give a 2 ohm load and you'll need some darn good amps to drive that (read: expensive). So what to do with the woofer? A very good option is to drive them separately with their own amp and control the gain to that amp to match the mid/tweeter pair. You can do this with an active crossover between the preamp and amps. That's not a hard thing to do, nor does it have to be costly.

But since you'll need new amps to drive this gear, why not just use a HT receiver? You'll also need a second amp (or even an old 2 channel receiver from a garage sale) for the subs. What you do is connect your source to the receiver as normal. Set the front speaker to "small" in the bass management section. Hook the sub out RCA jack through a Y connector to both channels of your sub amp which drives both subs. Use the bass management (or the sub amp's volume control if it's a receiver) to balance the overall gain.

Since the sub LP is usually around 80Hz, it's effectively omnidirectional so the fact that it's not 2 distinct bass stereo signals is not important. This has an added implication. If for some reason you get into trouble building your boxes, you can go small and just build cabs for the mid/tweeter combo. Then build just ONE sub and place it independently of the other two.

Hope this helps
-lou
llung
 
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Re: Help with a project

Postby malium » Sun Sep 05, 2010 7:40 pm

Dear lou,

You did help, quite much. Thanks!
I like the idea involving the AV receiver and the separate amp for woofers. Now, how much power should the amp be?
As in my country there is some hype going on about an old audio gear, it is almost impossible to find anything fair priced. I found this little thing on ebay :

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... TQ:US:1123

As I am far, far away, the thing would cost me about 200 USD with postage, is it worth it? I do have a "thing" for a HK...

Best regards,

Malium
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Re: Help with a project

Postby malium » Mon Sep 06, 2010 10:39 pm

One more question to You guys, before I start to build this monsters...

Would something like this be ok for running the woofers?

http://cgi.ebay.com/4-100-watt-4ohm-TK2 ... 3a5e69ded6

Could I use something like this to run only Jamos, while the rest would be run by the AV receiver? I would use this amps four outputs, one for each woofer, and I could connect such amp to a AV receiver subwoofer preout?

Thanks!
malium
 
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Re: Help with a project

Postby llung » Tue Sep 07, 2010 4:09 pm

malium wrote:One more question to You guys, before I start to build this monsters...

Would something like this be ok for running the woofers?

http://cgi.ebay.com/4-100-watt-4ohm-TK2 ... 3a5e69ded6

Could I use something like this to run only Jamos, while the rest would be run by the AV receiver? I would use this amps four outputs, one for each woofer, and I could connect such amp to a AV receiver subwoofer preout?

Thanks!


I've read some good thing about Tripath amps (these use the TK2050) but have never heard any myself. Looking at the spec and the distortion curve (http://www.datasheetcatalog.org/datashe ... yzwqtx.pdf) it looks like they're fine up to about 30 watts (8 ohms, 30V rails) but will distort badly above that. For 4 ohms, the spec says 75 watts at 30V rails with parallel outputs. You'll still need to provide an adequate power supply. 75 watts is probably enough since you'll have 4 drivers; but that's per woofer and using 2 amp outputs in parallel (8 channels total or 2 of these boards).

Remember that you may not need to use all 4 woofers. For example, right now I use two 12 inch subwoofers in a room measuring 12 ft x 25 ft (about 4 x 8 meters) with only 60 watts per sub, 90 dB sensitivity (2.83v). If you can borrow some amps, run some tests to see just how much power you really need in your room at the listening level you want.

good luck
-lou
llung
 
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Re: Help with a project

Postby malium » Wed Sep 22, 2010 9:19 pm

Hello again.

Sorry for not answering for some time, I was very busy. Many, many thanks for Your help!

I decided not to go playing with half finished amps, as I do not have any extra time to spare to play with it.

Instead I bought a first part for my new audio gear, the Nuvo P2100 power amp. I intend to use it to power my woofers.

http://www.nuvotechnologies.com/prozone ... n_rev3.pdf

It was pretty cheap (about 100 USD), brand new.

Anybody have some experience with it? Any thoughts on it?

Now I am starting to look for something to power the rest.

Soon I am starting to bring this project to reality, so expect a project log in the near future.

Best wishes,

Malium
malium
 
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