Thanks mate,
I'll keep an eye out, see how little I can spend, haha. I'm very happy that I only ended up spending $50 on the Sherwood now, would of been ropeable had I of paid more.
I'll keep an eye out, see how little I can spend, haha. I'm very happy that I only ended up spending $50 on the Sherwood now, would of been ropeable had I of paid more.
Ok Guys, help me get my head around something.
As I need a new amp to get the most out of my woofer towers, I've been trying to think up possible upgrade routes I can take. Clearly, getting a multi channel amp like the one moondog posted earlier is the easiest option, but I want to use this opportunity to expand my limited knowledge. Only problem is that I have a couple noobish questions.
1. My woofers are rated at 90W RMS, should I be trying to get an amp that can at least provide this sort of power to each woofer?
2. If I end up with a stereo amp that can (for example) provide 100W per channel into a 4ohm load, by paralleling the woofers in each box (each woofer is 8R nominal), will each woofer only see half that power?
Cheers.
As I need a new amp to get the most out of my woofer towers, I've been trying to think up possible upgrade routes I can take. Clearly, getting a multi channel amp like the one moondog posted earlier is the easiest option, but I want to use this opportunity to expand my limited knowledge. Only problem is that I have a couple noobish questions.
1. My woofers are rated at 90W RMS, should I be trying to get an amp that can at least provide this sort of power to each woofer?
2. If I end up with a stereo amp that can (for example) provide 100W per channel into a 4ohm load, by paralleling the woofers in each box (each woofer is 8R nominal), will each woofer only see half that power?
Cheers.
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Hi nipper. forget power handling for a minute. at bass frequencies it is irrelevant if the drivers X-Max can't deliver.
Let me say too that 12dB of bass boost is a hell of a lot. i have 400 watts available and I only use 5dB as I don't want to overdrive my woofers
Do a simulation of the driver in the box and see what the excursion is and how many watts are needed to drive the woofers to X-max plus 15%, that will be all the power you will need, It has been a while since I looked at these but I seem to remember 30 watts or similar doing it
Let me say too that 12dB of bass boost is a hell of a lot. i have 400 watts available and I only use 5dB as I don't want to overdrive my woofers
Do a simulation of the driver in the box and see what the excursion is and how many watts are needed to drive the woofers to X-max plus 15%, that will be all the power you will need, It has been a while since I looked at these but I seem to remember 30 watts or similar doing it
1. I like to use a rule of thumb along the lines of "intended listening level +10dB headroom"
So, for the sake of the maths, say your woofers are specced for 86dB at 1W at 1m, your listening distance is 4 metres, and you want to be able to listen at an average level of 90dB.
With 1 watt, you'd reach 80dB at 4 metres, so you'll need 10 watts to reach 90dB. Add 10dB of headroom (for songs that are supposed to be loud, or songs with loud peaks) and you're looking around 100 watts.
But 90dB is actually quite loud, and 86dB is fairly lousy efficiency, so you'll want to run the math using your own situation. In practice 50W is likely more than adequate.
EDIT: Should've read the rest of the thread. If you're using bass boost you'd need to take that into account, and Moondog's advice to check X-max is a faster way to find your upper bound.
2. Yes.
So, for the sake of the maths, say your woofers are specced for 86dB at 1W at 1m, your listening distance is 4 metres, and you want to be able to listen at an average level of 90dB.
With 1 watt, you'd reach 80dB at 4 metres, so you'll need 10 watts to reach 90dB. Add 10dB of headroom (for songs that are supposed to be loud, or songs with loud peaks) and you're looking around 100 watts.
But 90dB is actually quite loud, and 86dB is fairly lousy efficiency, so you'll want to run the math using your own situation. In practice 50W is likely more than adequate.
EDIT: Should've read the rest of the thread. If you're using bass boost you'd need to take that into account, and Moondog's advice to check X-max is a faster way to find your upper bound.
2. Yes.
Thanks for the tip, I assume I can simulate this in WinISD Pro? I think I recall seeing a cone excursion view option.
I'll have a go and get back if I have any dramas. The main reason I've started asking these questions is because I'm strongly considering building another amplifier kit and I'm trying to see what options I have.
Appreciate the help, the example helped a lot.
That analysis works in fre space (4 pi space). In a room you won't have the same fall0off of level. You probably get back 3-6 dB of the loss so you can use a starting point of 83-86 dB
dave
Planet 10: Quite so, but I find most people don't have a clear idea of what "90dB" sounds like anyway, so I try not to overcomplicate things by introducing correction for a 3dB error.
Add that to the low dynamic range in modern pop recordings and my method overestimates anyway.
Add that to the low dynamic range in modern pop recordings and my method overestimates anyway.
Pretty LOUD.
And into the area where WCB would be pounding on your door if it was a workplace.
dave
I have no idea what the xmax of this driver actually is. It seems I entered 6mm into the WinISD model but I have no idea where I grabbed that from. Not to dwell on this issue too much, I'm just going to assume that these 8" woofers have an xmax of 6mm. I expect that overestimating the power needed is better than underestimating resulting in driving the amp too hard.
Not sure if I've done this right. My woofers have no chance of producing sound down to 10Hz but I have no filter that prevents it from trying, so I guess I need to take that into consideration.
That's with 2 speakers selected in the drop box. How does winISD treat multiple driver simulations? Is it paralleling each driver or just summing the total amount of power needed assuming that each driver is being powered by its own amplifier?
Not sure if I've done this right. My woofers have no chance of producing sound down to 10Hz but I have no filter that prevents it from trying, so I guess I need to take that into consideration.
That's with 2 speakers selected in the drop box. How does winISD treat multiple driver simulations? Is it paralleling each driver or just summing the total amount of power needed assuming that each driver is being powered by its own amplifier?
"whoosh"
You thought right.
Thanks for dumbing it down, haha.
Pretty sure Win ISD parallels the drivers, thjose excursions look realistic and 6mm is about right for those woofers, how much power is that??
I am going to tell you to save you hearing and learn to listen at moderate levels, being deaf is no fun, although loud music didn't cause mine, but you probably won't listen; my kids don't
LOL
I am going to tell you to save you hearing and learn to listen at moderate levels, being deaf is no fun, although loud music didn't cause mine, but you probably won't listen; my kids don't
LOL
That's 37W.
Does that mean I only need 37W for both drivers in parallel? As in only needing a stereo amp capable of providing <50W per channel into a 4R nominal load?
EDIT:
If I were to bi-amp, how much power per driver would I need? Does it halve?
Don't worry, I'm not the type to have music blasting. The only time I've cranked my current setup is to show friends and family.
Does that mean I only need 37W for both drivers in parallel? As in only needing a stereo amp capable of providing <50W per channel into a 4R nominal load?
EDIT:
If I were to bi-amp, how much power per driver would I need? Does it halve?
Don't worry, I'm not the type to have music blasting. The only time I've cranked my current setup is to show friends and family.
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50 watt stereo amp if capable of 4 ohms will be plenty.
big chip amp for each box or a cheap old stereo, $35 // $55- on ebait or Craigs-list or gumtree
big chip amp for each box or a cheap old stereo, $35 // $55- on ebait or Craigs-list or gumtree
Awesome, going to see how cheaply I can build another amp for as I have the itch to do another. I could even build another gainclone with a 18v supply to make it suitable for 4 ohm loads, I should be able to build one cheaper than my first as I have plenty of materials left over. Dearest bit is the transformer.
Just for fun, I used my LM3875 gainclone to power one of my towers (bi-amped). Seems to drive the woofers to max excursion when the potentiometer is turned up half way, I assume that is what's happening as it sounds ugly. Below this volume it sounds good, next I'm going to test one tower on my gainclone and one on the sherwood to see if I can hear any differences in quality.
So it seems that a ~50W amp is more than enough for these woofers. I know I had a set budget that I forced myself to stick to for these speakers, but I wish I had woofers with greater excursion. I guess it also makes it easier to drive the woofers too hard configured this way considering each woofer is getting the full power available from each channel, rather than sharing a channel between two woofers.
I can say one thing safely, my next sub/woofer project is not going to have the same compromises I have made with this project. It's not that I'm unhappy with the end result, but I already want more. I didn't get the same satisfaction from them as I did after building my amp and 2ways.
It's all a HUGE learning curve.
So it seems that a ~50W amp is more than enough for these woofers. I know I had a set budget that I forced myself to stick to for these speakers, but I wish I had woofers with greater excursion. I guess it also makes it easier to drive the woofers too hard configured this way considering each woofer is getting the full power available from each channel, rather than sharing a channel between two woofers.
I can say one thing safely, my next sub/woofer project is not going to have the same compromises I have made with this project. It's not that I'm unhappy with the end result, but I already want more. I didn't get the same satisfaction from them as I did after building my amp and 2ways.
It's all a HUGE learning curve.
By looking at your WinISD excursion, your using these in a sealed enclosure. Generally sealed requires a higher xmax driver than vented. With vented you will get much lower excursion to a bit lower than Fb. You may want to model it to see the difference.
I can't remember if you are running dual woofers in parallel or single woofers but if they are running as dual, the operating excursion is close enough to halved when compared to a single driver.
Don't take too much notice of WinISD's excursion values as they don't relate to the real world... tone signals vs music signals. I've had plenty of drivers (such as Fostex FR) where WinISD had them clapping out at less than 1W but handled well over 30W on music.
I can't remember if you are running dual woofers in parallel or single woofers but if they are running as dual, the operating excursion is close enough to halved when compared to a single driver.
Don't take too much notice of WinISD's excursion values as they don't relate to the real world... tone signals vs music signals. I've had plenty of drivers (such as Fostex FR) where WinISD had them clapping out at less than 1W but handled well over 30W on music.
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Or your gainclone is running out of power.
What rails does your GC have? Speakers wired in parallel for 4 ohms?
dave
I think Dave mentioned it before but if your speaker impedance is around 4 ohm then you need to run with 25VDC rails as it helps low impedance performance dramatically on the LM3875.
For more power you can go to a parallel LM4780 but in this configuration can have very high DC offset values that causes drivers to sit away from the VC centre (moves inward or outward with no signal). A SC amp kit from Jaycar or Altronics would be better and more stable but a plate amp may be the best choice.
For more power you can go to a parallel LM4780 but in this configuration can have very high DC offset values that causes drivers to sit away from the VC centre (moves inward or outward with no signal). A SC amp kit from Jaycar or Altronics would be better and more stable but a plate amp may be the best choice.
Yes, these are in a sealed enclosure. I have modelled them in a vented enclosure to witness the difference, fairly considerable difference in response. The reason why these speakers weren't vented were simply to keep the build as simple as possible. There were other factors such as needing a larger enclosure for vented vs sealed, and supposedly getting tighter bass out of a sealed woofer. I would like to build a vented sub one day though, I think it would suit home theatre well.
I can choose to run these speakers independently or in parallel (depending on the amp I'm using). So when you say "doubled" I assume you mean paralleled? So two drivers are running off one amp channel, the excursion witnessed will only be half of what one driver would normally be?
I think you are correct, I have no real way of telling (that I know of) but I think my amp was struggling to drive them now. Is this related to the Audio Sector power supply lacking any real form of storage capacitors?
My toroidal transformer has two 25V secondary windings, can't remember what that value jumps to after rectification, but I wired one driver to each channel so the nominal impedance seen by each amp was 8 ohms (only ran one box, not both).
I recall reading that using a transformer with 18V secondary windings will make a gainclone safe for driving 4 ohm loads.
If I decide to go with paralleled amps, can't I just use caps on the input and NFB loop to take the DC offset down to practically 0VDC?
Thanks for the other suggestions, the jaycar/altronic kit is something that hadn't even crossed my mind, I'll have a look at them. I really like the idea of a plate amp, especially if it has a built in active XO, but can you buy a plate amp that will power more than one driver (If I paralleled the 4 woofers, the nominal impedance will drop to 2 ohms)?
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