Should have mentioned: this is 2 x 850490.
And, the specs used are the measured specs from the Australian distrivutor of these drivers. They vary from the Peerless specs but I've also plugged the Peerless specs in and the basic rersponse is not that different.
Mos
And, the specs used are the measured specs from the Australian distrivutor of these drivers. They vary from the Peerless specs but I've also plugged the Peerless specs in and the basic rersponse is not that different.
Mos
Mos Fetish said:
Yes and no. I avoid it in my designs, but I have heard more than a few speakers that have it and sound very good.
This isn't only a factor at very high excursions. In one of my prior day jobs I built RF amplifiers that worked over a very large frequency range (for RF devices that is) from 88MHz to 860MHz and 460MHz to 860MHz. Each one of these amplifiers had to deal with a lot of separate signals.
The reason I bring this up is that every driver in a speaker system has to deal with a lot of simultanious frequencies being applied to it. I am VERY familiar with this concept. Each of these signals can be relatively small, but occasionally the maximum for each signal can line up in time to create a very large signal. If the speaker (or amplifier, or microphone or...) can't handle this it's called intermodulation distortion.
The Faraday rings in the Peerless (and Scan-Speak, Seas Excel and some other very high end drivers) reduce this type of distortion a lot! I don't have distortion data on a Vifa P21 series driver, I wish I did to compare, but I haven't measured any drivers without a Faraday ring that have distortion as low as a competitor that does. (I posted the intermod distortion performance of the CSX 8" driver earlier in the thread....it's quite good for the money.)
At this point, unless I am designing a speaker for a certain "budget" price point I exclusively use drivers with Faraday rings or other such distortion reducing features in their motor structure.
No, it's perfectly reasonable. You've got 2 drivers in 32L, which is 16L each. The sensitivity of the driver is listed at 91.2dB so, 60Hz is about right. I just looked it up on my spreadsheet, in 20L with an F3 of 60Hz the theortical upper end limit for sensitivity is 91.6dB for a sealed system. I can't find my vented system spreadsheet right now.
If you're asking yourself about all of those "bookshelf" speaker systems that claim 89dB sensitivity and an F3 of mid to low 40's, well they are pretty much either lying or taking room gain, where the room boundries enforce low frequencies into account.
Try modeling the two 850490's in 70L, tuned to 35Hz, I show an F3 of 39Hz and reasonable group delay curves.
In short, I would go with the CSX or HDS drivers unless you really want the extra few Hz of bass extension. I would, and wouldn't look back. That said the Vifa drivers are used in a lot of high $ systems that sound quite good. They will have a little rounder sound in my opinion, but not as accurate. The Peerless may seem a little bass shy at first, but after a few minutes of listening you realize pretty easily that it's because they are much more articulate than what you might expect. That's been my experience with them.
Scott
Scott, thanks for your comments.
I have tried the 850490 as suggested and the graph is attached. Shows an F3 of 53hz. Eek!
BTW, Gert Christensen of Peerless in Denmark suggests a 70L box tuned to 40hz gving an F3 of 40hz with a 60 x 30mm (d x l) port. Mmm. Those parameters don't look good in WinISD or as I recollect, in Unibox.
Quite frankly, the CSX 10" gives a much more satisfying curve and it's only a couple of dollars dearer than the 850490.
Like to suggest a midrange to go with a couple of woofers producing 84db (before baffle loss)?
Mos
I have tried the 850490 as suggested and the graph is attached. Shows an F3 of 53hz. Eek!
BTW, Gert Christensen of Peerless in Denmark suggests a 70L box tuned to 40hz gving an F3 of 40hz with a 60 x 30mm (d x l) port. Mmm. Those parameters don't look good in WinISD or as I recollect, in Unibox.
Quite frankly, the CSX 10" gives a much more satisfying curve and it's only a couple of dollars dearer than the 850490.
Like to suggest a midrange to go with a couple of woofers producing 84db (before baffle loss)?
Mos
Attachments
Mos:
A) I plugged in a couple of HDS 8 inchers into WinISD. Not too bad, actually. I adjusted the sensitivity of the HDS from 91.3 down to 90 dB @ 1M/1W, because that is what the graph at Peerless' own site shows them as.
There is the issue of amplifier impedance. When two 8 ohm woofers are joined together in parallel, they become a 4 ohm unit. Their sensitivity, per 2.8 Volts, goes up 6 dB. However, 3 dB of that is because at 2.8 Volts, the 4 ohm pair is drawing 2 watts instead of 1 watt, which each one did when it was measured alone. So WinISD correctly assigns only 3 dB increase in sensitivity when two 8 ohmers are hooked up in parallel to yield one 4 ohm pair.
However, WinISD fails to tell you to take into consideration the following: What is your amp rated at? 4 ohms, 6 ohms, 8 ohms? this is important. If your amp is rated to delvier it's maximum power into 8 ohms, then it will deliver only half it's maximum rated power into a 4 ohm load. Works in reverse. If your amp is designed to deliver it's maximum rated power into 4 ohms, than an 8 ohms speaker will only be able to draw half it's maximum rated power.
So if you have an amp designed to deliver it's maximum rated pwer-say, 100 watts-into 8 ohms, then hooking two HDS woofers up will not result in any increase in max SPL. You'll be twice as sensitive, but your max power will only be half as much.
Some amps twll you how much they deliver into both 8 ohms and 4 ohms. If they only give you one number-like "100 watts into 8 ohms with .1% THD", then you can assume that it delivers 50 watts at 4 ohms.
B) Like I said, that curve isn't bad for the two HDS versus the 10 incher. I will post below. This is for the stated HDS specs, except I adjusted the sensitivity down -1.3 dB to match Peerless' own graph. the box is 80 Liters, both are tuned to maximum tuning. Going between 26 Hz and 30 Hz changes little.
The CSX 10 incher is in red
The HDS 8 onch pair is in blue
A) I plugged in a couple of HDS 8 inchers into WinISD. Not too bad, actually. I adjusted the sensitivity of the HDS from 91.3 down to 90 dB @ 1M/1W, because that is what the graph at Peerless' own site shows them as.
There is the issue of amplifier impedance. When two 8 ohm woofers are joined together in parallel, they become a 4 ohm unit. Their sensitivity, per 2.8 Volts, goes up 6 dB. However, 3 dB of that is because at 2.8 Volts, the 4 ohm pair is drawing 2 watts instead of 1 watt, which each one did when it was measured alone. So WinISD correctly assigns only 3 dB increase in sensitivity when two 8 ohmers are hooked up in parallel to yield one 4 ohm pair.
However, WinISD fails to tell you to take into consideration the following: What is your amp rated at? 4 ohms, 6 ohms, 8 ohms? this is important. If your amp is rated to delvier it's maximum power into 8 ohms, then it will deliver only half it's maximum rated power into a 4 ohm load. Works in reverse. If your amp is designed to deliver it's maximum rated power into 4 ohms, than an 8 ohms speaker will only be able to draw half it's maximum rated power.
So if you have an amp designed to deliver it's maximum rated pwer-say, 100 watts-into 8 ohms, then hooking two HDS woofers up will not result in any increase in max SPL. You'll be twice as sensitive, but your max power will only be half as much.
Some amps twll you how much they deliver into both 8 ohms and 4 ohms. If they only give you one number-like "100 watts into 8 ohms with .1% THD", then you can assume that it delivers 50 watts at 4 ohms.
B) Like I said, that curve isn't bad for the two HDS versus the 10 incher. I will post below. This is for the stated HDS specs, except I adjusted the sensitivity down -1.3 dB to match Peerless' own graph. the box is 80 Liters, both are tuned to maximum tuning. Going between 26 Hz and 30 Hz changes little.
The CSX 10 incher is in red
The HDS 8 onch pair is in blue
Attachments
Mos Fetish said:
Two ways. The easy way is to put the following chart into Favorites, or write down the URL.
http://www.diyaudio.com/forums/showthread.php?threadid=5668&highlight=displacement+SPL
Look at the chart. Go to 40 Hz. First line, 1.28 in³, will yield, at 40 Hz, an output between 81 and 82 dB. The next line up is 3.28 in³. That yield an output, at 40 Hz, of of just under 90 dB. 3.28 is 2.5 times larger than 1.28. Hence, the calculation.
The math way is to take the formula for two different Vd's, (Volume of displacement-Sd X ±excursion). They are Vd1 and Vd2.
and go:
20 Log (Vd1¸Vd2).
So if one Vd is 2.7 times greater than the other, you go:
20 Log 2.7 = 8.6 dB.
Increase Vd by 2 and you get:
20 Log 2 = 6 dB.
Increase by 4, and you get
20 Log 4 = 12 dB.
Increase Vd by 1.5, and you get:
20 Log 1.5 = 3.5 dB.
It's a nice way to measure the effects of cone excursion. If two 10 inchers are compared, and one has an excursion 1.5 as long as the other, we know that the long excursioned driver will be able to produce 3.5 dB more output in the bass range if put into a suitable box, and driven with adequate power.
Incidentally, I should mention that I don't bother too much with manufacturer's exact specs for cone area. Basically, in most cases when it comes to cone area, a 10 incher is a 10 incher, an 8 incher is an 8 incher, etc. Cone excursion is what varies.
For cone area, I just go by the following chart:
15 in = 132 in²
12 in = 82 in²
10 in = 56 in²
8 in = 32 in²
6½ = 21 in²
I have found this to be effective.
For cone area, I just go by the following chart:
15 in = 132 in²
12 in = 82 in²
10 in = 56 in²
8 in = 32 in²
6½ = 21 in²
I have found this to be effective.
Mos Fetish said:
Can you post the woofer parameters you are using? I can't seem to download a valid spec sheet for the 850490 from the Australian company you mentioned. I don't get an F3 with my program or parameters (which are factory).
What configuration are you using to come up with an 84dB sensitivity for two woofers? I'm confused. (again..must be the lack of coffee)
Scott
84db - I think he means 94db (2 drivers at 91db = 94db according to WinISD).
"F3 of 53hz" , but thats 92db at 50hz!
Now if you set your reference at 92db, the f3 occurs at 40hz - it's all relative.
I would go with Peerless suggestions & use two 850490 in a 70l box fb 40hz. As for the lower impedance if you use a large inductor with highish DCR say 1.5ohm then two drivers paralleled at 4ohm + 1.5 = 5.5ohm which is quite acceptable.
"F3 of 53hz" , but thats 92db at 50hz!
Now if you set your reference at 92db, the f3 occurs at 40hz - it's all relative.
I would go with Peerless suggestions & use two 850490 in a 70l box fb 40hz. As for the lower impedance if you use a large inductor with highish DCR say 1.5ohm then two drivers paralleled at 4ohm + 1.5 = 5.5ohm which is quite acceptable.
Scott:
Sorry, thought I'd replied to this.
Measured TS for Peerless 850490:
FS=30.8, Sens=90.5, QTS=.25, Qes=.28, Qms=2.85, Vas=70.9, Z=8, DCR=5.74, PE=150w rms
And, sorry, I did mean 94db. Thanks AP.
Mos
Sorry, thought I'd replied to this.
Measured TS for Peerless 850490:
FS=30.8, Sens=90.5, QTS=.25, Qes=.28, Qms=2.85, Vas=70.9, Z=8, DCR=5.74, PE=150w rms
And, sorry, I did mean 94db. Thanks AP.
Mos
Don't wanna start a new thread.....
Hmmm.. my speaker boxes are HOPEFULLY going to contain 8inch Peerless woofers... (850136) The cut out for these drivers is 197mm.... I designed my boxed to have a 200mm internal width... now that I have cut the wood, its only 199mm and I have a feeling this is going to become slightly less when I attach the baffel... OHH NO!! lol wait.. nah, its okay.. lol
hmm.. lol SEEEEYA!!
Hmmm.. my speaker boxes are HOPEFULLY going to contain 8inch Peerless woofers... (850136) The cut out for these drivers is 197mm.... I designed my boxed to have a 200mm internal width... now that I have cut the wood, its only 199mm and I have a feeling this is going to become slightly less when I attach the baffel... OHH NO!! lol wait.. nah, its okay.. lol
hmm.. lol SEEEEYA!!
Mos Fetish said:
Okay, within the differences that can be expected between modeling software I get about the same numbers you do.
I've attached a graph comparing the Peerless HDS 8" and the Vifa P21 8" woofer. Maximum output, and alignment. I doubt you'd here that much difference between the two bass alignments, but you will definately hear the difference in maximum output, distortion and power handling.
The woofers are set to maximum output by setting the excursion to maximum listed linear excursion above the tuning frequency. Below tuning frequency these alignments excede excursion limits, but this method is very common when deciding what woofer to use. If the F3 is relatively low<45Hz or so, it's rarely a problem in real life. For those little woofers with little cabinets, it can be an issue.
Scott
Attachments
Thanks for your simulation, Scott.
This doesn't make my decision any easier--P21 or 850490.
I have a friend who has some B&W 640, 3 way, floorstanders inc 2 x 8" woofers. The specs list them as having a freq range of 46hz to something 🙂. I've always been impressed by their tight bass response and there's plenty of it. And I assume at 46hz B&W are quoting the F3, after all, why would they quote anything higher--it's a selling point after all. Mighty impressive.
Mos
This doesn't make my decision any easier--P21 or 850490.
I have a friend who has some B&W 640, 3 way, floorstanders inc 2 x 8" woofers. The specs list them as having a freq range of 46hz to something 🙂. I've always been impressed by their tight bass response and there's plenty of it. And I assume at 46hz B&W are quoting the F3, after all, why would they quote anything higher--it's a selling point after all. Mighty impressive.
Mos
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