Goldwood 18" for OB sub - Page 2 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th March 2004, 07:37 AM   #11
diyAudio Member
 
Join Date: May 2002
Location: Los Gatos, CA
I don't understand why so many people here are so focused on xmax. With drivers of this size and efficiency I don't think xmax is really important as I don't think there will be any problem with moving enough air. That said, I think it's better to have low xmax drivers as they are more linear (less distortion) if used within their excursion limits. That's probably contraversial here, but that's my opinion.

Btw, excuse my ignorance but what is "no."

I haven't decided to go with the Goldwood just yet. I'm actually leaning towards the Pyramid at this point - I just wish I could get a hold of it's response and impedance plot.

Deon, that Goldwood 215 driver is too inefficient for me at 87db. I don't want to have to run six of these A 20 oz magnet and foam surrounds? This is stretching things as far as cheapness goes.
__________________
-Brad-
  Reply With Quote
Old 16th March 2004, 10:05 AM   #12
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally posted by bbaker6212
I "arrived" at the bump by looking at the response graph that Goldwood sent me. You can see it by clicking on the "104db bump" link I posted above.

Well in that case the quoted parameters are miles out ?

sreten.
  Reply With Quote
Old 16th March 2004, 12:13 PM   #13
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by sreten


Well in that case the quoted parameters are miles out ?

sreten.

Or the FR measurement is done in a closed box? It seems as if the resonance frequency is some 45 Hz, or a factor 52/30=1.7 higher than free air. Q in the box would be 2.6 or something, which is 2.6/1.07=2.4 times. (I get these figures by overlaying a simulation on the graph).
Anyway, since both Q and fres are higher than stated in the data sheet, I suspect that the box used is not infinitely large. Since the Vas is 524 litres, the box need not be *that* small to end up with this curve.
This would maybe also explain the baffle step (?) seen above 1kHz.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 16th March 2004, 12:37 PM   #14
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi Svante,

but we are talking open baffles here.

Baffle step above 1K doesn't happen for an 18" unit.
(The graph also states 1/2 space, i.e. a large baffle)

The graph also shows Fs at 27Hz.

Something is seriously wrong, modelling or measurement wise.

sreten.
  Reply With Quote
Old 16th March 2004, 01:41 PM   #15
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by sreten
Hi Svante,

but we are talking open baffles here.

Baffle step above 1K doesn't happen for an 18" unit.
(The graph also states 1/2 space, i.e. a large baffle)

The graph also shows Fs at 27Hz.

Something is seriously wrong, modelling or measurement wise.

sreten.
Yes, I realise that you are talking open baffles, but I suspected that the FR graph (but not the impedance graph) was measured in a large but not infinitely large box. Hmm, I am now realising that the measurement is *not* from the manufacturer as I thought, then I *do* wonder about the measurement conditions (and I don't trust the statement "half space" (yet at least )).

Anyway, I have seen such descrepancies between impedance and FR before on I think seas or vifa drivers. They state that they measure as Peerless (ie in a wall of an anechoic chamber), but it does not add up unless one uses a box for one of the graphs.

You are right that the baffle step cannot occur at 1kHz for a 18" driver, silly me.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 16th March 2004, 02:36 PM   #16
diyAudio Member
 
Join Date: Jan 2004
Location: Virginia, USA
Quote:
Originally posted by bbaker6212
I don't understand why so many people here are so focused on xmax. With drivers of this size and efficiency I don't think xmax is really important as I don't think there will be any problem with moving enough air. .
Efficiency has absolutely nothing to do with how much excursion/xmax you need in your drivers. For an 18" driver to produce a given SPL at a given frequncy in identical enclosures, a driver that's 80dB/W/m and one that's 105dB/W/m will both have to have exactly the same excursion, it'll just take a lot more power to get that excursion with the 80dB/W/m driver...

Peace
  Reply With Quote
Old 16th March 2004, 02:40 PM   #17
OMNIFEX is offline OMNIFEX  Jamaica
diyAudio Member
 
OMNIFEX's Avatar
 
Join Date: Mar 2003
Location: Locked Up In The Amp Rack
bbaker6212
I don't understand why so many people here are so focused on xmax. With drivers of this size and efficiency I don't think xmax is really important as I don't think there will be any problem with moving enough air. That said, I think it's better to have low xmax drivers as they are more linear (less distortion) if used within their excursion limits. That's probably contraversial here, but that's my opinion.

OMNIFEX

Well, when you decide to reproduce 80 Hertz down, its the
xmax that gives you the volume. This is why you can have
an 87 dB woofer with 12 mm xmax out shine a 92 dB woofer
with 3 mm xmax.


bbaker6212

Btw, excuse my ignorance but what is "no."

OMNIFEX

no.= The reference efficiency of a driver with a half-space acoustical load. I tend to use this more than the published
1 watt, 1 meter dB measurements on a spec sheet.


Put it like this. The Eminence Killomax 18 is known for
being inefficent in the Pro Audio World. This is
understandable due to the 9.8 mm xmax. The Goldwood
1858 is ruffly 3 dB less than the Killomax and has a 3.36 mm xmax. Most ifnot all 3 - 6 mm xmax 18 inch woofers have a
3 db lead over the Eminence Killomax 18.

Eminence Killomax 18: xmax 9.8 mm, 93.76 dB 1 watt, no. 1.433%

Eminence Omega 18: xmax 5.5 mm, 98 dB 1 watt, no. 2.997%

Goldwood 1858: xmax 3.36 mm, 91.61 dB 1 watt, no. 0.873%


As you can see this 18 has the efficency of a 12
subwoofer, and, the xmax of an 8 inch speaker.

Not to mention, you are using an open baffle, so
these numbers will reflect the amount of volume
you will encounter, considering you will not have
any spl gain from the cabinet.
__________________
OMNIFEX
  Reply With Quote
Old 16th March 2004, 05:29 PM   #18
diyAudio Member
 
Join Date: May 2002
Location: Los Gatos, CA
The FR graph did come drom Goldwood.

I still don't understand how you are calculating ".no"

Also, I'm not sure it's accurate to say the Goldwood 1858 has an efficiency of 92db when it has an output of 104db at 45hz - if the FR graph from Goldwood is accurate. Also, stating the "xmax of an 8 inch driver" doesn't make any sense to me. Xmax is excursion right? So what does the diameter of a driver have to do with it's excursion? This statement just makes me believe you have a bias against this driver (maybe because it is cheap?) instead of using accurate and logical analysis.

No, 80hz or not, xmax is not what gives you the volume. Xmax *and* surface area is what gives you the volume. So two 18" drivers with 4mm xmax will suffice for one 18" with twice the xmax. The only reason the lower efficiency, high xmax, driver will "outshine" it is if you feed it more power. This is not my case. I will be running low power, thus I want high efficiency.
__________________
-Brad-
  Reply With Quote
Old 16th March 2004, 07:18 PM   #19
diyAudio Member
 
Join Date: May 2002
Location: Los Gatos, CA
Quote:
Efficiency has absolutely nothing to do with how much excursion/xmax you need in your drivers. For an 18" driver to produce a given SPL at a given frequncy in identical enclosures, a driver that's 80dB/W/m and one that's 105dB/W/m will both have to have exactly the same excursion, it'll just take a lot more power to get that excursion with the 80dB/W/m driver...
If you have an efficiency of 98-107db from 30-45hz with only 1 watt (running two drivers), how much excursion do you think you need? It's not like you're going to be running 100 watts into the thing! This is in a home, not a stadium.
__________________
-Brad-
  Reply With Quote
Old 16th March 2004, 07:23 PM   #20
OMNIFEX is offline OMNIFEX  Jamaica
diyAudio Member
 
OMNIFEX's Avatar
 
Join Date: Mar 2003
Location: Locked Up In The Amp Rack
bbaker6212
The FR graph did come drom Goldwood.

OMNIFEX
Does the graph state the measurements are from an open baffle?

bbaker6212
I still don't understand how you are calculating ".no"

OMNIFEX
Actually, Bass Box Pro is doing the math

bbaker6212
Also, I'm not sure it's accurate to say the Goldwood 1858 has an efficiency of 92db when it has an output of 104db at 45hz - if the FR graph from Goldwood is accurate.

OMNIFEX
Well thatís the keyword IF DIY Builders know specs are not always what they seem. I can tell you that with such a high QTS, this woofer is getting its gain from being in a small enclosure. Parts Express list the QTS as 1.04 Now. With a small driver with a QTS of this size, you can build an enclosure and try to gain a flat signal. But, having an 18 inch woofer with QTS of 1.04? You are looking at are
Humongus sealed box.

bbaker6212
Also, stating the "xmax of an 8 inch driver" doesn't make any sense to me. Xmax is excursion right?

OMNIFEX
Yes.

bbaker6212
So what does the diameter of a driver have to do with it's excursion?

OMNIFEX
Large drivers that are designed for sealed enclosures must have a large Xmax to produce bass. If they donít, they will not produce enough SPLís at low frequencies, due to running out of xmax.

bbaker6212
This statement just makes me believe you have a bias against this driver (maybe because it is cheap?) instead of using accurate and logical analysis.

OMNIFEX
Bias?
Dude, the analysis I gave (Killomax, vs, Omega, vs, 1858) is as logical, as you can get. Maybe you need to download WinSID Pro
Punch in the numbers, feed all three the same wattage, checkout the excursion, and, SPL graphs, and see what I mean.

If you want to purchase the Goldwood 1858, by all means do so!
However, you did ask for opinions, and, we gave our opinions, in which no one was endorsing this driver. Its not because its cheap. Its because it was designed to work in a sealed cabinet that will increase its gain. This speaker has a large QTS, and, the only way
to increase the SPLís is to house it in a box smaller than its minimum enclosure requirements. You are using an open baffle. Where are you going to get the gain from?


bbaker6212
No, 80hz or not, xmax is not what gives you the volume. Xmax *and* surface area is what gives you the volume. So two 18" drivers with 4mm xmax will suffice for one 18" with twice the xmax. The only reason the lower efficiency, high xmax, driver will "outshine" it is if you feed it more power. This is not my case. I will be running low power, thus I want high efficiency.

OMNIFEX
Ok. It seems like your mind is already made up, regardless of what anyone says. Just keep in mind High Efficency 18ís have an EBP of 100. The 1858 are in the 20ís. But, I guess that doesnít matterÖÖÖ

You obviously have some kind of trick to make two Goldwood 1858ís be more efficient than one Eminence Omega 18 in an
open baffle.

Once you finish building your open baffles, you can tell us what you did to accomplish such a fete.


Please keep in mind that I was in no way in my posts
being sarcastic. I just feel that I am not giving you the
answers you are looking for. So, I let someone else share
their thoughts.

Best Regards,
__________________
OMNIFEX
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Goldwood G-8003 8" Fullrange Carlp Full Range 16 3rd August 2013 04:46 PM
anyone has experience with goldwood 10" woofers ? angeloitacare Multi-Way 0 6th January 2008 06:28 PM
Goldwood 15s on OB? Pano Multi-Way 0 6th January 2007 07:23 AM
8" 4 ohm heavy duty woofer/midbass needed, who's Goldwood? eRiCdWoNg Multi-Way 11 29th February 2004 07:11 PM


New To Site? Need Help?

All times are GMT. The time now is 03:38 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2