Decreasing speaker efficiency?

503Timber · 22nd May 2011, 03:09 PM

My question is......

Can you DECREASE a fullrange drivers efficiency level? In theory I want to take a 91db efficient speaker and bring it down to 88db or so.

talaerts · 22nd May 2011, 03:20 PM

I first thought you could put a resistor in series, (this will also change the behaviour in the low frequencies, if I am not mistaken), but then I thought about the following.
Now I may be making huge errors as I am far from the theoretical speaker guru, feel free to disagree with my reasoning:
You want to decrease with 3db, which in essence means that it should be half as loud.
To me this would mean that you need to put an 8 ohm resistor (when using an 8 ohm speaker) of ample wattage in series with the speaker to have this effect. Then (depending on the frequency) around half of the power would go to the speaker, the other half would warm up the resistor.
This is not efficient. I think it would be better to reduce this volume at the pre-amplifier side.
As I said, there may be big errors in my reasoning...

Nelson Pass · 22nd May 2011, 04:24 PM

It's easy enough to pick up an L pad from Parts Express for a few bucks
and give it a try.

planet10 · 22nd May 2011, 06:49 PM

Why are you trying to decrease the efficiency? We usually strive for more not less.

dave

503Timber · 22nd May 2011, 07:16 PM

First I need to lay out that I am new at all this so my "theories" may be worthless but here goes. My system is at my computer desk and is fed to a USB DAC to a DIY tube pre and DIY 6V6 PP amp, my speaker cables are DIY CAT5 and WireLogic Audio 500 interconnects all hooked to Fostex FE127E's in a small ported bookshelf cabinet on stands. My speakers are about 7' apart and I sit about 2' in front of them with a slight toe in.

The Fostex are a bit bright for me so taming that would be nice but foremost it seems as my amp opens up a bit at a higher volume......so if I decrease the sensitivity I was hoping to hit that "sweet spot" on my amp. As it is to hit the sweet spot is far to loud......I'm not sure if any of that makes sense.

18Hurts · 22nd May 2011, 07:24 PM

Guitarists do that with power resistors hooked up to their tube amps

They like the sound of tubes distorting at high levels so the resistor trick works well. They call them hot plates or dummy loads. Here is a link that goes through all the different ways to load down tube amps.

Grail Tone - Low Volume, Fat Tone

planet10 · 22nd May 2011, 08:04 PM

The FE127e is actually more like 90 dB measured. Perhaps a bit of BSC is what you need, would allow you to shelve down the mid/Highs without affecting the bass alignment.

dave

AstroSonic · 22nd May 2011, 08:49 PM

"foremost it seems as my amp opens up a bit at a higher volume......so if I decrease the sensitivity I was hoping to hit that "sweet spot" on my amp. As it is to hit the sweet spot is far to loud......"

Your class AB (?) PP amp should be running in class A to well over 90db in the near field with the 127e's.

It sounds like you are experiencing the improved sound quality that comes with spl's above about 80db, allowing you to hear bass in-balance with the mids and highs (see: Fletcher?Munson curves - Wikipedia, the free encyclopedia). The best solution is line-level 'loudness' compensation. Baffle step compensation would also help.

BTW, nice computer room system!

Regards,

Bob

503Timber · 22nd May 2011, 09:59 PM

Thanks guys! I think I'll look into BSC......could be just what the doctor ordered.

talaerts · 23rd May 2011, 06:35 AM

Perhaps try using the equalizer in itunes (or similar), based on the resulting curve you could design a filter, or simply use itunes as the filter.

22nd May 2011, 03:09 PM	#1
503Timber diyAudio Member Join Date: May 2011 Location: Portland Oregon	Decreasing speaker efficiency? My question is...... Can you DECREASE a fullrange drivers efficiency level? In theory I want to take a 91db efficient speaker and bring it down to 88db or so.

22nd May 2011, 06:49 PM	#4
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	Why are you trying to decrease the efficiency? We usually strive for more not less. dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

22nd May 2011, 08:04 PM	#7
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	The FE127e is actually more like 90 dB measured. Perhaps a bit of BSC is what you need, would allow you to shelve down the mid/Highs without affecting the bass alignment. dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

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22nd May 2011, 03:20 PM	#2
talaerts diyAudio Member Join Date: Oct 2005	I first thought you could put a resistor in series, (this will also change the behaviour in the low frequencies, if I am not mistaken), but then I thought about the following. Now I may be making huge errors as I am far from the theoretical speaker guru, feel free to disagree with my reasoning: You want to decrease with 3db, which in essence means that it should be half as loud. To me this would mean that you need to put an 8 ohm resistor (when using an 8 ohm speaker) of ample wattage in series with the speaker to have this effect. Then (depending on the frequency) around half of the power would go to the speaker, the other half would warm up the resistor. This is not efficient. I think it would be better to reduce this volume at the pre-amplifier side. As I said, there may be big errors in my reasoning...

22nd May 2011, 04:24 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	It's easy enough to pick up an L pad from Parts Express for a few bucks and give it a try.

22nd May 2011, 07:16 PM	#5
503Timber diyAudio Member Join Date: May 2011 Location: Portland Oregon	First I need to lay out that I am new at all this so my "theories" may be worthless but here goes. My system is at my computer desk and is fed to a USB DAC to a DIY tube pre and DIY 6V6 PP amp, my speaker cables are DIY CAT5 and WireLogic Audio 500 interconnects all hooked to Fostex FE127E's in a small ported bookshelf cabinet on stands. My speakers are about 7' apart and I sit about 2' in front of them with a slight toe in. The Fostex are a bit bright for me so taming that would be nice but foremost it seems as my amp opens up a bit at a higher volume......so if I decrease the sensitivity I was hoping to hit that "sweet spot" on my amp. As it is to hit the sweet spot is far to loud......I'm not sure if any of that makes sense.

22nd May 2011, 07:24 PM	#6
18Hurts diyAudio Member Join Date: Nov 2010	Guitarists do that with power resistors hooked up to their tube amps They like the sound of tubes distorting at high levels so the resistor trick works well. They call them hot plates or dummy loads. Here is a link that goes through all the different ways to load down tube amps. Grail Tone - Low Volume, Fat Tone

22nd May 2011, 08:49 PM	#8
AstroSonic diyAudio Member Join Date: Jun 2004 Location: central Pennsylvania, USA	"foremost it seems as my amp opens up a bit at a higher volume......so if I decrease the sensitivity I was hoping to hit that "sweet spot" on my amp. As it is to hit the sweet spot is far to loud......" Your class AB (?) PP amp should be running in class A to well over 90db in the near field with the 127e's. It sounds like you are experiencing the improved sound quality that comes with spl's above about 80db, allowing you to hear bass in-balance with the mids and highs (see: Fletcher?Munson curves - Wikipedia, the free encyclopedia). The best solution is line-level 'loudness' compensation. Baffle step compensation would also help. BTW, nice computer room system! Regards, Bob

22nd May 2011, 09:59 PM	#9
503Timber diyAudio Member Join Date: May 2011 Location: Portland Oregon	Thanks guys! I think I'll look into BSC......could be just what the doctor ordered.

23rd May 2011, 06:35 AM	#10
talaerts diyAudio Member Join Date: Oct 2005	Perhaps try using the equalizer in itunes (or similar), based on the resulting curve you could design a filter, or simply use itunes as the filter.

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