sreten said:
Right, sreten. Some people believe that the Usher drivers are simply cheap clones of the Scan-Speak classic drivers. This is not true. Usher people did not copy the SS design. They designed motors on their own. Particularly, the 8945P's motor is very different from the SS 8545's. And the 8945P measures better than the 8545 in nonlinear distortions. Even the Usher 8945A, which "looks" similar to the 8545, is different, as Zaph mentions:
"This woofer (8945A) was considered by many to be a clone of the Scan Speak 8545. The cone and surround are similar but there are some differences internally."
Trey,
As I said above, checking on drive units' distortion measurements will help you make an easier decision. The following are Zaph's harmonic distortion measurements of the Usher 8945P and two other drivers that have been used in many existing designs for their good cost-to-performance ratio:
Let's first compare 8945P and RS180. The RS180 is a very cost-effective 7" driver. Its distortions in a frequency range (below 1.8 kHz) in which it is normally used are relatively low compared to other inexpensive 7" drivers. But when compared to the 8945P, it turns out that the Usher is in a totally different league. Focus on acoustically obtrusive 3rd and 5th order harmonic distortions on the above graphs (indicated by blue and grey lines). On average, the 8945P's odd-order distortion levels are 15 to 20 dB lower than the RS180's in the range of 200 Hz to 1.5 kHz. Remember that a driver's harmonic distortions cannot be corrected by a crossover, that is, no matter how well the crossover is designed.
Now to the CA15RLY, due to Zaph's different measurement settings between 5.5" and 6.5" drivers, we need to subtract 4 to 5 dB from the CA15RLY distortion levels. But even if we do so, you'll see that the CA15RLY's odd-order harmonic distortion levels are even slightly higher than the RS180's in the same range as above mentioned.
This shows how low-distortion the 8945P is. Actually, as I already said in my above post, the quality of the Usher 8945P is top notch regardless of price. In a 2-way system, the midbass driver's quality is much more important than the tweeter's because a frequency range it covers is the range where most fundamental tones in music are played. But when a midbass driver is this good, we want to match it with a same low-distortion tweeter.
Also, note that in your situation of speaker placement in the room, you'll definitely need a reduced BSC crossover. Many existing designs don't have this option unless the designer is willing to modify the crossover for you.
As I said above, checking on drive units' distortion measurements will help you make an easier decision. The following are Zaph's harmonic distortion measurements of the Usher 8945P and two other drivers that have been used in many existing designs for their good cost-to-performance ratio:
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An externally hosted image should be here but it was not working when we last tested it.
Let's first compare 8945P and RS180. The RS180 is a very cost-effective 7" driver. Its distortions in a frequency range (below 1.8 kHz) in which it is normally used are relatively low compared to other inexpensive 7" drivers. But when compared to the 8945P, it turns out that the Usher is in a totally different league. Focus on acoustically obtrusive 3rd and 5th order harmonic distortions on the above graphs (indicated by blue and grey lines). On average, the 8945P's odd-order distortion levels are 15 to 20 dB lower than the RS180's in the range of 200 Hz to 1.5 kHz. Remember that a driver's harmonic distortions cannot be corrected by a crossover, that is, no matter how well the crossover is designed.
Now to the CA15RLY, due to Zaph's different measurement settings between 5.5" and 6.5" drivers, we need to subtract 4 to 5 dB from the CA15RLY distortion levels. But even if we do so, you'll see that the CA15RLY's odd-order harmonic distortion levels are even slightly higher than the RS180's in the same range as above mentioned.
This shows how low-distortion the 8945P is. Actually, as I already said in my above post, the quality of the Usher 8945P is top notch regardless of price. In a 2-way system, the midbass driver's quality is much more important than the tweeter's because a frequency range it covers is the range where most fundamental tones in music are played. But when a midbass driver is this good, we want to match it with a same low-distortion tweeter.
Also, note that in your situation of speaker placement in the room, you'll definitely need a reduced BSC crossover. Many existing designs don't have this option unless the designer is willing to modify the crossover for you.
Hi,
I wonder if the measurent of the RS180 is correct though. The Dayton´s fundamental´s curve stays close to 0dB, while the others -as it would be expected- show a HP-Response. This leads to a difference of up to 25dB at the lowest freqs between the Usher and the Dayton.
Besides in the freq-range of interest above 40Hz the differences are small and should be well below the treshold of recognition anyway.
jauu
Calvin
I wonder if the measurent of the RS180 is correct though. The Dayton´s fundamental´s curve stays close to 0dB, while the others -as it would be expected- show a HP-Response. This leads to a difference of up to 25dB at the lowest freqs between the Usher and the Dayton.
Besides in the freq-range of interest above 40Hz the differences are small and should be well below the treshold of recognition anyway.
jauu
Calvin
Hi,
ok, maybe its an artifakt (sure that this artifakt isn´t included in the distortion too?)
Anyway, the questions remains: "Do these differences matter?"
According to what can be read in another thread about harmonic distortion it is claimed to be a rather ´useless at all´ parameter.
Comparing with other scientifical reports dealing with recognition tresholds of distortion these tresholds are already high with stationary signals (sinewave) and rather unrecognizable with natural instrument sounds (stochastic signals with varying amplitudes and phases that already contain multiple harmonics). The values are so high that most of the drivers would have work under overload conditions.
Nonlinear Distortion is reported to be recognizable from >1% on using sinewave signals (IM-distortion, again with music the treshold is far higher).
Consequently IM distortion is quoted to be a more sensitive parameter than harmonic distortion measurements.
jauu
Calvin
ok, maybe its an artifakt (sure that this artifakt isn´t included in the distortion too?)
Anyway, the questions remains: "Do these differences matter?"
According to what can be read in another thread about harmonic distortion it is claimed to be a rather ´useless at all´ parameter.
Comparing with other scientifical reports dealing with recognition tresholds of distortion these tresholds are already high with stationary signals (sinewave) and rather unrecognizable with natural instrument sounds (stochastic signals with varying amplitudes and phases that already contain multiple harmonics). The values are so high that most of the drivers would have work under overload conditions.
Nonlinear Distortion is reported to be recognizable from >1% on using sinewave signals (IM-distortion, again with music the treshold is far higher).
Consequently IM distortion is quoted to be a more sensitive parameter than harmonic distortion measurements.
jauu
Calvin
Mark K has written up a very balanced view of this issue at his home page. But alas, he accidently deleted all this valuable info!
Anyway, in sum, non-linear distortions (including simple single-tone generated harmonics or multi-tone IM distortions) won't be an issue for well-designed low-distortion systems or drive units. But what's a well-designed system or drive unit? Normally, for a home system with limited size (e.g. equal to or less than 7-8" midbass drivers) and limited xmax, non-linear distortions matter. In my personal experience, I was abel to hear difference in midrange distortion levels between the RS180 and the 8945P during various music passages, even when I tried a low 1.5 kHz xover, higher order LP filter for the RS180 to mitigate its breakup-induced distortions.
Anyway, in sum, non-linear distortions (including simple single-tone generated harmonics or multi-tone IM distortions) won't be an issue for well-designed low-distortion systems or drive units. But what's a well-designed system or drive unit? Normally, for a home system with limited size (e.g. equal to or less than 7-8" midbass drivers) and limited xmax, non-linear distortions matter. In my personal experience, I was abel to hear difference in midrange distortion levels between the RS180 and the 8945P during various music passages, even when I tried a low 1.5 kHz xover, higher order LP filter for the RS180 to mitigate its breakup-induced distortions.
Re: MTM bookshelf
Of course, the RS180 is excellent for the price. But it's not the best, lowest-distortion driver money can buy. At a higher volume level, its distortion characteristic (a bit higher tall order harmonics excited by midrange tones in the range of 300 Hz to 1 kHz shown in Zaph's measurements) is clearly audible when compared to lower distortion drivers (e.g., Scan-Speak Revelator or in my case Usher 8945P). Note that distortions in this range cannot be corrected by a crossover, that is, no matter how well a crossover is designed. In my experiement, which I performed when I designed my RS180/27TDFC MT crossover, I used a 4th order electrical filter with a notch filter (just like Jon Marsh's C-E type) with a 1.5 kHz xover point for the RS180.
mlwebb said:
Of course, the RS180 is excellent for the price. But it's not the best, lowest-distortion driver money can buy. At a higher volume level, its distortion characteristic (a bit higher tall order harmonics excited by midrange tones in the range of 300 Hz to 1 kHz shown in Zaph's measurements) is clearly audible when compared to lower distortion drivers (e.g., Scan-Speak Revelator or in my case Usher 8945P). Note that distortions in this range cannot be corrected by a crossover, that is, no matter how well a crossover is designed. In my experiement, which I performed when I designed my RS180/27TDFC MT crossover, I used a 4th order electrical filter with a notch filter (just like Jon Marsh's C-E type) with a 1.5 kHz xover point for the RS180.
Calvin said:
Hi,
Well IMO a "useless at all" opinion taken to non-logical extremes.
Remember that distortion measurements are symtoms, very much
incomplete, so too much cannot be read into them, but then again
reading too little is an even worse travesty.
The distortion papers at Klippel.de are well worth a read. Especially
the analysis of symtoms and how they relate to various distortion
mechanisms. Low odd harmonic distortion is a very good thing ...
(And very much related to IM ...)
/sreten.Re: Usher 8945P 7" / Peerless HDS 1" MTM
A person is in the process of building this design as I said here:
http://www.diyaudio.com/forums/showthread.php?postid=1524298#post1524298
Jaanos said:
A person is in the process of building this design as I said here:
http://www.diyaudio.com/forums/showthread.php?postid=1524298#post1524298
Ok great, the design looks pretty much exactly what I am after!! but I am just a little sceptical building something that has never actually been 'heard' before if you know what I mean....
Do you think the MTM design will eliminate the need for a subwoofer when listening to music? Or am I beter off going with the TM design coupled with a seperate sub? I only say this as the above link refers to the TM slightly lacking in bass when compared to B&W's 802D's - at approx $12,000 a pair tho!!
Thanks in advance for any advice and please forgive my lack of knowledge......
CHEERS!!
Do you think the MTM design will eliminate the need for a subwoofer when listening to music? Or am I beter off going with the TM design coupled with a seperate sub? I only say this as the above link refers to the TM slightly lacking in bass when compared to B&W's 802D's - at approx $12,000 a pair tho!!
Thanks in advance for any advice and please forgive my lack of knowledge......
CHEERS!!
Hi,
An MTM gives no more bass extension than an MT, it simply plays
louder and is more sensistive (albeit 4 ohms) in a x2 size box.
MT (sealed) + active subwoofer is the way to go for deep bass.
(Properly designing the sub will always give more extension
and more SPL capability in the low bass. If not done properly
this is not guaranteed, one can make a sub that goes too
loud (and this is hardly ever needed) but not deep enough.)
Having said that there are alignments for the MTM in a bigger box
(1.5 to 1.8 cuft) than can be tuned low (28Hz to 22Hz), and with
optimal placement to use room gain (i.e. well away from, and
unequal distance to, walls) surprising bass extension can be
available. This is also true of the MT but at lower levels.
Bass loudness curves indicate the louder it is the deeper it appears
to go, with the proviso it goes deep in the first place, but at modest
levels that bass extension is not easily heard.
TBH most people have no idea what they really need in terms of
maximum levels, bass extension, whatever. An MT is in all respects
better than an MTM except for annoying the neighbours. The extra
volume capability of an MTM may not be needed most of the time.
FWIW the extended bass alignments can sound too "light" to some
depending on the room match. a modicum of adjustable passive
line level bass boost in the low bass region can work very well.
(when combined with an overdamped alignment)
/sreten.
An MTM gives no more bass extension than an MT, it simply plays
louder and is more sensistive (albeit 4 ohms) in a x2 size box.
MT (sealed) + active subwoofer is the way to go for deep bass.
(Properly designing the sub will always give more extension
and more SPL capability in the low bass. If not done properly
this is not guaranteed, one can make a sub that goes too
loud (and this is hardly ever needed) but not deep enough.)
Having said that there are alignments for the MTM in a bigger box
(1.5 to 1.8 cuft) than can be tuned low (28Hz to 22Hz), and with
optimal placement to use room gain (i.e. well away from, and
unequal distance to, walls) surprising bass extension can be
available. This is also true of the MT but at lower levels.
Bass loudness curves indicate the louder it is the deeper it appears
to go, with the proviso it goes deep in the first place, but at modest
levels that bass extension is not easily heard.
TBH most people have no idea what they really need in terms of
maximum levels, bass extension, whatever. An MT is in all respects
better than an MTM except for annoying the neighbours. The extra
volume capability of an MTM may not be needed most of the time.
FWIW the extended bass alignments can sound too "light" to some
depending on the room match. a modicum of adjustable passive
line level bass boost in the low bass region can work very well.
(when combined with an overdamped alignment)
/sreten.In my case, my speakers sound much more satisfying to me with the loudness switch on. Obviously something wrong in my setup in the 60 - 160Hz range I'm guessing. This has generally been the case in various rooms I've listened to the speakers. Room nodes, or just my hearing insensitvity down low could be the reason. Without the loudness, speakers tend to sound thin.... All I want is a bass guitar to not come "in or out" depending on the frequency being played
Well - something to address with the new speakers & placement.
David.
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