Bass distortion before tweeter distortion with a monitor at high volume?
I am looking at getting a set of monitors for a second system in a small room (12' x 10') , but I would also like the flexibility to play them in my main system in a room that is larger (13' x 25') with cathedral ceilings.
Let's assume that the small speaker I end up with won't be able to produce enough volume without distorting in the larger room. Most of what I have read indicates that a subwoofer would solve the problem. My understanding is that I would want to high-pass the bass on the speaker before it reaches the point of distortion, solving that issue.
If that is true, that leads me to believe that generally the tweeter would not be distorting unless the volume is at a higher level. Is this normally the case? If not, it seems there would be no point to using the sub.
To restate the question: With a high quality monitor, is it safe to say that the tweeter can play at higher volume without distorting compared to the woofer? I am speaking in general terms here - I am sure there are exceptions. Thanks.
My understanding is that I would want to high-pass the bass on the
speaker before it reaches the point of distortion, solving that issue.
Its not so much a distortion issue. You're just letting a different part of the system handle certain frequencies. That said, you can make just about anything distort if you push it hard enough. If you don't install a sub, that doesn't mean the lows are going to distort. If its a small speaker, its just not able to reproduce really low notes.
To restate the question: With a high quality monitor, is it safe to say
that the tweeter can play at higher volume without distorting compared
to the woofer?
No. At least for the most part. If your amp is struggling to drive a whole speaker and you use it just for the highs, you may be able to get more volume.
Here is what I don't understand. If I try to play a small speaker in a too large room and have to supply too much power to it, it will distort. True? It just can't play that loudly. So simply adding the subwoofer would not relieve the "strain" on the drivers, it would only provide more bass, but I would still have to live with the distortion, both from the woofer and from the tweeter (I'm talking about a two-way speaker).
If I did relieve the speaker of much of the bass load with a high pass filter, you are saying that you believe in most cases the part of the signal that goes to the main speaker would still be distorted?
I believe you would increase the headroom of the system significantly with a high-pass. This calculator (below) indicates that the necessary excursion of a driver producing 40hz is 4X greater than the same driver at 80hz. This would probably clean up your bass and midrange also.
"If your speaker manufacturer uses the same tweeter in a larger 3 or
even 4-way design, I would expect it to breeze along just fine."
Thanks for an excellent common sense answer. To find a real world example, I went to Kef's web site and looked at their Q series, which utilizes the Uni-Q driver in the Q100 bookshelf. The next speaker up in the line, the Q500, uses the same tweeter along with three other drivers for the frequencies below the tweeter's capability.
In this example, it seems I could use the bookshelf along with a quality high pass and a sub(s) to achieve the flexibility I am looking for. Sounds like a great solution. I know I could take this exercise only so far , but can it be that I am actually having my cake and eating it to? Thanks again.
I disagree with all. Distortion usually comes from the amp, not the speakers. By adding a sub, you are putting less stress on the amp which allows for more headroom in the monitors. Bass is the most demanding and therefor uses the most power. The tweeter will have its limits regardless of the sub since the crossover is limiting the signal to the tweeter. You are only alleviating the stress on the woofer. I have seen plenty of small speakers that can "crank" if given the right amp. Adding a sub will help regardless.
Distortion goes up significantly beyond 90db for almost all speakers. One of the online magazines does a signal-noise sweep using both 90db and 95db volumes. So with small speakers you're approaching the cliff with only 2 watts of power (assuming 87W sensitivity). 32W and your speaker distortion will be pretty bad.
Thanks for all the interesting answers and differing points of view. I don't have the knowledge of many of the experienced posters here and it is nice to be able to take advantage of it. It seems it might be a good idea to look for a speaker/tweeter that has a lower THD? Are there any graphs or measurements available to show this and it be worthwhile?
Here is the site I was referring to. In their distortion tests, they show the distortion as DB, not percentage. There are calculators if you want the actual numbers. In short, the number of db between the signal (top line) and distortion (bottom line) is what you are looking at.
The takeaway from the KEF LS50 graph is that little mid-woofers are really pretty terrible at bass. I think it also dispels the myth that most subs aren't "fast enough" to integrate. Most subs have many many times lower distortion at bass frequencies.
If you go to the Measurements menu and select speakers, there are quite a few speakers to choose from. For larger speakers, they do a test at both 90db and 95db.
It doesn't look like most tweeters have significant measurable distortion at 95db.
I can also tell you that if I plug the ports of my Revel M106s, the midrange clears up a good bit, so even limiting the woofer's excursion physically helps. Unfortunately, that makes integrating with a sub difficult because the sub has to play at a little higher frequency and I get localization of the sub's sound.
The specific type of distortion likely to occur in a small but high-quality two-way loudspeaker driven hard is due to the woofer being driven beyond its linear excursion limits. Over-excursion results in what's commonly called "fartout" in the prosound world. Some motor designs go more gracefully into over-excursion than others, but eventually just about all of them will get there. In extreme cases, a woofer could be driven to its physical limits, which can result in the voice coil hitting the backplate with a disturbing machine-gun-like snapping sound. This causes damage to the voice coil and/or voice coil former, which may or may not kill the woofer right then and there.
As noted by sboje above, cone excursion quadruples for each octave lower you go, for the same SPL. This would be true for a sealed box - for a vented box, it's more complicated. The backpressure from the port decreases excursion near the tuning frequency, but then excursion rises very rapidly below the tuning frequency. So if the small monitor speakers are ported, the main danger zone may be lower than you would have thought, but also more severe than you would have thought.
In my opinion not only the highpass filter frequency, but also the highpass filter slope, comes into play if safely getting higher SPL out of a small speaker system is the goal. Steeper slopes do a better job. With all due respect to Richard Vandersteen, in this situation, imo first-order slopes may well be inadequate.
Here is what I don't understand. If I try to play a small speaker in a
too large room and have to supply too much power to it, it will
distort. True? It just can't play that loudly."
So simply adding the subwoofer would not relieve the "strain" on the
drivers, it would only provide more bass, but I would still have to live
with the distortion, both from the woofer and from the tweeter (I'm
talking about a two-way speaker)."
If I did relieve the speaker of much of the bass load with a high pass
filter, you are saying that you believe in most cases the part of the
signal that goes to the main speaker would still be distorted?
It depends. There's several variables at play. If your amp wasn't straining to begin with, then you should still hear the distortion. A speaker can only play so loud. If removing some of the bass frequencies helps an amp that's being driven too hard, then you may be able to squeeze more volume out of the system.
That said, this is usually not an issue for your typical high end system. Most audiophiles are far more concerned with sound quality than volume. When an audiophile is looking for volume, it usually means something's wrong. When a system is sounding good, most people don't feel the need for loud music.
Your original theory, for the most part, is correct. Removing the low frequencies should allow a speaker to play louder, but its usually not a tactic used in high end systems. It's done all the time in car systems and pro installs like a night club.
So, you guys really think that my 92 db at 1 watt/1 meter Coincident monitors are actually distorting at 95 db? Is that when I overdrive them with my 100 watt tube monoblocks or my 325 wpc Mac amp? They will fill most rooms with sound. Adding a sub adds much needed bass but doesn't increase volume a bit. The stress on my amps is negligible. I also have a 10 watt triode amp that sings beautifully with them in my 15 x 25 living room.
I bet the Coincident's are great speakers and play well in a large room, but I am sure there are limits to the db it can achieve before it distorts.
The point of this thread is to discuss whether that distortion, which most seem to agree would occur on the bottom end first, could be relieved by high passing and allowing the sub to take the lowest range.
The point of this thread is to discuss whether that distortion, which
most seem to agree would occur on the bottom end first, could be
relieved by high passing and allowing the sub to take the lowest range."
That's not true. If you have to push an amp hard to drive your speakers, the highs will be more of a problem. And in reality, this is far more likely to happen.
I am not going to be pushing an amp hard. To the contrary, I will be using a Bryston 4bsst2, which has 300w at 8 ohms, and can coast and drive ( I would think ) any 2 way monitor I choose. Again, the point is, I want a small speaker that I can use in a small room primarily, and then occasionally use it in a larger room where it will be driven harder, hence the break-up in the woofer.
A well designed speaker should perform with almost flat response and just roll off in the bass due to size limitations. Also, how big is your "big" room and how loud do you listen? I've seen some monitors that rock better than some huge floor standers, take Revel for example. You can throw 300 watts at them. Where will my speakers distort if driven with a bryston 300 wpc amp? I would have to say that it depends on the music. Jimi Hendrix will distort and possibly fry the tweeters, while Pachelbel's Canon might overdrive the woofer. Something like Diana Krall will probably do the best since she tends to be more in the mid-range. A sub will help the amp more than the speakers unless you turn up the bass knob. On a last point: My favorite repairman always said that 1 watt of distortion will fry a speaker much faster than 100 clean watts.
If you have a Bryston 4, you're correct in thinking that it will be able to handle almost any small speaker with ease. But that doesn't solve the problem. There's 2 things you need to consider.Regardless of what happens with bass, all speakers are different. Some may be able to play loud enough for you, while others can't. It has to be taken on a case by case basis, and not generalize.
More importantly, If you have a small speaker, the sub will almost certainty not be able bridge the gap between sub frequencies and the lowest frequencies the small speakers put out. Using an xover to cut out the lowest frequencies in the small speaker is only going to make the problem worse. I think this is where the confusion is coming from. Subwoofers are not woofers. They are not meant to play low frequencies, they're meant to play sub frequencies. The right way to do this would be to use a sub with full range speakers. That way, everything is doing what they were designed to do.
You once again make some good points, particularly the gap you mention between the reproducible frequencies of the sub vs the speaker and your statement that subwoofers are not woofers.
I use a pair of Rel T5's and they have crossover capability of 30hz to 120hz. One of the criticisms I have heard regarding the Rels is that they in fact are not true subwoofers, but instead bass extenders. Maybe that could work to my advantage in this scenario.
I will use the Kef LS50 as an example of what I am thinking. The specs on the Kef show it going down to 47Hz. Let's say that the high pass turns the "woofer" duty over to the Rel at 60 or 65 Hz, relieving the Kef of that responsibility. Might that work?
I measured the KEF ls50s in my room and they seem to have a low pass crossover built in- the smooth drop off starts at 80 hz. If these are your reference speaker then you need not worry (and do not want to) add your own crossover. they can play as loudly as you want up to a large conference size room as long as your amp is not driven into clipping. You will want at least 100 WPC and 150 would not be too much power for them. they also integrate well with a subwoofer- i used the JL audio D110 and had a flat, smooth freq response down to 20Hz in room. to answer your original question a given speaker driver can handle more power the higher it is crossed over -say in an active system. however the distortion you would hear is from the amplifier distorting, not the speaker. i saw a demo of the ELAC small monitors where they were over fed power and the speaker voice coil bottomed out into the magnet core and mechanical noise resulted, not clipping.