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Home » Sponsored » Pi Speakers » 7 Pi treble edge! (How to try and reduce this?)
| 7 Pi treble edge! [message #59326] |
Mon, 01 June 2009 19:13  |
PaulW
Messages: 71
Registered: May 2009
Location: UK
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Viscount |
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Having built the 7's and enjoyed the results enormously but (there's always a 'but' isn't there?) for one issue, those in room bass modes causing poor, indistinct and boomy bass at certain frequencies. I tried Wayne's multi-sub approach by borrowing a few subs (3) to go with mine and I have to say it was very good. However, I really couldn't stand the extra cable runs and number of cabinets, plus the owners wanted their sub's back. So I then went down the passive route with a box resonator, followed by foam traps in all the corners against the ceiling. Then added one behind each mid unit, sitting on top of the bass cabs. The result was very good, delivering fast, articulate, integrated and musical bass, unfortunately (yes, another one of those 'buts'!) over the last few weeks I become more dissatisfied with the treble performance. This is mostly seems to show up in the upper vocal region, alto sax and plucked strings (though not on bowed violins strangely).
So, the question is, is this a room reflection problem that has been unmasked by the eradication of the previous bass issue? The room is small for these speakers at just under 200 square foot. I'm seated about (head position) 11 feet from the front of the speakers & their corner placement gives them a crossover point about 3 feet in front of me. The surfaces in the room which do not have anything to break-up/absorb treble are the ceiling and wall between the speakers. It's always difficult to describe the quality of a sound, but words like edgy, hard, beaming and resonant all seem to apply here.
Now I did mention this in an earlier post, where I stated that as the bass was improved, the treble seemed to worsen and pointed the finger at the B&C DE250, but as Wayne considers this to be
"..... one of the smoothest compression drivers I've ever heard or measured. For that matter, it's one of the smoothest tweeters of any type I've measured. It doesn't reach beyond 18kHz, but up to that point, it is smooth as silk. A DE250 on an H290 or a π wood horn is as good as it gets, in my opinion...."
I feel I either have to look at the room or perhaps some of the amplification, which is all basic Bottlehead stuff (Seduction, Foreplay and Paramours) but this is also not know for treble problems, based on what I've read on their forum, usually the opposite. Front end? Well I mostly listen to LP's and the turntable is set-up correctly and the cartridge used is a newish Denon DL304 which is considered very 'sweet' in the treble region, so I feel I'm back to looking at the room!
Any thoughts would be most welcome.
PaulW
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| Re: 7 Pi treble edge! [message #59329 is a reply to message #59326] |
Tue, 02 June 2009 00:27  |
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Wayne Parham
Messages: 18678
Registered: January 2001
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Illuminati (33rd Degree) |
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I think multisub is the way to go, in spite of the extra complexity. If you're looking for the best bass, the multisub approach is the way to get it.
Beyond that, there may be some issues in the upper modal range, which is actually fairly low in frequency. If voices sound kind of throaty or peaky, that's the upper modal range. It's hard to say from just a description, but from what you say about your sound sources and where they are located, I think that may be a possibility.
If it is higher, in the overtone region, it may be excessive reflections in the midrange or treble. Again, it's hard to say from a description, but in a small room, I'd look at those things. Small rooms can sound like echo chambers, sort of like singing in the shower. You might want to try hanging some thick material a few inches from the wall to see what extra acoustic damping at MF and HF would do. If it helps, it might be worth it to install acoustic wedges on the walls.
I have used a half dozen DE250 drivers and they all sounded smooth to me, right out of the box. However, I have noticed that some got beaten up pretty badly in transit. I've seen chips of magnet material in the bags they come in. They're not protected very well from damage, in my opinion. I suppose it might be possible that a driver could be damaged. Doubtful that you wouldn't have noticed it before now though.
Check your tubes too. I recently noticed that one channel of my amp was sounding not quite right, so today I got into the amp and found a cathode resistor was hot enough to melt solder. It would act intermittently like it was in and out of the circuit. Two are in parallel, so when one disconnects, the cathode voltage rises. The grid voltage was high, so there was excessive quiescent current flowing through the cathode to anode.
I've seen this before with bad coupling caps, so my first thought was it happened again. I lifted the input coupling cap and measured voltage on the grid. To my surprise, the voltage stayed high. It actually was normal from a cold start through several minutes of warm up. But then the tube started acting like it was in thermal runaway. I know that's not tube terminology, but that's what was happening. As the tube warmed up, it mysteriously biased itself on harder and harder.
No problem, I have several tubes in stock. Put a new one in and it was golden. I had made the problem harder than it had to be, going through all that before swapping tubes. But it was getting hot enough to melt solder, so I needed to flow some clean solder in anyway.
The point of all this - sorry for the long winded chatter - is that the amplifier sounded a little grungy, and had been for several days. It creeps in slowly, so you don't notice it at first. Seems like something else is wrong, bad source, bad speakers maybe. But in fact, it was a bad tube. Not totally, it still played music. Sort of a sleeper problem.
So don't stop looking. Swap things around until you're sure you've found it. I've never heard a DE250 on the H290 or my wood horn sound any way other than very smooth. The measurements say so too. But that doesn't necessarily mean this is always true, surely there are some lemons out there. Same thing for the midhorn with the Delta 10. It sounds silky smooth to me. But get one with a rubbing voice coil and it would sound terrible. Or if the room is too lively or the amplifier getting a little old, you just never know what is causing your harshness until you find it, then hindsight is 20/20. 
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| Acoustic wedges [message #59342 is a reply to message #59340] |
Thu, 04 June 2009 10:36 |
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Wayne Parham
Messages: 18678
Registered: January 2001
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Illuminati (33rd Degree) |
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I think the acoustic wedges will really work out nicely for you. You can put them on the side walls and behind, the walls adjacent to the installed corners. That will help decrease early reflections and soften the room.
Most times, the opposite wall is allowed to be reflective, although sometimes diffused. That reduces early reflections but leaves some late reflections for spaciousness.
In a very small room, however, everything is an early reflection, and high amplitude too, so it may make sense to add some wedges to the opposite wall as well. Diffusion doesn't really work either, if the room is too small, because the reflections are too loud and early. It just makes the sound field a jumbled mess. So in the case of a small, live room, I think the generous application of acoustic wedges probably makes the most sense.
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| Re: 7 Pi treble edge! [message #59345 is a reply to message #59344] |
Thu, 04 June 2009 20:27 |
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Wayne Parham
Messages: 18678
Registered: January 2001
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Illuminati (33rd Degree) |
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A very busy room, makes me feel right at home!
Honestly, I have seven π speakers in a room a lot like yours, with regards to size. It's my office/workroom and it's a lot like yours. I probably should get some foam wedges too. My room doesn't sound too bright, but I'll bet anything it would be improved with absorbent wedges on the walls adjacent to the corners where the speakers are.
If you can, try first lining the walls beside and behind the speakers. Make those as dead as possible first. Line the whole front wall, if possible, the one you're facing when you listen to the speakers.
The curtains help the left speaker, but since you say it's bright, it probably would sound better if you covered the right wall with something. The decorative cloth I see hanging near the right speaker won't do much of anything in terms of absorption.
If you want to do a test run of these ideas first, hang a few thick blankets. Space them out away from the wall a few inches. This spacing is important - it sort of catches the sound. It puts the absorbent material where it can do the most good. For starters, I'd cover the whole front wall this way, from the ceiling to the floor, wall to wall. I'd also hang a curtain on the right wall. Start there.
You can use the same method to try absorbent material on other boundaries. Since your room is small, the rear walls may be slapping you with a nasty early reflection. Might hang a blanket out a foot or so from that wall, wherever is convenient, just to see how it sounds.
These kinds of sound checks will let you know where you want wedges without having to buy them first. Once you know where you want absorbent material, you can decide how to arrange your room, your equipment, media, furniture and decorations.
Might be cool to put the equipment in the recess on the rear wall, and hang a curtain as a partition. This might double as an absorber and decoration. There are a lot of cool things you can do that will keep the treatments from being too intrusive.
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| Re: 7 Pi treble edge! [message #60359 is a reply to message #59326] |
Thu, 09 July 2009 13:29 |
Russellc
Messages: 397
Registered: May 2009
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Illuminati (1st Degree) |
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| PaulW wrote on Mon, 01 June 2009 19:13 | Having built the 7's and enjoyed the results enormously but (there's always a 'but' isn't there?) for one issue, those in room bass modes causing poor, indistinct and boomy bass at certain frequencies. I tried Wayne's multi-sub approach by borrowing a few subs (3) to go with mine and I have to say it was very good. However, I really couldn't stand the extra cable runs and number of cabinets, plus the owners wanted their sub's back. So I then went down the passive route with a box resonator, followed by foam traps in all the corners against the ceiling. Then added one behind each mid unit, sitting on top of the bass cabs. The result was very good, delivering fast, articulate, integrated and musical bass, unfortunately (yes, another one of those 'buts'!) over the last few weeks I become more dissatisfied with the treble performance. This is mostly seems to show up in the upper vocal region, alto sax and plucked strings (though not on bowed violins strangely).
So, the question is, is this a room reflection problem that has been unmasked by the eradication of the previous bass issue? The room is small for these speakers at just under 200 square foot. I'm seated about (head position) 11 feet from the front of the speakers & their corner placement gives them a crossover point about 3 feet in front of me. The surfaces in the room which do not have anything to break-up/absorb treble are the ceiling and wall between the speakers. It's always difficult to describe the quality of a sound, but words like edgy, hard, beaming and resonant all seem to apply here.
Now I did mention this in an earlier post, where I stated that as the bass was improved, the treble seemed to worsen and pointed the finger at the B&C DE250, but as Wayne considers this to be
"..... one of the smoothest compression drivers I've ever heard or measured. For that matter, it's one of the smoothest tweeters of any type I've measured. It doesn't reach beyond 18kHz, but up to that point, it is smooth as silk. A DE250 on an H290 or a π wood horn is as good as it gets, in my opinion...."
I feel I either have to look at the room or perhaps some of the amplification, which is all basic Bottlehead stuff (Seduction, Foreplay and Paramours) but this is also not know for treble problems, based on what I've read on their forum, usually the opposite. Front end? Well I mostly listen to LP's and the turntable is set-up correctly and the cartridge used is a newish Denon DL304 which is considered very 'sweet' in the treble region, so I feel I'm back to looking at the room!
Any thoughts would be most welcome.
PaulW
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I will agree on the "Smoothest part" but disagree as to the right out of the box part. Right out of the box, mine sounded like a cutting torch was going through your head unless I used an L-pad to severly reduce the output.
After a few weeks of play, I noticed I was slowly turning them up, until I was basically at the same place I was when the Selenium 220 Ti was installed. The Selenium sounds dry and fuzzy in comparison. Its a great driver, you can read of mine and others exploits with it over on AK with the E'wave thread.
I'm using the B&C DE 250 on top of a JBL 4507 box tuned to either 34 hz or about 30 hz depending on mood. The 5 cu ft 4507 box is currently loaded with JBL 2235H, and have also tried a pair of 2225H as well.
The B&C DE250 sounds way more clear and revealing than the Selenium 220 ti. Not to take anything away from this inexpensive driver, its amazing for the price, but the B&C DE 250 sounds a whole lot better, no small improvement. The selenium is very enjoyable in that project, the crossovers compensation is spot on. But with the B&C, another level is achieved. Clarity is much improved, truely an impressive driver, I would suggest run in time will cure your problem.
russellc
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