Adjusting Room sound using material damping methods (not DSP)

[danrubin]

>without grilles ?

I listen to my SHL5's without grilles since I discovered that low frequencies were creating some physical interaction between the cross-bar on the grille and the Radial driver surround. The sound is a bit brighter as you would expect and also more immediate, I suppose. For now at least, I prefer my Harbeths naked.

[airdavid]

>without grilles ?

I listen to my SHL5's without grilles since I discovered that low frequencies were creating some physical interaction between the cross-bar on the grille and the Radial driver surround. The sound is a bit brighter as you would expect and also more immediate, I suppose. For now at least, I prefer my Harbeths naked.

Alan, what do you think about it ?

David

[A.S.]

I've replied to this one in detail in Home, Technical Questions to the Harbeth Designer.

[A.S.]

Don: It's one of my Studers. Technically inferior to digital but beautiful to handle and watch. I've been promising myself for five years to align them - but just no time for such pleasures even though I know exactly how to and have all the gear.

[Ned Mast]

Alan, I don't want to belabor the amplifier power issue, but am not entirely clear about it. My 170 W(into 8 ohms) amp has meters that indicate that it rarely is using more than 3 or 4 watts; is that all the power that is reaching the voice coils of my SHL5's? Or is there more to the issue? Would I be better off getting a lower powered amp for my Harbeth's?

With thanks,

Ned Mast

[A.S.]

... my 170 W(into 8 ohms) amp has meters that indicate that it rarely is using more than 3 or 4 watts; is that all the power that is reaching the voice coils of my SHL5's?

No problem: a good chance to touch on this subject again. You might want to follow another thread running here at the moment concerning speaker efficiency.

Your observation about 3 or 4 Watts is exactly what I would expect, and indeed it is the figure I have quoted as a generalistaion for years, to disbelief. This whole machismo thing with big beefy amplifiers is quite beyond my logic orbit. Yes, I understand that the Bentley car owner with his 400BHP (at 1600rpm) has a huge and very thrilling power reserve, but when can he use it? And if he did how much of it could reach the road surface which is essential for that power to be useful.

Power is only effective (hence the term effective power) when it is doing work, and this implies that it is pushing against something*. It may be mechanical power pushing againt a piston rod or it may be electrical power pushing against a resistive load. The Bentley, standing in the garage being revved, is not doing effective work: for that the engine has to drive the wheels.

Take for example a power station. It burns coal and the process boils water which turns turbines (motors used in reverse) and bingo - electric current is produced. But if the power station is off-line, it is not, by definition, doing work, so it has 0% efficiency. It still consumes coal though to keep the turbines revolving. When those turbines are coupled to the national grid (can you imagine the momentary arking of the master switch?), the turbine's speed probably briefly sags as it starts to do work and needs time to build up again, and hence to reach maximum efficiency.

So, back to amplifiers. The manufacturers rating (170W in your case) means "this amplifier is capable, at a maximum, of doing 170W of work pushing power into a fixed and continuous resistive load connected across its terminals should the user feed a suitably large signal into the amp's inputs and turn the volume up to maximum". It does not mean 'this amplifier will give you, whether you like it or not, 170W of power, regardless of music, volume setting, your neighbours, your ears or your speaker's ability to take that power'.

In other words, the Bentley driver's foot on his throttle controlling the beast under the bonnet (hood) is the same as your hand on the volume control: if you don't draw on the power available, you are not given it out of the generosity of the amplifier - it is entirely your slave. You are the one with a hand on the master switch - thank goodess.

It's only recently dawned on me that many audiophiles think that power is being issued forth from the amplifier regardless of the music or the volume setting so that 100W of power generously issued must, surely, be better than 50W since the bigger amp is that much more benevolent. Not so: power is pulled from the amp at your command, so a 50W amp being driven hard will produce the same amount of power as a 100W being driven half as hard.

As you observed, you are commanding 3 or 4W from your amp. That means there is lots of power potential, idling, unneeded under the bonnet, (170-3 = 167W) of available power for you to draw on should you ever need it. But if you don't ever need it, you'd be in the same situation as having, say, a 50W amp and drawing 3 or 4W from that: still tons of power in reserve. In the city, why have 400BHP of power available when you can't draw on it? You might as well have a 50BHP engine and work it quite hard to maximise its efficiency.

I am not saying that smaller amps are better than bigger amps, since given the choice (and someone else was footing the bill - dream on) I'd rather be cruising around in Bentley than a Smartcar. I am a responsible driver (and listener) but in the hands of the wrong driver, too much power can be lethal.

Now, what is so often overlooked is this: having the power available at your command is one thing but can the speaker system actually handle all that raw power? No. Not likely!

Does this help at all?

Please also look at: http://www.harbeth.co.uk/usergroup/s...?p=865#post865

* One of the reasons that speaker efficiency is so low (about 1% electro-acoustic conversion) is because the speaker cone pushes against air - which is very thin. If your room was full of treacle the efficiency would dramatically increase because the drive unit could do some effective work. Same with car engines: if there is a leak in a cylinder, no matter how far the piston moves, it's not properly compressing the air mixture and power efficiency drops.

[chord]

Thanks for the effort in educating the hifi-audio community.

Is that true to say that since the efficiency is only about 1% and speakers are consuming about 3 - 4W (at normal listening level?), the power requirement is then 300-400W? Why would 50 - 100W power be sufficient? The effective power is only 0.5 - 1W?

Would you also please touch on damping factor and dynamic headroom of an amplifer? Does that bear any relationship with the power of an amplifer? It may be an important element to instantly draw on the power in reserve.

In another post, it is mentioned that 99% of the energy is dissipated as heat in voice coils. How can they unload the heat energy so quickly? The heat should be released in the listening room? I would expect the room to heat up very soon. It may help save some heating cost during winter time.

[A.S.]

Would you also please touch on damping factor and dynamic headroom of an amplifer? Does that bear any relationship with the power of an amplifer? It may be an important element to instantly draw on the power in reserve ... how can (voice coils) unload the heat energy so quickly?

I don't know enough about amps to accurately comment, but I have read reports that cast doubt on the claimed importance of 'damping factor'. As for dynamic headroom - I don't recognise the term.

Voice coils and heating: actually, some heat is also dissipated in the crossover, but mostly in the voice coil. How can the voice coil unload heat? Answer:

1. Thankfully, the voice coil is flapping about (because it is attached to the cone) when the music is playing, especially if there is significant bass in the music hence lots of cone movement. When the cone is in motion it creates a draught around the coil in the same way that ladies fan themselves a hot day.

2. No Harbeth customer is ever playing at the ridiculous power levels mentioned elsewhere. I stress again: speakers can not take more than a few Watts of continuous electrical power (key word: continuous) before the voice coil heats up to the point that its heat overwhelms the cooling draught effect. In the mid day heat, deep in the windless Sahara desert, no amount of fanning yourself is going to cool you down.

I've already shown what happens when that point is reached here: http://www.harbeth.co.uk/sales/servi...ifier-DC-F.jpg

As an example, the continuous power handling of the LS3/5a's bass unit is about 10W: yes, really. Yet it is paired with enormous amplifiers. The implication is that a) the amplifier can not be delivering very much power, proving how little really is necessary for music at home even wioth an inefficient speaker b) how the ratio of the instantaneous peaks to the average signal level in real music must be high, which helps minimise long-term voice coil heating.

3. Even a big amp (by which I mean, say, 150W+) driven carefully is fine providing the power is only transient so that the voice coils have time to dissipate the heat. This is the thermal recovery time constant of the driver, probably measured over periods of a minute or two. It's the accumulation of heat over minutes that does the damage as shown in the link above. So, if you have youngsters and they use your Harbeths for a disco, as the birds and booze combo starts to take effect and their hearing numbs, the continuous power delivered to the speakers rises - the heating effect of the energy pulse from the beats in pop music top-up the voice coil's temperature faster than it is fanned away. You discover the next day that your speakers are scratching (warped voice coils) or dead.

4. Don't forget as I have explained elsewhere, all of this amp stuff is very nice but misses the point: when the suspension of the driver simply can not permit the cone to excurt any further, you could have the biggest audio amp ever made but it's not going to produce any more sound for you: but it will burn-out your voice coil.

Once again we find that the perception the user has of the really very simple interrelationship between music, amplifier and speakers is just plain wrong. I think one of the most important attributes of a relaxed, fulfilled life is simplification: boiling issues down to their basics. It should be a by-word here.

P.S. I make stupid mistakes all too frequently. I have just scrapped some 100 hours of very careful adjustment of a new crossover on my simulator - many of them late into the night - because I made a careless mistake when I captured the original acoustic data. Hence, when I came to compare the simulated system frequency response on screen with that of the actual crossover driving the real speaker they were very different when they should have been identical. So, another Sunday afternoon on the farm (where our R&D space is located, along with the horses) tracking back through the entire project to find the mistake. Was it the microphone? No: It's the brand new B&K 4191. Perhaps I made a mistake wiring the crossover from the simulator printout. No. Is it the simulation itself? Perhaps the drive units have changed/are damaged. No. So it must be the original data ..... I'm writing this up just to cheer myself up before I start to resolve exactly why and how the original measurement data is wrong! Bang goes Sunday evening.

[Ned Mast]

Thanks, Alan -
Your response to my query regarding ampifier power (too much?) was clear and most helfpul. Were I to buy a new amplifier, I would go for one less powerful. But since I already had this one - and am very judicious with the volume control - I shall simply listen at the moderate levels I always do and not worry.

Best, Ned

[A.S.]

http://www.harbeth.co.uk/usergroup/s...=lastpost&t=48

I mentioned above the importance of a good quality carpet in reducing reflections. Here is a picture of an anechoic chanmber; I'm definitely not saying that this would make a good listening environment (it would completely kill the life in music) but it does show you the extreme opposite poistion to a typical music room at home.

Note how important it is to have the walls treated - but no less than the floor and ceiling. The idea is to minimise sound waves bouncing around, and they find it extremely easy to bounce of exactly parallel opposing walls. Think of a skipping wrope pulled taught, each end being an opposite wall.

Notice how the wedges are tapered - the shorter wavelengths (= higher frequencies) are soaked up on the tips and the lower frequencies penetrate deeper into the wedge where they are absorbed. The wedge shape creates a graduated absorption which is much more effective than letting a significant proportion of the sound waves just bounce off a smooth, albeit absorptive surface. I agree that to arrange such a surfact treatment at home would be impossible - and unnecessarily complex. But, several bookcases, with the books packed loosely and some open spaces between them does create a poor-man's absorber. Better still if the spines are turned inwards the high frequencies are absorbed in the page edges - but then you can't identify your books!

A simple rough-and-ready experiment that you can undertake yourself to check for reflections in your listening room:

You will need: yourself, a volunteer helper, a torch with a good stong beam and about 30 minutes.

Action plan:

1. Wait until dark. Ask your helper to sit in your normal, favourite 'hot spot'. Turn off all room lighting.

2. Squat down by each speaker in turn facing into the room as it does. Turn on the powerful beam and shine it around the room as if it is a beam of sound from the bass unit on the fron of the speaker. Sound behaves in a similar way to light: it reflects off hard surfaces so you are using light to simulate the attributes of sound.

3. Observe the face of your helper to see if there are any strong reflections of light from surfaces in the room. If there are no relections the helpers face will not be illuminated at all and you will not see the helper in the dark! (Impossible).

4. Treat those surfaces that cause the strongest reflections until there are no more reflections!

Note: The most prominent reflection will be, probably in this order ... a hard floor, the nearest (side) walls, the ceiling and glass or wooden objects in the room. You can't do much about the ceiling but you can damp the floor in front of the speakers and the side walls - and reposition the furniture.

That's it! Easy!

[Don Leman]

The arrival of a pair of Monitor 30's has served to remind me how important proper set up is. When the new speakers arrived I was anxious to give them an audition and used some available stands that were about the right height, placed the speakers in about the right spot, hooked up the speaker cable, popped in a CD and set back to enjoy. Big disappointment! Poor bass response, lack of good focus and just a general lack luster sound. I played around a bit but was continually frustrated with the results.

As my Skylan stands were on order and I didn't expect them for a week or so I decided to take the time to properly adjust the ones I had. I got out a level and ensured everything was level and the stand spikes were properly in contact with the concrete floor beneath the carpet and underlay. I was pleased with the improvement but still would have rated the Compact 7 or Super HL5 as more satisfying speakers.

The day arrived when the recommended Skylan stands were delivered. I quickly assembled them and filled them with sand. The result is each stand weighs about 55 lbs ! I will detail the steps I took to optimize my setup.

1. I placed a strip of masking tape on the top of the speaker stands located between the front two rod connectors. With a ruler I measured the center and marked it with a pencil. While not exact, I imagine this is about the geometric center of the mid/woofer unit.
2. I placed the speaker on the stand and measured the distance the mid/woofer was from the floor.
3. I entered this value into a spreadsheet which calculates various positions available which conform to the Allison placement rule
4. In my room I like to have the speakers about 110cm from the side walls. With the spreadsheet it's easy to see what distance the stands have to be from the back wall.
5. I place the stands using the pencil mark on the masking tape as the measuring point.
6. Once the stands are set up. I adjust the listening position to an equalateral triangle and then just a bit back from that
7. I adjust the speaker toe in to achieve a balance between soundstage width and image focus.
8. I have a little piece of masking tape on the center of the wall behind the listening position. I place a laser level on the side of each speaker and shine the beam on the back wall, adjusting the toe in of each speaker so that it is identical.
9. Finally I take the speakers off the stands and adjust the spikes so there is absolutely no rocking in any direction and that the stands are level front to back.
10. Place the speakers back on the stands and double check the toe-in.

I can say that after taking these steps the Monitor 30's showed me just what they are capable of. The biggest improvement was in the bass followed by focus. While the Super HL5 has to this point been my speaker of choice I feel no urgency to hook them up again, at least not until I've had a few more weeks of enjoying the Monitor 30's. I can certainly see why these stands are recommended.

If anyone would like a copy of the spreadsheet I use, feel free to contact me. I didn't originate it, David Fagan of the LS3/5a group gave it to me. I'll check but I'm sure he would be OK with passing it around... its not rocket science.

[James Beltran]

Remarkable, I thought I was the only fuss pot around. Is there any possible way to have the excel sheet posted as a download?Regards

[Don Leman]

James, I've sent you a private email as I don't believe file attachments are allowed.

[poison]

hai don leman,

i do not mind having a copy.
you mind passing it?

regards

[TNIC]

Best way to demo the system?

I find myself running more demos of my system and I am looking for tips on the best way to improve my demos and reveal the best sound to a new listener.

The common expectation of my listeners seems to be they will be shocked into saying wow rather than a discovery of the subtle nuances of good a good system!

The listener often arrives with a somewhat numb ear that is not ready to pick out the details a good reproduction can offer (I sympathize and need to warm up my ear to someone else?s system to). Do you have any technique for sensitizing your listener?s ears (short of tying them into a chair for a long period of time)?

Do you start off with a soft low volume complex piece of music to have he listener leaning forward and pick out the detail and then end with your best recordings? Or do you play music that is full of impact from the start? Or are you using some other technique. I of course want to make this productive and comfortable for the listener. But I would also like to somehow convey the depth of the quality a good system actully has to offer in a reasonable session.

Thanks in advance.

[Don Leman]

One technique I use is to just chat with them in the listening room for a while. I may explain a bit about the room, the equipment, the features of Harbeth speakers. Ask them about their system and the kind of music they listen to. The purpose of this besides getting to know about each other is that the talk will allow their ears and brain to get a sense of the room acoustics, reverberation time etc.

I usually start with something quiet, solo acoustic guitar is great, gradually move to a small jazz group then some female and male vocals. Then try some pop and if they like classical you can fit that in where appropiate. The same goes if they brought over music to listen to. I usually try and control things so they don't get out of hand. End with something quiet and thought provoking.

Hope this helps.

Don

[A.S.]

... talk will allow their ears and brain to get a sense of the room acoustics, reverberation time etc.

I had not thought about the importance of training the ear to the room (because I am the sole listener in my room and know it well), but this strikes me as the professional and correct approach to introducing a new listener to a listening room.

I assume all dealers are this professional - if not they really should take the hint. There is no better method than this.

[snarrow]

At the beginning I also tried to find out the best positions for my SHL5 using the described "measurement approach". The little weakness of this approach is that your listening room will never have an "acoustic symmetry".
So I started with a similar "measurement approach" to get an good starting position with minimized bass resonances.
After finding the starting position I used two signals from a test CD.
1. An Out-Of-Phase-Noise-Track and 2. an In-Phase-Noise-Track. The best results I got with the Out-Of-Phase-Noise-Signal.
My wife (Thanks Marianne!) moved one speaker (all direktions) around the starting position to the place where the noise volume was at minimum. This procedure took nearly 30 minutes....
Mark the "golden position" with tape that survives room cleaning.
Another major improvement came from finding the optimal height for the speakers based on my listening chair.
Before I bought speaker stands I used ordinary bricks (10 Cent each) to find out the optimal height of the speakers. After this I bought speaker stands and modified their height.

Have fun with the music! E.g. with one of my favored CDs: "Morph the cat" (Donald Fagen)

Frank

[Ned Mast]

Don Leman's setup procedure sounds promising. One alternative - which has worked out well for my SHL5s - is the Golden Cuboid or Golden Ratio 'formula' given on the Cardas web site. If you go to the site and then to INSIGHTS and then to ROOM SETUP you'll find it. (By the way, this has nothing to do with Cardas products - about which I know nothing and don't happen to use).

Ned

[Wolf]

I think it's speaker placement too. But you also have to consider the other things in the room. I had my speakers about 11 feet apart with my system stack and a low coffee table that my TV is on and storage for my CD collection between them. Some guys have dedicated listening rooms, I don't. I moved my left speaker to where my rack was and that is now in the left corner. Speakers are about 7 feet apart, and I'm about 8.5 feet from them. Tho the coffee table can't be moved or TV I think it's been better focus for the speakers. Now to get some SHL5s to replace my Spendor 2/3s.