Persian carpets: what type?

[Hipper]

Here's a view from the listening position taken with wide angle. The post-it notes indicate where the tweeter could be reflecting. I take no credit for the window installation. This is a very old house.

I thought we were talking about floor reflections?

If your tweeter is the same height as your ears when listening - which is the usual recommendation - the floor reflection centre point should be exactly half way between the tweeter and your ear. Looking at your picture, the footstool as placed will block the reflections from the floor of the right speaker but the left speaker's will get to your ears unless the sofa itself stops them. Furthermore that looks like a leather footstool which may also reflect. This means you may already be getting an unbalanced sound. If the footstool is normally in the middle under your feet you'll have to work out what happens.

As far as the ceiling goes, again it will depend on the dispersion characteristics of the tweeter. The manufacturer should be able to tell you that. You should definitely experiment to see if some absorbent material (a cushion say) can affect the sound before investing in something more suitable.

 

[Frgirard]

Reading Art Noxon’s post on Acoustic Carpets for High End Audio Applications it's clear that aside from cheap carpet on felt pad, beautiful Persian carpets can provide great acoustic benefit for floor reflections.

He mentions that:

• The pile is ⅝ to ¾ inches deep
• The knap is very dense, i.e. lots of threads, tightly packed together

Of course shopping for a Persian carpet is famous for being one of the hardest things to shop for, and can get expensive very quickly. Most shops don’t understand acoustics and rarely know pile height, knot count or even weight off-hand. It's very easy to make a very expensive mistake.

I thought that gabbeh carpets, which are used by nomadic peoples for sleeping on, would be ideal as they are so heavy, but the knap is apparently not very dense.

Do we have any Persian carpet aficionados in the house? What are the attributes/kinds to look for, and to avoid?

Here's a great map I found of carpets of Persia for reference. Looking forward to your responses! This is an under-discussed topic on this site.

it's a dealer.

 

[Frgirard]

I thought we were talking about floor reflections?

If your tweeter is the same height as your ears when listening - which is the usual recommendation - the floor reflection centre point should be exactly half way between the tweeter and your ear. Looking at your picture, the footstool as placed will block the reflections from the floor of the right speaker but the left speaker's will get to your ears unless the sofa itself stops them. Furthermore that looks like a leather footstool which may also reflect. This means you may already be getting an unbalanced sound. If the footstool is normally in the middle under your feet you'll have to work out what happens.

As far as the ceiling goes, again it will depend on the dispersion characteristics of the tweeter. The manufacturer should be able to tell you that. You should definitely experiment to see if some absorbent material (a cushion say) can affect the sound before investing in something more suitable.

the half way ? with a verticaly diffusion at 80 °, it's better to take a paper, draw the speaker, the cone with an opening angle of 80° and see what is toutch.

 

[sarumbear]

I understand the chart and your reasoning. Designing a room doesn't require certain decor. You can choose one thing and compensate with another.

I’m not talking about decor. You said a carpet won’t do anything to midrange. I told you to look at the data as you are clearly wrong.

Please suggest something else to compensate floor reflections other than a carpet?

 

[pozz]

I’m not talking about decor. You said a carpet won’t do anything to midrange. I told you to look at the data as you are clearly wrong.

Please suggest something else to compensate floor reflections other than a carpet?

I don't consider floor or ceiling reflections to present perceptual problems. If there is some overall issue with reverb times or strong late reflections those can be solved separately depending on the room itself.

Like I said, I've seen the data. I've even compiled resources here: https://www.audiosciencereview.com/forum/index.php?threads/master-review-index.11398/

 

[Vict0r]

This is also recommended in the article. Do you know another name for that type of carpet? Searching for "open weave wool carpet" is not fetching anything as fetching. Even the carpet pad looks different than what I see available in North America anyway.

The woolen rug is from Ikea! It's called the GADSTRUP. The felt underneath is just thick, organic felt I bought at a local fabrics market and cut to size.

 

[ripmixburn]

The woolen rug is from Ikea! It's called the GADSTRUP. The felt underneath is just thick, organic felt I bought at a local fabrics market and cut to size.

According to the article I linked to in the original post, this is the best alternative to an expensive Persian rug. I have an ottoman I need to slide around so loose knotted rugs won’t work for me.

 

[Trdat]

According to the article I linked to in the original post, this is the best alternative to an expensive Persian rug. I have an ottoman I need to slide around so loose knotted rugs won’t work for me.

Hand tufted rugs are very good quality of course it can't compete with hand made but a decent hand tufted rug usually is dense with an average pile height and 100% wool with a closed back. There still in the 1k range though definitely more affordable than a hand made Oriental rug or Persian rug for that matter.

 

[ripmixburn]

After speaking with a few experts, Bidjar (aka Bijar) and Bakhtiar types were recommended because many feature a dense knot count and high pile. I've updated the first post to save time for future readers.

 

[Vict0r]

Those Bidjar rugs go for like $3000 here. And that's just for a medium-sized one (2x2.5m) Imagine the amount of room treatment you can purchase for the price of one of those carpets.

 

[gvl]

Let’s send some rugs to @amirm to measure!

 

[SaltyCDogg]

After speaking with a few experts, Bidjar (aka Bijar) and Bakhtiar types were recommended because many feature a dense knot count and high pile. I've updated the first post to save time for future readers.

Interesting isn't it. Like a few replies here have show, you might assume that something shaggy would be best, like a microphone windsock. In the same way that you might assume a 30kg gold plated amp with lovely glowing tubes would sound amazing

Those Bidjar rugs go for like $3000 here. And that's just for a medium-sized one (2x2.5m) Imagine the amount of room treatment you can purchase for the price of one of those carpets.

Yes but an expensive rug should look great, hold its value reasonably well, especially if bought used and has a much higher WAF than room treatment

 

[ripmixburn]

Those Bidjar rugs go for like $3000 here. And that's just for a medium-sized one (2x2.5m) Imagine the amount of room treatment you can purchase for the price of one of those carpets.

Yikes, I'm hoping it's cheaper here but I haven't been shown Bijars yet to my knowledge. I think I can get away with a wide runner in front of the sofa, instead of paying double for a large one that goes under it (where it provides less benefit). Stay tuned.

 

[Godataloss]

+1 on the use of animal hides and long pile rugs. I use the sheep's hides and a Flokati rug on top of a heavy (supposedly acoustic) pad.

 

[fineMen]

Yikes, I'm hoping it's cheaper here but I haven't been shown Bijars yet to my knowledge. I think I can get away with a wide runner in front of the sofa, instead of paying double for a large one that goes under it (where it provides less benefit). Stay tuned.

Did You consider Nepalese / Tibetanian rugs? They are made with way less labor than Persian, but still are very fine quality. Regularly the wool is back breaking heavy about 1/2" upwards. For some reasons in Europe people sell these used for cheap. A professional wash mostly refreshes them close to new. Total cost stays below a 10th of a new. I purchased a few over time, while being very picky with the design. They can be woth it for their own.

If it has to be Persian the so called 'Heriz' may fit. I think it's Kaukasian, hence shall convey cosy warm isolation by a massive amount of wool. But there are mostly Indian copies around, which may be well suited for sound control, but neither are pleasent to the eye nor to bare feets.

In general Indian copies might better be avoided. "Nepalese" mostly spells "Indian" too. It's the shimmering quality of the wool, which makes the difference. I've seen that big of a span with the quality.

Ikea, not really?

An example I'll remove later: this is 300Euros, add 200 for the wash for utter renewal, 2,50 x 3,50 m^2. about 50kg ... ;-)

https://i.ebayimg.com/00/s/OTU3WDE2MDA=/z/FN8AAOSwI99f6tD7/$_59.JPG

 

[Bjorn]

No matter what carpet you use, it's a very bandlimited type of treatment. Meaning you're altering the spectral content.
It's really a lot more important to treat the ceiling reflections because it can actually be treated in a broadband matter.

That doesn't mean a carpet isn't better than anything (in most cases it is and especially it there's little treatment in the room), but it will always be a treatment with compromise with includes also going a step backwards. You have to weigh that againts the forward step.

Some sheepskin rugs from IKEA is likely to be better than expensive Persian carpets. You need a combination of thickness and softness to attenuate higher frequencies well.

Cowhide Rugs - Sheepskin Rugs

Check out our sheepskin rugs. We have cowhide rugs and much more to decorate your room with style. Shop online and in store today.

www.ikea.com

 

[fineMen]

... sheepskin rugs from IKEA is likely to be better than ...

A quick check, if my investment in lovely collectables was in vain:

mic placed close to the floor, once with, once without my most elegant, hence thinnest Nepal at work (1/3"):

One curve substracted from the other, as to directly show the difference:

It shows by how much the comb filtering effect from the floor reflection over which frequency range is reduced. May somebody else caculate from that (it can be done) how strong the absorption by the rug is. Subjectively without the rug in place it sounds to bright. There is a clearly discernable effect.

 

[fineMen]

May somebody else caculate from that (it can be done) how ...

Seems I lost You. The mike is positioned about 1m away from the speaker box, about 5" above the floor. By that the sound travels along two distinct pathes One goes direct from the driver to the mike, the other goes from the driver to the floor, where it is reflected towards the mike. Both pathes have different lengths. The individual contributions of both interferre in a characteristic manner, called comb filter effect.

That is what You see. Very deep 'nulls' in the frequency response, where the interferrence is destructive, and 'poles' up to a theoretical maximum of +6dB, where interferrence is constructive.

The pattern replicates itself over the frequency range, starting from some frequency, which is determined by the path length difference and the speed of sound. That simple.

Logically, if reflection is suppressed, namely by absorption, the second path loses amplitude, hence contributing less, and comb filter effect is mitigated. Taken the other way round, less comb filter effect means less reflection, means more absorption. I use this, to show how good the rug works. Again simple, right?

Here, with the rug in place the constructive interferrence vanishes nearly completly, the suck-outs are greatly reduced in depth. One might, as a first guess assume, that this relatively thin carpet, by whatever magic ;-) eats up all the sound, before it can reflect.

Two peculiarities, though. First the poles and nulls around 1,2--1,5kHz appear to be shifted! With the rug the null is lowered in frequency. How come? Look, the null is only there, because the rug loses appetite. Its effectivness declines towards lower freqeuncies. But still the heavy wool actually lowers the speed of sound in the medium. Lower speed of sound means bigger effective path length difference, placing the null deeper. Sidenote: this gives an indication on the frequency range the rug is effective in. It may start around 1kHz or even a bit below.

The other one is the irregularity around 4..5kHz. That is because the phase of the direct radiation towards the mike differs from the phase towards the floor. I missed that, sorry. The driver is a CD horn with a sharp edge in its dispersion, which (neccessarily) changes the phase as rapid over even a very small angle (way off the main axis, don't worry).

Sorry, it was just a very hasty check, because it was told, that my magic carpets don't work. I didn't attempt to go down. (I works by true faith, You know?)

 

[Bjorn]

A carpet will obviously absorb and thus minimize comb filtering. But it's still a very bandlimited type of treatment, mainly absorbing the treble and upper midrange. So it changes the spectral content, funtioning like a equalizer. Many carpets don't absorb higher frequencies particularly well either.

 

[fineMen]

A carpet will obviously absorb and thus minimize comb filtering. But it's still a very bandlimited type of treatment, mainly absorbing the treble and upper midrange. So it changes the spectral content, funtioning like a equalizer. Many carpets don't absorb higher frequencies particularly well either.

So that's why the quest for a qualified rug was risen. The analogy to an equalizer doesn't snug fit. An EQ would alter the direct and the indirect sound simultanously, a qualified rug just the reverberaton. There are numerous situations in which a fine rug might come handy. Weighing in non-audio criteria, which really exist for some, it may be the only viable solution. To get an esthetically pleasing one is another challenge. One can enjoy to search and find. It's always a statement, at least to non-audio people. So it should be.