I saw some somewhat similar threads here but not with a lot of replies, so I decided to start a new one. The topic came up in the Sigberg Audio Manta developmpent thread I guess derived from my post #115
there, which derailed that thread into a discussion between @TLS Guy
and me. I think this discussion is somewhat tangential to the topic of that thread, so I'm starting this thread in an attempt to continue the discussion here.
The core topic here I think is how an in-room response should look in order to get accurate sound reproduction across the audio band
So I'll start off by quoting the final post from TLS Guy on the matter from the other thread, if you want to read how we ended up here I guess you need to go to the #115 post from the other thread as linked above and read a couple of pages forward.
As evidenced from your shared graphs (see below), your own system has a 20dB drop from 20hz to 10khz (10dB from 100hz to 10khz)? So you need to elaborate on how that follows your idea of a straight line.
I'm very aware that I may be misunderstanding either what you mean by flat/straight and/or what this graph visualizes (actually I'm pretty confident it's one or the other). So I'm not saying you're contradicting yourself or that you are wrong, I'm asking for more information to understand your standpoint.
When I understand that, I will be happy to share my own views on this interesting subject as well.
in-room graph as shared in the other thread, if I understand his references correctly)
View attachment 58099
Well, that is a good question. However, that curve is taken at the MLP. So, the HF will taper at a distance which at the MLP in that room is about 16 ft.
Now the ear expects that. It will be the same taper for someone speaking in the room or playing an instrument. As I said, the ear expects that. Where you need the straight line is on axis of the tweeter at a distance of one to two meters. I use 2 meters as a rule. Then you have to let the room do the rest. It is my observation that you can not "force" the room by what your notion of what the room should do. I think somehow our brains are wired to know what the environment will do.
Even so, with speakers there is a fall off of HF as you move off axis, which will be dependent on tweeter design more than anything else. However as you move off axis the response must closely mirror the axis response except the off axis taper with increasing frequency. If not the our brains really cry foul.
So lets us look at the responses, the first on axis 2 meters distant from the tweeter. The taper above 15K is due to Omnimic, that is a well documented problem.
Now lets see one more time what the room does with it. There is room gain, AND the expected taper in the HF due to the room attenuation of the reflected portion of the HF spectrum. All rooms do this to a varying degree, and the ear expects this. If you try and modify it significantly the ear cries foul as it does not expect there not to be this room attenuation. I should state, there is no room Eq, using Audyssey, or anything like that.
That is exactly what you would expect a room to do at 12 to 16 ft. distances from the speaker. If you try an correct this, then it does not sound right at all.
The last two octaves are a different case though. Here we have room gain, and room long wave reflections with the potential for peaks and nulls. These are determined to a very large extent by the ratios of the room dimensions. If you have the luxury of designing and building your room, then you have the ability to optimize the room dimension ratios. This is an area where determining the best response here does benefit from room optimization, and critical listening here, without preconceived notions, achieves the best results. This is where your active design will give your customers a degree of optimization not generally available now.
These auto calibration programs, impose preconceived notions on the room, which likely have more chances of being suboptimal than not.
What, I and others have noted that from 1KHz to 10 KHz at 1 to 2 meters, the axis response needs to be as ruler straight as humanly possible, with the off axis responses falling off in a smooth fashion increasing their slope with frequency. That is the best a tweeters can currently offer.
The problem area is that range from 80 to I Khz or so, particularly from 80 to 500 Hz. This latter includes the Baffle Step compensation range of most speakers, and is a range where the involved drivers have to receive large amounts of power. This is where good motor design sorts the "wheat from the Chaff". It is a crucial band however. I pointed out previously that it contains the fundamental frequencies of a large number of instruments, especially the foundational instruments. This is not an area where you want to be lacking in power, or dip the response.
This is an area though, where room and speaker position do come into play. Here your active designs will have a huge advantage. I have found with my active feeds, with variable BSC, that the amount required is in fact highly room, and also speaker position in the room dependent.
So this does leave me with one piece of advice for you, to make the BSC variable, and also preferably have some way to allow the consumer to set it with instrumentation. Many members here already have that facility.