Big Speaker in a small room?

[oivavoi]

I don't know of any research that's studied this directly, but Harman's research into room curves dealt with it indirectly, in that it found that with flat on-axis measuring speakers listeners preferred a downward sloping in-room response. This must be partly the result of most flat-measuring speakers having wider radiation in the lower frequencies. It's not clear though AFAIK whether this is the room curve that listeners would have preferred had the speakers used been constant directivity right down to the bass (e.g. like Dutch&Dutch 8C, Danley Synergy series, etc.). AFAIK the Harman research used only speakers that had a downward sloping power response. I'm really hoping that Harman or someone else with the resources to do it properly does further research into this using a greater variety of different speakers, including true constant directivity designs and even perhaps omni, dipole or bipole.

Other relevant (also Harman) research into room correction DSP basically found that, below the Schroeder frequency, a smooth in-room response is more important than a smooth on-axis response, while the opposite is true above the Schroeder frequency. This would imply that baffle step compensation is necessary down to the Schroeder, but not below it (there are lots of opinions on this though and I don't think it's a settled question).

The way I see it, a lot of designers of home audio passive speaker have in fact basically been working on this principle for many years, by basing decisions about baffle step compensation on the size of the room the speaker is likely to be used in.

I think it's doubtful that trying to sacrifice the on-axis response to accommodate the room above the Schroeder frequency is a good idea (of course, the Schroeder frequency is a pretty slippery concept IRL and it's exact frequency in a given room can't be exactly defined).

My personal view is that room correction below the Schroeder frequency is important in small rooms, and that you may as well start with a speaker that measures flat on-axis and then correct from there. But where this is not possible or desired, the next best scenario would be a speaker that measured flat on-axis down to the Schroeder frequency and then - in very small rooms at least - gently slopes down a bit below there.

This makes passive closed box speakers a little more attractive in small rooms perhaps, or ported speakers that are tuned a little lower than textbook, giving a gentler, slower roll-off. It's also one reason why active monitors might not sound as good in small rooms without room correction: they tend to be (hopefully) ruler flat down to the their lowest frequency and then roll off at perhaps 48dB/octave below there.

Great explanation!

The question is, I think, whether the brain automatically compensates for any spectral imbalance caused by the room, baffle size, etc. I would tend to think it does. With regards to Harman’s research, there’s too many unknown variables, I think: how do we know that the preferred «flat» speakers were not simply better speakers overall? Do we know it was due to baffle step compensation?

Here’s a simple way to investigate this: use high-quality flat headphones as a reference (adapted to the ear canal etc of the testee). Compare it to two identical speakers, one with and one without baffle step compensation. Which speaker sounds most identical to the headphone reference? Et voila!

But unfortunately, the field of applied loudspeaker research is small, so unlikely to be undertaken professionally...

 

[KSTR]

Bass response needs to be tailored with EQ anyway in almost all cases so it doesn't matter much if baffle step is compensated or not, to whatever amount. Studio monitors typically have full compensation (and onboard EQ to deal with placement) because their spec is "flat on-axis anechoic", HiFi speakers often are only half compensated as sort of compromise.

 

[andreasmaaan]

Great explanation!

The question is, I think, whether the brain automatically compensates for any spectral imbalance caused by the room, baffle size, etc. I would tend to think it does. With regards to Harman’s research, there’s too many unknown variables, I think: how do we know that the preferred «flat» speakers were not simply better speakers overall? Do we know it was due to baffle step compensation?

Here’s a simple way to investigate this: use high-quality flat headphones as a reference (adapted to the ear canal etc of the testee). Compare it to two identical speakers, one with and one without baffle step compensation. Which speaker sounds most identical to the headphone reference? Et voila!

But unfortunately, the field of applied loudspeaker research is small, so unlikely to be undertaken professionally...

The problem is, there's no agreement on what constitutes flat headphones due to so many complexities regarding headphone measurement.

Just to clarify re: the Harman research on DSP, they weren't comparing different speakers and asking subjects which they preferred in this particular study. IIRC they were placing trained participants in a room (or rooms, I can't recall) with the same speakers and asking them to adjust an EQ until they had found the right balance.

Also too many variables of course to draw any absolute conclusions, but IIRC what they found was that below the Schroeder frequency, participants tended to EQ in a way that made the steady-state response at the listening position smoother, while above the Schroeder frequency they tended to EQ out non-linearities in the speakers' response.

However, I have to read this one again, it was a long time ago, so I'm not sure I've remembered all the details correctly. But it was certainly a more nuanced outcome than simply that people preferred better speakers.

The purpose of the study was actually to investigate the use of room-correction equalisation. But I think it implies something interesting about speaker design too, i.e. that the speaker should be flat on-axis down to Schroeder.

 

[Krunok]

I don't know of any research that's studied this directly, but Harman's research into room curves dealt with it indirectly, in that it found that with flat on-axis measuring speakers listeners preferred a downward sloping in-room response. This must be partly the result of most flat-measuring speakers having wider radiation in the lower frequencies. It's not clear though AFAIK whether this is the room curve that listeners would have preferred had the speakers used been constant directivity right down to the bass (e.g. like Dutch&Dutch 8C, Danley Synergy series, etc.). AFAIK the Harman research used only speakers that had a downward sloping power response. I'm really hoping that Harman or someone else with the resources to do it properly does further research into this using a greater variety of different speakers, including true constant directivity designs and even perhaps omni, dipole or bipole.

Other relevant (also Harman) research into room correction DSP basically found that, below the Schroeder frequency, a smooth in-room response is more important than a smooth on-axis response, while the opposite is true above the Schroeder frequency. This would imply that baffle step compensation is necessary down to the Schroeder, but not below it (there are lots of opinions on this though and I don't think it's a settled question).

The way I see it, a lot of designers of home audio passive speaker have in fact basically been working on this principle for many years, by basing decisions about baffle step compensation on the size of the room the speaker is likely to be used in.

I think it's doubtful that trying to sacrifice the on-axis response to accommodate the room above the Schroeder frequency is a good idea (of course, the Schroeder frequency is a pretty slippery concept IRL and it's exact frequency in a given room can't be exactly defined).

My personal view is that room correction below the Schroeder frequency is important in small rooms, and that you may as well start with a speaker that measures flat on-axis and then correct from there. But where this is not possible or desired, the next best scenario would be a speaker that measured flat on-axis down to the Schroeder frequency and then - in very small rooms at least - gently slopes down a bit below there.

This makes passive closed box speakers a little more attractive in small rooms perhaps, or ported speakers that are tuned a little lower than textbook, giving a gentler, slower roll-off. It's also one reason why active monitors might not sound as good in small rooms without room correction: they tend to be (hopefully) ruler flat down to the their lowest frequency and then roll off at perhaps 48dB/octave below there.

Very well said! My Castle Richmonds were marketed as bookshelf speakers so it is not reasonable to expect them to give their best when being put on a stands relatively far away from the walls.

I will repeat the test putting them close to the wall and report back about sound impressions tomorrow.

 

[DonH56]

The issue with "small" rooms and bass is less the peaks ("pressurization") caused by additive waves than the nulls caused by subtractive signals. Peaks can be readily EQ'd down and are fairly limited in magnitude (typ 6 dB or so) but nulls can be "infinitely" deep and are in general not amenable to EQ because x times (y - y) is still 0 no matter how large you make x. Real rooms with flexing walls and such prevent entering the land of infinity but you can still measure nulls in the 20~40 dB range and EQ usually only handles 10~12 dB or so. And you wouldn't really want to dump all that power into a null anyway; 10 dB increase in power is 10x in Watts, 20 dB is 100x Watts. Better have a big amp and speakers to handle it! And of course if you move a little way out of the null the bass will be overpowering, The usual, practical, solutions to nulls are to either move the listening spot, or to add additional subs to "drive" the null and obviate the cancellation.

IME/IMO/etc. - Don

 

[Krunok]

The usual, practical, solutions to nulls are to either move the listening spot, or to add additional subs to "drive" the null and obviate the cancellation.

IME/IMO/etc. - Don

Maybe I'm missing something, but wherever you put your listening spot wouldn't there always be a null spot at some frequency?

Unless of course you add a sub(s) which are not at the same distance fomr your listening spots as your main speakers, but that is not really the rason why people are putting subs into their rooms, right? Mayb the solution would be to put 2 subs that are not equidistant from listening position, but that solution has soooo low WAF (woman acceptance factor) which makes it only suitable for theoretical talk.

 

[DonH56]

Maybe I'm missing something, but wherever you put your listening spot wouldn't there always be a null spot at some frequency?

Unless of course you add a sub(s) which are not at the same distance fomr your listening spots as your main speakers, but that is not really the rason why people are putting subs into their rooms, right? Mayb the solution would be to put 2 subs that are not equidistant from listening position, but that solution has soooo low WAF (woman acceptance factor) which makes it only suitable for theoretical talk.

There are usually only one or two major bass nulls in a room and those are the ones you care about. For example a sealed room always has a fundamental null right in the middle of the room and that is all too often where people put their listening position. I use multiple subs to smooth the listening response and that is quite often the reason espoused for multiple subs. And yes mine are placed at different distances from the MLP as well as from other boundaries so they best compensate room modes at the MLP. The other common reason for multiple subs is greater output, but a single sub capable of higher output is often a better solution than multiple subs around the room if all you want is higher SPL (some do add a sub right next to the listening position for more tactile response).

HTH - Don

 

[Blumlein 88]

I don't know of any research that's studied this directly, but Harman's research into room curves dealt with it indirectly, in that it found that with flat on-axis measuring speakers listeners preferred a downward sloping in-room response. This must be partly the result of most flat-measuring speakers having wider radiation in the lower frequencies. It's not clear though AFAIK whether this is the room curve that listeners would have preferred had the speakers used been constant directivity right down to the bass (e.g. like Dutch&Dutch 8C, Danley Synergy series, etc.). AFAIK the Harman research used only speakers that had a downward sloping power response. I'm really hoping that Harman or someone else with the resources to do it properly does further research into this using a greater variety of different speakers, including true constant directivity designs and even perhaps omni, dipole or bipole.

Other relevant (also Harman) research into room correction DSP basically found that, below the Schroeder frequency, a smooth in-room response is more important than a smooth on-axis response, while the opposite is true above the Schroeder frequency. This would imply that baffle step compensation is necessary down to the Schroeder, but not below it (there are lots of opinions on this though and I don't think it's a settled question).

The way I see it, a lot of designers of home audio passive speaker have in fact basically been working on this principle for many years, by basing decisions about baffle step compensation on the size of the room the speaker is likely to be used in.

I think it's doubtful that trying to sacrifice the on-axis response to accommodate the room above the Schroeder frequency is a good idea (of course, the Schroeder frequency is a pretty slippery concept IRL and it's exact frequency in a given room can't be exactly defined).

My personal view is that room correction below the Schroeder frequency is important in small rooms, and that you may as well start with a speaker that measures flat on-axis and then correct from there. But where this is not possible or desired, the next best scenario would be a speaker that measured flat on-axis down to the Schroeder frequency and then - in very small rooms at least - gently slopes down a bit below there.

This makes passive closed box speakers a little more attractive in small rooms perhaps, or ported speakers that are tuned a little lower than textbook, giving a gentler, slower roll-off. It's also one reason why active monitors might not sound as good in small rooms without room correction: they tend to be (hopefully) ruler flat down to the their lowest frequency and then roll off at perhaps 48dB/octave below there.

Doing room correction, I have found it helps to shelve out the tilted response target curve in rooms with rather solid walls. I.E. concrete or basement rooms partly below ground level. I normally would have a flat target curve from 200 hz down and move it around until it sounds right. Otherwise I'd let the slope continue until about an octave above where the woofer response ends.

 

[Strictly Stereo]

I cannot comment on those Canton models, but I shoehorned some rather large speakers (Neat XL10, Kudos Titan T88 and Amphion Krypton) into the 3x4m "man cave" at our old place. All of those models performed remarkably well. The only problem is that they did not leave room for very much else.

 

[svart-hvitt]

I got a new perspective on room and speaker size when I visited this guy (Google translate):

https://www.stereopluss.no/index.php?id=6145436

He employs 12 woofers of the 24 inch variety for low frequencies, plus 6 woofers of 15 inches for mid bass. The ceiling is just 213 cm high. The room measures 30 square meters. Walla are concrete. Lots and lots of dampening, rock wool. So this is a room built around the speakers, so to speak. All people interested in speakers, room and DSP (he uses Audiolense across the entire frequency response) should pay him a visit; this is a laboratory! So I call him the nutty professor (he’s a carpenter by profession).

What you could hear in this room, in a very small sweet spot, is a very weird thing. I don’t know if it’s correct or effects that constitute the experience. The point is, I have never been a place where you could so easily hear the recording venue. You could also easily tell that high-quality ripped LPs were low in resolution, as if dimensions of information were taken away from the source material. So it is a special instrument for careful listening.

The whole experience was a bit like multichannel, when you see that more channels give you a different sensation, another perception. So I believe, based on this experience in particular, that size matters. The bigger, the better. Even in small rooms.

 

[Sal1950]

What you could hear in this room, in a very small sweet spot, is a very weird thing. I don’t know if it’s correct or effects that constitute the experience.

I'd love to hear that rig! I can only imagine the distribution of low freq among all those drivers allows for very low distortion in the mid to bottom end.

 

[KSTR]

^ Very good example of how close you can get to near perfect conditions, and we see a lot of care went into room treatment. Together with those quite beaming speakers the wavefront shapes around the head in the sweetspot will be close to optimum: flat, clean and undisturbed.